Species, population and individual specific odors in urine of mole rats (Spalax ehrenbergi) detected by laboratory rats

Analysis on Population Level Reveals Trappability of Wild Rodents Is Determined by Previous Trap Occupant

Live trapping is central to the study of small mammals. Thus, any bias needs to be understood and accounted for in subsequent analyses to ensure accurate population estimates. One rarely considered bias is the behavioural response of individuals to the trap, in particular the olfactory cues left behind by previous occupants (PO). We used a data set of 8,115 trap nights spanning 17 separate trapping sessions between August 2002 and November 2013 in Wytham Woods, Oxfordshire, UK to examine if the decision to enter a trap was affected by the PO, if this was detectable in traditional Capture-Mark-Recapture trapping data (i.e., individuals not uniquely marked), and if it was possible for this effect to bias the population estimates obtained. Data were collected on Apodemus sylvaticus, Myodes glareolus, and Microtus agrestis. Three Generalised Linear Models revealed a significant tendency for the three species to enter traps with same-species PO. With, for example, A. sylvaticus 9.1 times more likely to enter a same species PO trap compared to one that contained a M. agrestis in the grassland during the nocturnal period. Simulation highlighted that, when all other factors are equal, the species with the highest PO effect will have the highest capture rate and therefore return more accurate population estimates. Despite the large dataset, certain species-, sex-, and/ or age-combinations were under-represented, and thus no effects of any additional individual-specific characteristics could be evaluated. Uniquely marking individuals would allow for the PO effect to be disentangled from other biases such as trap-shyness and spatial heterogeneity, but may not be possible in all cases and will depend on the aims of the study and the resources available.

Social discrimination of cage-mates and non-cage-mates by rats

The ability to discriminate between group-mates and non-group-mates likely underpins the occurrence of affiliative and aggressive behaviour towards 'in-group' and 'out-group' individuals. Here we present two experiments aimed at testing the ability of rats (Rattus norvegicus) to discriminate between cage-mate (CM: animals residing in the subject's home cage) and non-cage-mate (NCM) conspecifics. In experiment 1, rats were trained to discriminate between different exemplars of CM and NCM using a lever pressing task employing symmetrical reinforcement. Subjects did not reach performance criterion, but they did show some evidence of discrimination between the two types of stimuli. In experiment 2, we employed a digging task to determine if rats can discriminate between odour cues from CM and NCM presented simultaneously on two sand-filled bowls. Subjects reached performance criterion on the first pair of odours, and on three more different pairs of CM and NCM odours. The results of a reversal task, using a fifth pair of odours, indicate that the rats were using a common factor to discriminate between social cues from CM and NCM conspecifics, rather than learning each pair independently. Possible candidates include a group-specific odour cue, or the development of a CM/NCM category concept.

Short-term contact elicits heterospecific behavioral discrimination of individual odors in mound-building mice (Mus spicilegus)

The authors used a habituation-dishabituation procedure to test the ability of male mound-building mice (Mus spicilegus) to discriminate individual odors from males of another species of mouse. Male mound-building mice failed to spontaneously discriminate individual odors from Mus musculus musculus males, a natural competitor. After 24-hr contact with a male of one of the M. musculus subspecies (M. m. musculus or M. m. domesticus), experienced M. spicilegus males discriminated the individual odors of unfamiliar males of the same subspecies. These results confirm that discrimination of individual chemosignals is not confined to olfactory cues of a single species and provide new information about the effect of short-term contact on discrimination of individual odors across species.

Individual odour similarities across species parallel phylogenetic relationships in the S. ehrenbergi superspecies of mole-rats

Research using habituation techniques has shown that rodents from the same kin group, population, or species share similarities in their individual odours that covary with shared genetic similarities between them, that is, the closer their genetic relatedness, the more similar their odours. We assessed similarities in individual odours across four sibling species of subterranean mole-rats from the Spalax ehrenbergi superspecies in Israel. Mole-rats were habituated to the urine odour of a same-sex individual from one species then tested with urine odours of individuals from two different species of the superspecies. Subjects treated urine odours of individuals from more closely genetically related species as similar compared with the odours of individuals from a less closely related species, showing that the covariance between odours and genes extends across species. These similarities in odour also paralleled genetic similarities determined by molecular analysis: odours of descendent species were perceived as similar to those of their closest ancestral species, suggesting that some qualities of the odour of the ancestral species persist in the descendent species. It is generally assumed that during speciation incipient species develop species-specific markers, including, for example, odour markers, to facilitate discrimination of conspecifics from close ancestral heterospecifics. Our findings indicate that similarities in odours across species are more salient than species-specific odour markers. Such findings may also have important implications for mechanisms of species recognition. Copyright 2000 The Association for the Study of Animal Behaviour.