Robin Lawson

Snake phylogeny: evidence from nuclear and mitochondrial genes

We constructed phylogenies of snakes from the c-mos and cytochrome b genes using conventional phylogenetic methods as well as the relatively new method of Bayesian inference. For all methods, there was excellent congruence between the c-mos and cytochrome b genes, implying a high level of support for the shared clades. Our results agree with previous studies in two important respects: first, that the scolecophidians and alethinophidians are monophyletic sister clades; and second, that the Colubroidea is a monophyletic group with the Acrochordidae as its sister clade. However, our results differ from previous studies in the finding that Loxocemus and Xenopeltis cluster with pythons. An additional noteworthy result from our data is that the genera Exiliboa and Ungaliophis, often placed with Tropidophis (and Trachyboa, not included in the present study) in the Tropidophiidae, are in reality boids.

COLOR-PATTERN VARIATION IN LAKE ERIE WATER SNAKES : THE ROLE OF GENE FLOW

In an effort to clarify the evolutionary processes influencing color‐pattern variation in Lake Erie island water snake (Nerodia sipedon) populations, rates of gene flow among island and mainland populations were estimated from patterns of allozymic variation detected using electrophoresis. Rates of gene flow were high with Nm, the number of migrants per generation, averaging 25.5 among island sites, 9.2 between the Ontario mainland and the islands, and 3.6 between the Ohio mainland and the islands. Based on estimates of current population size from mark‐recapture work and of past population size extrapolated from the extent of shoreline habitat, values of m between island and mainland populations ranged from 0.0008–0.01. Synthesis of estimates of the rate of gene flow with information on inheritance of color pattern, the strength of natural selection, and population history supports the hypothesis that color‐pattern variation in island populations results from a balance between gene flow and natural selection. However, depending on the mode of inheritance of color pattern, stochastic processes such as drift may have been important in the initial stages of differentiation between island and mainland populations.

Phylogeny of snakes (Serpentes): combining morphological and molecular data in likelihood, Bayesian and parsimony analyses

Abstract The phylogeny of living and fossil snakes is assessed using likelihood and parsimony approaches and a dataset combining 263 morphological characters with mitochondrial (2693 bp) and nuclear (1092 bp) gene sequences. The ‘no common mechanism’ (NCMr) and ‘Markovian’ (Mkv) models were employed for the morphological partition in likelihood analyses; likelihood scores in the NCMr model were more closely correlated with parsimony tree lengths. Both models accorded relatively less weight to the molecular data than did parsimony, with the effect being milder in the NCMr model. Partitioned branch and likelihood support values indicate that the mtDNA and nuclear gene partitions agree more closely with each other than with morphology. Despite differences between data partitions in phylogenetic signal, analytic models, and relative weighting, the parsimony and likelihood analyses all retrieved the following widely accepted groups: scolecophidians, alethinophidians, cylindrophiines, macrostomatans (sensu lato) and caenophidians. Anilius alone emerged as the most basal alethinophidian; the combined analyses resulted in a novel and stable position of uropeltines and cylindrophiines as the second‐most basal clade of alethinophidians. The limbed marine pachyophiids, along with Dinilysia and Wonambi, were always basal to all living snakes. Other results stable in all combined analyses include: Xenopeltis and Loxocemus were sister taxa (fide morphology) but clustered with pythonines (fide molecules), and Ungaliophis clustered with a boine‐erycine clade (fide molecules). Tropidophis remains enigmatic; it emerges as a basal alethinophidian in the parsimony analyses (fide molecules) but a derived form in the likelihood analyses (fide morphology), largely due to the different relative weighting accorded to data partitions.

A molecular approach to discerning the phylogenetic placement of the enigmatic snake Xenophidion schaeferi among the Alethinophidia

Maximum likelihood (ML) and Bayesian inference (BI) analyses of the complete nucleotide sequences of the cytochrome b gene (cytb) were used to examine the phylogenetic position of the rare snake Xenophidion schaeferi within the alethinophidian snakes. The cytochrome b sequence of this representative of the poorly known family Xenophiidae was compared with those of a large and comprehensive suite of alethinophidian taxa. The research presented here represents the first time all families of alethinophidian and caenophidian snakes have been included in a single molecular phylogenetic study. Results from ML and BI analyses suggest a possible sister taxon relationship between Xenophidion schaeferi and the Bolyeridae. Moreover, strong statistical support also indicates that Xenophiidae is a member of a clade that contains Pythonidae, Loxocemidae, Uropeltidae, Xenopeltidae and Bolyeriidae. Additionally, maximum parsimony and BI analyses of previously published morphological data revealed that these anatomical character states and potentially low taxonomic sampling produced little phylogenetic information valuable to understanding the relationship of Xenophiidae among the Alethinophidia.

Mitochondrial DNA, allozymes, morphology and historical biogeography in the Podarcis vaucheri (Lacertidae) species complex

Mitochondrial DNA analysis indicates that Podarcis vaucheri is a species complex with one clade inhabiting both north and south shores of the Strait of Gibraltar and one clade restricted to North Africa. While each clade exhibits differing morphology, allozyme analysis suggests varying degrees of reproductive contact among populations within clades. Ancestral P. vaucheri appears to have been restricted to insular areas of the Betic-Rif Massif and mainland Africa during Miocene, with major lineage differentiation occurring during Pliocene. Our analysis further confirms that Podarcis atrata warrants species status and suggests that it may be more widely distributed than previously reported.

Patterns of Population Subdivision and Gene Flow in Three Sympatric Natricine Snakes

Abstract Patterns of population subdivision and gene flow were quantified using allozymes in three sympatric species of natricine snakes from the island region of western Lake Erie. Species share similar population history (post-Pleistocene range expansion followed by subdivision into island and mainland demes) and life-history characteristics. However, species differ in anticipated rates of gene flow because of differences in body size and degree to which they use aquatic habitats. Significant population subdivision was present in all three species, and isolation by distance was evident in water snakes (Nerodia sipedon) and, to a lesser degree, in brown snakes (Storeria dekayi) but not in garter snakes (Thamnophis sirtalis). As predicted, water snakes, the largest and most aquatic of the three species, showed significantly less population structure (lower values of FST) than did the smaller and more terrestrial garter snakes and brown snakes. Furthermore, variance in locus-specific estimates of FST was highest for brown snakes, intermediate for garter snakes, and lowest for water snakes. Estimates of FST obtained in this study are similar in magnitude to those reported for other snake species that have undergone post-Pleistocene range expansion but are lower than those reported for some southern U.S. species that may have experienced longer periods of isolation.

Microevolution in Island Water Snakes

volutionary change can result from a variety of processes, including natural selection, gene flow, random genetic drift, and mutation. The potential importance of these processes became clear with the development of mathematical population genetics beginning in the early 1900s (for a historical account, see Provine 1971). Examples demonstrating the effectiveness of these processes in promoting evolutionary change have since accumulated. However, such examples often emphasize a single process, most frequently natural selection (Endler 1986); only in a few examples of microevolutionary change are the simultaneous effects of multiple processes well understood (e.g., McNeilly 1968, Riechert 1993, Ross and Keller 1995). Mode of inheritance of a trait (number of loci, degree of dominance, and epistatic and pleiotropic effects) and population history (changes in distribution and abundance) can also influence evolutionary change, but again, only in a few examples of microevolutionary change are the effects of mode of inheritance and population history well understood. The Lake Erie water snake Nerodia sipedon insularum is an example of such a rare case: Color pattern variation in

Escape to Alcatraz: evolutionary history of slender salamanders (Batrachoseps) on the islands of San Francisco Bay

BackgroundIsland populations are excellent model systems for studies of phenotypic, ecological and molecular evolution. In this study, molecular markers of mitochondrial and nuclear derivation were used to investigate the evolution, structure and origin of populations of the California slender salamander (Batrachoseps attenuatus) inhabiting the six major islands of San Francisco Bay, formed following the rising of sea level around 9,000 years ago.ResultsThere was a high degree of congruence in the results of analyses of nucleotide and allozyme data, both of which strongly support the hypothesis that, for the majority of the islands, salamanders are descended from hilltop populations that became isolated with the formation of the Bay ca. 9,000 years ago. There are two exceptions (Alcatraz and Yerba Buena) where the evidence suggests that salamander populations are wholly or in part, the result of anthropogenic introductions.Comparison of the molecular data and the interpretations drawn therefrom with an earlier morphological study of many of the same salamander populations show some of the same evolutionary trends.ConclusionIn spite of marked differences between the evolutionary rates of the two kinds of molecular markers, both indicate distinctive and similar patterns of population structure for B. attenuatus in the San Francisco Bay Area and its islands. With the two noted exceptions, it is clear that most island populations were established prior to the 9,000 years since the formation of the Bay. Results of coalescence-based analyses suggest that for most island populations the mtDNA lineages from which they were derived date from the Pleistocene.It can be said that, based on observed values of genetic diversity, the last 9,000 years of evolution on these islands have been characterized by relative stability, with the occasional extinction of some haplotypes or alleles that were formerly shared between island and mainland populations but overall maintaining high levels of variation (with the exception of Alcatraz). In contrast, there is some evidence for rapid morphological changes between populations in some islands and their closest mainland counterparts. This pattern of rapid morphological divergence (e. g., resulting from founder effects) is similar to that observed in other studies about recent colonization of island habitats.

TWO NEW SPECIES IN THE GENUS PSAMMODROMUS (REPTILIA: LACERTIDAE) FROM THE IBERIAN PENINSULA

ABSTRACT The lacertid lizard Psammodromus algirus has been considered a uniform species across its distribution area in North Africa and southwestern Europe. Coloration data and discriminant function analysis of morphological data corroborate mitochondrial DNA and allozyme data to indicate northern and southern Iberian populations represent unknown species that are described here. Additional work is needed to fully understand biogeography and variation in this species complex.

Historical biogeography, mitochondrial DNA, and allozymes of Psammodromus algirus (Lacertidae): a preliminary hypothesis

Abstract. Pairwise sequence polymorphism in mitochondrial DNA and levels of differentiation among presumptive gene loci(expressed as Nei’s D ˆ) tend to be greater between populations separated by the Strait of Gibraltar than between populationsinhabiting either Morocco or Spain. Ancestral Psammodromus algirus inhabiting Iberia and North Africa while the Strait ofGibraltar was being formed and stabilized (Miocene-Pliocene) evolved in association with physiogeographic change broughtabout by this barrier to gene exchange. Considered in units of genetic change per kilometer, mtDNA differentiation is greaterin Morocco than in Spain, and allozyme differentiation is slightly greater than, or equal to, that in Spain, suggesting that P . algirus has a longer and more complex history in Morocco than in Spain. Introduction Found virtually throughout Iberia, along theMediterranean coast of France, and acrossNorth Africa from southern Morocco to thenorthern half of Tunisia, Psammodromus al-girus is often one of the most common rep-tiles encountered (Guillaume, 1997; Schleichet al., 1996:444-447). Geographic change in-volving the formation of the Strait of Gibral-tar is fairly well understood (see Busack et al.,2005: fig. 5), but we are just beginning to un-derstand diverse effects this cataclysmic seriesof events had on amphibian and reptile popu-lations inhabiting the region. While no geneticchange is apparent in populations of the stripe-necked turtle,