Unveiling a hotspot of genetic diversity in southern Italy for the endangered Hermann's tortoise Testudo hermanni

Abstract

Background: Hotspots of intraspecific genetic diversity represent invaluable resources for species to cope with environmental changes, and their identification is increasingly recognized as a major goal of conservation ecology research. However, even for iconic and endangered species, conservation strategies are often planned without thorough information on the geographic patterns of genetic variation. Here, we investigated the spatial patterns of genetic variation of the endangered Hermann's tortoise Testudo hermanni in the Italian Peninsula by genotyping 174 individuals at 7 microsatellite loci, with the aim to contribute to planning effective conservation strategies.

Results: Ordination-based and Bayesian clustering analyses consistently identified three main genetic clusters, one spread in the central and northern part of the peninsula, and two restricted to southern Italy and Sicily, respectively. The highest levels of genetic diversity were found in populations of the southern cluster and, in particular, at the northern edges of its distribution (He > 0.6, Ar > 2.8 ), that correspond to areas of putative secondary contact and admixture between distinct lineages. Our results clearly identify a hotspot of genetic diversity for the Hermann's tortoise in southern Italy.

Conclusion: We inferred the evolutionary history and the spatial patterns of genetic variation of the Hermann's tortoise in the Italian Peninsula. We identified three main genetic clusters along the peninsula and a hotspot of intraspecific diversity in southern Italy. Our results underline the urgent need for conservation actions to warrant the long-term persistence of viable tortoise populations in this area. Furthrmore, these data add further evidence to the role of southern Italy as a biodiversity hotspot for temperate fauna, claiming for higher consideration of this area in large scale conservation programs.

Keywords: Biodiversity hotspots; Conservation genetics; Genetic structure; Italian Peninsula; Phylogeography; Threatened species.

Fig. 1

Results from the spatial principal component analysis (sPCA) on the Hermann’s tortoise Testudo hermanni in the Italian Peninsula. (a-b) projection of the individual scores from the first two principal components on a distribution map; the color of the boxes (black or white) corresponds to the sign of the score and the area is proportional to the absolute value of the score; therefore large circles indicate large differentiation with smaller circles indicating smaller differences; (c) lagged scores of the first two axes together in a single colour plot, so that individuals that are closely related in the multivariate space are more similar in colour; (d) barplot showing eigenvalues, positive eigenvalues (red, on the left) correspond to global structures, while negative eigenvalues (blues, on the right) indicate local patterns

Fig. 2

Genetic structure of Italian populations of Testudo hermanni at 7 microsatellite loci estimated using TESS. The bar plot on the left shows the admixture proportions of each individual for the three genetic clusters recovered; the pie diagrams on the maps show the frequency distributions of each cluster among the populations; circle size is proportional to the sample size; the line chart shows the mean values of the DIC statistics (averaged over 100 runs) for the number of genetic clusters (K) ranging from 2 to 9. The map was drawn using the software Canvas 11 (ACD Systems of America, Inc.)

Fig. 3

Principal Component Analysis (PCA) on individual genotypes for 7 microsatellites loci. Dots represent individuals, lines connect individuals from a same group. Colors represent the different clusters identified by the TESS analysis (cf. Figure 2)