Low but genetically variable male remating ability in a tropicalDrosophiladespite substantial fitness benefits

Abstract

Mating success is the main source of fitness variation in males, meaning that males should capitalise on all opportunities for mating. Strong selection on male mating success should also reduce genetic variation in male mating traits relative to other traits. We quantified mating latency, mating duration and productivity in males of the tropical fruitfly, Drosophila birchii, from 30 isofemale lines collected from across two elevational gradients, when they were given opportunities to mate with up to four females consecutively. Male remating rates were low compared to other Drosophila (only 14 – 27% of males achieved a fourth mating), with mean mating durations approximately doubling across successive copulations. However, although successive remating produced progressively fewer offspring, it consistently increased overall male reproductive success, with males that mated four times more than doubling offspring number compared to males mating only once. We also found no reduction in the productivity of sons emerging from later matings, indicating a sustained cumulative fitness benefit to remating. Heritable variation was observed for most traits (H2 = 0.035 – 0.292) except mating latency, but there was no divergence in trait means with elevation. The observed restricted remating ability of male D. birchii, despite the clear benefits of remating, may be due to a low encounter rate with females in the field, leading to high investment per gamete (or ejaculate). However, it remains unclear why genetic variation in these traits is high, given we observe no variation in these traits across elevational gradients known to affect local population density.

Environmental variation and biotic interactions limit adaptation at ecological margins: lessons from rainforestDrosophilaand European butterflies

“…relative fitness among genotypes), even if it causes abrupt reductions in population mean fitness, as seen in recent transplants of genotypes of Senecio daisies along elevational gradients in Sicily [88][89][90]. In addition, our recent work on Drosophila [66,91,92] reveals their complex responses to different sexual and social environments, all of which will affect population mean and relative fitness, and therefore adaptive potential. Effective modelling of evolutionary responses depends on incorporating such plastic responses, and their effect on adaptive potential, load and gradient steepness into theoretical models (Eriksson & Rafajlovic [93]) as well as empirical tests of plastic responses and their effects on fitness in the field.…”

“…'ecological' or 'fundamental' limits; see §2(i) above) may, therefore, limit species to particular places along environmental gradients, regardless of the effects of standing variation on local adaptation. Such effects may include antagonistic interactions with closely related species [65] (see below), or sexual interactions within species [66].…”