Social behaviour may drive asymmetries among accessory olfactory bulb subdomains: The case of octodontine rodents

摘要

Social behaviour may drive asymmetries among accessory olfactory bulb subdomains: The case of octodontine rodents In mammals, the accessory olfactory or vomeronasal system (VNS) exhibits a wide variety of anatomical arrangements. In caviomorph rodents, the accessory olfactory bulb (AOB) exhibits a dichotomic conformation, in which two subdomains, anterior (aAOB) and posterior (pAOB) can be readily distinguished. Inter- estingly, different species of this group exhibit biases of different sign between AOB subdomains (aAOB larger than pAOB or vice versa). Such specie-specific biases have been related with con- trasting differences in the habitat of the different species (arid vs humid), which would lead the preferential use of either V1R or V2R pathways. Aiming to deepen these observations, we performed a morphometric comparison of the AOB subdomains among two sis- ter species of octodontine rodents, Octodon lunatus and Octodon degus. Previous reports have shown that O. degus exhibits a highly asymmetric AOB, in which the aAOB have twice the size of the pAOB and features more and larger glomeruli in its glomerular layer (GL). We found that same as in O. degus, O. lunatus also exhibits a bias, albeit less pronounced, to a larger aAOB. In both species, this bias was evident at the mitral/tufted cell layer. But unlike in O. degus in O. lunatus this bias was not present at the GL. In comparison with O. degus, in O. lunatus the aAOB GL was significantly reduced in volume, while the pAOB GL display a similar volume. We con- clude that these sister species exhibit a very sharp difference in the anatomical conformation of the AOB, namely, the relative size of the glomerular layer of the aAOB subdomain, which is larger in O. degus than in O. lunatus. We discussed these results in the context of the differences in the life mode in these species, highlighting the differences in social behaviour, but not in ecological context, as a possible factor driving to distinct AOB mophometries.