Rapid shape divergences between natural and introduced populations of a horned beetle partly mirror divergences between species

Abstract

Onthophagus taurus is a polyphenic beetle in which males express alternative major (horned) and minor (hornless) morphologies largely dependent on larval nutrition. O. taurus was originally limited to a Turanic-European-Mediterranean distribution, but became introduced to several exotic regions in the late 1960s. Using geometric morphometrics, we investigate the present-day morphological shape differentiation patterns among native (Italian) and introduced (Western Australian and Eastern US) populations. We then contrast these divergences to those observed between native O. taurus and its sympatric sister species O. illyricus. Our analysis failed to find significant divergences between O. taurus populations in external morphological traits (head, pronotum) when analyses were conducted separately for each sex. However, when sexes and male morphs were analyzed together, three important differences among populations emerged. First, relative warp analyses showed that native and introduced populations diverged in certain shape components that normally distinguish major and minor male morphs. Second, comparison of covariation of body regions (head vs. pronotum) in the three populations showed that populations diverged in the nature of this covariation, suggesting that different body regions are not totally constrained to evolve in concert. Lastly, and most importantly, the analysis of genitalic shape revealed little to no divergence of female genitalia, but unexpected substantial differentiation of male genitalia among the three O. taurus populations. This suggests that genitalic shape divergence can occur extremely rapidly even in the absence of sympatry and possible reinforcement, and that the genitalia of males and females may diverge independent of one another, at least during the early stage of interpopulational divergence. Interpopulation divergences in O. taurus mirrored aspects of interspecific divergences between O. taurus and O. illyricus in some cases but not others.

Shape - but Not Size - Codivergence between Male and Female Copulatory Structures in Onthophagus Beetles

“…Several studies have also begun to investigate genital divergence within and between species of onthophagine beetles. Pizzo et al [11] found significant differences in paramere shape among recently diverged natural and exotic populations of O. taurus , and these divergences were qualitatively similar to those detected when the same species was compared to its sister species, O. illyricus . In contrast, the same study failed to detect corresponding differences in vaginal shape.…”

Interspecific shape divergence in Aphodiini dung beetles: the case of Amidorus obscurus and A. immaturus (Coleoptera: Scarabaeoidea)

“…Within this framework, the evolution of an exaggerated and complex primary sexual trait may have been an adaptation to avoid hybridization during and after the speciation event. All the above is in keeping with a tenet that assumes reproductive organs evolve quickly in insects (rapid genital evolution), and also with the results of several studies regarding the role of genital divergence in speciation (Dapporto 2010a, b;Gilligan and Wenzel 2008;House and Simmons 2003;Pretorius 2007, Mutanen et al 2007;Parzer and Moczek 2008;Pizzo et al 2008).…”

“…Discriminant function analysis was carried out on the whole data set of relative warp scores to obtain a classification matrix based on shape variation (in keeping with Janžekovič and Kryštufek 2004;Kryštufek and Janžekovič 2005;Pizzo et al 2006Pizzo et al , 2008 using SPSS v18. We used the percentage of correct classifications of cross-validation to further evaluate interspecific differences in shape (in cross-validation, each case is classified by the functions derived from all cases other than the case in question).…”

“…The pattern of relative constancy in external morphology exhibited by Aphodiini was compared with the pattern of great morphological diversification exhibited by the Onthophagini, which we also studied using geometric morphometrics Pizzo et al 2006Pizzo et al , 2008, with the main aim of identifying possible determinants of the evolution of the two divergent morphological patterns.…”

Variability in the Last Abdominal Sternum of Brontispa longissima Populations Using Outline-Based Geometric Morphometric Analysis

“…All specimens were digitized with three replicates in order to reduce the measurement error [9] and these were aligned by using a Generalized Procrustes Analysis (GPA) to superimpose the landmark configurations with least-squares estimates for translation and rotation parameters [10], thus they removed the non-shape effects of translation, rotation, and scale [11]. Each set of analysis under consideration was conducted separately for males and females.…”