Professor, Ecology & Evolutionary Biology
School of Biological Sciences

Plant population biology and evolutionary genetics of plant reproductive systems

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 have investigated 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. We have demonstrated in a number of species that the combined occurrence of high levels of self-fertilization and the expression of inbreeding depression favor the increase of females 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. We are also investigating native moths that visit many hermaphroditic species of Schiedea and contribute to outcrossing of these species.


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.

Sakai, A. K., S. G. Weller, W. Yang, S. Ching Harbin, T. Portner, G. Mansker, and M. Bruegmann. 2017. The intersection of basic research and conservation: a 30 year study of the Critically Endangered Schiedea adamantis (Caryophyllaceae) on Le‘ahi (Diamond Head Crater), Hawai‘i. Oryx: doi:10.1017/S0030605316001162

Weller, S. G., A. K. Sakai, D. R. Campbell, J. M. Powers, S. R. Peña, M. J. Keir, A. K. Loomis, S. M. Heintzman, and L. Weisenberger. 2017. An enigmatic Hawaiian moth is a missing link in the adaptive radiation of Schiedea. New Phytologist 213: 1533-1542.

Weller, S. G., A. K. Sakai, C. A. Lucas, J. J. Weber, C. A. Domínguez, and F. E. Molina-Freaner. 2015. Genetic basis of tristyly in tetraploid Oxalis alpina (Oxalidaceae). Botanical Journal of the Linnean Society 179: 308-318.

Weller, S.G., A. K. Sakai, T. Gray, J. J. Weber, O. V. Tsyusko, C. A. Domínguez, J. Fornoni, and F. E. Molina-Freaner. 2015. Variation in heterostylous breeding systems in neighboring populations of Oxalis alpina (Oxalidaceae). Plant Biology: doi:10.1111/plb.12340.

Weller, S. G., A. K. Sakai, T. M. Culley, L. Duong, and R. E. Danielson. 2014. Segregation of male sterility alleles across a species boundary. Journal of Evolutionary Biology 27: 429-436.

Weber, J. J., SD. G. Weller, A. K. Sakai, O. V. Tsyusko, T. C. Glenn, C. A. Domínguez, F. E. Molina-Freaner, J. Fornoni, M. Tran, N. Nguyen, K. Nguyen, L-K Tran, G. Joice, and E. Harding. 2013. The role of inbreeding depression and mating system in the evolution of heterostyly. Evolution 67: 2309-2322.

Sakai, A. K., S. G. Weller, D. R. Campbell, T. M. Culley, A. K. Dunbar-Wallis, and A. M. Andres. 2013. Measure for measure: comparing morphological and biomass traits for sex allocation in two gynodioecious species. American Journal of Botany 100: 1071-1082.

Weber, J. J., S. G. Weller, A. K. Sakai, L-Q Nguyen, and D. Khuu. 2013. Breeding system evolution in Oxalis alpina: asymmetrical expression of tristylous incompatibility. International Journal of Plant Sciences 174: 179-188.

Jürgens, Andreas, M. Bischoff, A. K. Sakai, and S. G. Weller. 2012. Floral scent of four Hawaiian Schiedea species (Caryophyllaceae). Biochemical Systematics and Ecology 45: 194-197.

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.

Sakai, A. K., S. G. Weller, W. Yang, S. Ching Harbin, T. Portner, G. Mansker, and M. Bruegmann. 2017. The intersection of basic research and conservation: a 30 year study of the Critically Endangered Schiedea adamantis (Caryophyllaceae) on Le‘ahi (Diamond Head Crater), Hawai‘i. Oryx: doi:10.1017/S0030605316001162

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.

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https://faculty.uci.edu/profile/?facultyId=2686

Last updated
04/21/2017