Abstract Detail

Anatomy and Morphology

Humphrey, Rebecca [1], Ossip-Drahos, Alison [2].

Selection imposed by pollination mode minimally influences evolution of pollen morphology in Thalictrum (Ranunculaceae).

The evolutionary implications of interactions between pollen grains and their environment are not fully resolved. Pollen grain morphology varies widely among angiosperms, and both pollination and fertilization success vary with aperture number and pollen grain size. As such, pollen transmission conditions may exert specific selective pressures on pollen morphology. This study examines the hypothesis that evolutionary shifts in pollen grain size and aperture number are correlated with transitions from insect to wind pollination systems. Within the genus Thalictrum (Ranunculaceae), we use phylogenetic comparative methods to examine correlated evolution between pollen morphology (grain size and aperture number), the selective context of pollination mode, and the species-level traits of sexual system and geographic origin. Additionally, we calculate phylogenetic heritabilities of pollen traits and test phylogenetic correlations between them. The selective context of pollination mode explained only a small amount of the variation in pollen grain size and aperture number. Pollen grain size shows high phylogenetic heritability and marginally lower variation within wind-pollinated species relative to insect-pollinated species. The calculated optimum aperture number was greater for insect-pollinated species than wind-pollinated species. Consistent with previous work, we find a high phylogenetic heritability for pollination mode, sexual system, and geographic origin in a pruned phylogeny. Differences in calculated optima for aperture-number and coefficient of variation in size between pollination modes correspond to predictions related to pollen-competition intensity and the constraints of pollen transmission. However, the effect of pollination mode on evolution of aperture number and grain size within Thalictrum is small. Additional study is required to fully understand these selective pressures and outcomes.

1 - Aquinas College, Biology, 1700 Fulton St. E, Grand Rapids, MI, 49506, United States
2 - Middle Georgia State University, Department of Natural Sciences, 100 College Station Drive, Macon, GA, 31206, USA

Phylogenetic Comparative Methods
pollen grain size
pollen aperture number
pollen heteromorphism

Presentation Type: Poster
Number: PAM004
Abstract ID:243
Candidate for Awards:None

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