Gradual evolution of male genitalia in a sibling species complex of millipedes (Diplopoda : Spirobolida : Rhinocricidae : Anadenobolus)

Abstract

Jamaican millipedes in the Anadenobolus species complex provide an unusual case study of arthropods having undergone speciation in the absence of conspicuous divergence of male genitalia. Using landmark-based morphometrics, we examined shape deformation of the male anterior copulatory device in three genetically divergent yet morphologically cryptic species. A multivariate analysis of variance and relative warp analysis of nonuniform components show that although male genitalic shape is statistically different among species, many specimens are 'misplaced' in morphological space, perhaps consistent with a condition analogous to incomplete lineage sorting. A simulation of neutral nuclear gene coalescence suggests that such incomplete sorting is expected, given the depth of mtDNA divergences observed across species. The pronounced contrast between deep molecular v. incomplete genitalic divergence is at odds with the paradigm of selection-driven rapid change in male copulatory structure during arthropod speciation. Alternatively, we suggest that male genitalic divergence is evolving neutrally or in concert with other components of the genome (pleiotropy). Although we recognise the empirical validity of rapid genitalic divergence via sexual selection or sexual conflict, such models must be empirically tested using multiple lines of evidence. Accepting the rapid and divergent hypothesis without such multiple evidence scrutiny may result in a gross underestimation of evolutionary diversity and, subsequently, the misinterpretation of processes shaping genitalic change.

Phylogeny and Classification of the Trapdoor Spider Genus Myrmekiaphila: An Integrative Approach to Evaluating Taxonomic Hypotheses

“…Bond et al [36] outlined three patterns of genitalic/molecular divergence evolution, the first one being a pattern comparable to what we see in M. coreyi in which the species' morphology has sorted ahead of the “neutral” molecular marker. We are more likely to infer SSFC-SC for M. coreyi as opposed to any of the other species given the relatively short branch lengths on which these individuals occur.…”

Hierarchical comparative analysis of genetic and genitalic geographical structure: testing patterns of male and female genital evolution in the scarab beetle Phyllophaga hirticula (Coleoptera: Scarabaeidae)

“…By contrast, two other comparative analyses did not find that genitalia were more structured than genetic markers (Bond et al. , 2003; Garnier et al.…”

“…To my knowledge, only two other studies have investigated male genitalic divergence patterns among populations in insects (Nice & Shapiro, 1999; Garnier et al. , 2005), with one additional study in the millipede species complex Anadenobolus excisus Karsch (Bond et al. , 2003).…”

Evolution of the male genitalia: morphological variation of the aedeagi in a natural population of Drosophila mediopunctata

“…In the absence of allometry, it is a size variable independent of (uncorrelated with) shape measures (Bookstein 1991;Bond et al 2003;Rohlf 2004).…”

“…There are several hypotheses for explaining the evolution of male genitalia (Eberhard 1990(Eberhard , 2004(Eberhard , 2005Lüpold et al 2004;Hosken and Stockley 2004). However, they may be grouped on three main hypotheses: lock-andkey (cited in Scudder 1971 andin Shapiro andPorter 1989;Ohno et al 2003;Sirot 2003), pleiotropy (Mayr 1963) and sexual selection (Eberhard 1990(Eberhard , 1993Rowe et al 1994;Arnqvist 1997;Arnqvist and Thornhill 1998;Bond et al 2003;Polihronakis 2006;Wenninger and Averill 2006). Arnqvist (1997) presented, in a seminal paper, some predictions to be expected for each of these hypotheses, particularly in studies dealing with a single population of a given species.…”