Genetic diversity of southern Ontario fish: Research by U of G professor Elizabeth Mandeville

The basic mechanism of hybridization, two species exchanging genes with one another, is not uncommon in nature. For instance, different species of African cichlids (Family: Cichlidae) will hybridize in muddy waters where individuals have a harder time distinguishing each other visually. Hybridization is also relatively common in North American freshwater fish. In addition to water quality, or more broadly, habitat quality, factors including species’ behaviours and selection of sites for reproduction can influence whether or not hybridization will occur.

Dr. Elizabeth Mandeville, Assistant Professor in the Department of Integrative Biology at the University of Guelph since January 2019, studies hybridization in fish, as well as how hybridization tests the boundaries of what defines a species and the biological mechanisms that maintain species as separate. She is interested in questions related to hybridization between species and genetic diversity within species. Are species boundaries being maintained and are we getting the same number of species as before? Or is hybridization occurring to such an extent that the parent species disappear and only hybrids remain, resulting in a net loss of biodiversity? Also, the effects of novel traits and ecological novelty that can arise from hybridization are less well understood in fish compared to other taxa such as plants.

Dr. Mandeville’s research ties into conservation issues as there is a fear of declines or loss of native species, especially when these species are already at risk. There are ethical implications with hybridization and conservation: do we value a species itself or its ecological role? And to what extent can hybrids play the same role as the parent species? One of the focuses of her work at the University of Guelph will be to explore how human activities may be “muddying the waters” thereby facilitating or hindering hybridization.

Humans have the ability to decrease reproductive isolation between fish species by intentionally or accidentally dispersing species and by altering the environment. For example, fish species that are desirable to anglers are actively stocked into waterways, whereas physical modifications to the environment leading to shifts in water flow or thermal regime, or reduced heterogeneity of spawning sites through channel grating, can affect timing of spawning and increase habitat overlap. These modifications can promote hybridization between species living in close proximity.

As part of a team of researchers supported through the Canada First Research Excellence Fund (CFREF), Dr. Mandeville will be exploring genetic diversity and the extent of hybridization in southern Ontario fish species, which are currently not well understood. She will also examine the effects that agricultural activities may be having on hybridization. The CFREF program offers collaborative research opportunities since many other scientists are working at the same field-sampling sites hence, there is a variety of data available on habitat quality, human activities, and information on fish communities.

This summer, she and her research team will conduct field work to identify the best fish species to study moving forward as some of the species at the CFREF sites are known to hybridize in the wild, although it is not yet known if they hybridize at these particular sites. An example of one of these ‘hybrid systems’ includes common shiner and creek chub, where the former may use a nest built by the latter during spawning season.

Her research team will obtain fin clips from fish caught at CFREF sites, extract the DNA, and characterize the genomes. The data will be used to develop baseline genetic diversity estimates for as many species as possible in order to make comparisons across sites and across species at a site. This information will be crucial as a foundation to Dr. Mandeville’s work since natural levels of genetic diversity for southern Ontario fish is currently unknown. Since genomes can produce an enormous amount of data (e.g., one fish genome is equivalent to 1000 copies of “War and Peace”), she will be using one of Canada’s super computers (SHARCNET) to assess genetic diversity and identify hybrids. Dr. Mandeville describes herself as a scientist who “owns waders but also does a lot of supercomputing”.

Ultimately, Dr. Mandeville’s research will further our understanding of how human activities influence fish hybridization and biodiversity in Ontario’s waterways, which will in turn inform fish management and conservation activities.

This article originally appeared on the Biodiversity Resilience Network website.