Repeatability and genetic architecture of adaptive introgression: a long-term experimental evolution study in sunflowers NSF 1257965 (to K. Whitney; L.H. Rieseberg; 2013-2019; $690,237) How frequently, and under what conditions, does evolution repeat itself? When populations do independently evolve the same characteristics, are the underlying genetic changes similar or different? Advances in genetic techniques are finally allowing answers to these fundamental questions about the way evolution works. However, these issues have not yet been explored in hybridizing lineages, despite the fact that hybridization (mating and cross-fertilization between different species) is widespread in wild plants, animals, and fungi. This project examines replicate populations of experimental hybrid sunflowers which have been evolving in the field in Texas. Morphological and physiological measurements will determine whether they are converging or diverging in their traits, and new genetic sequencing techniques will be used to determine whether the genetic basis of the trait change is similar or different across the replicates. This research is the first to experimentally examine the repeatability of hybrid evolution and characterize its genetic architecture in the wild. It will answer fundamental questions about the way that evolution produces biodiversity, and has the potential to inform plant and animal breeding.
Effects of population genetic diversity on colonization success NSF 1146203 (to S. Hovick and K. Whitney; 2/2012 - 1/2015; $310,822) Colonization is a critical process that affects both short-and long-term population dynamics and sets the stage for future evolutionary change. Colonization success is affected by many factors, among the most important of which is propagule number. However, propagule number is highly correlated with genetic diversity because introducing more propagules generally samples the source gene pool more completely. Theoretical considerations suggest that increased genetic diversity should enhance colonization success independently of propagule number, yet few experiments have investigated this issue and only one field study has decoupled propagule number from genetic diversity. The proposed research will assess the extent to which genetic diversity interacts with propagule number and variation in neighbor abundances to influence colonization success in plants, using as a framework recruitment functions such as the Beverton Holt. High genetic diversity is predicted to 1) enhance maximum colonization success, 2) enhance the per-propagule effect on colonization success at low propagule densities and 3) benefit founder populations in highly competitive environments more so than in less competitive ones. This study will examine the mechanisms underlying the effects of genetic diversity, testing whether sampling effects and complementarity shift in relative importance as propagule pressure increases and interspecific competition is reduced, and whether the importance of these two factors varies over time.
Long-term natural selection and adaptive introgression in weedy sunflowers NSF 0716868 (to K. Whitney, co-PI L. Rieseberg; 9/2007 - 8/2012; $577,527 Hybridization is a widespread phenomenon, yet its role in evolution is still under debate. Is it a maladaptive, homogenizing force (think mules) or can it contribute to adaptation and evolutionary diversification? We are currently implementing a novel approach that compares long-term evolutionary change in experimental hybrid and control (non-hybrid) lines in the field. These lines are modeled on (i.e. derived by crossing the parents of) a well-studied hybrid sunflower lineage, thus providing a rich context for interpretation. The proposed project asks: (1) Can introgression increase rates of adaptation?, (2) Can introgression increase rates of phenotypic evolution?, and (3) Are evolutionary trajectories in hybrid populations predictable? These questions will be addressed by tracking fitness, 20 traits, and 20 molecular markers (linked to quantitative trait loci, QTL) in the experimental hybrid and control populations over 5-10 generations. Evolutionary change will be distinguished from phenotypic plasticity by comparing the lines in replicated common gardens. The long-term predictability of change in hybrid systems will be examined by assessing whether the experimental hybrids converge phenotypically and genotypically on the natural hybrid upon which they are modeled. The proposed research is first experimental field study to examine the impact of hybridization on adaptive evolution over multiple generations in a wild (non-crop) system.
Yellow crazy ant invasion of the samoan archipelago: Do novel mutualisms amplify the ecological impacts? National Geographic Society 8237-07 (to A. Savage, J. Rudgers, and K. Whitney; 5/2007-9/2008; $20,000) Invasive species pose one of the greatest threats to global biodiversity, and tropical oceanic islands are particularly vulnerable to their negative impacts. For these systems, invasion by the yellow crazy ant (Anoplolepis gracilipes) is a major threat. Identified by the International Conservation Union as one of the world's 100 worst invaders, this species has already decimated some tropical island ecosystems. In Samoa, an island group integral to the Polynesia/Micronesia biodiversity hotspot, presence of the yellow crazy ant is of acute concern. Our data suggest that yellow crazy ants are at a critical stage in their invasion, possibly transitioning from low-level persistence into a phase of rapid population growth with potentially severe ecological consequences. We will investigate the ecological mechanisms that underlie yellow crazy ant success, examine early impacts of the invasion on native communities, and test how community dynamics, specifically novel beneficial relationships with native species, may feed back to influence the invasion. This work will both advance ecological theory and provide critical information needed for conservation planning.
DISSERTATION RESEARCH: Evolutionary ecology of defensive chemical variation in Xanthium strumarium. NSF 1011661 (to K. Whitney, co-PI J. Ahern; 6/2007 - 5/2012; $14,982) Plants produce a broad array of defenses that reduce damage from insect, vertebrate, and microbe pests. These defenses are diverse, ranging from spines and thorns to toxic chemicals like nicotine, and type and amount of defense varies substantially within and among populations. This study will advance understanding of the basis for maintenance of diverse defenses by documenting the specific factors that maintain variation in defensive chemistry of the common cocklebur (Xanthium strumarium) in replicated experimental gardens. Variation within and among populations in ecologically significant traits supplies the basis for biodiversity. Better understanding of the basis of plant defense has significant applications to agriculture. This project also includes interdisciplinary field and laboratory training for undergraduates and an active public outreach program.