Abstract
Successful reproduction requires the completion of many, often condition-dependent, stages, from mate searching and courtship through to sperm transfer, fertilisation and offspring production. Animals can plastically adjust their investment in each stage according to the physical and social environment, their own condition, their future reproductive potential, and the condition of their partner. Here we manipulate age and condition, through a nutritional challenge early or late in life, of both male and female Drosophila melanogaster and measure the effects on courtship, mating, and fitness when paired with a standardized (unmanipulated) partner. Older males were slower to start courting and mating, and courted at a slower rate, but males were indifferent to female age or condition despite older females laying and hatching fewer eggs. Female condition had a substantial effect on mating acceptance rate, which dropped dramatically after starvation, and particularly recent starvation experience. In contrast, male condition had little effect on any of the components of reproductive performance we measured. Intriguingly, we found no evidence for additive or multiplicative effects of ageing and starvation: the only significant interaction between these variables was on male latency to initiate courtship – older males were slower to start courting unless they had experienced starvation early in life. These results indicate that the immediate costs of mating differ between males and females, and that the sexes differ in their perception of the opportunity cost sustained by refusing a mating opportunity. Our results support the idea that ageing has more wide-ranging impact on reproductive behaviours than does nutritional challenge.
Highlights
Among animals, reproduction comprises a sequence of events or stages that incur costs for both sexes
Ageing and nutritional challenge are expected to lead to an overall reduction in reproductive capacity, this effect is not necessarily the consequence of a decline across all stages of reproduction
While ageing and starvation limit the total future reproductive capacity of an individual, they may initially increase reproductive investment in response to these stresses to compensate for low future opportunities for reproduction[4]
Summary
Reproduction comprises a sequence of events or stages that incur costs for both sexes. While ageing and starvation limit the total future reproductive capacity of an individual, they may initially increase reproductive investment in response to these stresses to compensate for low future opportunities for reproduction[4]. This phenomenon is termed terminal investment[6], and represents a trade-off of future against current reproductive investment. Older male Drosophila melanogaster decrease mating rate but increase mating duration[7], with www.nature.com/scientificreports/. The latter perhaps compensating for the effects of the former. Though, does not appear to be affected by their own nutritional status or age[11]
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