Foliar and floral evolution in geographic context: Cryptic evolution in the mycoheterotrophic Pyrola picta species complex (Ericaceae).

摘要

The Pyrola picta species complex (Pyroleae: Monotropoideae: Ericaceae) contains four species that are loosely restricted to the temperate conifer and oak-conifer forest assemblages of montane western North America. The phylogenetic relationships and biogeographic histories among these closely related species, and the factors influencing reproductive isolation are poorly known. With this dissertation, reproductive isolation among species in the P. picta complex is examined from three different angles. First, hypotheses concerning the monophyly and morphological identification of a new species, Pyrola crypta Jolles, are addressed and a taxonomic key to identifying this species is provided. Second, morphometric and phenological analyses are used to test whether there is divergent selection (via buzz pollination) for micromorphological differences in floral morphology among species. Finally, phylogeny and ancestral character state estimation are used to test whether species in the P. picta complex likely evolved in sympatry or in allopatry, and whether cladogenetic events in this group were associated with dispersal into different climates. Several aspects of reproductive isolation in genus Pyrola and in the P. picta species complex are implied from these studies. Cryptic species, retaining features of ancestral morphology but genetically divergent, are likely more common than is currently accounted for in genus Pyrola. Subtle heterospecific differences in floral morphology are mainly concentrated in anther characteristics, which may influence how pollen is released during visitation by buzz-pollinating Bombus species. Divergent flowering phenologies among species in sympatry suggest that selection may be reinforcing reproductive isolation. Biogeographic inference suggests that speciation in the P. picta complex occurred in allopatry following dispersal from the Sierra Nevada and dispersal from cool, relatively dry climates to increasingly warm, mesic environments corresponded to cladogenic events. These studies corroborate the idea that the P. picta species complex is relatively young and that processes such as dispersal and subsequent geographic isolation during glacial and interglacial cycles may be responsible for both speciation and present-day hybridization. Findings of these studies are broadly applicable to species and species complexes associated with the montane, temperate conifer forest assemblage of western North America.