“Artificial selection reveals high genetic variation in phenology at the trailing edge of a species range”

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Seema Nayan Sheth and Amy Lauren Angert

Plant populations with an edge on climate change

Scarlet monkeyflower (Mimulus cardinalis) near the southern range edge, Riverside County, California.
(© Seema Sheth)

How will species fare in the face of climate change? Can populations evolve rapidly enough to adapt in situ, or will they need to move across the landscape to track suitable conditions? Genetic variation is the raw material for evolution, so populations with less variation should have a harder time evolving in response to climatic changes compared to populations that are more genetically diverse. Adaptation to climate change often involves shifts in the timing of key events such as flowering. For example, as the climate warms, plant populations may need to flower earlier in the year to match the earlier onset of spring. In this study, Seema Sheth and Amy Angert compare genetic variation in flowering time among populations from the north, south, and center of the geographic range of the scarlet monkeyflower, a perennial herb that grows along seeps and streams from southern Oregon to northern Baja California. Populations near the borders of a species range might have more trouble adapting to new climates than populations at the center, as marginal populations are often small and inhabit the harshest environments.

When the authors grew plants from different populations together under controlled conditions, flowering time actually evolved far more rapidly in southern populations compared to central or northern edge populations. This result suggests that while the northern and central populations of the scarlet monkeyflower might have to rely on moving northward to track favorable conditions, the southern edge populations could stay put and adapt to changing conditions. Forecasts of how species will respond to climate change often ignore the potential for populations to adapt. Also, they typically assume that all populations of a species will respond in the same way. This study shows that while some populations can rapidly evolve in response to climate change, other populations may not be able to keep up with the pace of changing climate.