• Functional equivalence of grasping cerci and nuptial food gifts in promoting ejaculate transfer in katydids.

      Vahed, Karim; Gilbert, James D. J.; Barrientos-Lozano, Ludivina; Weissman, David; University of Derby; Department of Biological and Forensic Sciences; College of Life and Natural Sciences; University of Derby; Kedleston Rd Derby DE22 1GB United Kingdom; University of Sussex; John Maynard Smith Building; Falmer Brighton BN1 9QG United Kingdom; Department of Entomology; California Academy of Sciences; San Francisco California 94118; Instituto Tecnológico de Cd. Victoria; Boulevard Emilio Portes Gil No. 1301, Cd. Victoria; Tamaulipas 87010 México (Wiley, 2014-05-21)
      The function of nuptial gifts has generated longstanding debate. Nuptial gifts consumed during ejaculate transfer may allow males to transfer more ejaculate than is optimal for females. However, gifts may simultaneously represent male investment in offspring. Evolutionary loss of nuptial gifts can help elucidate pressures driving their evolution. In most katydids (Orthoptera: Tettigoniidae), males transfer a spermatophore comprising two parts: the ejaculate-containing ampulla and the spermatophylax-a gelatinous gift that females eat during ejaculate transfer. Many species, however, have reduced or no spermatophylaces and many have prolonged copulation. Across 44 katydid species, we tested whether spermatophylaces and prolonged copulation following spermatophore transfer are alternative adaptations to protect the ejaculate. We also tested whether prolonged copulation was associated with (i) male cercal adaptations, helping prevent female disengagement, and (ii) female resistance behavior. As predicted, prolonged copulation following (but not before) spermatophore transfer was associated with reduced nuptial gifts, differences in the functional morphology of male cerci, and behavioral resistance by females during copulation. Furthermore, longer copulation following spermatophore transfer was associated with larger ejaculates, across species with reduced nuptial gifts. Our results demonstrate that nuptial gifts and the use of grasping cerci to prolong ejaculate transfer are functionally equivalent.