Environment and pollinator-mediated selection on parapatric floral races of Mimulus aurantiacus.
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.
Streisfeld
M A
MA
Section of Ecology, Behavior and Evolution, Division of Biological Sciences, University of California San Diego, La Jolla, CA , USA. mstreisf@duke.edu
Kohn
J R
JR
D000818:Animals; D001717:Birds / Q000502:physiology*; D002140:California; D003710:Demography; D017753:Ecosystem; D005247:Feeding Behavior / Q000502:physiology; D035264:Flowers / Q000502:physiology*; D016014:Linear Models; D032241:Mimulus / Q000235:genetics* / Q000254:growth & development; D009036:Moths / Q000502:physiology*; D010858:Pigmentation / Q000502:physiology; D011058:Pollen / Q000502:physiology; D011156:Population Density; D012641:Selection, Genetic; D013045:Species Specificity