Sunday, 13 November 2011

Polyandry and Alternative Mating Tactics- Meet the Jacanas.

For my inaugural post I'd like to talk about Jacanas.

Jacanas are Charadiiformes and are therefore related to birds such as Sandpipers, Gulls and Plovers rather than Moorhens, which they superficially resemble in appearance and habits. There are 8 species spread around tropical and sub-tropical regions: Two in the Americas (Northern and Wattled); Three in Africa (African, Lesser and Madagascan); Two in Asia (Pheasant-tailed and Bronze-winged) and one in Australasia (Comb-crested). All species are found in wetland habitats, particularly those with floating vegetation where they can be seen walking on the lilypads feeding on small invertebrates whilst spreading their weight with their hugely elongated toes. These traits have earned them the colloquial name of Lily Trotters. 7 of the 8 are ornamented to certain degrees with combs, wattles or bright plumage, Sexes are similar however the female is always more brightly coloured and larger than the male. The one exception to this is the Lesser Jacana where the sexes are identical.

A Comb-crested Jacana taken by Hans & Judy Beste; Queensland, Australia.

Larger, more brightly coloured females are an unusual trait in nature, though there are several examples in a range of taxa from Phalarope to Pipefish. This trait is usually linked to male parental care and in the case of Jacanas it is the male that single-handedly incubates the eggs and raises the young, leaving the females to fight it out over the males. This has lead to polyandry being documented in several species such as the Northern Jacana. Polyandry is a breeding adaption in which females mate with more than one male and is analogous to the more usual polygyny where males mate with more than one female. While polyandry is much more common than previously thought in birds it is usually accompanied by social monogamy it is rare to find a system where the male takes complete control of the young.

This has given rise to the possibility of infanticide being carried out by female Jacanas. Observations described in a 1982 paper in Animal Behaviour seem to suggest just this going on in the Northern Jacana. A female was witnessed attacking a resident female's territory and driving her out followed by agitated distraction behaviour being employed by the male. Within one day the male's clutch had been destroyed, leaving the male free to remate again. Though it is important to point out that the destruction of the nest was not witnessed, however the paper does present strong evidence for infanticide.

Some great photos of Bronze-winged and Pheasant-tailed Jacanas can be seen here: http://www.pbase.com/peterericsson/jacanas

Emlen S. T. & Wrege P. H. (2004) Division of labour in parental care behaviour of a sex-role-reversed shorebird, the wattled jacana. Animal Behaviour 68: 847-855.

Stephens M. L. (1982) Mate takeover and possible infanticide by a female Northern jacana (Jacana spinosa) Animal Behaviour 30: 1253-1254.

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