Female mating competition alters female mating preferences in common gobies

Abstract

Mating decisions can be affected by intrasexual competition and sensitive to operational sex-ratio (OSR) changes in the population. Conceptually, it is assumed that both male and female mate-competition may interfere with female reproductive decisions. Experimentally, however, the focus has been on the effect of male competition on mate choice. In many species with paternal care as in the common goby Pomatoschistus microps, the OSR is often female-biased and female mate-competition for access to available nesting males occurs. Using the same protocol for 3 experiments testing the effect of a perceived risk of female mate-competition, I studied female preferences for nest-holding males differing in its nest size (large/small), body size (large/small), and nest status (with/without eggs already in nest) and measured mating decisions, spawning latencies, and clutch size. Regardless of the social context, females preferred males with larger nests. A preference for large males was only expressed in presence of additional females. For nest status, there was a tendency for females to prefer mating with males with an empty nest. Here, female-female competition increased the propensity to mate. The results of this study show that females are sensitive to a female competitive social environment and suggest that in choice situations, females respond to the social context mainly by mating decisions per se rather than by adjusting the clutch size or spawning latency. Females base their mating decisions not only on a male's nest size but also on male size as an additional cue of mate quality in the presence of additional females.

Keywords: Pomatoschistus microps; audience effect; intrasexual competition; mate sampling; parental care; sex-roles; size.

Figure 1.

(A) The setup of experimental tanks. Depicted is the design including additional audience females in the adjacent compartment. For all experimental runs, half of the tanks were with or without female competitors, respectively. Removable dividers are drawn as dashed lines. After an acclimation period, the female had free access to both nests and males. (B) The design of the experiment. Females chose between nests (1) and males (2) that were either small or large (indicated by differently sized symbols, respectively). In Experiment 3, females chose between males with nests that either had eggs or where eggs had been removed.

Figure 2.

Nest-size experiment (1): testing female preferences for nest size. The 2 male stimuli were size-matched. (A) The number of observed spawning decisions as binary outcomes with males in either the larger (black) or smaller (gray) nest under the 2 different social contexts, either with or without female competitors present in the adjacent compartment. (B) The time in minutes (mean ± SE) until the female spawned with 1 of the 2 males (in black matings with the male in the larger nest, in gray matings with the male in the smaller nest). (C) The clutch area in mm² (mean ± SE), the female spawned with the male in the larger (black) or smaller (gray) nest in the 2 different social contexts.

Figure 3.

Male-size experiment (2): testing female preferences for male size. The 2 nests were size-matched. (A) The number of observed binary spawning decisions with either the larger (black) or smaller (gray) male under the 2 different social contexts, either with or without female competitors present in the adjacent compartment. (B) The time in minutes (mean ± SE) until the female spawned with 1 of the 2 males (in black with the larger male, in gray with the smaller male). (C) The clutch area in mm² (mean ± SE), the female spawned with the larger (black) or smaller (gray) male in the 2 different social contexts.

Figure 4.

Nest-status experiment (3): testing female preferences for nest status. The 2 males and nests were size-matched. (A) The number of observed binary spawning decisions with the male in either the nest already with eggs (black) or the nest without eggs (gray) under the 2 different social contexts, either with or without female competitors present in the adjacent compartment. (B) The time in minutes (mean ± SE) until the female spawned with a male in 1 of the 2 nests (in black with eggs, in gray without eggs). (C) The clutch area in mm² (mean ± SE), the female spawned with the male in the egg-containing nest (black) or the nest without eggs (gray) in the 2 different social contexts.

Figure 5.

The relationship between clutch size (mm²) and female total length (mm) across all 3 experiments and both social context treatment. Larger females spawned more eggs (r² = 0.31, y = 30.07x−713.76).