Importance of dispersal routes that minimize open-ocean movement to the genetic structure of island populations.

Islands present a unique scenario in conservation biology, offering refuge yet imposing limitations on insular populations. The Kimberley region of northwestern Australia has more than 2500 islands that have recently come into focus as substantial conservation resources. It is therefore of great interest for managers to understand the driving forces of genetic structure of species within these island archipelagos. We used the ubiquitous bar-shouldered skink (Ctenotus inornatus) as a model species to represent the influence of landscape factors on genetic structure across the Kimberley islands. On 41 islands and 4 mainland locations in a remote area of Australia, we genotyped individuals across 18 nuclear (microsatellite) markers. Measures of genetic differentiation and diversity were used in two complementary analyses. We used circuit theory and Mantel tests to examine the influence of the landscape matrix on population connectivity and linear regression and model selection based on Akaike's information criterion to investigate landscape controls on genetic diversity. Genetic differentiation between islands was best predicted with circuit-theory models that accounted for the large difference in resistance to dispersal between land and ocean. In contrast, straight-line distances were unrelated to either resistance distances or genetic differentiation. Instead, connectivity was determined by island-hopping routes that allow organisms to minimize the distance of difficult ocean passages. Island populations of C. inornatus retained varying degrees of genetic diversity (NA = 1.83 - 7.39), but it was greatest on islands closer to the mainland, in terms of resistance-distance units. In contrast, genetic diversity was unrelated to island size. Our results highlight the potential for islands to contribute to both theoretical and applied conservation, provide strong evidence of the driving forces of population structure within undisturbed landscapes, and identify the islands most valuable for conservation based on their contributions to gene flow and genetic diversity.

Human migration is important in the international spread of exotic Salmonella serovars in animal and human populations.

The exposure of indigenous humans and native fauna in Australia and the Wallacea zoogeographical region of Indonesia to exotic Salmonella serovars commenced during the colonial period and has accelerated with urbanization and international travel. In this study, the distribution and prevalence of exotic Salmonella serovars are mapped to assess the extent to which introduced infections are invading native wildlife in areas of high natural biodiversity under threat from expanding human activity. The major exotic Salmonella serovars, Bovismorbificans, Derby, Javiana, Newport, Panama, Saintpaul and Typhimurium, isolated from wildlife on populated coastal islands in southern temperate areas of Western Australia, were mostly absent from reptiles and native mammals in less populated tropical areas of the state. They were also not recorded on the uninhabited Mitchell Plateau or islands of the Bonaparte Archipelago, adjacent to south-eastern Indonesia. Exotic serovars were, however, isolated in wildlife on 14/17 islands sampled in the Wallacea region of Indonesia and several islands off the west coast of Perth. Increases in international tourism, involving islands such as Bali, have resulted in the isolation of a high proportion of exotic serovar infections suggesting that densely populated island resorts in the Asian region are acting as staging posts for the interchange of Salmonella infections between tropical and temperate regions.

A GENETIC PERSPECTIVE OF MAMMALIAN VARIATION AND EVOLUTION IN THE INDONESIAN ARCHIPELAGO: BIOGEOGRAPHIC CORRELATES IN THE FRUIT BAT GENUS CYNOPTERUS.

This study investigated allozyme and morphometric variability within the genus Cynopterus, with particular emphasis on C. nusatenggara, which is endemic to Wallacea, the area encompassing the Oriental-Australian biogeographic interface. The genetic distances between Cynopterus species are small by mammalian standards and suggest that this genus has undergone a recent series of speciation events. The genetic distance between populations of C. nusatenggara is strongly correlated with both the contemporary sea-crossing distance between islands and the estimated sea crossing at the time of the last Pleistocene glacial maximum, 18,000 b.p. This observation, together with low levels of population substructure within islands as shown by F-statistics, indicates that the sea is a primary and formidable barrier to gene exchange. The genetic distance and the great-circle geographical distance between the populations of C. nusatenggara are not correlated, although a principal-coordinates analysis of genetic distance reveals relationships between the populations that are similar to their geographical arrangement. A strong negative correlation exists between the level of heterozygosity within island populations of C. nusatenggara and the minimum sea-crossing distance to the nearest large source population. This is interpreted as reflecting an isolation effect of the sea, leading to reduced heterozygosity in populations that have larger sea barriers between them and the large source islands. Independently of this, heterozygosity is negatively associated with longitude, which in turn is associated with systematic changes in the environment such as a gradual decline in rainfall from west to east. The association between heterozygosity and longitude is interpreted as reflecting an association between genetic and environmental variance and supports the niche-width theory of genetic variance. Morphometric variability did not show any of the main effects demonstrated in the genetic data. Furthermore, there was no evidence that, at the level of individuals, genetic and morphometric variability were associated.

The natural history of salmonellae in mammals of the tropical Kimberley region, Western Australia.

Screening for salmonellae was conducted on five occasions within a year on mammals from many different habitats in the Mitchell Plateau area of the tropical Kimberley Division of Western Australia. Some data were obtained from reptiles. Forty-two Salmonella serotypes, two Edwardsiella and one Arizona strain were isolated. Marsupials harbour significantly more (1.6 times) Salmonella serotypes than eutherians. Eleven Salmonella serotypes and one Arizona strain were isolated from reptiles. All Salmonella strains were common to the mammalian species. Varanid lizards showed higher prevalence of salmonellae than other reptilian families. Top carnivores (reptile and marsupial) show relatively high numbers of Salmonella serotypes and prevalence levels. Four mammalian species showed marked seasonal variation in the prevalence of salmonellae and three species in the number of serotypes isolated. Pooled mammalian community data for individual survey sites showed similar seasonal variation which reflected the pattern seen in the predominant host species on the site. Significant seasonal variation in the prevalence of salmonella was concurrent in three of the host species showing maximum prevalence in the wet season (January-summer) followed by a declining prevalence to the end of the dry season (October). Prevalence in the fourth species was also high in January, but continued to increase after the wet season (April) before decreasing as the dry season progressed (July and October). Dendrograms of association showed that the salmonella 'community' does not associate according to any systematic category of the hosts and no evidence of such communities was found using other criteria, such as site or coastal vs inland locations. No evidence was found for host or site specificity of given serotypes. Multiple serotype infections by salmonella were common, with up to three present in mammals and reptiles, and they occurred at random. When hosts in coastal habitats were compared with those in inland sites higher, lower or no difference was found in the prevalence of salmonella, depending upon which host was considered. Sites with similar mammals and vegetation sometimes showed marked differences in salmonella prevalence at a given time. Generally a given Salmonella serotype was lost from the host within congruent to 3 months. Surveys for salmonellae should be designed to include a range of species, replicated vegetation types and, especially, be repeated in several seasons. Edwardsiella tarda was isolated twice from a carnivorous marsupial.