The evolution of the adult body form of the crested newt (Triturus cristatus superspecies,Caudata, Salamandridae)

We characterized the adult body form of the crested newt (Triturus cristatus superspecies) and explored its evolution. From seven morphometric traits, we determined that body size, interlimb distance and head width define the body form. None of the morphometric traits showed a phylogenetic signal. Three body‐shape morphotypes (Triturus dobrogicus + T. cristatus, Triturus carnifex + Triturus macedonicus and Triturus karelinii + Triturus arntzeni) and three body‐size morphotypes (T. dobrogicus, T. cristatus and all other crested newts) could be recognized. The ancestral phenotype (a large body with a short trunk and a wide head) characterized T. karelinii and T. arntzeni. Triturus carnifex and T. macedonicus had a somewhat different phenotype (large body and wide head, accompanied by mild body elongation). The most derived phenotype included body size reduction and more pronounced body elongation in T. cristatus and, especially, in T. dobrogicus. Body elongation occurred by trunk lengthening but not head and tail lengthening. Additionally, contrary to other tetrapods, evolutionary axis elongation in crested newts was followed by a decrease in body size. We advocate the hypothesis that ecology drives the evolution of body form in crested newts.     

Evolution of skull and body shape in Triturus newts reconstructed from three‐dimensional morphometric data and phylogeny

To explore the relationship between morphological change and species diversification, we reconstructed the evolutionary changes in skull size, skull shape, and body elongation in a monophyletic group of eight species that make up salamander genus Triturus. Their well‐studied phylogenetic relationships and the marked difference in ecological preferences among five species groups makes this genus an excellent model system for the study of morphological evolution. The study involved three‐dimensional imagery of the skull and the number of trunk vertebrae, in material that represents the morphological, spatial, and molecular diversity of the genus. Morphological change largely followed the pattern of descent. The reconstruction of ancestral skull shape indicated that morphological change was mostly confined to two episodes, corresponding to the ancestral lineage that all crested newts have in common and the Triturus dobrogicus lineage. When corrected for common descent, evolution of skull shape was correlated to change in skull size. Also, skull size and shape, as well as body shape, as inferred from the number of trunk vertebrae, were correlated, indicating a marked impact of species' ecological preferences on morphological evolution, accompanied by a series of niche shifts, with the most pronounced one in the T. dobrogicus lineage. The presence of phylogenetic signal and correlated evolutionary changes in skull and body shape suggested complex interplay of niche shifts, natural selection, and constraints by a common developmental system. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 243–255.     

Sexual size and shape evolution in European newts (Amphibia: Caudata: Salamandridae) on the Balkan Peninsula

We used a phylogenetic perspective in an examination of the direction and extent of sexual dimorphism in body size and body shape in European newts from the Balkan Peninsula (alpine newts, Mesotriton alpestris; crested newts, Triturus cristatus superspecies; smooth newts, Lissotriton vulgaris). We found a strong, female‐biased sexual size dimorphism (SSD) in the analysed clades of alpine newt, whereas within crested newts we found a less stringent female‐biased SSD in Triturus carnifex, Triturus macedonicus and Triturus karelinii, and no significant SSD in T. cristatus or Triturus dobrogicus. Among the smooth newts, we found male‐biased SSD in Lissotriton vulgaris vularis and Lissotriton vulgaris greacus and no SSD in Lissotriton vulgaris meridionalis. Most of these newts also exhibit a significant sexual dimorphism in body shape, which varied more randomly than body size, regardless of SSD level. Female and male body size as well as the degree of SSD displayed statistically significant phylogenetic signal, while sexual dimorphism in body shape was phylogenetically independent. The relationship between independent contrast data for female size and male size indicated that SSD in European newts could be driven by a disproportionate increase in female size as increase in female size was not accompanied by a proportional increase in male size.     

GEOGRAPHIC VARIATION AND PHENOTYPIC PLASTICITY OF NUMBER OF TRUNK VERTEBRAE IN SLENDER SALAMANDERS,BATRACHOSEPS (CAUDATA: PLETHODONTIDAE)

To understand the evolutionary significance of geographic variation, one must identify the factors that generate phenotypic differences among populations. I examined the causes of geographic variation in and evolutionary history of number of trunk vertebrae in slender salamanders, Batrachoseps (Caudata: Plethodontidae). Number of trunk vertebrae varies at many taxonomic levels within Batrachoseps. Parallel clines in number occur along an environmental gradient in three lineages in the Coast Ranges of California. These parallel clines may signal either adaptation or a shared phenotypically plastic response to the environmental gradient. By raising eggs from 10 populations representing four species of Batrachoseps, I demonstrated that number of trunk vertebrae can be altered by the developmental temperature; however, the degree of plasticity is insufficient to account for geographic variation. Thus, the geographic variation results largely from genetic variation. Number of trunk vertebrae covaries with body size and shape in diverse vertebrate taxa, including Batrachoseps. I hypothesize that selection for different degrees of elongation, possibly related to fossoriality, has led to the extensive evolution of number of trunk vertebrae in Batrachoseps. Analysis of intrapopulational variation revealed sexual dimorphism in both body shape and number of trunk vertebrae, but no correlation between these variables in either sex. Females are more elongate than males, a pattern that has been attributed to fecundity selection in other taxa. Patterns of covariation among different classes of vertebrae suggest that some intrapopulational variation in number results from changes in vertebral identity rather than changes in segmentation.     

Helminth parasite populations in newts and their tadpoles

Five species of helminth parasites were found in adults and tadpoles of the newts Triturus helveticus, T. vulgaris, and T. cristatus, caught at eight different localities in Somerset. These parasites were Acanthocephalus anthuris, A. ranae, Megalobatra-chonema terdentatum, Thominx filiformis and Oswaldocruzia molgeta. Mean worm burdens did not change through the year, and egg-producing females of Acantho-cephalus anthuris and Megalobatrachonema terdentatum were found throughout. There was no difference in the level of infection of male and female newts.     

Evolving possibilities: postembryonic axial elongation in salamanders with biphasic (Eurcyea cirrigera,Eurycea longicauda,Eurycea quadridigitata) and paedomorphic life cycles (Eurycea nana and Ambystoma mexicanum)

Vaglia, JL., White, K, and Case, A. 2012. Evolving possibilities: postembryonic axial elongation in salamanders with biphasic (Eurcyea cirrigera, Eurycea longicauda, Eurycea quadridigitata) and paedomorphic life cycles (Eurycea nana and Ambystoma mexicanum). —Acta Zoologica (Stockholm) 93 : 2–13. Typically, the number of vertebrae an organism will have postembryonically is determined during embryogenesis via the development of paired somites. Our research investigates the phenomenon of postembryonic vertebral addition in salamander tails. We describe body and tail growth and patterns of postsacral vertebral addition and elongation in context with caudal morphology for four plethodontids (Eurycea) and one ambystomatid. Eurycea nana and Ambystoma mexicanum have paedomorphic life cycles; Eurcyea cirrigera, Eurycea longicauda and Eurycea quadridigitata are biphasic. Specimens were collected, borrowed and/or purchased, and cleared and stained for bone and cartilage. Data collected include snout‐vent length (SVL), tail length (TL), vertebral counts and centrum lengths. Eurycea species with biphasic life cycles had TLs that surpassed SVL following metamorphosis. Tails in paedomorphic species elongated but rarely exceeded body length. Larger TLs were associated with more vertebrae and longer vertebrae in all species. We observed that rates of postsacral vertebral addition varied little amongst species. Regional variation along the tail becomes prominent following metamorphosis in biphasic developers. In all species, vertebrae in the posterior one‐half of the tail taper towards the tip. We suggest that a developmental link might exist between the ability to continually add vertebrae and regeneration in salamanders.     

Acclimation is beneficial at extreme test temperatures in the Danube crested newt, Triturus dobrogicus (Caudata, Salamandridae)

Despite many studies demonstrating the effect of acclimation on behavioural or physiological traits, considerable debate still exists about the evolutionary significance of this phenomenon. One of the unresolved issues is whether acclimation to warmer temperature is beneficial at treatment or at more extreme test temperatures. To answer this question, we assessed the effect of thermal acclimation on preferred body temperatures ( T _ps), maximum swimming and running speed, and critical thermal maximum ( CT _max) in the Danube crested newt ( Triturus dobrogicus ). Adult newts were kept at 15 °C (control) and 25 °C (treatment) for 8 weeks prior to measurements. We measured T _ps in an aquatic thermal gradient over 24 h, maximum speeds in a linear racetrack at six temperatures (5–33 °C), and CT _max in a continuously heated water bath. T _ps were higher in newts kept at 15 °C than in those kept at 25 °C. The maximum swimming speed did not acclimate. The maximum running speed at 30–33 °C was substantially higher in newts kept at 25 °C than in those kept at 15 °C. CT _max increased with the treatment temperature. Hence, we conclude that the acclimation response to warm temperature is beneficial not at treatment but at more extreme temperatures in newts.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 627–636.     

Micro-habitat use within a guild of newt larvae (Trituridae) in an Alpine lake

Population and ecological parameters such as numbers of larvae, microhabitat use, niche breadth and niche overlap of three species of syntopic larval newts (Alpine newt Triturus alpestris, Italian crested newt T. carnifex, and common newt T. vulgaris) were studied for two years in a small pond at 1160 m a.s.l. in NE Slovenia. Differences in microhabitat partitioning among larval newts were small. The largest niche breadth was estimated for larval T. alpestris, and the narrowest estimate was for larval T. carnifex in both years. Ecological differences seem to be very small and quite variable among sites and years. It appears that the developmental stage and size of newt larvae are more important in explaining resource partitioning than the characteristics of each species. Because of the absence of potential invertebrate predators and adult newts in the second half of the breeding season, the injuries could only be caused by intra-and interspecific predation attempts.     

Skeletal Growth Marks and Testis Lobulation as Criteria for Age in Triturus spp. (Amphibia) in Central Norway

Two methods of age determination in newts. Triturus vulgaris and T. cristatus, have been examined and compared: (1) Counting growth rings in the bone tissue of humerus or femur is an accurate method, but possible supplementary rings may make the reading difficult. The innermost periosteal zone corresponds to the first year of life. Later, new zones are added each year. (2) Every second year after maturing a new lobe is developed on the testes. Knowing the juvenile life span in a population, it is possible to determine the age of male newts with a possible error of one year. The correlation between growth marks and testis lobes in T. vulgaris and T. cristatus is highly significant. The testis lobing method, however, is less applicable in older newts, since no more than three or four lobes can be developed on a testis.     

Do Experience and Body Size Play a Role in Responses of Larval Ringed Salamanders,Ambystoma annulatum,to Predator Kairomones? Laboratory and Field Assays

Prey may experience ontogenetic changes in vulnerability to some predators, either because of changes in morphology or experience. If prey match their level of antipredator behavior to the level of predatory threat, prey responses to predators should reflect the appropriate level of threat for their stage of development. For larval salamanders, responses to predators may change with body size because larger larvae are less vulnerable to predation by gape‐limited predators or because fleeing responses by large salamanders may be more effective than for smaller salamanders. In a field experiment, small larval ringed salamanders, Ambystoma annulatum, responded to chemical stimuli (‘kairomones’) from predatory newts, Notophthalmus viridescens, with an antipredator response (decreased activity). Laboratory‐reared larvae decreased their activity following exposure to newt kairomones, indicating that larval ringed salamanders do not require experience with newts to recognize them as predators. In both experiments, larvae distinguished between chemical stimuli from newts and stimuli from tadpoles (non‐predators) and a blank control. In a third experiment, field‐caught (experienced) larvae showed a graded response to newt kairomones based on their body size: small larvae tended to decrease their activity while larger larvae showed no change or an increase in activity. This graded response was not observed for neutral stimuli, indicating that it is predator‐specific. Therefore, ringed salamander larvae exhibit threat‐sensitive ontogenetic changes in their response to chemical stimuli from predatory newts.     

Ontogeny of skull size and shape changes within a framework of biphasic lifestyle: a case study in six <Emphasis Type="Italic">Triturus</Emphasis> species (Amphibia,Salamandridae)

As with many other amphibians, Triturus species are characterized by a biphasic life cycle with abrupt changes in the cranial skeleton during metamorphosis. The post-metamorphic shape changes of the cranial skeleton were investigated using geometric morphometric techniques in six species: Triturus alpestris, T. vulgaris, T. dobrogicus, T. cristatus, T. carnifex, and T. karelinii. The comparative analysis of ontogenetic trajectories revealed that these species have a conserved developmental rate with divergent ontogenetic trajectories of the ventral skull shape that mainly reflect phylogenetic relatedness. A striking exception in the ontogenetic pattern was possibly found in T. dobrogicus, characterized by a marked increase in the developmental rate compared to the other newt species. The size-related shape changes explained a large proportion of shape change during post-metamorphic growth within each species, with marked positive allometric growth of skull elements related to foraging.     

High aquatic niche overlap in the newts Triturus cristatus and T. marmoratus (Amphibia,Urodela)

We studied spatial niche metrics of large-bodied newts (Triturus cristatus and T. marmoratus) in three breeding ponds in western France. Adults and larvae were sampled with underwater funnel traps. Larvae were identified to the species with diagnostic microsatellite DNA markers. The distribution of adult T. cristatus and T. marmoratus across pond regions differed in one out of six cases, no differences were observed between larvae (two ponds studied). Niche overlap and niche breadth indices across resource states defined as pond regions or individual traps were high (Schoener's C: pond regions 0.60–0.98, traps 0.35–0.71; Levins' B: pond regions 0.71–0.98, traps 0.35–0.76). Adults of large-bodied newts significantly differed in resource use from small-bodied newts (T. helveticus). The results are discussed in view of the occurrence of interspecific breeding attempts, and the unpredictable ecological characteristics of newt breeding ponds.     

Alpine newts (Triturus alpestris) as top predators in a high-altitude karst lake: daily food consumption and impact on the copepod Arctodiaptomus alpinus

1. Population dynamics and feeding ecology of adult and larval alpine newts (Triturus alpestris, Laurenti) were investigated in a high-altitude karts lake to estimate their feeding pressure on the copepod Arctodiaptomus alpinuf (Imhof). Estimates of population size for reproducing adults ranged from 666 to 864 individuals in the lake during July and August. Total abundance of larvae before the onset of ice cover varied considerably between 4400 and 25400 individuals in different years. 2. Arctodiaptomus alpinus was an important prey item for adult and larval alpine newts. During the second half of their aquatic period, adult newts moved to deeper water where the copepod reached its highest densities near the sediment. Adults and larvae exhibited no periodic feeding pattern. The feeding rhythm was more synchronized among the larvae than among the adults. 3. Daily food consumption, estimated using the Elliott & Persson (1978) model, reached 4–21 mg dry biomass in adults. The daily ration of larvae was about 7% of body dry weight in the temperature range 6-11°C. Compared to published estimates of daily food consumption in salmonid fishes, the feeding pressure of newts appears low.     

Limitation of similarity and feeding habits in three syntopic species of newts (Triturus, Amphibia)

Differences in body size between both species and sex were observed to be close to Hutchinsonian ratios in an assemblage of three species of newts (Triturus italicus, T alpestris and T carnifex) in southern Italy According to feeding, differences in body size were not related with a strict food niche segregation The diet of larger newt included indeed all the prey eaten by smaller newts but showed new prey types Differences between species were more marked than between sexes of the same species, despite a strong sexual dimorphism in body size Larger newts foraged in a wider range of microhabitats and exhibited a greater diversity of foraging tactics Triturus italicus fed essentially on plankton and chironomids in shallow water at the banks of the pond Triturus alpestris foraged also in deeper water, particularly on lsopods in vegetation Prey fallen on the water surface constituted the main part of T carnifex diet According to recent data on newt evolution, speciation consisted in the reduction of body size Our data show that this process has been related with a specialization of the diet and of habitat use     

Testing the hybrid superiority hypothesis in crested and marbled newts

We tested the hybrid superiority hypothesis in the zone of overlap and hybridization of the newts Triturus cristatus and T. marmoratus. To do so, we compared size, age, and growth-related parameters in F₁ hybrids and both parental species in Mayenne, France. We found significant differences in snout-vent length (SVL), body mass and average lifespan between the parental species and hybrids, increasing from T. cristatus – T. marmoratus – hybrids. The relation between age and SVL fitted von Bertalanffy's growth model and showed that SVL_max was significantly larger in hybrids than in the parental species, while the growth coefficient was lower in hybrids and T. marmoratus than in T. cristatus. Triturus cristatus appears to be the better competitor, since it attains sexual maturity faster and thus achieves more annual breeding opportunities. At the evolutionary level, the observed heterosis appears not to have further consequences as the hybrids are largely infertile. Our results support the hypothesis raised for the genus Triturus, that infertile hybrids allocate resources to growth.     

Paedogenesis in european newts (Triturus: salamandridae): cranial morphology during ontogeny

A cross-sectional analysis using different ontogenetic stages (larvae, juveniles, paedotypic, and metamorphic adults) of the smooth newt, Triturus vulgaris, and the alpine newt, T.alpestris, revealed a broad spectrum of perennibranchiation influences on cranial ontogeny in European newts, more pronounced than previously thought. These influences included marked variation in ossification levels, pronounced morphometric variability of many cranial elements, and considerable skull shape changes in the transition from larvae to the adult stage. In comparison with metamorphosed individuals, paedotypic newts had a higher level of variability in both individual cranial traits and cranial shape changes. Sexual size difference of the skull traits was mostly negligible, especially in comparison to the influence of paedogenesis. The main changes in cranial shape of the European newts occurred during metamorphosis. Cranial morphological organization in the majority of examined paedotypes corresponds to cranial organization at late larval stages prior to metamorphosis or at the onset of metamorphosis.     

The arterial arches and their interpretation in Bipes and other amphisbaenians

The study of the arterial arches of Bipes, the only amphisbaenian with forelimbs, resolves the problem of the interpretation of the structure of the arterial arches in other forms of this group of squamate reptiles. In Bipes, as in turtles, the subclavian and common carotid arteries originate from a brachiocephalic trunk, which arises from an innominate trunk deriving from the right aortic loop. This interpretation is not only original but also emphasizes the important lengthening of the brachiocephalic part relative to the strictly carotidian one. It supposes the intercalation of a new “precardiac” region between the pectoral girdle and the heart; these two components are closely associated topographically in the quadrupedal Squamata. This lengthening, expressed by the increase in the number of precloacal vertebrae, is linked with the increase in the asymmetry of the aortic loop.     

Finding the neck–trunk boundary in snakes: Anteroposterior dissociation of myological characteristics in snakes and its implications for their neck and trunk body regionalization

The neck and trunk regionalization of the presacral musculoskeletal system in snakes and other limb‐reduced squamates was assessed based on observations on craniovertebral and body wall muscles. It was confirmed that myological features characterizing the neck in quadrupedal squamates (i.e., squamates with well‐developed limbs) are retained in all examined snakes, contradicting the complete lack of the neck in snakes hypothesized in previous studies. However, the posterior‐most origins of the craniovertebral muscles and the anterior‐most bony attachments of the body wall muscles that are located at around the neck–trunk boundary in quadrupedal squamates were found to be dissociated anteroposteriorly in snakes. Together with results of a recent study that the anterior expression boundaries of Hox genes coinciding with the neck–trunk boundary in quadrupedal amniotes were dissociated anteroposteriorly in a colubrid snake, these observations support the hypothesis that structures usually associated with the neck–trunk boundary in quadrupedal squamates are displaced relative to one another in snakes. Whereas certain craniovertebral muscles are elongated in some snakes, results of optimization on an ophidian cladogram show that the most recent common ancestor of extant snakes would have had the longest craniovertebral muscle, M. rectus capitis anterior, that is elongated only by several segments compared with that of quadrupedal squamates. Therefore, even such a posteriorly displaced “cervical” characteristic plesiomorphically lies fairly anteriorly in the greatly elongated precloacal region of snakes, suggesting that the trunk, not the neck, would have contributed most to the elongation of the snake precloacal region. A similar dissociation of structures usually associated with the neck–trunk boundary in quadrupedal squamates is observed in limb‐reduced squamates, suggesting that these forms and snakes may share a developmental mechanism producing modifications in the anterior–posterior patterning associated with body elongation. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

A molecular assessment of phylogenetic relationships and lineage accumulation rates within the family Salamandridae (Amphibia, Caudata)

We examine phylogenetic relationships among salamanders of the family Salamandridae using approximately 2700 bases of new mtDNA sequence data (the tRNALeu, ND1, tRNAIle, tRNAGln, tRNAMet, ND2, tRNATrp, tRNAAla, tRNAAsn, tRNACys, tRNATyr, and COI genes and the origin for light-strand replication) collected from 96 individuals representing 61 of the 66 recognized salamandrid species and outgroups. Phylogenetic analyses using maximum parsimony and Bayesian analysis are performed on the new data alone and combined with previously reported sequences from other parts of the mitochondrial genome. The basal phylogenetic split is a polytomy of lineages ancestral to (1) the Italian newt Salamandrina terdigitata, (2) a strongly supported clade comprising the "true" salamanders (genera Chioglossa, Mertensiella, Lyciasalamandra, and Salamandra), and (3) a strongly supported clade comprising all newts except S. terdigitata. Strongly supported clades within the true salamanders include monophyly of each genus and grouping Chioglossa and Mertensiella as the sister taxon to a clade comprising Lyciasalamandra and Salamandra. Among newts, genera Echinotriton, Pleurodeles, and Tylototriton form a strongly supported clade whose sister taxon comprises the genera Calotriton, Cynops, Euproctus, Neurergus, Notophthalmus, Pachytriton, Paramesotriton, Taricha, and Triturus. Our results strongly support monophyly of all polytypic newt genera except Paramesotriton and Triturus, which appear paraphyletic, and Calotriton, for which only one of the two species is sampled. Other well-supported clades within newts include (1) Asian genera Cynops, Pachytriton, and Paramesotriton, (2) North American genera Notophthalmus and Taricha, (3) the Triturus vulgaris species group, and (4) the Triturus cristatus species group; some additional groupings appear strong in Bayesian but not parsimony analyses. Rates of lineage accumulation through time are evaluated using this nearly comprehensive sampling of salamandrid species-level lineages. Rate of lineage accumulation appears constant throughout salamandrid evolutionary history with no obvious fluctuations associated with origins of morphological or ecological novelties.     

Cranial shape variation and molecular phylogenetic structure of crested newts (Triturus cristatus superspecies: Caudata,Salamandridae) in the Balkans

In the present study, we investigated the degree of congruence between phylogeny, as inferred from mitochondrial (mt)DNA sequences, and cranium shape variation of crested newts (Triturus cristatus superspecies) in the Balkans. These newts belong to four phylogenetic clades defined by mtDNA analysis, and significantly differed in cranial shape. Allometry explained a high percentage of shape variation in crested newts. The clade‐specific allometric slopes significantly diverged for both the ventral cranium and dorsal cranium, indicating that differences in shape between clades could not be a simple consequence of their difference in size. The analysis of hierarchical and spatial variation showed similarity in the patterns of global and spatially localized hierarchical variation of cranial shape. We also found significant congruence between the pattern of cranial shape variation and molecular phylogeny. The differences in morphology of Triturus dobrogicus in comparison to other crested newt clades, including marked differences in cranium shape, is discussed in the context of the evolution and ecology of crested newts. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 348–360.