Contrasting Influences of Geographic Range and Distribution of Populations on Patterns of Genetic Diversity in Two Sympatric Pilbara Acacias

Abstract

The influence of geographic range on species persistence has long been of interest and there is a need for a better understanding of the genetic consequences for species with restricted distributions, particularly with the increasing rate of global species extinctions. However, the genetic effects of restricted range are often confounded by the impacts of population distribution. We compared chloroplast and nuclear genetic diversity and differentiation in two acacias, the restricted, patchily distributed Acacia atkinsiana and the widespread, semi-continuously distributed A. ancistrocarpa. Lower intra-population diversity and higher differentiation between populations were seen in A. atkinsiana compared to its widespread congener, A. ancistrocarpa. There was little evidence of geographical influences on population genetic structure in A. ancistrocarpa whereas A. atkinsiana exhibited nuclear genetic structure with isolation by distance, differentiation of near-coastal populations from those in the ranges, and differentiation of peripheral populations from those in the centre of the distribution. These results are consistent with expectations of the effect of geographic range and population distribution on genetic diversity, but indicate that distribution of populations rather than geographic range has influenced the observed genetic structure. The contrasting patterns observed here demonstrate that conservation approaches for species management and ecological restoration need to consider the distribution of populations in geographically restricted species.

Refining expectations for environmental characteristics of refugia: two ranges of differing elevation and topographical complexity are mesic refugia in an arid landscape

“…This lack of genetic structure is consistent with results of studies of other Pilbara plants where little genetic structure has been found, e.g. E. camaldulensis (Butcher et al., ), A. ancistrocarpa and A. atkinsiana (Levy et al., ). The lack of structure associated with substrate or vegetation association is in contrast to the high level of association found in phylogenetic analysis of a number of reptile and invertebrate groups (see Pepper et al., ) and habitat specificity observed in taxa in the T basedowii species complex (Anderson et al., ).…”

“…() found that Pilbara populations of Callitris glaucophylla that are confined to the Hamersley Range were genetically distinct from non‐Pilbara populations providing evidence of confinement to microrefugia during the last glacial period. The widespread Acacia ancistrocarpa did not show a genetic signature of refugia in the Hamersley Range, but populations in the Range had greater genetic connectivity consistent with historical persistence and large effective population size (Levy et al., ). In contrast, an analysis of E. camaldulensis across Australia found limited diversity in Pilbara populations (Butcher, McDonald, & Bell, ).…”

Human footprint differentially impacts genetic connectivity of four wide-ranging mammals in a fragmented landscape

“…This has been demonstrated in a few recent studies on plants and birds. Two comparative studies on plants find that semi-continuously or continuously distributed populations have lower genetic differentiation than patchily distributed populations (Levy et al, 2016; Llorens et al, 2017). Robin et al (2015) studied an entire community of montane birds of the Western Ghats in India and found, with a few exceptions, highest genetic differentiation in montane-restricted species while the widespread species showed no genetic differentiation.…”

Human footprint differentially impacts genetic connectivity of four wide‐ranging mammals in a fragmented landscape

“…This has been demonstrated in a few recent studies on plants and birds. Two comparative studies on plants find that semi‐continuously or continuously distributed populations have lower genetic differentiation than patchily distributed populations (Levy et al, ; Llorens et al, ). Robin, Vishnudas, Gupta, and Ramakrishnan () studied an entire community of montane birds of the Western Ghats in India and found, with a few exceptions, highest genetic differentiation in montane‐restricted species, while the widespread species showed no genetic differentiation.…”