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Ecology Letters, (2008) 11: 1208–1215 doi: 10.1111/j.1461-0248.2008.01239.x LETTER Resource shifts in Malagasy dung beetles: contrasting processes revealed by dissimilar spatial genetic patterns
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Abstract Ilkka Hanski,1* Helena Wirta,1 The endemic dung beetle subtribe Helictopleurina has 65 species mostly in wet forests in Toshka Nyman1 and Pierre eastern Madagascar. There are no extant native ungulates in Madagascar, but three Rahagalala2 Helictopleurus species have shifted to the introduced cattle dung in open habitats in the 1 Department of Biological and past 1500 years. Helictopleurus neoamplicollis and Helictopleurus marsyas exhibit very limited Environmental Sciences, cytochrome oxidase subunit 1 haplotype diversity and a single haplotype is present University of Helsinki, across Madagascar, suggesting that these species shifted to cattle dung in a small region Viikinkaari 1, PO Box 65, followed by rapid range expansion. In contrast, patterns of molecular diversity in FI-00014, Helsinki, Finland 2 Helictopleurus quadripunctatus indicate a gradual diet shift across most of southern De´ partement dÕEntomologie, Faculte´ des Sciences, Universite´ Madagascar, consistent with somewhat broader diet in this species. The three cattle dÕAntananarivo, Antananarivo, dung-using Helictopleurus species have significantly greater geographical ranges than the B.P. 906, Madagascar forest-dwelling species, apparently because the shift to the currently very abundant new *Correspondence: E-mail: resource relaxed interspecific competition that hinders range expansion in the forest ilkka.hanski@helsinki.fi species.
Keywords Cattle dung, dung beetle, genetic diversity, host shift, Madagascar, range expansion, resource competition, resource shift.
Ecology Letters (2008) 11: 1208–1215
Atlantic to North America, where the European corn borer INTRODUCTION has become a serious pest. Host shift-induced range Shifts in resource use often punctuate both the ecological expansions may be common, but examples of it tend to and the evolutionary dynamics of species. Resource shifts be rather anecdotal. facilitate sympatric (Bush 1969; Harrison 1991; Schwarz Madagascar has a unique biota with an exceptionally high et al. 2005) and allopatric speciation (Huyse et al. 2005), and level of endemism due to its ancient isolation (Myers et al. are typically involved in adaptive radiations of entire species 2000; Briggs 2003; de Wit 2003). Malagasy communities lack assemblages (Schluter 2000). Resource shifts may lead to entire families and even orders of animals that are common range expansion and changes in population dynamics, as on the African mainland, but which never managed to exemplified by the European corn borer moth (Ostrinia colonize Madagascar. In mammals, there are no extant nubilalis), which has two sympatric host races in Europe, one native ungulates, and the largest Malagasy herbivores are feeding on Artemisia vulgaris and the other using maize. The primates (lemurs). This makes a big difference to dung latter race must have evolved through host shift following beetles, which we have studied. Most Malagasy dung beetles the introduction of maize to Europe 500 years ago belong to the subtribe Helictopleurina and to the tribe (Calcagno et al. 2007). The host shift has allowed the Canthonini, of which the former is endemic and started to maize-using race to greatly expand its range, even across the radiate with lemurs 37–23 Ma ago (Wirta et al. 2008). On the African continent, the majority of dung beetles occur in Reuse of this article is permitted in accordance with the grasslands using the dung of large-bodied herbivores and Creative Commons Deed, Attribution 2.5, which does not omnivores (Hanski & Cambefort 1991), but in Madagascar permit commercial exploitation. practically all native species occur in forests, where they use