Hybridization, Reproductive Barriers,
and Management of Red Wolves
(Canis rufus)
Rich Fredrickson
Outline
• A brief history of red wolves
• Inter-specific reproductive barriers
• Simulated red wolf populations
• Real red wolves in North Carolina
Historic Range
A brief history of red wolves
• 1973 Captive breeding started
• 1986 First captive born red wolves released
Reintroduction Chronology
• 1973 Captive breeding started
• 1986 First captive born red wolves released
• 1993 First hybridization with coyotes detected
• 2000 Sterilization of coyotes, removal of hybrids,
genetic assignment tests
What do we want?
• N > 220 red wolves in NE North Carolina
• At least 2 other population in historic range
• Preserve 80% to 90% of red wolf genetic
diversity for 150 years.
Inter-specific Reproductive Barriers
• Prezygotic barriers
• Postzygotic barriers
Reproductive barriers
• Prezygotic barriers
– Factors that prevent formation of a zygote.
• Postzygotic barriers
Reproductive barriers
• Prezygotic barriers
– Factors that prevent formation of a zygote.
– “…includes phenological isolation, habitat isolation
and sexual isolation that is due to assortative mating
or fertilization” (Seehausen et al. 2014)
• Postzygotic barriers
Reproductive barriers
• Prezygotic barriers
– Positive assortative mating
• Postzygotic barriers
– Intrinsic
– Extrinsic
Reproductive barriers
• Prezygotic barriers
– Positive assortative mating
• Postzygotic barriers
– Intrinsic - genetic incompatibilities
– Extrinsic
Reproductive barriers
• Prezygotic barriers
– Positive assortative mating
• Postzygotic barriers
– Intrinsic - genetic incompatibilities
– Extrinsic - “…result from divergent ecological or sexual
selection and depend on interaction either with the environment
or with other individuals; an example is reduced viability or
fertility of migrants and hybrids due to ecological or behavioural
factors” (Seehausen et al. 2014)
Reproductive barriers
• Prezygotic barriers
– Positive assortative mating
• Postzygotic barriers
– Extrinsic – Interspecific aggression, displacement,
and killing of coyotes and hybrids
Reproductive barriers
• Prezygotic barriers
– Positive assortative mating
• Postzygotic barriers
– Extrinsic – Interspecific aggression, displacement,
and killing of coyotes and hybrids
Could these barriers be sufficient to allow the
reintroduced red wolf population to grow to larger size
and persist?
Questions
1. What are the potential effects of
hybridization and introgression?
2. What parameters (and reproductive
barriers) most affect RW persistence?
3. Is sterilization effective in minimizing
introgression while allowing RW
population growth?
Methods – Simulation model
• Individual-based
• Continent-Island model of gene flow
• F1 hybrids backcross equally with both parental
species
Methods – reproductive barriers
• Positive assortative mating in RW in relation to
CY
• Positive assortative mating in RW & in hybrids
• Red wolf “challenges”
Methods – Sensitivity analysis
• 5000 iterations
• Parameter values randomly drawn from
plausible ranges
• Regression models of “quasiextinction” and
“persistence”
• Parameter importance - standardized regression
coefficients
Methods – Starting conditions
• Colonizing populations – 8 RW pairs
• Established populations – 50 RW pairs
Colonizing populations
1000
Red wolf pair extirpations
Number of red wolf pairs
50
40
30
Red wolves only
20
10
800
600
400
200
0
0
0
25
50
Year
75
100
0
20
40
60
Year
80 100
Colonizing populations
1000
Red wolf pair extirpations
Number of red wolf pairs
50
40
Red wolves only
30
Random mating
20
10
800
600
400
200
0
0
0
25
50
Year
75
100
0
20
40
60
Year
80 100
50
1000
40
800
Red wolves only
Assortative mating
30
Random mating
20
10
Red wolf pair extirpations
Number of red wolf pairs
Colonizing populations
600
400
200
0
0
0
25
50
Year
75
100
0
20
40
60
Year
80 100
Colonizing populations
1000
40
Red wolves only
Red wolf challenges
Assortative mating
Random mating
30
20
10
0
Red wolf pair extirpations
Number of red wolf pairs
50
800
600
400
200
0
0
25
50
Year
75
100
0
20
40
60
Year
80
100
Established populations
Sensitivity analysis results
• Frequency of successful challenges
• Strength of RW assortative mating relative to CY
• Adult RW survival / RW population growth rate
Little effect of CY and hybrid demography
Does sterilization (with assignment errors)
promote the success of colonizing red wolf
populations?
Non-extirpated
populations
Can red wolf populations be successful?
• Moderate frequency of successful challenges,
• Moderate to strong assortative mating,
• High RW population growth rate.
• High sterilization effort may promote population
growth if some reproductive barriers present.
Back to REAL red wolves…
• 1993 hybridization: 2 F1 males bred RW females & offspring
bred with RW.
• Cryptic hybridization – some F1 backcrosses considered pure
RW
• Genetic assignment tests started in 2000
• Result: >0.875 red wolf ancestry = “Red wolf”
• Large % of “Red wolves” have some Coyote ancestry
Hybrid zone composition
Bohling, J. 2011. Dissertation
RWEPA:
~50% Coyote
4% HY
Bohling, J. 2011. Dissertation
4% hybrids – how did they get there?
• Genetic assignment tests for every Canis
encountered
• Euthanizing all hybrid litters detected
• Removing coyotes
• Sterilizing select coyotes to be placeholders
Have RW colonized outside the
reintroduction area?
• 82 Canis spp. detected
• No red wolves
• 7 - 37 red wolf hybrids
• < 30% red wolf
ancestry
What causes red wolves to hybridize?
• Investigated 22 hybrid litters from 2001 – 2009.
What causes red wolves to hybridize?
• Investigated 22 hybrid litters from 2001 – 2009.
• 13 HY litters - stable RW breeding pairs disrupted
during or shortly before breeding season
• 11 disruptions human-caused
• 2 female RW paired with sterilized CY that were
killed or displaced by RW. Both female RW
repaired with unsterilized CY.
Canis lycaon
Algonquin Provincial Park
•
“We
conclude that the wolf culls transformed the
genetic composition of this unique eastern wolf
population by facilitating coyote introgression. These
results demonstrate that intense localized harvest of a
seemingly abundant species can lead to unexpected
hybridization events that encumber future
conservation efforts.”
Rutledge et al. 2011. Ecology & Evolution
Human caused mortality
• 46 of 60 RW mortalities 2011 – June 2014
were human-caused
Sensitivity analysis results
• Frequency of successful challenges
• Strength of RW assortative mating relative to CY
• Adult RW survival
One last thought…
Allee effect – few red wolves in a coyote /
hybrid swarm may swamp assortative mating
Questions?