"All knowledge degenerates into probability." 
- David Hume


Artificial Light at Night (ALAN)

The proliferation of artificial light at night is being increasing recognized as an environmental pollutant that disturbs natural foraging and habitat use patterns, predator-prey dynamics, and ancient circadian rhythms. My current research focuses on how artificial light at night affects invertebrate and fish communities in freshwater systems. Artificial light at night is primarily generated from urban environments, so much of our current work has focus on urban streams, rivers, reservoirs.
Downtown Columbus, OH over the Scioto River at night. 

Home Road over the Scioto River at night in Delaware, OH



Polyphenisms

My past research primarily focused on polyphenisms, which are an extreme form of phenotypic plasticity where multiple, environmentally-cued phenotypes stem from a single genotype. In particular, I am studying salamander facultative paedomorphosis, which is a retention of juvenile characteristics into adulthood. I am investigating the roles of both biotic and abiotic cues involved in eliciting alternative phenotypes along with their underlying hormonal mechanisms.





Proposed model incorporating endocrine mechanisms regulating facultative paedomorphosis. Under the paedomorph advantage hypothesis,  and above a minimum body size, larvae that are exposed to environmental stressors (e.g., crowding, pond drying, predator presence, starvation) and have at least reached the minimum body size required for metamorphosis (35 mm; (Semlitsch and Wilbur 1988)) are more likely to metamorphose than become paedomorphic. Stressors activate the HPI axis (blue arrow) releasing CRF from the hypothalamus and ACTH and TSH from the anterior pituitary. ACTH stimulates the adrenal gland to release CORT, while TSH stimulates the thyroid gland to release THs (T3/T4). CORT and THs act synergistically to affect gene expression in target tissues resulting in metamorphosis (left) (reviewed in Denver 2017). In the absence of stressors, the HPI axis is not activated and metamorphosis is delayed resulting in aquatic paedomorphs (right). Both metamorphs and paedomorphs attain sexual maturity, but paedomorphs reach sexual maturity earlier (Ryan and Semlitsch 1998), increasing lifetime expected fitness (Cole 1954, Roff 1992, Stearns 1992).


Typical Ambystoma talpoideum adult with terrestrial morphology. Most Ambystoma spp. have an aquatic larval phase and then metamorphose into terrestrial adults.
Paedomorphic adult Ambystoma talpoideum salamander with retention of gilled larval morphology. Paedomorphs are fully aquatic adults.
 

The complex life cycle of Notophthalmus viridescens. Eggs (1) are laid singly in aquatic vegetation and hatch into an aquatic larva (2). Larvae can either become paedomorphic or metamorphose. Paedomorphs are either complete neotenes (3), which have no degree of metamorphosis, or branchiates (4), which partially metamorphose. Both paedomorphic phenotypes retain gills, compressed tail fins and aquatic lifestyles. Metamorphosed phenotypes include aquatic juveniles (5), which are miniature adults, terrestrial efts (6) and semi-aquatic adults (7). Neotenes (3), branchiates (4) and semi-aquatic adults (7) are sexually mature while efts (6) and aquatic juveniles (5) are immature, but efts can take up to seven years longer than aquatic juveniles to reach sexual maturity. Illustration by Tatiana Tushyna.



Oviposition & Habitat Selection

Many of my side projects involve oviposition and habitat selection of tree frogs, mosquitoes and aquatic beetles. Using mesocosms, we construct artificial pond arrays to understand how patch characteristics influence community assembly and metapopulation and metacommunity dynamics. I am currently leading projects investigating the generality (or specificity) of fish avoidance, mass effects (i.e. density-dependence, spillover), patch quality trade-offs and temporal patterns along with their underlying mechanisms.