Males Prefer Small Females in a Dichotomous Choice Test in the Poeciliid Fish Heterandria formosa

Male choice is much less studied than female choice (Andersson 1994). However, males are expected to exhibit choice over mating partners when females differ in fecundity, the operational sex ratio is female biased or the risk of sperm competition differs between females (Parker 1983; Andersson 1994). Most commonly observed male mating preferences are those that maximize a male’s expected fertilization success in each mating (Bonduriansky 2001). Such preferences tend to favour female phenotypes associated with high fecundity or reduced sperm competition intensity (Bonduriansky 2001). Male choosiness is expected to increase when male parental investment increases (as shown by Simmons 1992 and Gwynne 1993). However, if variance in female quality is large, males can be choosy even if their investment in each mating is insignificant compared to the female investment (Parker 1983). The family Poeciliidae is an example of fishes, in which males exhibit low parental investment by only providing sperm at mating (Farr 1989). Despite this, male preference for large females has been found in all species studied in this respect (Table 1). In poeciliid fishes, as in fish in general, fecundity increases with size (Bagenal & Braum 1978; Travis et al. 1990; Herdman et al. 2004), and thus males mating with large females could gain benefits in terms of increased offspring number. In addition to fecundity, males may differentiate among females based on their expected success in sperm competition as first demonstrated by Schwagmeyer & Parker (1990) in 13-lined ground-squirrels (Spermophilus tridecemlineatus). Dosen & Montgomerie (2004b) showed that male guppies (Poecilia reticulata) Correspondence Outi Ala-Honkola, Department of Biological and Environmental Sciences, PO Box 65, 00014 University of Helsinki, Helsinki, Finland. E-mail: [email protected]