1. Environment and pollinator-mediated selection on parapatric floral races of Mimulus aurantiacus.
- Author
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Streisfeld MA and Kohn JR
- Subjects
- Animals, California, Feeding Behavior physiology, Linear Models, Mimulus growth & development, Pigmentation physiology, Pollen physiology, Population Density, Species Specificity, Birds physiology, Demography, Ecosystem, Flowers physiology, Mimulus genetics, Moths physiology, Selection, Genetic
- Abstract
We tested whether selection by pollinators could explain the parapatric distribution of coastal red- and inland yellow-flowered races of Mimulus aurantiacus (Phrymaceae) by examining visitation to natural and experimental populations. As a first step in evaluating whether indirect selection might explain floral divergence, we also tested for local adaptation in early life stages using a reciprocal transplant experiment. Hummingbirds visited flowers of each race at similar rates in natural populations but showed strong (>95%) preference for red flowers in all habitats in experimental arrays. Hawkmoths demonstrated nearly exclusive (>99% of visits) preference for yellow flowers and only visited in inland regions. Strong preferences for alternative floral forms support a direct role for pollinators in floral divergence. Despite these preferences, measures of plant performance across environments showed that red-flowered plants consistently survived better, grew larger and received more overall pollinator visits than yellow-flowered plants. Unmeasured components of fitness may favour the yellow race in inland habitats. Alternatively, we document a marked recent increase in inland hummingbird density that may have caused a change in the selective environment, favouring the eastward advance of red-flowered plants.
- Published
- 2007
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