KLIPS, ROBERT A. Department of Evolution, Ecology, and Organismal Biology, The Ohio State University at Marion, 1465 Mt. Vernon Ave., Marion OH 43302. - Inbreeding depression is variable among populations of rose mallows (Hibiscus species, Malvaceae).
The reduced fitness of progeny produced from selfing is an
evolutionary force that helps shape the mating system of many
self-compatible plant species. The rose-mallows (genus Hibiscus
section Muenchhusia) bear large self-compatible hermaphroditic flowers
that bloom for one day and possess simultaneously mature anthers and
stigmas. An insect visitor is required for pollination and they have a
mixed mating system. In tests to determine whether inbreeding
depression may have influenced the maintenance of features that foster
outcrossing, progeny produced by inbreeding were compared to progeny
derived from outcrossing in several populations of two Hibiscus
species: H. grandiflorus, which is restricted in distribution
to the southeastern Atlantic and Gulf coasts, and the widespread H.
moscheutos. Both taxa exhibited inbreeding depression in two
components of fitness expressed later in the life-cycle: seed
germination (in a few instances only), and (more frequently) progeny
growth. The populations that were more strongly affected by inbreeding
tended to be the more southerly ones, suggesting that the more
northerly ones may have gone through bottlenecks and so been purged of
the deleterious alleles and/or the beneficial polymorphisms as they
re-established the region following glacial retreat. The selfing rate
of one Ohio H. moscheutos population was estimated to be 0.44
using introduced plants with a foreign electrophoretic genotype.
Inbreeding depression appears likely to be maintaining floral features
which result in a substantial fraction of outcrossed offspring. A
related study is underway of variation in inbreeding depression among
populations of another rose-mallow, Hibiscus laevis, that
differ in their ability to self-pollinate autonomously.
Key words: Hibiscus, Inbreeding depression, outcrossing, rose mallows