Canadian Forest Service Publications

A spatially-explicit, individual-based demogenetic simulation framework for evaluating hybridization dynamics. 2019. Nathan, L.R.; Mamoozadeh, H.; Tumas, H.R.; Gunselman, S.; Klass, K.; Metcalfe, A.; Edge, C.; Waits, L.P.; Spruell, P.; Lowery, E.; Connor, E.; Bearlin, A.R.; Fortin, M.-J.; and Landguth, E. Ecological Modelling 401: 40-51.

Year: 2019

Issued by: Atlantic Forestry Centre

Catalog ID: 39613

Language: English

Availability: PDF (download)

Available from the Journal's Web site.
DOI: 10.1016/j.ecolmodel.2019.03.002

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Spatially explicit individual-based simulation models provide a valuable tool for exploring complex ecological and evolutionary processes that are not easily empirically measured. Here, we present modifications of a spatially explicit individual-based simulation model (CDMetaPOP) to accommodate a two-species system and simulations involving interspecific hybridization. We first describe how a hybrid (H) index is used to distinguish individuals of interspecific descent from those of either parental species. User-defined thresholds provide flexibility in the degree of admixture tolerated for classifying ‘pure’ individuals. We then detail relationships further informed by the H index, including individual growth, temperature-based fitness and selection, and mate preference behavior. Empirically derived species- and system-specific information can be incorporated into these relationships, for example, to produce differential growth among hybrids and parental species. Lastly, we demonstrate an application of this simulation framework by exploring the relative effects of temperature-based selection, mate preference behavior, and hybrid fitness on the rate and spatial extent of sympatric hybridization between two native riverine fish species, bull trout (Salvelinus confluentus) and Dolly Varden (Salvelinus malma), in the upper Skagit River system (United States and Canada). Results from this demonstration provide guidance for future empirical studies of bull trout, a federally threatened species. Understanding factors that contribute to the initiation and maintenance of hybridization, as well as the ecological and evolutionary consequences of this phenomenon, is of increasing importance given shifting species ranges due to large-scale landscape modification and a changing global climate. Our framework can be used to study a wide range of hybridization dynamics in any terrestrial or aquatic system, including comparisons of distinct environmental conditions or potential management responses.

Plain Language Summary

Closely related species with ranges that overlap are often separated by environmental factors that prevent hybridization between the two species from occurring. For example, two species may breed at different temperatures. If the environment changes, the two species may begin to interbreed, resulting in a loss of genetic diversity, phenotypic diversity, and ultimately the loss of a species. Loss of separation of species is of particular concern when one or both of the species is at risk of extinction due to specific habitat or environmental characteristics. Using a spatially explicit individual-based demographic model we explored how habitat use and hybridization between two species of trout, Bull Trout and Dolly Varden, may change under different climatic conditions in the future. Dolly Varden prefer to breed in colder water temperatures than Bull Trout. We demonstrate that under climate-change scenarios, the species will overlap more in space, and increased hybridization between Bull Trout and Dolly Varden will occur. As Dolly Varden are a faster growing species, we predict that the genetic and phenotypic diversity will more closely resemble Dolly Varden under strong climate-change scenarios.