Pheromones in social mole-rats and implications for the study of mammalian chemical communication
The work reported in this thesis represents an interdisciplinary approach on chemical (olfactory) communication in Zambian mole-rats of the genus Fukomys (family Bathyergidae, Rodentia). Although much attention has been given in this respect to rodents, the role of chemosensation (including acting signals) in these subterranean, eusocial mammals is still not well understood. Individual recognition and signals informing about the reproductive status, both providing the basis of incest avoidance and reproductive skew (Burda 1995), are of special interest particularly because their sensory mechanism remains obscure. The chapter Behavioural olfactory bioassays outlines the evidence for the importance of ano-genital odour in kinship- and individual recognition in mole-rats. Contrary, urine odours did not provide sufficient sensory information in this respect. Pilot endocrinological and colpocytological examinations in Fukomys reveal strong correlation between high mean estradiol- and progesterone values and sexual activity (chapter Steroids and reproductive status). Zambian Fukomys mole-rats are induced ovulators, primed exclusively through repeated and regular sexual activity and not solely through single copulation or separation from the queen as reported for the Damaraland mole-rats (cf., Molteno & Bennett 2000). The poorly understood molecular basis (outlined in the chapter Semiochemicals – HS-SPME-GC-MS-Analysis and in the chapter Lipocalines (MUP´s & Aphrodisin) – Proteomics) of chemosensation was studied, by means of a solvent-free HS-SPME-GS-MS, 2D-PAGE and MALDI-TOF/TOF-tandem MS developed within the framework of this research. Using this approach, it could be demonstrated, that 51 urinary compounds constituting individual volatile urinary pattern of the mole-rat were quite similar even between members of different families. A queen-specific component, 4-nonanone, and similarly 1-hexadecanol, typical for non-reproductive daughters, were identified by mass spectra. Reproductive males (kings) could, however, not be distinguished on the basis of their urinary volatile pattern from non-reproductive males. Males displayed higher amount of ß-caryophyllene in their volatile urinary pattern than females. Although altogether 41 different compounds were identified in urine of families, mole-rats cannot discriminate between different families on the base of odour. Carrot and potato diet influence the urinary composition. Generally, individual urine variations depend on sex (male or female) and reproductive status (queens or non-reproductive females) and not on individuality per se, supporting the outcomes of behavioural bioassays. Remarkably, a well-known lipocaline and sex pheromone of the golden hamster (Mesocricetus auratus) vaginal discharge, aphrodisin, was identified in the urine of Fukomys mole-rats, but without mass polymorphism and in atypically low concentration. In urine of two additionally examined genera of subterranean rodents (Spalax spp. and Spalacopus sp.), neither aphrodisin nor the lipocaline MUP (major urinary protein), generally present in the house mouse (Mus musculus musculus and Mus musculus domesticus1), was found. On these backgrounds, it is still questionable, if in Zambian Fukomys mole-rats aphrodisin takes on the role of a ligand carrier in the subterranean environment. Ligands such as the prospective 1-hexadecanol or 4-nonanone could be protected from degradation (once urine is deposited). Moreover, the slow release mechanism would prolong the olfactory signal which is proved with MUPs in the house mouse. Still it is not clear, if any or which meaning aphrodisin and/or the urinary volatiles have for the olfactory communication. Further research should concentrate on ano-genital odours (and body odours) because of the clear results of the behavioural assays.
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