Differential allocation of male-derived nutrients in two lampyrid beetles with contrasting life-history characteristics

Abstract

Across diverse animal taxa, sperm is transferred from males to females during mating within a spermatophore produced by male accessory glands. In some insects, male spermatophores provide females with nutrients that may be used to increase reproductive output or for somatic maintenance, while in others no such benefits have been detected. Boggs suggested that variation in the current function of spermatophores may be explained by considering ecological and life-history factors. This study examined spermatophore function in Ellychnia corrusca and Photinus ignitus (Coleoptera: Lampyridae), two beetles that exhibit marked differences in adult diet, adult life span, and overwintering stage. During mating, males of both species transfer to females a complex, proteinaceous spermatophore, which is subsequently digested in a specialized sac within the female reproductive tract. Males of each species were injected with 3 H‐radiolabeled amino acid mixtures and mated with conspecific females. The fate of spermatophore-derived proteins was determined by dissecting females at various times after mating with these radiolabeled males. Females of these two species showed markedly different patterns of incorporation of spermatophorederived nutrients. P. ignitus females incorporated the majority (62%) of spermatophore-derived protein into maturing oocytes within 2 days after mating. In contrast, in E. corrusca a large percentage of radiolabel (46%) appeared in female fat body at 6 days after mating, with a threefold lower allocation to maturing oocytes compared to P. ignitus. These findings support the prediction that short-lived, nonfeeding females are selected to allocate a greater proportion of male-derived nutrients to reproduction, while longer-lived, feeding females are selected to allocate a greater proportion to somatic reserves and maintenance. These results suggest that life-history characteristics may be useful in explaining observed differences in spermatophore function across taxa. Key words: Ellychnia, firefly, life history, nuptial gifts, paternal investment, Photinus, radiotracer, spermatophore. [Behav Ecol 10:97‐104 (1999)]