Zoological Letters最新文献

Numerous hypotheses try to explain the unusual appearance of the human eye with its bright sclera and transparent conjunctiva and how it could have evolved from a dark-eyed phenotype, as is present in many non-human primates. Recently, it has been argued that pigmentation defects induced by self-domestication may have led to bright-eyed ocular phenotypes in humans and some other primate lineages, such as marmosets. However, it has never been systematically studied whether actual domesticated mammals consistently deviate from wild mammals in regard to their conjunctival pigmentation and if this trait might therefore be part of a domestication syndrome. Here, we test this idea by drawing phylogenetically informed comparisons from a photographic dataset spanning 13 domesticated mammal species and their closest living wild relatives (n ≥ 15 photos per taxon). We did not recover significant differences in scleral appearance or irido-scleral contrast between domesticated and wild forms, suggesting that conjunctival depigmentation, unlike cutaneous pigmentation disorders, is not a general correlate of domestication. Regardless of their domestication status, macroscopically depigmented conjunctivae were observed in carnivorans and lagomorphs, whereas ungulates generally displayed darker eyes. For some taxa, we observed pronounced intraspecific variation, which should be addressed in more exhaustive future studies. Based on our dataset, we also present preliminary evidence for a general increase of conjunctival pigmentation with eye size in mammals. Our findings suggest that conjunctival depigmentation in humans is not a byproduct of self-domestication, even if we assume that our species has undergone such a process in its recent evolutionary history.

The hemiphractid frog genus Stefania is one of the many ancient (near-) endemic lineages of vertebrates inhabiting the biodiverse Pantepui biogeographical region in the Guiana Shield Highlands of northern South America-the famous "Lost World" of Arthur Conan Doyle. Previous molecular analyses of the genus Stefania have indicated that species boundaries and phylogenetic relationships are often incongruent with morphological traits in that clade. A substantial number of "taxonomically cryptic" species, often microendemic, remain to be described. This is notably the case for an isolated population from the summit of Wei-Assipu-tepui, a small table-top mountain at the border between Guyana and Brazil. That population was previously known as Stefania sp. 6 and belongs to the S. riveroi clade. The new species is phylogenetically distinct, but phenotypically extremely similar to S. riveroi, a taxon found only on the summit of Yuruaní-tepui in Venezuela and recovered as sister to all the other known species in the S. riveroi clade. The new taxon is described based on morphology and osteology. Data about genetic divergences within the S. riveroi clade are provided. A new synapomorphy for the genus Stefania is proposed: the presence of a distal process on the third metacarpal. Amended definitions are offered for the three other species in the S. riveroi clade (S. ayangannae, S. coxi, S. riveroi). The new species should be listed as Critically Endangered according to IUCN criteria.

It is well known that the celestial polarization is used as a compass cue by many species of insects and crustaceans. Although it has been shown that the sandhopper Talitrus saltator perceives polarized light and possesses an arrangement of the rhabdomeres that could allow e-vector interpretation and utilization, T. saltator does not use the e-vector of the skylight polarization as a compass cue when making excursions along the sea-land axis of sandy shores. We performed tests in confined conditions to clarify if skylight polarization is somehow involved in the zonal recovery of T. saltator. We observed the directional responses of sandhoppers in a transparent bowl under an artificial sky (an opaline Plexiglas dome). The bowl was covered by a blue gelatin filter with a grey filter (control condition) and a linear polarizing filter (experimental conditions) positioned under the blue one in such a way as to occupy half of the upper surface of the Plexiglas bowl so as to create a linear polarization gradient. Our experiments confirm that T. saltator perceives polarized light and highlight that this visual capability determines the perception, or perhaps the increase, of the radiance and/or spectral gradient and their use as compass cues in the zonal orientation. Moreover, our findings confirm that the radiance gradient is used as a chronometric compass orienting reference in the absence of other celestial orienting cues.

To address how organisms adapt to a new environment, subterranean organisms whose ancestors colonized subterranean habitats from surface habitats have been studied. Photoreception abilities have been shown to have degenerated in organisms living in caves and calcrete aquifers. Meanwhile, the organisms living in a shallow subterranean environment, which are inferred to reflect an intermediate stage in an evolutionary pathway to colonization of a deeper subterranean environment, have not been studied well. In the present study, we examined the photoreception ability in a trechine beetle, Trechiama kuznetsovi, which inhabits the upper hypogean zone and has a vestigial compound eye. By de novo assembly of genome and transcript sequences, we were able to identify photoreceptor genes and phototransduction genes. Specifically, we focused on opsin genes, where one long wavelength opsin gene and one ultraviolet opsin gene were identified. The encoded amino acid sequences had neither a premature stop codon nor a frameshift mutation, and appeared to be subject to purifying selection. Subsequently, we examined the internal structure of the compound eye and nerve tissue in the adult head, and found potential photoreceptor cells in the compound eye and nerve bundle connected to the brain. The present findings suggest that T. kuznetsovi has retained the ability of photoreception. This species represents a transitional stage of vision, in which the compound eye regresses, but it may retain the ability of photoreception using the vestigial eye.

Animals may show consistent among-individual behavioral differences over time and in different contexts, and these tendencies may be correlated to one another and emerge as behavioral syndromes. The cross-context variation in these behavioral tendencies, however, is rarely explored with animals in contexts associated with different locomotion modes. This study assessed the variation and repeatability in behavioral traits of bent-wing bats Miniopterus fuliginosus in southern Taiwan, and the effects of contextual settings associated with locomotion mode. The bats were sampled in the dry winter season, and their behaviors were measured in hole-board box (HB) and tunnel box (TB) tests, both suited for quadrupedal movements of the bats, and flight-tent (FT) tests that allowed for flying behaviors. The bats in the FT tests showed more interindividual and between-trial behavioral variation than those in the HB and TB tests. Nearly all of the behaviors in the TB and FT tests, but only half of those in the HB tests, showed medium to high repeatability. These repeatable behaviors were grouped into distinct behavioral traits of boldness, activity, and exploration, which were correlated to one another across contexts. In addition, we observed a consistently higher correlation between behavioral categories across the HB and TB contexts than between either of these contexts and the FT context. The results indicate consistent among-individual behavioral differences across time and contexts in wildly caught bent-wing bats. The findings of behavioral repeatability and cross-context correlations also indicate context-dependent variation and suggest that test devices which allow for flight behaviors, such as flight tents or cages, may provide a more suitable setting for measuring the behaviors and animal personalities of bats, particularly for those species that display less or little quadrupedal movements.

Background: The retinae of diurnal vertebrates have characteristics. Most lizards are strictly diurnal, and their retinal morphology is still unknown.

Materials and methods: The retina of the African five-lined skink (Trachylepis quinquetaeniata) was studied using light and transmission electron microscopy.

Results: The retina's ten layers were all detected. The inner nuclear layer was the thickest by an average of 67.66 μm, and the inner plexiform layer was 57.564 μm. There were elliptical, long cylindrical, and spherical melanosomes (small and large) in the pigment epithelial layer of the retina. The cylindrical melanosomes had a large area on the lateral surfaces of cones to increase light scatter absorption. The photoreceptor layer of the retina had cones only. There were single and double cones, with the double cones consisting of principal and accessory cones. The cones had inner and outer segments separated by oil droplets. A spherical paraboloid body existed between the limiting membrane and the ellipsoid. All single cones had a paraboloid, and double cones had a large paraboloid in the accessory cone. The presence of paraboloids and large ellipsoids with mitochondria of varying sizes may have helped focus the light on cone segments.

Conclusion: The African five-lined skink's eye was light-adapted due to a variety of retinal specializations related to the demands of its diurnal lifestyle in its environment.

Lungfish are the most closely related fish to tetrapods. The olfactory organ of lungfish contains lamellae and abundant recesses at the base of lamellae. Based on the ultrastructural and histochemical characteristics, the lamellar olfactory epithelium (OE), covering the surface of lamellae, and the recess epithelium, contained in the recesses, are thought to correspond to the OE of teleosts and the vomeronasal organ (VNO) of tetrapods. With increasing body size, the recesses increase in number and distribution range in the olfactory organ. In tetrapods, the expression of olfactory receptors is different between the OE and VNO; for instance, the type 1 vomeronasal receptor (V1R) is expressed only in the OE in amphibians and mainly in the VNO in mammals. We recently reported that V1R-expressing cells are contained mainly in the lamellar OE but also rarely in the recess epithelium in the olfactory organ of lungfish of approximately 30 cm body length. However, it is unclear whether the distribution of V1R-expressing cells in the olfactory organ varies during development. In this study, we compared the expression of V1Rs in the olfactory organs between juveniles and adults of the African lungfish Protopterus aethiopicus and South American lungfish, Lepidosiren paradoxa. The density of V1R-expressing cells was higher in the lamellae than in the recesses in all specimens evaluated, and this pattern was more pronounced in juveniles than adults. In addition, the juveniles showed a higher density of V1R-expressing cells in the lamellae compared with the adults. Our results imply that differences in lifestyle between juveniles and adults are related to differences in the density of V1R-expressing cells in the lamellae of lungfish.

Metazoans have several mechanisms of internal defense for their survival. The internal defense system evolved alongside the organisms. Annelidae have circulating coelomocytes that perform functions comparable to the phagocytic immune cells of vertebrates. Several studies have shown that these cells are involved in phagocytosis, opsonization, and pathogen recognition processes. Like vertebrate macrophages, these circulating cells that permeate organs from the coelomic cavity capture or encapsulate pathogens, reactive oxygen species (ROS), and nitric oxide (NO). Furthermore, they produce a range of bioactive proteins involved in immune response and perform detoxification functions through their lysosomal system. Coelomocytes can also participate in lithic reactions against target cells and the release of antimicrobial peptides. Our study immunohistochemically identify coelomocytes of Lumbricus terrestris scattered in the epidermal and the connective layer below, both in the longitudinal and in the smooth muscle layer, immunoreactive for TLR2, CD14 and α-Tubulin for the first time. TLR2 and CD14 are not fully colocalized with each other, suggesting that these coelomocytes may belong to two distinct families. The expression of these immune molecules on Annelidae coelomocytes confirms their crucial role in the internal defense system of these Oligochaeta protostomes, suggesting a phylogenetic conservation of these receptors. These data could provide further insights into the understanding of the internal defense system of the Annelida and of the complex mechanisms of the immune system in vertebrates.

Avian wings as organs for aerial locomotion are furnished with a highly specialized musculoskeletal system compared with the forelimbs of other tetrapod vertebrates. Among the specializations, the propatagium, which accompanies a skeletal muscle spanning between the shoulder and wrist on the leading edge of the wing, represents an evolutionary novelty established at a certain point in the lineage toward crown birds. However, because of the rarity of soft-tissue preservation in the fossil record, the evolutionary origin of the avian propatagium has remained elusive. Here we focus on articulated skeletons in the fossil record to show that angles of elbow joints in fossils are indicators of the propatagium in extant lineages of diapsids (crown birds and non-dinosaurian diapsids), and then use this relationship to narrow down the phylogenetic position acquiring the propatagium to the common ancestor of maniraptorans. Our analyses support the hypothesis that the preserved propatagium-like soft tissues in non-avian theropod dinosaurs (oviraptorosaurian Caudipteryx and dromaeosaurian Microraptor) are homologous with the avian propatagium, and indicate that all maniraptoran dinosaurs likely possessed the propatagium even before the origin of flight. On the other hand, the preserved angles of wrist joints in non-avian theropods are significantly greater than those in birds, suggesting that the avian interlocking wing-folding mechanism involving the ulna and radius had not fully evolved in non-avian theropods. Our study underscores that the avian wing was acquired through modifications of preexisting structures including the feather and propatagium.

Reproductive biology is an important topic that is well explored in many vertebrates, but information about frogs' reproductive mechanisms could be improved. Therefore, this review aims to provide organized and specific information on frog reproduction. First, we developed schemes that illustrate the general information regarding reproductive biological mechanisms in frogs in a specific way. Then, we described the physiological, histological, and morphological mechanisms of each organ of the reproductive system of male and female frogs. Finally, this manuscript may contribute to a broader understanding of anuran reproductive biology. Since, understanding frogs' reproductive system permits one to make a comparison with reproduction with other anurans.