Spermatophore Quality and Production in two Heliconius Butterflies with Contrasting Mating Systems

Abstract

Male investment in spermatophore quality is a function of the degree of polyandry. Among butterflies and other organisms that provide gifts, polyandry tends to select for gifts of better quality than monandry. Tropical butterfly species Heliconius erato and H. melpomene differ in mating systems and provide an ideal system to test expectations regarding allocation to spermatophore quality and production. Heliconius erato males mate with females while they emerge from pupa. Females mate for life and show no mate choice. In H. melpomene, females are courted by males and may mate several times in their lifetime. In order to evaluate whether spermatophore quality (mass and protein content) differed between the two species we conducted mating experiments with virgin males and virgin females in an outdoor insectary. In order to study the dynamics of spermatophore production during subsequent matings, males were also allowed to mate two or more times. Spermatophores of virgin H. melpomene males contained significantly more protein than those of H. erato, confirming theoretical expectations; spermatophore mass was not different. The polyandrous species also showed a significant reduction in mass and protein content in the second mating, while H. erato responses were mixed but non significant. Additionally, the effect of time between successive matings was dependent on species identity. Our results confirm that polyandrous Heliconius invest more in spermatophore quality than its monandrous congener. Two explanations are suggested for the observed loss of mass and protein content in polyandrous Heliconius, potential cost for production or strategic ejaculation.