Abstract
Olearia pannosa is a plant species listed as vulnerable in Australia. Two subspecies are currently recognised (O. pannosa subsp. pannosa (silver daisy) and O. pannosa subsp. cardiophylla (velvet daisy)), which have overlapping ranges but distinct leaf shape. Remnant populations face threats from habitat fragmentation and climate change. We analysed range-wide genomic data and leaf shape variation to assess population diversity and divergence and to inform conservation management strategies. We detected three distinct genetic groupings and a likely cryptic species. Samples identified as O. pannosa subsp. cardiophylla from the Flinders Ranges in South Australia were genetically distinct from all other samples and likely form a separate, range-restricted species. Remaining samples formed two genetic clusters, which aligned with leaf shape differences but not fully with current subspecies classifications. Levels of genetic diversity and inbreeding differed between the three genetic groups, suggesting each requires a separate management strategy. Additionally, we tested for associations between genetic and environmental variation and carried out habitat suitability modelling for O. pannosa subsp. pannosa populations. We found mean annual maximum temperature explained a significant proportion of genomic variance. Habitat suitability modelling identified mean summer maximum temperature, precipitation seasonality and mean annual rainfall as constraints on the distribution of O. pannosa subsp. pannosa, highlighting increasing aridity as a threat for populations located near suitability thresholds. Our results suggest maximum temperature is an important agent of selection on O. pannosa subsp. pannosa and should be considered in conservation strategies. We recommend taxonomic revision of O. pannosa and provide conservation management recommendations.
Highlights
While the BIC criterion from the Discriminant Analysis of Principal Components (DAPC) analysis (Figure A3) and CV error from the ADMIXTURE (Figure A2) both indicate that K = 5–6 is the most likely value of K, there is strong evidence of three key genetic groups within O. pannosa which have genetic barriers that cannot be explained by geographic isolation (Figure 2)
This was shown in samples from the Flinders Ranges in semi-arid South Australia identified as O. pannosa subsp. cardiophylla
To develop an appropriate conservation management plan for O. pannosa subsp. cardiophylla, there are several knowledge gaps which still need to be addressed, around the genetic divergence we observed between O. pannosa subsp. cardiophylla and the two other genetic groups, and the consequences that the high levels of substructure we found within this genetic group may have on mixing seed between localities
Summary
Populations of threatened plant species are typically small and fragmented, suffering low genetic diversity associated with increased genetic drift and elevated inbreeding rates [1,2,3,4,5]. Additional to these factors, a changing climate places increasing pressure on threatened populations. Plants can respond in one of three ways in the face of climate change: adapt to the new environment, migrate to locations with suitable conditions, or perish [6,7]. The sheer rate of climate change combined with limitations to migration and dispersal means that for many plant populations the likelihood of migrating at a suitable pace is low [13]
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