Functional morphology of the copulatory organs of a reed beetle and a shining leaf beetle (Coleoptera: Chrysomelidae: Donaciinae, Criocerinae) using X-ray micro-computed tomography.

Michael Schmitt,Gabriele Uhl

doi:10.3897/zookeys.547.7143

Abstract

For more than 100 years it has been known that the sclerotised median lobe of beetles harbours a membranous structure (the "internal sac" or "endophallus") which is everted during copula inside the female genital tract. In order to explore the functional role of this structure and those associated with it, we cryofixed copulating pairs of Donacia semicuprea and Lilioceris lilii and studied the relative position of the elements of the copulatory apparatus of males and females by micro-computer-tomography.We found that the everted endophallus fills the lumen of the bursa copulatrix completely. Our data suggest that in Lilioceris lilii the tip of the sclerotised distal part of the ejaculatory duct, the flagellum, is positioned exactly over the opening of the spermathecal duct inside the bursa copulatrix. The mouth of the bursa copulatrix in Donacia semicuprea is armed with a strong muscle ring, and the whole wall of the bursa is covered externally with a layer of muscle fibres. These morphological differences correspond with differences in mating behaviour: In reed beetles (Donaciinae), females seemingly can control mating to a higher degree than in lily beetles (Lilioceris spp.).

Highlights

As the primary role of copulatory organs is to secure transfer of sperm from males to females, they could, in principal, be shaped very
Lilioceris lilii: The median lobe of the aedeagus is inserted in the female abdomen, the endophallus is everted and inflated
We did not make an attempt to trace the ejaculatory duct because we focused on the relative position of male and female copulatory organs

Summary

Introduction

As the primary role of copulatory organs is to secure transfer of sperm from males to females, they could, in principal, be shaped very . Since Eberhard’s seminal book on "Sexual Selection and Animal Genitalia" (1985) zoologists have learned to interpret the morphology of genitalia in terms of individual fitness maximisation This paradigm explains why shape and function of male and female copulatory organs are normally species-specific, and it provides a framework for understanding the functional role of peculiar structural elements of the copulatory apparatus. According to Crowson, this organ consists of a median lobe – functionally a sclerotised tube, mostly bent, often termed "penis" – and attached elements (see Fig. 1). These latter elements are basically a sclerotised ring around the median lobe from which proximal apodemes and distal parameres arise. The morphology of the female copulatory organs has been largely neglected by taxonomists (an exception is, e.g., Döberl 1986)

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