Genetic diversity and translocation in the marron, Cherax tenuimanus (Smith): implications for management and conservation

Approximately 440 base pairs (bp) of the mitochondrial 16S ribosomal ribose nucleic acid (rRNA) coding region were sequenced from 13 marron, Cherax tenuimanus (Smith), samples from six locations and samples of two additional Cherax species from Western Australia. The results indicated that, with the exception of the Margaret River, no variation was found within or between marron populations. In contrast, marron from the Margaret River were found to be polymorphic for two divergent haplotypes (2.76% divergence). These findings were consistent with allozyme data that highlight the general lack of genetic variability within and between populations of this species apart from the Margaret River stocks. The genetic polymorphisms in the Margaret River stocks contrasted with earlier studies and indicated the recent translocation and mixing of genetically differentiated stocks within this river system. The implications of these findings for the conservation and management of genetic diversity within marron are discussed.

Sexual selection and individual genetic diversity in a songbird

Here, we report for the first time, to our knowledge, a strong correlation between a measure of individual genetic diversity and song complexity, a sexually selected male trait in sedge warblers, Acrocephalus schoenobaenus. We also find that females prefer to mate with males who will maximize this diversity in individual progeny. The genetic diversity of each offspring is further increased by means of nonrandom fertilization, as we also show that the fertilizing sperm contains a haplotype more genetically distant to that of the egg than expected by chance. These findings suggest that species' mating preferences may be subject to fine tuning aimed at increasing offspring viability through increased genetic diversity. This includes external and internal mechanisms of selection, even within the ejaculate of a single male.

Genetic diversity of brown and rainbow trout in Australia

Australian rainbow and brown trout were analysed using molecular genetic techniques to determine the effect translocation has had on the existing gene pool. There was some indication of loss of diversity associated with their translocation however no differences in genetic diversity between Australian hatchery and wild populations were apparent.

Conservation of genetic diversity in British populations of the diploid endemic Coincya monensis ssp monensis (Isle of Man Cabbage): the risk of hybridisation with the tetraploid alien, Coincya monensis ssp cheiranthos

Coincya monensis is represented in the British flora by two, cytologically distinct subspecies. Coincya monensis ssp monensis is an endemic diploid with a coastal sand dune distribution that includes a number of isolated populations. Coincya monensis ssp cheiranthos is a tetraploid alien, well established in South Wales in early successional habitats. Both subspecies share similar life form traits, flowering times and pollinators. Cluster analysis and phylogenetic reconstruction based on sequences of the mitochondrial nad4 gene confirmed the distinction between alien and endemic taxa. Tetraploid populations carry more polymorphic RAPDs loci and their genetic diversity is partitioned more within than among populations. In contrast, C. monensis ssp monensis has a distinct population genetic structure. Analysis of the multilocus genetic data confirmed a structure of genetically isolated, endemic population clusters in Scotland, Arran, the Isle of Man and South Wales. Experimental hybridisation showed the two subspecies are interfertile. Multivariate analysis of RAPDs data resolved hybrids between alien and endemic clusters and hybrids contained a proportion of alien-specific polymorphic loci. Hybrids of alien maternal parentage contained the mitochondrial nad4 sequence characteristic of the alien subspecies. Since the alien subspecies can invade mobile sand dune communities from urban sites and compete for pollinators, there is a risk that alien and endemic populations will mix and introgress. Conservation of endemic genetic diversity in Britain will require protection for all C. monensis ssp monensis populations. Currently, the most disjunct endemic population in South Wales is most at risk from introgression.

High genetic diversity is not essential for successful introduction

Some introduced populations thrive and evolve despite the presumed loss of diversity at introduction. We aimed to quantify the amount of genetic diversity retained at introduction in species that have shown evidence of adaptation to their introduced environments. Samples were taken from native and introduced ranges of Arctotheca populifolia and Petrorhagia nanteuilii. Using microsatellite data, we identified the source for each introduction, estimated genetic diversity in native and introduced populations and calculated the amount of diversity retained in introduced populations. These values were compared to those from a literature review of diversity in native, confamilial populations and to estimates of genetic diversity retained at introduction. Gene diversity in the native range of both species was significantly lower than for confamilials. We found that, on average, introduced populations showing evidence of adaptation to their new environments retained 81% of the genetic diversity from the native range. Introduced populations of P. nanteuilii had higher genetic diversity than found in the native source populations, whereas introduced populations of A. populifolia retained only 14% of its native diversity in one introduction and 1% in another. Our literature review has shown that most introductions demonstrating adaptive ability have lost diversity upon introduction. The two species studied here had exceptionally low native range genetic diversity. Further, the two introductions of A. populifolia represent the largest percentage loss of genetic diversity in a species showing evidence of substantial morphological change in the introduced range. While high genetic diversity may increase the likelihood of invasion success, the species examined here adapted to their new environments with very little neutral genetic diversity. This finding suggests that even introductions founded by small numbers of individuals have the potential to become invasive.

Low genetic diversity in pygmy blue whales is due to climate-induced diversification rather than anthropogenic impacts

Unusually low genetic diversity can be a warning of an urgent need to mitigate causative anthropogenic activities. However, current low levels of genetic diversity in a population could also be due to natural historical events, including recent evolutionary divergence, or long-term persistence at a small population size. Here, we determine whether the relatively low genetic diversity of pygmy blue whales (Balaenoptera musculus brevicauda) in Australia is due to natural causes or overexploitation. We apply recently developed analytical approaches in the largest genetic dataset ever compiled to study blue whales (297 samples collected after whaling and representing lineages from Australia, Antarctica and Chile). We find that low levels of genetic diversity in Australia are due to a natural founder event from Antarctic blue whales (Balaenoptera musculus intermedia) that occurred around the Last Glacial Maximum, followed by evolutionary divergence. Historical climate change has therefore driven the evolution of blue whales into genetically, phenotypically and behaviourally distinct lineages that will likely be influenced by future climate change.

Life history influences how fire affects genetic diversity in two lizard species

'Fire mosaics' are often maintained in landscapes to promote successional diversity in vegetation with little understanding of how this will affect ecological processes in animal populations such as dispersal, social organization and re-establishment. To investigate these processes, we conducted a replicated, spatiotemporal landscape genetics study of two Australian woodland lizard species [Amphibolurus norrisi (Agamidae) and Ctenotus atlas (Scincidae)]. Agamids have a more complex social and territory structure than skinks, so fire might have a greater impact on their population structure and thus genetic diversity. Genetic diversity increased with time since fire in C. atlas and decreased with time since fire in A. norrisi. For C. atlas, this might reflect its increasing population size after fire, but we could not detect increased gene flow that would reduce the loss of genetic diversity through genetic drift. Using landscape resistance analyses, we found no evidence that postfire habitat succession or topography affected gene flow in either species and we were unable to distinguish between survival and immigration as modes of postfire re-establishment. In A. norrisi, we detected female-biased dispersal, likely reflecting its territorial social structure and polygynous mating system. The increased genetic diversity in A. norrisi in recently burnt habitat might reflect a temporary disruption of its territoriality and increased male dispersal, a hypothesis that was supported with a simulation experiment. Our results suggest that the effects of disturbance on genetic diversity will be stronger for species with territorial social organization.