Sex-linked inheritance of a cuticular pigmentation marker in the marine isopod, Paracerceis sculpta holmes (Crustacea: Isopoda: Sphaeromatidae)

Cuticular pigmentation is highly variable in Paracerceis sculpta, a Gulf of California isopod. Individuals bearing the distinctive pattern we call Str (Stripe) exhibit a longitudinal band of dark pigmentation on the proximal portion of each dorsal body segment and appear 'striped' when viewed from above. In field samples collected over a 10 year period, over 90% of all individuals scored as Str (N = 62) were females (G = 21.3, P < .001, N = 9598). Three generations of laboratory-reared Str females, when crossed to unmarked males, yielded 1:1 sex ratios, 98% Str daughters (46/47) and no Str sons (N = 56). Sons from these families never produced Str daughters. The sex-limited expression of this cuticular marker in three consecutive generations indicates that sex determination in P. sculpta involves female heterogamety (ZW = females, ZZ = males) and that Str is W-linked. Our results are consistent with studies documenting female heterogamety in flabelliferan and oniscoidean isopods, and suggest that chromosomal sex determination may be common within the Isopoda.