title: Experimental reduction of intromittent organ length reduces male reproductive success in a bug.
abstract: It is now clear in many species that male and female genital evolution has been shaped by sexual selection. However, it has historically been difficult to confirm correlations between morphology and fitness, as genital traits are complex and manipulation tends to impair function significantly. In this study, we investigate the functional morphology of the elongate male intromittent organ (or processus) of the seed bug Lygaeus simulans, in two ways. We first use micro-computed tomography (micro-CT) and flash-freezing to reconstruct in high resolution the interaction between the male intromittent organ and the female internal reproductive anatomy during mating. We successfully trace the path of the male processus inside the female reproductive tract. We then confirm that male processus length influences sperm transfer by experimental ablation and show that males with shortened processi have significantly reduced post-copulatory reproductive success. Importantly, male insemination function is not affected by this manipulation per se. We thus present rare, direct experimental evidence that an internal genital trait functions to increase reproductive success and show that, with appropriate staining, micro-CT is an excellent tool for investigating the functional morphology of insect genitalia during copulation.
authors.affiliation: School of Biology, University of St Andrews, Harold Mitchell Building, St Andrews KY16 9TH, UK lrd5@st-andrews.ac.uk.
authors.forename: Liam R
authors.identifier: http://orcid.org/0000-0003-1406-0680
authors.initials: LR
authors.lastname: Dougherty
authors.affiliation: School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
authors.forename: Imran A
authors.initials: IA
authors.lastname: Rahman
authors.affiliation: School of Biology, University of St Andrews, Harold Mitchell Building, St Andrews KY16 9TH, UK.
authors.forename: Emily R
authors.initials: ER
authors.lastname: Burdfield-Steel
authors.affiliation: School of Biology, University of St Andrews, Harold Mitchell Building, St Andrews KY16 9TH, UK.
authors.forename: E V Ginny
authors.initials: EV
authors.lastname: Greenway
authors.affiliation: School of Biology, University of St Andrews, Harold Mitchell Building, St Andrews KY16 9TH, UK.
authors.forename: David M
authors.initials: DM
authors.lastname: Shuker
mesh_terms: D000818:Animals; D003307:Copulation; D005260:Female; D005836:Genitalia, Female / Q000648:ultrastructure; D005837:Genitalia, Male / Q000648:ultrastructure; D020062:Heteroptera / Q000502:physiology* / Q000648:ultrastructure*; D007314:Insemination; D008297:Male; D055114:X-Ray Microtomography
keywords: cryptic female choice; functional morphology; genital ablation; genital evolution; micro-computed tomography; post-copulatory