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| Author(s): |
Marcio Camargo Araujo João
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Rio Claro. 2022-01-25. |
| Institution: | Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro |
| Defense date: | 2022-01-20 |
| Advisor: | Marcelo Antonio Amaro Pinheiro; Rafael Campos Duarte |
| Abstract | |
Land crabs (Gecarcinidae family) are key species for the maintenance and stability of insular communities. However, this group is poorly studied and many species are directly impacted by the increasing of human colonization in oceanic islands, mainly for the introduction of exotic species. Johngarthia lagostoma is an endemic crab of South Atlantic oceanic islands and was evaluated as “Endangered” (EN) in the Brazilian territory following the IUCN criteria. This dissertation addresses some population aspects for this species from the Trindade Island (Brazil) across three chapters. In Chapter 1 the relative growth pattern and the chronology of sexual maturity was assessed for J. lagostoma males and females, being the first detailed study with this purpose for an insular gecarcinid species. Both sexes reach the morphological, physiological, and functional sexual maturity within a small carapace width range (~ 10 mm CW), with functionally mature male and females occurring at similar sizes (males: 56.4 mm CW; and females: 56.6 mm CW). These values corresponded to approximately half of the maximum size that J. lagostoma reaches in Trindade Island (105.5 mm CW), being close to those registered to other Gecarcinidae species. Chapter 2 addresses the structure and organization of a J. lagostoma population during the reproductive season in locals with distinct altitude degree in the Trindade Island, which would help us to identify reproductive areas and sites of high juvenile density. In general, males and adult crabs are predominant in the island, compared to females and juveniles. However, in one sampled beach (Andradas) it was observed the highest predominance of adults, as well as similar frequencies of reproductive individuals and the occurrence of ovigerous females, being considered a reproductive area. In contrast, in one moderate altitude hill (Príncipe Hill, 136 m) it was registered the higher proportion of juvenile crabs (12.9-56.6 mm CW), being categorized as a nursery area. Therefore, these two locations are considered here as a priority for the management and conservation of J. lagostoma in Trindade Island. Along the Chapter 3, the occurrence of distinct J. lagostoma color types in the Trindade Island were investigated, testing if this variation is regulated by ontogenetical, sexual and/or ecological aspects. In addition, it was tested the background matching between the color types and the predominant substrates occurring in beach and hill habitats where crabs were sampled. An ontogenetic color change was confirmed for J. lagostoma, with the smaller crabs (< 30 mm CW) exhibiting a black coloration, possibly with adaptive value for camouflage since they are able to conceal against the substrate where they recruit (sand beaches) and are more frequent (hill land substrates), both composed by volcanic dark sediments. On the other hand, larger crabs exhibit yellow and purple coloration, with no relationship to the sex of individuals, being the yellow pattern the most frequent in the island. However, it was not confirmed whether such color variation in adult crabs has any adaptive value, with color types being possibly maintained in the population by neutral selection, as described for other insular land crustaceans. Nevertheless, several color types apparently occur in many gecarcinid species, but this information is poorly investigated in the literature to date. Finally, our results compose important findings of the J. lagostoma life-history, mainly because this is an isolated and less impacted population. Therefore, future studies with J. lagostoma populations from other islands, as well with other insular land crab species, are essential to better understand the biology of this group. Increasing such type of studies is urgently need and can help us to give baseline information for the management and conservation of endemic species from oceanic island, which are highly sensible for environment changes caused by human activities. (AU) | |
| FAPESP's process: | 19/16581-9 - Population biology of yellow crab Johngarthia lagostoma (Brachyura: Gecarcinidae) on Trindad island, Brazil |
| Grantee: | Marcio Camargo Araujo João |
| Support Opportunities: | Scholarships in Brazil - Master |