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Size-assortative choice and mate availability influences hybridization between red wolves (Canis rufus ) and coyotes (Canis latrans )

Authors:

Abstract

Anthropogenic hybridization of historically isolated taxa has become a primary conservation challenge for many imperiled species. Indeed, hybridization between red wolves (Canis rufus) and coyotes (Canis latrans) poses a significant challenge to red wolf recovery. We considered seven hypotheses to assess factors influencing hybridi-zation between red wolves and coyotes via pair-bonding between the two species. Because long-term monogamy and defense of all-purpose territories are core characteristics of both species, mate choice has long-term consequences. Therefore, red wolves may choose similar-sized mates to acquire partners that behave similarly to themselves in the use of space and diet. We observed multiple factors influencing breeding pair formation by red wolves and found that most wolves paired with similar-sized conspecifics and wolves that formed congeneric pairs with nonwolves (coyotes and hybrids) were mostly female wolves, the smaller of the two sexes. Additionally, we observed that lower red wolf abundance relative to nonwolves and the absence of helpers increased the probability that wolves consorted with nonwolves. However, successful pairings between red wolves and nonwolves were associated with wolves that maintained small home ranges. Behaviors associated with territoriality are energetically demanding and behaviors (e.g., aggressive interactions, foraging, and space use) involved in maintaining territories are influenced by body size. Consequently, we propose the hypothesis that size disparities between consorting red wolves and coyotes influence positive assortative mating and may represent a reproductive barrier between the two species. We offer that it may be possible to maintain wild populations of red wolves in the presence of coyotes if management strategies increase red wolf abundance on the landscape by mitigating key threats, such as human-caused mortality and hybridization with coyotes. Increasing red wolf abundance would likely restore selection pressures that increase mean body and home-range sizes of red wolves and decrease hybridization rates via reduced occurrence of congeneric pairs.
Ecology and Evolution . 201 8 ;1–1 4 .    
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 1
www.ecolevol.org
Received:14January2017 
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  Revised:9J anuary2018 
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  Accepted:27Januar y2018
DOI:10.1002/ece3.3950
ORIGINAL RESEARCH
Size- assortative choice and mate availability influences
hybridization between red wolves (Canis rufus) and coyotes
(Canis latrans)
Joseph W. Hinton1| John L. Gittleman2| Frank T. van Manen3| Michael J. Chamberlain1
ThisisanopenaccessarticleunderthetermsoftheCreativeCommonsAttributionLicense,whichpermitsuse,distributionandreproductioninanymedium,
providedtheoriginalworkisproperlycited.
©2018TheAuthors.Ecology and EvolutionpublishedbyJohnWiley&SonsLtd.
1WarnellSchoolofForestryandNatural
Resources,UniversityofGeorgia,Athens,
GA,USA
2OdumSchoolofEcology,Universityof
Georgia,Athens,GA,USA
3U.S.GeologicalSurvey,NorthernRocky
MountainScienceCenter,Interagency
GrizzlyBearStudyTeam,Bozeman,MT,USA
Correspondence
JosephW.Hinton,WarnellSchoolof
ForestryandNaturalResources,University
ofGeorgia,Athens,GA,USA.
Email:jhinton@uga.edu
Funding information
WarnellSchoolofForestryandNatural
Resources
Abstract
Anthropogenichybridizationofhistoricallyisolatedtaxahasbecomeaprimarycon-
servationchallengefor many imperiledspecies.Indeed,hybridization between red
wolves (Canis rufus)and coyotes(Canis latrans)poses a significant challenge tored
wolfrecovery.Weconsideredsevenhypothesestoassessfactorsinfluencinghybridi-
zationbetweenredwolves and coyotes viapair-bonding betweenthe twospecies.
Becauselong-termmonogamyanddefenseofall-purposeterritoriesarecorecharac-
teristicsof both species, mate choicehas long-term consequences. Therefore,red
wolvesmaychoosesimilar-sizedmates to acquirepartners that behavesimilarlyto
themselvesinthe useofspace anddiet. Weobserved multiple factors influencing
breed ingpairformationbyre dwolvesandfoundthatm ostwolvespairedwit hsimilar-
sizedconspecificsandwolvesthatformedcongenericpairswithnonwolves(coyotes
andhybrids)weremostlyfemalewolves,thesmallerofthetwosexes.Additionally,
weobservedthatlowerredwolfabundancerelativetononwolvesandtheabsenceof
helpers increased the probabilitythatwolves consorted with nonwolves.However,
successfulpairingsbetweenredwolvesandnonwolveswereassociatedwithwolves
thatmaintainedsmallhomeranges.Behaviorsassociatedwithterritorialityareener-
geticallydemandingandbehaviors(e.g.,aggressiveinteractions,foraging,andspace
use)involvedinmaintainingterritoriesareinfluencedbybodysize.Consequently,we
proposethehypothesisthatsizedisparitiesbetweenconsortingredwolvesandcoy-
otesinfluencepositiveassortativematingandmayrepresentareproductivebarrier
betweenthetwospecies.Weofferthatitmaybepossibletomaintainwildpopula-
tionsofredwolvesinthepresenceofcoyotesifmanagementstrategiesincreasered
wolfabundanceonthelandscapebymitigating keythreats,such as human-caused
mortalityandhybridizationwithcoyotes.Increasingredwolfabundancewouldlikely
restore sel ection pressur es that increase mean b ody and home-range sizes of red
wolvesanddecreasehybridizationratesviareducedoccurrenceofcongenericpairs.
KEYWORDS
assortativemating,bodysize,Canis latrans,Canis rufus,coyote,hybridization,monogamous
breeding,redwolf,reproductivebarriers,spaceuse
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   HINTON eT al.
1 | INTRODUCTION
UnderMayr’s(1942)biologicalspeciesconcept,theoriginofspecies
involvesreproductiveisolationandevidencestillfavorstheviewthat
newspeciesusually ariseasbyproductsofevolutioningeographi-
cally isolatedpopulations(Coyne&Orr,2004; Hey,Fitch, &Ayala,
2005;Pfennig&Pfennig,2010;Schluter,2001).Globalenvironmen-
talchangecausedbyhumanactivityhaseliminatedmanygeographic
barriersthatprevented secondary contactbetweenclosely related
taxathatarosethroughallopatricspeciation.Secondarycontactand
reproductiveinteractionsfacilitatehybridizationamongformerlyal-
lopatricpopulationswithdivergentevolutionarylineages.Although
some studieshavepresentedhybridization as a positiveforce that
provides beneficial adaptive genetic variation fromone species to
another (Abbott etal.,2013; Brennan etal.,2014;Stebbins,1959;
vonHoldt, Brzeski, Wilcove, & Rutledge, 2017), others have at-
tributedhybridizationandintrogressionasathreattoimperiledpop-
ulationsandspecies(Genovart,2009;Ellstrandetal.,2010;Rhymer
& Simberloff, 1996; Todesco etal., 2016). Indeed, the literature
pertaining to reproductive barriers and speciation is voluminous,
butits broader integration into conservationandmanagementhas
beenunderappreciated(Allendorf,Leary,Spruell,&Wenburg,2001;
Rhymer & Si mberloff, 1996; Seehause n, Takimoto , Roy, & Jokela,
2008;vonHoldt,Brzeskietal.,2017).
Naturalhybridizationisobservedmorefrequentlyincertaintax-
onomicgroups,as25%ofplantand10%ofanimalspeciessurveyed
instudiesareknowntohybridize(Mallet, 2005),andhybridization
tends to concentrate in specific geographic regions (e.g., hybrid
zones; Barton & Hewitt, 1989; Benson, Patterson, & Wheeldon,
2012;Swenson&Howard,2005).Forexample,despitebirdshaving
greaterspeciationratesandachievinggreaterspeciesdiversitythan
mammals , they evolve complete hy brid inviability a t slower rates
than mammals (Fitzpatrick, 2004; Wilson, Maxon,& Sarich, 1974).
Severalstableandwell-studiedavianhybridzonesoccuracrosssig-
nificantareasoftheGreatPlainsoftheUnitedStates,whereranges
of14pairsofgeographicallyseparatedspeciesoverlap(Curry,2005;
Dixon,1989;Mettler&Spellman,2009).Hybridizationamongmam-
mal speci es in the Great Plain s is relatively rare (S hurtliff, 2013),
buthybridizingspeciesof severalmammaliangenera,suchasCanis
(Kyle etal., 20 06; Nowak, 20 02; Rutledge, Gar roway,L oveless, &
Patterson, 2010), Geomys (Genoways, Hamilton, Bell, Chambers,
& Bradley, 20 08; Heaney & T imm, 1985), and Odocoileus (Cathey,
Bickham , & Patton, 1998; Stub blefield, War ren, & Murphy, 1986),
havehistorically occurred. Regardlessoftaxonomy, populations of
congenersaremorelikelytointeractreproductivelyduringsecond-
ary contact if theyare recently divergedsistertaxa (Coyne&Orr,
2004), similar in some ecological, morphological, and behavioral
traits (Crossman,Taylor, & Barrett-Lennard, 2016;Montanari, van
Herwerden, Pratchett,Hobbs, & Fugedi, 2011),and exhibit a poor
abilitytodiscriminatebetweenspecies(Gill&Murray,1972;Myers
&Frankino,2012).
I np a r t i cu l a r, r e pr o d u c ti v e is o l a ti o n of c o yo t e s( Canis latrans), e as t-
ernwolves(Canis lycaon),andredwolves(Canis rufus)isincomplete,
inwhich gene flowoccurs between themvia hybridization andin-
trogression, andlikely has done so for much of their evolutionary
histor y where their ra nges overlapped ( Brzeski, DeB iasse, Rabon,
Chamberlain, &Taylor,2016;Kyleetal.,2006;Rutledge, Devillard,
Boone,Hohenlohe,&White,2015;Rutledge,Garrowayetal.,2010).
However, agricul tural conversio n of natural habit ats and pred ator
control pr ograms that ex tirpated wolf p opulations f acilitated coy-
oterangeexpansioninto thehistoricranges ofeasternwolvesand
redwolvesduringthe20thcentury(McCarley,1962;Nowak,2002;
Rutledge, White, Row, & Patterson, 2012; Stronen etal., 2012).
Researchsuggeststhatlimitedpopulationgrowthofwolvescaused
byexcessiveanthropogenic mortalitywastheprimarycausefacili-
tatinghybridizationbetweenthetwoeasternNorthAmericanwolf
speciesandcoyotes(Benson,Patterson,&Mahoney,2014;Bohling
& Waits, 2015; Hinton, Brzeski, Rabon, & Chamberlain, 2017;
Rutledge,Whiteetal.,2012).Asaresult,researchandmanagement
priorities for wolf conservation in eastern North America focused
onunderstandingtheextenttowhichreproductivelycompatiblebut
ecologicallydifferentCanistaxamaycoexistwithminimallevelsof
geneflow(Bensonetal.,2014;Geseetal.,2015;Rutledge,Wilson,
Klütsch,Patterson,&White,2012).
Endemic totheeasternUnitedStates, red wolvessharea com-
monancestorwithcoyotesanddifferentiatedfromtheminallopatry
duringthePleistocenebutbeganinterbreedingwithcoyotesinthe
southeastern United States during the early 20th century, when
remnantwolfpopulationsbeganinteractingwithexpanding coyote
populations(Chambers,Fain,Fazio,&Amaral,2012;Nowak,2002,
2003; W ilson etal., 20 00). By 1980, the re d wolf was extir pated
fromthewildbut,viaacaptivebreedingprogram,reintroducedinto
eastern North Carolina beginning in 1987 (Hinton, Chamberlain,
&Rabon, 2013; United StatesFish and Wildlife Service [USFWS],
1989). Meanwhile, coyotes rapidly colonized the red wolf’s his-
toricrangeandcurrentlyco-occurwiththesmallreintroducedwolf
populat ion in eastern N orth Car olina (Gese etal ., 2015; Hinton &
Chamberlain, 2014). Because hybridization with coyotes is a pri-
marychallengetoredwolfrecovery,theUSFWSRedWolfRecovery
Program (RecoveryProgram)implemented theRed Wolf Adaptive
ManagementPlantominimizehybridizationandpreventcoyotein-
trogressionvia sterilizationofcoyotespairedwithwolves (Gese&
Terletzky,2015;Geseetal.,2015).
Fundamentally,hybridization resultsfrommatechoiceby indi-
vidual red wolves. Previous asse ssments warned t hat female red
wolvespairingwithcoyotes(Kelly,Miller,&Seal,1999)andalackof
reproductive barriersbetweenwolves and coyotes (Fredrickson&
Hedrick,2006)wouldbeproblematicforredwolfrecovery.Studies
following t hose assessm ents repor ted that anth ropogenic fac tors,
specifically gunshotmortalitiesduring the breeding season,facili-
tated hybridization by disrupting red wolf breeding pairs with a
greaterproportionoffemalewolvesthanmalesbreedingwithcoy-
otes(Bohling&Waits,2015;Hinton,Brzeskietal.,2017).However,
coyoteintrogressionintothewildredwolfpopulationremained<4%
becausetheRecoveryProgram’suseofcoyotesandhybridsasster-
ileplaceholdersprovidedanartificialreproductivebarrier (Gese&
    
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HINTON eT a l.
Terletzky,2015).Althoughsterileplaceholderslimitedintrogression,
studiesofhybridization(Bohling&Waits,2015;Bohlingetal.,2016)
andbreedingpairdynamics (Hinton,Brzeskietal.,2017)observed
nonrandommating inthe reintroduced population,suggestingthat
assortative matingwas alsoplaying a roleinlimitingthe extentof
hybridization(Bohlingetal.,2016).
FactorsinfluencingassortativematinginCanistaxaarelikely
multifaceted with a diversity of behavioral and ecological cor-
relates that may influence hybridization (Benson & Patterson,
2013; Bohling etal., 2016; Hinton etal., 2013; Hinton, Ashley
etal., 2017; Rutledge, Garroway etal., 2010; Rutledge, White
etal.,2012).Essentially,hybridizationresultswhenindividualred
wolvesa ndcoyot esconsorttoformco nge ner icb ree din gpairsthat
defendterritoriesandproducehybridlitters(Hintonetal.,2013;
Hinton, Br zeski etal., 2017; Hinton, Ashley etal., 2017). Long-
term monogamy, defense of all-purpose territories, and group
living that involvesbi-parental careofoffspringarecorecharac-
teristicsofCanis(Bekoff,Diamond,&Mitton,1981;Geffenetal.,
1996;Gittleman,1989;Kleiman, 2011)and behaviors associated
with conso rting, mat e selection , and mate fidel ity may ser ve as
behavioralreproductivebarriersthatpreventhybridizationamong
sympatricCanis taxa. For example, studiesroutinely report that
graywolves(Canis lupus)and coyotes are reproductivelyisolated
inthewild(García-Moreno,Matocq,Roy,Geffen,&Wayne,1996;
Hohenloheetal.,2017;Kyleetal.,2006;Pilgrim,Boyd,&Forbes,
1998; Rutledge, Wilson etal., 2012; Wheeldon, Patterson, &
White,2010),althoughithasbeensuggestedthatthetwospecies
dohybridize (vonHoldt etal., 2011, 2016; vonHoldt, Cahilletal.,
2017). Gray wolf and coyote interactions are well documented
throughout North America and, despite routinely interacting
ecologicallyassympatricspecies(Arjo,Pletscher,&Ream,2002;
Atwood &Gese,2010;Switalski,2003),amicableconsorting be-
havior bet ween them is ex tremely r are (Hohenlo he etal., 2017;
Thiel, 2006). To our knowledge, congeneric pairings between
graywolvesandcoyoteshavenotbeenconfirmedinfieldstudies.
Howeve r,congene ricpairi ngsbet wee nr edwol vesan dcoyote sare
welldocumented(Gese & Terletzky,2015;Hinton,Brzeskietal.,
2017;Hinton, Ashley etal., 2017), implying that red wolves and
coyotesarecapableofsharingspaceandfoodresourcestoover-
comelimitedmatingopportunities.
Redwolfandcoyotebreeding pairs exhibitconstrainedmove-
me ntsovert hel ands cap e,a ssi tef ide lit yis exp ress edbyt heirco nsi s-
tentuseandterritorialdefenseofspecificlocalitiesviapassive(i.e.,
scent mark ing) and aggre ssive (i.e., physic al conflict) be haviors to
excludeconspecifics(Benson&Patterson,2013;Gese&Terletzky,
2015;Hinton,vanManen,&Chamberlain,2015;Hintonetal.,2016).
Thesespaceusepatternscomprisebehaviorsthatreflecthowboth
species usetheir environment in responsetointernalandexternal
pressures.Forexample, spaceuseispositivelycorrelatedwithcar-
nivorebodymass,wherelargercarnivoresrequirelargerterritories
than smaller carnivores to fulfill greater energetic requirements
(Gomppe r & Gittlema n, 1991;M cNab, 1963). Indeed, Hi nton, van
Manen etal . (2015) reporte d that coyote home range s in eastern
NorthCarolinarangedbetween13and47km2 andsuggestedthat
coyote body size co nstrained the ar ea they could effec tively ex-
ploitanddefend asterritories. Furthermore,Ward(2017) assessed
space use of 147 coyotes radio-marked with Global Positioning
System (GPS)collarsin Alabama, Georgia, andSouthCarolinaand
reported that 80% of resident coyotes maintained home ranges
below 20km2.The larger bodysize of redwolves allows them to,
on average,maintain largerterritories than coyotes, but somered
wolves maintainsimilar home-range sizes as coyotes(Hintonetal.,
2016). Because cooperation and coordination between breeding
pairsforbothspeciesiscrucialforefficientforaging,parentalcareof
offspring,andterritorydefense,Hinton,Ashleyetal.(2017)hypoth-
esizedthat whenindividualredwolvesrequirehomeranges larger
than consorting coyotes can maintain, asymmetric exploitation
of space bet ween larger wo lves and smalle r coyotes may prevent
congenericpairings.Ifthisistrue,thenassortativematingobserved
betweenredwolvesandcoyotesmayresultfromsize-basedchoice,
asasymmetry in partnersizes may makeittoocostlytostrive for
the best available options required by the larger or smaller mates
(Schuett,Tregenza,&Dall,2010;Taborsky,Guyer,&Taborsky,2009;
Taborsky&Taborsky,1999).
Currently, it is unknown whether innate preferences or envi-
ronmentalconditionsareresponsibleforreproductivebarriersob-
serve d in Canis taxa, but b oth condition s likely play an impo rtant
rolefacilitatinghybridization.Itiswidelyacknowledgedthathuman-
mediated mortalityof wolvesdisrupts the socialstructuresofwolf
packsandreducestheirabundanceonthelandscape(Bensonetal.,
2014;Borg,Brainerd,Meier,&Prugh,2015; Hinton,White,Rabon,
& Chamberlain, 2017; Hinton, Brzeski etal., 2017; Milleret etal.,
2017; Rutledge, Pat terson etal., 2010). B ecause gray wolves a nd
coyotesdonotexhibitconsortingbehaviorsthatleadtocongeneric
pairings,even whenwolf densities are low,there is no interaction
betweenhuman-caused mortality and hybridization between gray
wolves and coyotes in western Nort h America (Hohe nlohe etal.,
2017;Wheeldon etal., 2010). Conversely,redwolves andcoyotes
can form co ngeneric pair s likely because r ed wolves and coyotes
are sibling species that have recently diverged (Hohenlohe etal.,
2017; Kyle etal., 2006; R utledge etal., 2 015; Wilson etal., 20 00)
andhavenotevolvedstrongdiscriminatorybehaviorsthatfacilitate
complete reproductive isolation. However, behavioral traits that
promote assortative mating and prevent congeneric pairings likely
restrictgene flowbetweenredwolves andcoyotes(Bohlingetal.,
2016; Fredrick son & Hedrick , 2006). It is cur rently unknow n how
morphological andbehavioraldifferencesbetweenredwolvesand
coyotes influence consorting behaviors,but mate choice for these
species has long-term consequences and breeding pairs should
coordinat e behaviors ef ficientl y to defend terri tories and imp rove
offspring survival. Therefore,similarity in bodysizeand spaceuse
behavior s are likely two im portant i nnate traits i nfluencing ass or-
tativematingbetweenredwolvesandcoyotes,asthesetraitslikely
provide inf ormation on the be havioral consiste ncy and qualit y of
mates that t hey attempt to pair-bond wi th. Now that geogra phic
barriers(e.g.,pre-Columbianlandscapes)havebeeneliminatedand
4 
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   HINTON eT al.
the only w ild populatio n of red wolves co-occu rs with coyotes, it
isessentialtoidentifybehaviorsinfluencingpotentialreproductive
barrie rs between wolv es and coyotes. If repr oductive barr iers do
exist,theymayrepresentoneoftheonlyopportunitiestomaintain
awildpopulationofredwolves in thepresence of coyotes.Inthis
study,weusedadetaileddatasetonredwolfmateselectionspan-
ning20yearstoinvestigatefactorsinfluencingwolfmatingpatterns
andhybridizationwithcoyotes.
2 | MATERIAL AND METHODS
2.1 | Study area
Comprisingapproximately6,000km2offederal,state,andprivate
lands,theRedWolfRecoveryAreawaslocatedontheAlbemarle
Peninsula in northeastern North Carolina (Figure1). The land-
scapeconsistedofarow-cropagricultural-bottomlandforestma-
trixinwhichagriculturalcrops(i.e.,corn,cotton,soybean,winter
wheat) an d managed pine (Pinus spp.) comprisedapproximately
30%and15%ofvegetativecover,respectively.Otherprominent
vegetative cover on the Albemarle Peninsula included coastal
bottomlandforestsandpocosin (35%),herbaceous wetlandsand
saltwatermarshes (5%),andother minorvegetativecommunities
(10%).Further details of the studyarea canbe foundin Hinton,
Ashleyetal.(2017).
2.2 | Capture and monitoring
Since1987,RecoveryProgrambiologistsannuallytrappedredwolves
tofitindividualswithmortality-sensitivevery-high-frequency(VHF;
Teleonics, Mesa, AZ) and Global Positioning System (GPS; Lotek
4400S, Newmarket, Ontario, Canada) radio collars and regularly
monitoredradio-markedwolvesuntilindividualsdiedorradiocollars
failed(Hinton,Whiteetal.,2017).By1992,coyotesbegancolonizing
theRecoveryAreaandthefirsthybridizationeventoccurredduring
1993(Geseetal.,2015).Subsequently,coyotesweretrapped,fitted
withradiocollars,andmonitoredbytheRecoveryProgram(Gese&
Terletzky,2015;Hinton,Brzeskietal.,2017).Therefore,redwolves
and coyote moni tored for this study occurred during 1992–2012
whenconsortingbehaviorbetweenthetwospecieswereobserved.
FIGURE1 TheRedWolfRecoveryAreaontheAlbemarlePeninsulaofnortheasternNorthCarolina
    
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 5
HINTON eT a l.
Method s to capture, han dle, and proce ss red wolves and coyote s
were in cooperation and concordancewith the USFWS, approved
by the Louis iana State Univer sity Agri cultural Ins titutional A nimal
Care and Use Committee (Protocol Number AE2009-19), and met
guidelinesrecommendedbytheAmericanSocietyofMammalogists
(Sikes&Gannon,2011).
During October through May of each year, red wolves and
coyotes were capturedusing padded foot-holdtraps(Victor no.3
Softcatch,WoodstreamCorporation,Lititz,PA).Ages,speciesiden-
tity,andparentageofcapturedredwolveswereknownifindividuals
werecarryingasubcutaneouspassiveintegratedtransponder(PIT)
tagsinsertedintotheanimalduringannualsurveysofredwolfdens
(Gese etal., 2015; Hinton, Whiteetal., 2017).Ages of red wolves
withoutPITtagsandcoyoteswereestimatedbytoothwear(Gipson,
Ballard,Nowak, &Mech, 2000),and a blood sample was taken to
determi ne parentage an d species ident ity. Coyotes were take n to
alocal veterinaryclinic forsurgicalsterilization (Gese & Terletzky,
2015).Thisprocedurereduced hybridizationandintrogressionand
allowedtheRecoveryProgramtousesterilecoyotesasplaceholders
untilthosecoyotesweredisplacedbyredwolvesorwereremoved
formanagementreasons(Gese&Terletzky,2015).Onceredwolves
andcoyoteswerefullyprocessed,individualswerefittedwithradio
collars, released, and then monitored by the Recovery Program
during weeklytelemetry flights. Weekly monitoring effortsviaair-
craftallowedtheRecoveryProgramtoidentifyandmonitorterrito-
riesofradio-markedredwolvesandcoyotesonthelandscape.
Breeding pairs were identified as radio-collared individuals
of breedin g age (≥2year s old) that were tempo rally and spatiall y
associated with one another and were defending a territory for
≥6months (Hinton,Brzeskietal., 2017). Onlythree typesofCanis
breedingpairswere routinelymonitoredbytheRecoveryProgram:
redwolves(2redwolves),coyotes(2 coyotes),andcongeneric(red
wolveswithcoyotesorhybrids).Biologistsconfirmedbreedingpair
statusofredwolvesduringspringdenvisits(March–May)bylocat-
ing dens an d daybeds of femal es to verify th e presence of lit ters
ofknown, radio-collaredbreedingpairs(Beck,Lucash,&Stoskopf,
2009). Congenericpairs andcoyote pairswere confirmed through
fieldmonitoringandoccasionallybydenvisitsifcoyotesandhybrids
hadnotbeencapturedandsterilized.
2.3 | Data analyses
Many Canisbreedingpairs disbandedundernaturalandanthropo-
geniccauses, in which widowedredwolves and coyotes replaced
matesbyeithermaintainingtheirterritoriesand pair-bonding with
transientsorbecomingtransientsthemselvestoseekoutnewmates
andterritories(Hinton,vanManenetal.,2015;Hintonetal.,2016;
Hinton,Brzeskietal.,2017).Consequently,manyredwolvesinour
study had multiple mates during their lifetime. Therefore, we as-
sessed breedinghistoryforredwolvesmonitored bytheRecovery
Programduring1992–2012andclassifiedpairingsintotwocatego-
ries:conspecific(redwolvesthatpairedwithredwolves)andconge-
neric(redwolvesthatpairedwithcoyotesorhybrids).
Similar to previous studies (Bohling & Waits, 2015; Hinton,
Brzeski etal., 2017), we used qualitative descriptions of specific
eventsexperiencedbyeachredwolfwhentheyformedconspecific
and congeneric breeding pairs to assess whether anthropogenic
mortality (e.g., shootingdeaths) facilitated congenericpairings.We
simplifiedthiscategoryandassigned redwolvestooneoftwocat-
egories: thosethatwerewidowedorwereinpacksthatdisbanded
because of gunshot mortality and those that were not. Because
someredwolfbreedershadestablishedpackswithjuveniles(Hinton
&Chamberlain, 2010;Sparkman, Adams,Steury,Waits, & Murray,
2010; Spark man etal., 2011), we also classi fied wolves in pairi ng
events as eitherhaving helpers or not whenacquiringanewmate
to assess if p ack structu re influenced conge neric pairing s. To ex-
aminetheinfluenceofbreederexperienceonacquiringconspecific
andcongenericmates,weclassifiedredwolvesinpairingeventsas
first-timebreedersorexperiencedbreeders(Bohling&Waits,2015).
Because some red wolves were represented in multiple pairing
events,therewereinterdependenciesinourdata.Weaccountedfor
suchinterdependenciesinourunivariateanalysesbyincludingran-
dominterceptsforindividualredwolvesingeneralizedlinearmixed
models(GLMM)inR(RCoreTeam,2014;Bates,Maechler,Bolker,&
Walker,2015)thatcomparedthefrequencyofgunshotmortalities,
helpers,andfirst-timebreedersbetweenconspecificandcongeneric
pairings.Wethenusedthelikelihoodratiotestasameanstoattain
p-valuesbycomparingthelikelihoodof themodelwithafactorto
theintercept-onlymodel.
The Canispopulationinourstudyareaconsistedofacontin-
uumofcanidswithbodymassesrangingbetween7and39kgthat
redwolvescouldform breedingpairswith(Hinton&Chamberlain,
2014).Toassesstheinfluenceofbodysizeoncongenericpairings,
weusedbody traits of red wolves,coyotes, and hybrids that were
recordedforindividuals,whiletheywereprocessedandfittedwith
radiocollars(Hinton&Chamberlain,2014).Bodytraitsmeasuredin-
cluded bodymass,bodylength(anteriortipofthenosepadtothe
tailbase),taillength(tipofthefleshypartofthetailtothetailbase),
hindfootlength(hocktothetipofthedigitalpads),shoulderheight
(tipofthescapulatotipofthedigitalpads),lengthofhead(edgeof
thepremaxillaryto the mostposteriorpointoftheoccipitalbone),
width of head(widest points acrossthe zygomata), and earlength
(edgeoftheexternalauditorycanaltothetipoftheear).Weuseda
principalcomponentanalysis(PCA;JMPsoftware;SASInstitute)to
createasinglemeasurementofoverallbodysize.BasedonBrzeski,
Rabon,Chamberlain,Waits,andTaylor(2014),weassumedthePCA
segregat ed variation due to b ody size by linearly co mbining such
variationintothefirst principal component(PC1).Weusedthere-
strictedmaximumlikelihood(REML)method tocreateacompleted
datasettoperformthePCAandaddressmissingvalueswithinour
morphometricaldataset(Paul&Peng,2009).Weonlyincludedin-
dividuals≥10monthsofageinthePCA,asthesecanidsapproached
theirpotentialadultsizesandachievedtheminimumphysicalsizeto
safely wear radiocollars. Wethen createda measurement of mate
similaritybetweenredwolvesandtheirmatesbydividingPC1val-
uesofbreedingpairs.Forourunivariateanalyses,andtoaccountfor
6 
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interdependenciescausedbyredwolvesinvolvedinmultiplebreed-
ing events, we included random intercepts for individual wolves
in GLMM analysesthat compared sex andsimilarity values of red
wolves invol ved in conspecif ic and congeneric p airings. We again
used the li kelihood rati o test to attai n p-valu es by comparing t he
likelihoodofthemodelwithafactortotheintercept-onlymodel.
Toestimate space use patterns,we calculated home rangesof
red wolves and coyotes that had ≥30 telemetry lo cations during
theperiodtheywerepairedwithamateusingGeospatialModeling
Environment(GME;Beyer,2014)andArcMap10.3 (Environmental
SystemsResearchInstitute 2014).Wecreatedannualhomeranges
forindividualredwolvesandcoyotesinbreedingpairsbycalculat-
ing95%fixed kerneldensityestimatesusing the h-pluginsmooth-
ingparameterwithinGME(Seaman&Powell,1996;Worton,1989).
Because some red wolves were represented in multiple pairing
events,ourunivariateanalysesincludedrandominterceptsforindi-
vidualredwolvesinGLMManalysescomparinghome-rangesizesof
redwolvesinvolvedinconspecificandcongenericpairings.Weused
thelikelihoodratiotestasameanstoattainp-valuesbycomparing
thelikelihoodofthem odelwithafactortotheintercept-onlymodel.
Weusedtrappingdatatocalculateannual ratiosof redwolves
tononwolves(coyotesand hybrids)during 1992–2012to estimate
anindexofredwolfabundance(Hinton,Brzeskietal.,2017).Annual
trappingefforts were notstandardized temporally orspatially,be-
cause Recovery Program biologists also coordin ated with private
fur trap pers to capt ure as many Canis tax a as possible wit hin the
5-countyRecoveryArea.Nevertheless,trappingeffortssupporting
thelarge-scale,long-termmonitoringeffortsconductedacrossthe
RecoveryAreaprovidedareasonableproxyforrelativeabundances
of Canis specie s (Hinton, Brze ski etal., 2017; Stephens , Pettorelli,
Barlow, Whittingham, & Cadotte, 2015). We used linear regres-
sion to assesswhetherannual redwolf to nonwolfratiosdeclined
throughtime.
We used pairings as a binary response variable (1=conspe-
cific, 0=congeneric)inaGLMM with a logitlink in R (Batesetal.,
2015) to investigate factorsthat influenced mate selection byred
wolves. T hese factor s included se x of red wolves, bod y size ratio
betweenmates,wolfhome-rangesize,annualwolftononwolfratios,
anthropogenic-caused breakups ofbreedingpairs,thepresenceof
helpers,andpreviousbreeding experienceof wolves.Weincluded
randominterceptsforredwolvestoaccountforindividualvariation.
Prior to mo deling, we resc aled values f or all continuou s variables
bysubtractingtheir meananddividingby twostandarddeviations
(Gelman,2008) and conducted correlation analysis to ensure that
independentvariableswerenothighlycorrelated(r < .7).
Todevelopa necol ogi cal lymeaning fulap rio risetofmod els ,we
usedseven generalhypotheses (Table1) to test factors thatmay
influence congener ic pairings between red wolves and coyotes .
First,weincludedabinaryvariableforsex (1=female,0=male)
becausepreviousstudies(Bohling&Waits,2015;Hinton,Brzeski
etal., 2017) obs erved more fe male red wolves pai red with coy-
otesthanmales.Second,weincluded abodysizeratiobetween
breedingpairs derived from our PCA as ameasurement of mate
similarity because body size was the primary morphologic trait
distinguishingredwolvesfromnonwolves(Hinton&Chamberlain,
2014)and hypothesized toinfluencecongeneric pairings(Hinton,
Rabonetal.,2015;Hinton,Ashleyetal.,2017).Third,weincluded
home-range sizesof individualredwolvesforeachbreedingpair
event because we hypothesized that space use behaviors we re
likelyanimportantbehaviorinfluencingassortativemating(Hinton
etal., 2016;Hinton,Ashley etal.,2017).Fourth, we included an-
nualredwolftononwolfratiosbecausewehypothesizedthatthe
availabilityofwolf mates influencedcongenericpairings (Benson
etal., 2012;Bohling& Waits, 2015; Hinton, Brzeski etal., 2017;
Rutledge,Whiteetal.,2012).Fifth, weincludeda binaryvariable
foranthropogenic-causedbreakupsofbreedingpairs(1=pairing
TABLE1 Aselectionofecologicalfactorsaspotentialpredictorsofcongenericpairingsbetweenredwolvesandcoyotes
Factors Link to breeding pair formation Sources
Redwolftomatebodysize
ratio
Congenericpairingsmorelikelybetweencoyotesand
wolveswhentheyaresimilarinbodysize
Hinton,Rabonetal.(2015),Hintonetal.(2016),
Hinton,Ashleyetal.(2017)
Home-rangesize Congenericpairingsmorelikelybetweencoyotesand
wolveswhenwolvesmaintainsmallhomeranges(e.g.,
≤50km2)
Hinton,Rabonetal.(2015),Hintonetal.(2016),
Hinton,Ashleyetal.(2017)
Redwolftononwolfratio Congenericpairingsmorelikelywhencoyotesoutnumber
wolves
Bensonetal.(2012),Rutledge,Whiteetal.(2012),
BohlingandWaits(2015),Hinton,Brzeskietal.
(2017 )
Presenceofhelpers Congenericpairingsmorelikelybetweensolitarywolves
andcoyotes
Rutledge,Pattersonetal.(2010),Rutledge,White
etal.(2012),BohlingandWaits(2015)
Gunshotmortalities Congenericpairingsmorelikelyfollowingdisruptionof
packsbygunshots
Rutledge,Pattersonetal.(2010),Rutledge,White
etal.(2012),Bensonetal.(2014),Bohlingand
Waits(2015),Hinton,Brzeskietal.(2017)
Sex Congenericpairingsmorelikelybetweenfemalewolves
andmalecoyotes
BohlingandWaits(2015),Hinton,Brzeskietal.
(2017 )
Firstmatingevent Congenericpairingsmorelikelybetweencoyotesand
young,inexperiencedwolves
BohlingandWaits(2015)
    
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 7
HINTON eT a l.
occurredafterthelossofamatetogunshotmortality,0=pairing
didnotoccurafterth el ossofamatetogunshotmor t ality)bec ause
anthropogenicmortalitycanfacilitateCanishybridization(Benson
etal., 2014;Bohling &Waits,2015; Hinton, Brzeski etal., 2017;
Rutledge,Wilsonetal.,2012).Sixth,weincludedabinaryvariable
forpackstructure(1=presenceofhelpers,0=nohelpers)because
packstructurehasbeenidentifiedasanimpor tanttraitpreventing
hybridiz ation (Bohling & Wai ts, 2015; Rutled ge, Patterso n etal.,
2010).Fi nally,weinc lud edabina r yvariabl eforbreederex per ience
(1=first-timebreeder,0=experiencedbreeder) because Bohling
and Waits (2 015) reported th at first-time f emale breede rs were
responsible for a significantp roportion of hybridization events.
Red wolvesin pairing events that lacked body measurements or
home-range data were censored from our GLMM analysis. We
thenselectedvariablesforourmultivariateGLMManalysis using
theunivariatetestsofeachhypothesis,consideringonlyvariables
with significant tests (Bursac, Gauss,Williams,&Hosmer,2008).
Webasedthisonourlikelihoodtestsandap-valuecutoffof.25,
as more tr aditional level s (e.g., 0.05) can f ail to identif y import-
ant variab les (Bursac e tal., 2008). We the n used Akaike’s infor-
mation cri terion adjust ed for small samp le sizes (AICc) an d used
ΔAICctoselectwhichmodelsbestsupportedfactorsinfluencing
congenericpairingsbetweenredwolvesandnonwolves(Burnham
&Anderson,2002).
3 | RESULTS
During 1992–2012, we identif ied 131 pairing events i nvolving 96
redwolves(51males,45females)thatsuccessfullyformedbreeding
pairswithwolvesandnonwolves(coyotesandhybrids).Conspecific
pairingscomprised79%(104of131),whereas21%werecongeneric
pairings.Approximately86%(57of66)ofpairingsinvolvingmalered
wolveswereconspecific,whereas72%(47of65)ofpairingsinvolv-
ing female s were conspeci fic, as female s were more likely to p air
with nonwolvesthan males(
χ2
1
=5.69,p = .017;Figure2). Although
thefrequencyofhelperswasslightlygreaterforconspecificpairings
thancongeneric(
χ2
1
=2.82, p = .093),we observednodifferencein
thefrequencyoffirs t-t imeb re eders(
χ2
1
=0.89,p = .347)andgunshot
mortalities(
χ2
1
=0.02,p = .901)betweenconspecificandcongeneric
pairing s. Finally, annual red wo lf to nonwolf ratios de clined from
1992through2012(r2=.64,p < .0 01).
Our morphometric data set consisted of measurements re-
corded from462redwolves,252coyotes,and 161hybrids during
1987–2012.ThefirstPCexplained60%ofthecumulativevariation
in our data ( Table2). The eigenvec tor of PC1 had simila r loadings
that were al lp ositive, indi cating that P C1p rimarily acco unted for
variationinbodysize.MeanPC1scoresdifferedamongredwolves,
coyotes,andhybridsforf em ales(F2 ,420=323.11,p < .001)andmales
(F2,453=383 .32, p < .001), as hybr ids were intermedia te in size to
redwolvesandcoyotesforbothsexes(seeHinton &Chamberlain,
2014). Male (
χ2
1
=19.93, p < .0 01) and female (
χ2
1
=61.72, p < .001)
red wolves i n conspecific pa irs were more simil ar in body size to
their mates thanthose in congeneric pairs. Mean body size ratios
betweenmale redwolves andtheir mates in conspecificand con-
generic p airings were 1. 20±0.18 and 1.72±0.49,r espective ly,in
which mal e wolves were typ ically larger t han their femal e mates.
However, mean bod y size ratios for female r ed wolves and their
mates in conspecific andcongenericpairingswere0.92±0.13and
1.40±0.30,respectively,inwhichfemalewolvesweretypicallythe
smaller m ate when paired wit h wolves but the larg er mate when
pairedwithnonwolves.
Of131p airingevents,meansizeandstandarddeviationofred
wolfhomerangeswere54.2km2±19.4andrangedbetween19.0
and118.0km2.Of23coyotes,meansizeandstandarddeviation
of home ran ges were 30.0km2±11.7 and r anged between 5 .5
and50.6km2.Mean home-rangesizeofred wolveswasgreater
than coyotes(
χ2
1
=30.83,p < .001).When pooled,the body size
of red wolves and coyotes involved in pairings was positively
correlatedwithhome-range sizes(
χ2
1
=43.91,p < .001; Figure3).
Body size wa s not correlated wit h the size of home ran ges for
female coyote s (
χ2
1
=0.33, p = .583), whe reas there was a wea k
positive correlation for males(
χ2
1
=3.10,p = .077).Bodysizewas
weaklycorrelatedwithsizeofhomerangesforfemale(
χ2
1
=2.83,
p = .091) and male (
χ2
1
=3.17, p = .075) red wolves. Red wolves
in conspecific pairs had larger home-range sizes than wolves in
congenericpairs, whereashome-rangesizesof wolvesinconge-
neric pai rs were similar to coyo te home-r ange sizes (
χ2
1
=49.53,
p < .001;Figure4).
Whendevelopingourmodels,weexcludedthefactorsofbreeder
experienceandgunshotmortalitybecauseweobservednosignificant
effectofthesefactorson matingpatternsinourunivariateanalyses.
Therefore, we included five factors (sex, body size ratios between
mates,redwolfhome-rangesize,annualredwolftononwolfratio,and
thepresenceofhelpers)inourmultivariateanalysis.Theglobalmodel
best explained factors influencing assortative mating in redwolves
(Table3).Thetwostrongestparametersinourmodelwerebodysize
ratiosofmates andsexofredwolves,as decreasingbodysizeratios
betweenredwolvesandtheirmateswasstronglyassociatedwithcon-
specificpairsandmalewolvesoccurredproportionatelymoreoftenin
FIGURE2 Proportionofredwolvesinvolvedinconspecificand
congenericpairingsinnortheasternNorthCarolina,1992–2012
8 
|
   HINTON eT al.
conspecificpairsthandidfemales(Table4).Thestrongeffectofbody
sizesimilarityandsexinourmodelsuggests that redwolvesprefer
matesofsimilarsize and that male wolves mayhave stronger pref-
erencesfor largermatesthandofemales.Furthermore,home-range
size of red wolves was positively correlated with conspecific pairs
andsuggeststhatwolveswithlargehome-rangesizeswereinvolved
inconspecific pairs moreoftenthanwolveswithsmallhome ranges
(Table4).Theannualwolftononwolfratioswaspositivelyassociated
with conspecific pairs and the presence of helpers exerted a weak
positive correlationwith conspecific pairs, suggesting that red wolf
abundanceandpack structure increases the probabilitythatwolves
willacquireconspecificmates(Table4).
4 | DISCUSSION
Recent studies on Canis hybridization in eastern North America
havesuggestedthatpreyselection(Rutledge,Garrowayetal.,2010)
and terri torial aggressi on (Benson & Patte rson, 2013) may play a
role in reducing hybridization, but stressed that excessivehuman-
caused mortalityofwolvesultimatelyfacilitatedconditionsforhy-
bridizationbetweenwolvesandcoyotes ineasternNorthAmerica.
Additio nally, Bohling etal. (2016) foun d mating to be nonra ndom
andassortative between redwolves and coyotesineasternNorth
Carolina,inwhichmosthybridizationeventswerecorrelatedwith
excessiveanthropogenicmortalityandofteninvolvedyoungfemale
wolves(Bohling&Waits,2015).Theresultsofourstudylargelyare,
butnotcompletely,confirmatoryoftheseandotherpreviousstudies
inthatsuggestedbehavioral(spaceuse),demographic(availabilityof
mates),social(presenceofhelpers),andsex-biased(females)factors
influen ce mating patterns of r ed wolves. Additio nally, our results
suggestthatredwo lveslikelyse ekmatesofma tchingb odysi ze ,indi-
catingthatassortativematingbetweenwolvesandcoyotesmaybe
size-related.Thisisnotsurprisingasbehaviorsassociatedwithspace
use,diet,andinterspecificinteractionsofcarnivoresareconstrained
by their body size and energetic demands (Carbone, Teacher, &
Body measurements
Principal component 1 Principal component 2
Eigenvector Loading Eigenvector Loading
Bodymass 0.40 0.87 0.13 −0.12
Earlength 0.32 0.69 0.25 0. 24
Taillength 0. 23 0.52 0.74 0.72
Bodylength 0.35 0.75 0.18 −0.18
Hindfootlength 0.39 0.85 0.26 0.25
Shoulderheight 0.38 0.84 −0.20 −0.19
Headlength 0.39 0.84 −0.03 −0.03
Headwidth 0.34 0.74 −0.46 0.45
Eigenvalue 5.76 0.93
%oftotalvariance 59.4 6 11.57
TABLE2 Eigenvalues,shareoftotal
variancealongwitheigenvectors,and
factorloadingsofbodymeasurementsof
redwolvesinnortheasternNorth
Carolina,1992–2012.Significantloadings
showninbold
FIGURE3 Correlationbetweenhome-rangesizeandbody
sizeofmale(r2=.047,p = .075)andfemale(r2=.081,p = .091)
redwolvesandmale(r2=.142,p = .077)andfemale(r2=−.080,
p = .583)coyotesinbreedingpairs,northeasternNorthCarolina,
1992–2012.CorrelationforallCaniswasr2=.268(p < .001)
FIGURE4 Meanhome-rangesizesofredwolf,congeneric,and
coyotebreedingpairsinnortheasternNorthCarolina,1992–2012.
The95%confidenceintervalsarerepresentedbytheerrorbars.
Lettersabovethebarsrepresentstatisticaldifferencesamong
breedingpaircategories(P<0.05,Tukey’stest)
    
|
 9
HINTON eT a l.
Rowcliffe, 2007; Donadio & Buskirk, 2006; Gittleman & Harvey,
1982)and,forlong-termmonogamousbreeders,choosingapartner
assortativelyfromabehavioralperspectivecouldbeadvantageous
ifsimilarindividualsarecapableofcoordinatingtheirbehaviorsbet-
terthan nonassortative pairs(Schuett etal.,2010).However,local
environmentalvariablesthatinfluencematingpatterns,suchaspop-
ulation density,are largelyinfluencedbyanthropogenic factors.In
otherwords, human-causedmortality reducesredwolfabundance
onthe landscape andincreasesthe probabilityofwolves interact-
ingwithcoyotes, but mate similarity andvarying spaceusebehav-
iors of wolves influences whichindividuals arecapableofforming
congener ic pairs with coyot es. However, we found no as sociation
betweengunshot mortalityandcongenericpairings,despite previ-
ousstudiesthatsuggestedshooting deathsareaprimarydriverof
redwolfsurvivalandpopulationsize(Hinton,Whiteetal.,2017)and
arepositivelycorrelatedwithhybridizationevents(Bohling&Waits,
2015)andcongenericpairings(Hinton,Brzeskietal.,2017).
The link be tween behavi oral traits a nd mating patte rns in hy-
bridizingCanis taxaremains relatively unexplored,but our results
provide some novel insightsandsuggestthatassortativemating in
Canislikely involves multiple causes. Forinstance, thered wolf to
non-wolf ratiohadapositive association withconspecificpairings,
consistentwith themate availability hypothesis, wherethe spatial
distribution of potential mating partners influences the probabil-
ity of enco untering conspe cifics (Crespi , 1989; Pal, E rlandsson, &
Sköld, 20 06; Rowe & Arnqv ist, 1996). This is not surp rising given
thatwolfdensityhasbeentheprimarycommonalityamongstudies
of Canishybridization,withlowwolfdensitiescausedbyanthro-
pogenic mortality facilitatingoutbreeding withcoyotes by eastern
wolves(Bensonetal.,2012,2014;Rutledge,Pattersonetal.,2010;
Rutledge,Whiteetal.,2012)andredwolves(Bohling&Waits,2015;
Hinton, Brzeski etal.,2017). Additionally, low redwolf to nonwolf
ratioslikelyinfluencedthepositiveassociationoffemalewolvesand
lack of help ers with congen eric pairings . Previous stu dies of gray
wolves and eastern wolves reported female-biased subordinated
breedingandmale-biaseddispersaltopackswheredispersersfilled
vacantmalebreedingpositions(Jędrzejewskietal.,2005;Rutledge,
Pattersonetal.,2010;vonHoldtetal.,2008).Similarly,thesex-bias
inconspecificpairingssuggeststhatmaleandfemalebreedersmay
employdifferentstrategiestocompensateforthelossofmates,in
whichwidowedfemalesexhibitstronger fidelity to territories than
widowedm alesand ,conseq uently,a cquirenewma tesfromth et ran-
sientp opula tion.Becausecoyotesgr eatlyoutnu mberr edwolve s,fe-
malewolves likelyinteractmoreoften withtransient coyotesthan
transientwolves aftertheloss ofamate. Whenredwolfdensities
arelow,transientcoyotesaremorelikelytointeractwithsolitaryred
wolves,inwhichsuccess fulpairingsmaydependprimarilyonthead-
equacyofcoyotestodealwithenvironmentalfactors,suchashabi-
tatandpreyavailability.However,asredwolfdensitiesincrease(e.g.,
greaterwolftononwolfratios),coyotesaremorelikelytoencounter
widowed redwolves cohabiting territories with offspring (helpers)
frompreviousmatesandarethensubjectedtosocialselectionthat
involves winninginteractions withotherpack members whilecon-
testing to be a breeder(West-Eberhard, 1983). Therefore,greater
redwolftononwolfratiosincreases theprobability that wolves in-
teractmoreoftenwithwolvesthancoyotesandincreasekin-based
socialstructuresthatdiscourageamicableconsortingwithcoyotes.
Home-rangesizeofredwolveswasanimportantvariableinour
models,asextensive spaceusebehaviorsofwolveswas positively
correlated with conspecific breeding. This is consistent with the
mating cons traint hypothesis that sugge sts various costs of mat-
ing,suchasphysicalorenergeticbarriers,createdifficultiesduring
courtship, copulation, ormate guarding (Arnqvist, Rowe, Krupa,&
Sih, 1996; Crespi, 1989;Harari,Handler,&Landolt, 1999).In par-
ticular, red wolves generally maintained larger home ranges than
TABLE3 Generalizedlinearmixedmodelsforpredicting
probabilityofcongenericbreedingcorrespondingtodifferent
hypothesesoffactorsassociatedwithbreedingpairformationby
redwolvesinnortheasternNorthCarolina,1992–2012.Shownare
differencesamongAkaike’sinformationcriteriaforsmallsample
sizes(ΔAICc)
Model structure kDeviance ΔAICcAICcω
SRa+HRb+W:Cc+Helpersd
+Femalesf
739. 50 0.0 0.70
SR+HR+W:C+Females 6 45.20 2.88 0 .17
SR+HR+Helpers+Females 6 46.80 3.86 0.10
SR+HR+Females 5 51.50 7. 0 2 0.02
SR+W:C+Helpers+Females 6 52.40 8.05 0.01
aRedwolftomatesizeratio.
bRedwolfhome-rangesize.
cRedwolftononwolfratio.
dNumberofhelpersinpack.
fRedwolfsex.
Model variables βSE 95% CI z p
Intercept 4.213 0.956 2.654,6.966 4.4 07 <.001
Redwolftomate
sizeratio
−2. 856 0.657 −4.752,−1.759 −4.439 <.001
Home-rangesize 2.085 0.858 0.718,4.200 2.430 . 014
Redwolftononwolf
ratio
1.272 0.601 0.227,2.715 2.119 .034
Presenceofhelpers 3.0 07 1.918 0.129,7.486 1.568 .117
Females −3.165 1.067 −5.851,−1.303 −2.965 .003
TABLE4 Resultsfromgeneralized
linearmixedmodelsfortheglobalmodel
forpredictingprobabilityofcongeneric
breedingcorrespondingtodifferent
hypothesesoffactorsassociatedwith
breedingpairformationbyredwolvesin
northeasternNorthCarolina,1992–2012.
Shownareβcoefficients,standarderror
(SE),95%confidenceintervals(CI),
z-scores,andp-values
10 
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   HINTON eT al.
coyotes,buthome-rangesizesofwolvesandcoyotesoverlappedin
the 25–50km2 range (Figure4).Approximately 87% ofcongeneric
pairs ha d home ranges with in 25–50km2, whereas the remaining
home rangeswere between 52 and68km2. Because foraging and
territorialdefenseareenergeticallydemandingactivities,itislikely
that signif icant diffe rences in potentia l spatial (e.g., terr itory size)
anddietary (e.g., predation onwhite-taileddeer [Odocoileus virgin-
ianus]) requirem ents between c onsorting red wo lves and coyotes
discouragescongeneric pairings. Ultimately,when redwolvesand
coyotesarecapableofconsorting,aprimaryfactorthatleadstosuc-
cessfulpairingsappearstobeestablishingterritoriesbelow50km2,
arange of home-rangesizes that coyotescan adequately maintain
anddefend.
Our anal yses indicat ed that reduce d body size ratio sb etween
redwolvesandtheirmateswerethemostimportantvariableinour
models,as79%of observedwolfpairingswere conspecific despite
that wolves w ere generally ou tnumbered by coyotes . Assorta tive
matingbasedonsimilarityinsizeisoneofthemostprevalentmating
patternsintheanimalkingdom,anditisknowntoactasapremat-
ing reproductive barrier between distinct species and divergent
populations(Coyne&Orr,2004;Galipaud,Bollache,&Dechaume-
Moncharmont,2013;Jiang,Bolnick,&Kirkpatrick,2013).Therefore,
itisreasonabletoassumethateffectsofbodysizeweremanifestedin
Canisspaceusepatterns(Figure3),inwhichredwolveswithsmaller
homerangesweremorelikelytobecongenericbreedersthanthose
with largerhome ranges.Space usewaspositively correlated with
CanisbodymassineasternNorthCarolinaand,becausecoyotesare
smaller than red wolves,theupperlimittotheareascoyotescould
effec tively exploit and defend as territorie s was below the aver-
agehome-range size of wolves. Thelowproportion ofred wolves
≥27.5kgobservedincongenericpairingsmayindicateanimportant
threshold,asmostwolvesabovethatthresholddidnotformbreed-
ingpairswithcoyotesandhybrids.Althoughthistrendwaslargely
drivenbymaleredwolves,thelargerofthetwosexes,dissimilarity
inbodysizebetweencongenericpairsandtheirsmallhomeranges
suggestsapotentialcostwhencongenericpairsattempttoachieve
territor ysizeslargeenoughtoaccommodatethe wolf’sgreateren-
ergetic requirementsbutsmallenoughforcoyotesto defend.Asa
species with long-termmonogamy,acquiring mates and territories
arecriticaleventsforredwolves and likelyrequire extensivemate
assessmentbefore new pairsareformed.Female red wolveslikely
choose ma les that behave si milarly to them selves in use of spa ce
anddiet,asthese behaviors areconsistent andmayallow females
toidentifywhichmalescanprovidehighlevelsofterritorialdefense
andparentalcare.However,becausefemaleredwolvesarecloserin
bodysizetocoyotesandhybridsthanmales(Hinton&Chamberlain,
2014),theyarelikelymorecapableofreconcilingthecostsofhaving
smallercoyoteorhybridmatesandcanlikelycompensateandadjust
their spaceuse andforagingbehaviors accordingly to successfully
breedwithdissimilarmates.
Itisimportanttounderstandwhatcircumstancesfacilitatehybrid-
ization and how it affectsthe persistence of imperiled species and,
where possible and desired, to mitigate irreversible consequences
such as genetic swamping and loss of phenotypic uniqueness. It is
not surprising that our resultshighlight mate similarity in body size
andspace use behaviorsasimportantfactors preventingcongeneric
pairings, because territorial behavior is a fundamental life history
strategyforCanis taxa.Nearlyall ofourstudyareawasoccupiedby
territoriesofredwolvesandcoyotesand,becausevacant territories
werecommonly occupied by transients, there was intense competi-
tion for space.Territorialturnover for red wolvesand coyotes typi-
callyoccursafterthedeathofresidentbreeders,assurvivingresidents
arereceptiveto acquiringnewmatesfromthe transient population
(Hinton,vanManenetal.,2015;Hintonetal.,2016;Hinton,Brzeski
etal.,2017).Similartograywolves(Milleretetal.,2017),itisrarefor
healthyredwolvesandcoyotestodivorcetheirmatestoacquirenew
ones,andtherefore,transientsofbothspeciestypicallyencroachinto
territories experiencing mortality and replace lost resident breed-
ers.Forwidowedredwolves,thepredominantriskistheloss ofthe
territoryand the lossofa partnermay be detrimental if a widowed
wolfis not able to defend the territory against intruders.Therefore,
widowed residents may seek more contacts with, and be less ag-
gressivetoward,potential partnersbecausequickrepairingiscrucial
forwidowstokeeptheirterritories (Hinton,van Manenetal.,2015;
Hintonetal., 2016; Hinton, Brzeski etal., 2017).Similarly,transient
redwolvesarelikelydrivento pairing quickly toacquire a territory
andmate.Indeed,Hintonetal. (2016) stressedthat red wolvesand
coyotesuse the same habitats and, because transient wolves often
bideinlowerquality habitatsproximateto wolfterritories,theycan
destabilizecoyotepacksanddisplacecoyotesfromareasnotoccupied
byresidentwolves(butseeBenson&Patterson,2013).Consequently,
individualredwolvescompetewithcoyotesandotherwolvesforlim-
itedmatesandspace,andselectionpressureonwolvesandcoyotesis
likelygreatestduringtheacquisitionanddefenseofmatesandterri-
tories.Becausetherearesofewredwolvesinthecurrentpopulation
(Hinton,Whiteetal.,2017),most wolvesinteractand competewith
coyotestoacquirematesand defendterritories,whereashistorically
wolves competed with otherwolves for mates and space. In other
words,whenredwolvesweremorecommon,largerwolveslikelyhad
aselectiveadvantageoversmallerwolveswhenattemptingtoacquire
anddefend territories.Becausecoyotesgreatlyoutnumber therein-
troducedpopulation,smallerredwolvescurrentlyhaveaselectivead-
vantageoverlargerwolvesbecausesmallwolvesarestilllargeenough
tooutcompetecoyotesforspace,butarealsocapableofpairingwith
coyoteswhenwolfmatesarenotavailable.Thisisproblematicforred
wolfrecoverybecause the abilityofsmaller redwolves, particularly
females,toformcongenericpairsfacilitatesreproductiveinterference
bycoyotes(Gröning& Hochkirch,2008;Mallet,2005) and prevents
wolf compensation of losses to mortalityvia reproduction (Hinton,
Whiteetal.,2017).
Patter ns of assortat ive mating occur at th e population leve l
(Arnqvist etal., 1996; Crespi, 1989; Taborsky etal., 2009), and
we sugges t that assort ative mating can be m anaged simulta ne-
ously wit h other populati on-level pro cesses (i.e., bir ths, deaths ,
immigration, emigration) essential for population persistence.
Specifically, factors influencing assortative mating also depend
    
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 11
HINTON eT a l.
onpopulationprocessessensitivetoanthropogenicmortalityand
smallpopulationsizes.Forexample,Brzeskietal.(2014)reported
largeinbreedingcoefficients(averagef = 0.154)inwildredwolves
andfoundanegativecorrelationbetweenbodysizeandinbreed-
ing such that more inbred individuals were smaller. Inbreeding
in the wild population is exacerbated by a small population size
andhighanthropogenicmortality,andthosetwofactorsarealso
correlate d with hybridiz ation (Bohling & Wait s, 2015; Rutledge,
Whiteetal.,2012).Therefore,theUSFWSmayconsiderincreas-
ingab undanceofredwol ve sineasternNorthC arolinabyfocusing
onmitigationofhuman-causedmortalities(e.g.,gunshotmortali-
ties)andprovidingfurtherprotectionof acorepopulationofred
wolveswithin the 5-countyRecovery Area,whilealsoexpanding
recoveryefforts beyondthe Recovery Area to grow alarge and
robustregionalwolfpopulation.Thisapproachcouldimplement
similar legalprotectionasthoseused in Ontario, Canadatopro-
tect eastern wolves (Benson etal., 2014; Rutledge, Patterson
etal., 2010; Rutledge,White etal., 2012), which wouldincrease
red wolf abundance and improve pack structure whilerestoring
selection pressures favoring larger-sized red wolves to acquire
and defend breeding territoriesfrom other wolvesand not coy-
otes.Consequ ently,thiswouldlikelyincreas emeanb odysizesand
home-rangesizes of wildred wolvesand decrease hybridization
rateswithcoyotesbyreducingcongenericpairing.
ACKNOWLEDGMENTS
We dedicate t his study to our f riend and coll eague Chris topher
Lucash(1961–2016),whoassistedandsupportedallstagesofthis
project.Wethankhimforhis29yearsofcommitmenttorestoring
redwolvestothewildthathelpedlaythegroundworkforwolfre-
introductionsandfutur econser vat ionproj ect s.Weappre ciateth e
supportof the U.S.FishandWildlifeServiceRedWolfRecovery
Program , specifical ly R. Bartel , A. Beyer, C. Lucas h, F. Maune y,
M.Morse,R. Nordsven, andD.Rabon. We thankWeyerhaeuser
Companyforprovidingaccessto theirproperties.Weappreciate
funding provided by the Warnell SchoolofForestryand Natural
Resource s.Thefindingsandconclusionsinthisarticlearethoseof
theauthorsanddonotnecessarilyrepresenttheviewsoftheU.S.
FishandWildlifeService or WeyerhaeuserCompany.Anyuseof
trade,firm,orproductnamesisfordescriptivepurposesonlyand
doesnotimplyendorsementbytheU.S.Government.
CONFLICT OF INTEREST
Nonedeclared.
AUTHOR CONTRIBUTIONS
J.W.H.conceivedthe project, designed theexperiment, organized
anddidfieldwork, laboratorywork,data analysis, anddrafted the
manuscript; J.L.G. contributed intellectually and edited/approved
the manus cript; F.T.vM contribu ted to the projec t design, se cured
funding, and contributed intellectually and edited/approved the
manuscript;M.J.C.contributedtotheprojectdesign,securedfund-
ing,providedequipment,andcontributedintellectuallyandedited/
approvedthemanuscript.
DATA ACCESSIBILITY
Data available from the Dryad Digital Repository: https://doi.
org/10.5061/dryad.8rt51j0
ORCID
Joseph W. Hinton http://orcid.org/0000-0002-2602-0400
Frank T. van Manen http://orcid.org/0000-0001-5340-8489
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How to cite this article:HintonJW,GittlemanJL,vanManen
FT,ChamberlainMJ.Size-assortativechoiceandmate
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1–14 . https://doi.org/10.1002/ece3.3950
... We found a positive correlation between coyote body size and autosomal red wolf ancestry and observed no coyotes with the majority (>50%) of autosomal red wolf ancestry that weighed less than 15.5 kg. In North Carolina, body size can be a reliable predictor of home range size and thus species identity, with larger-bodied wolves often holding larger average home ranges than coyotes (55 and 30 km 2 , respectively) (39). Further, body size combined with space use contributes to red wolf and coyote assortative mating (39). ...
... In North Carolina, body size can be a reliable predictor of home range size and thus species identity, with larger-bodied wolves often holding larger average home ranges than coyotes (55 and 30 km 2 , respectively) (39). Further, body size combined with space use contributes to red wolf and coyote assortative mating (39). The X chromosome has a more complex mode and history upon which natural selection can act. ...
... Our study presents one of the first connections between the red wolf phenotype and genomic estimates of red wolf ancestry. Building upon previous work that supports red wolf-specific traits (32,35,39), we have documented a positive correlation between these traits and genomic ancestry in coyotes of the historic red wolf admixture zone (17). ...
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The last known red wolves were captured in southwestern Louisiana and eastern Texas in 1980 to establish a captive breeding population. Before their extirpation, gene flow with coyotes resulted in the persistence of endangered red wolf genetic variation in local coyote populations. We assessed genomic ancestry and morphology of coyotes in southwestern Louisiana. We detected that 38 to 62% of the coyote genomes contained red wolf ancestry acquired in the past 30 years and have an admixture profile similar to that of the canids captured before the extirpation of red wolves. We further documented a positive correlation between ancestry and weight. Our findings highlight the importance of hybrids and admixed genomes as a reservoir of endangered species ancestry for innovative conservation efforts. Together, this work presents an unprecedented system that conservation can leverage to enrich the recovery program of an endangered species.
... In fact, there is considerable evidence of human-facilitated interbreeding of wolves, coyotes, and dogs in captive environments (Fig. 7) [21,31,[42][43][44][45], whereas direct interbreeding (e.g., copulation; Fig. 7a) between coyote and dogs has not been documented in the wild (see review by von-Holdt and Aardema [46]) despite numerous research and monitoring programs and the common and widespread use of camera surveys in modern research. However, interbreeding between coyotes and red wolves in the wild has been repeatedly and comprehensively documented by ecological [47][48][49][50] and molecular [51][52][53] studies by which more realistic and parsimonious pathways (e.g., red wolf and coyote hybridization) can be formulated for how southeastern coyotes may have acquired melanistic traits and dog alleles. ...
... Mean home-range size of melanistic coyotes was 1.6 times larger than that observed for gray coyotes, and melanistic coyotes exhibited stronger selection for areas with canopy and wetland cover than did gray coyotes. Research on space use of coyotes and red wolves in the NC Recovery Area reported that body size influenced home range sizes and that coyote home range size was negatively correlated with agriculture [50,62]. Given that we detected no difference in body sizes of melanistic and gray coyotes, it is likely that differences in land cover preferences by coyotes influenced their home range sizes such as gray coyotes exhibiting stronger selection for agriculture than did melanistic coyotes. ...
... Large home ranges and differential use of land cover by melanistic coyotes may facilitate weak assortative mating in eastern coyote populations, whereby melanistic animals have lower success of finding compatible mates in comparison to their gray conspecifics. Indeed, space use behaviors influenced assortative mating in red wolves and coyotes [50] and melanistic coyotes selected for similar land cover types (i.e., wetland cover) as did red wolves in eastern North Carolina [65]. Furthermore, Hinton et al. [29] suggested that red wolf ancestry improved coyote dispersal capabilities, rather than their ability to kill deer [36,38,66], improving connectivity among coyote metapopulations in a region dominated by forest cover. ...
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Background Gloger’s rule postulates that animals should be darker colored in warm and humid regions where dense vegetation and dark environments are common. Although rare in Canis populations, melanism in wolves is more common in North America than other regions globally and is believed to follow Gloger’s rule. In the temperate forests of the southeastern United States, historical records of red wolf (Canis rufus) and coyote (Canis latrans) populations document a consistent presence of melanism. Today, the melanistic phenotype is extinct in red wolves while occurring in coyotes and red wolf-coyote hybrids who occupy the red wolf's historical range. To assess if Gloger’s rule could explain the occurrence and maintenance of melanistic phenotypes in Canis taxa, we investigated differences in morphology, habitat selection, and survival associated with pelage color using body measurements, GPS tracking data, and long-term capture-mark-recapture and radio-telemetry data collected on coyotes and hybrids across the southeastern United States. Results We found no correlation between morphometrics and pelage color for Canis taxa. However, we observed that melanistic coyotes and hybrids experienced greater annual survival than did their gray conspecifics. Furthermore, we observed that melanistic coyotes maintained larger home ranges and exhibited greater selection for areas with dense canopy cover and wetlands than did gray coyotes. Conclusions In the southeastern United States, pelage color influenced habitat selection by coyotes and annual survival of coyotes and hybrids providing evidence that Gloger’s rule is applicable to canids inhabiting regions with dense canopy cover and wetlands. Greater annual survival rates observed in melanistic Canis may be attributed to better concealment in areas with dense canopy cover such as coastal bottomland forests. We suggest that the larger home range sizes of melanistic coyotes may reflect the trade-off of reduced foraging efficiency in lower quality wetland habitat for improved survival. Larger home ranges and differential use of land cover by melanistic coyotes may facilitate weak assortative mating in eastern coyote populations, in which melanistic animals may have lower success of finding compatible mates in comparison to gray conspecifics. We offer that our observations provide a partial explanation for why melanism is relatively low (< 10%) but consistent within coyote populations throughout southeastern parts of their range.
... Since coyote expansion into the ARNWR in the early 1990s, the recovery programme has largely focused on (mitigating) hybridization with coyotes as the main threat to the species' recovery [34][35][36][37]. Once hybridization was successfully managed [38] and established as a consequence of anthropogenic mortality [39,40], concerns shifted to understanding red wolf mortality and specifically strategies to mitigate anthropogenic causes, given evidence of increased gunshot deaths since 1999 [35][36][37][40][41][42][43][44][45]. The reintroduced population initially grew steadily, peaking at royalsocietypublishing.org/journal/rsos R. Soc. ...
... 4(e) (Similarity of Appearance Cases) and seem not only necessary but urgent given that poaching is the main cause of mortality for red wolves and an impediment to population growth and recolonization. Our study indicates the protection of both coyotes and red wolves in the North Carolina recovery area may be an effective way to reduce anthropogenic mortality, which will allow for the establishment of a healthy red wolf population and minimize hybridization [39,40]. Therefore, protecting both canids in the North Carolina recovery area would align with the ESA and red wolf recovery plans, making the strategy resistant to court challenge. ...
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Poaching is the major cause of death for large carnivores in several regions, contributing to their global endangerment. The traditional hypothesis used in wildlife management (killing for tolerance) suggests reducing protections for a species will decrease poaching. However, recent studies suggest reducing protections will instead increase poaching (facilitated illegal killing) and its concealment (facilitated cryptic poaching). Here, we build survival and competing risk models for mortality and disappearances of adult collared red wolves ( Canis rufus ) released in North Carolina, USA from 1987 to 2020 ( n = 526). We evaluated how changes in federal and state policies protecting red wolves influenced the hazard and incidence of mortality and disappearance. We observed substantial increases in the hazard and incidence of red wolf reported poaching, and smaller increases in disappearances, during periods of reduced federal and state protections (including liberalizing hunting of coyotes, C. latrans ); white-tailed deer ( Odocoileus virginianus ) and American black bear ( Ursus americanus ) hunting seasons; and management phases. Observed increases in hazard (85–256%) and incidence of reported poaching (56–243%) support the ‘facilitated illegal killing' hypothesis. We suggest improving protective policies intended to conserve endangered species generally and large carnivores in particular, to mitigate environmental crimes and generally improve the protection of wild animals.
... It is therefore possible that the intermediate body size of Asiatic black bears also promoted the establishment of premating RI from its two parental lineages. Interestingly, a direct effect of differences in body size on mate choice or assortative mating has been reported in Canis species (37) and stickleback populations (38), supporting the existence of a relationship between body size and premating RI. In addition, many of the alternately inherited genes (SI Appendix, Fig. S8 and Table S12) are involved in the reproductive process, suggesting that hybridization is likely to have played a role in directly creating postmating RI due to BDM incompatibility RI between this hybrid species and its two parents (28,29). ...
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Bears are fascinating mammals because of their complex pattern of speciation and rapid evolution of distinct phenotypes. Interspecific hybridization has been common and has shaped the complex evolutionary history of bears. In this study, based on the largest population-level genomic dataset to date involving all Ursinae species and recently developed methods for detecting hybrid speciation, we provide explicit evidence for the hybrid origin of Asiatic black bears, which arose through historical hybridization between the ancestor of polar bear/brown bear/American black bears and the ancestor of sun bear/sloth bears. This was inferred to have occurred soon after the divergence of the two parental lineages in Eurasia due to climate-driven population expansion and dispersal. In addition, we found that the intermediate body size of this hybrid species arose from its combination of relevant genes derived from two parental lineages of contrasting sizes. This and alternate fixation of numerous other loci that had diverged between parental lineages may have initiated the reproductive isolation of the Asiatic black bear from its two parents. Our study sheds further light on the evolutionary history of bears and documents the importance of hybridization in new species formation and phenotypic evolution in mammals.
... Positive assortative mating, in which pairs of individuals that share similar traits or genetic backgrounds are more likely to breed than in a random mating system, can limit the functional connectivity of structurally connected populations by preventing gene flow despite dispersal movement between populations. Assortative mating in wildlife populations may be driven by genetic background (Tung et al. 2012) or by phenotypic traits such as size (Hinton et al. 2018), age (Farrell et al. 2011), color (Hedrick et al. 2016), or social behavior (Noer et al. 2017). Assortative mating may also occur as an incidental consequence of unrelated phenotypes such as habitat preference (Edelaar et al. 2008) or reproductive timing (Bearhop et al. 2005), rather than a direct result of mate choice (Ferrer and Penteriani 2003;Jiang et al. 2013). ...
Article
Species reintroductions are successful when established populations maintain both demographic stability and genetic diversity. Such a result may be obtained by ensuring both structural habitat connectivity and genetic connectivity among reintroduced and remnant populations. Nevertheless, prezygotic barriers such as assortative mating can prevent the flow of genetic material between populations, even when migration between populations is high. Limited gene flow may be particularly relevant for reintroductions that were sourced either from captive-bred populations or from disparate locations in the wild. American martens (Martes americana) have been reintroduced repeatedly in the Upper Midwestern United States in an effort to establish self-sustaining populations. We quantified levels of genetic diversity within and spatial genetic variance among four marten populations during two time periods separated by 10 years. Spatially informed and naïve discriminant analysis of principal components were used to assign individuals to populations. Results indicate that heterozygosity declined and inbreeding coefficients increased between the two collection periods, while genetic structure among populations also increased. Data are consistent with assortative mating contributing to reapportioning of genetic variation. Population assignment tests show that migration among populations is apparent, but admixture (based on cluster membership probabilities) is low and declined over time. Specifically, martens may be successfully dispersing between populations but a lack of admixture indicates a lack of reproductive contributions to genetic diversity by migrants. Because marten reintroductions in this region are well-documented and well-monitored, lessons can be derived from results to inform future reintroductions. We encourage a careful balance of supplementing genetic diversity via augmentation while avoiding translocation of animals from disparate populations that may result in reproductive isolation of migrants. In combination with the maintenance of a functionally connected landscape, this strategy would maximize the likelihood of a successful reintroduction in terms both of demography and genetics.
... Our study presents one of the first connections between the red wolf phenotype and genomic estimates of red wolf ancestry. Building upon previous work that clearly supports red wolf-specific traits (32,35,39), we have documented a positive correlation between such traits and genomic ancestry in coyotes of the historic red wolf admixture zone (17). ...
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Full-text available
The last red wolves were captured along the Gulf Coast in 1980, where they hybridized with coyote, to establish the captive breeding population. However, red wolf ancestry persists in local coyotes and could be leveraged by genomic innovations to support species persistence. We assessed genomic ancestry and morphology of coyotes in southwestern Louisiana, and find they carried 38-62% red wolf ancestry acquired in the last 30 years, which is enriched on land with minimal coyote hunting. These coyotes were also similar in ancestry to canids captured in the 1970s that initiated the red wolf captive breeding program. Further, we reported that coyotes with higher red wolf ancestry are larger in size. Our findings evidence the importance of hybrids as a reservoir of endangered species ancestry for contemporary conservation efforts. Admixed genomes are at the forefront of innovative solutions, with red wolf survival a prime candidate for this new paradigm. Teaser Coyotes along the American Gulf Coast carry genetic variation critical for the survival of the endangered red wolf species.
... We found low miscibility of the red wolf and coyote genomes in genomic regions known to disproportionately harbour reproductive isolation loci, as evidenced by the reduced red wolf ancestry on the coyote X chromosome which we hypothesize is due to effects of interference across large regions with extremely reduced recombination rates, and parallels results in other mammalian systems (Carneiro et al., 2010;Li et al., 2019). Previous work has documented size-assortative mating with respect to red wolf and coyote hybridization events (Hinton et al., 2017) and suggests sex-biased hybridization where female red wolves more often mate with male coyotes. ...
Article
Admixture and introgression play a critical role in adaptation and genetic rescue that has only recently gained a deeper appreciation. Here, we explored the geographic and genomic landscape of cryptic ancestry of the endangered red wolf that persists within the genome of a ubiquitous sister taxon, the coyote, all the while the red wolf has been extinct in the wild since the early 1980s. We assessed admixture across 120,621 SNP loci genotyped in 293 canid genomes. We found support for increased red wolf ancestry along an east‐to‐west gradient across the southern United States associated with historical admixture in the past 100 years. Southwestern Louisiana and southeastern Texas, the geographic zone where the last red wolves were known prior to extinction in the wild, contained the highest and oldest levels of red wolf ancestry. Further, given the paucity of inferences based on chromosome types, we compared patterns of ancestry on the X chromosome and autosomes. We additionally aimed to explore the relationship between admixture timing and recombination rate variation to investigate gene flow events. We found that X‐linked regions of low recombination rates were depleted of introgression, relative to the autosomes; consistent with the large X effect and enrichment with loci involved in maintaining reproductive isolation. Recombination rate was positively correlated with red wolf ancestry across coyote genomes, consistent with theoretical predictions. The geographic and genomic extent of cryptic red wolf ancestry can provide novel genomic resources for recovery plans targeting the conservation of the endangered red wolf.
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To mitigate coyote (Canis latrans) introgression in the wild red wolf (Canis rufus) genome, the United States Fish and Wildlife Service (USFWS) Red Wolf Recovery Program used a combination of reproductive sterilization and lethal removal of coyotes to minimize hybridization and increase the endangered red wolf population. Although sterilization assisted in limiting coyote introgression to ≤4% in the wild red wolf genome, its potential negative effect on coyote and hybrid abundance and density is unknown. Using long‐term capture–mark–recapture and radio‐telemetry data collected on red wolves, coyotes, and hybrids under the USFWS Red Wolf Adaptive Management Plan implemented during 2000–2013, we explored three areas of research: (1) spatial modeling to correlate land cover characteristics with the relative probabilities of capture for red wolves, coyotes, and hybrids; (2) survival analysis of radio‐marked canids; and (3) annual population estimates for the three Canis taxa. We detected no differences in the relative probability of capture among Canis taxa. Red wolves, coyotes, and hybrids were most frequently captured in areas proximate to road networks with low canopy cover (i.e., cropland) and away from coastal bottomland forests. Annual apparent survival for red wolves and hybrids was greater than survival for coyotes; however, wolves and hybrids exhibited similar annual survival. Mortality of coyotes and hybrids was predominately attributed to deliberate take through lethal control by the USFWS biologists and harvest by hunters and trappers. We observed annual densities of coyotes ranging between 2.5 and 21.5 coyotes/1000 km2, with densities annually increasing during 2005–2013 when the red wolf population plateaued before declining after 2013. Despite the increase in coyote density, our density estimates are less than most estimates reported throughout the coyote's geographic range, and similar to those reported in areas where coyote populations are limited by extreme environments such as their northern range limits in Alaska, United States, and Canada. Our findings indicate that red wolf presence and federal management of coyotes using fertility control may have limited coyote densities in northeastern North Carolina.
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On 17 June 2019, we collected a unique juvenile rattlesnake from a wildlife response call on Jekyll Island State Park, GA. The snake exhibited intermediate color patterns and gross anatomical features suggesting potential hybridization between Crotalus horridus (Canebrake/Timber Rattlesnake) and Crotalus adamanteus (Eastern Diamond-back Rattlesnake). Using mitochondrial and nuclear genetic sequencing, venom analyses, and morphological characteristics to test that hypothesis, we were able to verify that this specimen represents only the second documented observation of natural hybridization between C. adamanteus and C. horridus and the first reported with multiple lines of evidence sufficient for confirmation. Surprisingly, genetic analyses found evidence of previous intro-gression between these species, suggesting hybridization may not be a rare occurrence in the area (and perhaps specifically on Jekyll Island). We will continue to monitor the hybrid individual via radio-telemetry to assess its survival and any subsequent F2 hybridization reproduction events.
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The landscape of fear (LOF) hypothesis is a unifying idea explaining the effects of predators on the space use of their prey. However, empirical evidence for this hypothesis is mixed. Recent work suggests that the LOF is dynamic, depending on the daily activity of predators, which allows prey to utilize risky places during predator down times. While this notion clarifies some discrepancies between predictions and observations, support for a dynamic LOF remains mixed. The underlying assumption of a dynamic LOF is strong predictability in predator activity cycles. Work in multi‐predator systems demonstrates the effect of differential behavior between predator species on the predictions of prey space use. However, none have considered the effect of intraspecific variation in predator behavior. Most, if not all, dynamic LOF studies base inference on the species‐level average activity pattern, implicitly assuming similarity within the predator population. We examined the dynamics and intraspecific variation in activity cycles within a population of coyotes (Canis latrans). We found seasonality in the predictability of coyote behavior, as well as divergent nocturnal and crepuscular activity patterns between individuals during summer. Activity dynamics were not related to range size, sex, body mass, or habitat complexity, but did vary by year. These results suggest that the predictability of activity patterns is seasonally dynamic, and failure to account for intraspecific variation in activity may cloud inference in LOF studies. We argue that future studies should not neglect the potential complexity of predator behavior with simplistic assumptions. By considering intraspecific variation in activity patterns, we may gain a clear picture of LOF dynamics.
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Genome sequence and ancestry analysis confirm only two canid species in North America.
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The generation of genome-wide sequence data has brought with it both exciting opportunities for conservation and challenges for determining appropriate management practices in the face of complex evolutionary histories. Genomic data can provide deep insight into taxa with complex evolutionary origins, and is a powerful tool for biologists to obtain a more complete view of ancestry. Many policy decisions are encumbered by patterns of gene flow between species that reveal complex evolutionary histories. Here, we review conservation decisions in admixed species and highlight genomics research that demonstrates the commonality of hybridization in wildlife. We encourage a shift towards a web-of-life framework with emphasis on the need to incorporate flexibility in conservation practices by establishing a policy for lineages of admixed ancestry. In particular, we promote a conceptual framework under which hybridization, even extensive hybridization, no longer disqualifies a species from protection; instead, we encourage customized case-by-case management to protect evolutionary potential and maintain processes that sustain ecosystems.
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Foraging behaviors of red wolves (Canis rufus) and coyotes (Canis latrans) are complex and their ability to form congeneric breeding pairs and hybridize further complicates our understanding of factors influencing their diets. Through scat analysis, we assessed prey selection of red wolf, coyote, and congeneric breeding pairs formed by red wolves and coyotes, and found that all 3 had similar diets. However, red wolf and congeneric pairs consumed more white-tailed deer (Odocoileus virginianus) than coyote pairs. Coyotes forming breeding pairs with red wolves had 12% more white-tailed deer in their diet than conspecifics paired with coyotes. Contrary to many studies on coyotes in the southeastern United States, we found coyotes in eastern North Carolina to be primarily carnivorous with increased consumption of deer during winter. Although prey selection was generally similar among the 3 groups, differences in diet among different breeding pairs were strongly associated with body mass. Larger breeding pairs consumed more white-tailed deer, and fewer rabbits (Sylvilagus spp.) and other small mammals. Partitioning of food resources by sympatric red wolves and coyotes is likely via differences in the proportions of similar prey consumed, rather than differences in types of prey exploited. Consequently, our results suggest coexistence of red wolves and coyotes in the southeastern United States may not be possible because there are limited opportunities for niche partitioning to reduce competitive interactions.
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Recovery of large carnivores remains a challenge because complex spatial dynamics that facilitate population persistence are poorly understood. In particular, recovery of the critically endangered red wolf (Canis rufus) has been challenging because of its vulnerability to extinction via human-caused mortality and hybridization with coyotes (Canis latrans). Therefore, understanding red wolf space use and habitat selection is important to assist recovery because key aspects of wolf ecology such as interspecific competition, foraging, and habitat selection are well-known to influence population dynamics and persistence. During 2009–2011, we used global positioning system (GPS) radio-telemetry to quantify space use and 3rd-order habitat selection for resident and transient red wolves on the Albemarle Peninsula of eastern North Carolina. The Albemarle Peninsula was a predominantly agricultural landscape in which red wolves maintained spatially stable home ranges that varied between 25 km2 and 190 km2. Conversely, transient red wolves did not maintain home ranges and traversed areas between 122 km2 and 681 km2. Space use by transient red wolves was not spatially stable and exhibited shifting patterns until residency was achieved by individual wolves. Habitat selection was similar between resident and transient red wolves in which agricultural habitats were selected over forested habitats. However, transients showed stronger selection for edges and roads than resident red wolves. Behaviors of transient wolves are rarely reported in studies of space use and habitat selection because of technological limitations to observed extensive space use and because they do not contribute reproductively to populations. Transients in our study comprised displaced red wolves and younger dispersers that competed for limited space and mating opportunities. Therefore, our results suggest that transiency is likely an important life-history strategy for red wolves that facilitates metapopulation dynamics through short- and long-distance movements and eventual replacement of breeding residents lost to mortality.
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The origin and taxonomy of the red wolf (Canis rufus) have been the subject of considerable debate and it has been suggested that this taxon was recently formed as a result of hybridization between the coyote and gray wolf. Like the red wolf, the eastern Canadian wolf has been characterized as a small "deer-eating" wolf that hybridizes with coyotes (Canis latrans). While studying the population of eastern Canadian wolves in Algonquin Provincial Park we recognized similarities to the red wolf, based on DNA profiles at 8 microsatellite loci. We examined whether this relationship was due to similar levels of introgressed coyote genetic material by comparing the microsatellite alleles with those of other North American populations of wolves and coyotes. These analyses indicated that it was not coyote genetic material which led to the close genetic affinity between red wolves and eastern Canadian wolves. We then examined the control region of the mitochondrial DNA (mtDNA) and confirmed the presence of coyote sequences in both. However, we also found sequences in both that diverged by 150 000 - 300 000 years from sequences found in coyotes. None of the red wolves or eastern Canadian wolf samples from the 1960s contained gray wolf (Canis lupus) mtDNA sequences. The data are not consistent with the hypothesis that the eastern Canadian wolf is a subspecies of gray wolf as it is presently designated. We suggest that both the red wolf and the eastern Canadian wolf evolved in North America sharing a common lineage with the coyote until 150 000 - 300 000 years ago. We propose that it retain its original species designation, Canis lycaon.
Book
Carnivores have always fascinated us, even though they make up only 10% of all mammalian genera and only about 2% of all mammalian biomass. In Greek mythology most of the gods adorned their robes and helmets with depictions of carnivores, and the great hero Hercules' most famous feat was killing the "invulnerable" lion with his bare hands. Part· of our fascination with carnivores stems from fright and intrigue, and sometimes even hatred because of our direct competition with them. Cases of "man-eating" lions, bears, and wolves, as well as carnivores' reputation as killers of livestock and game, provoke communities and governrpents to adopt sweeping policies to exterminate them. Even President Theodore Roosevelt, proclaimer of a new wildlife protectionism, described the wolf as "the beast of waste and desolation. " The sheer presence and power of carnivores is daunt­ ing: they can move quickly yet silently through forests, attaining rapid bursts of speed when necessary; their massive muscles are aligned to deliver powerful attacks, their large canines and strong jaws rip open carcasses, and their scis­ sor-like carnassials slice meat. Partly because of our fear of these attributes, trophy hunting of carnivores has been, and to a certain extent still is, a sign of bravery and skill. Among some Alaskan Inuit, for example, a man is not eligible for marriage until he has killed a succession of animals of increasing size and dangerousness, culminating with the most menacing, the polar bear.
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Introgressive hybridization between mule deer (Odocoileus hemionus) and white-tailed deer (O. virginianus) was studied using sequence analysis of the paternally inherited, Y-linked, Zfy gene. The distribution of Zfy genotypes indicate that male white-tailed deer disperse into the range of mule deer and successfully breed with mule deer does. In western Texas, F1 hybrids are rare, but a relatively high proportion of backcross individuals was observed. Phylogenetic analysis of Zfy among white-tailed, mule, and black-tailed deer was consistent with traditional systematic placement of the latter two being sister-taxa, whereas previous mtDNA studies suggested mule and white-tailed deer were sister taxa.