Mating Behavior in the Streptocephalus Fairy Shrimps (Crustacea: Anostraca)

Abstract

Mating behavior in the Streptocephalus fairy shrimps consists of the following behavior patterns: detection and orientation, station taking, clasping, intromission, and disengagement. Since males have low parental investment in their offspring and since males must compete for receptive females, sexual selection should favor males which mate with undiscrimi- nating eagerness. While observations reported here generally support this prediction, males discriminate against clearly unsuitable mates both before and during station-taking. Females should choose their mates carefully, based on some quality related to male fitness, since each clutch of eggs represents a large parental investment, but the criteria used by females in mate choice remain obscure. Bateman (1948), in an important discussion of sexual selection in Drosophila, speculated that if males have low parental investment compared to females, males should mate with undiscriminating eagerness while females should mate with discriminating passivity. He reasoned that the reproductive success of a male is limited by the number of females he inseminates and not by the amount of sperm produced. Males, then, should try to mate with as many females as possible. Since the fitness of a female is likely to be limited by egg production, females might be expected to maximize their reproductive investment by choosing their mates with respect to some genetic quality related to the male's fitness. Bateman's predictions serve to focus the present study of sexual behavior of the Streptocephalus fairy shrimps. These animals inhabit temporary ponds, primarily in arid and semi-arid regions. Pond duration, which is sometimes very brief, imposes an element of urgency in the reproductive strategy of fairy shrimps; that is, they must reproduce quickly and often. This aspect of their biology makes them convenient animals for studies of sexual behavior. A review of the available literature on fairy shrimp mating behavior can be found in Moore and Ogren (1962), and it includes no reference to studies of Streptocephalus behavior. Consequently this paper includes a description of the sequence of behavior patterns in Streptocephalus courtship. METHODS. Laboratory populations of Streptocephalus fairy shrimps were established from many eggs taken in soil samples from temporary pond habitats during the dry stage. Soil samples were placed in 4-liter jars and flooded with aerated, distilled water. The fairy shrimps which hatched under these conditions were fed daily with either cultured green algae or with a suspension of baker's yeast. The animals generally reached reproductive maturity within 2 weeks and continued to