Search

When you take the time to observe another organism, there is a sort of gravity that can take hold, a mixture of curiosity and connection that expands and strengthens the more you interact with that organism. Yet, in research, a connection with one's study organism can, at times, feel countercultural. Study organisms are sometimes viewed more as tools to conveniently study biological questions. Here, we explicitly highlight the importance of organism-centered research not only in scientific discovery, but also in conservation and in the communication and perception of science., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Egg-laying amphibian females produce lipid-rich "milk" to feed offspring after hatching.

Natural history museums are vital repositories of specimens, samples and data that inform about the natural world; this Formal Comment revisits a Perspective that advocated for the adoption of compassionate collection practices, querying whether it will ever be possible to completely do away with whole animal specimen collection., Competing Interests: The authors have declared that no competing interests exist., (Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.)

Competing Interests: The author declares no competing interest.

The performance of an organism in its environment frequently depends more on its composite phenotype than on individual phenotypic traits. Thus, understanding environmental adaptation requires investigating patterns of covariation across functionally related traits. The replicated adaptive radiations of Greater Antillean Anolis lizards are characterized by ecological and morphological convergence, thus, providing an opportunity to examine the role of multiple phenotypes in microhabitat adaptation. Here, we examine integrated claw and toepad morphological evolution in relation to habitat partitioning across the adaptive radiations of Greater Antillean anoles. Based on analysis of 428 specimens from 57 species, we found that different aspects of claw morphology were associated with different perch dimensions, with claw height positively associated with perch diameter and claw curvature positively associated with perch height. Patterns of integration also varied across claw and toepad traits, likely driven by correlative selection for performance on smoother and rougher substrates. Finally, rates of evolution differed between claw and toepad traits, with claw length evolving faster than all other traits despite having no predicted functional importance. Our results highlight the multivariate nature of phenotypic adaptation and suggest that phenotypic integration across Greater Antillean anoles is driven by fine-scale correlative selection based on structural habitat specialization., (© 2018 The Author(s). Evolution © 2018 The Society for the Study of Evolution.)

Conservation of species and ecosystems is increasingly difficult because anthropogenic impacts are pervasive and accelerating. Under this rapid global change, maximizing conservation success requires a paradigm shift from maintaining ecosystems in idealized past states toward facilitating their adaptive and functional capacities, even as species ebb and flow individually. Developing effective strategies under this new paradigm will require deeper understanding of the long-term dynamics that govern ecosystem persistence and reconciliation of conflicts among approaches to conserving historical versus novel ecosystems. Integrating emerging information from conservation biology, paleobiology, and the Earth sciences is an important step forward on the path to success. Maintaining nature in all its aspects will also entail immediately addressing the overarching threats of growing human population, overconsumption, pollution, and climate change., (Copyright © 2017, American Association for the Advancement of Science.)

Live-bearing has evolved in all three orders of amphibians--frogs, salamanders, and caecilians. Developing young may be either yolk dependent, or maternal nutrients may be supplied after yolk is resorbed, depending on the species. Among frogs, embryos in two distantly related lineages develop in the skin of the maternal parents' backs; they are born either as advanced larvae or fully metamorphosed froglets, depending on the species. In other frogs, and in salamanders and caecilians, viviparity is intraoviductal; one lineage of salamanders includes species that are yolk dependent and born either as larvae or metamorphs, or that practice cannibalism and are born as metamorphs. Live-bearing caecilians all, so far as is known, exhaust yolk before hatching and mothers provide nutrients during the rest of the relatively long gestation period. The developing young that have maternal nutrition have a number of heterochronic changes, such as precocious development of the feeding apparatus and the gut. Furthermore, several of the fetal adaptations, such as a specialized dentition and a prolonged metamorphosis, are homoplasious and present in members of two or all three of the amphibian orders. At the same time, we know little about the developmental and functional bases for fetal adaptations, and less about the factors that drive their evolution and facilitate their maintenance., (© 2014 Wiley Periodicals, Inc.)

Although we are used to the idea that many organisms stop growing when they reach a predictable size, in many taxa, growth occurs throughout the life of an organism, a phenomenon referred to as indeterminate growth. Our comparative analysis suggests that indeterminate growth may indeed represent the ancestral condition, whereas the permanent arrest of growth may be a more derived state. Consistent with this idea, in diverse taxa, the basal branches show indeterminate growth, whereas more derived branches arrest their growth. Importantly, in some closely related taxa, the termination of growth has evolved in mechanistically distinct ways. Also, even within a single organism, different organs can differ with respect to whether they terminate their growth or not. Finally, the study of tooth development indicates that, even at the level of a single tissue, multiple determinate patterns of growth can evolve from an ancestral one that is indeterminate., (Copyright © 2016 Cold Spring Harbor Laboratory Press; all rights reserved.)

Despite several recent studies, the phylogeny of plethodontid salamanders is not yet fully resolved and the phylogenetic positions of several key genera, especially Aneides, Hemidactylium, Hydromantes and Karsenia, are contentious. Here we present a combined dataset of complete mitochondrial genomes and three nuclear loci for 20 species (16 genera) of plethodontids, representing all major clades in the family. The combined dataset without mitochondrial third codon positions provides a fully resolved, statistically well-supported tree. In this topology two major clades are recovered. A northern clade includes Aneides, Desmognathus, Ensatina, Hydromantes, Karsenia, Phaeognathus and Plethodon, with Plethodon being the sister taxon to the rest of the clade. Hydromantes and Karsenia are sister taxa, and Aneides is recovered as the sister taxon to Ensatina. Desmognathus+Phaeognathus form the sister taxon to Aneides+Ensatina. An eastern/southern clade comprises two subclades. One subclade, the spelerpines (Eurycea, Gyrinophilus, Pseudotriton, Stereochilus, Urspelerpes) is the sister taxon to a subclade comprising Hemidactylium, Batrachoseps and the tropical plethodontids (represented by Bolitoglossa, Nototriton and Thorius). In this topology Hemidactylium is well-supported as the sister taxon to Batrachoseps. Only when mitochondrial third codon positions are included using maximum likelihood analysis is Hemidactylium recovered as the sister taxon to Batrachoseps+tropical genera. Hypothesis testing of alternative topologies supports these conclusions. On the basis of these results we propose a conservative taxonomy for Plethodontidae., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Understanding the diversification of phenotypes through time--"descent with modification"--has been the focus of evolutionary biology for 150 years. If, contrary to expectations, similarity evolves in unrelated taxa, researchers are guided to uncover the genetic and developmental mechanisms responsible. Similar phenotypes may be retained from common ancestry (homology), but a phylogenetic context may instead reveal that they are independently derived, due to convergence or parallel evolution, or less likely, that they experienced reversal. Such examples of homoplasy present opportunities to discover the foundations of morphological traits. A common underlying mechanism may exist, and components may have been redeployed in a way that produces the "same" phenotype. New, robust phylogenetic hypotheses and molecular, genomic, and developmental techniques enable integrated exploration of the mechanisms by which similarity arises.

The recent discovery of a plethodontid salamander, Karsenia koreana, in Korea challenged our understanding of the biogeographic history of the family Plethodontidae, by far the largest family of salamanders, which otherwise is distributed in the New World with a few European species. Molecular studies suggest that Karsenia forms a clade with Hydromantes (sensu lato), which includes among its species the only other Old World plethodontids. We studied the skull of K. koreana and compared it with that of other plethodontid genera, especially members of the subfamily Plethodontinae, which it resembles most closely in general anatomy. The anatomy of its skull corresponds to the most generalized and apparently ancestral condition for plethodontids. No clearly autapomorphic states were detected, and no synapomorphies can be found that would link it to other genera. The Karsenia skull is cylindrical and well ossified, giving an impression of strength. In contrast, the skull of Hydromantes is highly derived; the skull is flattened and the bones are weakly ossified and articulated. Hydromantes and Karsenia share no unique anatomical features; differences between them are especially evident in the hyobranchial skeleton, which is generalized in Karsenia but highly modified in Hydromantes, which is well known for its highly projectile tongue. Plethodon and Plethodon-like species, including Karsenia and to a lesser degree Ensatina, represent the more generalized and apparently ancestral plethodontid morphology. Specialized morphologies have evolved along only a few morphological axes within the Plethodontidae, resulting in a pattern of rampant homoplasy. Our analysis of the anatomy of the new Asiatic lineage illuminates some potential mechanisms underlying adaptive morphological evolution within the Plethodontidae., ((c) 2009 Wiley-Liss, Inc.)

We report the discovery of a single specimen of a small, terrestrial, lungless caecilian, the second known taxon of lungless caecilians. It differs from all other caecilians in lacking open external nares, and from the large aquatic lungless species described by Nussbaum & Wilkinson (Nussbaum, R. A. & Wilkinson, M. 1995 Proc. R. Soc. Lond. B 261, 331-335) in having no significant skull modifications. All modifications are of 'soft morphology' (covered external nares and choanae, lung and pulmonary vessel loss, etc.). A new genus and species are described to accommodate this form. Aspects of its skull and visceral morphology are described and considered in terms of the possible life history and evolution of the species, and compared with those of other lungless amphibians.

The state of development of advanced embryos of the direct-developing Ecuadorian caecilian Caecilia orientalis (Caeciliidae: Gymnophiona: Amphibia) was examined. Because it is established that development is correlated with reproductive modes in a number of features, we included comparison with taxa that represent the major reproductive modes and all of the modern normal tables and ossification sequences. The embryos of C. orientalis most closely resemble those of stage 47/48 Gegeneophis ramaswamii, an Indian caeciliid, and stage 47/48 Hypogeophis rostratus, a Seychellian caeciliid, both direct developers, in details of bone mineralization, chondrocranial degeneration, and vertebrogenesis. They are most like stage 45 H. rostratus in external features (gills, pigmentation, etc.). They are less similar to prehatchings of Ichthyophis kohtaoensis, an ichthyophiid with free-living larvae, and to fetuses of the viviparous caeciliid Dermophis mexicanus and the viviparous typhlonectid Typhlonectes compressicauda at comparable total lengths in both skeletal development and external features. The similarity of developmental features among the direct-developers suggests a correlation with mode of life history. A noteworthy feature is that C. orientalis has an armature of multiple rows of teeth on the lower jaw with tooth crowns that resemble the "fetal" teeth of viviparous taxa and that are covered with a layer of oral mucosal epithelium until full development and eruption, but the upper jaw bears a single row of widely spaced, elongate, slightly recurved teeth that resemble those of the adult., ((c) 2009 Wiley-Liss, Inc.)

The caecilians, members of the amphibian Order Gymnophiona, are the least known Order of tetrapods, and their intra-relationships, especially within its largest group, the Family Caeciliidae (57% of all caecilian species), remain controversial. We sequenced thirteen complete caecilian mitochondrial genomes, including twelve species of caeciliids, using a universal primer set strategy. These new sequences, together with eight published caecilian mitochondrial genomes, were analyzed by maximum parsimony, partitioned maximum-likelihood and partitioned Bayesian approaches at both nucleotide and amino acid levels, to study the intra-relationships of caecilians. An additional multiple gene dataset including most of the caecilian nucleotide sequences currently available in GenBank produced phylogenetic results that are fully compatible with those based on the mitogenomic data. Our phylogenetic results are summarized as follow. The caecilian family Rhinatrematidae is the sister taxon to all other caecilians. Beyond Rhinatrematidae, a clade comprising the Ichthyophlidae and Uraeotyphlidae is separated from a clade containing all remaining caecilians (Scolecomorphidae, Typhlonectidae and Caeciliidae). Within this large clade, Scolecomorphidae is the sister taxon of Typhlonectidae and Caeciliidae but this placement did not receive strong support in all analyses. Caeciliidae is paraphyletic with regard to Typhlonectidae, and can be divided into three well-supported groups: Caeciliidae group 1 contains the African caeciliids Boulengerula and Herpele; Caeciliidae group 2 contains Caecilia and Oscaecilia and it is the sister taxon of Typhlonectidae; Caeciliidae group 3 comprises the remaining species of caeciliids. The mitochondrial genome data were also used to calculate divergence times for caecilian evolution using the penalized likelihood method implemented in the program R8S. The newly obtained dating results are compatible with (but a little older than) previous time estimates mainly based on nuclear gene data. The mitogenomic time tree of caecilians suggests that the initial diversification of extant caecilians most probably took place in Late Triassic about 228 (195-260) Ma. Caeciliids currently distributed in India and the Seychelles diverged from their African and American relatives most probably in Late Jurassic about 138 (112-165) Ma, fairly close to the time (approximately 130Ma) when Madagascar-India-Seychelles separated from Africa and South America. The split between the Indian caeciliid Gegeneophis and Seychellean caeciliids occurred about 103 (78-125) Ma, predated the rifting of India and the Seychelles (approximately 65Ma).

Phylogenetic relationships of members of the salamander family Salamandridae were examined using complete mitochondrial genomes collected from 42 species representing all 20 salamandrid genera and five outgroup taxa. Weighted maximum parsimony, partitioned maximum likelihood, and partitioned Bayesian approaches all produce an identical, well-resolved phylogeny; most branches are strongly supported with greater than 90% bootstrap values and 1.0 Bayesian posterior probabilities. Our results support recent taxonomic changes in finding the traditional genera Mertensiella, Euproctus, and Triturus to be non-monophyletic species assemblages. We successfully resolved the current polytomy at the base of the salamandrid tree: the Italian newt genus Salamandrina is sister to all remaining salamandrids. Beyond Salamandrina, a clade comprising all remaining newts is separated from a clade containing the true salamanders. Among these newts, the branching orders of well-supported clades are: primitive newts (Echinotriton, Pleurodeles, and Tylototriton), New World newts (Notophthalmus-Taricha), Corsica-Sardinia newts (Euproctus), and modern European newts (Calotriton, Lissotriton, Mesotriton, Neurergus, Ommatotriton, and Triturus) plus modern Asian newts (Cynops, Pachytriton, and Paramesotriton).Two alternative sets of calibration points and two Bayesian dating methods (BEAST and MultiDivTime) were used to estimate timescales for salamandrid evolution. The estimation difference by dating methods is slight and we propose two sets of timescales based on different calibration choices. The two timescales suggest that the initial diversification of extant salamandrids took place in Europe about 97 or 69Ma. North American salamandrids were derived from their European ancestors by dispersal through North Atlantic Land Bridges in the Late Cretaceous ( approximately 69Ma) or Middle Eocene ( approximately 43Ma). Ancestors of Asian salamandrids most probably dispersed to the eastern Asia from Europe, after withdrawal of the Turgai Sea ( approximately 29Ma).

The way in which novelties that lead to macroevolutionary events originate is a major question in evolutionary biology, and one that can be addressed using the fire salamander (Salamandra salamandra) as a model system. It is exceptional among amphibians in displaying intraspecific diversity of reproductive strategies. In S. salamandra, two distinct modes of reproduction co-occur: the common mode, ovoviviparity (females giving birth to many small larvae), and a phylogenetically derived reproductive strategy, viviparity (females producing only a few large, fully metamorphosed juveniles, which are nourished maternally). We examine the relationship between heterochronic modifications of the ontogeny and the evolution of the new reproductive mode in the fire salamander. The in vitro development of embryos of ovoviviparous and viviparous salamanders from fertilization to metamorphosis is compared, highlighting the key events that distinguish the two modes of reproduction. We identify the heterochronic events that, together with the intrauterine cannibalistic behavior, characterize the derived viviparous reproductive strategy. The ways in which evolutionary novelties can arise by modification of developmental programs can be studied in S. salamandra. Moreover, the variation in reproductive modes and the associated variation of sequences of development occur in neighboring, conspecific populations. Thus, S. salamandra is a unique biological system in which evolutionary developmental research questions can be addressed at the level of populations.

Caecilians have two functionally separate sets of jaw closing muscles. The jaw adductor muscles are parallel fibered muscles positioned close to the jaw joint and their lever mechanics suggests they are well suited to rapidly closing the jaws. A second set of muscles, the hypaxial interhyoideus posterior (IHP), levers the jaws closed by pulling on the retro-articular process (RA) of the lower jaw. Models of the lower jaw point out that the angle and length of the RA has a profound effect on the closure force exerted by the IHP. The caecilian skull is streptostylic - the quadrate-squamosal apparatus (QSA) moves relative to the rest of the skull, a condition that seems at odds with a well-ossified cranium. Modeling the contribution of this streptostylic suspension of the lower jaw shows that rotational freedom of the QSA amplifies the force of the IHP by redirecting force applied along the low axis of the lower jaw. Measurements from several species and life stages of preserved caecilians reveal a large variation in predicted bite force (as a multiple of IHP force) with age and phylogeny.

Comparative developmental biologists have proposed models to describe patterns of conserved features in vertebrate ontogeny. The hourglass model suggests evolutionary change is most difficult at an intermediate "phylotypic" stage, the adaptive penetrance model suggests change is easiest at an intermediate stage, and the early conservation model suggests change is easier later in ontogeny. Although versions of some of these models have been discussed since the nineteenth century, quantitative approaches have been proposed only recently. Here we present quantitative phylogenetic approaches to evaluating trends in the evolution of ontogeny. We apply these approaches to the proposed models and demonstrate that an existing approach to assessing these models is biased. We show that the hourglass, adaptive penetrance, and early conservation models are unnecessarily complex explanations of the patterns observed in developmental event data for 14 species of vertebrates. Rather, a simpler model that postulates that evolutionary change is easier between ontogenetically adjacent events is adequate.

Little is known about the developmental biology of caecilians-tropical, elongate, limbless, mostly fossorial amphibians that are members of the Order Gymnophiona. Ichthyophis kohtaoensis (Family Ichthyophiidae; southeast Asia) is an oviparous species in which maternal care of the clutch is provided. The clutch is laid in a burrow on land, and the embryos develop in their egg membranes, curved around a large yolk mass. Larvae are aquatic and exhibit characteristic features that are not present in the terrestrial adults. Because accurate descriptions of ontogenies and the establishment of standardized stages of embryonic and larval development are useful for both experimental and comparative embryology, a staging table for I.kohtaoensis was developed based on external morphological features. Development from the end of neurulation to metamorphosis was divided into 20 stages. Principal diagnostic features include development of the lateral line organs, formation of three pairs of external gills, development of the eyes, changes in yolk structure, changes in the structure of the cloacal aperture and growth of the tail, including the formation and regression of the tail fin. This study provides a comparison with descriptions of embryonic stages of I.glutinosus and Hypogeophis rostratus and with a recent staging table for the aquatic, viviparous caecilian Typhlonectes compressicauda, the only other caecilians for which reasonably complete ontogenetic information exists in the literature. Comparisons with established staging tables for selected frogs and salamanders are also presented., (Copyright 2000 Wiley-Liss, Inc.)

The structure and function of the oviducts of members of the three Orders of the Class Amphibia (Anura, frogs and toads; Urodela, salamanders and newts; Gymnophiona, caecilians) are well described for only a few species. Further, the majority of such descriptions relate only to temperate species that breed in water, lay their eggs there, and have free-living larvae, the presumed ancestral condition of oviparity. Many species of amphibians have derived reproductive modes. Such modes include breeding terrestrially and arboreally, making foam nests, parental transport of eggs and/or tadpoles, direct development (copulating on land, laying the eggs in terrestrial sites, fully metamorphosed juveniles hatching, obviating the free-living larval stage). Other derived modes are ovoviviparity (developing embryos retained in the oviducts, born at a diversity stages of development, no maternal nutrition in addition to yolk) and viviparity (oviductal retention of developing young, maternal nutrition after yolk is resorbed, young born as fully metamorphosed juveniles). The amphibian oviduct is regionally differentiated to secrete varying numbers of layers of material around each egg, which function in fertilization, etc.; it is responsive to endocrine output and environmental mediation during the reproductive cycle; and it maintains developing embryos in some members of all three orders, some with oviductal epithelial secretion of nutrients. However, little is known of the structure-function relationships of the oviduct in species with derived reproductive modes. A comparison of oviduct morphology, function, endocrinology, ecology and phylogeny in amphibians with diverse reproductive modes suggests a number of highly productive avenues of investigation.

The presence of spicules (also termed spines, teeth, or denticles) on the intromittent organ, a character unique to male members of some species in the African caecilian family Scolecomorphidae, has long been known (Noble, '31; Taylor, '68; Wake,'72; Nussbaum,'85). However, their organization and structure has not been examined. Series of males of three species of Scolecomorphus were examined in order to determine the gross and histological organization of the spicules. Spicule morphology changes with ontogeny within species and differs grossly among species. The cellular organization of the spicules is remarkably similar among species, however. The spicules are composed of chondroid cartilage. The large discoid cells are arranged in "stacks" to form the projections, which emerge from an extensive base plate of the same cartilage. The spicules have a connective tissue sheath, which is not continuous with the cloacal epithelium. The sheath of the spicules may or may not be mineralized; the cartilage itself does not appear to be calcified. Mineralization apparently is not correlated with age, reproductive status, or season. Cartilage in the cloaca of these few species poses a series of questions about the interactions of developmental, structural, functional, and phylogenetic properties in the evolution of the reproductive biology of caecilians. J. Morphol. 237:177-186, 1998. © 1998 Wiley-Liss, Inc., (Copyright © 1998 Wiley-Liss, Inc.)

Tectal development in a number of caecilian (Gymnophiona: Amphibia) species was examined and compared with that in frogs and salamanders. The caecilian optic tectum develops along the same rostrocaudal and lateromedial gradients as those of frogs and salamanders. However, differences exist in the time course of development. Our data suggest that, as in salamanders, simplification of morphological complexity in caecilians is due to a retardation or loss of late developmental stages. Differences in the time course of development (heterochrony) among different caecilian species are correlated with phylogenetic history as well as with variation in life histories. The most pronounced differences in development occur between the directly developing Hypogeophis rostratus and all other species examined. In this species, the increase in the degree of morphological complexity is greatly accelerated. J. Morphol. 236:233-246, 1998. © 1998 Wiley-Liss, Inc., (Copyright © 1998 Wiley-Liss, Inc.)

The morphology of the tectum mesencephali and the medial pallium is studied in species representing the six families of caecilians (Amphibia: Gymnophiona) in order to determine whether differences in brain morphology are related to function, phylogenetic history, or life history strategies. In general, the caecilian tectum is characterized by simplification in having little to no lamination and few migrated cells. The degree of morphological complexity differs between species and between brain regions. Our data suggest that changes in brain morphology are due to a mosaic of different influences. We did not find a strict correlation between visual system reduction and tectal morphologies. However, phylogenetic effects exist. The greatest degree of morphological complexity is found in members of the Rhinatrematidae, a family that is considered basal to the lineage. Thus, simplification of brain morphology in caecilians must be considered a secondary or derived rather than a primitive feature. Direct development and miniaturization are correlated with the greatest simplification in the tectum mesencephali and medial pallium. There is a relationship between differences in brain morphology and heterochrony in caecilians, as in other amphibians. J. Morphol. 231:11-27, 1997. © 1997 Wiley-Liss, Inc., (Copyright © 1997 Wiley-Liss, Inc.)

The organization of the motor nuclei of the glossopharyngeal, vagal, occipital, first spinal and second spinal nerves of Typhlonectes natans (Amphibia: Gymnophiona: Caeciliaidae: Typhlonectinae) was studied by using horseradish peroxidase reaction staining. Each nucleus has discrete patterns of cytoarchitecture and of topography. Nuclei are elongate and some overlap anteroposteriorly. The brainstem is elongate, with no distinct demarcation of brainstem from spinal cord. The occipital nerve emerges through a separate foramen from that for the vagus and glossopharyngeal nerves in the species studied, is distinct from both, and its nucleus is more similar to spinal nuclei in cytoarchitecture. The occipital nerve fuses with spinal nerves 1 and 2 to contribute to the hypoglossal trunk. A spinal accessory nerve is absent.

The pattern of lung ventilation in the terrestrial caecilian Dermophis mexicanus was investigated by recording pressure changes of buccal and pleuroperitoneal cavities and activity of the buccal musculature. This species uses a fairly typical sarcopterygian buccal pumping system to inflate its single lung. What distinguishes it from other amphibians is the large number of buccal pumping cycles that occur in each ventilatory cycle. Up to 29 buccal cycles were observed to occur in a single respiratory cycle, with a mean of 16.1 ± 3.0 buccal cycles. This long series of buccal cycles avoids the sarcopterygian pattern of rebreathing expired air because only the first buccal cycle pumps expired air back into the lung. The series of buccal cycles also generates pleuroperitoneal pressures that are three to ten times greater than those observed in other amphibians. We suggest that these high pleuroperitoneal pressures are necessary for the maintenance of body form and locomotor function in terrestrial caecilians. © 1995 Wiley-Liss, Inc., (Copyright © 1995 Wiley-Liss, Inc.)

The morphology of mature sperm from the testes of 22 genera and 29 species representing all five families of caecilians (Amphibia: Gymnophiona) was examined at the light microscope level in order to: (1) determine the effectiveness of silver-staining techniques on long-preserved, rare material, (2) assess the comparative morphology of sperm quantitatively, (3) compare patterns of caecilian sperm morphology with that of other amphibians, and (4) determine if sperm morphology presents any characters useful for systematic analysis. Although patterns of sperm morphology are quite consistent intragenerically and intrafamilially, there are inconsistencies as well. Two major types of sperm occur among caecilians: those with very long heads and pointed acrosomes, and those with shorter, wider heads and blunt acrosomes. Several taxa have sperm with undulating membranes on the flagella, but limitations of the technique likely prevented full determination of tail morphology among all taxa. Cluster analysis is more appropriate for these data than is phylogenetic analysis. © 1994 Wiley-Liss, Inc., (Copyright © 1994 Wiley-Liss, Inc.)

The ancestral gymnophione (caecilian) became elongate and limbless early in its history. Further structural reduction, including loss of components, followed by redirection and occasionally cooption of remaining structures, particularly muscles and nerves, has evolved. Function may remain that of the ancestral condition, or may change dramatically. Examples include the evolution of the tentacle, the jaw-closing apparatus, and the hypobranchial musculature, including their innervation. 'Regressive' evolution has provided opportunity for new structural-functional relationships and for increased variation.

The innervation of the musculature of the tongue and the hyobranchial apparatus of caecilians has long been assumed to be simple and to exhibit little interspecific variation. A study of 14 genera representing all six families of caecilians demonstrates that general patterns of innervation by the trigeminal, facial, glossopharyngeal, and vagus nerves are similar across taxa but that the composition of the "hypoglossal" nerve is highly variable. Probably in all caecilians, spinal nerves 1 and 2 contribute to the hypoglossal. In addition, in certain taxa, an "occipital," the vagus, and/or spinal 3 appear to contribute fibers to the composition of the hypoglossal nerve. These patterns, the lengths of fusion of the contributing elements, and the branching patterns of the hypoglossal are assessed according to the currently accepted hypothesis of phylogenetic relationships of caecilians, and of amphibians. An hypothesis is proposed that limblessness and a simple tongue, with concomitant reduced complexity of innervation of muscles associated with limbs and the tongue, has released a constraint on pattern of innervation. As a consequence, a greater diversity and, in several taxa, greater complexity of neuroanatomical associations of nerve roots to form the hypoglossal are expressed.

The structures of the dermal scales and the cells surrounding the scales in two species of gymnophione amphibians were studied using histochemistry and light, scanning and transmission electron microscopy. Scales are composed of a basal platt of several layers of unmineralized collagenous fibers topped with mineralized squamulae. Squamulae are composed of numerous mineralized globules and mineralized, thick collagen fibers. Mineralization is therefore both spheritic and inotropic. Isolated flattened cells lie on the outer surface of the squamulae and seem to be involved in mineral deposition. Cells that line the basal plate synthesize the collagenous stroma of the plate. Each scale lies in a thin connective tissue pocket, and a large connective tissue pouch includes several scales in each annulus. The similarities of gymnophione scales to elasmoid scales of osteichthyans are largely superficial. Aspects of mineralization and of pocket development differ considerably. There are also similarities, as well as differences, in the gymnophione scales and osteoderms of amphibians and of reptiles. We consider that such dermal structures have arisen many times in diverse lineages of vertebrates, and that these are expressions of properties of dermal collagen to support mineralization by specialized dermal cells. However, we recommend that the term "dermal scale" be used for the mineralized dermal units of osteichthyans and gymnophiones, and "osteoderm" for the dermal structures of frogs and squamates, with the understanding that the terminology recognizes certain convergent attributes of shape and structure, but not of process., (Copyright © 1990 Wiley-Liss, Inc.)

The morphology of both the main nasal cavity and the vomeronasal organ differs among species representing six families of caecilians. The main nasal cavity is either divided or undivided. The vomeronasal organ differs in position (mediolateral, lateral), size (large vomeronasal organ in the aquatic species), and shape (mediolateral extension, vomeronasal organ with a lateral rostral projection). The great amount of respiratory epithelium of the main nasal cavity, the large vomeronasal organ, and its extensive innervation in typhlonectids may reflect both phylogeny and habitat adaptation, for these taxa are secondarily aquatic or semiaquatic and have several concomitant morphological and physiological modifications. The vomeronasal organ is associated with the caecilian tentacle as the tentacular ducts open into it. This association is further evidence for the involvement of the caecilian tentacle in vomeronasal chemoperception and may represent the mechanism by which these animals smell though the main nasal cavity is closed during burrowing or swimming. Labelings of primary olfactory and vomeronasal projections by means of horseradish peroxidase reaction reveal that the pattern of vomeronasal projections is similar in Ichthyophis kohtaoensis, Dermophis mexicanus, and Typhlonectes natans, even though T. natans possess stronger vomeronasal projections relative to olfactory projections than I. kohtaoensis and D. mexicanus. However, there are differences with respect to the patterns of olfactory projections. The olfactory projection of I. kohtaoensis is characterized by many displaced glomeruli. T. natans has the smallest olfactory projection. The nervus terminalis is associated with the olfactory system as shown by selective labelings of olfactory projections. Six characters potentially useful for phylogenetic analysis emerge from this study of comparative morphology. The characters were subjected to analysis using PAUP to see (1) if any resolution occurred and (2) if any groups were distinguished, whether they corresponded to phylogenetic arrangements based on other morphological characters. The characters are too few to produce nested dichotomous sets for all cases, but they do support the two typhlonectid genera examined and Dermophis and Gymnopis as sister taxa discrete from other groups, and they show that species within genera cluster together., (Copyright © 1990 Wiley-Liss, Inc.)

Typhlonectes compressicauda has a diploid number of 28. Its karyotype, when compared to that of other caecilians, suggests some discordance in the hypothesized model of chromosome reduction in the evolution of amphibian lineages.

Morphometric analysis of vertebral structure in caecilians (Amphibia: Gymnophiona) is presented. Ontogenetic variation in Dermophis mexicanus is analyzed through the 100+ vertebrae composing the column. Vertebral structure in adult D. mexicanus is compared with that in Ichthyophis glutinosus and Typhlonectes compressicauda. Centra of the atlas, second, tenth, 20th, and 50th vertebrae grow at allometrically different rates in D. mexicanus, though the 20th and 50th are not significantly different. Growth appears significantly slower in several dimensions of anterior and posterior vertebrae relative to midtrunk vertebrae in all three species. Mensural patterns throughout the entire column are similar in the terrestrail burrowers D. mexicanus and I. glutinosus; patterns in the aquatic T. compressicauda differ substantially from those of the burrowing species and are strongly influenced by allometry. Of the 112 D. mexicanus examined, 13.4% had vertebral anomalies, usually fusions.

The development of the tentacle, a chemosensory and perhaps tactile structure unique among vertebrates to gymnophione amphibians is described in Dermophis mexicanus and Gymnopis multiplicata. The tentacle is associated with the vomeronasal organ and its glands, and utilizes several structures usually associated with the eye, such as the Harderian gland, the retractor and levator muscles, and their nerves. Innervation of the tentacle itself is from the trigeminal nerve. We present an hypothesis that the tentacle originated from modified eye components., (Copyright © 1987 Wiley-Liss, Inc.)

Innervation of the tongue and associated musculature in plethodontid salamanders was studied using Palmgren stained sectioned materials, fresh dissection, and whole mounts of experimental specimens treated with horseradish peroxidase (HRP). Species studied were chosen to represent modes of tongue projection recognized by Lombard and Wake ('77). Special attention was given to species of the genera Plethodon, Batrachoseps, Pseudoeurycea, and Hydromantes, but representatives of other genera were investigated. As expected we found that cranial nerves IX and X and spinal nerve 1 supplied the muscles involved in tongue movement. The peripheral courses of the nerves were traced, and both functionally related and phylogenetically determined routes were found. As relative projection length increases, the nerves supplying the tongue tip also increase in length. When the tongue is at rest the long nerves are stored in coils. The coil of ramus lingualis lies between the ceratobranchials, but that of ramus hypoglossus is more variable, although constant within a species. Ramus hypoglossus bifurcates into separate branches to tongue and anterior musculature of the floor of the mouth. In generalized, presumably primitive, modes the bifurcation and coiling are far anterior. In most of the tongue projection modes bifurcation is relatively posterior, but in one, bifurcation is anterior, but coiling is relatively posterior in position. The most unusual condition is in Hydromantes, in which bifurcation is relatively posterior and a coiled ramus hypoglossus joins a coiled ramus lingualis to form a unique, coiled common ramus to the tongue tip. Hydromantes has the greatest projection distance of any salamander.

The morphology of tooth crowns is variable inter-specifically among caecilians. Cusp number and shape, crown dimensions, and crown curvature characterize various species and have both functional and phylogenetic implications. Ichthyophis, Uraeotyphlus, Hypogeophis, and Geotrypetes have bicuspid teeth; Dermophis, Gymnopis, Caecilia, and Typhlonectes monocuspid. Crown morphology as revealed by scanning electron microscopy is associated with prey grasping and, in one case, possible specialization of prey type., (Copyright © 1979 Wiley-Liss, Inc.)

Tooth development and replacement in fetal and adult viviparous caecilians (Amphibia: Gymnophiona) are described and analyzed according to current theories of tooth succession. The fetal dentition differs from that of the adult in morphology, position, and function. Teeth are used by fetuses to scrape the oviducal epithelium, thus stimulating the secretion of a nutrient substance. Fetal dentitions vary in morphology and position in different species. The ontogeny of teeth of several species is described and the patterns of addition of loci and of replacement are analyzed. Loci are added both posteriorly along the jaw and between existing loci as the jaw grows prior to ossification; subsequently addition is restricted to the posterior part of the jaw. Tooth replacement is alternate. The several rows and patches of teeth are the result of retention of replacement series on the dentigerous elements. Tooth development and replacement in a series of juveniles and adults of different sizes in a single species are also considered. Post-fetal patterns of development and replacement are similar to those seen in larvae and adults of oviparous species. Variation in numbers of teeth and proportions of teeth at particular stages occurs ontogenetically and among individuals of the same size, though proportions occur in a similar pattern throughout the series. The general pattern of tooth replacement in fetuses and adults can be explained by either Edmund's Zahnreihen theory or by Osborn's Tooth Family theory, but replacement in fetal tooth patches and the fetal-adult dentitional transition are explained by neither.

Study of the innervation of the musculature related to feeding behavior in plethodontid salamanders by means of the horseradish peroxidase (HRP) technique has demonstrated the existence of a true spinal accessory nerve which innervates neck musculature, enters the brain via the ganglion of IX/X cranial nerves and has its motor neurons within the nucleus of the second spinal nerve. Further, it has been shown that the first spinal nerve, being strictly motor, alone constitutes the ramus hypoglossus and is, therefore, homologous to the hypoglossus of amniotes.

Teeth of fetuses of a caecilian, Dermophis mexicanus (Amphibia: Gymnophiona), show ontogenetic variation in crown structure from small, multidenticulate, and non-pedicellate to larger, spoon-shaped, pedicellate teeth with a single apical spike. Number of denticles decreases as enamel-secreting cells mature. Numbers of teeth and of tooth rows increase ontogenetically. A fetal vomeropalatine set of teeth is present in D. mexicanus but absent in species previously examined. Teeth transitional to the adult shape and arrangement appear shortly before birth. The transition is correlated with birth, not fetal size. There is relatively little increase in numbers of teeth during the juvenile period. The pattern of development does not fully agree with either morphogenetic field theory or with clone theory, both as defined by Osborn ('78). Sequence of initiation is appropriate to either. Tooth shape changes agree with aspects of clone theory. Multiple rows of fetal teeth and the transition to adult follow field theory. Clone theory holds that patterns of development and shape are self-regulated, field theory that they are controlled extrinsically. I suggest that substances regulating differentiation mediate early development, and hormones later development, including inception of adult teeth, and are comparable to "field substances" influencing primordia that originate according to clone theory. Components of both theories are appropriate to analyzing tooth development phenomena., (Copyright © 1980 Wiley-Liss, Inc.)