Generalizations of genetic conservation principles in islands are not always likely: a case study from a Neotropical insular cactus

Abstract

Cereus insularis (Cereeae, Cactaceae) is an insular endemic and dominant element of the vegetation of Fernando de Noronha Islands (FNI), a Neotropical archipelago 350 km from mainland Brazil. Here, we estimate the levels of genetic diversity for C. insularis and investigate its genetic relationship with the closely allied C. fernambucensis, which is widespread along the Brazilian coast. We genotyped and analysed 112 individuals for ten nuclear microsatellite markers to understand genetic connectivity between insular and mainland populations. The levels of genetic diversity for this species indicate an absence of genetic erosion. Furthermore, the expected heterozygosity in C. insularis is consistent with a long-term colonization process of FNI. We identify signatures of recent and bilateral gene flow among mainland and insular populations. We explain our results taking into consideration the biogeographic hypothesis to explain the peripatric origin of C. insularis. Overall, this is a case study suggesting that the generalizations of genetic conservation principles in oceanic islands, such as low levels of genetic diversity, are not always the case. Rather than challenge these principles, we stress that island dynamism throughout time should be an important factor in explaining levels of genetic diversity in insular species.