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The rare socially parasitic butterfly Maculinea alcon occurs in two forms, which are characteristic of hygric or xeric habitats, and which exploit different host plants and host ants. The status of these two forms has been the subject of considerable controversy. Populations of the two forms are usually spatially distinct, but at Răscruci in Romania both forms occurs syntopically. We examined the genetic differentiation between the two forms using eight microsatellite markers, using samples from a nearby hygric site as out group. Our results showed that while the two forms are strongly differentiated at Răscruci, it is the xeric form there that is most similar to the hygric form at Şardu, and Bayesian clustering algorithms suggest that these two populations have exchanged genes relatively recently. We found strong evidence for population substructuring, caused by high within-nest relatedness, not association with host ants use, indicating very limited dispersal of most ovipositing females. Our results are consistent with the results of larger scale phylogeographic studies that suggest that the two forms represent local ecotypes specialising on different host plants, each with a distinct flowering phenology, and is an example of a genetic barrier operating on a temporal scale rather than spatial
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Summary diversity indices and F-statistics for loci analyzed in Maculinea alcon
Locus name; Navg: average number of individuals per locus; A, number of alleles; AR, allelic richness adjusted for sample size using rarefaction (based on a minimum sample size of 13 individuals); HO, average observed heterozygosity; HS, Nei’s unbiased expected within-population heterozygosity; HT, Nei’s overall heterozygosity; f (FIS), Weir & Cockerham’s inbreeding coefficient; θ (FST), Weir & Cockerham’s genetic differentiation; GST': Nei's sample independent genetic differentiation, G'ST: Hedrick's standardized genetic differentiation, DEST: Jost's genetic differentiation. Values in parenthesis are standard errors; underlined values are significant after sequential Bonferroni correction; squared brackets are 95% bootstrap interval.
Comparison of the posterior probabilities of the number of clusters (K) identified by the Bayesian population assignment programs Structure, BAPS and InStruct
Each line shows the mean posterior probability for each value of K across simulations, with error bars representing the standard deviation across simulations. Also shown are the ΔK values of the posterior probabilities from Structure and InStruct using the method of Evanno, Regnaut & Goudet (2005) shown relative to the maximum value of ΔK. Peaks in the value of ΔK may represent different levels of population substructure.
Bayesian clustering of samples for selected values of K
Comparison of genetic clustering of samples into groups using the Bayesian clustering programs Structure, BAPS and InStruct based on the most likely number of clusters identified by each program (Fig. S2 and main text). Each column represents an individual, and is divided according to its probability of membership of different clusters, which are represented by different colours.
Raw data: multilocus genotypes of samples at the seven microsatellite loci used for analysis
Details of the allele sizes for each sample for each of the seven micro satellite loci used for analysis (see Table 1). Details are also given of the site and Myrmica nest from which each sample was collected.