Sperm Morphology

Cockroaches have extremely thin sperm, with long, actively motile flagellae (Baccetti, 1987). The sperm head and the tail are indistinguishable in some species, such as B. germanica, but can be distinct and variable among other examined cockroaches. The sperm head in Areni-vaga boliana, for example, is helical, and that of Su. longi-palpa is extremely elongated (Breland et al., 1968). Total sperm length varies considerably, with B. germanica and P. americana at the extremes of the range in 10 examined cockroach species (Breland et al., 1968). The limited data we have suggest that body size and sperm length may be negatively correlated (Table 6.1), but the relative influences of body size, cryptic choice mechanisms, and sperm competition have not been studied.

Dimorphic sperm have been described in P. americana (Richards, 1963). A small proportion are "giants," sperm that have big heads and tails that are similar in length but two or more times the diameter of typical sperm. These chunky little gametes swim at approximately the same speeds as the "normal," more streamlined, sperm, and are thought to be the result of multinucleate, diploid, or

Table 6.1. Sperm length relative to body length in cockroaches. Sperm data from Jamieson (1987) and VidliCka and Huckova (1993).

Species

Approximate1 body length length (mm)

Sperm length

Ratio body length:sperm length

Blattella germanica

12.0

450

27:1

Pycnoscelus indicus

~ 21.02

250

84:1

Nauphoeta cinerea

27.0

300

90:1

Periplaneta americana

37.5

85

441:1

Blaberus craniifer

55.0

180

306:1

1 Body length can range fairly widely within a species, for example, male B.germanica ranges from 9.6 to 13.8 mm in length (Roth, 1985). 2Body length based on its sibling species, Pyc.surinamensis.

1 Body length can range fairly widely within a species, for example, male B.germanica ranges from 9.6 to 13.8 mm in length (Roth, 1985). 2Body length based on its sibling species, Pyc.surinamensis.

higher degrees of heteroploidy. Giants range from 0-30% of the total in testes; smears from either seminal vesicles or spermathecae of females, however, yield a much lower percentage, just 0-2%. Most never leave the male gonads, and it is unknown whether those that do are capable of effecting fertilization. Alternate sperm forms are fairly common among invertebrates, and in some cases are specialized for functions in addition to or instead of fertilization (Eberhard, 1996). These include acting as nuptial gifts, suppressing the female's propensity to remate, and creating a hostile environment for rival sperm (e.g., Buckland-Nicks, 1998). The topic is thoroughly discussed in Swallow and Wilkinson (2002).

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