• Publications
  • Influence
Climate change and temperature-dependent sex determination in reptiles.
  • F. Janzen
  • Biology, Medicine
  • Proceedings of the National Academy of Sciences…
  • 2 August 1994
Monitoring of nests of a population of painted turtles with temperature-dependent sex determination found annual offspring sex ratio was highly correlated with mean July air temperature, validating concerns about the effect of climate change on population demography. Expand
Visualizing and quantifying natural selection.
Combinations of quantitative and visual analyses are providing researchers with new insights into the details of natural selection in the wild, through graphical representation of selection surfaces. Expand
  • F. Janzen, H. Stern
  • Biology, Medicine
  • Evolution; international journal of organic…
  • 1 December 1998
It is argued that the logistic regression model is more suitable than linear regression for analyzing data from selection studies with dichotomous fitness outcomes, and it is shown that estimates of selection obtained can be transformed easily to values that directly plug into equations describing adaptive microevolutionary change. Expand
Vegetational Cover Predicts the Sex Ratio of Hatchling Turtles in Natural Nests
A possible mechanism by which female turtles choose the thermal environment of nests and, hence, the sex ratio of their offspring is suggested: they may assess vegetational cover on the nest site at oviposition. Expand
Environmental Sex Determination in Reptiles: Ecology, Evolution, and Experimental Design
Physiological investigations of TSD have clarified the roles of steroid hormones, various enzymes, and H-Y antigen in sexual differentiation, whereas molecular studies have identified several plausible candidates for sex-determining genes in species with TSD. Expand
Heritable variation for sex ratio under environmental sex determination in the common snapping turtle (Chelydra serpentina).
The results in conjunction with the occurrence of TSD in this species provide support for three critical assumptions of Fisher's theory for the microevolution of sex ratio, and suggest that evolution of sex ratios would be slow even in response to strong selection by any rapid and/or substantial shifts in local temperatures, including those produced by changes in the global climate. Expand
Molecular phylogenetics and evolution of turtles.
Maximum parsimony analyses of RAG-1 alone and in combination with two mitochondrial genes suggest the earliest phylogenetic splits separating into three basal branches, the pig-nosed turtles (Carettochelyidae), the softshell turtles (Trionychidae), and a clade comprising all remaining extant turtles. Expand
Putting Eggs in One Basket: Ecological and Evolutionary Hypotheses for Variation in Oviposition-Site Choice
This work presents six hypotheses that have been used to explain nonrandom oviposition-site choice in insects, fish, amphibians, reptiles, and birds: maximizing embryo survival, maximizing maternal survival, modifying offspring phenotype, proximity to suitable habitat for offspring, and maintaining natal philopatry. Expand
bottlesim: a bottleneck simulation program for long-lived species with overlapping generations
bottlesim is a program for simulating bottlenecks to estimate the impact on genetic diversity; the novelties include an overlapping-generation model, a wide range of reproductive systems, and flexible population size settings. Expand
An Experimental Analysis of Natural Selection on Body Size of Hatchling Turtles
Larger hatchling Chelydra serpentine exhibited significantly greater survivorship than smaller individuals during movement from the nest site to water, suggesting that larger body size of hatchling turtles may not evolve rapidly because the strength of selection was moderate in magnitude and the heritability was relatively low. Expand