Adaptive significance of postcopulatory guarding of mates and nonmates by male Calopteryx maculata (Odonata)

Abstract

1. The postcopulatory behavior of the damselfly Calopteryx maculata (De Beauvois) (Odonata: Calopterygidae) was studied in field populations to determine the adaptive significance of guarding of ovipositing females by males. Of particular interest was an explanation for the guarding of ovipositing nonmates by males. A promiscuous mating system and the large variation in mating success (Table 1) among territorial males indicated that sexual selection may have been a significant factor in the evolution of C. maculata postcopulatory behavior. 2. Territorial males defend ovipositing mates by chasing and displaying toward conspecific males attempting takeovers. Guarded mates averaged 12–15 min of undisturbed oviposition while unguarded females averaged only 1–2 min of oviposition prior to disturbance by males. Postcopulatory guarding is advantageous to both sexes because it allows undisturbed oviposition. 3. During mating, 88%–100% of the sperm stored by a female from a previous mating was removed by a male before he transferred his own sperm to her storage organs. Given this potential for sperm displacement, postcopulatory guarding is advantageous to the guarding male since it assures him of fertilizing a substantial number of eggs prior to a subsequent mating by his mate. 4. The duration of guarding (interval between matings) for males was 10–15 min. It did not differ significantly between two populations in on year. Guarding duration did not significantly change with (a) time of day, (b) time devoted to defensive behavior, (c) female arrival rate, and (d) presence of absence of an ovipositing female (Table 2). 5. Males frequently guarded females with which they did not mate. Nonmates were guarded only when the male was simultaneously guarding a mate or had recently mated. These nonmates deposited eggs fertilized by rival males. Their presence did not significantly increase the time and energy expended by guarding males but did attract additional females (Table 3). However, these additional females did not lead to an increase in mating frequency for the guarding male. 6. Three factors appeared to limit the ability of guarding males to exclude or attempt matings with arriving nonmates: (a) a lack of individual recognition, (b) a risk of losing a previous mate while failing to copulate with an arriving female, and (c) a probable physiologic limit to mating frequency. These limitations in male postcopulatory behavior were exploited by females. 7. Some males were not territorial. While appearing less effective at obtaining mates, they devoted no time and energy to defending territories or mates. Because of sperm displacement, their reproductive success depended upon the ability of their mates to exploit the limitations in guarding behavior of territorial males.