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 ontogeny of sexual dimorphism in the facial skeleton of the African apes

This paper aims to test the contribution of ontogenetic scaling to sexual dimorphism of the facial skeleton in the African apes. Specifically, it addresses whether males and females of each species share a common postnatal ontogenetic shape trajectory for the facial skeleton. Where trajectories are found to differ, it is tested whether male and female trajectories: 1) diverge early, or 2) diverge later after sharing a common trajectory earlier in the postnatal period. Where ontogenetic shape trajectories are found to be shared, it is also tested whether males and females are ontogenetically scaled. This study uses geometric morphometric analyses of 28 landmarks from the facial skeletons of 137 G. g. gorilla (62 adults; 75 juveniles), 95 P. paniscus (34 adults; 61 juveniles), and 115 P. t. troglodytes (58 adults; 57 juveniles). On average, males and females share a common ontogenetic shape trajectory until around the eruption of the second permanent molars. In addition, for the same period, males and females in each species share a common ontogenetic scaling trajectory. After this period, males and females diverge both from each other and from the common juvenile ontogenetic shape and scaling trajectories within each species. Thus, the male and female facial skeleton shows ontogenetic scaling until around the point of the eruption of the second molar (i.e., around puberty and the development of secondary sexual characteristics), but subsequent sexual dimorphism occurs via divergent trajectories and not via ontogenetic scaling.     

The impact of larval predators and competitors on the morphology and fitness of juvenile treefrogs

Studies of phenotypic plasticity typically focus on traits in single ontogenetic stages. However, plastic responses can be induced in multiple ontogenetic stages and traits induced early in ontogeny may have lasting effects. We examined how gray treefrog larvae altered their morphology in four different larval environments and whether different larval environments affected the survival, growth, development, and morphology of juvenile frogs at metamorphosis. We then reared these juveniles in terrestrial environments under high and low intraspecific competition to determine whether the initial differences in traits at metamorphosis affected subsequent survival and growth, whether the initial phenotypic differences converged over time, and whether competition in the terrestrial environment induced further phenotypic changes. Larval and juvenile environments both affected treefrog traits. Larval predators induced relatively deep tail fins and short bodies, but there was no impact on larval development. In contrast, larval competitors induced relatively short tails and long bodies, reduced larval growth, and slowed larval development. At metamorphosis, larval predators had no effect on juvenile growth or relative morphology while larval competitors produced juveniles that were smaller and possessed relatively shorter limbs and shorter bodies. After 1 month of terrestrial competition among the juvenile frogs, the initial differences in juvenile morphology did not converge. There were no differences in growth due to larval treatment but there were differences in survival. Individuals that experienced low competition as tadpoles experienced near perfect survival as juvenile frogs but individuals that experienced high competition as tadpoles suffered an 18% decrease in survival as juvenile frogs. There were also morphological responses to juvenile competition, but these changes appear to be due, at least in part, to allometric effects. Collectively, these results demonstrate that larval environments can have profound impacts on the traits and fitness of organisms later in ontogeny.     

Evolution of adaptation through allometric shifts in a marine snail

Variation in ontogenetic development among individuals may be a major contributor to morphological variation within species. Evolution of different growth trajectories might, for example, evolve as a response to varying ecological contexts of individuals living in different environments, or by life-stage or gender differences. The intertidal periwinkle Littorina saxatilis is strongly polymorphic in shell shape. We compared ontogenetic trajectories between life stages, local populations, and sexes to understand how different morphological end points are reached during ontogeny and what might cause these differences. Applying landmark-based geometric morphometrics, we captured shell shape variation for four Swedish populations of this species. We also derived a method to visualize ontogenetic trajectories described by the relationship of size to the multivariate shape space. We found that growth trajectories differed between individuals living in different habitats, as well as between sexes and maturity stages. Males living on rocky cliffs grew isometrically throughout life, whereas females from the same habitat switched from isometric growth as juveniles to allometric growth as adults. In contrast, males and females living on boulders grew allometrically as juveniles but changed to isometric growth at sexual maturity. Thus, in this species, ontogenetic growth seems influenced by habitat-associated selection as well as by gender and age-specific selection. These differing selection regimes result in ontogenetic shifts in allometry in three of the four groups examined.     

The impact of metamorphosis on the cranial osteology of giant salamanders of the genus Dicamptodon

Pacific giant salamanders (Dicamptodon) rank among the largest terrestrial caudates. Their ontogeny produces two distinct morphs—larval‐neotenic and metamorphosed—which differ in many morphological traits. We identified changes that are initiated by metamorphosis (distinguishing transformed from neotenic specimens) and also recognized age‐related changes occurring irrespective of transformation. During metamorphosis, specimens remodel the palate, rearrange the vomerine dentition, expand the maxilla, broaden the cheek, foreshorten the posterior skull table and develop specific serrated suture patterns in the dermal bones. Instead, large larvae grow a robust pterygoid sutured with a fully ossified trapezoidal vomer and a short maxilla. Small larvae are readily distinguished by tooth count, morphology and arrangement from more advanced larvae. Age‐related features, irrespective of metamorphosis, include pedicellate teeth, morphological differentiation of parasphenoid, enlargement of the orbitosphenoid, distal expansion of columella, and loss of coronoid teeth.     

Effects of head shape variation on growth, metamorphosis and survivorship in larval salamanders (Hynobius retardatus)

The effects of head shape variation on growth and metamorphosis in larval salamander (Hynobius retardatus) were examined by a laboratory experiment and a field experiment. In the laboratory experiment, each larva was fed equal amounts and was prevented from accessing others in both the solitary and group treatments, although chemical cues could be transmitted through water in the group treatment. The relative head width of larvae became larger in the group treatment during the early periods but having a large head width did not finally influence growth rate and days for metamorphosis. In the field experiment, larvae were allowed to contact each other directly in two density conditions. The enlarged relative head width was linked to high growth rate in the high-density treatment but not in the low-density treatment. The larval body size distribution in the high-density condition tended to be smaller, and there was a small proportion of large-sized individuals with a broad head width. Moreover, the small number of large larvae metamorphosed much earlier than the others. The mortality of larvae in high-density conditions was much higher than that in the low-density treatments. This would be a consequence of cannibalism in the high-density condition. From the experimental results obtained, it is argued that for the larvae of H. retardatus having a large head is an adaptive tactic that maximizes fitness, particularly in temporary ponds with an unpredictable environment and in crowded conditions.     

Morphological evolution of newly metamorphosed sea urchins--a phylogenetic and functional analysis

Newly metamorphosed juvenile sea urchins are highly variable across taxa. This contribution documents and illustrates structural, functional, and phylogenetic variation among newly metamorphosed juvenile sea urchins for 31 species from 12 ordinal or familial lineages. The classic juvenile with five primary podia, 20 interambulacral spines, and variable numbers of juvenile spines is found commonly among new metamorphs across lineages, but there are many examples, which depart from this pattern and most likely reflect adaptation to settlement habitats. At metamorphosis juveniles can have 5-25 functional podia. They can have 0-65 spines, 0 or 5 sphaeridia (balance organs). They may have zero or up to eight pedicellariae. While competent larvae that delay metamorphosis may continue to develop juvenile structures, variation across species is much greater than within species and there are strong phylogenetic and functional differences among juveniles. Heterochronic changes in expression of these structures can account for differences among taxa. Based on this sample, juvenile characters such as spines, podia, and larval pedicellariae are expressed in ways that suggest they are developmental modules whose expression can be readily changed relative to one another and to the time of metamorphosis.     

Characterization and expression of calmodulin gene during larval settlement and metamorphosis of the polychaete Hydroides elegans

The polychaete Hydroides elegans (Serpulidae, Lophotrochozoa) is a problematic marine fouling organism in most tropical and subtropical coastal environment. Competent larvae of H. elegans undergo the transition from the swimming larval stage to the sessile juvenile stage with substantial morphological, physiological, and behavior changes. This transition is often referred to as larval settlement and metamorphosis. In this study, we examined the possible involvement of calmodulin (CaM) - a multifunctional calcium metabolism regulator, in the larval settlement and metamorphosis of H. elegans. A full-length CaM cDNA was successfully cloned from H. elegans (He-CaM) and it contained an open reading frame of 450 bp, encoding 149 amino acid residues. It was highly expressed in 12h post-metamorphic juveniles, and remained high in adults. In situ hybridization conducted in competent larvae and juveniles revealed that He-CaM gene was continuously expressed in the putative growth zones, branchial rudiments, and collar region, suggesting that He-CaM might be involved in tissue differentiation and development. Our subsequent bioassay revealed that the CaM inhibitor W7 could effectively inhibit larval settlement and metamorphosis, and cause some morphological defects of unsettled larvae. In conclusion, our results revealed that CaM has important functions in the larval settlement and metamorphosis of H. elegans.     

Divergent ontogenies of trophic morphology in two closely related haplochromine cichlids

Fish develop morphological specializations in their trophic and locomotor systems as a result of varying functional demands in response to environmental pressures at different life stages. These specializations should maximize particular performances in specialists, adapting them to their trophic and habitat niches at each ontogenetic stage. Because differential growth rates of the structural components comprised in the head are likely to be linked to the diet of a fish throughout its development, we investigated the ontogenetic development of two haplochromine cichlid species belonging to different trophic guilds. We employed geometric morphometric techniques to evaluate whether starting from morphologically similar fry they diverge into phenotypes that characterize trophic guilds and locomotor types. Our examination of overall body shape shows that certain specialized morphological features are already present in fry, whereas other traits diverge through ontogeny due to differences in species‐specific allometric variation. Allometric shape variation was found to be more relevant for the biter specialist than for the sucker morphotype. Our results confirm that phenotypic changes during ontogeny can be linked to dietary and habitat shifts in these fish. Furthermore, evidence for an integrated development of trophic and locomotor specializations in morphology was observed. J. Morphol. 276:860–871, 2015. © 2015 Wiley Periodicals, Inc.     

An association of melanophores appearing at metamorphosis as vehicles of asymmetric skin color formation with pigment anomalies developed under hatchery conditions in the Japanese flounder, Paralichthys olivaceus

The mechanisms for asymmetric skin color formation in the Japanese flounder are studied with particular concerns to causes for pigment disorder (hypomelanosis) occurring under hatchery conditions. For an analysis of normal pigmentation, fish were raised with wild zooplanktons in an indoor hatchery, whilst for hypomelanosis, they were raised with Brazilian Artemia nauplii, a diet used in the hatcheries. Morphological observations, counting of melanophores, histochemical assay of DOPA-positive immature cells (melanoblasts), and radiometric estimation of tyrosinase activities in skins of developing larvae and juveniles indicate that 1) the structural plan for pigmentation in this species is bilaterally symmetric until metamorphosis, utilizing large-sized melanophores (hence larval melanophores) as main vehicles, and 2) an asymmetric coloration characteristic to metamorphosed juveniles is formed by an intensive development of smaller-sized melanophores (hence adult-type melanophores) appearing selectively in the ocular side at the later stages of metamorphosis and by an absence of it in the blind. These findings apparently indicate that 1) two types of melanophores occur in this species which differ with respect to morphological properties and developmental fate, and 2) selective differentiation of adult type melanophores in the ocular side of the body at or after metamorphosis is primarily responsible for an asymmetric coloration of its adult form. The similar assays on the fish fed with Artemia nauplii indicate that defective development of adult-type melanophores results in hypomelanosis in their ocular-sided skins, yielding a pigmentary pattern seen in the blind side of the metamorphosed juveniles with normal pigmentation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Patterns of cranial ontogeny in lacertid lizards: morphological and allometric disparity

We explored the ontogenetic dynamics of the morphological and allometric disparity in the cranium shapes of twelve lacertid lizard species. The analysed species (Darevskia praticola, Dinarolacerta mosorensis, Iberolacerta horvathi, Lacerta agilis, L. trilineata, L. viridis, Podarcis erhardii, P. melisellensis, P. muralis, P. sicula, P. taurica and Zootoca vivipara) can be classified into different ecomorphs: terrestrial lizards that inhabit vegetated habitats (habitats with lush or sparse vegetation), saxicolous and shrub‐climbing lizards. We observed that there was an overall increase in the morphological disparity (MD) during the ontogeny of the lacertid lizards. The ventral cranium, which is involved in the mechanics of jaw movement and feeding, showed higher levels of MD, an ontogenetic shift in the morphospace planes and more variable allometric patterns than more conserved dorsal crania. With respect to ecology, the allometric trajectories of the shrub‐climbing species tended to cluster together, whereas the allometric trajectories of the saxicolous species were highly dispersed. Our results indicate that the ontogenetic patterns of morphological and allometric disparity in the lacertid lizards are modified by ecology and functional constraints and that the identical mechanisms that lead to intraspecific morphological variation also produce morphological divergence at higher taxonomic levels.     

Ontogeny of sexual dimorphism and phenotypic integration in heritable morphs

In this study we investigated the developmental basis of adult phenotypes in a non-model organism, a polymorphic damselfly (Ischnura elegans) with three female colour morphs. This polymorphic species presents an ideal opportunity to study intraspecific variation in growth trajectories, morphological variation in size and shape during the course of ontogeny, and to relate these juvenile differences to the phenotypic differences of the discrete adult phenotypes; the two sexes and the three female morphs. We raised larvae of different families in individual enclosures in the laboratory, and traced morphological changes during the course of ontogeny. We used principal components analysis to examine the effects of Sex, Maternal morph, and Own morph on body size and body shape. We also investigated the larval fitness consequences of variation in size and shape by relating these factors to emergence success. Females grew faster than males and were larger as adults, and there was sexual dimorphism in body shape in both larval and adult stages. There were also significant effects of both maternal morph and own morph on growth rate and body shape in the larval stage. There were significant differences in body shape, but not body size, between the adult female morphs, indicating phenotypic integration between colour, melanin patterning, and body shape. Individuals that emerged successfully grew faster and had different body shape in the larval stage, indicating internal (non-ecological) selection on larval morphology. Overall, morphological differences between individuals at the larval stage carried over to the adult stage. Thus, selection in the larval stage can potentially result in correlated responses in adult phenotypes and vice versa.     

The evolution of ontogenetic allometric trajectories in mammalian domestication

Morphological divergence of domesticated as compared to wild forms must result from changes in the ontogenetic process. Species‐specific tests for heterochrony have rejected a single explanation of domestic forms representing juveniles of their wild relatives. Ontogenetic allometric trajectories for 12 pairs of wild and domestic mammals were examined using skull growth data for 1070 specimens, including representatives from all lineages in which domestication has occurred. A suite of tests were performed to quantify allometric disparity in wild and domestic forms and assess the extent and patterning of modification to allometric trajectories. Domestication has modified postnatal ontogenetic allometric trajectories in mammals, and has generated disparity, achieved through lengthening of trajectory slopes and alteration to slope angles. Allometric disparity was similar for domestic forms compared to their wild relatives, whereas the magnitude of dispersion along allometric vectors differed between precocial mammals and altricial mammals, underscoring the importance of life history and shared evolutionary history in patterns of ontogenetic variation. The results verify the importance of scaling in the morphological changes associated with domestication. The response to domestication for all measured trajectory parameters was variable across species, suggesting multiple pathways of change.     

Structure-function relationships in the integument of Salamandra salamandra during ontogenetic development

Morphological, cytological and transport properties of the integument of Salamandra salamandra were investigated during natural ontogenetic development, from birth to adult. Three stages were operationally defined: I, larvae, from birth to metamorphosis; II, metamorphosis (judged externally by the colour change and loss of the gills); and III, post-metamorphosis to adult. Pieces of skin were fixed at various stages for immunocytochemical examinations, and the electrical properties were investigated on parallel pieces. Distinct cellular changes take place in the skin during metamorphosis, and lectin (PNA, WGA and ConA) binding indicates profound changes in glycoprotein composition of cell membranes, following metamorphosis. Band 3 and carbonic anhydrase I (CA I) were confined to mitochondria-rich (MR)-like cells, and were detected only in the larval stage. CA II on the other hand, was detected both in MR-like and in MR cells following metamorphosis. The electrical studies show that the skin becomes more tight (transepithelial resistance increases) upon metamorphosis, followed by manifestation of amiloride-sensitive short-circuit current (I(SC)) indicating that functional Na+ uptake has been acquired. The skin of metamorphosed adults had no finite transepithelial Cl- conductance, and band 3 was not detected in its MR cells. The functional properties of MR-like and MR cells remain to be established.     

Poor Nutritional Conditions During the Early Larval Stage Reduce Risk‐Taking Activities of Fire Salamander Larvae (Salamandra salamandra)

Environmental conditions experienced early in life have been shown to significantly affect growth trajectories at later stages in many vertebrate species. Amphibians typically have a biphasic life history, with an aquatic larval phase during early development and a subsequent terrestrial adult phase after completed metamorphosis. Thus, the early conditions have an especially strong impact on the future survival and fitness of amphibians. We studied whether early nutritional conditions affect the behavioural reaction of fire salamander larvae (Salamandra salamandra) before completion of metamorphosis. Fire salamander larvae reared under rich nutritional conditions were heavier and larger, displayed better body condition overall throughout the first three month of life and metamorphosed earlier compared with larvae raised under poor nutritional conditions. Specifically, we tested whether larvae reared under these different conditions differed with respect to their risk‐taking behaviour and activity. We found no differences in the activity of larvae with respect to their experienced early food conditions. However, larvae reared under poor nutritional conditions hid significantly more often in a risk‐taking test than larvae reared under rich food conditions. This increase in shelter‐seeking behaviour might be an adaptation to reduce the risk of larval drift or an adaptation to compensate for physiological deficits in part by appropriate behavioural reactions. Our results indicate that environmental conditions, such as food availability, may lead to different behavioural strategies.     

The ontogeny of functional design: metamorphosis of feeding behaviour in the tiger salamander (Ambystoma tigrinum)

The ontogeny of feeding behaviour was studied quantitatively in the tiger salamander, Ambystoma tigrinum , to elucidate the relative importance of morphological and environmental changes on form and function. High-speed films of prey capture provided data for a frame-by-frame analysis of seven kinematic parameters of feeding behaviour. By comparing underwater feeding of larval and metamorphosed individuals, the effect of morphological changes occurring at metamorphosis on the feeding kinematic pattern was determined. By comparing metamorphosed animals feeding in the water and on land, changes in feeding kinematics associated with the environmental transition (and thus the differing physical properties of water and air) were determined. Both univariate and multivariate analyses failed to demonstrate any differences between larval and metamorphosed aquatic feedings for seven kinematic variables. However, when individuals feed on land, a radical shift in hyoid kinematics was observed. In addition, multivariate analysis showed that terrestrial feedings differed from aquatic feedings in having longer duration head movements. The lack of a kinematic difference between larval and metamorphosed individuals feeding in the water indicates that the morphological changes occurring at metamorphosis do not impose any obligatory kinematic consequences. Rather, metamorphosed Ambystoma tigrinum acquire the ability to modulate their kinematic pattern depending on the environment.     

Peculiarities of early ontogenesis of the tubenose poacher, <Emphasis Type="Italic">Pallasina barbata</Emphasis> steindachner, 1876 (Pisces,Agonidae) from Peter the Great Bay (Sea of Japan)

Based on the analysis of original material (52 specimens of Pallasina barbata larvae and juveniles), sampled in the Peter the Great Bay (Sea of Japan) from 1992 to 2006, the ontogenetic stages of this species were described for the first time. It is shown that P. barbata has a planktonic larval stage in its development. The major morphologic features that are typical for larvae and juveniles during their development were revealed. It was shown that snout length, head length and pectoral fin size are increased with growth; at the same time body height and eye diameter are decreased, and the nature of larval pigmentation is changed. The main differences between P. barbata and close species are shown. Original illustrations of larvae and juvenile are provided.     

Can differences in the structure of larval,juvenile and adult coral‐reef fish assemblages be detected at the family level?

Processes occurring at the end of the larval stage are of major importance in shaping spatial structure of fish assemblages in coral reefs. However, because of the difficulty in identifying larvae to species, many studies dealing with these stages are limited to the family level. It remains unknown if variation in the spatial structure of coral‐reef fish assemblages across life stages can be detected at such a coarse taxonomic level. Two different surveys conducted in a similar area of New Caledonia, Southwest Pacific, provided the opportunity to compare the structure of coral‐reef fish assemblages collected as pre‐settlement larvae, juveniles and adults along a coast to barrier reef gradient. Adult and juvenile fish were sampled using underwater visual counts (UVC) during the warm seasons of 2004 and 2005. Pre‐settlement larvae were sampled with light‐traps during the same seasons. In order to standardize data between sampling methods, analyses were conducted on the relative abundance (for larvae) and density (for juveniles and adults) of 21 families commonly collected with both methods. Relative abundances/densities of families were analysed as a function of life stage (larvae, juveniles or adults), large‐scale spatial location (coast, lagoon or barrier) and years (2004, 2005) using non‐parametric multidimensional scaling (nMDS) and permutational multivariate analysis of variance (permanova ). Kruskal–Wallis tests were then used to examine differences among life stages and locations for individual families. Different levels of spatial and temporal variability characterized fish assemblages from different life stages, and differences among life stages were detected at all locations and years. Differences among life stages were also significant at the level of individual families. Overall results indicate that studies conducted at the family level may efficiently reveal changes in coral‐reef fish spatial structure among successive life stages when large spatial scales are considered.     

Shape and size variation: Growth and development of the dusky grouper (Epinephelus marginatus Lowe, 1834)

Demersal fishes have complex life cycles that involve an ontogenetic change in morphology, physiology, and behavior, as their pelagic larval stages colonize benthic habitats. The developmental transition between larvae and juveniles leads to very complex processes of morphogenesis and differentiation. These processes primarily determine changes in external morphology, which is shaped by selective pressures to optimize performance for basic activities such as swimming, escape from predators, and feeding. Fishes have provided fertile grounds for ecomorphological investigations throughout ontogeny, as the role of changing morphology in inducing ontogenetic niche shifts is not always clear. In this framework, some studies have demonstrated that certain species undergo gradual changes, whereas other species experience threshold effects in their ecomorphological relationships during ontogeny. In this study, the intraspecific allometry of the dusky grouper was examined. Geometric morphometric tools were used to quantify shape changes through the development, and a modular approach was also applied to analyze the pattern of covariation between three distinct blocks (head, trunk, and tail). For this purpose, a two‐block Partial Least Square was computed. This method reveals that the pattern of changes in the overall body shape is the result of the modularized changes of these blocks. J. Morphol., 2009. © 2008 Wiley‐Liss, Inc.