Sperm Competition and Paternity in the Endangered Firefly Pyrocoelia pectoralis (Coleoptera: Lampyridae: Lampyrinae)

Abstract

The endangered terrestrial firefly Pyrocoelia pectoralis (Olivier) is endemic to China. Populations of P. pectoralis have decreased dramatically due to urbanization and pollution. Breeding and re-introduction to a suitable habitat may save the species from becoming extinct. Because of its polyandrous character, an investigation into the possibility of sperm competition and paternity outcomes from multiple matings was initiated to better understand its reproductive physiology. To achieve these goals, 13 SSR markers were developed. The results of paternity experiments indicate there is a significant difference between P3 and P1 or P2. The female reproductive system has three spermathecae which accept sperm from different matings, and no bursa or spermatophore-digesting organ is developed. Our research established that multiple inseminations with sperm from different males occur, leading to competition between ejaculates. The benefits of such competition include an increasing number of sperm in the ejaculates of competing males and the consequential increase in fertilized eggs (thus, fecundity), and thereby a higher chance of genetic diversity and fitness in the offspring of the firefly P. pectoralis.

Keywords: SSR; breeding; conservation; firefly; paternity; reproductive system; sperm competition.

Figure 1

Anatomy of reproductive systems in P. pectoralis: (a) male reproductive system. T, testes; SED, seminal duct; ED, ejaculatory duct; SV, seminal vesicle; AG, accessory glands; AE, aedeagus; (b,c) female reproductive system (scale bar, 1 mm). OV, ovary; LOV, lateral oviduct; MOV, median oviduct; FAG, female accessory glands; S, spermatheca; V, vagina. (d) Two small (S2) spermathecae (scale bar, 1 mm); (e) structure and shape of spermathecae in female mated only once; (f) structure and shape of spermathecae in female mated three times; (g) sperm cell in S1; (h,i) sperm cell in S2; (j) individual sperm cell with long tail. (scale bar: a,e,f = 500 μm; b = 1 mm; c = 2 mm; d = 200 μm; g,h,i = 100 μm; j = 50 μm).

Figure 2

Box and whisker plot chart showing the percentage of paternity distribution at different times. The upper and lower edges of the boxes indicate the 75th and 25th percentiles, respectively. Whiskers represent the minimum and maximum, the line within the box indicates the median, the black spot within the box indicates the mean value, and the asterisks indicate the outliers. (a) Treatment 1: one female mated with two different males (P1 and P2); (b) Treatment 2: one female mated with three different males (P1, P2, P3).