Flexible mate choice when mates are rare and time is short

Abstract

Female mate choice is much more dynamic than we once thought. Mating decisions depend on both intrinsic and extrinsic factors, and these two may interact with one another. In this study, we investigate how responses to the social mating environment (extrinsic) change as individuals age (intrinsic). We first conducted a field survey to examine the extent of natural variation in mate availability in a population of threespine sticklebacks. We then manipulated the sex ratio in the laboratory to determine the impact of variation in mate availability on sexual signaling, competition, and mating decisions that are made throughout life. Field surveys revealed within season heterogeneity in mate availability across breeding sites, providing evidence for the variation necessary for the evolution of plastic preferences. In our laboratory study, males from both female-biased and male-biased treatments invested most in sexual signaling late in life, although they competed most early in life. Females became more responsive to courtship over time, and those experiencing female-biased, but not male-biased sex ratios, relaxed their mating decisions late in life. Our results suggest that social experience and age interact to affect sexual signaling and female mating decisions. Flexible behavior could mediate the potentially negative effects of environmental change on population viability, allowing reproductive success even when preferred mates are rare.

Keywords: Age; mate choice; operational sex ratio; plasticity; stickleback.

Figure 1

Limnetic (top) and benthic (bottom) male threespine stickleback from Paxton Lake, British Columbia.

Figure 2

Operational sex ratio of limnetic (gray) and benthic (black) threespine stickleback from Paxton Lake, early, mid, and late in the breeding season. Means ± SE are illustrated.

Figure 3

Female experience with nuptial throat coloration (0–10; A) and male–male competitive behavior (B) in female-biased and male-biased treatment tanks early, mid, and late in the breeding season. Means ± SE are illustrated.

Figure 4

Responsiveness (follows/lead) of females as they aged (over three clutches). Females became more responsive as they aged, but sex ratio did not influence responsiveness. Means ± SE are illustrated.

Figure 5

Preference score (0–4; A) of females from female-biased (black) and male-biased (gray) treatments as they aged (over clutches 1, 2, and 3). Preference score measures how far in the courtship sequence a given courting pair proceeded. Females from female-biased, but not male-biased treatments, increased their preference scores with all males, regardless of color, as they aged. Females maintained their preference for bright males over mid and dull ones, regardless of age and sex ratio (B). Means ± SE are illustrated.