Ian A. W. Scott

RAPID AND REPEATED ORIGIN OF INSULAR GIGANTISM AND DWARFISM IN AUSTRALIAN TIGER SNAKES

Abstract It is a well‐known phenomenon that islands can support populations of gigantic or dwarf forms of mainland conspecifics, but the variety of explanatory hypotheses for this phenomenon have been difficult to disentangle. The highly venomous Australian tiger snakes (genus Notechis) represent a well‐known and extreme example of insular body size variation. They are of special interest because there are multiple populations of dwarfs and giants and the age of the islands and thus the age of the tiger snake populations are known from detailed sea level studies. Most are 5000–7000 years old and all are less than 10,000 years old. Here we discriminate between two competing hypotheses with a molecular phylogeography dataset comprising approximately 4800 bp of mtDNA and demonstrate that populations of island dwarfs and giants have evolved five times independently. In each case the closest relatives of the giant or dwarf populations are mainland tiger snakes, and in four of the five cases, the closest relatives are also the most geographically proximate mainland tiger snakes. Moreover, these body size shifts have evolved extremely rapidly and this is reflected in the genetic divergence between island body size variants and mainland snakes. Within south eastern Australia, where populations of island giants, populations of island dwarfs, and mainland tiger snakes all occur, the maximum genetic divergence is only 0.38%. Dwarf tiger snakes are restricted to prey items that are much smaller than the prey items of mainland tiger snakes and giant tiger snakes are restricted to seasonally available prey items that are up three times larger than the prey items of mainland tiger snakes. We support the hypotheses that these body size shifts are due to strong selection imposed by the size of available prey items, rather than shared evolutionary history, and our results are consistent with the notion that adaptive plasticity also has played an important role in body size shifts. We suggest that plasticity displayed early on in the occupation of these new islands provided the flexibility necessary as the islands available prey items became more depauperate, but once the size range of available prey items was reduced, strong natural selection followed by genetic assimilation worked to optimize snake body size. The rate of body size divergence in haldanes is similar for dwarfs (hg= 0.0010) and giants (hg= 0.0020‐ 0.0025) and is in line with other studies of rapid evolution. Our data provide strong evidence for rapid and repeated morphological divergence in the wild due to similar selective pressures acting in different directions.

Molecular determination of paternity in a natural population of the multiply mating polygynous lizard Eulamprus heatwolei

We studied the mating system of the southern water skink, Eulamprus heatwolei, during spring and summer (encompassing the breeding season) in a population in southeastern Australia. We examined potential attributes that might influence the mating system and male reproductive success including home range size, physical proximity of adults and body size, and then genotyped all mothers, offspring and potential sires. Home range overlap of both sexes was extensive, with adult females sharing the greatest amount of space with each other and adult males the least amount of space with each other. However, not all adults hold home ranges. We classified approximately one quarter of adult males as home range holders and the rest as ‘floaters’. Adult females occupy home ranges more than males, with approximately three‐quarters classified as home range holders. Home range ownership is not correlated with body size for either sex, however, male body size is positively correlated with the number of adult female home ranges that his home range overlaps and adult male home ranges are larger than those of females. We used microsatellite genotyping to assign paternities to 55 offspring from 17 litters and then compared this data with our home range and behavioural observations. This species displays extreme levels of multiple paternity given the small mean clutch size of three. Multiple paternity was confirmed in 11 (64.7%) of 17 clutches but three other clutches (for a total of 82.4%) also may display multiple paternity. A total of 30 offspring from 12 litters were assigned to 10 of the 32 genotyped adult males from our study site. Of these 10 adult males, half were home range holders. Five complete clutches and a total of 25 out of the 55 offspring could not be positively assigned to any male surveyed as part of the study and were attributed to floater males or resident males adjacent to our study site that had not been genotyped. While sample sizes are small, neither male home range ownership nor body size is significantly correlated with the number of paternities a male obtained. Our study suggests a polygynous mating system for this species.

Molecular phylogeny of viviparous Australian elapid snakes: affinities of Echiopsis atriceps (Storr, 1980) and Drysdalia coronata (Schlegel, 1837), with description of a new genus

The rare Australian venomous elapid snake ‘Echiopsis’ atriceps has been the subject of considerable taxonomic instability with the five known specimens assigned to four genera by various authorities. Phylogenetic affinities of the rare Elapognathus minor also are poorly understood and have been the subject of some disagreement. To examine the phylogenetic affinities of these two rare taxa, a molecular data set comprising 1680 base pairs of mtDNA was assembled from a representative of each of the terrestrial Australian viviparous elapid genera and two species of Drysdalia, a genus about which there also has been phylogenetic controversy. A total of 936 base pairs of 12S rRNA, 454 base pairs of 16S rRNA and 290 base pairs of cytochrome b mtDNA were sequenced for 15 species. The Asian elapid Naja naja was used as the outgroup. These mtDNA regions provided 195, 38 and 72 parsimony informative sites, respectively, for a total of 315 parsimony informative characters. Unweighted phylogenetic analyses were performed under both parsimony and neighbour-joining criteria. Parsimony analyses of the unweighted, combined data set resulted in a single fully resolved most parsimonious tree 1225 steps long. The neighbour-joining tree differed by only a single weakly supported branch. These data strongly support a sister group relationship between ‘Echiopsis’ atriceps and the Australian broadheaded snakes of the genus Hoplocephalus with a bootstrap value of 99%. Templeton tests soundly reject all previous taxonomic arrangements for this species. Our data also strongly support a sister group relationship between Elapognathus minor and Drysdalia coronata with a bootstrap value of 98%. Importantly, Drysdalia coronata and Drysdalia coronoides do not form a monophyletic group, supporting some previous studies. Based on our results, we allocate ‘Echiopsis’ atriceps to a new monotypic genus and re-describe Elapognathus to include ‘Drysdalia’ coronata.

Conservation genetics of the endangered grassland earless dragon Tympanocryptis pinguicolla (Reptilia: Agamidae) in Southeastern Australia

The grassland earless dragon, Tympanocryptis pinguicolla, islisted as endangered throughout its range. A recent taxonomic studybased on both morphological and allozyme data elevatedpinguicolla from a subspecies of T. lineata to fullspecies status, but the allozyme data showed considerabledifferentiation among pinguicolla populations. To investigatethe magnitude and nature of these differences with an independent dataset, we targeted key pinguicolla populations and sequenced anapproximately 900 base pair DNA fragment of the mitochondrial genomethat includes half of the ND4 gene and three tRNA genes. We obtainedsequence data from 21 individuals drawn from the three T.pinguicolla populations, included representatives of two otherTympanocryptis species and used an Amphibolurusspecies as an outgroup. Seven mitochondrial haplotypes were found amongthe 21 T. pinguicolla samples – two in the AustralianCapital Territory (ACT) and five in the Cooma region, Phylogeneticsignal in the data sets was extremely strong and a variety ofphylogenetic analyses of the data all resulted in the same single fullyresolved tree. There are 37 unique differences in the ND4 gene betweenthe ACT and Cooma populations. This translates into genetic differencesof between 5.76% and 6.23% between the two populations. Incomparison to studies on other reptile groups in which the same fragmentof DNA was used, the differences found between the ACT and Coomapopulations are more in line with species-level differences thandifferences within a single species and suggests that these populationsshould be considered separate taxonomic units.

Molecular phylogeography of Rosenberg's goanna (Reptilia:Varanidae: Varanus rosenbergi ) and its conservation status in New South Wales

Abstract Rosenbergs goanna, Varanus rosenbergi, is listed as ‘Vulnerable’ in New South Wales, but it is not currently listed nationally in Australia as large populations exist on Kangaroo Island in South Australia. There are several significant morphological and behavioural differences between populations in NSW and those in the rest of Australia and some researchers believe these differences may be great enough to warrant separate taxonomic status. To investigate the magnitude and nature of these differences with an independent data set, we sequenced a 867 base pair DNA fragment of the mitochondrial genome that includes half of the ND4 gene and three tRNA genes. We obtained sequence data from 30 individuals of V. rosenbergi drawn from across its range in southern Australia, and also included representatives of two other Varanus species, V. gouldii and V. varius. Thirteen mitochondrial haplotypes were found among the 30 V. rosenbergi samples. Phylogenetic signal in the data sets was strong and a variety of phylogenetic analyses of the data all resulted in the same single fully resolved tree. The differences observed between populations of V. rosenbergi are not considered great enough to support the description of new taxa, but are sufficient to clearly define five evolutionary significant units, one of which is comprised of the threatened NSW/ACT populations.