Habitat use, non-breeding groupings and chromatic pattern in Johngarthia lagostoma (H. Milne Edwards, 1837) (Decapoda, Gecarcinidae) in Trindade Island, South Atlantic Ocean

Abstract

The land crab Johngarthia lagostoma is endemic to Trindade Island, Atol das Rocas, Fernando de Noronha and Ascension Islands. The natural history of the species in non-breeding periods is little known. Therefore, here we reported the formation of non-breeding groups and evaluated the chromatic populational pattern of J. lagostoma in Trindade Island. Records were obtained between April and June 2015. The groups were characterized according to their location, terrain elevation, environmental characteristics and specimens’ behavior. The chromatic pattern was defined by the classification of individuals between yellow and purple, and the proportion of each color was compared between populational units (previously defined based on genetic differences). Non-breeding groups were recorded in four locations in Trindade Island, at altitudes < 40 m, and all of them were in locations with food resources and sediment suitable for the construction of shelters. Isolated individuals or the absence of the species were observed in the most inhospitable places, indicating that the maintenance of the species depends on portions of suitable habitat amid the currently arid matrix. Yellow individuals (96.4%) were predominant on Trindade Island and the chromatic pattern differed from the other populations. Color patterns seem to follow genetic differences between populations, and the founder effect may account for current patterns. From the data obtained, we emphasize that the maintenance of the species may depend on food, sediment suitable for shelters construction, humidity and shade. Due to the significant population decline in other regions, the need to define guidelines for the conservation of the species on Trindade Island is highlighted. In this context, the regeneration of insular vegetation and prohibiting the known anthropic consumption of individuals may represent important strategies for the maintenance of the species Island and the last on Ascension Island (Rodríguez-Rey et al. 2016). This highlights that the conservation of every populational unit is important for the maintenance of the genetic variability of the species. Although most populations are located in Brazil, studies on J. lagostoma are scarce in the country (e.g., Teixeira 1996; Lira 2017; Oliveira 2021), and detailed information on the biology and use of the habitat is restricted to Ascension Island (e.g., Hartnoll et al. 2006; Hartnoll et al. 2009). Furthermore, there is no detailed information about the behavior of the species in the non-breeding periods. Here we aim to report the formation of non-breeding groups, provide information on habitat use and evaluated the chromatic populational pattern of J. lagostoma in Trindade Island, providing subsidies for its conservation.