Raw Data - Article Plasticity in sex roles and female competition in Neotropical dung roller beetles

Description

In dung roller beetles, the encounter of sexes occurs at the food source; males are commonly reported cutting, forming balls and attracting females. Intrasexual competition has been particularly associated with fights for mate acquisition among males, while females heavily invest in parental care. Here, we test the hypothesis that females have high motivation to compete for balls and mates due to the striking relevance of gaining fertilizations before nesting. This competition is expected to be more intense when the operational sex ratio is biased, affecting behaviors related to ball acquisition (ball production and fights for ball possession) and access to mates (male-female pair formation, courtship and mating). We used the Neotropical dung roller beetle Canthon bispinus and exposed males and females to two experimental groups differing in the operational sex ratio: Female and Male Bias group. We examined the proportion of successful trials for females and males. We found that males were very active in food search in both groups, while fighting with each other in the Male Bias group. In contrast, females became highly competitive, actively engaging in ball rolling and fights in the Female Bias group. Our findings revealed an elevated competition for mates at the food source and that sexual selection may also operate on females in dung roller beetles.

Steps to reproduce

We created two experimental groups differing in the operational sex ratio: Female Bias group that included a male with three females and Male Bias group, which included a female with two males. Because we have limited sample size, females and males were randomly and repeatedly exposed in both groups, and individual repeated measurement effects were controlled in the statistical analyses. We observed individuals’ interactions during 4h, registering those behaviors related to competition for food and mates. We annotated the occurrence of male-female pair formation, this is, when a male and a female interacted producing and/or rolling a ball and the behaviors occurring before and after this event. In each trial, we recorded which sex arrived first to the food and the time taken to arrive; the occurrence of ball production either by females or males separately, as well as when they both encountered at the food source and produced it together. Because courtship and mating did not occur during the first 4h of trials, we developed a second experimental design. This included the 4h direct observation with the same two groups, while afterwards individuals remained in the experimental arena for three days. For this set up, we video recorded each experimental cage with network cameras (Hikvision Model DS-2CD2022WD-I) and observed the videos afterwards, analyzing ball occurrence, as well as the occurrence and duration of courtship (the male vibrates his antennae and body over the female) and mating (aedeagus organ intromission). We performed statistical analyses using R Version 2023.12.1 (R Core Team, 2023). We analyzed the data using Generalized Linear Mixed Models (GLMMs), incorporating individual ID (number of female and male) as a random effect and we performed Generalized Linear Models (GLMs) for examining variables related to courtship and mating.

Institutions

• Universidad de la Republica Uruguay

  Montevideo, Montevideo

Categories

Funders

• Programa de Desarrollo de las Ciencias Básicas

  Montevideo Department, Uruguay

  Grant ID: Caldeyro-Barcia National Science Award
• Agencia Nacional de Investigación e Innovación

  Montevideo Department, Uruguay

  Grant ID: SNI

Licence