"Long before it's in the papers"
June 04, 2013


The inbred—betrayed by scent?

April 17, 2008
Courtesy Current Biology
and World Science staff

Fe­male mice can avoid in­bred males based on scent alone, ac­cord­ing to new re­search whose au­thors say the same might be true of oth­er spe­cies.

More in­bred mice pro­duce a skimpier va­ri­e­ty of a type of mol­e­cule called ma­jor uri­nary pro­teins, or MUPs—and whose whiff be­trays the short­com­ing, ac­cord­ing to the group.

The whiff of in­breed­ing? New re­search sug­gests fe­male mice avoid in­bred males based on scent alone. (Image cour­tesy U.S. Nat'l Inst. of Health)

“Fe­male mice can iden­ti­fy more out­bred males by the high­er di­vers­ity of uri­nary pro­teins,” said Mi­chael Thom of the Uni­ver­s­ity of Liv­er­pool, U.K., one of the sci­en­tists. The find­ings ap­pear April 17 in the on­line is­sue of the re­search jour­nal Cur­rent Bi­ol­o­gy.

Ear­li­er, the same group found wild mice use the pro­teins to de­tect and avoid mat­ing with close rel­a­tives. Anal­o­gous mech­a­nisms have been noted in hu­mans. But the new study was dif­fer­ent in that it ex­am­ined how an­i­mals may steer clear of po­ten­tial mates who are them­selves in­bred.

Many an­i­mals in­stinc­tively avoid in­breed­ing, as it cre­ates off­spring with di­min­ished ge­net­ic va­ri­e­ty, re­sult­ing in po­ten­tial de­fects and health prob­lems. But some­times these flaws emerge only in lat­er genera­t­ions, not the first. This raises the ques­tion of how one might avoid mat­ing not only with one’s rel­a­tives, but with non-rel­a­tives who are healthy, yet in­bred.

Fe­male mice may do this “simply by ‘count­ing’ the num­ber of pro­teins [males] pro­duce, with­out wait­ing to see which might win in a fight,” said Thorn. MUPs were al­ready known to have func­tions in in­forma­t­ion sig­nal­ing with­in the body, he added, so the new re­search sug­gests they al­so serve as “sig­nals” for oth­er in­di­vid­u­als.

The find­ings are the first ev­i­dence that fe­males can rec­og­nize in­bred males based on in­di­ca­tors that don’t di­rectly re­flect health, he con­tin­ued, adding that si­m­i­lar mech­a­nisms might be wide­spread among an­i­mals, in­clud­ing hu­mans.

For the stu­dy, the re­search­ers—led by Jane Hurst, al­so of the uni­ver­s­ity—spe­cially bred male mice to elim­i­nate a nor­mal rela­t­ion­ship be­tween MUP va­ri­e­ty and over­all ge­net­ic di­vers­ity. The pur­pose was to make sure female mice would choose based on the uri­nary pro­teins, rath­er than on oth­er, per­haps un­known in­di­ca­tors of ge­net­ic qual­ity.

The un­kind irony, in fact, was that all the male mice used were in­bred. This was de­lib­er­ate to en­sure they had a un­iform ge­net­ic make­up, fur­ther re­duc­ing fe­ma­les’ abil­ity to choose based on an­y­thing but MUPs. The males were al­so kept apart so that fe­males could­n’t dis­crim­i­nate by fight­ing abil­ity. The female mice went for MUP-rich mates sig­nif­i­cantly more of­ten than oth­ers, the in­ves­ti­ga­tors found. 

Us­ing si­m­i­lar meth­ods, the sci­en­tists al­so tested wheth­er mice might de­tect in­breed­ing based on anoth­er set of mol­e­cules, called the ma­jor his­to­com­pat­i­bil­ity com­plex. These are those that in hu­mans are be­lieved to op­er­ate for avoid­ing re­lat­ed part­ners, again through scent. But these pro­teins did­n’t seem rel­e­vant in the mouse case, the in­ves­ti­ga­tors said.

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Female mice can avoid inbred males based on scent alone, according to new research whose authors say the same might be true of other species. Inbred mice produce a skimpier variety of a type of molecule called major urinary proteins, or MUPs—and whose whiff betrays the shortcoming, according to the group. “Female mice can identify more outbred males by the higher diversity of urinary proteins,” said Michael Thom of the University of Liverpool, U.K., one of the scientists. The findings appear April 17 in the online issue of the research journal Current Biology. An earlier study by the same group found wild mice use the proteins to detect and avoid mating with close relatives. Analogous mechanisms have been found in humans. But the new study was different in that it examined how animals may steer clear of potential mates who are themselves inbred. Many animals instinctively avoid inbreeding because it creates offspring with diminished genetic variety, resulting in potential defects and health problems. But sometimes these flaws emerge only in later generations, not the first offspring. This leaves the problem of how to avoid mating not only with relatives, but with non-relatives who are healthy, yet inbred. Female mice may thus spot “superior males simply by ‘counting’ the number of proteins they produce, without waiting to see which might win in a fight,” said Thorn. MUPs were already known to have functions in information signaling within the body, he added, so the new research suggests they also serve as “signals” for other individuals. The findings are the first evidence that females can recognize inbred males based on indicators that don’t directly reflect their health, he continued, adding that again, similar mechanisms might be widespread among animals. For the study, the researchers—led by Jane Hurst, also of the university—specially bred male mice to eliminate a normal relationship between MUP variety and overall genetic diversity. The purpose was to make sure female mice would choose based on the urinary proteins, rather than on other, perhaps unknown indicators of genetic quality. The unkind irony, in fact, was that all the male mice were inbred. This was deliberate to ensure they had a uniform genetic makeup, further reducing females’ ability to choose based on anything but MUPs. The males were also kept apart so that females couldn’t discriminate by fighting ability. The female mice went for MUP-rich mates significantly more often than others, the investigators found. Using similar methods, the scientists also tested whether mice might detect inbreeding based on another set of molecules, called the major histocompatibility complex. These are those that in humans are believed to operate for avoiding related partners, again through scent. But these proteins didn’t seem relevant in the mice, the investigators said.