Kear B.P.,Uppsala University |
Zammit M.,South Australian Museum
Geological Magazine | Year: 2014
Ichthyosaurians provide some of the most famous examples of 'live birth' in the amniote fossil record based on spectacular complete skeletons of gravid females. Such remains facilitate direct comparisons between adult and foetal life stages, and thus have significant impact on phylogenetic hypotheses that require discrete character states to be ontogenetically uncoupled. This is especially true for Cretaceous ichthyosaurian taxa, the majority of which have been established using single specimens of assumed osteological maturity. Our assessment of in utero ichthyosaurian remains from the late Albian of Australia was therefore aimed at testing ontogenetic stability amongst key traits defining the most ubiquitous Cretaceous taxon: Platypterygius. Surprisingly, almost all of the salient features were identifiable in our sample of undoubtedly immature individuals. Indeed, only the proportions of the sclerotic ring, relative ossification and fusion of various basicranial elements, development of the axial skeleton, prominence of the deltopectoral crest and dorsal trochanter, and formation (but seemingly not number) of distal articular facets on the humerus were found to vary from larger-bodied members of the same species (P. australis). Ontogenetic continuity amongst the majority of other phylogenetically pertinent skeletal structures advocates their application for cladistic analyses, and suggests that many classic characters used to differentiate Platypterygius remain diagnostic irrespective of growth stage. Copyright © Cambridge University Press 2013.
King B.,Flinders University |
Lee M.S.Y.,University of Adelaide |
Lee M.S.Y.,South Australian Museum
Systematic Biology | Year: 2015
Virtually all models for reconstructing ancestral states for discrete characters make the crucial assumption that the trait of interest evolves at a uniform rate across the entire tree. However, this assumption is unlikely to hold in many situations, particularly as ancestral state reconstructions are being performed on increasingly large phylogenies. Here, we show how failure to account for such variable evolutionary rates can cause highly anomalous (and likely incorrect) results, while three methods that accommodate rate variability yield the opposite, more plausible, and more robust reconstructions. The random local clock method, implemented in BEAST, estimates the position and magnitude of rate changes on the tree; split BiSSE estimates separate rate parameters for pre-specified clades; and the hidden rates model partitions each character state into a number of rate categories. Simulations show the inadequacy of traditional models when characters evolve with both asymmetry (different rates of change between states within a character) and heterotachy (different rates of character evolution across different clades). The importance of accounting for rate heterogeneity in ancestral state reconstruction is highlighted empirically with a new analysis of the evolution of viviparity in squamate reptiles, which reveal a predominance of forward (oviparous-viviparous) transitions and very few reversals. © 2015 © The Author(s) 2015. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved. For Permissions, please email: email@example.com.
Smales L.R.,South Australian Museum
Journal of Parasitology | Year: 2013
Eight species of Neoechinorhynchus were reported from Australian waters. Neoechinorhynchus vittiformis n. Sp. is described from Eleutheronema tetradactylum (Shaw). It can be distinguished from all its congeners by the following combination of characters: long cylindrical trunk without cuticular plaques, globular proboscis, proboscis armature with the anterior circle of hooks larger with simple roots and the middle and posterior hooks the same size and smaller, short neck, lemnisci nearly equal, almost reaching the anterior testis which is more than half the length of the posterior testis. Neoechinorhynchus (Neoechinorhynchus) bryanti n. Sp., described from Liza subviridis (Valenciennes), also with an elongated trunk, can be distinguished from its congeners by the combination of a wider anterior trunk without cuticular plaques, a relatively long conical neck, a subglobular proboscis having anterior hooks with manubria, the hooks becoming gradually smaller posteriorly, the lemnisci not reaching level of testes and the anterior testis being longer than posterior testis. Neoechinorhynchus sp. resembled Neoechinorhynchus aldrichettae Edmonds, 1971 but had a rectangular-shaped proboscis with larger anterior hooks. New host and locality records were presented for N. aldrichettae, Neoechinorhynchus (Hebesoma) agilis (Rudolphi) and Neoechinorhynchus tylosuri Yamaguti, 1939. No additional specimens of either Neoechinorhynchus ningalooensis Pichelin and Cribb, 2001 or the species inquirenda, Neoechinorhynchus magnus Southwell and Macfie, 1925, were available for study. Of the 8 putative species listed here, 5 (N. [N.] bryanti, N. magnus, N. ningalooensis, N. vittiformis, and Neoechinorhynchus sp.) are endemic to Australian waters. By comparison with the North American fauna the Australian fauna was considered impoverished. The morphological and zoogeographical similarities within the group of 8 long, slender neoechinorhynchid species found in the African, Indo Malayan, and Western Pacific Regions, including the 3 found in Australia, may reflect a degree of evolutionary affinity. © 2013 American Society of Parasitologists.
Frankham R.,Macquarie University |
Frankham R.,South Australian Museum
Heredity | Year: 2012
Levels of genetic diversity in finite populations are crucial in conservation and evolutionary biology. Genetic diversity is required for populations to evolve and its loss is related to inbreeding in random mating populations, and thus to reduced population fitness and increased extinction risk. Neutral theory is widely used to predict levels of genetic diversity. I review levels of genetic diversity in finite populations in relation to predictions of neutral theory. Positive associations between genetic diversity and population size, as predicted by neutral theory, are observed for microsatellites, allozymes, quantitative genetic variation and usually for mitochondrial DNA (mtDNA). However, there are frequently significant deviations from neutral theory owing to indirect selection at linked loci caused by balancing selection, selective sweeps and background selection. Substantially lower genetic diversity than predicted under neutrality was found for chromosomes with low recombination rates and high linkage disequilibrium (compared with normally recombining chromosomes within species and adjusted for different copy numbers and mutation rates), including W (median 100% lower) and Y (89% lower) chromosomes, dot fourth chromosomes in Drosophila (94% lower) and mtDNA (67% lower). Further, microsatellite genetic and allelic diversity were lost at 12 and 33% faster rates than expected in populations adapting to captivity, owing to widespread selective sweeps. Overall, neither neutral theory nor most versions of the genetic draft hypothesis are compatible with all empirical results. © 2012 Macmillan Publishers Limited All rights reserved.
Rabosky D.L.,University of Michigan |
Donnellan S.C.,South Australian Museum |
Donnellan S.C.,University of Adelaide |
Grundler M.,University of Michigan |
Lovette I.J.,Cornell University
Systematic Biology | Year: 2014
The correlation between species diversification and morphological evolution has long been of interest in evolutionary biology. We investigated the relationship between these processes during the radiation of 250∈+∈scincid lizards that constitute Australia's most species-rich clade of terrestrial vertebrates. We generated a time-calibrated phylogenetic tree for the group that was more than 85% complete at the species level and collected multivariate morphometric data for 183 species. We reconstructed the dynamics of species diversification and trait evolution using a Bayesian statistical framework (BAMM) that simultaneously accounts for variation in evolutionary rates through time and among lineages. We extended the BAMM model to accommodate time-dependent phenotypic evolution, and we describe several new methods for summarizing and visualizing macroevolutionary rate heterogeneity on phylogenetic trees. Two major clades (Lerista, Ctenotus;∈>∈90 spp. each) are associated with high rates of species diversification relative to the background rate across Australian sphenomorphine skinks. The Lerista clade is characterized by relatively high lability of body form and has undergone repeated instances of limb reduction, but Ctenotus is characterized by an extreme deceleration in the rate of body shape evolution. We estimate that rates of phenotypic evolution decreased by more than an order of magnitude in the common ancestor of the Ctenotus clade. These results provide evidence for a modal shift in phenotypic evolutionary dynamics and demonstrate that major axes of morphological variation can be decoupled from species diversification. More generally, the Bayesian framework described here can be used to identify and characterize complex mixtures of dynamic processes on phylogenetic trees. [Bayesian; diversification; evolvability; lizard; macroevolution, punctuated equilibrium, speciation.] © 2014 The Author(s).