Interspecific shape divergence in Aphodiini dung beetles: the case of Amidorus obscurus and A. immaturus (Coleoptera: Sc
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ORIGINAL ARTICLE
Interspecific shape divergence in Aphodiini dung beetles: the case of Amidorus obscurus and A. immaturus (Coleoptera: Scarabaeoidea) Claudia Tocco & Angela Roggero & Antonio Rolando & Claudia Palestrini
Received: 20 December 2010 / Accepted: 22 August 2011 / Published online: 4 September 2011 # Gesellschaft für Biologische Systematik 2011
Abstract The dung beetles Amidorus obscurus and A. immaturus are nearly indistinguishable, being characterized by a marked constancy in external morphological traits and little sexual dimorphism in adults. We studied two syntopic populations from the Italian Alps by means of geometric morphometric analyses. To identify possible undetected shape differences between species, we focused on the head, pronotum and scutellum (three external traits) and the epipharynx. Results indicate that the external traits are rather similar in the two species, whereas the epipharynx is clearly different. Interspecific differences in the aedeagus were also taken into account; these are noteworthy because parameres of A. immaturus differ in shape and are at least three times longer than those of A. obscurus. If it is assumed that the diversification of the two species took place during the quaternary ice age, A. immaturus would have evolved these marked differences rather quickly, in keeping with the hypothesis of rapid genital evolution. In an ontogenetic trajectory framework, we also considered the morphology of larvae. Interspecific divergence in the shape of the epipharynx is already evident at the preimaginal stage, whereas that of the genital disc is not. Accordingly, we hypothesise that the feeding and reproductive traits of these two species diverged morphologically when they become functional. C. Tocco : A. Roggero : A. Rolando : C. Palestrini Dipartimento di Biologia Animale e dell’uomo, Via Accademia Albertina 13, 10123 Torino, Italy A. Roggero (*) Department of Biologia Animale e dell’uomo, University of Torino, 10123 Torino, Italy e-mail: [email protected]
Finally, by considering recent advances in ecological and evolutionary knowledge of dung beetles, the pattern of relative constancy in external morphology exhibited by the tribe Aphodiini, and that of great morphological diversification displayed by Onthophagini, were compared, and hypotheses about the origins of these differences discussed. Keywords Constancy in external morphology . Divergent evolution . Larval instars . Geometric morphometrics . Trait functionality
Introduction The subfamily Aphodiinae is a very speciose group (about 2000 species) that includes the dung beetle tribe Aphodiini. With about 1,000 species being described so far (Scholtz et al. 2009), this tribe is characterized by its worldwide distribution, with a focus on temperate regions. Aphodiini display a rather uniform foraging behavior, with both adults and preimaginal instars of most species being coprophagous and dung-dwelling (Dellacasa and Dellacasa 2006). The remarkable taxonomic diversity of Aphodiini shows a certain constancy in
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