Variation in Mate Choice: Major Urinary Proteins as a Sexual Signal in Rats (#151)
What does the tail of a peacock, antlers of a deer and pheromones in rat urine have in common? These are sexually dimorphic traits - primarily seen in males- and have evolved with the purpose to attract mates. Sexual selection gives rise to traits that aim to maximize reproductive success, often at the expense of survival due to the demands it places on the signaler. An individual’s fitness determines how it copes with this cost, leading to variation in strength of sexual signal which females use to choose a mate. In rodents, such social information can be relayed by male odors, often via urinary cues. A putative candidate for a sexual signal in rats is Major Urinary Proteins (MUPs) which is a member of the lipocalin family that transports small hydrophobic molecules (volatiles). It is secreted in copious amounts in the urine which is a common communication mode of rats, making it a good way to advertise sexual fitness. Preliminary work in rats has demonstrated the sufficiency and necessity of MUPs to attract females. We show that MUPs mediate sexual signaling in a dose dependant manner and we have correlated female preference for males with more MUPs. Moreover, a dynamic sexual signal will also be open to manipulation. Parasites are known to exploit such avenues to enhance transmission efficiency. We have used a relevant perturbation model in Toxoplasma gondii andhave shown that it manipulates mate choice, causing females to prefer infected male rats and is sexually transmissible. Thus, a parasite that can enhance sexually selected traits of a host will benefit from blunted selection pressure from the host and gain advantage of transmission. To this end, we show that infected male rats have greater levels of MUPs in their liver and urine, giving credence to idea of MUPs as a sexual signal.
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