|Title||Context-dependent concordance between physiological divergence and phenotypic selection in sister taxa with contrasting phenology and mating systems|
|Publication Type||Journal Article|
|Year of Publication||In Press|
|Authors||Mazer, Susan J., David J. Hunter, Alisa A. Hove, and Leah S. Dudley|
|Journal||American Journal of Botany|
|Keywords||adaptation, Clarkia, climate change; herbarium; herbarium specimens; pheno‐climatic models; phenological index; phenology, divergence, gas exchange, mating system evolution, phenology, phenotypic selection, water use efficiency|
PREMISE: The study of phenotypic divergence of, and selection on, functional traits in closely
41 related taxa provides the opportunity to detect the role of natural selection in driving
42 diversification. When selection in field populations differs between taxa in a pattern that is
43 consistent with the phenotypic difference between them, this provides evidence that natural
44 selection reinforces the divergence. Few studies have sought evidence for such concordance for
45 physiological traits.
47 METHODS: Herbarium specimen records were used to detect phenological differences between
48 sister taxa independent of the effects on flowering time of long-term variation in the climate
49 across collection sites. In the field, physiological divergence in photosynthetic rate, transpiration
50 rate, and instantaneous water use efficiency were recorded during vegetative growth and
51 flowering in 13 field populations of two taxon pairs of Clarkia, each comprised of a self52
pollinating and a outcrossing taxon.
54 RESULTS: Historically, each selfing taxon flowered earlier than its outcrossing sister taxon,
55 independent of the effects of local long-term climatic conditions. Sister taxa differed in all focal
56 traits, but the degree and (in one case) the direction of divergence depended on life stage. In
57 general, self-pollinating taxa exhibited higher gas exchange rates, consistent with their earlier
58 maturation. In 6 of 18 comparisons, patterns of selection were concordant with the phenotypic
59 divergence (or lack thereof) between sister taxa.
61 CONCLUSIONS: Patterns of selection on physiological traits measured in heterogeneous
62 conditions do not reliably reflect divergence between sister taxa, underscoring the need for
63 replicated studies of the direction of selection within and among taxa.
65 Keywords: adaptation, Clarkia, divergence, gas exchange, mating system evolution, phenology,
66 phenotypic selection, water use efficiency, climate.