Nursing gerbils unravel benefit of multiple mothers in collective mammals

In mam­mals such as rodents that raise their young as a group, infants will nurse from their mother as well as other females, a dynamic known as allo­suck­ling. Ecol­o­gists have long hypoth­e­sized that allo­suck­ling lets new­borns stock­pile anti­bod­ies to var­i­ous dis­eases, but the exper­i­men­tal proof has been lack­ing until now. An in-press report in the jour­nal Mam­malian Biol­ogy found that infant Mon­go­lian ger­bils that suck­led from females given sep­a­rate vac­cines for two dif­fer­ent dis­eases wound up with anti­bod­ies for both illnesses.

The find­ings not only demon­strate the poten­tial pur­pose of allo­suck­ling, but also pro­vide the first frame­work for fur­ther study­ing it in the wild by using trace­able anti­bod­ies, said first author Romain Gar­nier, a post­doc­toral researcher in Prince­ton University's Depart­ment of Ecol­ogy and Evo­lu­tion­ary Biol­ogy. Gar­nier con­ducted the research with Syl­vain Gan­don and Thierry Boulin­ier of the Cen­ter for Func­tional and Evo­lu­tion­ary Ecol­ogy in France, and with Yan­nick Chaval and Nathalie Char­bon­nel at the Cen­ter for Biol­ogy and Man­age­ment of Pop­u­la­tions in France.

Gar­nier and his coau­thors admin­is­tered an influenza vac­cine to one group of female ger­bils, and a vac­cine for Bor­re­lia burgdor­feri -- the bac­te­r­ial agent of Lyme dis­ease -- to another group. Once impreg­nated, female ger­bils from each vac­cine group were paired and, as the ger­bils do in nature, kept sep­a­rate from the male ger­bils to birth and rear their young. In the wild, females can choose which young to nurse and infant ger­bils can like­wise choose which female to suckle. In the typ­i­cal lab, how­ever, one male, one female and their young are housed together, the researchers wrote.

When screened upon birth, all the infant ger­bils had no detectable anti­bod­ies against influenza while one had anti­bod­ies against B. burgdor­feri, accord­ing to the paper. But after eight days of nurs­ing, all the infants con­tained high lev­els of anti­bod­ies for both influenza and B. burgdor­feri, sug­gest­ing that the females nursed the young -- their own and those of the other female -- evenly. These results sug­gest that allo­suck­ling is indeed intended to expose new­born ani­mals to a host of antibodies.

This ben­e­fit sheds light on a pecu­liar arrange­ment in coop­er­a­tive mam­mals that ecol­o­gists have puz­zled over, the authors wrote. In social species, females usu­ally fall into dom­i­nant or sub­or­di­nate groups with the sub­or­di­nate females typ­i­cally involved in tend­ing to the young pro­duced by dom­i­nant females. Yet, in many cases, sub­or­di­nate females are "allowed" to breed. Gar­nier and his col­leagues sug­gest that the poten­tially larger anti­body pool avail­able through nurs­ing might be one of the rea­sons why.

Source: Princeton University