OUTCROSSING RATES AND INFERRED LEVELS OF INBREEDING DEPRESSION IN GYNODIOECIOUS CUCURBITA-FOETIDISSIMA (CUCURBITACEAE)

Sex-specific outcrossing rates and the inbreeding coefficient of adult s in two populations of gynodioecious Cucurbita foetidissima were esti mated using progeny array data from four allozyme loci to compare the frequencies of self-fertilization and the estimated levels of inbreedi ng depression to predictions from sex ratio theory. The frequencies of self-fertilization by hermaphrodites in both populations were similar and averaged 73 per cent. The outcrossing rate for females in one pop ulation was not different from unity-whereas the estimated rate of out crossing by females in the second population (t=0.593, SE 0.178) indic ated the occurrence of biparental inbreeding. Despite considerable sel f-fertilization by hermaphrodites, inbreeding coefficients of adult pl ants in both populations were not different from zero and thus inferre d values of inbreeding depression were not different from one. Electro phoretically inferred levels of inbreeding depression are somewhat in excess of the value of 0.71 (SE 0.07) obtained in a previous field exp eriment which tested first-year survival of selfed and outcrossed seed s in this long-lived perennial. The high frequency of self-fertilizati on by hermaphrodites combined with severe inbreeding depression provid es a strong selective force which, along with increased seed-set by fe males, is sufficient to maintain observed frequencies of females in na tural populations of C. foetidissima.