Abstract Arthropods must periodically moult their exoskeleton to permit growth, a conserved developmental process whose morphological and behavioural execution varies widely among lineages. Horseshoe crabs (Limulidae) are members of Xiphosura, a chelicerate lineage with a fossil record extending as far back as the Ordovician and provide a valuable evolutionary context for studying the evolution of moulting strategies in Arthropoda. Despite their importance, morphological characterization of moulting in horseshoe crabs remains scarce, limiting developmental studies and broader comparative analyses. Here, we provide a qualitative morphological characterization of the moulting process in the Atlantic horseshoe crab Limulus polyphemus. Morphological changes in specific anatomical structures, including the anterior margin of the prosoma, lateral spines and dorsal spinous process of the opisthosoma, were observed during the moulting process. By tracking these morphological markers, such as retraction of the epidermis from the cuticle and degree of corrugation of the epidermis, we were able to identify individuals in the early and late pre-moult stage, identify individuals approaching ecdysis and distinguish post-moult and intermoult stages. We compare ecdysis patterns in L. polyphemus with other arthropod taxa, both extant and fossil. We find that, despite differences in behavioural execution, ecdysis in L. polyphemus shares features with other chelicerates, and that both phylogenetic signal and convergent patterns are evident across Arthropoda. This study offers a practical, non-invasive method for determining moult stages in juvenile horseshoe crabs and provides insights into the diversity and constraints of ecdysis in Arthropoda.
Abstract Arboreal mammals display a remarkable diversity of locomotor and postural behaviors, shaped by long-term evolutionary adaptations to canopy environments. Hainan gibbon (Nomascus hainanus), among the world’s rarest primates, serves as an ideal model for examining behavioral adaptations under habitat constraints. From March 2023 to September 2024, we quantified the positional behavior and substrate utilization of three gibbon groups using instantaneous scan sampling in the Bawangling region of Hainan Tropical Rainforest National Park, China. Gibbons employed a repertoire of 14 positional modes, with sitting (51.1%), brachiation (26.5%), and suspending (13.9%) being predominant. Positional behavior varied markedly with activity type: brachiation dominated during travel, whereas feeding involved frequent use of both sitting and suspensory postures. Notably, substrate characteristics strongly influenced behavioral performance: suspensory postures predominated on branches, brachiation and leaping were favored on upward-sloping substrates, and both sitting and suspensory postures peaked at canopy heights of 16–20 m. These patterns demonstrate that Hainan gibbons adjust their positional strategies flexibly in response to immediate substrate conditions and activity demands. These findings confirm that the Critically Endangered species retains behavioral adaptability in secondary forests, highlighting the conservation value of regenerated habitats for population recovery.
Abstract This study presents the first systematic review of 118 nominal species of marine fish formally described from Malaysian waters between 1830 and 2025, spanning 22 orders and 53 families. Distinct temporal phases in taxonomic activity were identified: the pre-2000 era dominated by colonial-era expeditions yielded 94 species, with Cantor's 1849 Penang survey contributing 34 species. The post-2000 era represents a fundamental restructuring, with Malaysian-associated ichthyologists now active in species descriptions, establishing local repositories and adopting modern designation practices. Bibliometric analysis shows authorship remains concentrated among core contributors, with growing local taxonomic capacity. DNA barcoding of 63 morphospecies revealed substantial cryptic diversity, with RESL and GMYC delimitation identifying 131 and 134 molecular operational taxonomic units (MOTUs), respectively. A total of 27 species comprised multiple MOTUs, with 9 priority taxa exhibiting cryptic complexity, including Otolithes ruber, Glossogobius giuris, Uranoscopus cognatus, Taeniamia fucata, and Pisodonophis cancrivorus, and commercially important species such as Sardinella albella, Ilisha elongata, Cynoglossus arel, and Lethrinus lentjan requiring integrative taxonomic revision. This study establishes a framework for biodiversity research, identifies gaps in molecular representation, and demonstrates the value of integrating historical taxonomy with molecular approaches in one of the world's most species-rich marine regions.
Abstract Animals encounter various predators, including native and non-native species. While native species develop defensive strategies to counter native predators, these defenses vary in efficacy against non-native predators. Bombardier beetles (Coleoptera: Carabidae: Brachinini) employ an explosive chemical defense, discharging toxic chemicals at nearly 100°C. However, experimental evaluations of this defense against non-native predators are limited. To test its effectiveness, we investigated the defense efficacy of a native bombardier beetle species (Brachinus incomptus) against its potential predators, two native frog species (Pelophylax nigromaculatus and Fejervarya kawamurai) and an invasive non-native species (the American bullfrog, Lithobates catesbeianus), which co-occur with this beetle species in Japan. Behavioral interactions between these frogs and adult B. incomptus were observed under laboratory conditions. In predation trials, 90%, 100%, and 65% of P. nigromaculatus, F. kawamurai, and L. catesbeianus, respectively, rejected adult B. incomptus, suggesting that the beetles’ defenses were effective against both native and non-native frogs. When frogs were offered beetles that had been repeatedly stimulated until no further explosive discharges were elicited, 80%, 95%, and 10% of P. nigromaculatus, F. kawamurai, and L. catesbeianus, respectively, rejected the treated beetles. This treatment did not significantly affect defensive success against native frogs but notably decreased it against the non-native frog. Our findings suggest that explosive chemical discharges may make a smaller relative contribution to defense against the native frogs tested than against the non-native American bullfrog.
Abstract Social and spatial environments shape the way individuals associate and impact their social network structure. However, nowhere are social and spatial mechanisms more likely to be simultaneously entangled and potentially misinterpreted than in colonial species. We color-banded 124 Atlantic puffins, georeferenced their burrows, and tracked their associations on land using a scan sampling approach (regular observation through the plot) during the breeding season to understand how the spatial distribution of the burrows constrained their associations. We tested how the distance between nests in a colony affected 1) individual probability of association and the dyadic weight (number of associations between 2 individuals) and 2) their community structure (when connections are stronger within rather than among modules). We also tested for the presence of non-random associations across different distances. We found that the distance between burrows strongly influenced the social network structure of Atlantic puffins. Individuals associated more often with close neighbors, but there was no evidence of favored associations. However, contrary to expectation, we found that groups of individuals formed communities and evidence that distant associations with conspecifics were not all random. We suggest that individuals may seek each other out if it provides mutual benefits or have similar spatial and temporal requirements.
