Abstract
We test the morphology based hypothesis that the Western Palaearctic spurge hawkmoths represent two species, the Eurasian H. euphorbiae and Afro-Macaronesian H. tithymali. It has been suggested that these species merged into several hybrid swarm populations, although a mitochondrial phylogeography revealed substructure with local differentiation. We analysed a three-gene mt-dataset (889 individuals) and 12 microsatellite loci (892 individuals). Microsatellite analyses revealed an overall weak differentiation and corroborated the superordinate division into two clusters. The data indicate that the populations studied belong to only one species according to the biological species concept, refuting the opening hypothesis. A future taxonomic revision appears necessary to reflect the division into two subgroups. Ancestral mitochondrial polymorphisms are retained in H. euphorbiae, indicating gene flow within a broad ‘glacial refuge belt’ and ongoing postglacial gene flow. Diverse patterns of extensive mito-nuclear discordance in the Mediterranean and the Middle East presumably evolved by more recent processes. This discordance indicates introgression of H. tithymali-related mitochondrial haplogroups, accompanied (to a lesser degree) by nuclear alleles, into Italian and Aegean H. euphorbiae populations as recently as the late Holocene. The complex mosaic of divergence and reintegration is assumed to have been influenced by locally differing environmental barriers to gene flow.
Highlights
The discipline of phylogeography has substantially advanced our understanding of the formation of geographically structured diversity within and among closely related species and enabled intriguing insights into the origin of species[1,2]
A specimen each from Pantelleria (*PAN) and northern Tunisia (*TUN), both showing the local population’s morphology, were found to carry a haplotype of the distinct Sardo-Corso-Balearic endemic H. dahlii
‘robertsi’ haplogroup is restricted to Iran, Iranian H. robertsi (IRA), where it is mixed with ‘euphorbiae’ and ‘enigmatica’ (Fig. 3a) in the species H. robertsi
Summary
The discipline of phylogeography has substantially advanced our understanding of the formation of geographically structured diversity within and among closely related species and enabled intriguing insights into the origin of species[1,2]. Geographic distributions of larval and adult colour pattern morphotypes[17,20] (Fig. 1; for illustrations see Danner et al.21), as well as initial molecular studies based mainly on mitochondrial genes[14,15,16,18], led several authors (e.g. Hundsdoerfer et al.[14,15,16,18,20], Pittaway17) to hypothesise that the Eurasian H. euphorbiae and the Arab-Afro-Macaronesian H. tithymali hybridise in the Mediterranean They readily hybridise in captivity without any evidence for reduced hybrid fitness, i.e. postzygotic isolation (see summary in Hundsdoerfer et al.[14]). ‘tithymali’-related haplogroups, ‘italica’ and ‘cretica’, predominate in southern Italy (corresponding to populations *CIT, *SIT, *SIC in this study) and southern Aegean Islands (*CRE) suggesting these areas represent glacial refugia of distinct taxa rather than hybrid zones
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