Previous research has demonstrated that, irrespective of prior familiarity, both social and solitary rodent species respond differentially to odours of other individuals based on the degree of genetic relatedness between them. To investigate whether eusocial species also make odour-based genetic relatedness discriminations, male and female Ansell’s mole-rats (Cryptomys anselli) were exposed to ano-genital odours of unfamiliar opposite-sex conspecifics (one unrelated individual and one “estranged” sibling, from whom they had been separated for 27 days). Habituation tests with the odours of “estranged” siblings and courtship tests confirmed that the “estranged” siblings and their odours were treated as unfamiliar. Subjects spent significantly more time investigating unrelated individuals and their odours, than their “estranged” siblings and their odours, indicating discriminative behaviour toward less genetically similar individuals. The findings suggest that eusocial mole-rats can respond differentially to odours based on their degree of relatedness to the odour donors.
We studied the inner ear of Ctenomys talarum, a small solitary subterranean rodent distributed in the southern region of Buenos Aires Province (Argentina) using standard staining techniques. The inner ear of this subterranean rodent is characterized by a long basilar membrane, a higher density of cochlear receptors in the apical region of the basilar membrane and a gradual increment of the width of the triad of outer hair cells from the base towards the apex. These anatomical features of the cochlea of C. talarum can be interpreted as biomechanical specializations to enhance low-frequency sound reception.
According to a hypothesis addressing the evolution of eusociality in mole-rats, the female (queen) is not able to raise her (first) offspring without a mate and thus to found a family. Therefore, we predict that the reproductive male (king) has to be socially faithful. In this study we tested this prediction and addressed the related question whether or not the presentation of a new female provokes enhanced sexual interest in male Ansell’s mole-rats (Fukomys anselli).
We performed behavioral partner preference tests in Ansell’s mole-rats where two animals of choice were presented to a subject without allowing direct access. The kings spent significantly more time sniffing an unfamiliar queen or female than their own mate. If given the choice between an unfamiliar queen and her respective non-reproductive daughter, however, the tested kings significantly preferred the queen. In contrast, queens did not show a preference for either their own mate, an unrelated unfamiliar king, or a non-reproductive male.
In a second experiment, we allowed the males to access the compartment of an unfamiliar female while their respective family stayed in an adjacent compartment. Only the non-reproductive adult males seized their chances to copulate with the unfamiliar female whereas the kings remained faithful. When reversing the test condition (i.e. females were given access to an unfamiliar male), aggressiveness of the males impeded sexual encounters in most cases. We recorded only three copulations, all of them between queens and non-reproductive males.
We conclude that the reproductive status is crucial for reproductive decisions. Furthermore, the presence of family members influences the kings’ behavior. Since in Ansell’s mole-rats, repeated copulations over a longer period of cohabitation are necessary for ovulation and fertilization, the kings’ sexual fidelity could have been expected. We postulate that the maintenance of Ansell’s mole-rats’ families depends on the kings’ faithfulness.