Genetic impacts of habitat loss on the rare Banded Ironstone Formation endemic Ricinocarpos brevis (Euphorbiaceae)

Ricinocarpos brevis (Euphorbiaceae) is a declared rare species currently known from only three Banded Ironstone Formation (BIF) ranges (Perrinvale, Johnston and Windarling Ranges) in the Yilgarn region of Western Australia. The present study assessed the potential impact of proposed mining on genetic diversity within R. brevis. Approximately 30 plants were sampled from each of 14 sites across the known distribution of R. brevis. Genetic variation and its spatial structure was assessed with 144 polymorphic AFLP markers that were generated by two independent primer pairs: M-CTG/P-AC (81 markers) and M-CTA/P-AC (63 markers). Hierarchical spatial genetic structure was assessed by an analysis of molecular variance (AMOVA), Mantel tests of association between genetic- and geographic-distance and ordination. Specific attention was given to the extent of genetic differentiation of the three populations on the Windarling Range W4 deposit, which was proposed for mining operations. Strong genetic differentiation (Φ_PT = 0.186-0.298) among the three ranges was found. Genetic differentiation of the Johnston Range populations from Windarling and Perrinvale was greater than expected under isolation by distance predictions, suggesting adaptive genetic differentiation driven by site environmental differences, reflected by differences in plant community, substrate and landscape features. In contrast, genetic differentiation among the three Windarling Range regions (W2, W3, W4) was weaker (Φ_PT = 0.055-0.096). Mean pairwise Φ_PT = 0.078 for the 10 Windarling sites, which was unchanged with the removal of the W4 populations. In addition, none of the markers scored were unique to the W4 populations. Thus, for this set of markers, the removal of plants on the Windarling Range W4 deposit had little impact on genetic diversity within R. brevis. Strong concordance in results from the independent datasets generated by the two AFLP primer pairs provides overall support for the conclusions drawn.