Male genital lobe morphology affects the chance to copulate in Drosophila pachea

Abstract

Introduction Male genitalia are thought to ensure transfer of sperm through direct physical contact with female during copulation. However, little attention has been given to their pre-copulatory role with respect to sexual selection and sexual conflict. Males of the fruitfly Drosophila pachea have a pair of asymmetric external genital lobes, which are primary sexual structures and stabilize the copulatory complex of female and male genitalia. We wondered if genital lobes in D. pachea may have a role before or at the onset of copulation, before genitalia contacts are made. Results We tested this hypothesis with a D. pachea stock where males have variable lobe lengths. In 92 mate competition trials with a single female and two males, females preferentially engaged into a first copulation with males that had a longer left lobe and that displayed increased courtship vigor. In 53 additional trials with both males having partially amputated left lobes of different lengths, we observed a weaker and non-significant effect of left lobe length on copulation success. Courtship durations significantly increased with female age and when two males courted the female simultaneously, compared to trials with only one courting male. In addition, lobe length did not affect sperm transfer once copulation was established. Conclusion Left lobe length affects the chance of a male to engage into copulation. The morphology of this primary sexual trait may affect reproductive success by mediating courtship signals or by facilitating the establishment of genital contacts at the onset of copulation.

No evidence for asymmetric sperm deposition in a species with asymmetric male genitalia

“…Future studies must analyze uterus shapes with progression of sperm and the eggs. However, D. pachea is rarely observed to lay eggs after a single copulation (Pitnick, 1993; Lefèvre et al, 2021), indicating that uterus reshaping might be related to other processes.…”

“…In the laboratory, D. pachea copulation lasts for about 30 min (Lang & Orgogozo, 2012; Rhebergen et al, 2016; Acurio et al, 2019; Lefèvre et al, 2021). To further examine when during copulation sperm transfer would take place, we interrupted copulation of a single couple by vigorous shaking at various time points after copulation start and examined the presence of ejaculate about 24 h later in the female sperm storage organs (Table S2).…”

No evidence for asymmetric sperm deposition in a species with asymmetric male genitalia

“…Future studies must analyze uterus shapes with progression of sperm and the eggs. Female D. pachea are rarely observed to lay eggs after a single copulation ( Pitnick, 1993 ; Lefèvre et al, 2021 ), indicating that uterus reshaping might be related to other processes.…”

“…In the laboratory, D. pachea copulation lasts for about 30–40 min ( Pitnick, 1993 ; Lang & Orgogozo, 2012 ; Rhebergen et al, 2016 ; Acurio et al, 2019 ; Lefèvre et al, 2021 ). To further examine when sperm transfer would take place during copulation, we interrupted copulation of a single couple by vigorous shaking at various time points after copulation start and examined the presence of ejaculate about 24 h later in the female sperm storage organs ( Table S2 ).…”

“…For data analysis, file-names were replaced by a three-digit random number so that sperm presence was quantified blindly with respect to the annotated copulation duration. Ejaculate presence or absence in the spermathecae was annotated based on visual inspection according to previously published protocols ( Jefferson, 1977 ; Lefèvre et al, 2021 ).…”