I will discuss data from studies of two closely related butterfly species where the aim was to evaluate the uniqueness of marginal relict populations in relation to more central counterparts. Patterns in neutral genetic markers and values of adaptive wing traits among populations of the scarce heath species (Coenonympha hero, Linnaeus, 1761) and the pearly heath species(C. arcania, Linnaeus, 1761) from three biogeographically different regions were compared; one central (central Russia for C. hero and central Europe for C. arcania), one peripheral but connected to the main area of distribution (the Baltic states for both species and termed peripheral region in the following text) and one peripheral and isolated (Sweden for both species and termed isolated region in the following text) (Fig. 1a,b).
The Scandinavian populations of C. hero are relicts of a former more widespread distribution within the Scandinavian peninsula (Berglind 1990, 2007) and the species is therefore classified as "near threatened" in the Swedish Red Data Book (Gardenfors 2005). On a global scale C. hero is widespread, although locally threatened, with a distribution ranging from Japan in the East through central Russia to central Europe in the West. The distribution is fragmentary in Western and Northern Europe and the species is considered threatened in most countries (Eliasson 2005; Kudrna 2002; Tolman and Lewington 1998).
C. arcania has a similar distribution as C. hero with peripheral populations in the Baltic states and Scandinavia, with the difference that it is widely distributed in Europe, from the Northern Mediterranean to South-central Scandinavia and central Estonia (Keskula 1992; Kudrna 2002). In the East, it is found in Turkey, in Southern Russia and central parts of the Ural Mts. and Transcaucasia (Kudrna 2002; Tolman and Lewington 1998). Although the Swedish populations of C. arcania represent no typical relict due to their distribution being more stable in Scandinavia, they can serve as an illustrating example and a replicate within the described study frame.
Fig. 1 Distribution range (marked in light grey) of (a) the scarce heath butterfly (Coenonympha hero) and (b) the pearly heath butterfly (Coenonympha arcania) in Europe and western Asia. Dark grey circles indicate sampling sites of both species representing central (C), peripheral (P) and isolated (I) parts of their distributions
In this study design the aim was to evaluate the patterns found not only in the light of the relative geographic locations of the populations, but also on their history inferred from neutral genetic marker. I discuss results obtained from selectively neutral traits, i.e. allozymes (Besold et al. 2008; Cassel and Tammaru 2003), and traits under selection represented by traits describing wing morphology (Cassel-Lundhagen et al. 2009). The allozyme data presented here for C. arcania are based on a subset of populations included in Besold et al. (2008) to make the data sets in each region comparable.
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