Abstract Detail

Molecular Ecology

Wenzell, Katherine [1], McDonnell, Angela [2], Fant, Jeremie [3], Skogen, Krissa [4].

Variation in floral traits across taxonomic and geographic scales as a model for species divergence in Castilleja.

Across their distributions, species are thought to remain cohesive through shared selection and gene flow. These processes may fracture at wide geographic scales, allowing for divergence and speciation. Yet, examples of widespread, cohesive species and narrow, recently diverged species challenge these expectations. In such cases, variable reproductive traits may constitute isolating barriers, warranting examination. Here, we investigate species cohesion and divergence via population-level floral trait variation in a group of recently diverged Castilleja. We characterized variation in eight floral traits in 26 populations of two focal groups within Castilleja: the widespread C. sessiliflora and the three species of the more restricted C. purpurea complex. Using target enrichment enabled by the Angiosperms353 probe set, we investigated evolutionary relationships among populations. We then compared geographic and evolutionary distance as predictors of floral trait distance. Our findings suggest a similar degree of floral trait variation within C. sessiliflora as in the three C. purpurea complex species combined. Whereas the C. purpurea species are clearly delineated by floral traits across narrow clines, C. sessiliflora demonstrates intergradation across its range. While evolutionary distance varied relative to expectations, geographic distance poorly predicted floral trait distance between species, implying species boundaries are maintained despite introgression. In conclusion, we identified a pattern of cohesion across a wide distribution (C. sessiliflora) and divergence across narrow ranges (the C. purpurea complex), whereby taxonomy and evolutionary history shape floral traits more than geography alone, even in a recently radiated genus known for hybridization. Nonetheless, floral traits vary throughout the range of C. sessiliflora, particularly in the south, suggesting local selection on floral traits combined with widespread gene flow. Our approach combines trait variation among populations with a robust understanding of their evolutionary history to gain insight into the evolutionary ecology of how species arise and are maintained across landscapes.

1 - Northwestern University and Chicago Botanic Garden, Plant Science Center, Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, Illinois, 60022, United States
2 - Chicago Botanic Garden, Science Dept., 1000 Lake Cook Road, Glencoe, IL, 60022, United States
3 - Chicago Botanic Gardens, Plant Biology And Conservation , 1000 Lake Cook Rd, Glencoe, IL, 60022, United States
4 - 1000 Lake Cook Road, Glencoe, IL, 60022, United States

Keywords:
polymorphic traits
geographic cline
species boundaries
instraspecific variation
gene flow
Natural Selection.

Presentation Type: Oral Paper
Session: MOL1, Molecular Ecology
Location: Virtual/Virtual
Date: Tuesday, July 28th, 2020
Time: 1:45 PM
Number: MOL1006
Abstract ID:349
Candidate for Awards:None