Abstract
Although hybridization in plants has been recognized as an important pathway in plant speciation, it may also affect the ecology and evolution of associated communities. Cottonwood species (Populus angustifolia and P. fremontii) and their naturally occurring hybrids are known to support different plant, animal, and microbial communities, but no studies have examined community structure within the context of phylogenetic history. Using a community composed of 199 arthropod species, we tested for differences in arthropod phylogenetic patterns within and among hybrid and parental tree types in a common garden. Three major patterns emerged. (1) Phylogenetic diversity (PD) was significantly different between arthropod communities on hybrids and Fremont cottonwood when pooled by tree type. (2) Mean phylogenetic distance (MPD) and net relatedness index (NRI) indicated that communities on hybrid trees were significantly more phylogenetically overdispersed than communities on either parental tree type. (3) Community distance (D pw) indicated that communities on hybrids were significantly different than parental species. Our results show that arthropod communities on parental and hybrid cottonwoods exhibit significantly different patterns of phylogenetic structure. This suggests that arthropod community assembly is driven, in part, by plant–arthropod interactions at the level of cottonwood tree type. We discuss potential hypotheses to explain the effect of plant genetic dissimilarity on arthropod phylogenetic community structure, including the role of competition and environmental filtering. Our findings suggest that cottonwood species and their hybrids function as evolutionarily significant units (ESUs) that affect the assembly and composition of associated arthropod communities and deserve high priority for conservation.
Highlights
Plant hybridization is believed to have played an important role in the diversification and speciation of many plant species (Hegarty & Hiscock, 2005; Mallet, 2007; Rieseberg, 1997)
Our analyses show that arthropod communities, when pooled by parental and hybrid tree type, differ with respect to mean phylogenetic distance (MPD), net relatedness index (NRI), and community distance (Dpw), as well as phylogenetic diversity (PD) between Fremont trees and hybrids
We found these patterns to be generally consistent across 4 years of arthropod community surveys, suggesting that community phylogenetic structure is a stable feature among parental and hybrid trees
Summary
Plant hybridization is believed to have played an important role in the diversification and speciation of many plant species (Hegarty & Hiscock, 2005; Mallet, 2007; Rieseberg, 1997). Abundance and species diversity in hybrids may not result in greater phylogenetic diversity or overdispersion, because hybrids may not provide an environment that selects for unique community phylogenetic structure We considered this parental–hybrid system an important test case for examining community phylogenetic patterns as they relate to arthropod colonization of cottonwoods, because hybrid trees are known to differ from their parental species in diverse functional traits ranging from phytochemistry (Rehill et al, 2006), phenology (Floate, Kearsley, & Whitham, 1993), architecture (Bailey et al, 2004), productivity (Lojewski et al, 2009), and soil carbon fluxes (Lojewski et al, 2012). We are aware of no studies that have examined how hybridization affects phylogenetic relationships of any one community and ours is the first to examine how hybridization impacts community phylogenetic structure in arthropods
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