Approved by COSEWIC in November 2018

In response to the increasing numbers of Wildlife Species whose distribution or genetic make-up have been manipulated by humans, deliberately or accidentally, these guidelines have been developed to assist COSEWIC in determining in what context manipulated components will be considered in Wildlife Species status assessments.

The Species at Risk Act (SARA) and COSEWIC definition of “wildlife species” includes requirements that are relevant to COSEWIC’s consideration of manipulated organisms. Wildlife Species, also referred to as Designatable Units (DUs) by COSEWIC, must be native to Canada (see Definitions and Abbreviations and Assessment Process and Criteria) and excludes those that have been introduced to Canada via human intervention. Wildlife Species must also be “wild by nature”, a term that is not defined in SARA, but which, according to some legal interpretations, might include captive individuals with recent wild ancestors. SARA provides no direction for the assessment of Wildlife Species with re-introduced, hybrid, or supplemented populations or organisms managed for purposes other than conservation.

Prohibitions specified by SARA apply to individuals in the population identified and assessed by COSEWIC. Clear definition of whether wild and manipulated components are part of the assessed population (i.e., the “wildlife species”), is essential to determining which individuals or components would be subject to prohibitions. Guidelines herein concerning introduced, hybrid, or supplemented populations may be applied to exclude components of a Wildlife Species, on the condition that the manipulated components are genetically or geographically distinct from the Wildlife Species being assessed. The term “genetically or geographically distinct population” appears in the SARA definition of “wildlife species” along with “species, subspecies”, and “variety”. The requirement that excludable manipulated components be genetically or geographically distinct from the DU being assessed thereby ensures that the exclusion is consistent with the SARA definition of “wildlife species”.

Some Wildlife Species population components undergoing manipulation by humans may be genetically distinct, depending on the number of generations over which they have been manipulated. Other population components, for which sufficient time may not have elapsed for genetic differences to have accumulated, might nonetheless be considered geographically distinct. COSEWIC considers the term “distinct” in this case to mean “distinguishable”, which may be less robust than the terms “discrete” and “evolutionarily significant” as used in COSEWIC's Guidelines for Recognizing Designatable Units. In other words, the recognition of a valid Wildlife Species (= Designatable Unit, DU) requires it to be both “discrete” and “evolutionarily significant” with respect to other closely related populations or taxa. By contrast, excluding a manipulated population component that otherwise meets all parts of the Wildlife Species definition, only requires it to be genetically or geographically distinct (distinguishable) from the assessed Wildlife Species.

Two types of considerations related to manipulated populations must be addressed in COSEWIC status assessments:

1. Is the manipulated population component part of the Wildlife Species (= Designatable Unit) being assessed?
2. If the answer to “A” is yes, should individuals from the manipulated population component be included when applying quantitative criteria to determine status (i.e., based on decline rates, on numbers of mature individuals)?

The guidelines that follow clarify COSEWIC’s position on: (i) whether or not manipulated population components are to be part of the Wildlife Species being assessed, and (ii) where such manipulated population components are considered part of the Wildlife Species, whether or not application of quantitative criteria applies to these components. Given the breadth of taxonomic groups, some degree of flexibility needs to be retained in the application of the guidelines to allow for the consideration of specific circumstances associated with different Wildlife Species. In addition, the long-term consequences of various manipulations of Wildlife Species are often difficult to predict; thus, uncertainty should be addressed in a precautionary manner.

These guidelines consider three types of manipulated population components:

1. Captive or cultivated
2. Introduced/re-introduced or supplemented
3. Hybrid

1. Captive or Cultivated Population Components

Captive and cultivated population components may be maintained for ex situ conservation or commercial purposes. For example, captive breeding might be an integral component of recovery programs for Wildlife Species unable to survive in the wild under current conditions. Reproduction may or may not be based on pedigree tracking, and human intervention may be required for successful breeding. Such populations may be founded by wild-caught individuals from a single source, or result from the mixing of disparate genetic sources, some of which may have been subjected to artificial selection. For example, captive-breeding programmes of Swift fox, Peregrine Falcon, and Vancouver Island Marmot either are or have been in place in Canada in the recent past. Another example is the conservation technique known as head starting, which involves capturing individuals from natural populations and maintaining them in captivity (either in situ or ex situ) during a particularly vulnerable life stage, usually near birth or germination. For example, head starting is intended to decrease predation on caribou calves.

Artificial selection for traits best suited to captivity begins immediately upon being contained in a captive environment (e.g., Lynch and O’Hely 2001); this is called domestication selection. The greater the number of generations in captivity, the greater the effect of domestication is on heritable traits and non-heritable, learned behaviours. Although efforts to minimize domestication have been made in some conservation-based captive breeding programmes, such changes are impossible to prevent entirely. Regardless, where populations are maintained in captivity for conservation purposes, the intent to release individuals into the wild at some time exists.

For example, animals maintained in zoo facilities would be included as part of the Wildlife Species being assessed but their numbers would not be counted in population estimates. The Vancouver Island Marmot Recovery Centre maintains captive marmots which are bred and released into natural habitats periodically. Captive held individuals would be included in the Wildlife Species being assessed but not as part of the population size estimate given that their contribution to the wild population cannot be confirmed.

2. Introduced or Reintroduced or Supplemented Population Components

Numerous plant and animal species have been either introduced to new areas within (intra-limital) or outside (extra-limital) their natural range or reintroduced to areas where the original occupants had disappeared within their natural range as a result of intentional or unintentional human activities. The decision about whether to include such established, (re)introduced populations as part of the Wildlife Species being assessed may depend on whether or not the introduction is intra-limital or extra-limital and on its predicted or demonstrated impact on the Wildlife Species in its natural range and on other components of biodiversity. Supplemented populations are those that receive introductions of individuals within their range. The decision about whether to include such established, supplemented populations as part of the Wildlife Species being assessed may depend on the predicted impact of such supplementation on the Wildlife Species.

(i) Reintroductions occur within the natural range and in the natural habitat of a Wildlife Species. They may include translocations (establishment in a new area, using wild individuals from another area within the natural range) or reintroductions to an area where a Wildlife Species has been extirpated. Reintroductions may include populations established from escaped or intentionally transplanted, captive-reared/maintained populations that themselves were established using individuals from within the natural range of the Wildlife Species. For example, Swift Foxes were reintroduced to the Canadian prairies using both captive-reared and wild-caught foxes from American prairie states. Similarly, captive-bred Peregrine Falcons were released in parts of Canada where they had been extirpated.

Regardless of the intent or means of the original introduction (conservation-based or not, intentional or not), the IUCN recommends that self-sustaining populations resulting from translocations and reintroductions be included in Wildlife Species assessments (IUCN Standards and Petitions Working Group 2016).

(ii) Extra-limital introductions are outside the historical range of the Wildlife Species and may originate from translocated wild individuals or captive-reared individuals. For example, Westslope Cutthroat Trout subpopulations in the North Saskatchewan and Ram River drainages of Alberta, established using hatchery-reared individuals, or Plains Bison in Pink Mountain, BC, are outside the historical range of the Wildlife Species.

(iii) Supplemented population components arise when extant native populations receive captive bred/reared (or cultivated) individuals or wild-to-wild translocations, intentionally or unintentionally. Supplementation is accomplished using individuals originating from the same Wildlife Species.

Supplementation is undertaken to provide harvestable individuals or to rebuild depressed or genetically-depauperate populations, as is being attempted with captive reared Vancouver Island Marmots.Unplanned or undocumented supplementation may occur if individuals escape from captivity or cultivation and contribute to recruitment in a wild population.

3. Hybrid populations

Interbreeding can occur along a continuum ranging from between individuals from genetically different populations of the same taxonomic species to between individuals from different biological species. Rhymer and Simberloff (1996) define hybridization as ‘interbreeding of individuals from what are believed to be genetically distinct populations, regardless of the taxonomic status’. Although hybridization usually refers to mating between heterospecific individuals, it can also apply to mating between individuals of different sub-species or genetically-differentiated populations (and therefore between DUs). Introgression is the transfer of genetic material from one species to another by mating of F1 or later generation hybrids with one of the parental species. There is no universally-accepted species concept (Hey 2006; Haig et al. 2006; Hausdorf 2011), and the definition of subspecies is even more controversial (Haig et al. 2006). Consequently, the level of hybridization should not define a rigid threshold for assessment or conservation purposes. Rather, when considering hybrid populations for assessment, the consequences of the hybridization should be examined from an evolutionary perspective. The more genetically differentiated the two groups, the greater the probability of consequences such as outbreeding depression and the loss of adaptive gene complexes. Alternatively, for small populations where inbreeding depression is evident, introductions of novel genotypes from non-native sources may be beneficial. Natural hybridization and gene flow play important roles in the continuing evolution of some organisms and in the maintenance of genetic diversity. The following sections consider these concepts further in the context of three types of mechanisms resulting in hybridization.

(i) Natural hybridization - Some hybridization occurs independently of human activities and may result in new biological species or novel recombinant genotypes (see references in Stein and Uy 2006, also Seehausen 2004). Hybrid zones in which two closely-related taxa naturally overlap in distribution occur in several taxonomic groups and may remain stable when parental genotypes maintain their integrity (Hagen and Taylor 2001) or continue to change (introgression, Stein and Uy 2006). Furthermore, hybridization is considered a common feature of parapatric or sympatric populations (Mallet 1995), and it can be followed by stabilization and perpetuation of the hybrid derivative as a distinct taxonomic entity (Stebbins 1969). One example of natural hybridization is that between Steelhead Trout and Coastal Cutthroat Trout, where the two Wildlife Species naturally occur together, and the Misty Lake Stickleback, where ‘intermediate’ hybrid forms between the stream and lake sticklebacks are part of the evolutionary process.

Where suitable morphological or genetic markers exist, Fn hybrids and backcrosses may be assigned to one of the parent Wildlife Species where they can be categorized as consisting of >51% of the genome of one of the two parental Wildlife Species. F1 hybrids could not be allocated to either parent as they contain 50% of each genome.

Hybrids resulting from interbreeding between the Wildlife Species under assessment and cultivated individuals (see Definitions and Abbreviations, Appendix C) originating from the same Wildlife Species are not considered to be the product of natural hybridization (e.g., interbreeding of wild and escaped farmed Atlantic Salmon).

(ii) Human-mediated hybridization – Hybridization can be a direct or indirect consequence of human activities. Activities affecting hybridization directly include the introduction of individuals from a genetically distinct population into the natural range of another genetically distinct population or the intentional crossbreeding of two genetically distinct populations, regardless of taxonomic status, such as different DUs. Human activities that can indirectly lead to hybridization include the destruction or modification of suitable habitat and the loss of reproductive barriers (including geographical, physical, or behavioural) that previously existed between the two genetically distinct native populations

The result of the initial hybridization event between two pure parental genotypes is an F1 hybrid. Hybrids may be sterile, have reduced fitness, or be fully capable of breeding with other F1s or of backcrossing with parental genotypes (introgression). Although hybrids that are sterile or have low fitness may not affect the genetic composition of the pure populations, they represent a loss to production and may pose a risk to the viability of at least one parental population, particularly if it is small. Backcrossing and continued successful breeding can lead to increasing levels of genetic introgression resulting in: (1) hybrid swarms where neither of the original pure genotypes exists or (2) unidirectional introgression with the loss of one of the pure parental populations.

Where human-mediated hybridization occurs, Fn hybrids and backcrossed progeny should generally be considered a loss to the Wildlife Species and a threat to its persistence; hybrids do not represent either original taxonomic group, and they do not contribute to the evolutionary lineage of either group. For example, many subpopulations of Westslope Cutthroat Trout in Alberta have experienced introgression from introduced Rainbow Trout and Yellowstone Cutthroat Trout. However, for closely related taxa, it may be difficult to differentiate between ancient polymorphisms shared by the two groups and low levels of introgression. For example, Allendorf et al. (2004) proposed an introgression threshold for Westslope Cutthroat Trout subpopulations: a subpopulation may be considered genetically pure if it expresses <1% admixture (i.e., 1% or fewer of a sample of alleles from a population of putatively pure species “A” can be attributed to introgression with species “B”). This threshold should be assessed using assays from an adequate sample of diagnostic selectively neutral molecular markers and individuals that results in at least a 95% probability that a minimum 1% introgression will be identified if it is occurring in the population (e.g., COSEWIC 2006).

Exceptions may exist where the gene pool of a Wildlife Species is so small that inbreeding depression is evident, and genetic variability cannot be increased using individuals from the same genetic pool. In such situations, it may be prudent to interbreed the Wildlife Species with another closely-related population of the same species to increase genetic variability and benefit from hybrid vigour, particularly where the Wildlife Species in question is otherwise expected to go extinct (Whiteley et al. 2015). This will at least preserve some of the genetic composition of the Wildlife Species and may restore its ecological role. However, the resultant recombinant population may be assessed as a separate DU, with the original one considered extinct, if interbreeding occurred with individuals from other DUs (= Wildlife Species). Furthermore, this recombinant population would only be eligible if it is not dependent on continued introductions to persist and it does not pose a threat to the donor Wildlife Species contributing to the interbreeding efforts.

(iii) Genetically-modified organisms comprise those whose genome has been modified directly by the insertion of genetic material from another species (transgenic organisms) or indirectly by selective breeding to increase the frequency of specific traits. Transgenic organisms and those where selective breeding has been conducted for commercial purposes will always be excluded as Wildlife Species and from the assessment, although they may be identified as a threat. In cases where selective breeding or transgenic manipulations have taken place for conservation purposes (e.g., to increase disease resistance in organisms released to the wild, or to counteract the effects of genetic drift and inbreeding depression in small populations), such organisms may be included in assessments if such manipulations are suspected or demonstrated to be of net positive benefit to the fitness of individuals of the Wildlife Species being assessed (e.g., Wisely et al. 2015).

References:

Allendorf, F., R. Leary, N. Hitt, K. Knudsen, L. Lundquist, and P. Spruell. 2004. Intercrosses and the U.S. Endangered Species Act: should hybridized populations be included as Westslope cutthroat trout? Conservation Biology 18:1203-1213.

Boyer, M. 2006. Rainbow trout invasion and the spread of hybridization with native Westslope cutthroat trout. M.Sc. Thesis, University of Montana.

COSEWIC . 2006. COSEWIC assessment and update status report on the Westslope Cutthroat Trout Oncorhynchus clarkii lewisi (British Columbia population and Alberta population) in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 67 pp. SARA Registry.

Hagen, J., and E.B. Taylor. 2001. Habitat partitioning as a factor limiting gene flow in hybridizing populations of Dolly Varden char (Salvelinus malma) and bull trout (S. confluentus). Canadian Journal of Fisheries and Aquatic Sciences 58:2037–2047.

Haig, S., E. Beever, S. Chambers, H. Draheim, B. Dugger, S. Duhham, E. Smith, J. Fontaine, D. Kesler, B. Knaus, I. Lopes, P. Loschl, T. Mullins, and L. Sheffield. 2006. Taxonomic considerations in listing subspecies under the U.S. Endangered Species Act. Conservation Biology 20:1584-1594.

Hausdorf, B. 2011. Progress toward a general species concept. Evolution 65:923-931.

Hey. J. 2006. On the failure of modern species concepts. Trends in Ecology & Evolution 21:447-450.

IUCN. 1998. Guidelines for re-introductions. Prepared by the IUCN/SSC Re-introduction Specialist Group, IUCN, Gland, Switzerland and Cambridge. UK. 10 pp.

IUCN Standards and Petitions Working Group. 2016. Guidelines for using the IUCN Red List Categories and Criteria. Version 12. Prepared by the Standards and Petitions Working group of the IUCN SSC Biodiversity Assessments Sub-Committee. February (and updated versions thereafter).

Lynch, M., and M. O’Hely. 2001. Captive breeding and the genetic fitness of natural populations. Conservation Genetics 2:363-378.

Mallet, J. 1995. A species definition for the modern synthesis. Trends Ecological Evolution 10: 294-299.

Rhymer, J., and D. Simberloff. 1996 Extinction by Hybridization and Introgression. Annual Review of Ecology and Systematics 27:83-109.

Seehausen, O. 2004. Hybridization and adaptive radiation. Trends in Ecology & Evolution 19:199-207.

Stebbins, G. 1969. The significance of hybridization for plant Taxonomy and evolution. Taxon, Vol. 18, No. 1, Smithsonian Summer Institute in Systematics 1968, Part 1 (Feb., 1969), pp. 26-35

Stein, A., and A. Uy. 2006. Unidirectional introgression of a sexually selected trait across an avian hybrid zone: a role for female choice? Evolution 60:1476-1485.

Whiteley, A.R., S.W. Fitzpatrick, W.C. Funk, and D.A. Tallmon. 2015. Genetic rescue to the rescue. Trends in Ecology & Evolution 30:42-49.

Wisely, S.M., O.A. Ryder, R.M. Santymire, J.F. Engelhardt, and B.J. Novak. 2015. A road map for 21st century genetic restoration: gene pool enrichment of the black-footed ferret. Journal of Heredity 106:581-592.

(1) When significant threats (e.g., poaching, disease) affecting a Wildlife Species at risk are likely to be exacerbated by manipulated population components, the manipulated population components should clearly be considered as a threat to the Wildlife Species at risk.

(2) Based on IUCN definition of benign introduction.