Spermathecal Shape

Two "basic"spermathecal shapes are represented in cockroaches: the tubular form, with little difference in width between the duct and the spermatheca proper (= ampulla), and the capitate form, shaped like a lollipop. Shape varies widely across cockroach species and sometimes within a species. In Agmoblatta thaxteri each spermatheca has a double terminal bulb, like a figure 8 (Gurney and Roth, 1966). The genus Tryonicus can be inter- and in-traspecifically polymorphic (Fig. 6.18) (Roth, 1987b); however, some apparent variation in spermathecal shape may be due to the amount of ejaculate stored or to the preservation of specimens at different stages of muscular activity. Both the ampulla and ducts are surrounded by a sheath of profusely innervated striated muscle (Gupta and Smith, 1969). The sheath is best developed at the base, where it consists mainly of circular fibers and functions as a sphincter in opening and closing the entry (van Wyk, 1952).

It has been suggested that spermathecal shape can pre-

Fig. 6.17 Drawing of the anterior view of the female genitalia of Rhyparobia maderae, showing the tubular spermathecae (spth, shaded gray) and extensive, branched spermathecal gland (sp gl). Slightly modified from McKittrick (1964).

Fig. 6.16 Morphological variation in cockroach spermathecae (A) Arenivaga bolliana; (B) Hypercompsa fieberi; (C) Neoblat-tella sp.; (D) Plecoptera sp.; (E) Miriamrothschildia notulatus; (F) Pseudomops septentrionalis; (G) Parcoblatta virginica; (H) Blattellagermanica; (I) Ectobiuspallidus; (J) Loboptera decipi-ens; (K) Xestoblatta festae. From McKittrick (1964) and Gurney and Roth (1966).

Fig. 6.18 Inter- and intraspecific variation in spermathecae of cockroaches in the genus Tryonicus (Blattidae: Tryonicinae). (A) Tryonicus parvus; large, bulbous reservoir arising preapi-cally from a convoluted duct. (B) Tryonicicus angusta; reservoir spherical, sclerotized at one end and club-shaped on the other. (C) Tryonicus sp. 1; large spermathecal duct is same diameter as the spermathecal branch beyond the point of insertion of main reservoir. (D) Tryonicus monteithi from five locations in Queensland, Australia. After Roth (1987b). Scale bar is 0.5 mm in all cases.

Fig. 6.18 Inter- and intraspecific variation in spermathecae of cockroaches in the genus Tryonicus (Blattidae: Tryonicinae). (A) Tryonicus parvus; large, bulbous reservoir arising preapi-cally from a convoluted duct. (B) Tryonicicus angusta; reservoir spherical, sclerotized at one end and club-shaped on the other. (C) Tryonicus sp. 1; large spermathecal duct is same diameter as the spermathecal branch beyond the point of insertion of main reservoir. (D) Tryonicus monteithi from five locations in Queensland, Australia. After Roth (1987b). Scale bar is 0.5 mm in all cases.

dict sperm use patterns (Walker, 1980),but the functional significance of spermathecal shape is complex (Otronen, 1997) and not yet clear (Ridley, 1989). Large, globular ampullae may be associated with sperm mixing. Long tubular spermathecae may promote the layering of ejaculates, enhancing the "last in, first out" pattern of sperm precedence, or may serve as "sperm traps" to imprison the sperm of less favored males. Spermatozoa of R. maderae are apparently stored chiefly in the distal portion of the female's tubular spermatheca. The proximal portion is filled with a granular secretion, which, according to van Wyk (1952), probably serves as food for the sperm.

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