Browsing by Author "Manos, Paul Steven"

The genus Anthurium represents one of the largest genera restricted to the neotropics and has long been recognized as one of the "megagenera" of flowering plants, in addition to claiming the bulk of diversity (~25%) in its family, the Araceae. Despite this vast and beguiling array of morphologic diversity, observations on the biotic interactions that Anthurium participate with other living organisms in are scant. Although these types of observations help establish foundational knowledge on the natural history of organisms and are well-known from other large clades of neotropical herbs (i.e., orchids), the few observations that have been made for Anthurium are scattered throughout the literature, and no attempt has been made to synthesize this information. Primary literature documents were procured largely through the Duke Univeristy Library system. A total of 316 discrete biotic interactions are referenced here, 22 of which are evidenced here as new. Previously considered to be pollinated primarily by euglossine bees (Dressler 1968, Williams & Dressler 1976; Croat 1980), this review evidences a diverse assemblage of biotic interactors that complements the taxonomic, morphologic, and ecologic diversity of Anthurium. It is hoped that this information can provide a starting point for current and future researchers to springboard from as they continue to demystify the evolutionary forces that facilitated the diversification of this understudied megagenus

Edaphic factors--those pertaining to the substrate or soil--are thought to play an important role in the diversification of flowering plants. Although edaphic factors are widely interpreted as causal agents in plant diversification, little is known about the evolutionary origin of most edaphic endemic plants, preventing inference of potential mechanisms by which substrate properties may influence speciation. The North American plant genus Ceanothus (Rhamnaceae) contains 9 edaphic-endemic species, taxa restricted to soils derived from specific geological materials. The three components of my dissertation research aim to improve understanding of how edaphic ecology has influenced the diversification of Ceanothus. First, I use DNA sequence data from the low-copy nuclear gene nitrate reductase to reconstruct the phylogeny of Ceanothus and elucidate diversification of this group into the California Floristic Province (CFP) of western North America, including the evolution of edaphic endemism. This research indicates that diversification of the two Ceanothus subgenera (Cerastes and Ceanothus) is centered on the CFP and is characterized by shallow divergence and phylogenetic relationships defined predominantly by geography. Divergence time estimation suggests that diversification of both Ceanothus subgenera began approximately 6 Ma. The nine edaphic-endemic taxa are not phylogenetically clustered in my analyses, suggesting that the origin of edaphic endemism has occurred on multiple occasions, including multiple examples of serpentine endemism. The second chapter of my dissertation uses soil chemistry data in combination with a more detailed examination of genetic variation in nitrate reductase to elucidate the evolution of a single edaphic endemic species.

Because species respond individually to climate change, understanding community assembly requires examination of multiple species from a diversity of forest niches. I present the post-glacial phylogeographic history of an understory, parasitic herb (Epifagus virginiana, beechdrop) that has an obligate and host specific relationship with a common eastern North American hardwood tree (Fagus grandifolia, American beech). The migration histories of the host and parasite are compared to elucidate potential limits on the parasite's range and to understand their responses to shared climate change. Two chloroplast DNA regions were sequenced and 9 microsatellite loci genotyped from parasite specimens collected throughout the host's range. These data were compared with available cpDNA sequences from the host (McLachlan et al. 2005) and host fossil pollen records from the last 21,000 years (Williams et al. 2004). Analyses of genetic diversity reveal high population differentiation in the parasite's southern range, a possible result of long term isolation within multiple southern glacial refuges. Estimates of migration rates and divergence times using Bayesian coalescent methods show the parasite initiating its post-glacial range expansion by migrating northward into the northeast from southern areas, then westward into the midwest, a pattern consistent with the development of high density beech forests. This result is strongly confirmed through spatial linear regression models, which show host density plays a significant role in structuring parasite populations, while the initial migration routes of the host are irrelevant to parasite colonization patterns. Host density is then used as a proxy for the parasite's habitat quality in an effort to identify the geographic locations of its migration corridors. Habitat cost models are parameterized through use of the parasite's genetic data, and landscape path analyses based on the habitat map show a major migration corridor south of the Great Lakes connecting the northeast and midwest. Host density was the major determinant controlling the parasite's range expansion, suggesting a lag time between host and parasite colonization of new territory. Parasites and other highly specialized species may generally migrate slower due to their complex landscape requirements, resulting in disassociation of forest assemblages during these times. From these results, the low migration capacities of highly specialized species may be insufficient to outrun extirpation from their current ranges.

It is increasingly evident that evolutionary processes play a role in how ecological communities are assembled. However the extend to which evolution influences how plants respond to spatial and environmental gradients and interact with each other is less clear. In this dissertation I leverage evolutionary tools and thinking to understand how space and environment affect community composition and patterns of gene flow in a unique system of Atlantic rainforest and restinga (sandy coastal plains) habitats in Southeastern Brazil.

In chapter one I investigate how space and environment affect the population genetic structure and gene flow of Aechmea nudicaulis, a bromeliad species that co-occurs in forest and restinga habitats. I genotyped seven microsatellite loci and sequenced one chloroplast DNA region for individuals collected in 7 pairs of forest / restinga sites. Bayesian genetic clustering analyses show that populations of A. nudicaulis are geographically structured in northern and southern populations, a pattern consistent with broader scale phylogeographic dynamics of the Atlantic rainforest. On the other hand, explicit migration models based on the coalescent estimate that inter-habitat gene flow is less common than gene flow between populations in the same habitat type, despite their geographic discontinuity. I conclude that there is evidence for repeated colonization of the restingas from forest populations even though the steep environmental gradient between habitats is a stronger barrier to gene flow than geographic distance.

In chapter two I use data on 2800 individual plants finely mapped in a restinga plot and on first-year survival of 500 seedlings to understand the roles of phylogeny, functional traits and abiotic conditions in the spatial structuring of that community. I demonstrate that phylogeny is a poor predictor of functional traits in and that convergence in these traits is pervasive. In general, the community is not phylogenetically structured, with at best 14% of the plots deviating significantly from the null model. The functional traits SLA, leaf dry matter content (LDMC), and maximum height also showed no clear pattern of spatial structuring. On the other hand, leaf area is strongly overdispersed across all spatial scales. Although leaf area overdispersion would be generally taken as evidence of competition, I argue that interpretation is probably misleading. Finally, I show that seedling survival is dramatically increased when they grow shaded by an adult individual, suggesting that seedlings are being facilitated. Phylogenetic distance to their adult neighbor has no influence on rates of survival though. Taken together, these results indicate that phylogeny has very limited influence on the fine scale assembly of restinga communities.

*Designated as an exemplary master's project for 2015-16*