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David K. Skelly
Yale University
School of Forestry & Environmental Studies
370 Prospect Street
New Haven, CT 06511 USA

Yale FES



Max Lambert

Lab: Greeley Laboratory, Room 119
Phone: (619) 990-7242
Fax: (203) 432-3929

B.S. Wildlife, Fish, & Cons. Biology
UC Davis
M.E.Sc. Forestry & Env. Studies
Yale University
Ph.D. Forestry & Env. Studies
Yale University

My interests lie in developmental biology, physiology, landscape ecology, and evolution. Broadly, my current work asks 1) if and how the surrounding landscape influences sexual development and 2) whether environmental sex determination has adaptive consequences. The question of whether an individual becomes a male or a female is a surprisingly complicated problem in biology.

It is clear that the environment, in addition to sex chromosomes, determines the sex of an individual. For reptiles, temperature can phenotypically reverse the sex of an individual. The offspring of many fish species can similarly exhibit complete sex reversal in response to temperature and pH during early development. In many small mammals, it is known that the intra-uterine position of an individual can influence the sexual phenotype; whereby a female located between two male siblings in the uterus will become “masculinized exhibiting a male-like phenotype than her more feminine counterparts. Birds, and some mammals, are a different case where the female can actually “choose” the sex of her offspring depending on environmental conditions. It is clear that vertebrates exhibit varying levels of environmental sex determination.

The Question: Although amphibians are the original model organism and have been used extensively for embryological and developmental studies, our knowledge of amphibian sex determination and sex ratios is extraordinarily depauperate. The relative contribution of genes and environmental drivers to sex determination in amphibians is virtually unexplored. Because of this, we have little data on primary sex ratios in natural amphibian populations and how sex ratios might vary in accordance with environmental characteristics. I am asking, generally, how both natural and anthropogenic environments alter sex determination and primary sex ratios in amphibians.

Doctoral Work: I am employing observational studies with laboratory experiments to understand drivers of amphibian sex determination. Furthermore, I am interested in how environmental sex determination influences life history trajectories. Whether or not feminization or masculinization can be an adaptive trait is becoming an increasingly interesting question. My goal is to begin understanding if there is adaptive value to being a sex-reversed individual, a masculinized female, or a feminized male.

Master’s Research: The results of my master’s research contributed to this research agenda. I found that green frog (Rana clamitans) metamorph phenotypic sex ratios varied as a function of human land use. Specifically, metamorphs from relatively undeveloped forested landscapes consistently yielded primary sex ratios of ~1/3 female whereas cohorts from suburban ponds yielded primary sex ratios of ~1/2. Using GIS analysis, it seems that the amount of lawn cover was actually an important predictor of sex ratio, where increasing lawn cover was correlated with more females in a metamorphic cohort. This indicates that plants, and potentially phytoestrogens, may play a downstream role in regulating sexual development in amphibian larvae.




Lambert, M. R., Nielsen, S. N., Wright, A. N., Thomson, R. C., and H. B. Shaffer. 2013. Habitat features determine the basking distribution of introduced red-eared sliders and native western pond turtles. Chelonian Conservation and Biology 12: 192-199.

Lambert, M. R., Yasuda, C. M., and B. D. Todd. 2013. Ontogenetic shift in habitat use in the western fence lizard (Sceloporus occidentalis) in northern California. Herpetological Review: 579-582.

Lambert, M. R., Yasuda, C. M., and B. D. Todd. 2012. Estimating snout-vent length (SVL) in lizards using image analysis. Herpetological Conservation and Biology. Herpetological Conservation and Biology 7: 83-88.


Lambert, M. R. and C. M. Donihue. In Prep. Adaptive Evolution in Urban Ecosystems.

Lambert, M. R., Giller, G. S. J., Barber, L. B., Fitzgerald, K. C., and D. K. Skelly. In Prep. Suburbanization, estrogen contamination, and sex ratio in wild amphibian populations.

Lambert, M. R., Skelly, D. K., and R. G. Bribiescas. In Prep. Suburbanization induces both male-biased and female-biased variability in estrogen concentrations among metamorphosing frog populations along a suburban-rural gradient.

Giller, G. S. J., Lambert, M. R., Skelly, D. K., and L. B. Barber. In Prep. Trace elements patterns from surface and ground waters across a forested – suburban landscape.

Screen, R., McKenzie, J., Lambert, M. R., Clause, A. G., Johnson, B. B., Mount, G. G., Pauly, G. B., and H. B. Shaffer. In Prep. Experimental removal of invasive red-eared sliders (Trachemys scripta elegans) induced a shift in habitat use by native western pond turtles (Emys marmorata).

Ambystoma maculatum and Ambystoma opacum at the Yale Preserve.

Red-belled newt (Taricha rivularis) in Montgomery Woods, CA.

Chrysemys picta picta at the Yale Preserve.