Development of the nidicolous tadpoles of Eupsophus emiliopugini (Anura: Cycloramphidae) until metamorphosis,with comments on systematic relationships of the species and its endotrophic developmental mode

Vera Candioti, M.F., Nuñez, J.J. and Úbeda, C. 2011. Development of the nidicolous tadpoles of Eupsophus emiliopugini (Anura: Cycloramphidae) until metamorphosis, with comments on systematic relationships of the species and its endotrophic developmental mode. —Acta Zoologica (Stockholm) 92 : 27–45. Species of Eupsophus are unique within Alsodinae in having nidicolous tadpoles. They are characterized by traits typical of generalized exotrophic (e.g., oral disc and spiracular tube) and endotrophic larvae (e.g., scant pigmentation and large hind limbs). The larval morphology and development of E. emiliopugini, including external, buccal, and musculoskeletal features, is described herein. Like the larvae of other alsodines, these larvae have four lingual and four infralabial papillae, quadratoethmoid process, and an m. rectus cervicis with a double insertion. Among the traits exclusive to the genus are: the absence of the pseudopterygoid process and quadrato‐orbital commissure; presence of the m. subarcualis rectus I with two slips; and presence of the m. subarcualis rectus II–IV inserting on Ceratobranchial II. The development and metamorphosis of Eupsophus include some characters that develop later (e.g., degeneration of mouthparts and chondrocranium with minimum calcification), characters that develop earlier (e.g., hind‐limb appearance and jaw and suspensorium ossification), and characters that develop at the same time (e.g., most external features and cranial muscles) than in most exotrophic species. Some distinctive characters (third lower labial ridge absent, general configuration of the hyobranchial skeleton, skeletal development with retention of larval traits) resemble those of other endotrophic species, and the precocious ossification of jaws and suspensorium is shared with several direct‐developing species among recent amphibians.     

Experimental heterochrony in hydractiniid hydroids: Why mechanisms matter

As with most clonal organisms, hydractiniid hydroids display a range of morphological variation from sheet-like to runner-like forms. Life history differences correlate with these morphological traits, exhibiting patterns commonly found in studies of heterochrony. Experimental studies of two hydractiniid species show that both morphological and life history heterochronies correlate with patterns of gastrovascular circulation. Similar experimental perturbations of energy metabolism, however, have opposite heterochronic effects on the two species. Treatment with 2,4-dinitrophenol, an uncoupler of oxidative phosphorylation, produced diminished peripheral circulation and sheet-like peramorphic morphologies in the runner-like species, Podocoryne carnea. In contrast, similar manipulations of the sheet-like species, Hydractinia symbiolongicarpus, produced variable peripheral circulation and more runner-like, juvenilized morphologies. These results diverge at the level of morphological and life history pattern, but are consistent when viewed in terms of the physiology of the gastrovascular system. Interpretations of patterns of heterochrony must focus on the physiological and developmental mechanisms which mediate the expression of heterochronic traits.     

Heterochrony in Shell Sculpture Development within the Ostracode Genus Hemicythere

The evolutionary issues of taxonomic significance of the shell sculpture in Ostracoda are addressed. This is a comparative ontogenetic study of three types of lateral sculpture (fossa-mural reticulation, punctation, and foveolation), as well as flanges, ridges, and tubercles is made in different age stages and morphological variations of three ostracode species with different strengths of the expression of sculpture: Hemicythere borealis (Brady, 1868), H. villosa (Sars, 1866), and H. nana (Schornikov, 1974). It is shown that the development of each sculpture type proceeds relatively independently and represents a mosaic; developmental stages are accompanied by numerous heterochronies. This results in many parallelisms, and even the trend of the evolution of a structure can change. The pathways of morphological evolution of Hemicythere species are discussed.     

Shaping intraspecific variation: Development,ecology and the evolution of morphology and life history variation in tiger salamanders

The tiger salamander,Ambystoma tigrinum, is a geographically widespread, morphologically variable, polytipic species. It is among the most variable species of salamanders in morphology and life history with two larval morphs (typical and cannibal) and three adult morphs (metamorphosed, typical branchiate, cannibal branchiate) that vary in frequency between subspecies and between populations within subspecies. We report morphometric evidence suggesting that branchiate cannibals arose through intraspecific change in the onset or timing of development resulting in the wider head and hypertrophied tooth-bearing skull bones characteristic of this phenotype. We also quantified bilateral symmetry of gill raker counts and abnormalities, then evaluated fluctuating asymmetry as a measure of the developmental stability of each morph. There was a significant interaction between fluctuating asymmetry of developmental abnormalities in cannibals and typicals and the locality where they were collected, suggesting that relative stability of each phenotype could vary among populations. While altered timing of developmental events appears to have a role in the evolution and maintenance of morphs, novel phenotypes persist only under favorable ecological conditions. Predictability of the aquatic habitat, genetic variation, kinship, body size, intraspecific competition and predation all affect expression and survival of the morphs inA. tigrinum. This taxon provides an excellent model for understanding the diversity and complexity of developmental and ecological variables controlling the evolution and maintenance of novel phenotypes.     

Patterns of evolution among lower Jurassic crinoids

The crinoid families Isocrinidae and Pentacrinitidae are well represented in the British Lower Jurassic, allowing a detailed investigation of their evolution at this time. The pseudopelagic pentacrinitids diverged from the benthic isocrinids during the Triassic. Seirocrinus arose from Pentacrinites through hyper‐morphosis prior to the start of the Jurassic but both genera subsequently show extreme evolutionary conservatism, perhaps attributable to constraints imposed by their unusual life‐style. From a single species in the Hettangian, the benthic isocrinids diversified in the Sinemurian and Carixian. A “central lineage”;, comprising three species of Chladocrinus, evolved along a peramorphocline by “intermittent anagenesis”;, prolonged periods of evolutionary stasis punctuated by short periods of gradualistic change. Two main offshoots, Balanocrinus and Hispidocrinus gen. nov., represent shifts into new habitats. Balanocrinus arose through progenesis, with subsequent evolution along a paedomorphocline, while Hispidocrinus may have arisen through extreme peramorphosis, although its spinose brachials are an evolutionary innovation. Both genera show an apparently punctuated mode of evolution. There is some correlation between morphology and faciès, and also between the emergence of new species and times of high sea level. Benthic isocrinids appear to have been greatly affected by the early Toarcian anoxic event but the pseudopelagic pentacrinitids were not.     

Diversification rates have declined in the Malagasy herpetofauna

The evolutionary origins of Madagascar''s biodiversity remain mysterious despite the fact that relative to land area, there is no other place with consistently high levels of species richness and endemism across a range of taxonomic levels. Most efforts to explain diversification on the island have focused on geographical models of speciation, but recent studies have begun to address the island''s accumulation of species through time, although with conflicting results. Prevailing hypotheses for diversification on the island involve either constant diversification rates or scenarios where rates decline through time. Using relative-time-calibrated phylogenies for seven endemic vertebrate clades and a model-fitting framework, I find evidence that diversification rates have declined through time on Madagascar. I show that diversification rates have clearly declined throughout the history of each clade, and models invoking diversity-dependent reductions to diversification rates best explain the diversification histories for each clade. These results are consistent with the ecological theory of adaptive radiation, and, coupled with ancillary observations about ecomorphological and life-history evolution, strongly suggest that adaptive radiation was an important formative process for one of the most species-rich regions on the Earth. These results cast the Malagasy biota in a new light and provide macroevolutionary justification for conservation initiatives.     

The systematic position of Aspidytidae, the diversification of Dytiscoidea (Coleoptera, Adephaga) and the phylogenetic signal of third codon positions

Characters of the newly discovered larvae of the South African Cliff Water Beetle Aspidytes niobe were examined and integrated into a data matrix including all families of Dytiscoidea as well as Haliplidae. Fifty-three morphological characters of adults and larvae were analysed separately and combined with molecular data from six nuclear and mitochondrial genes. The phylogeny of the group is reconstructed for the study of the evolution of swimming behaviour and larval feeding habits, as well as the shift in diversification rates leading to the two most speciose lineages. The parsimony analysis of all equally weighted morphological and molecular characters combined resulted in a single well supported tree with the topology (Noteridae (Hygrobiidae ((Aspidytidae, Amphizoidae) Dytiscidae))), in agreement with the molecular data alone, but in contradiction to the morphological data, which favoured a topology in which Hygrobiidae is sister to Dytiscidae. The exclusion of third codon positions of the three protein coding genes resulted in a topology identical to that obtained with the morphological data alone, but the use of Bayesian probabilities or the amino acid sequence resulted in the same topology as that of the tree obtained with parsimony using all equally weighted characters. We concluded that interactions of third codon positions with the other data are complex, and their removal is not justified. There was a significant increase in the diversification rate at the base of the richest families (Noteridae and Dytiscidae), which could be associated with the development of simultaneous stroke and higher swimming performance, although data on the swimming behaviour of some basal groups of Noteridae are incomplete. The presence of larval mandibular sucking channels may have contributed to the diversification of Dytiscidae and the species-rich noterid genera Hydrocanthus and Canthydrus .