Male reproductive allocation in fireflies (Photinus spp.)

Resource allocation between somatic and reproductive structures has important fitness consequences for individuals, and optimal trade-offs are expected to depend not only on mating system differences among species but also on levels of resource stress within species. We tested the prediction that polyandry ( associated with increased sperm competition) will increase male reproductive allocation in bioluminescent fireflies in Photinus spp. by comparing the relative mass of testes, seminal vesicles, and reproductive accessory glands among a monandrous and several polyandrous species. In addition, we examined a single population of a polyandrous species, Photinus greeni, to see how reproductive allocation might shift between years in response to different levels of larval resource stress. As predicted, males of P. collustrans, a monandrous species, showed a fivefold lower allocation to sperm production and a 100-fold lower allocation to reproductive accessory glands compared with males from polyandrous species. We also found evidence within P. greeni of a trade-off between allocation either to reproduction or to somatic tissue; following larval resource stress, males eclosed at significantly shorter body lengths, yet showed a 35% increase in their reproductive allocation. These results demonstrate that mating systems strongly influence male allocation to reproductive accessory glands as well as to sperm production. Furthermore, these results suggest that under larval resource stress males of Photinus spp. increase their allocation to reproduction at the expense of somatic tissue, thus maximizing their ability to produce nuptial gifts required for reproductive success.