Zoology最新文献

Epidermal club cells (ECCs) are present in many species of teleost fish. In an attempt to justify their presence in the epidermis of fish, they have been associated with numerous functions. One proposed function is communication with conspecifics during a predation event, as these cells may passively release substances upon rupture, which may occur during predation. We identified the presence and distribution of ECCs in the body skin of adult cardinal tetra, Paracheirodon axelrodi (Schultz, 1956) and analyzed the animal’s behavioral response to conspecific skin extract in a laboratory setting. The identification and distribution of ECCs in the epidermis of the animals were confirmed by conventional histology and immunohistochemistry. Our results demonstrated that: ECCs are present in the skin of the entire body; a high density is observed in the dorsal side from head to tail, in the insertion of the fins and in the epidermis covering them; and ventral distribution is less extensive and more dispersed than dorsal distribution. Treatment of P. axelrodi specimens with skin preparations of conspecifics resulted in behavioral changes in the animals: they showed erratic swimming movements, they showed avoidance of the area of stimulus application and they decreased the time spent moving. Overall, these results allow us to conclude that P. axelrodi possesses ECCs throughout the body, with a greater presence in areas of high exposure to predation events (dorsal area and fins). Animals exposed to conspecific skin extract showed a significant increase in behaviors described as anti-predatory in other species. This supports the hypothesis that ECCs may be the origin of chemical alarm cues that are passively released when skin damage occurs, alerting the rest of the group to the risk of predation.

Estrogens, acting through their receptors (ERα and ERβ), regulate cell turnover in the pituitary gland, influencing cell proliferation and apoptosis across various species. However, their role in pituitary processes in seasonally reproducing animals remains poorly understood. This study aims to investigate the influence of estrogens, through the expression of their specific receptors, on the apoptosis of PD cells in relation to sexual maturity, the reproductive cycle, and pregnancy in a seasonal reproductive rodent (Lagostomus maximus maximus). ERα and caspase-3-cleaved (CASP3c) immunoreactive (-ir) cells were identified through immunohistochemistry. Apoptotic cells were detected using the TUNEL technique, with quantitative analysis facilitated by image analysis software, alongside measurement of serum estradiol levels using radioimmunoassay The immunostaining pattern for ERα included nuclear (ERαn) and cytoplasmic (ERαc) staining. In male viscachas, ERα expression significantly increases from immature to adult animals, correlating with the rise in serum estradiol levels and a decrease in the percentage of apoptotic cells. During the gonadal regression period in adult males, a decrease in the number of ER-ir cells and serum levels of estradiol corresponds with an increase in the number of apoptotic cells. In females, serum levels of estradiol peaked during mid-pregnancy, coinciding with a significant decrease in the number of apoptotic cells in the PD. Simultaneously, the percentage of ERαn-ir cells reaches its maximum value during late pregnancy, indicating the need to maintain the protective action of this gonadal hormone throughout the extensive pregnancy in these rodents. Regional ERα receptor expression and apoptotic cells appear to be associated with distinct PD cell populations and their hormonal responses. Finally, elevated estradiol levels coincide with diminished apoptotic cells in the male reproductive cycle and during pregnancy, suggesting an antiapoptotic role of estradiol in this species.

Vertebrates first emerged from water to land in the Paleozoic. Our understanding about the process has been steadily refined through paleontological studies, although the soft-body traits and behavior of these early animals remain poorly known. Mudskippers, extant amphibious gobies, could give insight into this question. This study reports on the ontogenetic transition from water to land of the mudskipper Periophthalmus modestus under laboratory conditions. After about 30 days after hatching (dah), the fish gradually changed their preference from water to an artificial shore and then to land. After about five days of periodic volitional emersion, the fish became able to propel themselves on land using the pectoral fins and after a further 13 days they began feeding on land. During the transition, the head morphology altered to suit for terrestrial existence. Tissue contents of triiodothyronine (T₃) and thyroxine (T₄) sharply increased at 30 dah. Forced underwater confinement of larvae at the last pelagic stage (27–29 dah) for 40–42 days resulted in no statistically significant difference in survival or gross morphology of the body and the gills. Growth was slightly stimulated. Our results show that mudskippers emerge on land with little morphological alteration during ontogenesis, much less than the changes observed for amphibians, and that emersion was not indispensable for survival or growth under our laboratory conditions. Further analysis of how and why mudskippers make their way across the water’s edge will shed valuable light on what morphological, behavioral and physiological traits were needed for, and what environmental conditions may have driven the earliest steps of the water-to-land transition in ancient fishes.

The diversity of primary freshwater crabs of Central America is underestimated and poorly known, specially when considering both Atlantic and Pacific drainages distribution. Among the family Pseudothelphusidae Ortmann, 1893, the genus Ptychophallus Smalley, 1964 was recently revised using morphological data and encompassing 14 valid species, which are distributed exclusively in Costa Rica and Panama. Despite the informative scenario constructed with this previous study, some uncertainties remained such as those related to the populations distributed along different drainages and the lack of complete information regarding the phylogenetic relationships among the species that belong to this genus. Our phylogenetic reconstruction based on multigenes revealed four lineages. Ptychophallus costaricensis, P. colombianus, P. lavallensis, P. montanus, and P. tumimanus are well-established species, while P. paraxanthusi, P. exilipes and P. tristani were recovered as non-monophyletic in some relationships. Ptychophallus tristani and P. paraxanthusi were determined to be close relatives one with other, but with some representatives showing no clear correspondence and positioning in the molecular phylogeny, which raised doubts about the validity as separate species and/or the accuracy of identifications for some GenBank sequences. Ptychophallus tumimanus and P. montanus are morphologically very similar, but they are positioned in distinct clades. The genetic results confirmed a previous proposal that P. barbillaensis is a junior synonym of P. uncinatus, and P. bilobatus is closely related to P. uncinatus. The findings revealed the presence of one peculiar lineage with one species from Costa Rica compound by the resurrected P. campylus and another species from Costa Rica, originally identified as “P. cf. exilipes”; its morphology, however, did not match with any other analyzed species, which requires further analysis. Finally, possible misidentification in some sequences deposited in the GenBank were detected and should be reviewed. The reconstructed molecular phylogeny for the genus that inhabits both Atlantic and Pacific drainages of Central America provides a better understanding of the knowledge on the evolution of freshwater crabs and represents key information that will serve as baseline for further taxonomic studies on the cryptic biodiversity of this group.

Squamates exhibit evident diversity in their limb morphology. Gekkotans are a particularly diverse group in this respect. The appearance of toepads in gekkotans usually cooccurs with the reduction or loss of claws. The gecko Tarentola (Phyllodactylidae) shows a unique combination of features among geckos, with toepads, hyperphalangy, and dimorphism of claw expression (claws are retained on digits III and IV, but lost (manus) or strongly reduced (pes) on the remaining digits). Despite being a candidate model for studying embryonic skeletal development of the autopodium, no studies have investigated the autopodial development of the gecko Tarentola in detail. Here, we aim to follow up the development of the autopodial skeleton in T. annularis and T. mauritanica using acid-free double staining. The results indicate that the terminal phalanges of claw-bearing digits III and IV ossify earlier than in the remaining digits. This confirms the differential ossification as a result of claw regression in Tarentola. The strongly reduced second phalanges of digits IV in both the fore- and hindlimbs are the last ossifying phalanges. Such late ossification may precede the evolutionary loss of this phalanx. If this is correct, the autopodia of Tarentola would be an interesting example of both the hyperphalangy in digit I and the process of phalanx loss in digit IV. Delay in ossification of the miniaturised phalanx probably represents an example of paedomorphosis.

The functional morphology of the skin of Malapteruridae is presumably evolved to cope with a diversified range of ambient physiological, environmental, and behavioral conditions. Herein, we firstly characterized the microstructures and intriguing patterning of the skin of twelve adult electric catfish (Malapterurus electricus, Malapteruridae) using histological, histochemical, immunofluorescent, and ELISA standard methodology. The skin comprises three sequentially–oriented layers: the epidermis, dermis, and hypodermis with a significantly increased thickness of the former. The epidermis contains four types of cells: the surface epithelial cells, mucous cells, granular cells, and club cells. We defined distinctive ampullary electroreceptors in the outer epidermis that possess flask-shaped sensory crypt containing electroreceptor cells together with vertical collagen rods. Dermis and hypodermis are composed of connective tissue; however, the former is much more coarse and dense with comparable reactivity for Masson–Goldner trichrome (MT). Placing our data in the context of the limited body of previous work, we showed subtle changes in the expression of mucin subunits together with cytoskeletal fractions of collagens, myosin, F-actin, keratins, and tubulins. Taken as a whole, our results convincingly showed that the skin of M. electricus shares some structural similarities to other Siluriformes, however, it has some functional modifications that are implicated in protection, defense, and foraging behavior.

The evolution of the tongue in tetrapods is associated with feeding in the terrestrial environment. This study analyzes the tongue morphology of two closely related frog species, Telmatobius oxycephalus and T. rubigo, which exhibit contrasting feeding mechanisms. Telmatobius oxycephalus, a semi-aquatic species, relies on its tongue to capture terrestrial prey whereas T. rubigo, a secondarily aquatic species, uses suction feeding not involving the tongue. Through anatomical, histological and scanning electron microscopy analyses, we revealed remarkable differences in tongue morphology between these species. Telmatobius oxycephalus exhibits a well-developed tongue whose dorsal epithelium has numerous and slender filiform papillae. The epithelial cells of the papillae are protruded and have a complex array of microridges. In contrast, T. rubigo possesses a reduced tongue with flat and less numerous filiform papillae. The epithelial cells are completely flat and lack microridges. These findings highlight the remarkable adaptability of lingual morphology in Telmatobius to respond to the contrasting ecological niches and prey capture mechanisms. This study sheds light on the relationship between tongue shape and the different functional demands, contributing to our understanding of the evolution of prey capture mechanisms in amphibians.

Osteoglossiformes (bonytongue fishes) possess many morphological specializations associated with functions such as airbreathing, feeding, and electroreception. The olfactory organ also varies among species, notably in the family Osteoglossidae. Herein, we describe the olfactory organ of an osteoglossid, Heterotis niloticus, to compare it with the olfactory organs of other osteoglossiforms. We demonstrate the presence of an olfactory rosette within the olfactory chamber. This structure consists of a short median raphe surrounded by olfactory lamellae, which possess dorsal lamellar processes. On the surface of the olfactory lamellae, there are secondary lamellae formed by the olfactory epithelium. Within the olfactory epithelium, two zones can be distinguished: parallel brands of sensory cells located in the cavities between the secondary lamellae and a nonsensory area covering the remaining part of the olfactory lamellae. The olfactory epithelium is formed by ciliated and microvillus olfactory sensory neurons, supporting cells, goblet cells, basal cells and ciliated nonsensory cells. Additionally, rodlet cells were observed. The results confirm large variability in terms of the olfactory organ of Osteoglossiformes, particularly of Osteoglossidae, and support the secondary lamellae evolution hypothesis within this family.

Bioenergetics and biothermodynamics are valuable tools in research on growth and metabolic processes of a wide range of organisms, including viruses, bacteria, fungi, algae and plants, as is shown by the many publications on this topic in the literature. These studies provide insight into growth and metabolism of individual species, as well as interactions between species, like the virus-host interaction (infection) and virus-virus interaction (competition). However, this approach has not yet been applied to animal species. The universality of biothermodynamics and bioenergetics provides a good motive to apply them in analysis of animals. In this research, we made a bioenergetic, biothermodynamic and kinetic characterization for the first time for an animal species – Anguilla anguilla L. (European eel). We made a comparative analysis on yellow (young adult) and silver (mature adult) phases. Metabolic processes were modeled as chemical reactions with characteristic thermodynamic properties: enthalpy, entropy and Gibbs energy. Moreover, Gibbs energy explained growth rates, through phenomenological equations. This analysis of animal metabolism and growth explained metabolic properties of yellow and silver A. anguilla, including the bioenergetic aspect of life history. Moreover, we compared thermodynamic properties of A. anguilla with those of its main macromolecular components and other organisms. The thermodynamic properties were explained by the structural properties of organisms. This research extends the bioenergetic and biothermodynamic approaches to zoology, which should allow analysis of the energetic aspect of animal metabolic processes, interactions with their environment and interactions with other organisms. Furthermore, it connects the macroscopic perspective of zoology with the microscopic perspectives of biochemistry, bioenergetics and biothermodynamics. This will provide a basis for development of mechanistic models of animal growth and metabolism.

Ladybirds (Coccinellidae) use toxic compounds, mostly alkaloids in their haemolymph, for defence against predators and other enemies. The toxicity of ladybirds to predators cannot be directly assessed because predators show avoidance reactions without ingesting the beetles. The alkaloid of ladybird Harmonia axyridis showed wide range toxicity to diverse non-target organisms. Thus, we used a quick, inexpensive and easy-to-perform method using bioassays on water flea Daphnia magna for comparative quantification of the toxicity (LD₅₀) of whole body extracts from several species of ladybirds that differ in their warning colouration. Alien invasive aposematic polymorphic ladybird H. axyridis was more toxic than all the other species examined: aposematic Adalia bipunctata > cryptic Cynegetis impunctata > aposematic Coccinella septempunctata > slightly aposematic Calvia quatuordecimguttata. Three month old adults of H. axyridis were 3.8 times more toxic than two week and one month old adults. The two most common colour morphs (non-melanic novemdecimsignata and melanic spectabilis) did not differ in their toxicity. High toxicity of H. axyridis as compared to all other species examined may contribute to the invasiveness of this species.