Case, Andrea L , Caruso, Christina .
Does inbreeding affect the relationship between population size and sex ratio in gynodioecious Lobelia siphilitica?
Variation in population sex ratio can be influenced by natural selection on alternate sex phenotypes as well as non-selective mechanisms, such as inbreeding, founder effects, and genetic drift, which can alter the frequency of sex determining alleles. In gynodioecious Lobelia siphilitica, females are more common in populations with higher annual temperatures, lower soil moisture, and lower predation on female fruits, consistent with sex-specific selection. However, females are also more common in small populations, consistent with non-selective mechanisms. We are particularly interested in the possibility that inbreeding may be contributing to higher female frequencies in small populations if increased homozygosity increases the expression of male sterility. If so, then we can make two predictions: 1) the production of female offspring should be negatively related to inbreeding, such that selfing would result in more females than biparental inbreeding, and both would result in more than outcrossing, and 2) the relationship between inbreeding and offspring sex ratio should be more evident in small than large populations. We performed a series of self- and outcross pollinations between plants from small and large populations to evaluate the effect of inbreeding and population size on the frequency of female offspring. Selfed hermaphrodites from all populations produced similar offspring sex ratios, which had significantly fewer female offspring compared with outcrossing or biparental inbreeding. Female mothers from small populations produced significantly more female offspring than those from large populations regardless of cross type. These data indicate that inbreeding would not necessarily contribute to increased female frequency in small populations. It is likely that genetic drift or founder effects in small populations have stronger influence on population sex ratio by reducing the diversity of sex-determining alleles.
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1 - Kent State University, Biological Sciences, Box 5190, 256 Cunningham Hall, Kent, OH, 44242-0001, USA
2 - University of Guelph, Integrative Biology, Axelrod Building, 50 Stone Road, Guelph, Ontario, N1G 2W1, Canada
Presentation Type: Oral Paper:Papers for Sections
Location: Williford B/Hilton
Date: Tuesday, July 10th, 2007
Time: 4:15 PM