Repeated copulation and sperm precedence: paternity assurance for a male brooding water bug

Ultrastructure of mature spermatozoa of a minute featherwing beetle from Sri Lanka (Coleoptera, Ptiliidae: Bambara)

The fine structure of the mature spermatozoa of the feather-wing beetle (Coleoptera: Bambara new species no. 2) is described. Mature spermatozoa are extremely large in proportion to the size of the beetle. Under a light microscope a distinct head, midbody, and tail region can be seen with external coils in both the head and tail regions. Although the beetles were collected and preserved for skeletal anatomical study and not for histological preservation, the substructure comprising the spermatozoa was sufficiently well-preserved for their uniqueness to be appreciated. Observations with an electron microscope show that the axoneme is not contained in the tail region but is threaded through the head coils and then tightly wrapped around the midbody, terminating at the end of the midbody region. Sections through the midbody reveal three distinct layers: an inner electron dense core, a middle very elaborate crystalline Jattice-like matrix, and an outer axonemal wrapping. The structures observed in the head and tail regions appear to be modifications of those present in the midbody region. The possible functional significance of these unusual structures is discussed.

The fitness of categories and vice versa

Two basic propositions are developed as useful in an evolutionary analysis of the origins of complex biobehavioral categories: 1. Such categories derive from the gradual accumulation of a very large number of categoric alternatives, each of which is very small, and 2. Fitness considerations provide valuable insight into the ultimate decision process whereby these micro-categories, and thus eventually, all more complex categories, are achieved.

Sexual Difference Theory: Mormon Crickets Show Role Reversal in Mate Choice

Male Mormon crickets produce a large spermatophore that the female eats. Spermatophore proteins are important to female reproduction, and females compete for access to singing males. Males reject most receptive females as mates, and those accepted are more fecund than rejected individuals. This role reversal in courtship is in contrast to the behavior of the sexes in katydid species in which the males produce small spermatophores.

Studies of esterase 6 in Drosophila melanogaster. VI. ejaculate competitive abilities of males having null or active alleles

Recent studies of the function of the polymorphic seminal fluid enzyme, esterase 6, of Drosophila melanogaster suggested that it may act in the process of sperm displacement (Gilbert, Richmond and Sheehan, 1981a). This report examines the competitive ability of ejaculates from males homozygous for null or active alleles of esterase 6 under three experimental conditions that model aspects of sexual selection affecting males. The results demonstrate no significant difference in ejaculate competition between esterase 6 null or active male types, but marker males used for paternity identification had poorly competitive ejaculates. The proportion of second-male progeny, P2, used as an index of competition is primarily influenced by second-male genotype and uninfluenced by female genotype, P2 can change with time from remating and be unaffected by different intensities of competition, which suggests a complex ejaculate competition mechanism.