The Reproductive Biology of Zamia (Cycadales: Zamiaceae) in Puerto Rico: Implications for Patterns of Genetic Structure and Species Conservation
Lazcano Lara, Julio C.
Ackerman, James D. (Consejero)
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Variation in plant reproductive success is affected by how ecological conditions interact with a plant’s sexual, mating, and pollination systems. Long-term viability of natural populations is dependent on the maintenance of sufficient levels of genetic diversity. However, many genetically rich species are continuously driven into threatened status by the cumulative effect of human actions. This dissertation is focused on the hypothesis that the spatial distribution of individuals within populations affects reproductive success and the patterns of intra-population genetic structure. I used Zamia portoricensis, a short, dioecious gymnosperm, with an underground stem, limited pollen and seed dispersal, as a model system. I answered the following questions: (1) does pollen availability, expressed as the frequency of male and female plants in the vicinity of a target female, affect seed set?, (2) how does distance to the nearest mate affect seed set?, (3) is there a clear pattern of spatial genetic structure (SGS) that can be observed at local, fine scale in Z. portoricensis, and (4) are genotypes spatially arranged in a pattern that reflects limited pollen and seed dispersal? The relationship between spatial distribution of individuals and reproductive success was addressed through observational field studies in two populations of Z. portoricensis located on a serpentine outcrop of southern Puerto Rico. The relationship between spatial distribution and the pattern of genetic structure was addressed by the characterization of SGS in Z. portoricensis using microsatellite markers. The data indicated that: (1) as a trend, female plants located in vicinities with more males than females have higher reproductive success than those located in vicinities with more females than males; (2) reproductive success is highly variable but, as a trend, it exhibits an inverse relationship with the distance to the nearest male; (3) at the local, fine-scale used in this study, Z. portoricensis exhibits a significant SGS; (4) there are identifiable discontinuities in the spatial distribution of genotypes. In addition, I evaluated the current conservation status of the genus Zamia in the island using the International Union for the Conservation of Nature criteria. Newly proposed Red List categories for the Puerto Rican zamias are: Zamia erosa Least Concern instead of Vulnerable, Zamia portoricensis Vulnerable instead of Endangered, and Zamia pumila Critically Endangered instead of Near Threatened.