An analysis of reproductive potential can elucidate significant aspects of the population biology and evolution of brachyuran crabs, providing a crucial baseline for conservation efforts concerning endangered species. Johngarthia lagostoma is an endemic species to Atlantic Oceanic islands (Rocas Atoll, Fernando de Noronha, Ascension, and Trindade), and it is classified as endangered (EN) in Brazilian territory according to IUCN criteria. Until now, the reproductive potential of this species has only been described for the Ascension Island population. Therefore, we assessed the reproductive effort and fecundity of J. lagostoma on Trindade Island. A total of 43 ovigerous females in the final stage of embryonic development were analyzed. Their egg masses were removed, weighed, and counted using a volumetric method. The carapace width ranged from 55.3 to 100.1 mm (mean ± standard deviation: 75.2 ± 13.1 mm). It exhibited a good fit and positive correlation with the egg weight and fecundity data but a poor fit and negative correlation with reproductive effort. The contrasting results of fecundity (82,938 ± 43,673 eggs) and reproductive effort (10.5 ± 1.5 %) recorded for J. lagostoma reveal a well-established population on Trindade Island compared to Ascension Island. These observations provide valuable information for proposing more effective management strategies for this endangered species across these Atlantic oceanic islands.

This study describes the reproductive systems of male and female Johngarthia lagostoma , a land crab endemic to South Atlantic oceanic islands, focusing on spermatozoa production and storage. Specimens from Trindade Island (Brazil) were analysed for anatomy, histology, and histochemistry. The male system includes a pair of tubular testes showing different stages of spermatogenesis and spermiogenesis, leading to mature spermatozoa. These move to the anterior vas deferens (AVD), which has proximal and distal portions, the latter containing coenospermic spermatophores surrounded by secretion type I, reactive to proteins and acidic and neutral polysaccharides. The median (MVD) and posterior (PVD) vas deferens produce type II (strongly protein-reactive) and type III (weakly protein-reactive) secretions. Accessory glands between the MVD and PVD produce the same secretions plus a secretion type IV, reactive to neutral polysaccharides. These mix with the spermatophores and other vas deferens secretions, increasing the PVD’s secretion volume, crucial for the initial release of spermatophores into the seminal receptacle. The female reproductive system features voluminous seminal receptacles connected to the ovary, comprising mesodermal and ectodermal regions classified as ventral-type connection. Plugs and sperm packets are absent, with the seminal receptacles filled with free spermatozoa, suggesting dehiscence occurs shortly after sperm transfer. The influence of male and female secretions on this process is suggested, alongside their roles in sperm maintenance and fertilization facilitation.

In Brachyura, reproduction involves a range of behavioral, morphological, and physiological mechanisms that contribute to reproductive success. The land crab Johngarthia lagostoma , endemic to four oceanic islands in the South Atlantic, shows no clear pre- or post-copulatory guarding behavior, and the mechanisms involved in sexual selection remain uncertain. This study investigated the ontogenetic development of the first gonopod using relative growth analyses and high-resolution imaging techniques, with special emphasis on the corneous unguis, a distal non-calcified structure of unknown function. Morphometric analyses were performed using carapace width as the independent variable and measurements from different gonopod regions, including the corneous unguis, as dependent variables. Relative growth was evaluated using power function, and growth shifts were estimated from the intersection between juvenile and adult growth phases. Nano-computed tomography and X-ray analyses were used to describe the overall morphology of the gonopod and provided detailed visualization of its distal region, including the horny claw and associated setae field. Most biometric relationships showed growth shifts at similar sizes (50–55 mm CW ). In contrast, the corneous unguis showed a delayed ontogenetic transition (64.9 mm CW ), indicating a developmental trajectory distinct from that of the other gonopod regions. The coordinated maturation of most gonopod regions, together with the delayed development of the corneous unguis, indicates differential developmental timing among components of the copulatory apparatus. Although the functional role of the corneous unguis remains uncertain, its distinct ontogenetic pattern supports the hypothesis that it may be involved in post-copulatory reproductive processes associated with sperm transfer and/or ejaculate processing.