Rise and fall of island butterfly diversity: Understanding genetic differentiation and extinction in a highly diverse archipelago

Abstract

AimWe describe fine‐scale diversity patterns of the entire butterfly fauna occurring on the Tuscan Archipelago. By assessing the traits associated with population diversification, haplotype uniqueness and extinction, we aim to identify the factors determining the origin and maintenance of genetic diversity, and population vulnerability to environmental changes.LocationTuscan Archipelago, Sardinia, Tuscany (Italy) and Corsica (France).MethodsWe built a mtDNA dataset (1,303 COI sequences) for the 52 butterfly species reported in the Archipelago, also including specimens from neighbouring areas, and compiled data on 12 species traits and on the apparent extinction of species from the main islands. We calculated indices that measure genetic differentiation, and using phylogenetic regressions we evaluated the relationships between these indices and species traits. Finally, we inferred which traits are associated with disappearance of species on individual islands using phylogenetic regression.ResultsThe overall spatial pattern of genetic diversity corresponded with the proximity of the areas, but strong contrasts were also identified between geographically close areas. Together with the island endemics, several common and widespread species had a high genetic diversification among islands and mainland. Phylogenetic regressions revealed that smaller‐sized, more specialized species, with a preference for drier regions, displayed greater genetic structure and/or haplotype uniqueness. Species that disappeared from islands had a higher population diversification. Capraia has experienced a notable loss of diversity, which significantly affected species with shorter flight periods.Main conclusionsTuscan island butterflies are characterized by strong genetic contrasts and species differ in their contribution to the overall genetic diversity. By ranking the species for their contribution to genetic diversity and identifying the traits linked to the emergence and maintenance of diversity, we have developed a valuable tool for prioritizing populations as targets for monitoring and conservation action. The dataset constructed also represents a valuable resource for testing biogeographical hypotheses.

Integrating three comprehensive data sets shows that mitochondrial DNA variation is linked to species traits and paleogeographic events in European butterflies

“…The fifth cluster separated the Alps and Pyrenees from the Italian peninsula, with Corsica and circum‐Italian islands resembling more the Pyrenees‐Alps, reflecting a recurrent phylogeographic pattern found in several butterfly species (Dapporto et al, ; Figure e). The sixth cluster produced the expected division between the Alps and Pyrenees with Corsica, Elba and Giglio resembling more the Pyrenees than the spatially closer Alps (Dapporto et al, ; Figure f).…”

“…We also included a series of variables describing (4) the climatic preference and tolerance (physiological trait) according to Schweiger, Harpke, Wiemers, and Settele (). Although these climatic niche indices cannot be considered as functional traits (Moretti et al, ), they are widely used as proxies for the traits responsible for ecophysiological responses to climate (Dapporto et al, ; Devictor et al, ). The variables we included were: (vii) mean annual temperature, (viii) mean annual precipitation, (ix) standard deviation of mean temperature, (x) standard deviation of mean precipitation, (xi) upper 95% confidence limit of temperature mean, and (xii) lower 95% confidence limit of precipitation mean.…”

“…Butterfly traits are usually highly intercorrelated and can be reduced to factors by using ordination methods (Dapporto et al, ; Middleton‐Welling, Wade, Dennis, Dapporto, & Shreeve, ). Principal Component Analysis was applied to life history and physiology traits using the R function “rda” and the components with eigenvalues higher than one have been retained as variables.…”

“…While several studies searching for fingerprints of effective population size and other species traits on DNA polymorphism have been carried out through interspecific comparisons (Allio et al, ; Bazin et al, ; Fujisawa et al, ; Leffler et al, ; Nabholz et al, ; Romiguier et al, ), there are very few comparative phylogeographic studies which adopted a spatially explicit framework (Burney & Brumfield, ; Dapporto et al, ; Moritz et al, ), facilitating understanding inter‐population patterns of genetic diversity and its determinants. The primary challenge for phylogeography is to adequately map current genetic diversity to allow the testing hypotheses that explain such variation.…”

“…Currently, public DNA barcode libraries contain millions of sequences (Kress, García‐Robledo, Uriarte, & Erickson, ; Ratnasingham & Hebert, ) and now allow unknown samples to be identified, often to species level. The accumulation of DNA barcode data for an increasing number of groups, and in particular European butterflies, in public repositories (GenBank, BOLD) generated by widescale research surveys (Dapporto et al, ; Dincă et al, ; Hausmann et al, ; Huemer, Mutanen, Sefc, & Hebert, ) is now extensive.…”