Research
My research focuses on how animals respond to human-caused environmental change. I examine the role of the environment (biotic and abiotic) in shaping phenotypes via plasticity, I quantify natural selection in the wild, and I study the evolution and ecology of maternal effects. My research questions are generated from ecological and evolutionary theory, observations of animals in the field, and conservation needs. I rely heavily on manipulative field experiments, which are supplemented with observational field studies and physiological laboratory work.
My work is characterized by straightforward experimental designs that maximize ecological relevance while answering important biological questions.
Below are a few examples of past and present research projects.
Cost effective revegetation in Minnesota's roadsides: After road construction occurs, contractors reseed the road right-of-ways. Sometimes, these right-of-ways are seeded with quick growing non-native plants that are relatively inexpensive, and sometimes they are seeded with expensive native seed mixes that include a diversity of native grasses and forbs. Of course the hope is that the native seed mixes produce a diverse plant community full of native plants, but these roadsides are not resurveyed and thus the efficacy of these seeding practices are unknown. I am currently heading a project that is surveying native and non-native seeded roadsides to assess that plant and insect communities, including the threatened monarch butterfly and endangered rusty patch bumblebee. Results from this project will inform policies on revegetation after construction projects.
Optimizing roadside nutrition for pollinators: Sodium is often limiting in terrestrial herbivore diets, and salt-seeking behavior is common for these animals. Roadside plants are often elevated in sodium due to road salt runoff, and have the potential to simultaneously attract and poison pollinators, setting an ecological trap. I have led projects measuring sodium-seeking and avoidance behavior during oviposition and larval feeding in monarch butterflies (Mitchell et al. 2019), and showing the movement of road salt from soil to host plant, to caterpillar , while demonstrating that sodium content in milkweed scales with traffic volume (Mitchell, under review). Results from this research will be incorporated into roadside restoration and pollinator management.
Maternal effects: As mammals, it's very obvious to us that our mothers are important. After all, we develop within their body and they provide our only source of food for some time after birth. It might not be so obvious that mothers are important for organisms without parental care. Much of my research revolves around the evolutionary ecology of maternal effects in oviparous reptiles and insects. In these animals, where and when eggs are laid and what resources are allocated to those eggs can have a substantial influence of the phenotypes and survival of those offspring. I have performed a series of field experiments that have shown the importance of these maternal effects to shaping phenotypes of offspring and that these phenotypes are under selection during multiple early life stages (Mitchell et al. 2013, Ecology; Mitchell et al. 2013 Proc Roy Soc B. Mitchell et al. 2015, Funct Ecol).
Natural selection: Genetic, parental, and environmental factors all shape phenotypic variation, but is that phenotypic variation relevant? Does it matter that some females can produce larger eggs and consequently larger offspring? Or are animals that perform better at physical challenges in the lab more likely to survive in the wild? To answer questions like these, I quantify selection under ecologically relevant conditions in the wild (Mitchell et al. 2013, Ecology; Mitchell et al. 2015, Funct Ecol; Mitchell et al. 2016, Biol J Lin Soc). I do this using capture mark recapture studies, and my past work has produced some novel findings (i.e. such that egg size is under selection during incubation in the field). However, this relationship is not always consistent (in other words, the relationship between phenotype and fitness is dependent on the environmental context).
Phenotypic plasticity in the wild: Both environmental and genetic factors contribute to variation in phenotypic traits. Much research on phenotypic plasticity carefully modifies the environment in the lab, while controlling for all other factors. In my research, I rely on manipulative field experiments to alter environmental factors of interest, while allowing other factors to vary naturally. For example, I mentored an undergraduate on a project that tracked the phenotypic consequences of altering turtle nest moisture in the field (Bodensteiner et al. 2015 Funct Ecol). Using large outdoor pond enclosures, I have investigated the influence of winter environment on nesting behaviors of turtles (Mitchell et al. 2017, Evol Ecol Res). I am currently investigating how the post hatching social and abiotic environment shapes life-history traits in the brown anole lizard. Utilizing small spoil islands located along the Florida coast, I have performed population-level age structure manipulations, and released marked cohorts of individual hatchlings. Given their known environmental histories I am currently tracking phenotypes, behavior, and reproduction are carefully monitored. We are currently conducting parentage analysis of offspring produced during replicated mating trials, which will provide ideal measures of fitness (i.e., reproductive success). Field experiments of this nature uniquely advance our understanding of the ecology and evolution of phenotypic plasticity.
Organismal response to climate change: Many reptiles, painted turtles included, have temperature-dependent sex determination (TSD). This means the temperature that an egg experiences during a sensitive period during incubation will determine if developing embryo becomes a male or female. This fascinating trait makes turtles and other organisms with TSD particularly vulnerable to climate change. I am interested in how turtles (already one of the most imperiled groups on earth) will respond to climate change. I am heavily involved in several large-scale collaborative projects that address this issue. The first project is powerful because of its longevity. This project is a long-term observational study of a single population of painted turtles, which was started by Fred Janzen during his Ph.D. in the late 1980s, and continues today. Among many other things, this project allows us to repeatedly track the same turtles through their lifetime. Additionally, we are able to see how weather patterns influence offspring survival and sex ratios across many years, and how this influences the population. The second major project I am currently involved in, also funded by the NSF, examines how painted turtles have locally adapted to the drastically different environments they live in. Painted turtles have a broad geographic range, from the cool climates of the Canadian Shield to the much hotter climates of the Great Plains and Southwest USA. By exploring how turtles have adapted to existing climatic variation, we may have a better sense how they will respond to changing climates.
Undergraduate Research Mentoring: My research is conceptually and methodologically approachable by undergraduate students, and I have substantial experience with mentoring students on independent and small team research projects. I have personally mentored 25 undergraduate and high-school students on independent research projects through various internship and research experience programs. These projects have resulted in many student authored posters and oral presentations at scientific meetings, and publications.
For example, I worked with Kammie Voves (an REU student at Iowa State) design a project to look at whether visual camouflage in turtle nests reduces predation risk. Anyone who has searched for painted turtle nests knows that some are easy to spot while others are not. We wondered whether visual camouflage reduced predation from mammalian predators. Our findings suggest they did not. It turns out raccoons are just really good at finding turtle nests, which is not too surprising given their keen sense of smell (Voves et al. 2016, Am Mid Nat).
For example, I worked with Kammie Voves (an REU student at Iowa State) design a project to look at whether visual camouflage in turtle nests reduces predation risk. Anyone who has searched for painted turtle nests knows that some are easy to spot while others are not. We wondered whether visual camouflage reduced predation from mammalian predators. Our findings suggest they did not. It turns out raccoons are just really good at finding turtle nests, which is not too surprising given their keen sense of smell (Voves et al. 2016, Am Mid Nat).
Miscellaneous: Not all of my research fits into the categories above. I have studied other diverse topics such as animal detection probability, embryonic thermoregulation within eggs, embryo physiology and animal orientation.
Funding: Research described here has primarily been funded by the National Science Foundation. Research costs from my work at Iowa State were partially supported by several grants (LTREB DEB-0640932, DEB-1242510, and IOS-1257857) to Fred Janzen. Stipend support during two years of my PhD were from an NSF GK-12 Fellowship (DGE-1007911). Current support comes from my NSF Postdoc Fellowship (DBI-1402202). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.