Editing Brown rat (section)

=== Adaptations in Laboratory Populations ===
{{main|Laboratory rat}}
Brown rats’ interactions with human environments have resulted in a number of identifiable changes in traits. This is especially well documented in laboratory rats. Despite significant levels of inbreeding through [[Selective breeding|artificial selection]], domesticated laboratory rats maintain higher genetic diversity than [[Laboratory mouse|laboratory mice]].<ref>{{Cite journal |last=Canzian |first=F |date=March 1997 |title=Phylogenetics of the laboratory rat Rattus norvegicus. |url=http://genome.cshlp.org/lookup/doi/10.1101/gr.7.3.262 |journal=Genome Research |language=en |volume=7 |issue=3 |pages=262–267 |doi=10.1101/gr.7.3.262 |pmid=9074929 |issn=1088-9051|doi-access=free }}</ref> [[Population structure (genetics)|Population structure]] among strains of domesticated rats is so powerful that distinctions are detectable between rats bred in different rooms of the same facilities.<ref>{{Cite journal |last1=Gileta |first1=Alexander F. |last2=Fitzpatrick |first2=Christopher J. |last3=Chitre |first3=Apurva S. |last4=St. Pierre |first4=Celine L. |last5=Joyce |first5=Elizabeth V. |last6=Maguire |first6=Rachael J. |last7=McLeod |first7=Africa M. |last8=Gonzales |first8=Natalia M. |last9=Williams |first9=April E. |last10=Morrow |first10=Jonathan D. |last11=Robinson |first11=Terry E. |last12=Flagel |first12=Shelly B. |last13=Palmer |first13=Abraham A. |date=2022-05-31 |editor-last=Kukekova |editor-first=Anna V. |title=Genetic characterization of outbred Sprague Dawley rats and utility for genome-wide association studies |journal=PLOS Genetics |language=en |volume=18 |issue=5 |pages=e1010234 |doi=10.1371/journal.pgen.1010234 |doi-access=free |pmid=35639796 |pmc=9187121 |issn=1553-7404}}</ref> The earliest evidence of differentiation from wild populations is the early proliferation of color variants among domesticated strains. This was documented in the 18th century in Japan and by the 19th century in Europe.<ref>{{Cite journal |last=Kuramoto |first=Takashi |date=2011 |title=Yoso-Tama-No-Kakehashi; The First Japanese Guidebook on Raising Rats |url=http://www.jstage.jst.go.jp/article/expanim/60/1/60_1_1/_article |journal=Experimental Animals |language=en |volume=60 |issue=1 |pages=1–6 |doi=10.1538/expanim.60.1 |pmid=21325747 |issn=1341-1357}}</ref><ref name="Hulme-Beaman" />

Today’s laboratory rats exhibit physical and behavioral adaptations. Rats bred for laboratory use develop smaller testes and have smaller neocortexes.<ref>{{Cite journal |last=Richter |first=Curt P. |date=January 1959 |title=Rats, man, and the welfare state. |url=https://doi.apa.org/doi/10.1037/h0043834 |journal=American Psychologist |language=en |volume=14 |issue=1 |pages=18–28 |doi=10.1037/h0043834 |issn=1935-990X}}</ref><ref>{{Cite journal |last1=Welniak-Kaminska |first1=Marlena |last2=Fiedorowicz |first2=Michal |last3=Orzel |first3=Jaroslaw |last4=Bogorodzki |first4=Piotr |last5=Modlinska |first5=Klaudia |last6=Stryjek |first6=Rafel |last7=Chrzanowska |first7=Anna |last8=Pisula |first8=Wojciech |last9=Grieb |first9=Pawel |date=April 11, 2019 |title=Volumes of brain structures in captive wild-type and laboratory rats: 7T magnetic resonance in vivo automatic atlas-based study |journal=PLOS ONE |volume=14 |issue=4 |pages=e0215348 |doi=10.1371/journal.pone.0215348 |doi-access=free |pmid=30973956 |bibcode=2019PLoSO..1415348W }}</ref> They struggle significantly more with digging and swimming than wild rats when placed under identical conditions.[17] This latter difference results in an aversion in domesticated rats that allows researchers to test memory using the [[Morris water navigation task|Morris water maze]].[19] Rats will recall an unseen platform’s location in a pool and swim to it to avoid swimming.  Other differences contribute to testing in more direct fashions; domesticated rats are able to learn faster and have lower resting levels of stress hormones.[19] On the other hand, laboratory rats’ increased agonistic behavior is less beneficial and not intentionally selected for.[19] A mixture of artificial selection and random variation through [[genetic drift]] is likely responsible for these differences. 

Unique adaptations have been observed in [[Albinism|albino]] strains of laboratory rats. Albinos have smaller [[Visual cortex|visual cortices]] and are less active during the day than their pigmented counterparts.<ref name=":10">{{Cite journal |last1=Stryjek |first1=Rafał |last2=Modlińska |first2=Klaudia |last3=Turlejski |first3=Krzysztof |last4=Pisula |first4=Wojciech |date=2013-06-07 |title=Circadian Rhythm of Outside-Nest Activity in Wild (WWCPS), Albino and Pigmented Laboratory Rats |journal=PLOS ONE |language=en |volume=8 |issue=6 |pages=e66055 |doi=10.1371/journal.pone.0066055 |doi-access=free |issn=1932-6203 |pmc=3676357 |pmid=23762462|bibcode=2013PLoSO...866055S }}</ref><ref name="Modlinska" /> Both of these adaptations are believed to be connected to their diminished visual acuity.

Differences between laboratory rats and wild populations have led to increasing concerns over the representativeness of psychological studies using inbred strains. Some researchers point to the effects of selective breeding on fear response and brain size as warping the results’ applicability to human fear mechanisms.<ref>{{Cite journal |last1=Stryjek |first1=Rafal |last2=Parsons |first2=Michael H. |last3=Fendt |first3=Markus |last4=Święcicki |first4=Jan |last5=Bębas |first5=Piotr |date=October 2021 |title=Let's get wild: A review of free-ranging rat assays as context-enriched supplements to traditional laboratory models |url=https://linkinghub.elsevier.com/retrieve/pii/S0165027021002387 |journal=Journal of Neuroscience Methods |language=en |volume=362 |pages=109303 |doi=10.1016/j.jneumeth.2021.109303|pmid=34352335 |doi-access=free }}</ref>