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Most plant species have one
type of flower, but several species have two different types of flowers on
the same individual:
Chasmogamous (CH) flowers
are often large, showy, and attractive to pollinators. In contrast,
cleistogamous (CL) flowers are very small and resemble buds that form
directly into seed capsules. It is often thought that CH flowers are
produced to attract insects and to facilitate outcrossing, while CL flowers
are the "back-up plan" in case pollinators are scarce any particular year.
However, Stewart (1994) has shown that CH flowers may actually be capable of
self-pollination in some species. My research involves determining the
factors involved in the production of CH/CL flowers and the genetic
consequences of this mating system in violets. CH and CL Seed
Production - In 1997, many of the seeds produced
in an Ohio population of V. pubescens came from CH flowers, mainly
because more CH flowers successfully formed and dispersed seed than CL
flowers. On a per plant basis, both floral types produced similar numbers
of flowers, and both capsule types had similar numbers of seeds per capsule,
in addition to similar abortion and predation rates. There was no
difference in mean seed mass between CH and CL seeds. [Int. J. Plant Sci.
163(1): 113-122] Selfing in CH flowers
- CH flowers in both V. pubescens and V. canadensis are able
to self-pollinate if left unvisited (through a delayed selfing mechanism).
This has important implications for the population genetics of the species
because selfing rates in CH flowers may be higher than previously expected.
A selfing rate study recently revealed that V. pubescens is capable
of substanial, but variable selfing rates from year to year (s = 0.07 -
0.60). [Int. J. Plant Sci. 163(1): 113-122] Inbreeding Depression
- The level of inbreeding depression was measured in CH flowers of V.
canadensis and was found to be very small (0.10). Thus, there is little
disadvantage to selfing in this species. In addition, there were some
measurable fitness differences between progeny from self-pollinated CH and
CL flowers, indicating that floral type differences may exist in CH/CL
species. [Can. J. Bot. 78(11): 1420-1429] Genetic Variation - As measured by both isozyme and ISSR (Inter-Simple Sequence Repeat) molecular markers, the amount of genetic variation is rather high in V. pubescens (e.g., P=77%). However there still appears to be some genetic structuring, as indicated by a non-zero Fst (0.29 with isozyme data). For more information on the ISSR technique, visit my Protocol page, or see the ISSR Resource Website, including a page detailing my primer optimization work. [Heredity 86(5): 545-556] FAVORITE LINKS: I also am interested in statistical genetics and population variability estimates. Here are a few of my favorite programs: SAS
- for all types of statistics (in my opinion, the best out there!) |
