A poor start in life negatively affects dominance status in adulthood independent of body size in green swordtails Xiphophorus helleri

Abstract

Whilst there is an abundance of studies revealing how dominance interactions affect access to resources critical for survival and reproductive success, very little is known about how dominance status is influenced by early life experiences. However, there is increasing evidence that early developmental trajectories can shape the physiology and behaviour of the adult. In particular, compensatory growth following a period of poor nutrition can have long-term effects on the phenotype. Since catch-up growth increases daily energy requirements and hence the motivation to acquire sufficient resources, it might either increase or decrease competitive ability and aggression. Here we test whether growth compensation early in life subsequently affects the dominance status of adult male swordtail fishes Xiphophorus helleri, a species with strong sexual dimorphism and male-male competition. Males that experienced a period of restricted food early in life subsequently caught up and achieved the same adult body and ornament size as control males that had been raised on ad libitum food throughout development, but were subordinate to size-matched controls, suggesting a trade-off between sexual attractiveness and competitive ability. This indicates that early life history and/or growth trajectory can be an important determinant of competitive ability independent of current body size.

Figure 1

Body size (SL) of GG (filled squares) and PG (open squares) males in relation to age. Repeated measures ANOVA on SL at 2, 6 and 10 months of age; SL×treatment, F_2,48=4.55, p=0.016. Contrasts indicate that PG males are smaller at six months than GG males, but not at two or 10 months; quadratic F_1,24=20.47, p<0.0005. Means±95% confidence intervals.

Figure 2

Absolute growth increments (where SL2 is final size, and SL1 is initial size, in mm) for GG (light shaded bars) and PG (dark shaded bars) males for successive periods of growth (2–6 and 6–10 months). Bars represent means with ±95% confidence intervals.

Figure 3

Percentage of total time spent on (a) aggressive and (b) defensive behaviours in relation to treatment. Lines connect individuals within dyads. Three pairs in (a) and two in (b) had identical relationships within dyads, so the total number of lines shown is less than 13; shared lines are marked.