Inbreeding depression, autonomous self-pollination, and the genetic affinities of a rare taxon within the rose-mallows, Hibiscus section Muenchhusia.

摘要

Progeny produced by inbreeding were compared to outcrossed progeny in two species of rose mallow (Hibiscus section Muenchhusia): H. grandiflorus (two populations) and H. moscheutos (five populations). Both exhibited inbreeding depression in two late-stage components of fitness: seed germination and progeny growth. Southern populations were more susceptible to inbreeding depression, suggesting the northern ones may have gone through bottlenecks and been purged of deleterious alleles while re-colonizing the region following glacial retreat.;Style recurvature progressive with flower aging in the smooth rose mallow, H. laevis appears to effect selfing when the stigma lobes contact the uppermost stamens. In greenhouse tests all 12 plants from a Delaware County, Ohio population proved capable of selfing in this manner, but their reproductive output was lower than hand-pollinated controls. Selfing is facultative both through its late timing and the absence of recurvature by styles that receive pollen loads early in the day. In a natural stand the mean seed set of flowers modified to prevent selfing was only slightly less than that of either unmanipulated or hand-pollinated controls, suggesting that autonomous selfing may be important in establishing new populations but not in maintaining existing ones. Small-scale greenhouse tests of additional populations revealed substantial variation in the ability to set fruit in the absence of pollinators.;Hibiscus dasycalyx is a rare Texas endemic sharing key morphologic traits with two sympatric congeners, H. laevis and H. moscheutos, suspected of being ancestors of the endemic through recombinational speciation. Electrophoretic screening was conducted to determine whether the endemic exhibits a hybrid genetic profile. The three taxa share predominant alleles for all tested enzyme systems except ADH, GPI and PGM, for which H. dasycalyx and H. laevis display similar banding patterns which differ from H. moscheutos. Hibiscus laevis showed variation in diagnostic leaf shape and calyx pubescence, including forms intermediate between typical H. laevis and H. dasycalyx. In hand-pollinations, H. dasycalyx was compatible with H. laevis. Hibiscus dasycalyx may be better regarded as a variety of B. laevis. Conservation efforts should consider the potential effects of contaminating gene flow with typical H. laevis.