Population dynamics under parasitic sex ratio distortion

We analyse the population dynamic effects of sex ratio distortion by vertic ally transmitted, feminizing parasites, We show that, for diploid hosts, se x ratio distortion may lead to extinction as males become too rare to maint ain the host population through reproduction. Feminizers can magnify Allee effects, broadening the range of conditions leading to extinction of small populations, Depending on male mating constraints and strength of density d ependence, feminizers may either increase or decrease the equilibrium host density. Under conditions leading to deterministic host extinction, stochas tic elimination of the parasite may allow the host population to recover. H ence, infection by parasitic sex ratio distorters may be transient in finit e populations. We consider the implications of this process for parasite pr evalence, host population regulation, and sex ratio evolution. (C) 1999 Aca demic Press.