WHEN it comes to choosing a mate, there鈥檚 nothing better than the perfume of
a protein-eating male to set a female meadow vole鈥檚 hormones racing. Researchers
in the US believe the scent of a well-fed male must be a signal to the female of
the fitness of her potential mate.
Mike Firken of the University of Memphis, Tennessee, and his colleagues
reached this conclusion after studying the effects of different diets on the
voles. For much of the year both sexes of the vole, Microtus
pennsylvanicus, are solitary creatures. However, when a female is ready to
breed, her scent attracts several males and she chooses a mate.
The team fed captive male voles on diets with a protein content of 9, 15 and
25 per cent. Smears were taken from the voles鈥� anal glands and these were
presented to separately housed females, whose preference was determined by the
length of time spent sniffing and licking the odour-coated object in her cage.
The amount of female interest was proportional to the amount of protein in the
diet of the donor male.
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The researchers do not know how the high-protein diet changes the males鈥�
odour. 鈥淏ut it could be via some of the sulphur-rich compounds in proteins,鈥�
says Robert Johnston of Cornell University in New York, one of the team. The
team reports the results in the latest issue of Journal of Animal
Behaviour (vol 53, p 133).
The mating behaviour of meadow voles intrigued the researchers because in the
wild, females are very choosy. On meeting a potential mate, the female first
attacks him. 鈥淭hen, if she likes him, she鈥檒l nudge the groggy male in the ribs
with her nose to encourage him to mate,鈥� says Firken.
The female is receptive for several days and several males may be accepted,
resulting in a mixed-paternity litter. Even so, in any vole population, only 10
to 20 per cent of the males account for 90 per cent of matings. 鈥淥nly a few
males make the grade and it鈥檚 the female that decides,鈥� says Firken.
But why should females prefer the smell of a male with a protein-rich diet?
You might think, says Johnston, that the female is choosing a male who must be
fit because he is able to defend a large territory and so has access to a large
supply of nourishing food. 鈥淗owever, the males only defend the area directly
around their sleeping area,鈥� says Johnston. 鈥淭hey range over 150 to 200 square
metres, and for an eight-centimetre animal that is simply too big to
诲别蹿别苍诲.鈥�
However, a male鈥檚 smell could still be an indicator of quality because
protein-rich vegetation is very patchily distributed. 鈥淪o even if it says
nothing much about his fighting ability, the odour of eaten protein tells you a
lot about a male鈥檚 finding capacity, which is also an indication of quality,鈥�
comments Firken.
鈥淎lternatively,鈥� he adds wryly, 鈥渢he male may have simply got lucky and just
bumped into some great forage in the last few days. It鈥檚 a system that seems far
from perfect, but this may be the best measure of male fitness that鈥檚
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Lee Drickhamer, a zoologist at Southern Illinois University in Carbondale,
says the finding that female voles use odour clues to assess a male鈥檚 quality is
an important step forward. 鈥淭he authors should test further the notion that
there is some within-sex use of these same odour clues鈥攆or example, in
males judging a potential opponent,鈥� he adds.