Abstract
Male mating investment can strongly influence fitness gained from a mating. Yet, male mating investment often changes with age. Life history theory predicts that mating investment should increase with age, and males should become less discriminatory about their mate as they age. Understanding age-dependent changes in male behavior and their effects on fitness is important for understanding how selection acts in age-structured populations. Although the independent effects of male or female age have been studied in many species, how these interact to influence male mating investment and fitness is less well understood. We mated Drosophila pseudoobscura males of five different age classes (4-, 8-, 11-, 15-, 19-day old) to either young (4-day) or old (11-day) females, and measured copulation duration and early post-mating fecundity. Along with their independent effects, we found a strong interaction between the effects of male and female ages on male mating investment and fitness from individual matings. Male mating investment increased with male age, but this increase was more prominent in matings with young females. Male D. pseudoobscura made smaller investments when mating with old females. The level of such discrimination based on female age, however, also changed with male age. Intermediate aged males were most discriminatory, while the youngest and the oldest males did not discriminate between females of different ages. We also found that larger male mating investments resulted in higher fitness payoffs. Our results show that male and female ages interact to form a complex pattern of age-specific male mating investment and fitness.
Highlights
Male reproductive success is generally limited by the number of available mates [1]
We evaluated how male and female age interact to affect copulation duration and female fecundity immediately after mating
We found that investment in mating generally increases with male age, but that intermediate-aged males make the largest investment in mating
Summary
Male reproductive success is generally limited by the number of available mates [1]. males are expected to mate indiscriminately so as to maximize the number of matings they obtain [2], [3]. If mating involves high costs for males (e.g. due to expensive ejaculates), males may discriminate between potential mates by preferring, or providing greater investment in, fitness-enhancing mates [3], [4], [5], [6], [7] This discrimination by males is often expressed as facultative adjustments in their mating investment depending on female size, age, or fecundity [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. Life history theory predicts that males should invest more resources in current matings, and should become less discriminatory as they age [23], [24], [25], [26], [27], [28]
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