Acta Zoologica最新文献

Walking is a locomotion mode in which animals move over the ground using their appendages. Walking is observed in both terrestrial and aquatic animals, but the morphology and diversity of appendages in the latter group have been less extensively studied. The present paper reports on the “adhesive areas,” which may represent morphological and physiological adaptations for stable aquatic walking, in the paintpot cuttlefish, Ascarosepion tullbergi. This animal employs arm IV as a forelimb and an ambulatory flap as a hindlimb for walking, resulting in a gait-like manner of movement. The structure of the adhesive area is exclusively located on the ventral skin surface of arm IV and the ambulatory flap, which are in contact with the ground during walking. The “adhesive areas” are characterized by a dense population of adhesive mucus-secreting cells and the development of numerous wrinkles on the surface. These features may enhance the gripping and sticking capacity of the ground-contact area, thus improving walking stability. The use of adhesive areas for walking is a unique feature of A. tullbergi, as other cuttlefish with adhesive areas primarily use them for attaching to substrata in strong currents. Our results contribute to the understanding of the locomotion strategy of cuttlefish.

Capturing data on the life of fossorial vertebrates is difficult since access to the subterranean environment is made unfeasible by its density and opacity. Collecting specimens is only possible through excavation work, causing damage or even death to the specimens. Due to the obstacles of in situ studies, the scarce information comes from reports obtained indirectly, mainly through specimens preserved in museums. Considering the adaptations to fossoriality, investments in studying these groups could be very enlightening since they would contribute enormously to the knowledge of the evolutionary strategies developed throughout the colonisation of the subterranean world. Amphisbaena alba is the species of Amphisbaenia with the broadest geographic distribution in the world. It occupies virtually all countries in South America except for Chile and southern Argentina. This study, carried out over the last 36 years, aims to provide data on the biology and behaviour of A. alba in captivity and in the field. Our main objective is to provide subsidies to expand the knowledge of the life history of this species and, by extension, of amphisbaenians in general.

Larval morphology is a valuable tool for understanding the life history of decapod crustaceans. This approach has proven valuable in confirming taxonomic revisions based on molecular or adult morphology analyses. Therefore, the present study aimed to compare larval traits (e.g. development time, morphology, and larval size) between Macrobrachium amazonicum and M. pantanalense, two closely related species that are separated by a low genetic distance. The first five zoeal stages of each phenotype and species were analysed. Differences in larval development time, morphology, and size were observed. M. amazonicum exhibits faster development during the early larval stages compared to M. pantanalense. The main morphological difference between the two species is related to the stage at which pereiopod five develops as a functional appendage, namely zoea IV in M. amazonicum and zoea III in M. pantanalense. In addition, size variation was observed, with M. pantanalense larvae being larger in the early stages. The differences found between the two species corroborate that M. amazonicum and M. pantanalense are distinct lineages. Even though these groups are separated by a low genetic distance, the existing differences are conclusive, and therefore, these organisms can be considered as two distinct taxonomic entities.

One of the rarest and most unusual iguanas on the planet is the Galápagos pink land iguana (Conolophus marthae). There have been a number of hypotheses on the source of their pink coloration, including that the colour is from blood and a relative lack of dermal pigmentation. We obtained full thickness skin biopsies of three species and compared tissue from darkly pigmented areas and lightly pigmented surfaces. “Pink” areas of pink iguanas are devoid of pigment cells (e.g. melanophores) and the dermal tissue is rich with aggregates of confluent capillaries. This was in sharp contrast to the minimally vascular (only capillaries were observed) dermal areas of the marine and yellow iguanas. The dermal stratum laxum of every biopsy site contained melanophores except for the pink skin of pink iguanas. Interestingly, marine iguanas have a much thicker epidermal stratum germinativum/granulosum, between 2 and 10 cells thick depending on location, compared to the thinner epidermal stratum germinativum/granulosum of land iguanas (one to three cells thick with most areas possessing just one or two cell layers). These microscopic differences might reflect differences in habitat and ecology of the three species.

The current biodiversity crisis warrants accurate measuring of biodiversity, often achieved by counting species or higher taxonomic units, with morphological or molecular methods. Alternatively, trait-centred approaches categorise organisms into distinct ecological roles and then count the number of occupied roles to measure biodiversity. Even combinations of trait-based and taxonomic approaches are utilised. However, when investigating the theoretical aspects, all these approaches have significant shortcomings, which complicate a reliable biodiversity measurement, that is, the ignorance of polymorphic species, the sensitivity to the initial classification or the knowledge gap concerning the ecology of the organisms. We outline a non-discrete ecospace approach for which neither pronounced taxonomic expertise nor in-depth knowledge about the ecology of the organisms is required. A morphospace based on quantitative morphological properties is used as a proxy for an ecospace, thus resulting in a continuous morpho-ecospace. With this, decision-making concerning taxonomy or ecology is reduced, as morphology is directly used instead of being first interpreted. Differences usually not considered due to polymorphism or ontogeny can be included in this approach, as well as fossils without species determination. This morpho-ecospace approach is easily applicable and can be combined with already existing approaches, making it broadly applicable.

The present review formulates an evolutionary hypothesis on the distribution of regeneration in invertebrates and vertebrates. Regeneration is a basal ancestral property of animals living in aqueous environment where life was generated. The specific life cycles that evolved in each phylum indicate that only adult aquatic animals with asexual reproduction, larval stages and metamorphosis, possess broad regenerative abilities, protostomes or deuterostomes. Regeneration derives from the re-utilization in different forms of numerous developmental gene pathways active during development and the transitional phases of larval metamorphosis. An injured adult animal, composed of differentiated tissues, cannot repeat the same sequence of gene activation of embryogenesis, resulting in a variable regeneration (most aquatic invertebrates and anamiotes). In contrast, species with a genome that is not programmed for producing larvae and intense metamorphosis, mainly terrestrial (numerous nematodes, arthropods and amniotes), cannot regenerate their organs after injury. It is hypothesized that during the evolution of terrestrial animals, they lost genes involved in regeneration so that they repair by wound healing associated with grow (regengrow) or by scarring. Future molecular knowledge on developmental pathways that evolved in regenerating competent animals will tell us whether or not organ regeneration in regenerative incompetent animals will be feasible.