Stephen G. Weller
Professor, Ecology & Evolutionary Biology
|Plant population biology and evolutionary genetics of plant reproductive systems|
|URL||lab web page|
Smithsonian Institution. Senior Mellon Fellow, 1993-1994.
McBryde Chair in Hawaiian Plant Sciences, National Tropical Botanical Garden, 1995-1998.
Chancellor’s Award for Distinguished Fostering of Undergraduate Research, 2008, University of California, Irvine.
Fellow, AAAS, 2009
William Evans Fellow, University of Otago, Dunedin, New Zealand, 2012
Self-fertilization in hermaphroditic plant species is avoided by a variety of breeding systems that promote outcrossing. My research interests focus on plant population biology and the evolutionary genetics of breeding systems leading to outcrossing. One widespread mechanism preventing self-fertilization is dioecy, the occurrence of separate sexes in populations. Genetic models predict that dioecy will evolve in populations when the product of the selfing rate and inbreeding depression (the loss of fitness that occurs when normally outcrossed individuals produce inbred offspring) is sufficiently high. To test this model, Ann K. Sakai and I are investigating the combined occurrence of inbreeding depression and selfing rates in a genus of Hawaiian plants (Schiedea) showing extensive variability in the expression of dioecy. Some species show only the initial stages in the evolution of dioecy, while in other species full or nearly full dioecy has evolved. Our tests for inbreeding depression are carried out in the greenhouse, where we also are raising progeny from naturally pollinated individuals in order to measure selfing rates under field conditions. Variation in allozymes scored with starch gel electrophoresis is used to assess the degree of selfing in populations.
In addition, we are testing the role of ecological factors in the evolution of dioecy. Shifts in resource allocation, habitat partitioning by sexes, and modifications of pollination syndromes have been proposed as important factors, and Schiedea species present excellent opportunities for investigating these phenomena because they occur in diverse habitats and may be wind or insect pollinated, depending on the species. Using information independent of the breeding system, we are assessing phylogenetic relationships in Schiedea. With this information we will be able to determine whether dioecy appeared on a single occasion or evolved repeatedly. We believe our comparative approach will provide one of the most complete analyses available for the evolution of dioecy.
I also am interested in the evolutionary genetics of self-incompatibility, where self-matings and matings among members of the same incompatibility group are prevented by a genetically controlled polymorphism. In heterostylous species self-incompatibility guarantees outcrossing; reciprocal floral morphology may promote cross-pollination among intercompatible floral morphs. Trimorphic incompatibility appears to be unstable over evolutionary time, and I am interested in the selective factors that have led to the breakdown of this reproductive system.
|Publications||Weber, J. J., S. G. Weller, A. K. Sakai, A. Nguyen, N. D. Tai, C. A. Domínguez, and F. E. Molina-Freaner. 2012. Purging of inbreeding depression within a population of Oxalis alpina (Oxalidaceae). American Journal of Botany 99: 923-932.|
|Baena-Díaz, F., J. Fornoni, P. Sosenski, F. E. Molina-Freaner, S. G. Weller, R. Pérez-Ishiwara, and C. A. Domínguez. 2012. Changes in reciprocal herkogamy during the tristyly-distyly transition in Oxalis alpina increase efficiency in pollen transfer. Journal of Evolutionary Biology 25: 574-583.|
|Wallace, L. E., T. M. Culley, S. G. Weller, A. K. Sakai, A. Kuenzi, T. Roy, W. L. Wagner, and M. Nepokroeff. 2011. Asymmetrical gene flow in a hybrid zone of Hawaiian Schiedea (Caryophyllaceae) species with contrasting mating systems. PLoS ONE 6: 1-12.|
|Vary, L., A. K. Sakai, and S. G. Weller. 2011. Morphological and functional sex expression in the Malagasy endemic, Tina striata (Sapindaceae). American J. Botany 98: 1040-1048|
|Kutaka, J. J., S. G. Weller, C. A. Domínguez, A. K. Sakai, F. E. Molina-Freaner, P. Sosenski, and J. Fornoni. 2011. Female and male mediation of incompatibility modifications during the tristyly-distyly transition in Oxalis alpina. International Journal of Plant Sciences 172: 644-654.|
|Willyard, A., L. E. Wallace, W. L. Wagner, S. G. Weller, A. K. Sakai, and M. Nepokroeff. 2011. Estimating the species tree for Hawaiian Schiedea (Caryophyllaceae) from multiple loci in the presence of reticulate evolution. Molecular Phylogenetics and Evolution 60: 29-48.|
|Campbell, D. R., S. G. Weller, A. K. Sakai, T. M. Culley, P. N. Dang, and A. K. Dunbar-Wallis. 2010. Genetic variation and covariation in floral allocation of two species of Schiedea with contrasting levels of sexual dimorphism. Evolution 65: 757-770.|
|Pérez-Alquicira, J., E. Martínez-Meyer, F. E. Molina-Freaner, D. Piñero, J. Rozas, S. G. Weller, and C. A. Domínguez. 2010. The role of historical factors and natural selection in the evolution of breeding systems of Oxalis alpina in the Sonoran desert ‘Sky Islands.’ Journal of Evolutionary Biology 23: 2163-2175.|
Sosenski, P., J. Fornoni, F. E. Molina-Freaner, S. G. Weller and C. A. Domínguez. 2010.
Changes in sexual organ reciprocity and phenotypic floral integration during the tristyly-distyly
transition in Oxalis alpina. New Phytologist: 185: 829-840.
|Weller, S. G., R. J. Cabin, D. H. Lorence, S. Perlman, K. Wood, T. Flynn, and A. K. Sakai. 2011. Alien plant invasions, introduced ungulates, and alternative states in a mesic forest in Hawaii. Restoration Ecology 19: 671-680.|
Weller, S. G. 2009. The different forms of flowers – what have we learned since Darwin?
Botanical Journal of the Linnean Society 160: 249-261.
Wallace, L. E., S. G. Weller, W. L. Wagner, A. K. Sakai, and M. Nepokroeff. 2009.
Phylogeographic patterns and demographic history of Schiedea globosa (Caryophyllaceae) on the
Hawaiian Islands. American Journal of Botany 96: 958-967.
|Sakai, A. K., Weller, S. G., Culley, T. M., Campbell, D. R., Dunbar-Wallis, A. K. and A. Andres. 2008. Sexual dimorphism and the genetic potential for evolution of sex allocation in the gynodioecious plant, Schiedea salicaria. Journal of Evolutionary Biology 21: 18-29.|
Weller, S. G., C. A. Domínguez, F. E. Molina-Freaner, J. Fornoni, and G. LeBuhn. 2007.
The evolution of distyly from tristyly in populations of Oxalis alpina in the Sky Islands of the Sonoran Desert. American Journal of Botany 94: 972-985.
|Weller, S. G., A. K. Sakai, T. M. Culley, D. R. Campbell, P. Ngo, and A. K. Dunbar-Wallis. 2007. Sexually dimorphic inflorescence traits in a wind-pollinated species: heritabilities and genetic correlations in Schiedea adamantis (Caryophyllaceae). American Journal of Botany 94: 1716-1725.|
|Sakai, A. K., Weller, S. G., Culley, T. M., Campbell, D. R., Dunbar-Wallis, A. K. and A. Andres. 2007. Sexual dimorphism and the genetic potential for evolution of sex allocation in the gynodioecious plant, Schiedea salicaria. Journal of Evolutionary Biology 21: 18-29.|
|Poulin, J., A. K. Sakai, S. G. Weller, and T. Nguyen. 2007. Phenotypic plasticity, precipitation, and invasiveness in the fire-promoting grass Pennisetum setaceum (Poaceae). American Journal of Botany 94: 533-541.|
|Sakai, A. K., S. G. Weller, W. L. Wagner, M. Nepokroeff, and T. M. Culley. 2006. Adaptive radiation and evolution of breeding systems in Schiedea (Caryophyllaceae), an endemic Hawaiian genus. Annals of the Missouri Botanical Garden 93: 49-63.|
|Weller, S. G., A. K. Sakai, D. R. Campbell, T. M. Culley, and A. Dunbar-Wallis. 2006. Predicting the pathway to wind pollination: heritabilities and genetic correlations of inflorescence traits associated with wind pollination in Schiedea salicaria (Caryophyllaceae). Journal of Evolutionary Biology 19: 331-342.|
|Wagner, W. L., S. G. Weller, and A. K. Sakai. 2005. Monograph of Schiedea (Caryophyllaceae subfam. Alsinoideae). Systematic Botany Monographs 72:1-169.|
|Weller, S. G. and A. K. Sakai. 2005. Selfing and resource allocation in Schiedea salicaria (Caryophyllaceae), a gynodioecious species. Journal of Evolutionary Biology 18: 301-308.|
|Poulin, J., S. G. Weller, and A. K. Sakai. 2005. Genetic factors affecting the invasiveness of fountain grass (Pennisetum setaceum) in Arizona, California, and Hawaii. Diversity and Distributions 11: 241-247.|
|Golonka, A., A. K. Sakai, and S. G. Weller. 2005. Evolution of wind pollination and sexual dimorphism: phenotypic changes in floral traits of Schiedea (Caryophyllaceae). American Journal of Botany 92: 1492-1502.|
|Weller, S. G., A. K. Sakai, D. A. Thai, J. Tom, and A. E. Rankin. 2005. Inbreeding depression and heterosis in populations of Schiedea viscosa, a highly selfing species. Journal of Evolutionary Biology 18: 1434-1444|
|Rankin, A. E., S. G. Weller, and A. K. Sakai. 2002. Mating system instability in Schiedea menziesii (Caryophyllaceae). Evolution 56: 1574-1585.|
|Culley, T. M., S. G. Weller, and A. K. Sakai. 2002. The evolution of wind pollination in angiosperms. Trends in Ecology & Evolution 17: 361-369.|
|Cabin, R. J., S. G. Weller, D. H. Lorence, S. Cordell, L. J. Hadway, R. Montgomery, D. Goo, and A. Urakami. 2002. Effects of light, alien grass, and native species additions on Hawaiian dry forest restoration. Ecological Applications 12:1595-1610.|
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