No abstract

Hypotheses regarding the function of elaborate male genitalia were tested in a sample of insects and spiders by comparing their allometric values (slopes in log-log regressions on indicators of body size) with those of other body parts. Male genitalia consistently had lower slopes than other body parts. Perhaps as a consequence of this pattern, genitalic size also tended, though less consistently, to have lower coefficients of variation than did the size of other body parts. The morphological details of coupling between males and females in several species clearly indicated that selection favoring mechanical fit is not responsible for these trends. Sexual selection on male courtship structures that are brought into contact with females in precise ways may favor relatively low allometric values, in contrast to the high values seen in the other sexually selected characters (usually visual display devices) that have been studied previously, because a female's own size will influence her perception of the contact courtship devices of a male.

Details of web-construction behaviour and morphology support the monophyly of nephiline spiders with Phonognatha as the sister-group to the remaining nephiline genera examined in this study. Phylogenetic analysis of the behavioural data suggests that specialisations in nephiline building behaviour and web architecture did not evolve concurrently, and that some preceded the female giantism (not male dwarfism) for which nephiline spiders are well-known. Cladistic analysis of 60 characters supports the monophyly of both Tetragnathidae and Tetragnathinae. New data from spinneret silk gland spigots, combined with other morphological and behavioural characters, provide the first concrete evidence that 'metine' genera, occasionally regarded as either a distinct family or subfamily, are a paraphyletic assemblage.

This chapter discusses sexual selection by cryptic female choice (CFC) and other possible types of selection on traits involved in male-female interactions during and following copulation. Morphological, behavioral, and probably also physiological traits all show the typical earmarks of sexual selection: puzzlingly extravagant, apparently non-utilitarian design; and rapid divergent evolution.