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Abstract Detail

Speciation Mechanisms in Plants

Sianta, Shelley [1], Kay, Kathleen [2].

The roles of fitness trade-offs and habitat isolation in speciation via ecological divergence.

Ecological divergence has long been posited as a driver of speciation. Yet, speciation is not the only evolutionary outcome of ecological divergence, as evidenced by species composed of locally-adapted ecotypes. The probability of speciation via ecological divergence may increase when adaptation to one habitat comes with fitness trade-offs in another habitat, which reduces gene flow through habitat isolation. However, it is unclear how often fitness trade-offs and habitat isolation accompany local adaptation, what selective factors drive fitness trade-offs and if they are associated with speciation. Here, we used replicates of parallel ecological divergence across soil types in the California serpentine flora to ask whether speciation in this system is associated with strong fitness trade-offs and habitat isolation. Adaptation to serpentine soils is associated with the evolution of new serpentine endemic species and the evolution of ecotypes within tolerator species. We formed serpentine-nonserpentine sister taxa pairs from 8 serpentine endemic species (between-species pairs) and 9 serpentine tolerator species (within-species pairs), and performed greenhouse-based reciprocal transplants in field soil to quantify soil-mediated habitat isolation. Moreover, we test a classic hypothesis in the serpentine literature that serpentine adaptation comes with larger fitness trade-offs in competitive ability, rendering serpentine taxa unfit in more productive nonserpentine habitats, for endemics species than for serpentine tolerator species. We find that soil-mediated habitat isolation is greatest in serpentine soil, and that while there is more variation in habitat isolation among within-species sister taxa pairs than among between-species sister taxa pairs, the overall magnitude of habitat isolation in serpentine soils does not differ between within- vs between-species pairs. There is little evidence for habitat isolation across all pairs in nonserpentine soil, suggesting serpentine-adapted taxa do not experience soil-mediated fitness trade-offs. However, we do find evidence that serpentine endemic species have incurred greater losses in competitive ability than serpentine tolerator species, which is the first multi-species experimental evidence that supports trade-offs between serpentine adaptation and competitive ability. Greater trade-offs in endemic lineages may have caused and/or currently maintain reproductive isolation by preventing serpentine-adapted individuals from migrating through productive nonserpentine habitat.

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1 - University of Minnesota, Plant and Microbial Biology, St. Paul, MN, 55108, USA
2 - University of California - Santa Cruz, CA

Reproductive Isolation
local adaptation
competitive ability.

Presentation Type: Colloquium Presentations
Session: C09, Speciation Mechanisms in Plants
Location: /
Date: Thursday, July 22nd, 2021
Time: 3:00 PM(EDT)
Number: C09006
Abstract ID:116
Candidate for Awards:None

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