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Enquête Diane, Proserpine, Aristoloches









Ceci est une version archivée de Dapporto2010 à 2010-10-29 18:55:23.

DAPPORTO Leonardo, 2010


Istituto Comprensivo Materna Elementare Media Convenevole da Prato, Prato, Italy

Speciation in Mediterranean refugia and post-glacial expansion of Zerynthia polyxena (Lepidoptera, Papilionidae)
Leonardo Dapporto

Abstract


Migration of populations to and from glacial refugia is responsible for various cases of speciation and subspeciation in Europe. The pattern of distribution and the degree of diversification between lineages originated by isolation in different glacial refugia usually depends on ecological traits, especially to their dispersal ability. Zerynthia polyxena is a philopatric species, scattered in small populations and rarely colonizing mountain areas. These characteristics probably caused repeated isolation during the Quaternary and may have favoured diversification. Actually two studies, based on both morphological and genetic data, suggest the Existence of two highly distinct lineages in Europe having in Northern Italy their contact zone. In this study, I applied geometric morphometrics to male genitalia and demonstrated that (i) two morphotypes exist in Europe approximately facing on the two sides of the Po River; (ii) the two lineages probably survived glaciations in Italy and the Balkan Peninsula, respectively; then the Balkans lineage expanded to Central and Eastern Europe; (iii) no hybrid populations seem to exist in the contact area and, in one locality at least, the two lineages live in sympatry without any evidence of intermediates. These results suggest that (i) two sister
species of Zerynthia exist in Europe. Accordingly, Papilio cassandra Geyer, 1828 is reinstated, as Zerynthia cassandra stat. rev., as the species to which the Zerynthia from Italy South of the Po River belong. Male genitalia differences with Zerynthia polyxena are described.

Key words: Biogeography – butterflies – Europe – speciation – glacial refugia – colonization routes – Zerynthia cassandra – Zerynthia polyxena

Introduction


Due to its peculiar latitude and topography, Southern Europe represents a model area to study consequences of Quaternary
climatic oscillations on living organisms phylogeography (Taberlet et al. 1998; Hewitt 1999, 2000, 2004; Schmitt
2007). During glaciations, Central European climate was too cold and dry for most temperate species. Many taxa survived
cold periods at lower latitudes and altitudes in the three large peninsulas of Southern Europe: Iberia, Italy and the Balkans.
These areas were isolated from each other during glacial maxima because of the presence of mountain chains representing
extensive and insurmountable ice areas (Taberlet et al. 1998; Hewitt 1999, 2000). As a consequence, Southern European populations have been repeatedly isolated in the three peninsulas during Quaternary glacial stages. During warm periods, species tended to expand northwards to Central and Northern Europe, but sometimes mountain chains still represented important barriers. Comparative phylogeography shows that each taxon largely represents a unique case with its own contraction⁄expansion history (Taberlet et al. 1998), nevertheless some common patterns, referred to as colonization paradigms have been described (Hewitt 1999, 2000). In particular, the generalized high genetic discrepancy between Italian lineages and those from the
remaining of Europe suggests that the Alps represented the main barrier to northward post-glacial expansions (Taberlet
et al. 1998). Consequently, Italy retains many endemic lineages evolved by isolation and successively trapped by the
Alpine chain (Taberlet et al. 1998). To a lower extent, the Pyrenees were also an obstacle to the post-glacial spreading of
several Iberian populations (Hewitt 1999, 2000). In contrast, Balkan lineages did not face important barriers to their expansion and their genomes predominate in most Central European taxa (Taberlet et al. 1998; Hewitt 1999, 2000, 2004; Schmitt 2007).

In several butterfly species, glacial and postglacial isolation produced diversification among lineages belonging to different
refugia (Schmitt 2007). However, in most cases this diversification did not produce taxa differentiated at the specific level
(Porter et al. 1997; Schmitt et al. 2005). This is probably due to the relatively brief isolation periods and to the high dispersal
ability of butterflies. Actually, when different butterfly lineages met during their expansion, they formed hybrid zones (Schmitt
2007). In Europe, hybrid zones are clustered in suture zones mostly located between the Alps and the Pyrenees (Schmitt 2007).

The differing rates of colonization through geographical barriers are responsible for most of the observed distributions (Taberlet et al. 1998). Dispersal ability depends on several species traits and divergence among lineages is expected to be higher in taxa showing low mobility, strict habitat requirements and inaptitude to live at high altitudes (Schmitt et al. 2003; Dapporto and Dennis 2009). Indeed, in these cases, gene flow across mountain chains is drastically reduced in glacial periods and it might still be impossible in warmer periods. The papilionid butterfly Zerynthia polyxena (Denis and Schiffermu¨ ller, 1775) offers an opportunity to study the consequences of long-term lineage isolation in butterflies. Indeed, this species is strictly linked to micro-habitats where the larval food plant (Aristolochia spp.) grows and it is very unusual to find vagrant individuals far from such areas (Verity 1947). Furthermore, it is well know that Z. polyxena is a thermophilic species rarely found at altitudes higher than 900 m (Higgins and Riley 1983; Tolman and Lewington 1997). Finally, it has a unique annual generation flying for few weeks. All these factors suggest that Z. polyxena may have experienced long-isolation periods in its glacial refugia during the Quaternary.
Intriguingly, two papers independently suggested the existence in Europe of two highly differentiated lineages of Zerynthia. Coutsis (1989) described differences in male genitalia between specimens belonging to Sicily and Florence


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