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Professional Interests - Publications - Contact Information - Lab Personnel Professional Interests of Tia-Lynn Ashman
Publication
Archive Recent Publications of Tia-Lynn Ashman
Steets, J.A., D.E. Wolf, J.R. Auld, and T.-L. Ashman (2007) The role of natural enemies in the expression and evolution of mixed mating in hermaphrodite plants and animals. Evolution 61:2043-2055 How to Contact Tia-Lynn Ashman
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Why are some plants male or female whereas others are both? Why are some flowers showy and fragrant while others are plain and faintly scented? Why do some flowers live for months and others live for only a few hours? The research in my lab aims to address these, and other questions by studying the evolution of separate sexes and floral phenotype within the general constructs provided by life history and sex allocation theories, and by integrating the study of plant-animal interactions (e.g., pollination and herbivory), physiological and chemical ecology with quantitative genetics and evolutionary biology.
What conditions generate selection for males in gynodioecious populations?
One main objective is to determine the conditions necessary for hermaphrodites of gynodioecious species to be selected to become more male, i.e. the conditions that facilitate the "second step" in the evolution of dioecy. Our work and that of others suggest that maleness may be favored when females are frequent and soil resources are scarce. In a collaboration with Dr. Mary Ashley at UIC, we are testing the hypothesis that certain ecological contexts intensify selection for maleness of hermaphrodites by manipulating female frequency and resource availability in arrays of plants and then quantifying phenotypic selection on pollen production, and other male traits, directly with the aid of microsatellite DNA markers to determine male fitness. This work will be the first to provide not only an understanding of the selective dynamics of the gynodioecy-dioecy transition, but also the first to directly address theory-based predictions regarding the environmental causes of selection for maleness.
What are the constraints on the evolution of males from hermaphrodites?
A second goal of our research has been to assess the universality of genetic constraint imposed on the independent evolution of sexual phenotype and determine if constraints differ under different selective regimes (i.e., female frequencies), as well as to rigorously test the genetic assumptions of sex allocation theory under field conditions. We have revealed broad-sense heritability for male and female traits of hermaphrodites, as well as, a negative genetic correlation between pollen production and fruit setting ability, and thus have verified basic assumptions of sex allocation theory. We are now in the process of determining the degree of narrow sense genetic variation and genetic correlation between sexual traits shared by the sex morphs (e.g., ovule number and fruit set) in populations of wild strawberry that differ in their female frequency, and thus represent different stages along the gynodioecy-dioecy continuum.
What role do enemies play in the evolution of males from hermaphrodites?
Recently, our research has turned to a little explored aspect of the environmental context for the evolution of dioecy, that is, the enemy dimension of the environment. Herbivory in dimorphic species can be profoundly male-biased, and we are exploring whether herbivores hold the key to why traditional explanations for breeding system variation sometimes fall short. We are using the wild strawberry and it's flower bud-clipping herbivore (Anthonomous signatus) as a model system to explore several novel hypotheses as to how male-biased herbivory may impede the transition from gynodioecy to dioecy. Ultimately, we aim to expand our understanding of the environmental context for the evolution of dioecy beyond abiotic attributes and mutualists to include enemies.
How and when does sexual dimorphism in attractive traits evolve?
While it is well established that male plants are more attractive (i.e., have larger flowers and more of them) than female plants, it is not clear how this sexual dimorphism comes about. Traditionally, pollinator-mediated selection that acts differently through male and female fitness has been invoked to explain sexual dimorphism. To begin to understand the role that pollinator behavior plays in the evolution of attractive traits (petal and stamen size) in F. virginiana my lab has conducted a set of interrelated experiments in which we manipulated several aspects of flower phenotype, sex ratio, and pollinator fauna and then measured plant fitness response. Our results indicate that 1) a whole suite of characters contribute to the greater attractiveness (to pollinators) of hermaphrodite flowers relative to female flowers, 2) only certain conditions generate male-biased selection, and thus could lead to selection-driven male-biased petal size dimorphism, 3) flexible pollinator foraging may be an important mechanism by which sex ratio influences selection on attractive traits, 4) variation in sex ratio could limit the evolution of sexual dimorphism, and/or could maintain genetic variation in attractive traits. In addition, results from quantitative genetic experiments suggest that the sex morphs may not be equally capable of responding to selection. We are currently extending this line of inquiry to whole plant traits and to directly measure male fitness to get the first glimpse at how sexual dimorphism and gender coevolve.
Why are some flowers not very fragrant?
Recently our lab has begun to explore how herbivores and pollinators respond to variation in floral odor in a collaboration with Dr. Robert Raguso at USC. We are determining the role of floral and pollen scent in bringing about sex differences in attractiveness of strawberry flowers to herbivores (clipper weevils) and pollinators by offering fragrance enhanced artificial flowers, natural buds and flowers to insects and quantifying their responses. We aim to determine if strawberry floral fragrance is under opposing selection pressures through pollinators and herbivores, and if this is why they are so weakly scented.
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