Genetic variability in the social bee Lasioglossum marginatum and a cryptic undescribed sibling species, as detected by DNA fingerprinting and allozyme electrophoresis

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Abstract
DNA fingerprints (DNAfp) were obtained for three widely separated samples of bee related to Lasioglossum marginatum using the M13 sequence as a probe. Bee samples were obtained from France (three localities separated by at most 20 km), Greece and India. All European populations exhibited almost identical profiles with similarity indices (S) of over 98% within a French sample, 94% among Greek bees and 90% between Greek and French bees. The DNAfp profiles of Indian bees showed more polymorphism (intrapopulation S= 77%) and were quite dissimilar to the European samples (S= 55% and 56% to French and Greek samples, respectively). The similarity between populations separated by over 2000 km is higher than among unrelated individuals within a population in two other bee species and the tsetse fly. Data from allozyme electrophoresis shows parallel variation to that obtained with DNAfp and the genetic differences between Indian and European samples are strikingly large (Indian and European populations shared no alleles at 14 out of 47 loci surveyed) such that no more than one species must be involved. Nonetheless, the samples are indistinguishable morphologically. We argue that chronically low effective population size in these species results in low levels of genetic variability and that this, combined with a genetic bottleneck during the speciation event and colonization of Europe, may have resulted in both the extremely low levels of DNAfp variation in European bees and the large number of fixed allelic differences between European and Indian samples. We conclude that DNAfp may be particularly useful as a tool to study population level phenomena in organisms with only moderate levels of DNAfp variability and that the Hymenoptera may be particularly appropriate model systems for such research.