Biologia populacional do caranguejo-amarelo Johngarthia lagostoma (H. Milne Edwards, 1837) (Crustacea: Brachyura: Gecarcinidae), na Ilha da Trindade, Brasil
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Data
2022-01-20
Autores
João, Marcio Camargo Araujo [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Os caranguejos terrestres (família Gecarcinidae) são espécies-chave para a manutenção e equilíbrio de comunidades insulares. No entanto, os estudos biológicos sobre estes caranguejos ainda são incipientes. Além disso, a maioria das espécies deste grupo sofrem impactos devido a antropização das ilhas oceânicas, principalmente pela introdução de espécies invasoras. O caranguejo Johngarthia lagostoma é endêmico de ilhas oceânicas do Atlântico Sul e categorizado como “Em perigo (EN)” de extinção no território brasileiro, segundo os critérios da IUCN. Esta dissertação aborda alguns parâmetros populacionais para esta espécie na Ilha da Trindade (Brasil), por meio de três capítulos distintos. No Capítulo 1, foram avaliados os padrões de crescimento relativo e a cronologia da maturidade sexual de J. lagostoma. Trata-se de estudo pioneiro e devidamente detalhado para os gecarcinídeos insulares. De modo geral, ambos os sexos alcançaram sua maturidade morfológica, fisiológica e funcional dentro de um reduzido intervalo de largura cefalotorácica (~10 mm LC), com sincronia entre o tamanho em que cada sexo está funcionalmente apto à reprodução (machos: 56,4 mm LC; e fêmeas: 56,6 mm LC). Similarmente aos outros gecarcinídeos, J. lagostoma alcança a maturidade com cerca de metade de seu tamanho máximo registrado em campo (105,5 mm LC), valor este que pode ser utilizado com propósitos de manejo. O Capítulo 2 aborda a estrutura e organização de uma população de J. lagostoma durante seu período reprodutivo, em locais de distintas altitudes na Ilha da Trindade, identificando áreas de reprodução e maior adensamento juvenil. Para o geral da ilha, ocorreu um predomínio de machos e indivíduos adultos, em detrimento das fêmeas e caranguejos juvenis. Porém, para uma das praias (Andradas) ocorreu o maior adensamento de indivíduos adultos, frequência similar entre os indivíduos reprodutivos de ambos os sexos e o registro de fêmeas ovígeras, caracterizando este local como uma área reprodutiva. Por outro lado, no Morro do Príncipe, local de altitude moderada (136m), foi registrado o maior adensamento de juvenis (12,9-56,6 mm LC). Assim, ambos os locais são considerados como de prioridade ao manejo e conservação da espécie na Ilha da Trindade. Ao longo do Capítulo 3, foram investigadas as ocorrências de distintos tipos cromáticos de J. lagostoma, testando se esta variação é influenciada por fatores ontogenéticos, sexuais e locais na Ilha da Trindade. Além disso, foi verificado se os tipos de cor se assemelham à coloração dos substratos disponíveis nos ambientes de praia e morro. Neste sentido, foi confirmada uma variação ontogenética para a espécie, com os menores caranguejos (< 30 mm LC) apresentando a coloração preta, com valor adaptativo para camuflagem, por se assemelhar ao substrato onde recrutam (areia das praias) e se adensam (terra de morro), que são compostos por sedimento de origem vulcânica, com coloração escura. Os adultos, por outro lado, compreendem dois padrões cromáticos (roxo e amarelo), indistintamente entre os sexos, com os amarelos predominando em toda a ilha. No entanto, não foi confirmado se esta variação dicromática dos adultos tem valor adaptativo, sendo postulada a hipótese de uma seleção neutra sobre esta variação de cor, como já descrito para outros crustáceos terrestres insulares. Não obstante, adultos com distintos padrões cromáticos aparentemente ocorrem em diversas espécies de caranguejos terrestres, o que é timidamente detalhado na literatura. Por fim, os resultados apresentados nesta dissertação compõem importantes informações sobre a história de vida de J. lagostoma, principalmente por se tratar de uma população habitando uma ilha isolada e, ainda, pouco impactada antropicamente. No entanto, estudos que envolvam outras localidades de distribuição dessa espécie, bem como de outras espécies de caranguejos terrestres insulares são essenciais. O incremento destes estudos é premente, somando conhecimento ao melhor embasamento do manejo e conservação destas espécies endêmicas em ilhas oceânicas, que são altamente sensíveis à antropização.
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.
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.
Descrição
Palavras-chave
Brachyura, Coloração, Espécie Ameaçada, Ilha Oceânica, Reprodução, Coloration, Endangered Species, Oceanic Island, Reproduction