A Histological Study on Copulation Duration, Patterns of Sperm Transfer and Organization inside the Spermatheca of a Grasshopper, Dichromorpha viridis (Scudder)

Abstract

The mechanism of sperm transfer and sperm organization inside the spermatheca was investigated in Dichromorpha viridis (Scudder). Spermathecae from single-and multiple-mated females whose copulations were interrupted at various prescribed time intervals, were examined histologically. Sperm organization inside the spermatheca from 24 to 120 hours after copulation had terminated was also investigated. The first observation of sperm inside the spermatheca did not occur until 30 minutes had passed into copulation. The majority of sperm transferred into the spermatheca were in the form of sperm bundles, or spermatodesmes, and the rate at which sperm bundles were transferred appeared to decrease after 13 hours into copulation (average mating duration in the laboratory was 28 hours). The occurrence of abundant sperm with sperm bundles was observed only in females that had mated before and less than 9 hours into copulation, and so believed to be from previous matings. As mating continued, less and less individual sperm was observed, and by 15 hours into copulation only sperm bundles were observed inside the spermatheca. The interrupted multiple matings indicate that at least some sperm bundles remain inside the spermatheca while individual sperm were removed by some mechanism, possibly sperm flushing by an excess of seminal fluid provided by the mating male. Some sperm bundles were shown to keep their bundle integrity for at least 7 days after copulation had terminated. The sperm bundles must disassociate into individual sperm prior to fertilizing the female's eggs; therefore, it may be the female that provides the mechanism or chemical stimulus to initiate sperm bundle disassociation prior to oviposition and/or a multiple mating. The results of this investigation implicate sperm competition, perhaps mediated by female choice, as a primary reason for lengthy copulations in D. viridis. Males may also act as mechanical plugs by remaining in copula for an extended duration after a sufficient amount of sperm has been transferred, or males may be overcompensating the process of sperm removal by transferring an excess of seminal fluid to "flush-out" any sperm present from previous matings.

Spermatophore number transferred increases linearly with copulation duration in Melanoplus differentialis (Orthoptera: Acrididae)

“…Likewise, parasite load, which may influence overall male condition, and thus relative ability to produce spermatophores, was unknown. Our findings are also in keeping with studies of mating behavior, and studies where spermatophore numbers transferred are reported to vary among individuals and with copulation duration (Cueva Del Castillo 1999, Johnson & Niedzlek-Feaver 1998, Kyl 1938, Otte 1970, Pickford & Gillott 1976, Uvarov 1966. In this study, whether all spermatophores transferred during mating were equivalent in content was also not monitored.…”

“…Males in other grasshopper species have also been noted to leave sperm plugs in the females' genital tract, that act as mechanical barriers to subsequent spermatophore transfer by other males (Gregory 1965, Loher & Chandrashekaran 1970, Parker & Smith 1975. As suggested for some species (López-León et al1993, Johnson & Niedzlek-Feaver 1998, lengthy copulation may be more effective as the male himself acts as a sperm plug. In M. differentialis, however, pairs not only maintained genital contact, but males continuously transferred spermatophores for the entire duration of copulation.…”

“…Species either deliver multiple, relatively small, spermatophores, each containing a sperm bundle and other material, during a mating or copulation, or species deliver one large spermatophore. During copulation in the latter group, sperm bundles were delivered at intervals, with delivery of other material interspersed between sperm delivery (Johnson & Niedzlek-Feaver 1998).…”

Sex‐specific repeatabilities and effects of relatedness and mating status on copulation duration in an acridid grasshopper

“…Further reasons for prolonged copulations may include in‐copula mate guarding (Alcock, ) or the possibility to transfer a larger ejaculate, which has been shown for the acridid grasshoppers Dichromorpha viridis (Johnson & Niedzlek‐Feaver, ), Melanoplus differentialis (Hinn & Niedzlek‐Feaver, ), and the desert locust Schistocerca gregaria (Dushimirimana, Hance, & Damiens, ; Pickford & Padgham, ). Pickford and Padgham () also demonstrated that males of S. gregaria regularly transfer not only more spermatozoa but also more than one spermatophore in a single copulation, which needs more time the more spermatophores will be produced and transferred.…”