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.
The external morphology and ultra-surface structures of the oromandibular area (comprising of barbels and lips); and paired fins (pectoral and pelvic) have been studied for the first time in a hill stream fish Schistura multifasciata (Day, 1878) recorded from a semi-torrential hill stream Basistha, at Guwahati city, Assam, India. Schistura is one of the most adaptive Asian fish species dwelling in hill streams, mostly preferring a semi-torrential habitat. The aim of the study is to document the morphological peculiarities present in Schistura multifasciata that enable such hill stream fishes thrive in semi-torrential habitats. The study was conducted with mature individuals of this species using standard protocols of experimentation. The oromandibular area and paired fins were initially studied under a light microscope; and were further analysed under the Scanning Electron Microscope. The study has helped in revealing peculiarities in the ultra-surface structures of the oromandibular area and paired fins of Schistura multifasciata; that defines their differential adaptation strategies. Cumulative action of Type I II taste buds, microvilli, mucous pores, microridges, unculi; and papillated outgrowths present in the oromandibular area and paired fins of this species helps in effective adaptation to hill stream habitats; and this is the major highlight of this study.
The potential of shape variation to distinguish between species can be examined using quantitative approaches such as 2D or 3D geometric morphometrics (GM). As these methods differ in requirements and effort, their ability to resolve between different species is crucial. Thus, we tested two hypotheses: (1) approaches perform better with increasing complexity, i.e., 3D GM > 2D GM and (2) 2D approach performs comparatively better in flat and rather 2-dimensional structures than in complex 3-dimensional structures. These hypotheses were tested using crania and mandibles of four mole species of the genus Talpa (T. stankovici, T. europaea, T. caeca, T. martinorum) from the Balkan and Italian peninsula. Our results based on 3D CT scans and 2D images rejected both hypotheses: (1) 2D GM performs equally well in the highly 3-dimensional cranium. This becomes evident only when the 3D dorsal and ventral landmarks are analysed separately from each other (2) on the other hand 3D GM performs better in the flat mandible in relation to 2D. A potential explanation lies in the complexity of the structures, which was measured by calculating the Dirichlet Normal Energy (DNE). Our results showed that DNE is higher in the 3-dimensional cranium than in the flat mandible. However, the landmark-based mesh of the mandible had a higher complexity than the one of the cranium. This implies that the landmark selection and number have a stronger impact on performance than the method itself. Nevertheless, a broader comparison between different structures and organisms is required to confirm these patterns.
Pinelema elinae spiders, described from seven caves located in the Serra do Ramalho and Chapada Diamantina regions, in the state of Bahia, represent a troglobitic and relict species in the Neotropical context. Its wide geographic distribution, contrasted with low dispersal ability, high levels of endemism, and the punctual records of other species of the genus Pinelema, constitutes a biogeographical dilemma and raises the hypothesis that this taxon may represent a complex of cryptic species. In this context, the present study employed linear and geometric morphometric analyses to compare different populations from the karst area of Serra do Ramalho, aiming to assess the existence of morphological differentiation among them. Natural history observations indicate that individuals are restricted to the aphotic zone of the caves, lack visual structures, and exhibit a female-biased sex ratio (3.33:1) that varies among populations, together with clear ontogenetic differences in pigmentation, body size, and microhabitat use between juveniles and adults. Morphometric analyses reveal morphological differences among P. elinae populations from Serra do Ramalho associated with body size and with the shape of the sternum and pedipalp bulb, whereas carapace shape did not differ significantly among populations. These heterogeneous, structure-specific patterns of differentiation are consistent with the hypothesis that this taxon represents a cryptic species complex, possibly resulting from geographic isolation and local selective pressures.
To better understand the communication mechanisms involved in the search for host plants and the location of sexual partners, this study aimed to identify the presence of sexual dimorphism in the external morphology, distribution, and typology of the antennal sensilla of male and female Eueides isabella dianasa (Hübner, 1806) (Lepidoptera: Nymphalidae) using Scanning Electron Microscopy (SEM). Six individuals (three males and three females) were analysed. Observations revealed that the species exhibits sexual dimorphism, with claviform antennae displaying evident external morphological differences between the sexes. Five types of sensilla were identified: Sensilla basiconica (SBa), sensilla coeloconica (SCo), sensilla chaetica (SC), sensilla trichodea (STr) and sensilla squamiformia (SSq). Morphometric analysis revealed significant differences in the length and width of some sensilla between males and females, suggesting the presence of functional sexual dimorphism, particularly in the length variations of SC I, SC III, Ssq I, and STr III, as well as in the width of SC III and STr III. The results contribute to the knowledge of the types of sensilla in E. i. dianasa, as well as to the understanding of the sensory system of butterflies, particularly those of the genus Eueides.
