The mole's thumb -- evolution of the hand skeleton in talpids (Mammalia)

Osteological specimens representing 15 out of the 16 currently recognized talpid genera were examined and scored for seven discrete morphological characters of the hand. The phylogenetic distribution of these characters was studied in the context of alternative hypotheses of talpid relationships, using three species of shrews and a hedgehog as outgroups. All talpids show a similar number and arrangement of carpal bones. The most obvious differences concern the presence of additional sesamoid bones, the relative size of the os falciforme when present, and the degree of fusion of the scaphoid and lunate in the proximal carpal row. Marked differences in the relative length and proportions of the metacarpals also exist. The development of the carpals in Talpa europaea was studied through examination of histological sections of the hand of an embryo and a neonate. Whereas carpal anatomy in the neonate mirrors the arrangement and proportions of the adult, in the embryo the scaphoid and lunate are still separate, there are no signs of the os falciforme, and the size proportions of metacarpals to carpals are obviously different to those of the adult. A prehallux or tibial sesamoid, serial homologue to the os falciforme or prepollex (a radial sesamoid), does not have an obvious functional role, and its presence might be the result of a common epigenetic control in the hand and the foot resulting in a non-adaptive structure in the latter.     

Evolution of territoriality in Hylinae treefrogs: Ecological and morphological correlates and lineage diversification

Given the diverse nature of traits involved in territorial defence, they may respond to different selective pressures and then exhibit distinct patterns of evolution. These selective pressures also may cause territorial behaviour to be associated with environmental and morphological variables. Such associations, however, have mostly been studied at the intraspecific level, being phylogenetic analyses of territoriality in a broad taxonomic framework rare in the literature. We used the anuran subfamily Hylinae to test (1) whether two territorial-behaviour traits with different levels of aggression—territorial call and physical combat—are evolutionarily more labile than a morphological trait used in physical combat—the spine-shaped prepollex; (2) whether reproduction in lentic waters and phytotelmata, as well as resource scarcity, might favour the occurrence of territoriality; (3) if physical combat is more important than territorial call for the evolution of body size and sexual size dimorphism and (4) the relationships between territorial-behaviour traits and lineage diversification. We mainly used the literature to build two datasets with different levels of certainty. Territorial-behaviour traits exhibited intermediate levels of phylogenetic signal in Hylinae, whereas the phylogenetic signal for the presence of the spine-shaped prepollex was strong. We found support for the hypothesis that reproduction in lentic water favours the occurrence of territorial behaviour, because the expression of territorial-behaviour traits was more associated with reproduction in lentic than in lotic waters. Territorial-behaviour traits were not correlated with annual precipitation nor with habitat complexity. Body size and sexual size dimorphism were not correlated with the presence of territorial call nor with physical combat. We identified negative correlations between diversification rates and physical combat. Relationships of territorial call and physical combat with diversification rates suggest that these territorial behaviours influence evolutionary processes in different ways.     

The evolution of the hallucial tarsometatarsal joint in the Anthropoidea

Changes in the hallucial tarsometatarsal joint, which forms the fulcrum for the grasping hallux, have played a significant role in primate evolution. Comparative studies suggest that one of the morphological novelties heralding the attainment of a monkey grade of structure was the incorporation of the prehallux within this joint. Such a joint is found in the extant Ceboidea and, paradoxically, the Hylobatidae. Hallux and prehallux then form a composite distal articular surface; the proximal surface on the medial cuneiform is completed inferomedially by a convex facet for the prehallux. Divergence of the hallux into the attitude of opposition is accompanied by conjunct rotation, screwing these joint components into a stable, close-packed position. Suppression of the prehallux is accompanied by clear osteological indicators — the absence of prehallux facets on the first metatarsal and medial cuneiform. This modification of the joint is a feature of cercopithecoid evolution, and has also occurred in the hominoid line, after divergence of the ancestral gibbons and apparently after the Dryopithecus (Proconsul) stage. The cladistic relationships indicated by these morphological changes are in striking accord with recent results on primate evolution at the molecular level.     

Development of the pseudothumb in frogs

Frogs have highly conserved hand and foot morphology, possessing four fingers and five toes. As an exception, two Japanese ranid frog species, the Otton frog Babina subaspera and the dagger frog Babina holsti, possess a unique thumb-like structure (the pseudothumb) in the forelimb, giving an appearance of a total of five fingers on the hand. To obtain insights into the developmental mechanisms that generate this novel character, we investigated the hand morphogenesis of the Otton frog. The unique morphological pattern of the pseudothumb was already established in juveniles. Surprisingly, the bud-like structure, which is similar to the area of inductive activity (e.g. feather buds in birds and the carapacial ridge in turtles), was detected over the site where the future prepollex develops in larvae. By contrast, this bud-like structure was not found in larvae of other ranid species. We discuss possible scenarios that would favour the evolution of this very unusual trait in frogs.     

Ontogenetic,intraspecific, and interspecific variation of the prehallux in primates: Implications for its utility in the assessment of phylogeny

The prehallux is a sesamoid bone occurring in the region of the hallucial tarso-metatarsal joint in a number of metatherian and eutherian orders and in some nonmammalian tetrapods. Within the order Primates, it occurs invariably in ceboids and Hylobates, with extreme infrequency in pongids and Homo, and is absent in other primates groups. It has been suggested that, first, the prehallux is homologous both within and across the infraclasses Metatheria and Eutheria; second, it has functional significance in that it contributes to joint stability and is an adaptation to arboreality; third, its presence results in diagnostic features on the entocuneiform and hallucial metatarsal, so that original presence or absence can be unambiguously assessed in instances when the bone itself is not preserved; and fourth, because of presumed homology, it may be employed in the reconstruction of phylogenetic relationships. The present study concludes that the homologous nature of the bone is open to reasonable doubt, the assumption of homology does not yield significantly more parsimonious phylogeny reconstructions than does the assumption of analogy, there are no invariant diagnostic features associated with its presence, and functional explanations currently offered are of questionable validity. Thus, the prehallux is at present of little utility in either establishing or precluding phylogenetic relationships among primates.     

A large‐scale survey of heterochrony in anuran cranial ossification patterns

Most anurans have a biphasic life cycle, which includes metamorphosis from a tadpole stage to an adult frog. This process involves extensive transformations of the cranial skeleton, which have been of long‐standing interest with respect to anuran skeletal evolution and taxonomy. In this study, large‐scale patterns of anuran skeletal ossification are assessed by collecting the most comprehensive data set on anuran cranial ossification to date from the literature, including data for 45 anuran and one caudate outgroup species. Ossification sequences were translated into event‐pair matrices for explorative phylogenetic analysis and phylogenetically informed parsimony search for heterochrony using the Parsimov algorithm. Rank variability of single bones across species was also analysed. Little phylogenetic signal was retrieved from a parsimony‐based phylogenetic analysis of event‐pairs, and only a few species that are generally agreed to be closely related are placed close to each other (e.g. some Pipidae and Costata). Parsimov analysis revealed some clade‐specific heterochrony in anuran clades of varying inclusiveness. Our results show that relating heterochronic changes in anuran cranial ontogeny to parameters such as direct development or miniaturization is problematic because of the high evolvability of cranial ossification sequences. Rank variation analysis suggests that anuran cranial bones are highly variable in their sequence positioning, possibly because tadpole and adult cranial morphology do not co‐evolve. Elements which are lost in some species ossify at the end of the sequence, providing evidence for the notion that failure of anuran cranial elements to ossify is due to processes of paedomorphosis.     

Influence of damming on anuran species richness in riparian areas: A test of the serial discontinuity concept

Almost all large rivers worldwide are fragmented by dams, and their impacts have been modeled using the serial discontinuity concept (SDC), a series of predictions regarding responses of key biotic and abiotic variables. We evaluated the effects of damming on anuran communities along a 245‐km river corridor by conducting repeated, time‐constrained anuran calling surveys at 42 locations along the Broad and Pacolet Rivers in South Carolina, USA. Using a hierarchical Bayesian analysis, we test the biodiversity prediction of the SDC (modified for floodplain rivers) by evaluating anuran occupancy and species diversity relative to dams and degree of urbanized land use. The mean response of the anuran community indicated that occupancy and species richness were maximized when sites were farther downstream from dams. Sites at the farthest distances downstream of dams (47.5 km) had an estimated ~3 more species than those just below dams. Similarly, species‐specific occupancy estimates showed a trend of higher occupancy downstream from dams. Therefore, using empirical estimation within the context of a 245‐km river riparian landscape, our study supports SDC predictions for a meandering river. We demonstrate that with increasing distance downstream from dams, riparian anuran communities have higher species richness. Reduced species richness immediately downstream of dams is likely driven by alterations in flow regime that reduce or eliminate flows which sustain riparian wetlands that serve as anuran breeding habitat. Therefore, to maintain anuran biodiversity, we suggest that flow regulation should be managed to ensure water releases inundate riparian wetlands during amphibian breeding seasons and aseasonal releases, which can displace adults, larvae, and eggs, are avoided. These outcomes could be achieved by emulating pre‐dam seasonal discharge data, mirroring discharge of an undammed tributary within the focal watershed, or by basing real‐time flow releases on current environmental conditions.     

Background to work on retinoids and amphibian limb regeneration: Studies on anuran tadpoles—a retrospect

Studies on the effects of exogenous vitamin A palminate on limb development and regeneration in anuran tadpoles carried out since late 1960s at the author’s laboratory are reviewed and discussed. Most significant was the initial discovery that vitamin A causes regeneration of complete or nearly complete limbs instead of only the missing distal part, thus altering the P-D pattern of regeneration—a phenomenon now called proximalization. Often more than one such regenerates develop per stump. Vitamin A produces proximalizing effect on regeneration cells during their dedifferentiation and blastema formation but inhibits regeneration if given once redifferentiation begins. Shank-level blastemas from treated tadpoles grafted into orbits of previously treated/untreated host tadpoles formed complete limbs. Proximalizing effect is proportionate to vitamin A concentration, duration of treatment, amputational level and stage of tadpoles. Vitamin A produces this effect also if given only prior to amputation. Its influence persists after cessation of treatment, declining with time. Proximalizing effect is correlated with natural ability in limbs to regenerate. Vitamin A improves regenerative ability and can induce it to some extent in non-regenerating limbs. Vitamin A excess retards limb development and produces stage dependent teratogenic defects. Further development of only that limb region is prevented in which differentiation is beginning when vitamin A is given. Short treatment of tadpoles beginning with limbs at spatula/paddle stage inhibited foot development in the unoperated limbs hut promoted regeneration of complete limbs from the contra-lateral amputated limbs. These dual effects were due to cells of the former differentiating and of the latter dedifferentiating when exposed to vitamin A palmitate.     

Variation, plasticity and modularity in anuran development

Although anuran development is generally thought to be relatively conservative, a great deal of variation is evident when different species are compared. This report summarizes the results of comparative analyses of different aspects of anuran development. These include differences in sequence and timing of developmental events, the effects of genome size, and the effects of different life history strategies on anuran embryogenesis. The results show that anuran development is plastic at the evolutionary level, and many changes can occur in the developmental processes of anurans throughout their evolution. Changes are apparently rapid, and are as common as cladogenic events. This evolutionary plasticity can be attributed to the modular nature of anuran development. Different modules can shift relative to one another in time or in space, creating variations in the observed developmental patterns. However, shifts in modules can occur even without having a significant effect on the ultimate outcome of the process. I discuss the implications of the modular nature of development on the evolution of anuran development, and of the group in general.     

Global patterns in anuran–prey networks: structure mediated by latitude

Life on Earth is supported by an infinite number of interactions among organisms. Species interactions in these networks are influenced by latitude, evolutionary history and species traits. We performed a global‐scale literature analysis to build up a database of interactions between anuran communities and their preys, from a wide range of geographical areas, using a network approach. For this purpose, we compiled a total of 55 weighted anuran–prey interaction networks, 39 located in the tropics and 16 in temperate areas. We tested the influence of latitude, as well as anuran taxonomic, functional and phylogenetic richness on network metrics. We found that anuran–prey networks are not nested, exhibit low complementary specialization and modularity and high connectance when compared to other types of networks. The main effects on network metrics were related to latitude, followed by anuran taxonomic, functional and phylogenetic richness, a pattern similar to the emerging in mutualistic networks. Our study is the first integrated analysis of the structural patterns in anuran–prey antagonistic interaction networks in different parts of the world. We suggest that different processes, mediated mainly by latitude, are modeling the architecture of anuran–prey networks across the globe.     

中国43种蛙类鸣声特征数据集

无尾两栖动物的鸣声通常具有物种特异性,了解其鸣声特征信息,是利用生物声学进行物种多样性调查及物种监测的前提。本文汇总、整理了2012–2020年间利用高保真录音设备在野外记录的43种(隶属于7科26属)无尾两栖动物的鸣声数据,以及相应的鸣声采集信息。对音频文件进行降噪处理后,提供了由61个鸣声的波形图及语图组成的鸣声特征数据集。本数据集展示了鸣声的多种时域和频域信息,如单音节或多音节、音节数、音节时长、音节间隔、鸣声时长、主频、基频、谐波等,为我国无尾两栖类的声学研究、物种多样性调查及鸣声监测提供了数据支持。     

Kin distribution of amphibian larvae in the wild

According to kin selection theory, the location of an individual with respect to its relatives can have important ramifications for its fitness. Perhaps more than any other vertebrate group, anuran amphibian larvae have been the subject of many experiments on this topic. Some anuran species have been shown in the laboratory to recognize and associate with their siblings and half-siblings. However, due to the difficulty of identifying sibships, no kinship studies with anuran larvae have been conducted in the wild. Here, we use microsatellite analysis to show that wood frog (Rana sylvatica) tadpoles were nonrandomly distributed in two ponds with respect to their relatives. In one pond, the tadpoles were significantly clumped with their siblings or half-siblings as expected from other published laboratory studies on this species. However, in another pond, the tadpoles were significantly nonrandomly dispersed from their siblings or half-siblings. This is the first example of kin repulsion of nonreproductive animals in the wild and the first time a species has been shown to display both aggregation and repulsion under different circumstances. These results suggest that kin distribution is context dependent and demonstrate the importance of testing kin selection hypotheses under natural conditions.     

Initiation of limb regeneration: the critical steps for regenerative capacity

While urodele amphibians (newts and salamanders) can regenerate limbs as adults, other tetrapods (reptiles, birds and mammals) cannot and just undergo wound healing. In adult mammals such as mice and humans, the wound heals and a scar is formed after injury, while wound healing is completed without scarring in an embryonic mouse. Completion of regeneration and wound healing takes a long time in regenerative and non-regenerative limbs, respectively. However, it is the early steps that are critical for determining the extent of regenerative response after limb amputation, ranging from wound healing with scar formation, scar-free wound healing, hypomorphic limb regeneration to complete limb regeneration. In addition to the accumulation of information on gene expression during limb regeneration, functional analysis of signaling molecules has recently shown important roles of fibroblast growth factor (FGF), Wnt/beta-catenin and bone morphogenic protein (BMP)/Msx signaling. Here, the routine steps of wound healing/limb regeneration and signaling molecules specifically involved in limb regeneration are summarized. Regeneration of embryonic mouse digit tips and anuran amphibian (Xenopus) limbs shows intermediate regenerative responses between the two extremes, those of adult mammals (least regenerative) and urodele amphibians (more regenerative), providing a range of models to study the various abilities of limbs to regenerate.     

A Phylogenetic Lineage of Closely Related Trypanosomes (Trypanosomatidae,Kinetoplastida) of Anurans and Sand Flies (Psychodidae,Diptera) Sharing the Same Ecotopes in Brazilian Amazonia1

ABSTRACT. Analysis of the phylogenetic relationships among trypanosomes from vertebrates and invertebrates disclosed a new lineage of trypanosomes circulating among anurans and sand flies that share the same ecotopes in Brazilian Amazonia. This assemblage of closely related trypanosomes was determined by comparing whole SSU rDNA sequences of anuran trypanosomes from the Brazilian biomes of Amazonia, the Pantanal, and the Atlantic Forest and from Europe, North America, and Africa, and from trypanosomes of sand flies from Amazonia. Phylogenetic trees based on maximum likelihood and parsimony corroborated the positioning of all new anuran trypanosomes in the aquatic clade but did not support the monophyly of anuran trypanosomes. However, all analyses always supported four major clades (An01‐04) of anuran trypanosomes. Clade An04 is composed of trypanosomes from exotic anurans. Isolates in clades An01 and An02 were from Brazilian frogs and toads captured in the three biomes studied, Amazonia, the Pantanal and the Atlantic Forest. Clade An01 contains mostly isolates from Hylidae whereas clade An02 comprises mostly isolates from Bufonidae; and clade An03 contains trypanosomes from sand flies and anurans of Bufonidae, Leptodactylidae, and Leiuperidae exclusively from Amazonia. To our knowledge, this is the first study describing morphological and growth features, and molecular phylogenetic affiliation of trypanosomes from anurans and phlebotomines, incriminating these flies as invertebrate hosts and probably also as important vectors of Amazonian terrestrial anuran trypanosomes.     

Bony-tailed tadpoles: the development of supernumerary caudal vertebrae in larval megophryids (Anura)

The axial skeleton in most anuran families consists of or=7). Tadpoles from each genus are typically found in streams, where their extended caudal skeleton anchors muscles that facilitate tadpoles wiggling between plant debris and rocks or even burrowing into the stream bed. The extra centra of megophryids ossify differently in each genus. In Leptobrachella and Ophryophryne, the caudal centra ossify around the entire notochord, whereas in Megophrys and Xenophrys each develops from dorsal and ventral pairs of ossifications that expand to meet each other. The evolutionary loss of caudal centra, an apomorphic anuran trait, is reversed in larval megophryids and confirms that the machinery for caudal vertebral development has been retained in some modern anurans. A likely driving force in the reappearance of the trait in megophryids is the selective pressure associated with a riparian lifestyle.     

Vitamin A induced homeotic hindlimb formation on dorsal and ventral sides of regenerating tissue of amputated tails of Japanese brown frog tadpoles

When anuran tadpoles are treated with vitamin A after tail amputation, hindlimb‐like structures can be generated instead of the lost tail part at the amputation site. This homeotic transformation was initially expected to be a key to understanding the body plan of vertebrates. Unfortunately, homeotic limb formation has been reproduced in only some Indian frog species and a European species, but not in experimental anurans such as Xenopus laevis or Rana catesbeiana. Consequently, this fascinating phenomenon has not been well analyzed, especially at the molecular level. In addition, the initial processes of ectopic limb development are also unclear because morphological changes in the early phases have not been analyzed in detail. In this study, we report the induction of homeotic transformation using Japanese brown frogs and present a detailed morphological analysis. Unexpectedly, the ectopic limbs developed not only at the ventral sites, but also at the dorsal sites of the tail regenerates of vitamin A‐treated tadpoles. The relationship between position and axial orientation of ectopic limbs suggested the double duplication of positional value order along the rostral‐caudal axis and the dorsal‐ventral axis of the tail regenerates.     

A method for hormonal induction of sperm release in anurans (eight species) and in vitro fertilization in Lepidobatrachus species

Injections of synthetic human gonadotropin releasing hormone (GnRH) into the dorsal pelvic area were used in an attempt to stimulate sperm release in isolated males of eight anuran species including Xenopus laevis, Rana pipiens and Lepidobatrachus laevis . Sperm were obtained within 1–5 h post injection either by mechanical stimulation or by cloacal lavage. Sperm suspensions varied from 8 μL to 7 mL and the cell densities ranged from 4 × 10⁵ to 4 × 10⁷ sperm/mL. The sperm obtained from seven species using GnRH-induced release were viable based on light microscopic observations of motility. In addition, sperm preparations fertilized eggs in vitro and produced normal tadpoles in the case of L. laevis and L. llanensis . This hormonal method of anuran sperm collection will provide a convenient non-injurious way to obtain anuran sperm for basic studies of reproduction and development.     

Variations in anuran embryogenesis: yolk-rich embryos of Hyperolius puncticulatus (Hyperoliidae)

Anuran development is usually described using model species, most notably Xenopus laevis and Rana pipiens. We describe the development of the East African Reed Frog, Hyperolius puncticulatus, a species displaying development that is highly divergent from the "classic" anuran developmental pattern. Although having small eggs, the eggs of H. puncticulatus are characterized by a large amount of yolk, and embryonic development is reminiscent of species with large eggs. The eggs are teleolecithal and the cleavage is holoblastic, with a "pseudo-meroblastic" pattern. Gastrulation proceeds primarily at the dorsal lip and is characterized by reduced embryonic cavities. Gastrulation ends with a thickened "embryonic mantle" that sits upon a large yolk mass and forms most of the tissues of the embryo. The embryonic axis curves across the yolk mass, instead of the typical lengthening of anuran embryos. The tadpole hatches with a large ventral yolk mass which is gradually absorbed. We hypothesize about the developmental mechanisms that underlie this unusual development, based on comparisons with other anuran and fish species. We suggest that this type of development is not unique to this species, but can be found in many species of different anuran taxonomic groups. Comparing the development of H. puncticulatus and similar species to what is known about the development of model species, such as X. laevis, shows us the variation in early anuran embryogenesis. Knowing the existing diversity is a prerequisite to understanding the evolution of early anuran development and the changes in patterning mechanisms in different lineages.