Dr. Craig F. Purchase

Evolutionary Ecology of Fishes

Research Program















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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. I do not focus on any particular kind, but research to date has been concentrated on those found in eastern North America and includes marine, diadromous and freshwater species. 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.


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. A particularly interesting area of work is plasticity in plasticity, i.e. how the phenotype produced to one environmental cue depends upon something else.


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.

If phenotypic variability is observed among populations it is not possible to determine if it is caused by plasticity or local adaptation without detailed investigation. Additionally, there can be local adaptation in plasticity, i.e. different populations have different reaction norms for the same trait exposed to the same environmental conditions.


*Some of our current work (2016 – ) connects these fields. We are focused on gamete ecology, much of which includes plasticity of sperm performance to abiotic conditions (including natural and unnatural stress), biotic conditions (post-copulatory cryptic female choice of sperm via female secretions), their interactions, and how these patterns may differ among locally adapted populations.


Other key areas


In addition to my primary areas of concentration (described below), I maintain an interest in all aspects of fish biology and have published in areas as far ranging as quantification of bycatch from commercial fisheries, ideal free distribution theory, morphology, aquaculture production, mercury bioaccumulation, behaviour, maximum sustainable fisheries yields, to seminal fluid chemistry.


Life history variability: Much of my work has 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.


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.


Study species

Our work is not species specific and we use the most appropriate species available to address a specific question. In recent years we used the following local species:

·         Atlantic cod (marine) – breeding interactions, sperm behaviour, inter-population hybridization, escape mechanisms from fish farms

·         Sandlance (marine) – ageing sensitivity, long term changes in life histories

·         Atlantic herring (marine) – long term changes in life histories

·         Capelin (marine smelt) – mate choice, sperm behaviour, embryo development

·         Rainbow smelt (anadromous smelt) – embryo and sperm comparisons with capelin, inter-population hybridization

·         Atlantic salmon (native Salmo) – early development and habitat use, reintroduction of extirpated populations, egg quality, migration, competition with brown trout

·         Brown trout (invasive Salmo) – habitat use, sperm behaviour, early development, otolith microchemistry

·         Brook trout (native Salvelinus) – sperm behaviour, plasticity in embryo development

·         Arctic charr (native Salvelinus) – variation in early life history, otolith microstructure formation

·         Banded killifish (Newfoundland’s most unique freshwater fish) – spawning behaviour and embryo development



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


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