Bat pollination, genetic structure and gene flow in Crescentia alata trees in Western Mexico.

摘要

Bats are important pollinators of flowering trees in the tropics. Tropical forests are facing increasing threats from fragmentation, but it is unclear how this affects pollinators, or gene flow in bat-pollinated trees. The goals of this dissertation are to evaluate the impact of forest fragmentation on the abundance of pollinating bats, the reproductive success of trees, and contemporary pollen flow in a bat-pollinated tropical tree species, Crescentia alata. We also describe the genetic structure of this plant species, to better understand if the loss of its theorized seed disperser in the Pleistocene has caused restricted seed dispersal. To assess the impact of forest fragmentation, we sampled bat pollinator abundance and seedling genotypes in sites in continuous and fragmented forest, in the area of the Chamela-Cuixmala Biosphere Reserve, in Jalisco, Mexico. We also sampled adult trees at a slightly larger geographic scale. We developed neutral molecular markers for this species and employed spatial genetic structure analyses to understand gene flow patterns. We hypothesized that adult populations of Crescentia alata have high genetic structuring due to the loss of its seed disperser, but that seedlings will show low pollen pool genetic structure, resulting from high gene flow from the long distance foraging movements of bats. We found evidence that bat abundance is a function of floral display, and seems unaffected by forest fragmentation around flowering trees. Fruit-set was higher in fragmented forest sites, as was pollen flow, although the majority of diversity was found at the level of fruit, rather than at the level of site (sub-population).There was little evidence for restricted seed dispersal among adults, which may be due to high pollen flow or seed dispersal by seasonal floods. These findings contradict the idea that pollen flow is reduced by forest fragmentation, and suggest that bats are moving pollen widely across the landscape, and carrying genetically diverse pollen loads to each flower. These results highlight the important role bat pollinators play in maintaining genetic connectivity among plant populations.