Abstract Suárez et al. 2008

The mammalian vomeronasal system (VNS) is remarkably diverse, reflecting the particularities of natural history and behavior among species. The accessory olfactory bulb (AOB), the first synaptic loci of the VNS, ranges from very large in south american caviomorph rodents, to very small in carnivores, to its complete absence in old world (catarrhine) primates, most bats, and marine species.
The opossum, the rabbit, and all rodents studied so far have a segregated VNS, where two different populations of sensory neurons, expressing either Gi or Go protein, send projections to the rostral (rAOB) and caudal (cAOB) halves of the AOB respectively. However, in marmosets, shrews, goats, horses and dogs the Gi projection terminates uniformly throughout the AOB, and no Go-expressing glomeruli can be detected.
Based on molecular phylogenies, we previously proposed that the segregated AOB is the basal condition in mammals and that those species with a uniform (Gi-expressing only) AOB were members of the Laurasiatheria clade and Primates (superorder Euarchontoglires), so that at least two independent events of Go-cAOB degeneration might have occurred. Moreover, we noticed that both lineages show conspicuous sexual dimorphisms in secondary characters, allowing the detection of conspecifics gender at distance. Thus, we proposed that the Go-cAOB deterioration may be related to the emergence of sexual dimorphisms.
Here we show that a complete loss of the Go-expressing cAOB have also occurred in two additional sexually dimorphic species: the california ground squirrel Spermophilus beecheyi (Euarchontoglires: Rodentia) and the rock hyrax Procavia capensis (Afrotheria: Hyracoidea), both species nested in lineages with segregated AOB.
These results support our previous hypothesis and states that the events of Go-cAOB degeneration have occurred independently at least four times in placental mammals, as a case of systemic convergence associated to the ability to detect other males at distance. FINANCIAL SUPPORT: FONDECYT Nº 1030522, 1080094

poster SFN 2008 final