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Intraspecific color diversity and camouflage associated with ontogeny in an insular land crab

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Abstract

Many species exhibit high intraspecific color variation between sexes or ontogenetic phases due to sexual selection or sex-/age-specific differential predation. In crabs, the function and adaptive value of carapace coloration have been investigated mainly in aquatic and/or intertidal species, and it is poorly understood in terrestrial species (Gecarcinidae), which are exposed to different selective pressures. Using digital photography and image analysis, we tested if the coloration of the insular land crab Johngarthia lagostoma in Trindade Island (Brazil) varies according to individuals’ size, sex and ecological processes related to the differential occupation of the available habitats. Three color types were observed (black, purple and yellow), with black crabs being exclusive and predominant in the smaller size classes (carapace width < 30 mm). After this size threshold, yellow crabs dominate throughout ontogeny, while purple individuals are less frequent. Crabs of the three color types occur in both sexes, and the frequency of each type, as well as their brightness and color metrics, was similar between males and females. Black and purple crabs occupy mainly hill areas, but yellow crabs predominate throughout the island. Camouflage by background matching seems to be particularly important for small black crabs at recruitment (sand of the beaches) and resident areas (hills vegetation and soil), where individuals exhibit higher color matching. However, although yellow and purple crabs conceal better against hill and beach backgrounds, respectively, their coloration is probably under neutral selection and has no function for camouflage, since large J. lagostoma crabs are rarely predated in nature.

Significance statement

Intraspecific color variability is common in many animal species and can be linked to different ecological processes. In crabs, the function of body coloration for camouflage has been studied mainly in aquatic species that are exposed to high-predation pressure. However, land crabs also exhibit a remarkable intraspecific color variation, but are exposed to reduced predation pressure especially on oceanic islands, and therefore, the function of coloration remains unexplained. We used digital photography and image analysis to assess the general appearance of an insular land crab species. Our results indicate that small individuals, which are under high predation and cannibalism risk, are black and match background color, while large crabs are purple or yellow, but their coloration probably has no camouflage function.

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All data was submitted as electronic supplementary material.

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Acknowledgements

We are thankful to the Brazilian Navy (1st District), SECIRM (Inter-ministerial Secretariat for Marine Resources), and PROTRINDADE (Research Program of the Trindade Island) in the person of the commanders L. Felipe S. Santos and C. C. Vitória Regia, who guaranteed the presence of the authors in the Trindade Island and helped with the project logistic. The authors thank Isis Batistela, Nicholas Kriegler and Vanessa Martins for helping during the field sampling. We also thank Tim Caro and one anonymous referee for their helpful comments on the manuscript.

Funding

MCAJ and RCD thanks to “Fundação de Amparo à Pesquisa do Estado de São Paulo – FAPESP” by the master (FAPESP 2019/16581–9) and postdoctoral (FAPESP 2019/01934–3; 2022/00946–0) fellowships, respectively. MAAP thanks “Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq” due to the financial support provided by “Oceanic Island Crabs” Project (CNPq no. 404224–2016), which guaranteed this study, as well as by the Research Productivity Fellowship granted to ASF and MAAP (CNPq no. 311994/2016–4 and no. 305957/2019–8, respectively).

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Contributions

MCAJ, RCD, and MAAP conceived the idea and design the study. MCAJ sampled and photographed the crabs. MCAJ analyzed all the images and data. MCAJ wrote the first version of the manuscript with the supervision of RCD and MAAP. All authors contributed to the revisions and approved the final version of the manuscript.

Corresponding author

Correspondence to Marcio C. A. João.

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Ethical approval

All samples were conducted following permission and rules of Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) and supported by Sistema de Autorização e Informação da Biodiversidade (SISBIO no. 65446).

Conflict of interest

The authors declare no competing interests.

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Communicated by T. Breithaupt.

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João, M.C.A., Duarte, R.C., Freire, A.S. et al. Intraspecific color diversity and camouflage associated with ontogeny in an insular land crab. Behav Ecol Sociobiol 77, 120 (2023). https://doi.org/10.1007/s00265-023-03394-8

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  • DOI: https://doi.org/10.1007/s00265-023-03394-8

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