Dr. Craig F. Purchase

Evolutionary Ecology of Fishes

Research Program















ship small




As an evolutionary ecologist I am interested in how organisms have adapted to their environment, as a result of interactions with individuals of their own and other species, and with abiotic conditions. Within this context, I conduct research on fishes. Fishes are good study organisms; they are the most specious of all vertebrates, they exhibit a huge diversity in morphology, remarkable variability in how and where they live, and they have social and economic value that enables certain types of research that would otherwise be impossible.


My group does different types of research: (1) we do “environmental monitoring” sort of things where we measure characteristics of wild fish populations (e.g., juvenile densities, adult “health” – size/colour/shape/energy), and (2) using gametes collected from wild fish, we do lab experiments, where we manipulate the conditions of fertilization (and monitor sperm performance or fertilization success) or incubation (and monitor offspring performance).


Our research is relevant for diverse fields, including: evolutionary biology, ecology, invasive species, biodiversity, conservation biology, toxicology, and fisheries productivity.



Areas of concentration


Fish reproductive biology: I have a general interest in reproductive biology and I use reproductive traits as tools for questions related to plasticity and adaptation. Recent work has included spawning site selection, courtship behaviour, temporal/spatial variation in egg size-number tradeoffs, egg quality, ovarian fluid, sperm morphology and quality, sperm behaviour, sperm competition, fertilization variability, embryo development under different conditions, and hatch characteristics.


Phenotypic plasticity: Phenotypic plasticity occurs when a single genotype produces different phenotypes when exposed to different environments. The shape of this response is known as a reaction norm. This plasticity can be adaptive, neutral, or maladaptive depending on the trait and context. Just about any trait can be plastic (e.g., escape behaviour, gut length, pigmentation, spine length, growth rate, maturation age, fish swimming speed, sperm swimming speed), and my research has investigated many different sources of environmental variation and responses to it. Two particularly interesting areas of work are plasticity in plasticity (how the phenotype produced to one environmental cue depends upon something else), and transgenerational plasticity (how parental experience affects offspring).


Local adaptation: Within a species, populations often adapt to local conditions if (1) there is an environmental gradient that is selectively important, (2) variability in the trait in question which is heritable, and (3) at least some degree in reproductive isolation from other populations. Such adaptation constitutes within-species genetic variation that is ecologically important, as it may influence overall species productivity and resilience to extinction. Local adaption among populations is well documented for a wide variety of traits, including growth rates, energy assimilation efficiency, maturation age, egg size, and swimming performance. Hybridization between locally adapted populations destroys intra-specific biodiversity, as does hybridization between related species. I am interested in causes and consequences of such hybridization.


Life history variability: Much of my earlier work focused on life history variability. Life history traits directly influence an organism’s ability to pass genes to the next generation and greatly affect yield in harvested populations. Traits like maturation age and reproductive investment vary widely among- and within-species, and are influenced by both genetics and environment. Understanding this variation is therefore critical for conservation and resource management. I investigate within-species life history variability of fishes at different levels: among populations, generations, families, sexes and individuals.


Invasion biology: Invasive organisms are becoming an increasing threat to biodiversity. My group has been conducting a variety of studies on brown trout, which are labeled as one of the world’s top 100 worst invaders. Invasive species by definition cause concern outside of their native distribution to other species. Less obvious to the public are ecological and evolutionary problems caused when non-native populations of a given species are either purposely or accidentally released into the range of conspecifics. These “invading” individuals can interbreed with native fish and genetically pollute local adaptation. Stocking from hatcheries and escapes from aquaculture are common sources of this problem. I am interesting in the reproductive biology of invasive fishes.


Conservation biology: Within the context above, some of my research has direct conservation implications. Of particular concern is how the loss of local adaptation within a species affects the long-term existence and/or productivity of the species as a whole. As in the business world, this is known ecologically as the portfolio effect. Most of my interest in this area focuses around reproduction.




My research program at Memorial University has received funding through the following sources:

·      Memorial University

·      Natural Sciences & Engineering Research Council of Canada

·      Canada Foundation for Innovation

·      Newfoundland & Labrador Research & Development Corporation

·      Newfoundland & Labrador Department of Environment & Conservation

·      Fisheries and Oceans Canada

·      Salmonid Association of Eastern Newfoundland

·      Ireland Canada University Foundation

·      Atlantic Salmon Conservation Foundation

·      My students also received support from many additional sources


pollock small


killifish small