Predation Risk as a Driving Force for Sexual Segregation: A Cross-Population Comparison

Abstract

Sexual segregation is widespread throughout the animal kingdom. Although a number of hypotheses have been proposed to account for observed patterns, the generality of the mechanisms remains debated. One possible reason for this is the focus on segregation patterns in large mammals such as ungulates, where the majority of studies are descriptions of a single population. Here, we present the results of a cross‐population comparison of patterns of sexual segregation in the Trinidadian guppy, Poecilia reticulata. We relate observed patterns to experimental quantification of predation risk and sexual harassment of females by males in eight populations. We find that the degree of segregation increases with predation risk, with deeper waters becoming increasingly female biased. Furthermore, we observed that levels of male harassment are lower in deeper water but only in those rivers that contain major guppy predators. We conclude that sexual segregation in guppies is consistent with the predation risk hypothesis: sexual segregation results from a combination of predation risk driving males (the more vulnerable sex) into less risky habitats and females gaining benefits of reduced sexual harassment by remaining in high‐predation environments.

Sex differences in antipredator tail-waving displays of the diurnal yellow-headed gecko Gonatodes albogularis from tropical forests of Colombia

“…Similarly, in Crotaphytus dickersonae males fled sooner and tended to use more the refuges than females, which probably indicates stronger predation pressure on males (Plasman et al 2007). Therefore, as predator risk is generally higher for males than females (Ellingson 1994;Croft et al 2006), the sexual differences in antipredator behavior of several species of reptiles, including G. albogularis, are in agreement with theoretical predictions (Caro 1995;Ruxton et al 2004). …”

Balancing the Dilution and Oddity Effects: Decisions Depend on Body Size

“…Here, we found that only large-bodied fish showed a significant preference for the size matched shoal, suggesting an increased importance of oddity for large fish compared to small ones. Large guppies are likely to be preferentially targeted by their predators [25], as they have a higher calorific value than small guppies, and major predators such as C. frenata are unlikely to be gape limited [35]. This, combined with their increased conspicuousness to visual predators, may make phenotypic matching highly important for large fish.…”

“…We carried out this study at the University of the West Indies Biology Department laboratories in Tunapuna, Trinidad, using guppies from seven well known field sites in the rivers of the northern mountain range (table 2), representing a range of predation risks for the guppy [35], [46]. Guppies are sympatric with a variety of aquatic predators: the most significant of these is Crenicichla frenata which is large enough to consume even the largest guppies.…”

Sex-specific plasticity in brain morphology depends on social environment of the guppy, Poecilia reticulata

“…For the separate brain structures, we detected sexual dimorphism in both the olfactory bulbs and the cerebellum, which were larger in females (controlled for body size 2 and 14 %, respectively). Female guppies are generally much more active than males in terms of foraging activity, partially to compensate for costs associated with male harassment through increased foraging (Magurran and Seghers 1994;Croft et al 2006;Piyapong et al 2010). Females are also more innovative in a feeding situation, better at locating food and respond quicker to novel food sources (Laland and Reader 1999b;Laland and Reader 1999a).…”