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Sleepy lizards guard mates. (journal extracts).

ALTHOUGH monogamy is common enough in birds and mammals, lizards tend to have more promiscuous or potygynous breeding systems in which males attempt to mate with several females in a defended territory. Only two lizard species are known to form monogamous relationships, of more than a few days, in a breeding season. Both are Australian skinks: the gidgee skink and the sleepy lizard, the latter a close relative of the blue-tongued lizard.

Dr Travis How and Dr Michael Butt, of Hinders University, say that sleepy lizards, large herbivorous skinks of semi-arid Lands, form monogamous pairs each spring that last six to eight weeks before mating. The bond is strong. One male lizard remained close to his partner for two days after she died.

In many species monogamy is thought to improve survival of offspring because males stay around to help raise young. But this does not occur with sleepy lizards. Another hypothesis is that males guard females to keep rival males at bay. MaLes have wider heads and stronger jaw muscles than females and these are used in mate-to-mate combat, especially when females are close to mating. Genetic analysis also shows that most monogamous pairs of sleepy lizards produce litters fathered by one male, suggesting successful mate-guarding.

But doubts about the function of the pair bonds remain. Why do males guard their females for so long before mating? Were rival males a threat?

The scientists tested two predictions of the mate-guarding hypothesis in sleepy lizards: that females should play a passive role in maintaining the pair bond, and that males should become more attentive as the time of mating draws near. In experiments over three breeding seasons, in the shrubtands of South Australia, they separated lizard pairs and observed the re-uniting behaviour.

The males were found more likely to return to females than vice versa, and reunion vigour was greater in mates as mating-time approached. This supports the mate-guarding explanation, but other results suggested this might not be the only function of monogamy in the lizard. Females were active in maintaining the relationship, often seeking reunion. They may also gain some advantage from pair-bonding, perhaps guaranteed access to a fertile male or better vigilance against predators.

How TL and Bull CM (2002) Reunion vigour: an experimental test of the mate guarding hypothesis in the monogamous sleepy lizard (Tiliqua rugosa). Journal of Zoology, London, 257:333-338.
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Author:Davidson, Steve
Publication:Ecos
Geographic Code:8AUST
Date:Oct 1, 2002
Words:395
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