Does losing reduce the tendency to engage with rivals to reach mates? An experimental test

Abstract

Male-male contests for access to females or breeding resources are critical in determining male reproductive success. Larger males and those with more effective weaponry are more likely to win fights. However, even after controlling for such predictors of fighting ability, studies have reported a winner-loser effect: previous winners are more likely to win subsequent contests, while losers often suffer repeated defeats. While the effect of winning-losing is well-documented for the outcome of future fights, its effect on other behaviors (e.g. mating) remains poorly investigated. Here, we test whether a winning versus losing experience influenced subsequent behaviors of male mosquitofish (Gambusia holbrooki) toward rivals and potential mates. We housed focal males with either a smaller or larger opponent for 24 h to manipulate their fighting experience to become winners or losers, respectively. The focal males then underwent tests that required them to enter and swim through a narrow corridor to reach females, bypassing a cylinder that contained either a larger rival male (competitive scenario), a juvenile or was empty (non-competitive scenarios). The tests were repeated after 1 wk. Winners were more likely to leave the start area and to reach the females, but only when a larger rival was presented, indicating higher levels of risk-taking behavior in aggressive interactions. This winner-loser effect persisted for at least 1 wk. We suggest that male mosquitofish adjust their assessment of their own and/or their rival's fighting ability following contests in ways whose detection by researchers depends on the social context.

Keywords: contests; male–male competition; mosquitofish; sexual selection; winner–loser effect.

Fig. 1.

Illustration of the experimental design. A pair of size-matched males (winner and loser) was randomly selected and subjected to the same procedure (sequence 1 or sequence 2). In sequence 1, the males were first exposed to winning or losing contests for 24 h and then immediately underwent their first encounter test (Test I). Subsequently, the males were isolated in individual tanks for a week before their second encounter test (Test II) (n = 23 pairs). In sequence 2, males underwent the first encounter test prior to any contest experience. Afterwards these males were transferred into individual tanks for a week before having a winning or losing experience for 24 h. Immediately afterwards they immediately underwent a second encounter test (Test III) (n = 23 pairs).

Fig. 2.

Experimental apparatus for the encounter test. Prior to each trial, a focal male was placed into a mesh cylinder (A), with 2 juveniles were housed in an adjacent transparent cylinder (B). The position of cylinder (B) was rotated between trials (left or right relative to the focal male). Another transparent cylinder (C) in the corridor contained either a large rival male, a juvenile (control), or was empty (control). Four females in a transparent tank (D) were placed at the end of the aquarium in the reward area. The start area (blue), the encounter area (orange: < 3 cm around the transparent cylinder in the corridor), and the reward area (green) are shown.

Fig. 3.

The difference between losers (red) and winners (blue) for males from Test I and Test III in the percentage of males: (a) leaving the start area, (c) entering the encounter area, (e) entering the reward area and the time (mean ± s.e.) taken on a logarithmic scale: (a) to leave the start area, (b) spent in the encounter area, and (c) to enter the reward area for the 3 encounter types (n = 46 pairs of winner/loser). Asterisks above encounter types indicate significant differences between winners and losers, while lines with asterisks indicate significant differences across encounter (*P < 0.05; non-significant differences are not indicated).

Fig. 4.

The percentage of males: (a) leaving the start area and (b) entering the reward area in second encounter tests either immediately after contest experience (Test III) or 1 wk after contest experience (Test II). Losers = red; winners = blue.