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Captivity Adaptation Impacts Conservation and Research
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Animals!are!kept!in!captivity!for!many!reasons.!One!example!is!when!scientists!use!
model!organisms!to!conduct!research.!Conservation!organizations!on!the!other!hand!often!
house!endangered!animals!in!facilities!to!better!care!for!them.!Livestock!are!raised!on!
farms!around!the!world!for!food!and!labor,!and!millions!of!people!also!own!domestic!pets!
like!cats,!dogs,!and!snakes.!
In!some!of!these!cases,!adaptation!to!captivity!is!a!big!problem.!Much!of!the!
scientific!research!using!animal!models!work!based!on!the!premise!that!lab!animals!are!
good!representations!of!their!wild!counterparts!(Frankham!and!Loebel!1992).!If!the!lab!
and!wild!populations!significantly!differ!in!one!respect!or!another,!the!conclusions!drawn!
from!months!and!years!of!research!may!become!invalid.!This!is!also!a!concern!for!
conservation!scientists!because!endangered!species!bred!in!facilities!may!become!adapted!
to!their!domestic!environment!and!so!be!less!capable!to!survive!when!released!into!their!
natural!habitats!(Christie!et!al.!2012).!Even!when!it!is!not!important!for!lab!animals!to!
retain!their!wild!characteristics,!as!is!the!case!for!mice!in!breast!cancer!research,!it!could!
still!be!pertinent!for!scientists!to!know!the!unintentional!effects!of!captivity.!
Domestic!adaptation!often!occurs!when!animals!are!housed!in!conditions!unlike!
their!natural!habitats!(Price!1999).!Certain!aspects!of!the!domestic!environment!may!then!
cause!changes!in!the!population.!The!environment!might!be!too!favorable,!where!subjects!
are!given!abundant!food,!water,!and!attention!to!increase!their!likelihood!of!surviving!
(Frankham!and!Loebel!1992).!The!environment!may!also!select!for!traits!different!from!
those!selected!for!in!the!wild.!As!an!example,!animals!such!as!insects!and!fish!are!often!
confined!in!close!proximity!to!one!another!for!convenience.!Having!lower!aggression!would!
- 2. therefore!be!more!beneficial!as!increased!conflicts!are!associated!with!higher!mortality!
(Holway!et!al.!1998).!!
Undoubtedly,!there!are!important!implications!for!breeding!animals!in!captivity.!I!
discuss!below!examples!specifically!relating!to!conservation!biology,!biological!controls,!
and!basic!science!research.!!
CONSERVATION!
For!conservationists,!the!negative!effects!of!captive!rearing!may!prove!disastrous!
for!species!that!are!bred!in!enclosed!environments!but!meant!for!eventual!reUrelease.!This!
is!because!there!can!be!relaxed!selection!and!the!rise!of!maladaptive!traits!in!captive!
individuals!that!makes!them!illUsuited!to!their!natural!habitats.!!
Frankham,!R.!2008.!Genetic!adaptation!to!captivity!in!species!conservation!programs.!
Molecular!Ecology!17:325–333.!
!
One!example!of!relaxed!selection!is!discussed!in!Frankham’s!2008!paper.!In!his!
work,!Frankham!argues!that!adaptation!to!captivity!is!primarily!due!to!higher!occurrences!
of!deleterious!alleles!normally!rare!and!partially!recessive!in!the!wild.!The!rate!at!which!
these!alleles!become!common!depends!on!many!factors,!including!selection!intensity,!
genetic!diversity!of!the!individuals,!population!size!held!captive,!and!the!number!of!
generations!animals!are!kept!in!captivity.!Were!individuals!with!these!alleles!released,!they!
would!not!survive!for!long.!!
Montgomery,!M.!E.,!L.!M.!Woodworth,!P.!R.!England,!D.!A.!Briscoe,!and!R.!Frankham.!2010.!
Widespread!selective!sweeps!affecting!microsatellites!in!Drosophila!populations!adapting!
to!captivity:!Implications!for!captive!breeding!programs.!Biological!Conservation!
143:1842–1849.!
!
Another!study!found!that!microsatellite!heterozygosity!was!lost!at!a!faster!rate!in!
captive!populations!as!compared!to!nonUcaptive!populations.!As!Montgomery!et!al.!state,!
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“The!objective!of!genetic!management!in!captivity!is!to!‘freeze’!evolution.”!That!is,!they!aim!
to!imitate!the!wild!environment!as!closely!as!possible!to!maintain!genetic!diversity!and!
avoid!adaptation!to!captivity.!However,!domestic!environments!cannot!truly!replicate!wild!
environments.!As!a!result,!there!is!often!a!divergence!in!some!characteristic!between!the!
two!populations.!!
Lewis,!O.!T.,!and!C.!D.!Thomas.!2001.!Adaptations!to!captivity!in!the!butterfly!Pieris!
brassicae!(L.)!and!the!implications!for!ex!situ!conservation.!Journal!of!Insect!Conservation!
5:55–63.!
!
Reproductive!success!can!also!be!affected!in!captivity.!Lewis!and!Thomas!found!that!
butterflies!held!captive!for!approximately!100U150!generations!laid!more!eggs!and!had!
higher!ovary!mass!at!peak!egg!production!than!their!wild!counterparts.!However!
individuals!raised!in!captivity!were!also!heavier,!with!smaller!wings!and!lower!wing!aspect!
ratios.!This!may!indicate!a!tradeoff!in!energy!investment!between!growth!and!
reproduction.!Because!their!captive!environment!was!likely!more!crowded!than!in!their!
natural!environments,!the!butterflies!had!no!need!to!invest!in!producing!large!wings.!More!
of!their!energy!could!then!go!into!producing!eggs.!Such!phenotypic!changes!may!be!
beneficial!in!captivity,!but!they!may!prove!disadvantageous!in!the!wild.!!
McPhee,!M.!E.!2004.!Morphological!change!in!wild!and!captive!oldfield!mice!Peromyscus!
polionotus!subgriseus.!Journal!of!Mammalogy!85:1130–1137.!
!
One!study!of!oldfield!mice!showed!morphological!changes!in!skull!size!and!shape.!
Specifically,!the!cranial!and!mandibular!size!and!shape!were!significantly!different!in!wild!
versus!captive!mice.!Since!jaw!size!and!shape!can!radically!alter!feeding!strategies!and!
overall!fitness,!having!these!substantial!changes!in!a!population!may!make!it!more!difficult!
for!released!individuals!to!compete!in!a!natural!environment.!!
- 4. ! These!findings!represent!a!small!fraction!of!the!scientific!literature!revealing!
overwhelming!evidence!that!captive!breeding!can!induce!significant!changes!in!a!
population.!Because!of!this,!many!conservation!scientists!advocate!it!only!as!a!last!resort.!
Unfortunately,!few!solutions!alternative!to!captive!rearing!are!present!for!endangered!
species!(Snyder!et!al.!1996).!The!best!course!of!action!may!instead!be!to!address!and!
minimize!the!changes!observed!due!to!captivity.!
BIOLOGICAL!CONTROL!
Biological!control!is!a!method!of!controlling!pests!such!as!weeds!and!insects!using!
other!living!organisms.!They!can!be!implemented!several!ways,!some!of!which!include!
releasing!the!pest’s!natural!predator/parasite!in!large!numbers.!Another!common!type!of!
control!is!called!the!Sterile!Insect!Technique.!Using!this!technique,!a!mass!of!sterilized!pest!
individuals!are!released!to!mate!with!wild!individuals.!All!these!methods!have!the!eventual!
goal!of!decreasing!the!pest!population.!
Where!biological!controls!are!needed,!it!is!essential!that!the!released!individuals!not!
have!too!low!or!too!high!of!fitness.!In!the!former!case,!they!would!die!too!easily!and!so!be!
ineffective;!in!the!latter,!they!may!outcompete!and!drive!out!closely!related!native!species!
(Cory!and!Myers!2000).!!
Baumhover,!A.!H.,!A.!J.!Graham,!B.!A.!Bitter,!D.!E.!Hopkins,!W.!D.!New,!F.!H.!Dudley,!and!R.!C.!
Bushland.!1955.!ScrewUWorm!Control!Through!Release!of!Sterilized!Flies.!Journal!of!
Economic!Entomology!48:462–466.!
!
One!example!of!biological!control!involves!screwworms!in!cattle.!In!warm!and!
tropical!areas,!these!parasites!predominantly!breed!in!the!open!wounds!of!cattle,!causing!
deep!screwUlike!lesions.!By!irradiating!them,!scientists!were!able!to!sterilize!the!flies,!
hundreds!of!which!were!then!released!en!masse.!The!experiments!conducted!by!
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Baumhover!et!al.!were!successful,!and!the!percentage!of!sterile!egg!masses!that!the!flies!
laid!increased!from!69%!to!100%!in!just!8!weeks.!Since!the!publication!of!this!study!and!
numerous!others,!this!technique!has!been!used!to!control!many!different!kinds!of!pests!
around!the!globe.!
Mastrangelo,!T.,!P.!Fresia,!M.!L.!Lyra,!R.!A.!Rodrigues,!and!A.!M.!L.!AzeredoUEspin.!2014.!
Genetic!diversity!and!population!structure!of!the!New!World!screwworm!fly!from!the!
Amazon!region!of!Brazil.!Acta!Tropica!138:S26–S33.!
!
However,!in!order!for!the!sterile!insect!technique!to!work,!released!individuals!must!
maintain!as!high!a!level!of!genetic!diversity!as!wild!individuals.!Among!nine!populations!of!
the!screwworm!fly!in!the!Brazilian!Amazon,!this!2014!study!found!that!there!are!high!
levels!of!genetic!diversity!and!population!structure.!But!for!many!breeding!facilities,!the!
same!might!not!be!true.!Since!large!numbers!of!a!pest!must!be!released!together!to!
effectively!control!the!population,!sterile!individuals!are!bred!in!facilities!at!high!densities.!
As!mentioned!before,!such!captive!breeding!may!decrease!genetic!variability.!Adaptation!to!
captivity!is!a!big!concern!for!researchers!using!biological!controls!exactly!because!releasing!
individuals!that!do!not!mate!with!the!wild!population!renders!the!biological!control!
useless.!!
Mlonyeni,!X.!O.,!B.!D.!Wingfield,!M.!J.!Wingfield,!R.!Ahumada,!P.!Klasmer,!I.!Leal,!P.!de!Groot,!
and!B.!Slippers.!2011.!Extreme!homozygosity!in!Southern!Hemisphere!populations!of!
Deladenus!siricidicola,!a!biological!control!agent!of!Sirex!noctilio.!Biological!Control!
59:348–353.!
!
As!a!case!in!point,!nematodes!used!as!biological!controls!for!wasps!are!speculated!to!
have!a!decreased!ability!to!adapt!and!survive!because!of!their!lack!of!genetic!diversity.!
Other!than!relaxed!selection!and!maladaptive!traits,!there!may!also!be!inbreeding!in!lab!
- 6. colonies.!Inbreeding!is!widely!known!to!decrease!an!individual’s!fitness,!and!so!for!species!
used!as!biological!controls!this!affects!their!ability!to!work!properly.!!
Smith,!L.,!E.!de!Lillo,!and!J.!W.!Amrine.!2010.!Effectiveness!of!eriophyid!mites!for!biological!
control!of!weedy!plants!and!challenges!for!future!research.!Experimental!and!Applied!
Acarology!51:115–149.!
!
Eriophyid!mites!used!to!control!weedy!plants!are!another!example.!In!Smith!et!al.!
the!mites!had!a!reduced!effectiveness!due!to!natural!enemies,!resistant!plants,!and!abiotic!
conditions.!Some!plants!had!even!coevolved!so!closely!with!the!mites!that!they!had!become!
resistant.!!
Shelly,!T.!E.,!J.!Edu,!and!E.!Pahio.!2007.!AgeUdependent!variation!in!mating!success!of!sterile!
male!Mediterranean!fruit!flies!(Diptera :!Tephritidae):!Implications!for!sterile!insect!
technique.!Journal!of!Economic!Entomology!100:1180–1187.!
!
In!breeding!facilities,!researchers!must!try!to!release!as!many!sterile!individuals!as!
possible!but!still!keep!them!viable!as!controls.!The!male!Mediterranean!fruit!flies!were!
found!to!be!more!effective!when!released!at!older!life!stages.!Unfortunately,!many!of!the!
flies!at!the!facility!had!faster!maturation!rates!than!their!wild!counterparts,!causing!them!to!
be!released!prematurely.!This!finding!once!again!supports!that!there!is!selection!in!captive!
environments,!which!has!implications!for!the!field!of!biological!controls.!
BASIC!SCIENCE!
! Here!in!the!Zuk!lab,!we!are!especially!concerned!about!how!lab!selection!and!
adaptation!to!captivity!will!affect!basic!science!research.!If!labUbred!individuals!are!
significantly!different!in!genetics,!behavior,!or!other!aspects!from!their!wild!counterparts,!
the!conclusions!drawn!from!such!research!may!be!incorrect.!Although!the!examples!given!
above!were!discussed!in!the!context!of!conservation!biology!and!biological!controls,!almost!
all!of!them!also!apply!to!basic!research.!!
- 8. Author! Year! Title! Summary! Implications!
Baumhover!
et!al.!
1955! ScrewUworm!
control!
through!
release!of!
sterilized!
flies!
Experimental!trials!released!
irradiated!&!sterile!screw!
worm!flies,!successfully!
eradicating!the!fly!population!
in!lab!goats!
Example!of!successful!
SIT!for!biological!
control.!
Christie!et!
al.!
2012! Genetic!
adaptation!to!
captivity!can!
occur!in!a!
single!
generation!
“Those!with!greatest!fitness!
in!a!captive!environment!
produced!offspring!that!
performed!the!worst!in!the!
wild.”!
Such!lab!selection!is!
negative!especially!
for!conservation!
science!and!biological!
controls.!
Cory!and!
Myers!
2000! Direct!and!
indirect!
ecological!
effects!of!bio!
control!
Bio!control!programs!have!
had!negative!indirect!and!
direct!effects.!Some!controls!
have!attacked!nontarget!
hosts,!displaced!native!
species,!!
Pathogens!from!
captivity!may!be!
introduced!to!wild!
popn;!released!
individuals!may!be!
reproductively!
superior!and!become!
invasive,!drive!out!
other!species,!or!
reduce!biodiversity!
Frankham! 2008! Genetic!
adaptation!to!
captivity!in!
species!
conservation!
programs!
Where!they!are!knocked!out!
in!the!wild,!rare!alleles!are!
not!selected!against!in!
captivity.!Population!
fragmentation!and!crossing!
captive!individuals!may!be!
possible!ways!to!reduce!
captivity!effects!
Bad!for!animal!
rerelease!into!wild!
Frankham!
and!Loebel!
1992! Modeling!
problems!in!
conservation!
genetics!&!
adaptation!to!
captivity!
Reproductive!fitness!of!
Drosophila'melanogaster!for!
captive!population!twice!of!
wild!population!
Relaxed!selection!for!
reproduction!–!may!
have!either!positive!
or!negative!effects!on!
a!population.!Bad!for!
basic!science.'
Holway!et!
al.!
1998! Loss!of!
intraspecific!
aggression!
In!increased!population!
densities,!there!is!reduced!
intraspecific!aggression,!with!
lower!mortality!and!greater!
brood!production!
Captive!individuals!
may!have!decreased!
aggression,!lower!
mortality,!and!larger!
broods!as!compared!
to!wild!individuals!
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Author! Year! Title! Summary! Implications!
Lewis!and!
Thomas!
2001! Adaptations!
to!captivity!in!
the!butterfly!
Compared!to!wild!
individuals,!captive!females!
laid!more!eggs!and!had!
higher!ovary!mass!at!peak!
egg!production!!
Relaxed!selection!!
Excess!resources!
affecting!egg!
production!
Mastrangel
o!et!al.!
2014! Genetic!
diversity!and!
population!
structure!of!
the!NW!
screwworm!
fly!
mdDNA!and!microsatellite!
data!find!that!there!is!much!
genetic!diversity!within!
multiple!screwworm!
populations!
In!order!for!SIT!to!
work,!the!sterile!
males!must!also!have!
much!genetic!
diversity!to!
significantly!affect!
the!wild!population!
McPhee! 2004! Morphologica
l!change!in!
wild!and!
captive!mice!
Morphological!changes!
increased!with!generations!in!
captivity!most!likely!due!to!
relaxed!selective!pressures!
and!founder!effects!
Relaxed!selection!
Macroevolution!
Mlonyeni!et!
al.!
2011! Extreme!
homozygosit
y!
in…populatio
ns!of!D.!
siricidicola,!a!
biological!
control!agent!
Lack!of!genetic!diversity!in!
the!nematode!bred!as!a!
biological!control!for!wasps!
affects!the!nematode’s!ability!
to!adapt!and!survive.!
If!captive!rearing!
decreases!genetic!
diversity!of!biological!
controls,!they!could!
be!rendered!useless!
Montgomer
y!et!al.!
2010! Widespread!
selective!
sweeps!
affecting!
Drosophila!
adapting!to!
captivity!
Microsatellite!heterozygosity!
loss!significantly!faster!than!
in!normal!nonUcaptive!
populations,!with!great!
neutral!changes!in!allele!
frequencies!as!well!
Microevolution!
Homogenous!gene!
pool!
Price! 1999! Behavioral!
development!
in!animals!
undergoing!
domesticatio
n!
Differences!in!food,!space,!
and!predator!availability!
among!other!things!often!
precipitate!adaptation!to!
captivity!and!domestication!
Implications!of!
changes!to!captivity!
widespread!
Seddon!et!
al.!
2007! Developing!
the!science!of!
reintroductio
n!biology!
Researchers!thinking!about!
reintroduction!of!species!
after!captivity!should!plan!
carefully!beforehand!
HUGE!overview!of!
cases!of!species!
reintroduction!!
- 10. Author! Year! Title! Summary! Implications!
Shelley!et!
al.!
2007! AgeU
dependent!
variation!in!
the!mating!
success!of!
sterile!male!
fruit!flies!
Older!sterile!males!are!more!
effective!as!bio!controls!than!
younger!ones.!Important!
because!production!facilities!
release!sterile!males!too!soon!
due!to!faster!maturation!
(caused!by!mass!rearing).!
Problems!with!sterile!
male!technique!in!
flies!used!as!a!
biological!control!
Smith!et!al.! 2010! Effectiveness!
of!eriophyid!
males!for!
biological!
control!of!
weedy!plants!
Review!of!prev.!work!shows!
that!mites!might!not!be!very!
good!biological!controls!
because!their!effectiveness!
was!reduced!by!natural!
enemies,!resistant!plant!
genotypes,!and!many!other!
factors.!
LabUbred!mites!must!
be!able!to!overcome!
natural!obstacles!in!
the!wild!to!be!
successful!as!
biological!controls!
Snyder!et!
al.!
1996! Limitations!of!
captive!
breeding!in!
endangered!
species!
recovery!
Captive!breeding!should!be!a!
last!resort!because!of!the!
genetic!and!phenotypic!
changes!that!occur!
Micro!and!
macroevolution!
Bad!for!rerelease!
Epizootic!disease!and!
other!problems!in!
endangered!sp.!
Taylor!et!al.! 1991! Reproductive!
compatibility
…of!newU
world!
screwworm!
Examination!of!massU
produced!screwworm!
genetics!indicates!that!they!
are!reproductively!
compatible!with!the!wild!
strain!and!so!may!be!used!as!
a!means!of!screwworm!
eradication.!
Tests!now!may!
indicate!wild!and!
domestic!population!
compatibility,!but!
after!many!
generations!in!
captivity,!will!they!
still!be?!!
! 2014! Using!model!
organisms!to!
study!health!
and!disease!
Model!organisms!are!used!for!
research!because!they!have!
shorter!generations!and!are!
easy!to!rear!
Shorter!generation!
time!means!
organisms!are!more!
susceptible!to!
adaptation!to!
captivity!
Walker! 1999! House!
Cricket,!
Acheta'
domesticus…!
Discussion!of!the!spread!of!
Acheta'domesticus!across!the!
United!States!
!
!
! !
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CITATIONS!
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Baumhover,!A.!H.,!A.!J.!Graham,!B.!A.!Bitter,!D.!E.!Hopkins,!W.!D.!New,!F.!H.!Dudley,!and!R.!C.!
Bushland.!1955.!ScrewUWorm!Control!Through!Release!of!Sterilized!Flies.!Journal!of!
Economic!Entomology!48:462–466.!
Christie,!M.!R.,!M.!L.!Marine,!R.!A.!French,!and!M.!S.!Blouin.!2012.!Genetic!adaptation!to!
captivity!can!occur!in!a!single!generation.!Proceedings!of!the!National!Academy!of!
Sciences!of!the!United!States!of!America!109:238–242.!
Cory,!J.!S.,!and!J.!H.!Myers.!2000.!Direct!and!indirect!ecological!effects!of!biological!control.!
Trends!in!Ecology!&!Evolution!15:137–139.!
Frankham,!R.!2008.!Genetic!adaptation!to!captivity!in!species!conservation!programs.!
Molecular!Ecology!17:325–333.!
Frankham,!R.,!and!D.!Loebel.!1992.!Modeling!Problems!in!Conservation!Genetics!Using!
Captive!Drosophila!Populations!U!Rapid!Genetic!Adaptation!to!Captivity.!Zoo!Biology!
11:333–342.!
Holway,!D.!A.,!A.!V.!Suarez,!and!T.!J.!Case.!1998.!Loss!of!Intraspecific!Aggression!in!the!
Success!of!a!Widespread!Invasive!Social!Insect.!Science!282:949–952.!
Lewis,!O.!T.,!and!C.!D.!Thomas.!2001.!Adaptations!to!captivity!in!the!butterfly!Pieris!
brassicae!(L.)!and!the!implications!for!ex!situ!conservation.!Journal!of!Insect!
Conservation!5:55–63.!
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