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7.6 Chameleonspecies spends most of its life as an egg


Chameleonspecies spends most of its life as an egg

By John Timmer | Published:June 30, 2008 - 06:48PM CT

Most of us are probablyfamiliar with various species of insects that mature, mate, and die veryrapidly, having spent most of their lives in some immature form. But later thisweek, PNAS will be publishinga paper describing similar behavior in an unexpected place: among thevertebrates. The authors of the paper describe a species of chameleon where theentire adult population dies every year, after having spent only four monthsout of the egg.

The species is Furcifer labordi, shown at right, andit lives in some of the drier regions of Madagascar. The authors spent a coupleof years tracking it in the field, catching and releasing marked animals andfitting some with radio collars. The attention allowed them to describe afantastic lifestyle, one that's compressed and skewed compared to most othervertebrates we're aware of.

The first of a given year'sgeneration of chameleons emerge from their eggs in mid-November, as theregion's rainy season is getting started. From there, they put on prodigiousgrowth spurts, with females increasing their body mass by two percent daily,and males by an impressive four percent every day. At that pace, they reachedmaximum size sixty days later, in early February. Mating and egg laying startedalmost immediately, with females putting over 35 percent of their body massinto the eggs.

By the end of February, amass die-off started; the researchers literally watched as animals fell fromthe trees. By April, the population had plunged, and adult labordi were nowhere to be seen by thetime the dry season started in June. The cycle started over again in November,suggesting that the animal spends roughly seven months developing in its eggfor a mere four or five months of life.

The researchers note thatevolutionary theory suggests that a short life cycle would be favored whenadult mortality is high. This is apparently the case with labordi, as they spotted several adultsfall victim to predation during the mating season. A related species that has alonger life cycle saw its population plunge during the dry season, suggestingit made for hard times for these reptiles. The research suggests that, by ridingthe dry season out as an egg, the species ensures enough survive to enjoy thebetter times during the rainy season.

PNAS,2008. DOI: 10.1073/pnas.0802468105



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