Sperm co‐operation in the Fishfly, Parachauliodes japonicus

Abstract

Summary Males of the Fishfly Parachauliodes japonicus (McLachlan) produce sperm in bundles. Each bundle consists of hundreds of sperm with their heads agglutinated. At copulation, on average 500 bundles are packed in a single spermatophore which is attached externally to the female genitalia. The bundles swim forward by synchronous flagellate movements in viscous seminal fluids and finally enter a spermatheca of the female. Females detach the spermatophore without guarding by the male; males guard the spermatophore for 5 h. 2. In this study, the effects of sperm-bundle size and medium viscosity on their swimming velocities were examined. As sperm-bundle mass increased, the amount of time it took to move a unit length decreased. As viscosity increased, those sperm-bundles with greater mass moved faster than sperm-bundles with less mass. 3. The distance sperm move seems to be longer in P. japonicus than in most other insects that ejaculate directly or place the spermatophore internally in the female storage organs. Thus, large sperm-bundles may be an advantage for sperm of P. japonicus who move over a long distance in a viscous environment.

Sperm competition promotes diversity of sperm bundles in Ohomopterus ground beetles

“…The positive association between male genital morphology and sperm bundle size suggests Residual copulatory piece length Residual large sperm bundle length Numbers within plots refer to nodes shown in Fig. 2 the possibility that spermatophore displacement has selected for larger sperm bundles because the larger sperm bundles may swim faster so that they can reach the spermatheca earlier, as shown in fishflies (Hayashi 1998). Additionally, longer postcopulatory guarding may have evolved under the higher risk of sperm competition, but longer guarding may, in turn, avoid multiple mating and reduce sperm competition.…”

“…Their function may be in providing nutrients to the female, moving rapidly to the fertilization site, or enhancing the longevity of the sperm by providing nutrients, by guarding their acrosomes or by avoiding toxins that are secreted by rival males to incapacitate sperm within the female (Sivinski 1984;Siva-Jothy 1997;Holman and Snook 2006). In opossum (Moore 1996), fishflies (Hayashi 1998) and wood mice (Moore et al 2002), paired or aggregated sperm improve swimming speed within viscous environments probably because of synchronized flagella movements, giving support to the motility hypothesis (but see Ishijima et al 1999). Sperm bundles with high motility may be adaptive in fishflies, especially when the female removes attached spermatophores upon premature sperm transfer (Hayashi 1996).…”

Sperm wars and the evolution of male fertility

“…In a variety of species, sperm can form conjugates of two or more individuals, who collectively swim faster than can Sperm wars individual sperm (Hayashi 1998, Moore et al 2002, Fisher & Hoekstra 2010. Among carabid ground beetles, the size of sperm bundles increases with traits known to be subject to selection from sperm competition, such as postcopulatory mate guarding and genital complexity (Takami & Sota 2007).…”

Sperm bundle and reproductive organs of carabid beetles tribe Pterostichini (Coleoptera: Carabidae)

“…For example, in some Drosophila species, males produce sperms that are longer than their body (Pitnik et al 1999); fishflies, Parachauliodes japonicus, produce sperm bundles composed of hundreds of sperm (Hayashi 1998), and sperm dimorphism is recognized in some lepidopteran and dipteran species (Joly and Lachaise 1994;Presgraves et al 1999). In most cases, different forms of sperm among species are associated with the different reproductive strategies of each species (Simmons 2001).…”