Acta Zoologica最新文献

Urodele amphibians possess remarkable regenerative abilities, allowing them to rebuild lost body parts. Contrary to lizards, salamanders can fully restore their tails, including the neural spine and components of the vertebral column. The axolotl (Ambystoma mexicanum) is the vertebrate model organism for regeneration research due to its ease of breeding in captivity. However, axolotls are paedomorphic, retaining larval somatic features throughout adulthood and do not naturally undergo metamorphosis, a transition phase from aquatic larvae to terrestrial adults with profound morphological and physiological changes. We investigate the influence of metamorphosis on salamander tail regeneration after conspecific biting in the metamorphosing sister taxon Ambystoma tigrinum using histological analysis to answer two key questions: (1) Does regeneration continue during metamorphosis, or is it halted? (2) How does regeneration differ histologically among larval, metamorphosing and postmetamorphic individuals? Our findings demonstrate that regeneration continues even during metamorphic climax, indicating the simultaneous coordination of metamorphosis and regeneration. Additionally, notable distinctions were observed between developmental stages concerning the speed of regeneration and structural differences in the formation of an apical epithelial cap (AEC). While the approach taken in this study necessarily restricts sample size, it offers valuable insights into regeneration in a metamorphosing species under natural conditions.

The reproductive cycle of Hemiodus unimaculatus in the upstream area of the Tucuruí reservoir in the Tocantins River was described. The animals were collected monthly for 1 year in the Tauiry Village, municipality of Itupiranga, Pará. The individuals had their biometry taken, the gonads removed and weighed to calculate the gonadossomatic index and processed for histological analysis. A total of 103 animals were collected, 87 females and 16 males (sex ratio of 5 females:1 male). The total length and weight of the animals did not vary significantly during the year, the females had an average length of 21,867 ± 1.55 cm and an average weight of 118.63 ± 23.4 g. The males had average length of 20.353 ± 1.39 cm and an average weight of 96.90 ± 20.2 g. Females and males were in developing phases during fall and winter, and Spawning Capable in spring and summer. Spawning Capable females were collected in the fall. The closed fishing season determined for the species does not fully cover its reproductive period. This associated with the imbalance of the sex ratio, and over-fishing of the species may be leading the species population to decline upstream of the Tucuruí reservoir on the Tocantins River.

Squamata is one of the groups of sauropsids with the greatest diversity in life histories. The timing and expression of events related to reproductive phenology are considered among the most important components of squamate life histories. Here we studied the male and female reproductive patterns, clutch size, and clutch frequency of the oviparous lizard Sceloporus aeneus from a population in the southeast of Hidalgo State, Mexico, from April 2010 to March 2011. The gonadal analysis showed that the minimum snout-vent length at sexual maturity in males and females was 46 mm. Both sexes exhibit seasonal reproductive patterns; males present maximum gonadal activity in winter-spring (February–May), and females are vitellogenic in spring-summer (May–July). Clutch size averaged 7 eggs (range 5–9) and did not show a relationship with female body size. Females produce at least two clutches per breeding season. The reproductive patterns described in this study were similar to those observed in other populations of S. aeneus, although some events in the reproductive phenology of both sexes appear to be related to local environmental factors.

Extrinsic thoracic limb muscles are a muscular group that supports the thoracic limb in mammals without the clavicle and serve to move the scapula and shoulder joint. However, there are few evolutionary studies of these muscles in Felis catus, which should take into account the topology and innervation of the muscles to hypothesize the muscle derivation from a common ancestor. The main objective of this study was to check the extrinsic thoracic limb muscles in ten cadavers. Intra- and interspecific anatomical variants were found with that formerly described and other felids. Based on the topology and innervation found in this study, the evolutionary derivation was hypothesized. Therefore, the omotransversarius and rhomboideus muscles are derived from the serratus ventralis cervicis muscle. The cleidobrachialis muscle is derived mainly from the m. deltoideus and accessorily from the supracoracoid muscular group. The pectoantebrachialis and pectoralis abdominalis muscles are derived from the pectoralis descendens and cutaneus trunci muscles, respectively. In conclusion, most extrinsic thoracic limb muscles of F. catus may have evolutionary derivations from the last common ancestor of mammals, while some of them are from the last common ancestor of carnivorans or within the family Felidae.

Caudal autotomy is a behaviour in lizards that favours survival but brings with it some associated costs, mainly loss of energy, which is related to the position of the breaking point. Moreover, the frequency of tail loss can vary at different levels, between sexes, populations, seasons and at an intra- and inter-population level. In this study, we analysed the breaking position of the tails in individuals and frequencies of tail loss between years, sexes, seasons and populations of the lizard Sceloporus variabilis that inhabit contrasting environments. The results showed a low frequency of tail loss at the ends (distal and proximal) of this organ (except for individuals from the xeric scrubland population) and there was a higher proportion of complete than incomplete tails in lizards for all analysed populations. Also, there was no variation in the frequency of tail loss among populations, sexes (except in one population), years or seasons. A higher proportion of organisms with complete tails suggests that this organ is an important element for these lizards. In addition, the lack of variation in the frequency of tail loss may indicate a similar behaviour such as escape from predators among the groups analysed.

Tail regeneration in lizards derives from the formation of a regenerative blastema. Numerous snoRNAs exclusively up-regulated in the regenerating tail but absent in the scarring limb of the lizard Podarcis muralis have been detected suggesting they are key genes for regeneration. While most snord-, snora- and scarna-RNAs are activators of protein synthesis and cell proliferation (oncogenes) some may also be tumour suppressors. A tail blastema of 2–3 mm in length consists of proliferating mesenchymal cells, fibroblasts and keratinocytes with active nucleoli, rosette-patterned ribosomes and few rough endoplasmic cisternae. In few days, the blastema grows into a new tail indicating intense protein synthesis within this short period. A quantitative RT-PCR analysis of snord87, snord26, snord74, snora63, scarna11, U2 and U4 shows that, aside snord87, the other ncRNAs are up-regulated, particularly, U2, U4 and scarna11. These ncRNAs might regulate the rate of production of ribosomes from the nucleolus (snora- and snord-RNAs), the splicing process (snord- and scarna-RNAs, U2 and U4), the speed of protein synthesis (snora- and snord-RNAs) and cell proliferation in the blastema. These non-coding-RNAs are hypothesized to intensify the production of more functional ribosomes that accelerate the rate of protein synthesis and rapid growth of the blastema into a new tail.

Otolith morphology in the toothcarps of the family Aphaniidae is an important source of taxonomic information. However, little is known about the ontogenetic variation in otolith morphology. In this study, the development of otolith morphology in different life stages of Aphaniops kruppi, an endemic toothcarp of the Arabian Peninsula, is described and discussed. The results reveal (i) a significant correlation between standard length and otolith size (length) in larval and early juvenile stages, (ii) clear differences in otolith morphology between larvae/early juveniles and adults, and (iii) a temporal link between the appearance of the sulcus on the otolith's inner face and lifestyles, that is demersal in larvae and early juveniles, and pelagic in adults. Moreover, our new data on otoliths of Ap. kruppi propose that otoliths of larvae or early juveniles of Ap. kruppi can be recognized by adults not only because of their small size but also based on their short and rounded rostrum and antirostrum and shallow, wide excisura. As the above-mentioned characteristics are also found in the otoliths of juveniles and larvae of several other studied aphaniids, it can be concluded that otoliths are not diagnostic at the species level in Ap. kruppi, and this holds for other closely related species.

Ciliated and non-ciliated mechanosensory cells in invertebrates have intricate cytoskeletal structures that, combined with microtubules, act as a mechanical link between external stimulus and signal processing. As a result, they can perceive forces like touch, cuticle deformation, gravity and sound. Through the expression of antibodies against serotonin (5-HT), calbindin, inducible nitric oxide synthase (iNOS) and α-smooth muscle actin (αSMA), this research aims to investigate mechanosensory cells in the integument of Lumbricus terrestris (Linnaeus, 1758) in an evolutionary perspective. In the epidermis, we discovered isolated mechanosensory cells that were immunopositive to every antibody examined. Our findings improve the knowledge and the evolution of annelid sensory biology adding new insights on the sensory signal transduction and help to better understand the morpho-structural adaptations of invertebrate skin on an evolutionary scale and to give more taxonomic data for species distinction.

Secondary sexual dimorphism is an interesting and stupendous subject of research study due to the fact that it is a result of sexual selection, mostly attributed to either female mate choice or male–male competition. This study aims to investigate the microscopic characterization of scales and fin rays in several aphaniids (Cyprinodontiformes: Aphaniidae) to find out the possibility of using these structures as secondary sexual dimorphism traits and discuss their taxonomic and evolutionary significance. Herein, the results reveal that (i) male individuals of aphaniid species of the genera Aphanius, Aphaniops and Paraphanius present contact organs in the forms of ctenus-like structure (in posterior margin of the scales) and spicule-like structure (in anal fin rays) that show sexual dimorphism of scales and fins; (ii) number, position, size and shape of contact organs provide taxonomic signal to distinguish members of the genus Aphaniops from two other genera; (iii) females of Aphaniops ginaonis also represent contact organs in scales but fewer than males and (iv) as the sexual dimorphism results from different sexual selection pressures acting on males and females, it provides evolutionary signals.

This study aims to characterize the gonads, folliculogenesis, and spermatogenesis processes of male and female Rhinella bergi through anatomical, histological and morphometric analysis. We worked with specimens previously collected in the spring and summer seasons (2014–2015), in which the gonads were studied based on morphological, histological and morphometric analysis. The reproductive system was analyzed using a stereoscopic microscope and a scanning electron microscope (SEM). Histological preparations were made following the conventional protocol of dehydration, inclusion in paraffin and stained with haematoxylin–eosin, Mallory trichrome and PAS histochemical reactions. The anatomical and morphometric characteristics and the gametogenesis in R. bergi agree with what was proposed for other analyzed species of the Bufonidae family. Females with ovaries with oocytes in different stages of maturity and postovulatory females were found. The males presented continuous spermatogenesis. The results of this work serve as a basis for the characterization of the reproductive cycle in R. bergi and, at the same time, provide background information on the analysis of gametogenic activity. Future investigations will be focused on evaluating the reproductive cycle in this species, both in ovaries and testes as well as Bidder's organ, to compare and correlate with the results obtained in this study.