Assisted dispersal and reproductive success in an ant species with matchmaking

Abstract

Workers of the ant Cardiocondyla elegans drop female sexuals into the nest entrance of other colonies to promote outbreeding with unrelated, wingless males. Corroborating the results from previous years, we document that carrier and carried female sexuals are typically related and that the transfer initially occurs mostly from their joint natal colonies to unrelated colonies. Female sexuals mate multiply with up to seven genetically distinguishable males. Contrary to our expectation, the colony growth rate of multiple-mated and outbred female sexuals was lower than that of inbred or single-mated females, leading to the question of why female sexuals mate multiply at all. Despite the obvious costs, multiple mating might be a way for female sexuals to "pay rent" for hibernation in an alien nest. We argue that in addition to evade inbreeding depression from regular sibling mating over many generations, assisted dispersal might also be a strategy for minimizing the risk of losing all reproductive investment when nests are flooded in winter.

Keywords: Formicidae; Hymenoptera; mating behavior; outbreeding; polyandry; population structure.

FIGURE 1

Picture of a worker carrying a winged female sexual in the ant Cardiocondyla elegans to the nest entrance of another colony (Beaucaire, Gard, France, 2020; photo by M. Vidal).

FIGURE 2

Small artificial vertical nests for the maintenance of Cardiocondyla elegans under near‐natural conditions in the laboratory. Both pictures show a plaster nest, either open (a) or closed and with a plaster basis to keep it in an upright position (b). Isolated queens were kept in these nests, and their offspring production was monitored by opening the lid and through the transparent red plastic (photo by M. Vidal).

FIGURE 3

Survival time of female sexuals of the ant Cardiocondyla elegans from Southern France that produced worker offspring in the laboratory (○) or failed to do so (￭). The symbol + indicates censored information. Unproductive female sexuals had a significantly shorter life expectancy.

FIGURE 4

Offspring production by female sexuals of the ant Cardiocondyla elegans that had access only to brothers or in addition to one to seven unrelated males. Multiple‐mated individuals appeared to produce considerably fewer offspring than inbred or outbred, single‐ or double‐mated female sexuals.