Multiple Storage Sites

Most examined cockroaches have just one or two sper-mathecal lobes. The Blattellidae are extraordinary, however, in that some species have two, others, including Blattella, have four, and in some, the spermathecae look like a fistful of balloons (Fig. 6.16J). Each spermatheca may have its own opening (i.e., multiple spermathecae) (Nyctibora—Fig. 6.15J), or multiple branches may share a common orifice. In the latter case, the ducts may be arborescent (Fig. 6.16J),or branch from a single point (Fig. 6.16K).

Multiple storage sites offer potential for allowing a female to separate the sperm of different males spatially, giving her greater scope for choosing among potential sires and for postponing mate choice until oviposition. The bias can take the form of differential transport to storage sites, biased sperm survival in different sperma-thecal lobes, or differential transport from storage to the site of fertilization. Multiple spermathecae may also pre vent male genitalic structures from accessing previously stored sperm, and allow specialization for more than one function, such as long- versus short-term storage (Eberhard, 1996; Otronen et al., 1997; Hellriegel and Ward, 1998; Pitnick et al., 1999). It is known, for example, that in the fly Dryomyza anilis, sperm movements in and out of individual spermathecae occur independently (Otro-nen, 1997). Differential sperm storage is also known in the fly Scatophaga stercoria, and is mediated by female muscular activity (Hellriegel and Bernasconi, 2000). A detailed examination of the fates of different ejaculates within blattellid cockroaches is clearly indicated. The only relevant information known to us is from B. germanica. When the spermatophore is transferred to the female, the two sperm sac openings align directly with two of the spermathecal pores (Khalifa, 1950); nonetheless, sperm can be found in all four spermathecae of mated females (van Wyk, 1952; Marks and Lawson, 1962). Cochran's (1979b) study of sperm precedence in the species suggests that selective use of sperm may be possible in multiply mated females (Fig. 6.6).

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