The Rollinson Lab 

Evolutionary ecology, maternal effects, herpetology, conservation

Research Themes

1. Temperature, body size, and fitness

Why do individuals that inhabit cold environments attain enormous body sizes? For example, in central Canada's Algonquin Park, we catch snapping turtles that weigh over 18kg (more than 40 lbs); this is much larger than this species becomes in southern environments. Also, think of animals like the Chinese giant salamander, which inhabit relatively cool streams; individuals of this species can measure over 1.5m long and weigh up to 30kg (66lbs). Using meta-data, long-term data monitoring data, and experimental manipulation, my group integrate principles of life-history theory and physiological ecology to understand how body size and life-histories are optimized with respect to temperature and growing season length. Some general questions include: how have life-history traits in northern reptiles evolved since post-glacial range expansion? What are the benefits of indeterminate growth in environments that are strongly seasonal compared to environments that are less seasonal? Are Bergmann clines more closely associated with temperature or growing season length, and why do these clines vary in direction in different clades? How have decadal warming patterns affected growth and reproduction in northern reptiles and amphibians?

2. Maternal effects in contemporary populations

Size at birth has a profound effect on individual fitness, as it predicts both survival rate and life-history trajectories. Yet, size at birth is constrained by the parental trade-off between investment per offspring and fecundity. Parents therefore face a perennial dilemma, producing either many small offspring with low fitness or a few larger offspring with high fitness. While classical life-history theory predicts that all parents should ultimately produce offspring of the same size in a given environment, a common observation is that relatively large females produce large offspring,  whereas smaller females produce small offspring. The result is that larger females tend to contribute disproportionately to recruitment, even over and above the contribution made by increased fecundity, because larger offspring invariably have greater survival. This simple  observation is one of the most perplexing life-history puzzles of our time, and no current theory can explain it. To fit pieces of this puzzle, a variety of interesting questions need to be answered: Does the strength of the association between maternal size and offspring size vary predictably with the environment? Do life-histories (e.g., longevity, age-at-maturity) differ between offspring produced by large vs small females? Do larger females have a larger influence on adult fitness traits of their offspring? Over-and-above correlations between female body size and offspring size, I'm generally interested in maternal effects and how they influence model predictions in population ecology and evolutionary biology.

3. Temperature-dependent sex determination
In many reptiles, sex is determined by the temperatures experienced during development. In Algonquin Provincial Park, naturally produced hatchling sex ratios of snapping turtles were monitored from 1981 to 1999, as part of the long term life-history study. Fast forward to the year 2016, which saw the hottest July in recorded history. In 2016, we re-initiated long-term monitoring of snapping turtle sex ratios. With these data, both historic and new, we are beginning to unravel how sex is determined in snapping turtles, and how rapid climate change is influencing sex ratios in general. Long-term study of embryo development is also being coupled with selection experiments to estimate how selection on nest timing is changing as growing season length increases.

4. The micro- and macro-evolution of body size

Classic life-history theory predicts that parents trade off the fitness accrued from an increase in resource investment per offspring (i.e., juvenile size) against the fitness losses resulting from a reduction in parental fecundity. This trade-off generates parent-offspring conflict over body size: given that size is positively related to fitness, the level of investment per offspring that maximizes parental fitness is lower than the level that maximizes offspring fitness. As a result, parents produce juveniles of a size that is optimal from the parents’ perspective, but suboptimal from the juveniles’ perspective. The predicted effect of this trade-off is recurrent upward selection on juvenile size in every generation of offspring production. This argument extends to selection on adult size as well, provided genetic variation in adult size is attributable to variation in investment per offspring (i.e., maternal-genetic variation for body size). I am currently extending these principles to help explain macro-evolutionary trajectories of life-histories.

I am also interested in the macro-evolution of body size and life-histories in ectotherms, particularly from the perspective of temperature-induced oxygen limitation (the "temperature-size rule"). Using a large database on amphibian biology (see below), we are currently exploring how temperature and oxygen limitation affect the evolution of both body size and the maternal effect on body size in amphibians of the world.

5. The amphibian megabase project
Inspired by the work of Stephen DeLisle, and with the help of Lauren Malatesta (University of Toronto), I've spent a few years compiling a very large database on the biology of amphibians. The database currently includes life-history data (e.g., egg size, clutch size, body size, age at maturity, reproductive mode), environmental data (e.g., mean precipitation, mean annual temperature, mean humidity), ecological data (e.g., range size), and the status (e.g., IUCN conservation status, invasive species status) for over 1200 species of anurans and caudatans. This database is being used to explore relationships among life-histories, range size, invasiveness, and extinction risk, as well as to tackle relationships between reproductive mode and the allometric scaling of life-history traits with body size.

6. The ecology, evolution, and conservation of coldwater fishes

In the near future, we will have a coldwater aqulab here at the University of Toronto. Research will focus on the evolutionary ecology and conservation of cold-water fishes.
Mentors and collaborators
Locke Rowe (Toronto)
Jeff Hutchings (Halifax)
Ron Brooks (Guelph)
Justin Congdon (Georgia)
Fred Janzen (Iowa)
Jackie Litzgus (Sudbury)
Christopher Edge (Toronto)
John Iverson (Indiana)
Doug Armstrong (New Zealand)
Candling a snapper embryos (by M. Massey)
Correlational s' in early life (Punzalan & Rollinson, unpubl.)
Turtle B03, putting around in a snowstorm
Testing new theory with metadata (Evol 2015:2441)
Juvenile salmon (Bay of Fundy, Nova Scotia)
Inter-specific scaling of LH traits (Evol 2015:2441)