Testing the hypothesis of low genetic diversity and population structure in narrow endemic species: the endangered Antirrhinum charidemi (Plantaginaceae)

Narrow endemics have historically been hypothesized to have low levels of genetic diversity. However, recent research has shown an opposite pattern in numerous plants. Antirrhinum charidemi is a narrow range endemic, critically endangered snapdragon from south-eastern Spain. The genetic diversity and its distribution are described based on eight sampling sites across its range (10 × 4 km) using plastid DNA haplotypes, amplified fragment length polymorphism (AFLP) markers, and nuclear simple sequence repeats (SSRs). Plastid diversity was high, with seven haplotypes (h = 0.58), and differentiation among populations was strong and significant (GST = 0.470). Nuclear genetic diversity was also medium to high; for SSRs, there were four to 15 alleles per locus and Ht = 0.48, and for AFLP 90% of loci were polymorphic and Ht = 0.243. The genetic structure was weak but significant (FST = 0.095 for SSRs, 0.096 for AFLP) although Bayesian analysis could not detect more than a single gene pool with any confidence. Antirrhinum charidemi therefore displays medium to high levels of genetic diversity despite its narrow distribution and endemicity. A survey of levels of genetic diversity in narrow endemic angiosperms gave congruent results and revealed a different view than the traditional hypothesis in population genetics. Indeed, narrow endemics do not necessarily harbour low levels of genetic diversity, which appears to depend strongly on multiple factors, particularly the evolutionary history of the populations