First Evidence of Inclusive Sexual Selection in the Ant Cataglyphis cursor: Worker Aggressions Differentially Affect Male Access to Virgin Queens

Abstract

Sexual selection typically shapes the traits of individuals capable of reproduction. However, in social species, it may also affect the behaviour of non‐reproductive individuals if this increases their inclusive fitness. We examined the potential role of workers during mating in the polyandrous ant Cataglyphis cursor. In this species, mating takes place on the ground near the nest entrance, and workers chase away foreign males trying to mate with young queens (gynes). We investigated the effects of worker aggression on male mating attempts by placing three or four males in the presence of one foreign gyne and 20 of her nestmate workers and contrasted this with a second group of 3–4 males in the presence of another gyne without nestmate workers (n = 8 paired replicates). Workers strongly attacked males (more than 20 aggressions per minute), although this did not affect the total number of mating attempts by the 3–4 males or the skew in the number of mating attempts among these males. However, there was an interaction between worker aggression and relative male weight, as relatively heavy males attempted to mate more often than lighter males in the absence of worker whereas the reverse occurred in the presence of workers. Our study is the first to experimentally test the potential role of non‐reproductive individuals in sexual selection. It shows that workers could potentially change male mating success by disfavouring heavier males.

Social Life in Arid Environments: The Case Study of Cataglyphis Ants

“…Multiple mating by queens and males sets the stage for sexual selection. In species producing new colonies by colony fission (see Section 3.2), mating occurs near the nest entrance where workers may affect precopulatory mate choice (73,74). Moreover, sperm competition may generate intense directional selection on sperm traits that enhance fertilization success, such as sperm production and size (16).…”

Differences in Long-Chained Cuticular Hydrocarbons between Males and Gynes inCataglyphisDesert Ants

“…Another possible mechanism related to precopulatory sexual selection may involve altering acceptance threshold making males able to get closer to gynes without being harassed by workers (Helft et al 2016; Helft et al 2015). There is, indeed, evidence of males mimicking the queen’s chemical bouquet in ants, thus allowing them to escape aggression from other males (Cremer et al 2002) or from workers (Franks and Hölldobler 1987).…”

No evidence of pre-copulatory mate choice by gynes in the facultatively parthenogenetic ant Cataglyphis cursor

“…The involvement of workers in mate choice has been suggested in army ants (Franks & Hölldobler 1987), Argentine ants (in the invasive range, Sunamura et al 2011) and the facultatively parthenogenetic ant Cataglyphis cursor (Cronin et al 2011;Helft et al 2015). In the latter two species, workers are aggressive towards all foreign males who enter or come near the nest searching for a receptive gyne.…”

“…This is indeed what occurs in C. cursor. Gynes are produced by the multiply mated queen (Lenoir et al 1988;Pearcy et al 2004) and workers are highly related to both parthenogenetically produced gynes (clones of their mother, r ~ 0.5) and sexually produced gynes (r = 0.44 on average) (Doums et al 2013), and a recent study showed that worker aggression toward males affected male relative mating potential, increasing it for lighter males and decreasing it for heavier males (Helft et al 2015). The present study therefore aims at determining whether C. cursor gynes exercise pre-copulatory mate choice or not.…”

“…Simultaneously, one male was placed in another box containing a second gyne in a mesh cage, so that he could perceive her presence but could not mate (treatment without workers or W-). A second male was placed in a third box containing the third gyne, also encaged, but with the addition of 50 of the gyne's nestmate workers that could aggress the male as shown in Helft et al (2015) (male W+). After 10 minutes, the two males were moved to the mating arena containing the focal gyne and matings were observed for 10 minutes.…”