High levels of population differentiation in two New Caledonian Scaevola species (Goodeniaceae) and its implications for conservation prioritisation and restoration

Abstract

Population genetic structure was studied in two Scaevola (Goodeniaceae) species across their ranges in New Caledonia. Scaevola montana is locally common and distributed primarily on ultramafic substrates, and is used for ecological restoration of mining sites. Scaevola coccinea is a narrow endemic restricted to ultramafic soils in a single valley, where intensive mining activity occurs. We compared levels of diversity and differentiation in the two species using nuclear microsatellites, so as to understand the spatial scale at which populations become isolated. We also measured environmental distances among sites as a crude proxy to estimate where adaptive differentiation may occur. Populations of S. montana were sampled over a total distance of ~500 km. In contrast, the total range of S. coccinea is 12 × 6 km. Greater allelic diversity and gene diversity was detected within populations of S. montana than S. coccinea. Both species show high levels of population differentiation (S. montana FʹST = 0.437; S. coccinea FʹST = 0.54). The marked population structure in S. coccinea despite the close proximity of the sampled populations is associated with its pollination by territorial birds and no observed seed-dispersal agents, compared with the greater vagility of insect pollination and bird dispersal of S. montana. In S. coccinea, given the high levels of differentiation, we highlight the importance of each individual population for the conservation of intra-specific biodiversity in this species. In S. montana, we used a combination of the genetic data and environmental characteristics of each of the sample sites to outline general guidelines on seed sources for restoration programs.