Marine Biology (2003) 142: 427–440 DOI 10.1007/s00227-002-0956-9 J.L. Maté Ecological, genetic, and morphological differences among three Pavona (Cnidaria: Anthozoa) species from the Pacific coast of Panama I. P. varians, P. chiriqiensis, and P. frondifera Received: 22 January 2002 / Accepted: 12 September 2002 / Published online: 3 December 2002
Springer-Verlag 2002 Abstract Ecological, genetic, and morphological differences among three Panamanian Pacific Pavona species with strongly developed collines (Pavona varians, P. frondifera, and P. chiriquiensis) were examined. Ecological factors included geographical distributions of species, habitat preferences, interspecific interactions, reproductive ecology, and tolerance to bleaching. Genetic differences were based on the electrophoretic analysis of ten allozyme loci. Morphological analyses consisted of tissue coloration, colony morphology, and measurements and counts of ten macro- and microskeletal characters. P. varians, present on reefs or in coral communities, is the most widely distributed and shows considerable morphological variation. P. chiriquiensis, a recently described species, encrusts basalt rock and has little morphological variation. P. frondifera is a reef dweller with a compact foliose morphology. Tissue coloration varies from light to dark brown in P. varians, from pink to brown in P. frondifera, and from brick red to brown or silvery in Pavona chiriquiensis. Also, the white to silvery polyp mouths of the latter species are a diagnostic feature that allows an easy identification in the field. Aggressive dominance during short-term interspecific interactions were as follows: Pavona chiriquiensis>P. varians>P. frondifera. P. chiriquiensis and P. varians showed contrasting responses to sea warming during the 1997–1998 El Niño Southern Oscillation. Whereas entire P. chiriquiensis bleached and died within 4 weeks of exposure to 30–31C, colonies of P. varians did so only on their upper surfaces. The response of P. frondifera to elevated temperatures was not observed because it is mainly present in the Gulf of Panama where coral bleaching was absent in 1997–1998. The genetic data indicated that P. chiriquiensis differed strongly from both P. varians and P. frondifera, with Nei’s unbiased genetic distances of 0.434 and 0.379, respectively. A fixed difference between P. varians and P. frondifera, and P. chiriquiensis exists at the triose phosphate isomerase (TPI-2) locus. A nearly fixed difference between P. chiriquiensis and P. frondifera and between P. chiriquiensis and P. varians was found at the hexokinase (HK) locus. P. varians differed slightly from P. frondifera with Nei’s unbiased genetic distance of 0.068. No fixed difference was found between P. varians and P. frondifera. There were strong differences between P. chiriquiensis and P. varians in spawning times and gamete characteristics. Spawning in P. varians and P. chiriquiensis is 12 h out of phase. Also, eggs of the former species are white to beige and positively buoyant whereas those of the latter species are dark green and neutrally to negatively buoyant. No reproductive data are yet available for P. frondifera. Calicular diameters are significantly greater in P. chiriquiensis than in the other two species. In contrast, corallum thickness is greater in P. varians and P. frondifera than in P. chiriquiensis. Canonical discriminant function analysis readily separated the three species. Communicated by P.W. Sammarco, Chauvin Introduction J.L. Maté Division of Marine Biology and Fisheries, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149-1098, USA Pavona varians Verrill, 1864 (Verrill 1864); P. chiriquiensis Glynn, Maté, and Stemann, 2001 (Glynn et al. 2001b); and P. frondifera Lamarck, 1816 (Lamarck 1816) are similar members of the genus on the Pacific coast of Panama. In addition to their often small size, they differ from other Panamanian Pavona by their strong development of collines. P. varians and P. frondifera are distributed throughout the Indo-Pacific region E-mail: matej@naos.si.edu Present address: J.L. Maté Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Republic of Panama 428 (Dana 1846; Dai and Lin 1992; Veron 1993). However, P. chiriquiensis is presumed to be endemic to the eastern tropical Pacific (Glynn et al. 2001b). In the eastern Pacific, P. varians is the most widespread species. It has been found at 10 of 11 (90.9%) major sites examined (Glynn and Ault 2000). The other two species are less common, with P. chiriquiensis present at 6 sites (54.5%) and P. frondifera present at just 2 sites (18.2%). In this region, P. frondifera is only found in Costa Rica (Cortés and Guzmán 1998) and Panama (Glynn and Ault 2000). All three species have been shown to form locally abundant populations, but their contributions to reef building are typically relatively low (Glynn 1974a, b, 1976; Glynn et al. 1982; Glynn and Wellington 1983; Guzmán and Cortés 1989; Vargas-Ángel 1996), particularly for P. chiriquiensis, which is usually found at inter-reef sites. These three species of Pavona are considered the most taxonomically difficult Pavona in the Panamanian Pacific. P. varians, as the name implies, shows considerable morphological variation that may be closely related to variation in the environmental conditions resulting from the wide habitat preferences of the species (Glynn 1976, 1983; Veron and Pichon 1979). Extreme variation in morphology may even occur within the same colony (Glynn and Wellington 1983). These extremes in morphological variation may cause this species to be confused with P. chiriquiensis or P. frondifera in certain environments. P. chiriquiensis was considered for many years to be a morphological variant of P. varians and later was recognized as a separate species (Glynn et al. 2000). However, P. chiriquiensis has recently been described in terms of multiple differences in ecology, allozymes, and morphological characteristics that clearly set it apart from P. varians (Glynn et al. 2001b). Although P. frondifera has been recognized from the Pacific coast of Panama (Glynn and Maté 1997), it has been poorly studied. In many cases, the species status has been impossible to validate because of its morphological similarities with P. varians. Additionally, P. frondifera is a rare species that in Panama is restricted to only a few sites. The recognition of species boundaries is a necessary step to understand the biogeographic and ecological distribution of organisms, as well as the mechanisms by which speciation occurs (McFadden 1999). Traditionally, scleractinian coral species have been classified primarily on the basis of their skeleton, since this is readily available in museum collections (Vaughan and Wells 1943; Potts et al. 1993). However, the high levels of polymorphism attributed to local environmental conditions or genetic differences among populations are among the most difficult problems confronting coral systematists (Budd 1993; Weil and Knowlton 1994). The use of non-skeletal characteristics to circumvent problems arising from this classical approach has figured prominently in the characterization of only a few scleractinian species (Lang 1984). Molecular studies have recently proved useful in delineating species boundaries, particularly in marine species with few informative morphological characteristics and high intraspecific phenotypic diversity (e.g. Avise 1974, 1994; Weil and Knowlton 1994; Williams 2000; Glynn et al. 2001b). In sympatry, fixed genetic differences are enough. But sometimes genetic differences are not fixed. Then, other characters are especially useful (e.g. Montastraea) when concordant. Multi-character approaches have been successfully used to separate problematic coral species, for example, two Acropora species on the Great Barrier Reef by Ayre et al. (1991), three Montastraea species from the Caribbean by Knowlton et al. (1992) and Weil and Knowlton (1994), four Pacific Porites species by Potts and Garthwaite (1991), and four Caribbean Porites species by Potts et al. (1993). In this study, I examined the differences among three Pavona species with collines from the Pacific coast of Panama by means of a multi-character approach that united the ecological, molecular, and morphological characteristics. The ecological aspects of the study included species distributions, habitat preferences, interspecific interactions, reproductive ecology, and responses to the 1997–1998 El Niño sea-warming event. Allozyme electrophoresis was used to examine the genetic differences between species because of its high resolving power with closely related species (Avise 1974, 1994). The morphological analyses included colony form, tissue coloration, and the traditional macro- and micro-morphological characteristics of the coral skeleton. Materials and methods Collections and sample preparation Samples of Pavona varians, P. chiriquiensis, and P. frondifera (Fig. 1A–C, respectively) were collected at several sites in both the non-upwelling Gulf of Chiriquı́ and the upwelling Gulf of Panama on the Pacific coast of Panama (Table 1, Fig. 2A–D). Forty-four sites, including reef and inter-reef habitats, were surveyed in both areas. During diving surveys information on habitat, depth, and colony coloration was recorded for sampled specimens. Large coral fragments (up to 735 cm2) were collected when possible to allow for a morphological analysis after the required tissue for electrophoresis was taken. The size of fragments removed was adjusted to minimize colony death. Tissue samples for electrophoretic analysis were removed from the coral skeleton using flat-tip pliers or chisels, placed in cryovials, and mixed with five drops of Stoddart grinding buffer (Stoddart 1983) before being frozen in liquid nitrogen. The remainder of the coral skeleton was bleached in 10% sodium hypochlorite, rinsed, dried, catalogued, and stored until later morphological analyses. The identifications of P. varians and P. frondifera were performed according to the taxonomic treatments of Yabe et al. (1936); Veron and Pichon (1979); and Dai and Lin (1992), as well as the original descriptions by species authors (Lamarck 1816; Verrill 1864). The identification of P. chiriquiensis follows the species description (Glynn et al. 2001b). Most collections were made in early 1997, before the beginning of the El Niño event. Interspecific tissue interactions Field surveys were conducted to observe coral-to-coral interactions (Lang 1973) among Pavona species. Those Pavona species observed to interact in the field (P. chiriquiensis and P. varians) were brought to the laboratory for interaction studies. Fragments of two colonies 429 larly full moons during the dry season that extends from midDecember to mid-May (Glynn et al. 2000). Detailed field and laboratory methodologies related to spawning observations and fertilization trials can be found in Glynn et al. (2000). No reproductive data are available for P. frondifera. Coral bleaching and mortality The 1997–1998 El Niño provided an opportunity to study the effects of anomalous sea warming on corals, particularly those species considered here. Warm waters from El Niño influenced only sites in the Gulf of Chiriquı́. Sea temperatures were not unduly elevated in the upwelling Gulf of Panama. El Niño warming effects were monitored in P. varians and P. chiriquiensis in the Gulf of Chiriquı́, but not in P. frondifera due to its rarity there. A flexible measuring tape calibrated in millimeters or a square wire mesh (2.5·2.5 cm) was used to measure the areas of normal, bleached, and dead tissues. Colonies were recorded as normal only when their natural brown coloration predominated. Bleached colonies exhibited loss of coloration (from pale to fully bleached). Dead areas were in most cases covered with filamentous algae. In some colonies it was possible to identify two or more categories. The percentage of each condition was recorded. In situ temperature recorders (Onset Computers) provided information on the timing of the two sea-warming events that led to the bleaching and mortality of corals (see Fig. 5 in Glynn et al. 2001a). The anomalous El Niño warming affected corals in two different periods, August 1997 and March 1998. Species affected by the first bleaching event were monitored monthly from September through December 1997. Effects from the second bleaching event and recovery were observed during March 1998, May 1999, and May 2000. Electrophoretic analysis Fig. 1 Live in situ colonies of A Pavona varians (Uva Island, site 5, 3.2 m depth, May 1997); B P. chiriquiensis (Uva Island, site 5, 3 m depth, May 1997); and C P. frondifera (Saboga Island, site 1, 2.5 m depth, May 1999). Note long ridges and valleys and uniform darkbrown coloration of polyps and coenosarc in P. varians (A), white oral discs and mouths, hydnophorae, and short collines in P. chiriquiensis (B), and long ridges and valleys, foliose morphology, and uniform light-brown coloration of polyps and coenosarc in P. frondifera (C) (from 2·2 cm to 10·15 cm) of the same or different species were placed in immediate contact so they barely touched. The contacts were observed daily for a maximum of 7 days and included observations on extension of mesenterial filaments, time of onset of the interaction, and extent of tissue mortality. Reproductive ecology The timing of spawning of P. chiriquiensis and P. varians was estimated from histological slides to occur around new and particu- Horizontal starch (SIGMA S-4501) gel electrophoresis was used to analyze seven enzymes coding for ten loci under two buffer systems. Enzymes, buffers, and running conditions are presented in Table 2. On the day of the electrophoresis run, a small portion of the tissue was placed on a grinding plate cell and macerated in three drops of Stoddart’s buffer (Stoddart 1983). A piece of Miracloth filter (Calbiochem Inc.) was placed on top of the homogenate to reduce the amount of coral mucus that would adhere to the paper wicks (Whatman #3 filter paper), which were loaded onto starch gels and run at 4C. After the electrophoretic run, gels were sectioned with a custom-designed ‘‘guitar-string’’ slicer. Zymograms were visualized using stain recipes modified by Williams (1992) and Weil and Weigt (1996) from Harris and Hopkinson (1976). Alleles were labeled alphabetically according to their mobility from fastest to slowest. For those enzymes having two loci, the loci were labeled numerically starting with the fastest migrating one. The BIOSYS-1 software package (Swofford and Selander 1989) was used to calculate gene frequencies and Nei’s (1978) unbiased genetic distances (D) among samples and to perform an unweighted pair group method average (UPGMA) cluster analysis. Morphometrics Digital images of skeletal characters were generated using a Kodak DCS 420 digital camera fitted with a 1:1 SIGMA macro lens. Images were imported into the SigmaScanPro (SPSS, Inc.) image analysis package where linear measurements and counts were made on ten morphological characters (Table 3, Fig. 3). Characters were measured and counted on six corallites per colony, from which a colony mean was calculated. Ten colonies per locality were generally used in the analyses, except for those localities with fewer numbers of individuals (Table 1). The statistical packages Sigma Stat and SPSS (SPSS, Inc.) were used for all univariate and multivariate analyses, respectively. Pavona species groups were separated by discriminant canonical analysis that tested the hypothesis that the three groups were homogeneous. 430 Table 1 Locality, total number of colonies collected of each species (n), and depth ranges with reference to mean lower low water for each locality. See Fig. 2 for geographic location of sites by site number Locality Site Species Pavona chiriquiensis n Gulf of Panama Saboga Island Iguana Island Gulf of Chiriquı́ Jicarita Island Coiba Island Uva Island Secas Island Silva de Afuera Island Montuosa Island Restinge Island 1 2 1 6 3 4 5 6 7 8 9 6 1 36 0 5 7 4 Results Distribution, abundance, and habitat preference All three Pavona species are found in both the Gulf of Panama (Fig. 2A–C) and the Gulf of Chiriquı́ (Fig. 2A, D). P. varians is the most widely distributed, being found at 46.7% of the sites (Fig. 4A). P. chiriquiensis Fig. 2 A Map of Panama showing explored and collecting sites in detail; B Bay of Panama; C Pearl Islands; and D The central portion of the Gulf of Chiriquı́. Black arrows point to the 44 sites explored during this study. Circled numbers in A, C, and D indicate collecting sites: 1 Saboga Island; 2 Iguana Island; 3 Jicarita Island; 4 Coiba Island; 5 Uva Island; 6 Secas Island; 7 Silva de Afuera Island; and 8 Montuosa Island Depth (m) 6.7 4.2 4.5 6.3 3.0–9.0 – 16.7 6.6 4.6 P. varians P. frondifera n Depth (m) n Depth (m) 58 5 5.0–9.0 1.5–15.2 40 0 3.5 – 2 15 94 9 5 9 2 4.5 4.5–9.0 1.2–15.1 4.5–9.0 15.1 5.1–16.7 3.0 0 2 2 0 0 0 0 – 6.1 13.0 – – – – and P. frondifera were found at 24.4% and 6.7% of the sites examined, respectively (Fig. 4B, C). Depth distributions demonstrate the overlapping occurrences of the three species (Table 1). At Saboga Island (site 1, Fig. 2C) and Uva Island (site 5, Fig. 2D), P. varians is particularly abundant, with more than 100 colonies seen at each of these sites. The rocky shores of Uva Island and Jicarita Island (site 3, Fig. 2D) harbor the largest known populations of P. chiriquiensis. P. varians has the broadest habitat preference of the three species. It lives free or attached to reef frameworks or to rocky substrates, in the rubble zone, and in soft bottom areas. It also occurs on open substrates, in crevices, caves, and overhangs. P. chiriquiensis typically encrusts basaltic outcrops with only four specimens being found in reef areas. P. frondifera has been found 431 Table 2 Enzyme buffer systems employed in the electrophoretic analysis of ten putative loci in three Pavona species. E.C. Enzyme Commission Enzyme E.C. number Number of loci Buffer system Glucose phosphate isomerase (GPI) Glutamate dehydrogenase (GTDH) Hexokinase (HK) Leucyl-proline peptidase (LPP) Leucyl-valine-peptidase (LVP) Phosphogluconate dehydrogenase (PGDH) Triose phosphate isomerase (TPI) 5.3.1.9 1.4.1.2 2.7.1.1 3.4.11/13 3.4.11/13 1.1.1.44 5.3.1.1 1 2 1 1 2 1 2 TC 8.0a TC 8.0 LiOH 8-1-8.4b LiOH 8-1-8.4 LiOH 8-1-8.4 TC 8.0 LiOH 8-1-8.4 a b Tris citrate (TC 8.0), pH 8.0, 90 mA, 6–8 h (Selander et al. 1971) Tris citrate borate (LiOH), pH 8.4, 350 V, 4–6 h (Selander et al. 1971, modified by Harris and Hopkinson 1976) Table 3 Macro- and micromorphometric measurements taken in three species of Pavona with strongly developed collines. See Fig. 3 for a graphic representation of most characters Skeletal characters measured Code Description Maximum calicular diameter CD1 Maximum distance across the inside area of the corallite not including the walls CD2 Maximum distance across the inside area of the corallite not including the walls but perpendicular to the maximum calicular diameter SL Linear distance of the largest septa reaching the columella CL1 Maximum distance across the columella CL2 Maximum distance across the columella perpendicular to the columella maximum diameter CW Linear distance across the flat top of the ridge NS1 Count of the total number of septa NS2 Count of the total number of septa that join the columella Minimum calicular diameter Main septa length Maximum columellar diameter Minimum columellar diameter Colline width Number of septa Number of septa reaching the columella Number of septocostae Corallum thickness SC CT Count of colline septocostae in 1 mm Maximum distance from the base to the top of the corallum P. varians may exist under weak to strong current regimes, but rarely in high-energy environments. P. chiriquiensis occurs on protected rock surfaces, not exposed to direct wave assault. P. frondifera occurs only in protected reef areas. Polyp expansion and interspecific tissue interactions Fig. 3 Measurements made on individual corallites for morphometric analyses. CD Calicular diameter (measured as the maximum and minimum diameter); CL columella diameter (measured as the maximum and minimum diameter); SL septum length; and CW colline width None of the three Pavona species displays expanded polyps during the day except during periods of rapid water flow. In all species, polyps are usually extended at night and colony surfaces are ruffled. Field contact interactions between colonies of P. chiriquiensis and P. varians at Uva Island (n=1) and at Jicarita Island (n=2) showed P. varians overgrowing P. chiriquiensis by overtopping with a free laminar edge. Laboratory contact experiments demonstrated unilateral extracoelenteric destructive effects by P. chiriquiensis (Table 4). Also, P. varians killed the tissues of P. frondifera. Stand-offs were evident between P. chiriquiensis and P. varians, as well as in all intraspecific contact trials (Table 4). Coral bleaching and mortality exclusively in reef rubble areas where it occurs mainly as attached colonies. Larger colonies of P. frondifera encrust substrata; smaller ones occur free or are lightly attached to the substrata. P. chiriquiensis was the most sensitive species to the 1997–1998 El Niño warming event. Uniform bleaching (100%) occurred in P. chiriquiensis approximately 432 mortality was evident. Mortality rates in P. varians were of the order of 1–15% of the live surface cover (see also Glynn et al. 2001a). Reproductive ecology Spawning in P. varians and P. chiriquiensis occurs in sympatry about 12 h apart during the crepuscular period on the same day. P. varians spawns 15 min to 2 h before sunrise whereas P. chiriquiensis spawns shortly after sunset. The white mouths of P. chiriquiensis become extremely distended prior to spawning. No evident change in mouth size was noted in P. varians. In P. varians and P. chiriquiensis sperm was released as a diffuse cloud. In P. varians the barely visible eggs, which are white to beige, are confined to mucus strings and rise slowly to the surface; in P. chiriquiensis, eggs are released as clouds, have a dark green color, and are neutrally to negatively buoyant (see Glynn et al. 2000). Allozyme electrophoresis Fig. 4 Distributional maps of A P. varians; B P. chiriquiensis; and C P. frondifera. Black arrows indicate species presence at a site. See Fig. 2A–D and Table 1 for names of localities 3 weeks after the warming began. A month later, tissue mortality was 99%. However, once temperatures returned to ambient levels, surviving fragments had rapidly regained their normal coloration. This species recovered quickly. In contrast, P. varians underwent partial bleaching and mortality on its upper surfaces only. P. varians colonies with an encrusting growth form bleached in a similar way to P. chiriquiensis, but no All 40 P. frondifera colonies sampled at Saboga Island showed identical banding patterns and fixed heterozygosity at the HK locus. In P. chiriquiensis, there were 39 different multi-locus genotypes in 61 specimens examined (63.9%). In P. varians, there were 75 in 173 specimens examined (43.4%). Eight enzymes were polymorphic (Table 5). The allozyme comparison of eight populations of P. varians, six populations of P. chiriquiensis, and three populations of P. frondifera indicated the distinctiveness of P. chiriquiensis. P. chiriquiensis differed strongly from both P. varians and P. frondifera, with Nei’s unbiased genetic distances of 0.434 (6.40 m.y.a.) and 0.379 (5.57 m.y.a.), respectively. A fixed difference was found at the triose phosphate isomerase (TPI-2) locus (Table 5). Nearly fixed differences exist between P. chiriquiensis and the other two species at the hexokinase (HK), the phosphogluconate dehydrogenase (PGDH), and the glutamate dehydrogenase (GTDH-2) loci. P. varians differed slightly from P. frondifera with Nei’s unbiased genetic Table 4 Intra- and interspecific contact-induced mortality in three Pavona species as measured by visible tissue loss. Maximum tissue dissolution for all interactions was approximately 1·1 mm. No mortality of the dominant species was observed. Duration of interactions was 3–7 days Pairing type Number of pairs Interspecific P. chiriquiensis–P. varians 50 P. chiriquiensis–P. frondifera 10 P. varians–P. frondifera 10 Intraspecific (fragments from different colonies) P. chiriquiensis–P. chiriquiensis 10 P. varians–P. varians 10 P. frondifera–P. frondifera 10 % of pairs aggressive % of stand-offs 50 100 100 50 0 0 0 0 0 100 100 100 Dominant species Onset days P. chiriquiensis P. chiriquiensis P. varians 1 1 1 – – – – – – 433 Table 5 Summary chart of sample size, number of genotypes, and gene frequencies for six populations of P. chiriquiensis, eight populations of P. varians, and three populations of P. frondifera collected on the Pacific coast of Panama. 1 Saboga Island; 2 Iguana P. chiriquiensis Site 2 n 6 Geno- 2 types Locus/Allele TPI-2 A 0 B 0.500 C 0.500 D 0 E 0 HK A 0 B 0 C 0 D 0 E 0 F 0 G 0 H 1.0 I 0 GPI A 0 B 0.167 C 0 D 0 E 0.833 F 0 PGDH A 0 B 0 C 1.0 D 0 E 0 F 0 GTDH-2 A 0 B 1.0 C 0 D 0 E 0 F 0 G 0 LVP-2 A 0 B 1.0 C 0 D 0 E 0 LPP A 0 B 0 C 0.500 D 0 E 0.500 F 0 GTDH-1 A 0 B 1.0 Island; 3 Jicarita Island; 4 Coiba Island; 5 Uva Island; 6 Secas Island; 7 Silva de Afuera Island; and 8 Montuosa Island. See Fig. 2 for geographical reference. LVP-1 and TPI-1 are monomorphic; n number of individuals P. varians 3 6 4 4 1 1 0 0.917 0.083 0 0 0 0.500 0.500 0 0 0 0 0 0 0.083 0 0 0 0.917 5 36 24 7 5 3 8 7 5 0.069 0.222 0.708 0 0 0 0.900 0.100 0 0 0 0.571 0.429 0 0 0 0 0 0 0 0 0 0.500 0.500 0 0 0.028 0 0 0.014 0.056 0.361 0.542 0 0 0 0 0 0 0 0.100 0.900 0 0 0 0 1.0 0 0 0 0 0 1.0 0 0.015 0.324 0.044 0.265 0.338 0.015 0 0 1.0 0 0 0 0 0 1.0 0 0 0 1.0 0 0 0 0 0 0 1 51 10 P. frondifera 2 5 5 3 2 1 6 9 5 7 5 3 8 9 6 0 0 0 1.0 0 0 0 0 0.9000 0.100 0 0 0 1.0 0 0 0 0 0.933 0.067 0 0 0 0.935 0.065 0 0 0 0.944 0.056 0 0 0 1.0 0 0 0 0 1.0 0 0 0 0 0 0 0 0 0.643 0.357 0 0 0.500 0.250 0 0 0 0.056 0.194 0 0 0 0 0 0 0 0.500 0.500 0 0 0 1.0 0 0 0 0 0 0.100 0 0.467 0.367 0 0 0 0 0.067 0 0 0.864 0.093 0 0 0 0.042 0 0 0 0.667 0.222 0 0 0 0.056 0.056 0 0 0.800 0.200 0 0 0 0 0 0 0.125 0 0.500 0.375 0 0 0.083 0 0.333 0.167 0.417 0.063 0.302 0.083 0 0.552 0 0 0 0 0 1.0 0 0 0 0 0 1.0 0 0 0 0.033 0.033 0.933 0 0 0.081 0.027 0 0.892 0 0 0.222 0.056 0 0.722 0 0 0 0.956 0.015 0.029 0 0 0 1.0 0 0 0 0 0 0.917 0 0.083 0 0 0 0 0 1.0 0 0 0 0.100 0.200 0.700 0 0 0 0 0 1.0 0 0 0 0 0 0.967 0.033 0 0.066 0.098 0 0.836 0 0 1.0 0 0 0 0 0 0.143 0.619 0.214 0.024 0 0 0 0 0.900 0.100 0 0 0 0 0 1.0 0 0 0 0 0 0 0 0.179 0 0.786 0.036 0 0 0.833 0.167 0 0 0 0 0 0 0 0 1.0 0 0 0 0 0.633 0 0.300 0.067 0 0 1.0 0 0 0 0 1.0 0 0 0 0 1.0 0 0 0 0 1.0 0 0 0 0 0.833 0.167 0 0 0 1.0 0 0 0 0.400 0.600 0 0 0 0 1.0 0 0 0 0.167 0 0.667 0 0.167 0 0 0 1.0 0 0 0 0.250 0 0.458 0 0.292 0 0 0 1.0 0 0 0 0 0 1.0 0 0 0 0.214 0 0.786 0 0 0 0 0.500 0.500 0 0 0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 distance of 0.068 (1 m.y.a.). No fixed differences were found between these species. The UPGMA phenogram shows all populations of P. chiriquiensis grouping 4 15 11 5 77 34 1 40 1 4 1 1 5 2 2 0 0 0 1.0 0 0 0 0 1.0 0 0 0 0 0.750 0.250 0.111 0 0.500 0.389 0 0 0 0 0 0.500 0.500 0 0 0 0 0 0 0 0 0 0.500 0.500 0 0 0 0 0 0 0 0.500 0.500 0 0 0 0 0 0 0.200 0 0 0.800 0 0 0 0.222 0 0.778 0 0 0 0 0 1.0 0 0 0 0 0 1.0 0 0 0 0 0 1.0 0 0 0 0 0 1.0 0 0 0 0 0 1.0 0 0.222 0 0 0 0.778 0 0 0 0 0 1.0 0 0 0 0 0 1.0 0 0 1.0 0 0 0 0 0 0.023 0.136 0 0.091 0.682 0.068 0 0 0.063 0 0.563 0.313 0.063 0 0 0.750 0 0.250 0 0 0 0 0 0 0.444 0.556 0 0 0 0 0 1.0 0 0 0 0 1.0 0 0 0 0 0 0 1.0 0 0 0 0 0 0.821 0.179 0 0 0 0.951 0 0.024 0.024 0 1.0 0 0 0 0 0 1.0 0 0 0.125 0.250 0.625 0 0 0 1.0 0 0 0 0 1.0 0 0 0 0 1.0 0 0 0 0.500 0 0.500 0 0 0 0 0.056 0.556 0 0.389 0 0 0.009 0.269 0.019 0.435 0.269 0 0 0 0 1.0 0 0 0 0 0 1.0 0 0 0.222 0.556 0 0.222 0 0 0 0 0 1.0 0 0 0 1.0 0 0 0 0 0 0 0 1.0 0 0 1.0 0 1.0 0.031 0.969 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 together before joining the other two species (Fig. 5). P. varians and P. frondifera did not show independent clustering (Fig. 5). 434 Fig. 5 Unweighted pair group method average phenogram using Nei’s unbiased genetic distances (Nei 1978) summarizing the relationships among 17 populations of three Pavona species from the Pacific coast of Panama. See Fig. 2A–D for locations of collection sites. The insert to the left summarizes the species relationships once all clonemates have been removed from the analysis Colony morphology, coloration, and morphometrics Colony morphology in P. varians is highly variable. It can be (1) encrusting to slightly massive on basalt rock, (2) platy or laminar on the skirts of massive colonies, on coralline and rocky ledges, and in crevices, (3) massive in reef habitats, on rubble, and soft bottoms, or (4) with secondary bifacial folia on platy or massive colonies on soft bottoms. Two or more growth forms may be found on different parts of the same colony. P. chiriquiensis and P. frondifera showed little or no variation in colony morphology. P. chiriquiensis is always encrusting and deposits a thin veneer of skeleton over the substrate, mainly basaltic rock. Colonies of P. frondifera are always encrusting with a compact foliose morphology. Encrusting colonies of P. varians and P. chiriquiensis follow the contour of the underlying substrate (from nearly horizontal to completely vertical). Slightly massive growth forms in P. varians may develop on portions of the encrusting colonies but rarely reach thicknesses greater than 10 cm. The platy growth forms of P. varians have a wedge appearance (i.e., thicker at the attachment point and gradually decreasing in thickness distally) and are always unifacial, and the calices are restricted to the upper surface. Massive colonies may be firmly attached to the substrata or completely free. Free colonies may occur as coralliths (Glynn 1974a), dome-shaped colonies, or other irregular shapes with tops showing partial or total mortality. Most coralla of P. varians are <30 cm in diameter, although some encrusting colonies may surpass 2.5 m. Colonies of P. chiriquiensis are generally small (<0.5 m2) but may rarely cover up to 10 m2 of substrate. The largest observed colony of P. frondifera measured only 78 cm in length by 50 cm in width. The polyps and coenosarc of P. chiriquiensis are light to dark brown, brick red to brown, or silvery blue and contrast with the bright white to silvery oral discs and tentacles (see also Glynn et al. 2001b). This contrast between the coenosarc and oral discs is a diagnostic feature of the species (Fig. 1B). Silvery blue and brick red colonies of P. chiriquiensis have been observed exclusively at Iguana Island (site 2, Fig. 2A) and at Silva de Afuera Island (site 7, Fig. 2D), respectively. Coenosarc, oral discs, and tentacles of both P. varians and P. frondifera are usually uniform in color (Fig. 1A, C). The color of P. varians varies from light to dark brown whereas the tissues of P. frondifera are pink to light or dark brown. Extremely dark colonies may be found in low-light habitats, such as crevices or the undersides of ledges. Canonical variate 1 (CV1) accounted for 83.6% of the variance. A chi-square analysis of the Wilk’s lambda showed the two canonical functions to have a significant discriminating power (P<0.001). CV1 separated P. chiriquiensis from P. varians and P. frondifera. CV2 separated P. frondifera from P. varians and further separated P. chiriquiensis from P. frondifera. CV1 was most heavily weighted for maximum calicular diameter (CD1), corallum thickness (CT), and maximum columellar diameter (CL1). CV2 was most heavily weighted for main septa length (SL), number of septa (NS1), minimum calicular diameter (CD2), and number of septa reaching the columella (NS2; see Table 3 for a description of skeletal characters measured and counted). 435 Differences between two of the three Pavona species were found in eight of the ten skeletal characters (Table 6). However, no single morphological character was simultaneously significantly different between all three species. P. chiriquiensis had significantly larger calicular and columellar diameters, and thinner corallum thickness than P. varians and P. frondifera (Table 6). Columellar diameter was smaller and the total number of septa were significantly lower in P. frondifera (Table 6). A discriminant canonical analysis of 19 populations of Pavona readily separated the three Pavona species in accordance with morphometric and genetic metrics (Fig. 6). The jackknife analysis indicated that 91.2% of all P. varians, 96.7% of P. chiriquiensis, and 90.0% of P. frondifera were correctly classified by the discriminant function. Discussion Consistent differences in habitat preferences, tissue coloration, skeletal morphology, allozyme patterns, and reproductive ecology have confirmed the separate specific status of Pavona varians, P. frondifera, and P. chiriquiensis (Table 7). The congruence of independent Table 6 Morphometric comparisons of the three Pavona species. Ph P. chiriquiensis, Pv P. varians, Pf P. frondifera. SNK Student– Newman–Keuls. NS not significant. See Table 3 and Fig. 3 for a description of characters Character Code P. chiriquiensis Mean±SE P. varians Mean±SE P. frondifera Mean±SE P a posteriori results of SNK Maximum calicular diameter Minimum calicular diameter Main septa length Maximum columellar diameter Minimum columellar diameter Colline width Number of septa Number of septa reaching the columella Number of septocostae Corallum thickness CD1 CD2 SL CL1 CL2 CW NS1 NS2 SC CT 1.85±0.05 1.11±0.04 0.62±0.02 0.34±0.03 0.20±0.02 0.90±0.02 20.02±0.53 7.17±0.16 6.77±0.50 15.14±1.48 1.31±0.03 1.50±0.02 0.47±0.01 0.26±0.01 0.16±0.01 0.50±0.03 19.86±0.62 7.88±0.15 7.08±0.20 55.52±3.64 1.23±0.04 1.04±0.03 0.53±0.02 0.17±0.01 0.12±0.01 0.56±0.05 15.96±0.74 6.73±0.28 6.66±0.80 92.27±11.57 *** *** *** *** *** NS * *** NS *** Ph>Pv, Pf Ph>Pv, Pf Ph, Pf>Pv Ph, Pv>Pf Ph, Pv>Pf – Ph, Pv>Pf Pv>Ph, Pf – Pv, Pf>Ph * P<0.05; *** P<0.001 Fig. 6 Canonical discriminant function scores for P. varians, P. chiriquiensis, and P. frondifera. Note that polygons enclosing all individuals of the same species show little overlap except for P. varians and P. frondifera, which are the most similar genetically. Stars represent group centroids. Corallite detail is shown for all species (Scales in mm) 436 characters has been shown to be a compelling argument to support species separations in scleractinian corals (Knowlton et al. 1992; Szmant et al. 1997). This study has also validated the use of traditional morphological analyses in the genus Pavona. However, members of this genus have posed some difficulties, as have members of the genus Leptoseris (see Dinesen 1980). Both genera belong to the family Agariciidae, which is characterized by thamnasteroid corallites (Wells 1956; Veron and Pichon 1979). These corallites lack a well-defined wall, making calicular measurements dependent upon one’s designation of the corallite border. Calicular diameter can be more easily estimated in those corallites located within collines. However, these corallites in general have a larger number of septa than those in open areas because many septocostae are inserted within the corallite. Macro-morphology is not a good character for distinguishing species boundaries among these three Pavona species. This is particularly true for P. varians, a species with high phenotypic plasticity. Even within a single colony it is possible to find three or four different growth forms that appear to reflect micro-habitat differences. In the western Pacific coral Pavona cactus Forskål, 1775 (Forskål 1775), there is a strong associa- tion between genotype and growth form (Ayre and Willis 1988). Although this type of association has not been investigated in Panamanian P. varians, this does not appear to be the case for this species, since multiple morphologies are found within a single colony. In contrast, P. chiriquiensis and P. frondifera appear to show little intraspecific variation, perhaps in part related to the narrower habitat preferences of these species. Skeletal plasticity similar to that observed in P. varians has also been observed in other coral species such as Montastraea spp. (Budd 1993), and Pocillopora damicornis (Veron and Pichon 1976). An important result of this study is the agreement between the reproductive findings and the allozyme data. Pavona varians and P. chiriquiensis were shown to be reproductively isolated in sympatry, both in terms of timing of spawning and gamete characteristics (Glynn et al. 2000; this study). Also, the genetic data indicate that P. chiriquiensis is clearly distinct from both P. varians and P. frondifera, and that P. varians differs less strongly from P. frondifera. The levels of divergence observed between species (0.068–0.434) are consistent with that reported for congeneric pairs of invertebrates (Thorpe 1983), as well as for other coral species (Weil and Knowlton 1994). Table 7 Species characteristics for Panamanian P. varians, P. chiriquiensis, and P. frondifera Character P. varians Growth morphology Thick and compact branching, Always encrusting, rarely encrusting on substrate with massive build-up; thin veneer of skeleton Pink to brown; polyps, oral disc, Light to dark brown, Light to dark brown; polyps, tentacles, and coenosarc oral disc, tentacles, and red-brick to brown, silvery blue of uniform coloration coenosarc of uniform coloration to brown; mouths and tentacles always white to silvery Dawn spawner, 1 h before Sunset spawner, 1 h after sunset; Unknown sunrise; eggs in mucus clouds of eggs and sperm strings; clouds of sperm White to beige eggs, Unknown Dark green eggs, 100.3±2.4 lm; 105.2±2.3 lm; positively neutrally to negatively buoyant; buoyant; eggs without eggs without zooxanthellae zooxanthellae Coloration Spawning characteristics Gamete characteristics Distribution Gulf of Panama Gulf of Chiriquı́ Other areas Habitat Depth range Colline type Corallite series From Baker (1999) P. frondifera Massive, encrusting, platy or laminar, rolling stone Abundant to rare depending on site Common to rare depending on site Indo-west Pacific Reef, rocky substrata, soft sediments (coarse sand–muddy) Shallow to deep, 1–16.7 m Short or long collines, uniform; collines one or many corallites in width Most commonly >4; may reach 17 in skirt platy growth forms Calice diameter (mean±SE) 0.825–2.11 mm (1.37±0.04) Number of septa (mean) 13–36 (20) C1 Zooxanthella cladea Corallum thickness 27–110 mm a P. chiriquiensis Rare at the two sites found Abundant to rare depending on site Restricted to the eastern Pacific Almost exclusively on basalt; only four specimens found on reefs Shallow to deep, 3–15.1 m Short collines, mostly irregular; many hydnophorae; collines commonly one corallite in width, rarely more than two corallites in width Commonly 2–4; in rare occasions may reach 5–7 1.25–2.32 mm (1.91±0.07) 10–28 (21) C1 5–40 mm Present at only one locality, a single clone Extremely rare; found at just two sites Indo-west Pacific Almost exclusively a reef species; two specimens found on soft bottom Mostly shallow, 3.5–13 m Generally long collines; collines in general one corallite in width Commonly >5; may reach 16 0.95–1.42 mm (1.25±0.03) 14–18 (16) C1 45–157 mm 437 The use of electrophoretic data to identify precisely even completely reproductively isolated species may only be possible if the species have evolved some ‘‘fixed’’ allelic differences at one or more loci (Richardson et al. 1986). These reproductively isolated taxa will, in time, accumulate additional fixed genetic differences (Knowlton and Weigt 1997). The fixed and the two nearly fixed differences between P. varians and P. chiriquiensis confirm that these species are indeed reproductively isolated distinct species in the biological sense (Mayr 1970). It has been suggested that some reproductively isolated taxa may exhibit only small levels of genetic differentiation due to a recent origin, slow rates of molecular evolution, or large population sizes (McFadden 1999). This may be the case for P. frondifera, but additional studies are needed on its reproductive biology and other life-history characteristics. The reproductive patterns observed in P. varians and P. chiriquiensis suggest likely mechanisms underlying the maintenance of species boundaries by extreme prezygotic barriers to successful fertilization (both temporal and gamete characteristics). Differences in reproductive timing or in gamete recognition systems that control fertilization have been recognized as the most likely barriers to reproduction among octocorals in the Alcyonium coralloides complex (McFadden 1999). Similarly, dilution (increasing with time), duration of gamete viability (decreasing with time), and egg–sperm contact time have been reported to reduce fertilization success in other marine organisms with external fertilization (Levitan et al. 1991; Oliver and Babcock 1992; Palumbi 1994; Szmant et al. 1997; Willis et al. 1997; Maté et al. 1998), thus minimizing interspecific hybridization. Knowlton et al. (1997) noted that a difference in spawning times of just 1–2 h was sufficient to maintain reproductive isolation between Montastraea franksi and M. annularis on the Caribbean coast of Panama. Thus, spawning in P. varians and P. chiriquiensis, being out of phase by more than 12 h, should prevent successful fertilization under field conditions. Dawn spawners are rare in corals and may be restricted to the genus Pavona. P. cactus on the Great Barrier Reef (Marshall and Stephenson 1933) and P. varians in Panama (this study) are the only dawn spawners known to date. Even though P. varians and P. chiriquiensis spawn near extreme high-water stands, the eggs of P. chiriquiensis are negatively buoyant, possibly facilitating retention on the reef during peak spring tides (Babcock et al. 1986). However, the eggs of P. varians are positively buoyant, and thus likely to be dispersed off-reef. Thus, the characteristics of the gametes may possibly help explain the distributional patterns of both species. Colonies of P. cactus with the same genotype have been shown to be separated by distances of up to 93 m (Ayre and Willis 1988). This lack of genetic variation is consistent with an asexual reproductive mode (Ayre and Willis 1988; McFadden 1999). Populations of species with asexual reproduction are often dominated locally by individuals belonging to one or a few clones (Wright 1969; Jain 1976; Suomaleinen et al. 1976; Baur and Klemm 1989). From the allozyme data of P. frondifera at Saboga Island (Gulf of Panama), the 40 colonies studied were genetically identical and thus probably asexually produced. Allozyme patterns in P. varians and P. chiriquiensis also provide evidence of the presence for clonal reproduction within populations. Most of the collections for allozyme work were completed before the 1997–1998 El Niño event. At that time, adjacent colonies were considered to have recruited sexually on the basaltic substrata. However, six colonies monitored at Uva Island (Gulf of Chiriquı́) before, during, and after the 1997–1998 El Niño event suggested that these adjacent colonies were surviving fragments of a larger colony that probably suffered partial mortality in previous disturbances. Colonies that ranged in size from 1.5 to 7 m in length suffered massive mortalities during the 1997–1998 El Niño and produced 10–115 isolated fragments each, some close to each other, some farther apart. Although this hypothesis of clonality by partial colony mortality may seem feasible for P. chiriquiensis, it is less likely for P. varians. Coral mortality in P. varians during the 1982–1983 and 1997–1998 El Niño events was low and limited to the upper surfaces and did not fragment larger colonies into smaller ones. The activities of predatory fishes that feed on boring Lithophaga bivalves may provide an alternative explanation for P. varians. Fish like Pseudobalistes naufragium Jordan and Starks and Balistes polylepis Steindachner have been observed to remove chunks of skeleton from Pavona varians in search of those bivalves (see Glynn et al. 1972, Fig. 12, p. 503). These broken fragments may survive and later grow larger colonies in relatively close proximity to their parent colony. The high sensitivity of P. chiriquiensis to warm waters that accompanied the 1997–1998 El Niño is compared to that of fire corals in the genus Millepora (Glynn 1990; Glynn and Feingold 1992; Glynn et al. 2001a, b). However, the ability of P. chiriquiensis to recover from this disturbance surpasses that of the fire corals. Five years after the event, most of the colonies of P. chiriquiensis had increased considerably in size, approximating colony sizes before the disturbance (see Table 7 in Glynn et al. 2001a). Millepora colonies, however, had not yet recovered (Glynn et al. 2001a). Reef-building corals maintain an obligate association with endosymbiotic zooxanthellae. However, not until recently has the importance of this symbiosis, in terms of zooxanthellae diversity, been recognized as a possible determinant of coral zonation (Rowan and Knowlton 1995) and coral bleaching (Rowan et al. 1997). Whereas in the Caribbean coral genus Montastraea bleaching differences can be attributed to the zooxanthella genotypes they harbor, bleaching in Panamanian Pavona cannot be attributed to differences in the symbionts hosted since the species harbor the same type (clade C1) of symbiont (Baker 1999; Glynn et al. 2001a). Thus, zooxanthella genetic 438 diversity does not appear to impart ecological or taxonomic differences between these Pavona species. Although tissue colors are considered the most common ‘‘live coral’’ trait mentioned by systematists (Lang 1984), in most species diagnoses this trait is omitted. Glynn et al. (2001b) showed that tissue coloration is a diagnostic field character for P. chiriquiensis. The validity of this character has been confirmed by the present study. All specimens observed in Panama had dark polyps and coenosarc, and contrasting bright white to silvery oral discs and tentacles. Other coral species descriptions that have included tissue coloration as a diagnostic character include those of Scolymia spp. (Lang 1971) and Mycetophillia spp. (Wells 1973). In terms of species distributions, the case of P. chiriquiensis may be the most interesting one. The distribution of this species in Panama may suggest the preference for year-round warm habitats (it is common in the Gulf of Chiriquı́ but rare in the Gulf of Panama). However, this species is also abundant in the relatively cool waters of the Galápagos Islands (Glynn et al. 2001b). It is possible that the distributional pattern of this species may be related to the peak reproductive season from January to June (Glynn et al. 2000) when the Gulf of Panama experiences cold (16–25C) seasonal upwelling (Glynn and Maté 1997). Although the low water temperatures may not be that critical for the survival of adult colonies, they may affect fecundity and larval survival, becoming a physical barrier for the expansion of the species into the Gulf of Panama. In the Galápagos Islands, the peak of the reproductive season occurs from January to May (Glynn et al. 2000), which spans the warmest months of the year there (Podestá and Glynn 1997). This may explain the high abundance of the species at several localities within the Galápagos Islands. Still, we do not know how the species got established there, nor why P. varians with its reproductive peak at the same time as P. chiriquiensis is abundant in the Gulf of Panama. Corals can compete for space by direct and indirect means (Jackson and Hughes 1985). Direct interactions, such as those observed in the Caribbean coral genus Scolymia (see Lang 1973), normally involve an aggressive behavior wherein the dominant colony or species digests the tissues of the subordinate neighbor. In contrast, indirect interactions involve the growth of one colony above another, depriving it of light or food (Connell 1973). P. varians and P. chiriquiensis exhibited both types of interactions. During the direct interaction phase, P. chiriquiensis is able to digest rapidly the tissues of P. varians (within 1 day). In the longer term, however, P. varians is able indirectly to outcompete P. chiriquiensis by overtopping it. Similar reversals have been observed between P. gigantea Verrill, 1869 (Verrill 1869) and Pocillopora damicornis Linnaeus in Panama (see Wellington 1980). In the laboratory, Pavona frondifera is the subordinate species of the three herein tested. In conclusion, P. varians, P. chiriquiensis, and P. frondifera are three distinct species that show clear differences in almost all of the characters considered in this study. Acknowledgements I would especially like to thank N. Budd, L. D’Croz, P.W. Glynn, H. Guzmán, J.B.C. Jackson, J. Leal, H. Lessios, N. Knowlton, B. Vargas-Ángel, and S. Williams, who offered helpful discussions during this work. Most of this work was accomplished at the Naos Marine Laboratory facilities of the Smithsonian Tropical Research Institute (STRI) in the Republic of Panama. The government of Panama granted permission for coral collections through the Autoridad Nacional del Ambiente (ANAM). Material for this work was collected during several cruises to study sites in Panama. I am grateful for assistance offered in the field by the captains and crews of the R.V. ‘‘Urracá.’’ Field assistance was kindly given by A. Armitage, A. Baker, O. Barrio, J. Borger, A. Calderón, R. Cohen, S.B. Colley, M. Eakin, P. Fong, C. Hueerkamp, M. Medina, J.B. Del Rosario, J. Jara, E. Peña, D.R. Robertson, F. Rodrı́guez, J. Smith, T. Smith and A. Velarde. For assistance with laboratory work, I would like to thank M. Calderón, A. Domingo, E. Gómez, I. Hernández, and E. Peña. For providing access to specimens from museums, thanks are due E. Lazo-Wasem, Peabody Museum of Natural History, Yale University; S.D. Cairns, U.S. National Museum of Natural History, Smithsonian Institution; N. Voss, Division of Marine Biology and Fisheries, University of Miami; M.B. Goodwin, Museum of Paleontology, University of California, Berkeley. Thanks to N. Budd, L. D’Croz, P.W. Glynn, H. Guzmán, J.B.C. Jackson, and N. Knowlton for providing working space. Financial support comes from the U.S. National Science Foundation Grant OCE-9711529 (and earlier awards to P.W. Glynn), STRI, and Smithsonian Institution predoctoral fellowship, the PADI Project Aware Foundation, the Sigma Xi Society, the Lerner-Gray Fund for Marine Research (American Museum of Natural History), and the Founders Research Award and an Anonymous Donor Award, both from the Rosenstiel School of Marine and Atmospheric Science. References Avise JC (1974) Systematic value of electrophoretic data. Syst Zool 23:465–481 Avise JC (1994) Molecular markers, natural history and evolution. Chapman and Hall, New York Ayre DJ, Willis BL (1988) Population structure in the coral Pavona cactus: clonal genotypes show little phenotypic plasticity. Mar Biol 99:496–505 Ayre DJ, Veron JEN, Dufty SL (1991) The corals Acropora palifera and Acropora cuneata are genetically and ecologically distinct. Coral Reefs 10:13–18 Babcock RC, Bull GD, Harrison PL, Heyward AJ, Oliver JK, Wallace CC, Willis BL (1986) Synchronous spawnings of 105 scleractinian coral species on the Great Barrier Reef. Mar Biol 90:379–394 Baker AC (1999) The symbiosis ecology of reef-building corals. PhD dissertation, University of Miami Baur B, Klemm M (1989) Absence of isozyme variation in geographically isolated populations of the land snail Chondrina clienta. Heredity (Lond) 63:239–244 Budd AF (1993) Variation within and among morphospecies of Montastraea. Courier Forsch Inst Senckenberg 164:241–254 Connell JH (1973) Population biology of reef-building coral. In: Jones OA, Endean R (eds) Biology and geology of coral reefs, vol 2. Academic Press, New York, pp 205–245 Cortés J, Guzmán H (1998) Organismos de los arrecifes coralinos de Costa Rica: descripción, distribución geográfica e historia natural de los corales zooxantelados (Anthozoa: Scleractinia) del Pacı́fico. Rev Biol Trop 46:55–92 Dai C-F, Lin C-H (1992) Scleractinia of Taiwan III. Family Agariciidae. Acta Oceanogr Taiwan 28:80–101 Dana JD (1846) United States exploring expedition during the years 1838, 1839, 1840, 1841, 1842. Under the command of Charles Wilkes, USN. Zoophytes. Lea & Blanchard, Philadelphia 439 Dinesen ZD (1980) A revision of the coral genus Leptoseris (Scleractinia: Fungiina: Agariciidae). Mem Queensl Mus 20:181–235 Forskål P (1775) Descriptiones Animalium, Avium, Amphibiorum, Piscium, Insectorum, Vermium que in intinere orientali observavit Petrus Forskål IV. Corallia. Hauniae 131–139 Glynn PW (1974a) Rolling stones among the Scleractinia mobile coralliths in the Gulf of Panamá. Proc 2nd Int Coral Reef Symp 2:183–198 Glynn PW (1974b) The impact of Acanthaster on corals and coral reefs in the eastern Pacific. Environ Conserv 1:295–304 Glynn PW (1976) Some physical and biological determinants of coral community structure in the eastern Pacific. Ecol Monogr 46:431–456 Glynn PW (1983) Extensive bleaching and death of reef corals on the Pacific coast of Panama. Environ Conserv 10:149–154 Glynn PW (1990) Coral mortality and disturbances to coral reefs in the tropical eastern Pacific. In: Glynn PW (ed) Global ecological consequences of the 1982–1983 El Niño-Southern Oscillation. Elsevier, Amsterdam, pp 55–126 Glynn PW, Ault J (2000) A biogeographic analysis and review of the far eastern Pacific coral reef region. Coral Reefs 19:1–23 Glynn PW, Feingold JS (1992) Hydrocoral species not extinct. Science 257:1845 Glynn PW, Maté JL (1997) Field guide to the Pacific coral reefs of Panamá. Proc 8th Int Coral Reef Symp 1:145–166 Glynn PW, Wellington GM (1983) Corals and coral reefs of the Galápagos Islands. University of California Press, Berkeley Glynn PW, Stewart RH, McCosker JE (1972) Pacific coral reefs of Panamá: structure, distribution and predators. Geol Rundschau 61:483–519 Glynn PW, Prahl H von, Guhl F (1982) Coral reefs of Gorgona Island, Colombia, with special reference to corallivores and their influence on community structure and reef development. Ann Inst Inv Mar Punta de Betin 12:185–214 Glynn PW, Colley SB, Ting JH, Maté TJL, Guzmán HM (2000) Reef coral reproduction in the eastern Pacific: Costa Rica, Panamá, and Galápagos Islands (Ecuador) IV. Agariciidae (Pavona varians and Pavona sp. a). Mar Biol 136:785–805 Glynn PW, Maté JL, Baker A, Calderón MO (2001a) Coral bleaching and mortality in Panamá and Ecuador during the 1997–98 El Niño-Southern Oscillation event: spatial/temporal patterns and comparisons with the 1982–83 event. Bull Mar Sci 69:79–109 Glynn PW, Maté JL, Stemann T (2001b) Pavona chiriquiensis, a new species of zooxanthellate scleractinian coral (Cnidaria: Anthozoa: Agariciidae) from the eastern tropical Pacific. Bull Biol Soc Wash 10:210–225 Guzmán HM, Cortés J (1989) Growth rates of eight species of scleractinian corals in the eastern Pacific (Costa Rica). Bull Mar Sci 44:1186–1194 Harris H, Hopkinson DA (1976) Handbook of enzyme electrophoresis in human genetics. Elsevier, New York Jackson JBC, Hughes TC (1985) Adaptative strategies of coral-reef invertebrates. Am Sci 73:265–274 Jain SK (1976) The evolution of inbreeding plants. Annu Rev Ecol Syst 7:469–495 Knowlton N, Weigt LA (1997) Species of marine invertebrates: a comparison of the biological and phylogenetic species concepts. In: Claridge MF, Dawah HA, Wilson MR (eds) Species: the units of biodiversity. Chapman & Hall, London, pp 199–219 Knowlton N, Weil E, Weigt LA, Guzmán HM (1992) Sibling species in Montastraea annularis, coral bleaching, and coral climate record. Science 255:330–333 Knowlton N, Maté JL, Guzmán HM, Rowan R, Jara J (1997) Direct evidence for reproductive isolation among the three species of the Montastraea annularis complex in Central America (Panamá and Honduras). Mar Biol 127:705–711 Lamarck JBP (1816) Historie naturelle des animaux sans vertèbres, vol 2. Verdière, Paris Lang J (1971) Interspecific aggression by scleractinian corals 1. The rediscovery of Scolymia cubensis (Milne Edwards & Haime). Bull Mar Sci 21:952–959 Lang J (1973) Interspecific aggression by scleractinian corals 2. Why the race is not only to the swift. Bull Mar Sci 23:260–279 Lang JC (1984) Whatever works: the variable importance of skeletal and of non-skeletal characters in scleractinian taxonomy. Palaeontogr Am 54:18–44 Levitan DR, Sewell MA, Chia F-S (1991) Kinetics of fertilization in the sea urchin Strongylocentrotus franciscanus: interaction of gamete dilution, age, and contact time. Biol Bull 181:371–378 Marshall SM, Stephenson TA (1933) The breeding of reef animals, part I. The corals. Sci Rep Great Barrier Reef Exped 1928–29 3:219–245 Maté TJL, Wilson J, Field S, Neves E (1998) Fertilization dynamics and larval development of the scleractinian coral Montipora verrucosa in Hawaii. (Technical report no. 42) University of Hawaii and Hawaii Institute of Marine Biology, Kaneohe, Hawaii, pp 27–39 Mayr E (1970) Populations, species, and evolution. Harvard University Press, Cambridge, Mass. McFadden CS (1999) Genetic and taxonomic relationships among Northeastern Atlantic and Mediterranean populations of the soft coral Alcyonium coralloides. Mar Biol 133:171–184 Nei M (1978) Estimation of average heterozygosity and genetic distance from a small number of individuals. Genetics 89:583– 590 Oliver JK, Babcock RC (1992) Aspects of the fertilization ecology of broadcast spawning corals: sperm dilution effects and in situ measurements of fertilization. Biol Bull 183:409–417 Palumbi SR (1994) Genetic divergence, reproductive isolation, and marine speciation. Annu Rev Ecol Syst 25:547–572 Podestá GP, Glynn PW (1997) Sea surface temperature variability in Panamá and Galápagos: extreme temperatures causing coral bleaching. J Geophys Res 102:15749–15759 Potts DC, Garthwaite RL (1991) Evolution of reef-building corals during periods of rapid global change. In: Dudley EC (ed) The unity of evolutionary biology: proceedings of the fourth international congress of systematic and evolutionary biology, vol 1. Dioscoroides Press, Portland, Ore., pp 170–178 Potts DC, Budd AF, Garthwaite RL (1993) Soft tissue vs. skeletal approaches to species recognition and phylogeny reconstruction in corals. Courier Forsch Inst Senckenberg 164:221–223 Richardson BJ, Baverstock PR, Adams M (1986) Allozyme electrophoresis: a handbook for animal systematics and population studies. Academic Press, New York Rowan R, Knowlton N (1995) Intraspecific diversity and ecological zonation in coral-algal symbiosis. Proc Natl Acad Sci U S A 92:2850–2853 Rowan R, Knowlton N, Baker A, Jara J (1997) Landscape ecology of algal symbionts creates variation in episodes of coral bleaching. Nature 388:265–269 Selander RK, Smith MH, Yang SY, Johnson WE, Gentry JR (1971) Biochemical polymorphism and systematics in the genus Peromyscus. Stud Genet VI. Univ Texas Publ 7103:49–90 Stoddart JA (1983) Asexual production of planulae in the coral Pocillopora damicornis. Mar Biol 76:279–284 Suomaleinen E, Saura A, Lokki J (1976) Evolution of parthenogenetic insects. Evol Biol 9:209–257 Swofford DL, Selander RB (1989) BIOSYS-1. A computer program for the analysis of allelic variation in population genetics and biochemical systematics, release 1.7. Illinois Natural History Survey, Champaign, Ill. Szmant AM, Weil E, Miller MW, Colón DE (1997) Hybridization within the species complex of the scleractinain coral Montastraea annularis. Mar Biol 129:561–572 Thorpe JP (1983) Enzyme variation, genetic distance and evolutionary divergence in relation to levels of taxonomic separation. In: Oxford GS, Rollinson D (eds) Protein polymorphism: adaptative and taxonomic significance. Academic Press, London, pp 131–152 440 Vargas-Ángel B (1996) Distribution and community structure of the reef corals of Ensenada de Utrı́a, Pacific coast of Colombia. Rev Biol Trop 44:643–651 Vaughan TW, Wells JW (1943) Revision of the suborders, families, and genera of the Scleractinia. (Special paper 44) Geological Society of America and University of Kansas Press, Lawrence, Kan. Veron JEN (1993) A biogeographic database of hermatypic corals. Species of the central Indo-Pacific genera of the world. Aust Inst Mar Sci Monogr Ser 10:1–433 Veron JEN, Pichon M (1976) Scleractinia of eastern Australia Part I. Families Thamnasteriidae, Astrocoeniidae, Pocilloporidae. Aust Inst Mar Sci Monogr Ser 1:1–86 Veron, JEN, Pichon M (1979) Scleractinia of eastern Australia, part III. Families Agariciidae, Siderastreidae, Fungiidae, Oculinidae, Merulinidae, Mussidae, Pectiniidae, Caryophylliidae, Dendrophylliidae. Aust Inst Mar Sci Monogr Ser 4:1–459 Verrill AE (1864) List of the polyps and coral sent by the Museum of Comparative Zoology to other institutions in exchange, with annotations. Bull Mus Comp Zool Harvard Univ 1:29–60 Verrill AE (1869) Review of the corals and polyps of the west coast of America. Trans Conn Acad Arts Sci 1:377–596 Weil E, Knowlton N (1994) A multi-character analysis of the Caribbean coral Montastraea annularis (Ellis and Solander, 1786) and its two sibling species, M. faveolata (Ellis and Solander, 1876) and M. franksi (Gregory 1895). Bull Mar Sci 55:151–175 Weil E, Weigt LA (1996) Protein starch-gel electrophoresis in scleractinian corals: a report on techniques and troubleshooting. CMRC Tech Rep Ser 96-13:1–35 Wellington GM (1980) Reversal of digestive interactions between Pacific reef corals: mediation by sweeper tentacles. Oecologia 47:340–343 Wells JW (1956) Scleractinia. In: Moore RC (ed) Treatise on invertebrate paleontology, vol F. Geological Society of America and University of Kansas Press, Lawrence, Kan., p F328 Wells JW (1973) New and old scleractinian corals from Jamaica. Bull Mar Sci 23:16–58 Williams ST (1992) Methods for the analysis of genetic variation in the starfish, Linckia laevigata, using allozyme electrophoresis. Aust Inst Mar Sci Rep 6:1–34 Williams ST (2000) Species boundaries in the starfish genus Linckia. Mar Biol 136:137–148 Willis BL, Babcock RC, Harrison PL, Wallace CC (1997) Hybridization and breeding incompatibilities within the mating systems of mass spawning reef corals. Proc 8th Int Coral Reef Symp 1:81–90 Wright S (1969) Evolution and the genetics of populations, vol 2. The theory of gene frequencies. University of Chicago Press, Chicago Yabe H, Sugiyama T, Eguchi M (1936) Recent reef-building corals from Japan and the south sea islands under the Japanese mandate I. Sci Rep Tohoku Univ Geol (2) spec 1:1–66