Post Doctoral Fellow, with Loren Rieseberg,
Dept. of Botany
, Univ. of British Columbia, Canada



  B.Sc. Hon. Biology &

  Computing Science

(1997-2001) Queen’s University, Canada. Thesis title (Biology): The relative roles of propagule pressure and environmental factors in the invasion of purple loosestrife (Lythrum salicaria).
Thesis title (Computing Science): Application of COM (component object model) software engineering principles to statistical analysis of biological data.

  M. Sc. Biology


(2001-2004) Queen’s University, Canada. Thesis title: Geographical perspective on the reproductive ecology and genetics of peripheral populations for a federally listed plant, Vaccinium stamineum (deerberry).

  Ph. D.

Botany (2012) University of Toronto, Canada. Thesis title: The maintenance of two sexual systems, monoecy and dioecy, in Sagittaria latifolia


Current Position

Ph.D. student, Professor Barrett's lab,
Department of Ecology and Evolutionary Biology, University of Toronto

Sagittaria pic





I am interested in understanding the processes that maintain diverse mating strategies in the aquatic perennial, Sagittaria latifolia (Alismataceae). Sagittaria latifolia exhibits three sex phenotypes including female, male, and hermaphrodite. These phenotypes occur in populations as two sexual systems: monoecious (combined sex; hermaphrodites) and dioecious (separate sex; females and males) populations (Figure 1a) that occur in divergent ecological habitats, and are associated with differentiated life history strategies. Monoecious populations tend to occur in open, disturbed habitat, while dioecious populations tend to occur in more competitive, stable wetland habitat. In turn, monoecious plants are small but invest more in reproduction and flower earlier relative to dioecious plants (Dorken and Barrett 2003). The two sexual systems often occur in populations of close geographic proximity, yet remain distinct.
Thus, my thesis research focuses on two fundamental questions concerned with gender strategies in plants: (1) What are the contemporary ecological and genetic mechanisms maintaining two distinct sexual systems in S. latifolia? (2) Are there conditions under which the ecological isolation of two sexual systems breaks down? Investigation of natural variation of the ecological and genetic context under which combined vs. separate sexes occur should allow inference of the costs and benefits associated with each strategy. I will also use experimental field manipulations and molecular genetic techniques to understand the processes underlying the distribution of sex phenotypes within and among populations.

  1. Mechanisms of reproductive isolation


Ecological variation is thought to drive processes of evolution. In the case of S. latifolia, ecological factors associated with two sexual systems exhibiting different life history strategies seem likely to maintain the isolation of the two systems. I will test the hypothesis that divergent selection has occurred among populations, and also promotes reproductive isolation (Schluter 2001). Because monoecious and dioecious individuals are completely inter-fertile, the two sexual systems may remain distinct through: (1) Pre-zygotic isolation in the form of reduced survival of immigrants occurring in the ‘wrong’ habitat, and/or (2) Post-zygotic isolation either in the form of intrinsic genetic incompatibilities expressed in hybrids, or reduced hybrid fitness in either parental environment. I will identify these pre- and post-zygotic mechanisms of reproductive isolation by conducting a transplant experiment that involves (1) comparison of relative performance in reciprocal transplants of dioecious individuals into monoecious habitats, and monoecious individuals into dioecious habitats, and (2) comparison of performance between transplants of parents and hybrids (between pairs of monoecious and dioecious populations).

  2. Evolution of sex-ratio in a geographic context


Although monoecy and dioecy typically occur in ecologically isolated populations, there exists variation in the distribution of three sex phenotypes (female, male, hermaphrodite) above and beyond what is expected from size-dependent gender variation (Figure 1b). For example, in Ontario NE of the Lake Ontario, many populations display deviations from these patterns. Because variation in sex-ratio changes the way each sex gains fitness, this natural variation provides a unique opportunity to study the dynamics of sex-ratio evolution. I will use the following approaches to investigate sex-ratio variation: (1) Revealing the origin of high-frequency hermaphrodites in dioecious populations could be particularly informative for understanding sex-ratio variation. I will distinguish between the hybridization vs. sex-inconstancy hypothesis (Figure 1c) using molecular markers. (2) I will investigate the role of clonal structure in causing sex-ratio variation by comparing the ramet vs. genet level sex-ratios of populations. I will estimate clone sizes for females, males, and hermaphrodites using AFLP markers. (3) Variation in sex ratio provides an interesting context in which to study the evolution of sexual dimorphism. In collaboration with Melanie Glaettli (postdoctoral fellow), I will investigate whether low-female-frequency populations are associated with exaggerated floral dimorphism due to increased male competition for female flowers.


  • Charlesworth, B. & Charlesworth D. (1978). A model for the evolution of dioecy and gynodioecy. American Naturalist 112,975-997.
  • Dorken, M.E. & Barrett, S.C.H. (2003). Life-history differentiation and the maintenance of monoecy and dioecy in Sagittaria latifolia (Alismataceae). Evolution 57, 1973-1988.
  • Dorken, M.E. & Barrett, S.C.H. (2004). Sex determination and the evolution of dioecy from monoecy in Sagittaria latifolia (Alismataceae). Proceedings of the Royal Society of London B 271, 213-219.
  • Sarkissian, T.S., Barrett, S.C.H. & Harder L.D. (2001). Gender variation in Sagittaria latifolia (Alismataceae): is size all that matters? Ecology 82,360-373.
  • Schluter, D. (2001). Ecology and the origin of species. TREE 16, 372-380.


  1. Yakimowski, S.B., H. A. Hager, and C.G. Eckert. (2005) Limits and effects of invasion by the nonindigenous plant Lythrum salicaria (purple loosestrife): a seed bank analysis. Biological Invasions.7: 687-698.

  2. Yakimowski, S.B., and C.G. Eckert. Threatened peripheral populations in context: geographical variation in population frequency and size and sexual reproduction in a clonal woody shrub, Vaccinium stamineum (Ericaceae). Conservation Biology. 21: 811-822.

  3. Yakimowski, S.B. and C.G. Eckert. Analysis of variation in population genetic structure across the geographical range in a clonal, woody plant, Vaccinium stamineum (Ericaceae). New Phytologist 180: 534-544.

  4. Yakimowski, S.B., Rymer, P.D., Stone, H., Barrett, S.C.H., & Dorken, M.E. (2008). Isolation and characterization of 11 microsatellite markers from Sagittaria latifolia (Alismataceae). Molecular Ecology Resources

  5. Barrett, S.C.H., Yakimowski, S.B., Field, D.L., Pickup M. & Barrett S.C.H. (2010). Ecological genetics of sex ratios in plant populations. Philosophical Transactions of the Royal Society of London Ser. B. 365: 2549–2557. (pdf)


Yakimowski, S.B. and C.G. Eckert. Life on the edge – relating demography, population structure, and genetic structure in a broad geographic context. Ontario Ecology and Ethology Colloquium. Ottawa, ON. May, 2005.
Yakimowski, S.B. Life on the edge – a geographic perspective on the ecology and genetics of peripheral populations for conservation. Queen’s Ecological and Evolutionary Biology Seminar Series. Kingston, ON. January, 2004.

Yakimowski, S.B. & C.G. Eckert. Life on the edge – ecological & genetic properties of peripheral populations: conservation of Canadian species-at-risk, deerberry (Vaccinium stamineum). Science and Management of Protected Areas Association’s (SAMPAA) Conference. Victoria, BC. May, 2003.

Yakimowski, S.B. & C.G. Eckert. Geographic patterns of reproductive mode and population structure of a Canadian species-at-risk, Vaccinium stamineum (deerberry). Ontario Ecology and Ethology Colloquium. Kingston, ON. April, 2002.

Yakimowski, S.B., H.A. Hager, and C.G. Eckert. The role of propagule pressure in causing variation in the invasion of purple loosestrife within and between wetlands. Ontario Ecology and Ethology Conference (OEEC). Guelph, ON. May 2001.

Hager, H.A., S.B. Yakimowski, and C.G. Eckert. Spread and invasion of Lythrum salicaria (purple loosestrife): relative effects of seed supply and environmental factors. Ecological Society of America (ESA) conference. Madison, WI, USA. August 2001.



Field Research

Evolution of selfing in a geographic context (2004): Assistant for manipulative field experiment regarding the role of pollen and resource availability for selfing in Camissonia cheiranthifolia along the Californian coastal dune system.

Geographic surveys of invasive species (2001-2003): Surveying populations of invasive, aquatic species Lythrum salicaria (purple loosestrife) and Butomus umbellatus (flowering rush) throughout eastern N.A.

Research assistant (1998-1999): Research assistant for long-term research project on competitive interactions between prairie grass and shrub species (University of Regina, SK)

Rare Species and Conservation
Invited Talk (2004): ‘Rare species research’ to Conservation Biology class (Queen’s University).
Parks Canada Contract (2004): Prepared written document ‘Development Of Site Selection Criteria and Experimental Strategy for Re-introduction of Deerberry (Vaccinium stamineum)’

Graduate Teaching Assistant
Queen’s University, ON (2001-2002): Data Management and Analysis; Evolutionary Genetics
University of Toronto, ON (2005): Statistics for Biologists; Studies in Evolution, Ecology, and Behaviour