The Kalisz lab explores concepts and theories relating to the evolution, ecology and conservation of plants. We address a wide array of topics including the conditions that favor or maintain self-pollination, pollination ecology, mating barriers among and the biogeography of Collinsia, the role of enemies and mutualists on population demography, and the developmental genetics of floral symmetry and mating system. We work in a wide array of field sites locally in PA, OH, and WV including the University’s field station; the west coast including CA, WA, OR and CA; and the upper peninsula of MI. Most of our projects combine field, molecular, phylogenetic, experimental, and statistical approaches. The techniques we use depend on the questions we are asking, but range from field population or community studies of mutualistic effects of pollinators (Collinsia and Solanum) and mycorrhizal fungi (Ariseama, Polygonatum, Smilacina, Trillium); the negative effects of herbivores (Ariseama, Floerkia, Polygonatum, Sanguinaria, Smilacina, Trillium) and invaders (Alliaria, Microstegium), and their interactions; sex ratio theory (Ariseama); genetic studies in the greenhouse and growth chamber (Collinsia and Tonella); as well as studies on the molecular and developmental genetics of mating system and floral development (Antirrhinum and Collinsia).
- Mating System Evolution
- Herbivores and Invaders
- Evolution of Reproductive Isolation
- Sex Ratio Evolution
- Seed Dormancy
- Molecular Genetics of Floral Development
We are investigating phenotypic, genetic, and ecological factors that influence mating system evolution. In particular, we are testing the extent to which selfing is an evolutionary dead end, exploring the developmental and phenotypic correlates of autonomous selfing, and the role of the pollinator environment and inbreeding depression on the expression of selfing rate.
- Is selfing a dead-end? Conflicting hypotheses have been proposed to explain the evolution and maintenance of selfing strategies. One critical question is when outcrossing populations evolve to be selfing lineages, do they ultimately end in extinction? Or can outcrossing evolve from selfing across long-term evolutionary history? These questions remain unanswered. Resolving these issues is a primary goal of our research. We are focusing on the tribe Collinsieae, a diverse group of 23 self-compatible annual herbaceous species native to North America. In collaboration with Bruce Baldwin and Scott Armbruster, we have a well-resolved phylogeny based on the sequence variation in the nuclear gene CYCLOIDEA and ITS, ETS, cpDNA MK introns that provides a backbone for answering these questions. My lab has polymorphic microsatellite markers for all species in the genus. We are using these to estimate population level selfing rates for all species, and then map the mating system onto the phylogeny to test mating system evolution in this group. This project is collaborative with Bruce Baldwin and Scott Armbruster.
- Can selfing vs. outbreeding strategies be reliably identified by floral traits thought to correlate with selfing? Flower size, display size, the timing of autonomous self-pollination or floral longevity are often used as correlates of selfing rate. We have grown all 24 species of Collinsia to flowering in the University of Pittsburgh’s Greenhouse Complex. Coupling floral shape and size analyses with measurements of floral developmental traits, we are assessing the floral phenotypic correlates of selfing and outcrossing in the genus Collinisa. These mating system data are being correlated with floral trait data and mapped on the phylogeny.
- Under what ecological and genetic conditions does self-pollination evolve and create stable mixed mating? Pollination environment, population size, and the level of inbreeding depression can all influence the evolution of autonomous selfing. In a set of field experiments, we have shown that the average annual selfing rate increases when pollinator visitation rate is low in Collinsia verna populations. Surprisingly, these populations’ average inbreeding depression is also low. We are currently investigating family level inbreeding depression in this and other species to test the generality of this result.
A striking example of human-mediated environmental change is seen in the recent increase in white-tailed deer populations on a large regional scale. We have established long-term replicated deer exclosure and control plots at Trillium Trail Wildflower Reserve (left). Instead of just measuring abundance, we are directly quantifying the plant responses to intense deer pressure (both direct and indirect effects) by examining how deer alter the vital rates seven species in the herbaceous understory community using demographic analyses. Six native species are represented in our study including three perennial palatable species (Trillium erectum (below), Smilacina racemosa, Polygonatum biflorum, two unpalatable perennial species (Hydrophyllum virginianum and Arisaema triphyllum) and one annual species (Floerkia proserpinacoides). We have also included two invasive species in our study: Alliaria petiolata and Microstegium viminium. We are conducting life table response experimental analyses Elucidating plant responses is central to understanding the potential recovery, persistence and/or decline of plant species within their communities and of the communities themselves. Two key results are detailed below.
- Generalist herbivore facilitates invasion success:
Our recent analyses demonstrate that deer facilitate the population growth rate and invasion of the forest understory communities by Alliaria petiolata (right) in the control plots. Further, the exclusion of deer reverses this process. Population growth rate (lambda) of A. petiolata in the presence of deer is significantly higher than in the plots where deer are excluded. Our data provide the first empirical evidence that directly link deer with the demographic responses and invasive spread of A. petiolata in forest understory communities.
- Unpalatable native species decline in the presence of deer. Unpalatable species are predicted to increase in frequency or even replace palatable species in communities where generalist herbivore pressure is high. Surprisingly, we find that common unpalatable native perennial species have significantly declined in abundance and individual plant size in the deer access plots, in a magnitude similar to the negative effects observed for our focal palatable species. We are currently investigating the mechanistic basis of these declines including indirect effects of deer, effects of invaders or a combination of these factors.
Deer Access (control) Deer Excluded
Trillium Trail Wilflower Reserve is a 16-hectare Natural Area owned and stewarded by Fox Chapel Borough in Allegheny County, Pennsylvania. The spectacular bloom of spring ephemerals draws people from all over the region to experience its natural beauty. Fox Chapel Borough has been cooperating with our lab in our research on the effect of deer on plant populations since 1999. Lists of woody plant species and herbaceous plant species occuring at Trillium Trail, as of 2009.
Elucidating evolutionary processes that lead to the origin and maintenance of new species is of paramount importance for understanding the diversity of life on earth. Speciation, the process by which distinct lineages arise, is fundamentally related to the formation of isolating barriers. Thus better understand the process of speciation one must understand the evolution of isolating barriers. We are simultaneously testing two prominent hypotheses related to the evolution of isolating barriers among closely related species in a monophyletic group of annual plants, Collinsia. First, we are testing the Dobzhansky-Muller (D-M) model of speciation by asking if the strength of postzygotic isolation among species is positively correlated with divergence time. Second, because our analyses suggest that many Collinsia species diverged in allopatry, but are now found in sympatry, we are testing for reinforcement of reproductive barriers in sympatry. Specifically, we are asking if prezygotic isolating barriers are greater between sympatric species of Collinsia than between allopatric species.
Jack-in-the-pulpits have size-dependent gender expression, gender diphasy. As plants increase in biomass from year to year they express non-flowering, flowering-male, and flowering-female life stages, often taking several years to reach the female stage. In many of our research sites the growth environment is stressful enough that many Jack-in-the-pulpit individuals do not get large enough to become female, resulting in extremely male biased population sex-ratios and severely limiting potential for recruitment. This line of research seeks to determine the flexibility of gender allocation rules for a gender diphasic plant and measure the responsiveness of these rules to their environment.
Seed dormancy: My lab has a long-standing interest in the evolution of seed dormancy and the formation of natural soil seed banks. Models of the evolution of seed banks predict that the probability of a dormant seed dying in the soil should be positively correlated with the percent emerging and negatively correlated with the percent dormant. We have conducted a complex set of field and controlled environment studies using subsets of 24 populations to quantify correlations among these three seed fates (emerging, dormant and dead), to examine the size of the dormant seed bank in the field, and to quantify the broad-sense heritabilities (h2b ) of seed fates. Our experiments clearly indicate that phenotypic differences in seed fates that contribute to the variance in seed bank formation among populations and significant h2b for seed fates. Counter to expectations, correlations across populations showed that percent emergence was strongly and negatively correlated with percent dead while percent dormant was uncorrelated with percent dead. These correlations were highly consistent between the field and controlled environment experiments. These projects are collaborative with Mark McPeek and Denise Thiede.
We are exploring the role of genes in the floral symmetry gene network (FSGN) on stamen development and breeding system evolution. The floral symmetry gene networks affect both the shape and the development of male and female parts within flowers. Our preliminary results from Antirrhinum suggest that genes in the FSGN may also influence the timing of male and female phase expression with a flower. We are now using CYCLOIDEA as a candidate gene to conduct RT PCR expression and development studies in Collinsia. In addition, we are investigation CYCLOIDEA gene evolution and duplication in the genus Collinsia. These projects are collaborative with Tingshuang Yi and Lena Hileman.