Contrasting genetic structure of rear edge and continuous range populations of a parasitic butterfly infected by Wolbachia

Abstract

BackgroundClimatic oscillations are among the long-term factors shaping the molecular features of animals and plants and it is generally supposed that the rear edges (i.e., the low-latitude limits of distribution of any given specialised species) situated closer to glacial refugia are vital long-term stores of genetic diversity. In the present study, we compared the genetic structure of several populations of an endangered and obligate myrmecophilous butterfly (Maculinea arion) from two distinct and geographically distant parts of its European distribution (i.e., Italy and Poland), which fully represent the ecological and morphological variation occurring across the continent.ResultsWe sequenced the COI mitochondrial DNA gene (the ‘barcoding gene’) and the EF-1α nuclear gene and found substantial genetic differentiation among M. arion Italian populations in both markers. Eleven mtDNA haplotypes were present in Italy. In contrast, almost no mtDNA polymorphisms was found in the Polish M. arion populations, where genetic differentiation at the nuclear gene was low to moderate. Interestingly, the within-population diversity levels in the EF-1α gene observed in Italy and in Poland were comparable. The genetic data did not support any subspecies divisions or any ecological specialisations. All of the populations studied were infected with a single strain of Wolbachia and our screening suggested 100% prevalence of the bacterium.ConclusionsDifferences in the genetic structure of M. arion observed in Italy and in Poland may be explained by the rear edge theory. Although we were not able to pinpoint any specific evolutionarily significant units, we suggest that the Italian peninsula should be considered as a region of special conservation concern and one that is important for maintaining the genetic diversity of M. arion in Europe. The observed pattern of mtDNA differentiation among the populations could not be explained by an endosymbiotic infection.

Controversial patterns of Wolbachia infestation in the social parasitic Maculinea butterflies (Lepidoptera: Lycaenidae)

“…However, mitochondrial haplotype diversity varies according to geographical regions in Italy. Generally, Italian populations share variable mitochondrial haplotypes apart from some Northern and Central Italian populations which have reduced diversity (Patricelli et al 2013). In both species, the nuclear elongation factor 1α characterised by low substitution rate showed higher variability than the mitochondrial sequences whose evolutionary speed is commonly known to be high.…”

“…Reduced mitochondrial diversity refers to Wolbachia-induced selective sweeps in M. alcon ([Denis & Schiffermüller], 1775) and M. arion (Linnaeus, 1758) (Bereczki et al 2014;Patricelli et al 2013;Sielezniew et al 2012). In addition, the possibility of CI also arises in M. arion.…”

“…Wolbachia are also present in the social parasitic Maculinea butterflies (Sielezniew et al 2012;Patricelli et al 2013;Ritter et al 2013;Bereczki et al 2014). Reduced mitochondrial diversity refers to Wolbachia-induced selective sweeps in M. alcon ([Denis & Schiffermüller], 1775) and M. arion (Linnaeus, 1758) (Bereczki et al 2014;Patricelli et al 2013;Sielezniew et al 2012).…”

Forest vegetation in western Romania in relation to climate variables: Does community composition reflect modelled tree species distribution?

“…It is assumed that such spatially isolated populations persisted periods of climate change in the past, and are thus particularly important for the conservation of biodiversity in the future (Rose et al 2009, Hampe & Jump 2011. The rear edge populations situated at or near glacial refugia are supposed to be vital long-term pools of genetic diversity (Hampe & Petit 2005, Patricelli et al 2013) and can be regarded as references for the estimation of species and community susceptibility to climate change (Mellert et al 2016). Favoured presumably by increased CO 2 -concentration, continued nitrogen deposition and a longer vegetation period, rear edge beech populations in Albania and Macedonia showed a recent growth increase despite increasing temperature and drought (Tegel et al 2014).…”

Population structure of the expansive wasp spider (Argiope bruennichi) at the edge of its range

“…Analyses of genetic structure indicated similarity between the Polish and Italian populations, and while the Alps are known to have acted as an initial barrier to the possible northward expansion of Mediterranean genetic pools (Bilton et al 1998;Hewitt 1999), the Appenine Peninsula might be a possible source area of invertebrate populations in Central and Northern Europe (Patricelli et al 2013). This observation supports previous results obtained by Krehenwinkel & Tautz (2013), suggesting that northern territories of Europe were colonized from southern localities rather than from eastern areas.…”