Biochemistry
R. Bentley
J. Brodsky
J. Franzen
P. Grabowski
J. Hempel
L. Jen-Jacobson
K. Kiselyov
C. Peebles
J. Rosenberg
A. Schwacha

Cell Biology
J. Brodsky
A. Chung
J. Hildebrand
L. Jacobson
N. Kaufmann
K. Kiselyov
J. Pipas
M.-T. Sáens-Robles
W. Saunders
C. Walsh

Computational Biology
M. Grabe
J. Lawrence
J. Rosenberg

Developmental Biology
G. Campbell
D. Chapman
J. Hildebrand
B. Roman
S. Shostak
B. Stronach
V. Twombly

Ecology
T.-L. Ashman
W. Carson
W. Coffman
S. Kalisz
T. Katzner
R. Relyea
S. Tonsor
B. Traw

Evolution
T.-L. Ashman
A. Bledsoe
S. Kalisz
J. Lawrence
Z.-X. Luo
R. Relyea
S. Shostak
S. Tonsor
B. Traw

Genetics
K. Arndt
T.-L. Ashman
G. Campbell
D. Chapman
G. Hatfull
J. Hildebrand
L. Jacobson
S. Kalisz
J. Martens
W. Saunders
B. Stronach
S. Tonsor
R. Wood

Microbiology
J. Boyle
G. Hatfull
R. Hendrix
J. Lawrence
J. Pipas
M. Popa
R.L. Duda
S. Godfrey
V. Oke

Molecular Biology
K. Arndt
J. Franzen
P. Grabowski
G. Hatfull
R. Hendrix
L. Jen-Jacobson
J. Martens
C. Peebles
J. Pipas
J. Rosenberg
A. Schwacha
C. Walsh

Plant Biology
T.-L. Ashman
W. Carson
S. Kalisz
V. Oke
C. Partanen
S. Tonsor
B. Traw

Science Education
A. Bledsoe
K. Curto
L. Daniels
S. Godfrey
N. Kaufmann
C. LaFave
J. Newman
E. Polinko
M. Popa
L. Roberts
T. Seiflein
R. Sherwin
A. Slinskey Legg

Structural Biology
M. Grabe
J. Hempel
R. Hendrix
L. Jen-Jacobson
J. Rosenberg
A. VanDemark

Former Faculty

Professional Interests - Publications - Contact Information - Lab Personnel

Professional Interests of Tia-Lynn Ashman

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.

Currently, a major focus of the lab is addressing a question that has intrigued evolutionary biologists since Darwin, that is, how separate sexes (dioecy) evolved from combined sexed ancestors (hermaphrodites). We still don't have a complete picture of how this transition occurs, but an intensively modeled theory predicts that populations with females and hermaphrodites are an intermediate step to dioecy. We aim to go beyond description of reproductive variation to comprehensively evaluate the roles of adaptation and constraint in the evolution of separate sexes and sexual dimorphism using wild strawberry (Fragaria virginiana) and a quantitative genetic model as a framework for this research.

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. A common theme of the research in my lab is to determine how the floral phenotype is shaped by selection through pollinators, herbivores and/or the abiotic environment. We often explore this in the context of sexual dimorphism because the sex morphs provide an elegant natural comparison. However, we are also interested in evolution of floral variation in general, and in terms of less well-studied characters, such as floral fragrance and longevity.

Why are some flowers showy and fragrant while others are plain and faintly scented? Our lab is exploring how herbivores and pollinators respond to variation in floral odor in collaboration with Dr. Robert Raguso at Cornell University. 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. 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. With Dr. Cassie Majetic we are determining whether floral color and scent are biochemically linked as well as which is more important for fitness-- color or odor in Hespersis and Ipomea, among other species. Here we aim to determine whether floral-color odor associations are the product of correlational selection or genetic constraint. How long should flowers live? An on-going interest in the lab is the evolution of flower longevity. We have, in collaboration with Dr. Daniel Schoen at McGill University, studied the adaptive significance of flower life time. This work has shown that the optimal flower longevity of a species or population reflects the balance between the relative cost of flower construction and maintenance, and the accrual rates of pollen deposition and removal.

How does biodiversity affect pollination? We have had a long-standing interest in plant pollinator interactions and understanding what factors influence pollination sufficiency. In collaboration with several scientists our lab has been involved in understanding the causes and consequences of pollen limitation of plant reproduction, including the evolutionary response to and demographic consequences of limited pollination. Recently our interests have turned to the importance of plant-plant-pollinator interactions, and how community composition and diversity can affect pollen sufficiency. Current work centers on the role of quality versus quantity limitation in creating the positive relationship between species richness and pollen limitation, and we are especially interested in the role of endemism in pollen limitation in biodiversity hotspots. This work is in conjunction with Drs. Conchita Alonso, Jana Vamosi and Pitt Alumnae Drs. Tiffany Knight and Janette Steets.

Publication Archive
64 Citations
48 Abstracts
53 PDFs

Recent Publications of Tia-Lynn Ashman

Alonso, C., J. Vamosi, T.M. Knight, J. Steets, and T.-L. Ashman (2010) Is reproduction of endemic plant species particularly pollen limited in biodiversity hotspots? Oikos :In Press

Rohde, A.S., and T.-L. Ashman (2010) The effects of florivory and inbreeding on reproduction in hermaphrodites of the wild strawberry, Fragaria virginiana. Int. J. Plant Sci. :In Press

Case, A.L., and T.-L. Ashman (2009) Resources and pollinators contribute to population sex ratio bias and pollen limitation in gynodioecious wild strawberry (Fragaria virginiana). Oikos 118:1250-1260 (PDF Reprint: 226 kb)

Burd, M., T.-L. Ashman, D.R. Campbell, M.R. Dudash, M.O. Johnson, T.M. Knight, S.J. Mazer, R.J. Mitchell, J.A. Steets, and J.C. Vamosi (2009) Ovule number per flower in a world of unpredictable pollination. Am. J. Bot. 96:1159-1167 (PDF Reprint: 539 kb)

Ashman, T.-L. (2009) Sniffing out patterns of sexual dimorphism in floral scent. Functional Ecol. 23:852-862 (PDF Reprint: 171 kb)

Majetic, C.J., R. Raguso, and T.-L. Ashman (2009) Sources of floral scent variation: can environment define floral scent phenotype? Plant Signaling Behav. 4:129-131

Majetic, C.J., R. Raguso, and T.-L. Ashman (2009) The sweet smell of success: Floral scent affects pollinator attraction and seed fitness in Hesperis matronalis (Brassicaceae). Functional Ecol. 3:480-487 (PDF Reprint: 377 kb)

Majetic, C.J., R. Raguso, and T.-L. Ashman (2008) The impact of biochemistry vs. population membership on floral scent profiles in colour polymorphic Hesperis matronalis. Ann. Bot. 102:911-922 (PDF Reprint: 265 kb)

Botham, R., C.L. Collin, and T.-L. Ashman (2008) Plant-mycorrhizal fungal interactions affect inbreeding depression in wild strawberry. Int. J. Bot. 170:143-150 (PDF Reprint: 310 kb)

Penet, L., C.L. Collin, and T.-L. Ashman (2008) Florivory increases selfing: an experimental study in the wild strawberry, Fragaria virginiana. Plant Biol. 11:38-45 (PDF Reprint: 100 kb)

Spigler, R.B., K.S. Lewers, D. Main, and T.-L. Ashman (2008) Genetic mapping of sex determination in a wild strawberry, Fragaria virginiana reveals earliest form of sex chromosome. Heredity 2008:1-11 (PDF Reprint: 199 kb)

Quesada-Aguilar, A., S. Kalisz, and T.-L. Ashman (2008) Flower morphology and pollinator dynamics in Solanum carolinense L (Solanaceae): implications for the evolution of andromonoecy. Am. J. Bot. 95:1-11 (PDF Reprint: 935 kb)

Matchell, R.M., and T.-L. Ashman (2008) Invited Commentary: Predicting the evolutionary consequences of pollinator declines: the long and short of floral evolution. New Phytol. 177:576-579 (PDF Reprint: 204 kb)

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 (PDF Reprint: 148 kb)

Steets, J.A., T.M. Knight, and T.-L. Ashman (2007) The interactive effects of herbivory and mixed mating for the population dynamics of Impatiens capensis. Am. Nat. 170:113-127 (PDF Reprint: 401 kb)

How to Contact Tia-Lynn Ashman

 
This Site is maintained by the Bioscience Webmaster; this page was last modified 19 January 2010