Abstract
Organisms allocate resources to reproduction in response to the costs and benefits of current and future reproductive opportunities. According to the differential allocation hypothesis, females allocate more resources to high-quality males. We tested whether a fish species lacking parental care (zebrafish, Danio rerio) expresses male size-dependent differential allocation in monogamous spawning trials. In addition, we tested whether reproductive allocation by females is affected by previous experience of different-quality males, potentially indicating plasticity in mate choice. To that end, females were conditioned to large, small or random-sized males (controls) for 14 days to manipulate females' expectations of the future mate quality. Females showed a clear preference for large males in terms of spawning probability and clutch size independent of the conditioning treatment. However, when females experienced variation in male size (random-sized conditioning treatment) they discriminated less against small males compared to females conditioned to large and small males. This might suggest that differential allocation and size-dependent sexual selection is of less relevance in nature than revealed in the present laboratory study.
Highlights
Sexual selection represents selection for traits that increase an individual’s reproductive success
The average clutch size was significantly higher among females crossed with large males (169625.1) compared to females crossed with small males (94.9618.5; Figure 1b, Table 2) when pooled across the conditioning treatments
In accordance with our study hypothesis, we demonstrated that zebrafish females differentially allocate reproductive resources in terms of egg numbers based on the size-dependent attractiveness of their mate, and they showed a greater propensity to spawn with larger males
Summary
Sexual selection represents selection for traits that increase an individual’s reproductive success. Female mate choice is believed to have evolved because it provides females with direct, material benefits (e.g., nutrition, parental care) [2,3] or indirect, genetic benefits (sexy son and good genes hypotheses) [4,5,6] that collectively should increase female’s fitness. In species that lack obvious secondary sexual traits, male body size may constitute an important sexually selected character. Females may exercise size-dependent mate choice in the absence of any obvious material resources offered by the male (i.e., species with a resource free mating system), in which case mating preferences must be a result of indirect, e.g. genetic, benefits offered by the male [5]
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