Abstract Detail

Ecology

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

The evolution of serpentine endemism is associated with adaptation to less competitive, but not chemically harsher, serpentine habitats.

Speciation driven by edaphic divergence is common in biodiversity hotspots like the California Floristic Province, but adaptation to edaphic habitats does not always lead to speciation. The serpentine flora of California is ideal to understand the process of speciation because in replicate instances adaptation to serpentine has either led to speciation (i.e., resulting in an endemic species restricted to serpentine) or hasn’t led to speciation (i.e., resulting in a tolerator species with populations on and off serpentine). Here, we hypothesize that adaptation to serpentine soils facilitates speciation when high costs are associated with adaptation, because selection against serpentine individuals in nonserpentine habitats will prevent gene flow between edaphic ecotypes. We predict that a trade-off in serpentine soil tolerance and competitive ability is associated with speciation of serpentine endemics. We compared soil chemistry and percent cover of bare ground (as a proxy for competitive ability) in serpentine habitats of 8 endemic species and 8 tolerator species to test the predictions that endemics adapt to more toxic serpentine soils and that endemics occur in less competitive habitats. Our results show that endemics occur in barer serpentine habitats than tolerators, suggesting that endemics are poorer competitors than tolerators, but we find no difference in the chemical harshness of serpentine soil in which endemics and tolerators occur. We then compared each of the 16 serpentine taxa with a nonserpentine sister taxon to ask whether adaptation to serpentine is accompanied by greater divergence in soil chemistry and/or a greater loss in competitive ability in endemic lineages than in tolerator lineages. In the majority of the sister taxa pairs the serpentine population occurred in barer habitats, suggesting that, in general, adaptation to serpentine is associated with occupying less competitive habitats. There is a marginally significant trend that endemic sister taxa have undergone more divergence in bare ground than tolerator sister taxa, indicating that the evolution of endemism may be associated with higher costs in competitive ability. However, we do not find any difference in the amount of soil divergence in endemic and tolerator pairs. The costs of serpentine adaptation in competitive ability may drive stronger habitat isolation, promoting speciation, in endemic lineages than in tolerator lineages.

1 - UC - Santa Cruz, Ecology And Evolutionary Biology, Kay Lab, 130 McAllister Way, Santa Cruz, CA, 95060, United States
2 - UC-Santa Cruz, Ecology and Evolutionary Biology, Coastal Biology Building, 130 McAllister Way, Santa Cruz, CA, 95060, USA

Keywords:
Speciation
edaphic adaptation
Endemism
competition
Serpentine.

Presentation Type: Oral Paper
Session: 7, Ecology Section - Community Interactions and Responses
Location: 106/Mayo Civic Center
Date: Monday, July 23rd, 2018
Time: 11:30 AM
Number: 7012
Abstract ID:1034
Candidate for Awards:Ecological Section Best Graduate Student Paper