A Multi Pronged Approach to Remnant Maple (Acer spp.) Populations in Tropical America

Abstract

The distribution range of species can contract and expand as a result of climatic fluctuations. Expansions and contractions affect population abundance and genetic structure. Sugar maple (Acer saccharum) has experienced range contractions and expansions during glacial and interglacial periods; however the post-glacial genetic and ecological consequences of these range fluctuations have been unexplored. This dissertation characterizes relict sugar maple populations and the associated vegetation in tropical regions of North America, evaluates patterns of genetic diversity, structure and subdivision of sugar maple populations across the geographic range in the United States, Mexico and Guatemala and the temporal consistency of those patterns with the Pleistocene climatic events, establishes the taxonomic status of maple species present in Mexico and Central America and their phylogenetic placement, and integrates the results to suggest conservation strategies for the maple species. Sugar maple presence and abundance in tropical America is constrained by elevation, soil nutrient concentrations and disturbances. Chloroplast and nuclear DNA data indicates that sugar maple populations in south Mexico-Central America share chloroplast haplotypes with southeastern USA and Ohio, but are different from those further west in the midwestern USA and western Mexico. Bayesian phylogenetic reconstruction supported the midwestern USA haplotypes as a distinct lineage. Populations in the southern geographic limit are fragmented; with the absence of gene flow, they are experiencing genetic bottlenecks and increases in homozygosity, all exacerbated by anthropogenic activity. Acer aragonii is proposed as a new species restricted to western Mexico and deserving the Endangered (EN B1ab(i,ii,iii,iv,v)) category under IUCN Red List guidelines. Acer negundo has three infraspecific entities in Mexico: A. negundo subsp. interius, A. negundo var. texanum, and A. negundo subsp. mexicanum. The distribution of A. negundo subsp. mexicanum also includes Guatemala and Honduras. In adition, two other species are present in northern Mexico: A. glabrum var. neomexicanum and A. grandidentatum.