IISc: How seasons drive a lizard's life

The current year’s juveniles were the breeding males the next year

December 23, 2017 06:19 pm | Updated 06:21 pm IST

A fast breed:  The backs of male agamas turn yellow-orange during the breeding season.

A fast breed: The backs of male agamas turn yellow-orange during the breeding season.

Winter blues and summer lows may be the only ways the weather affects human behaviour, but scientists have found that seasonal climatic changes govern the life cycle of a species of tropical lizard. The breeding of the rock agama shows a distinct annual cycle, tracking periods of hot weather and rain in its habitat. Changes in global climate, which can affect regional temperature and rainfall, could affect the biology of such cold-blooded reptiles, write the scientists.

While temperate systems show distinct seasons with climatic conditions varying drastically, the tropics are usually less variable. However, in some parts of the tropics, such as the Rishi Valley in southern Andhra Pradesh, the extremes are apparent. Here, summer temperatures peak between March and May ranging between 8-41 degree C, and rainfall is highly seasonal.

Scientists at the Indian Institute of Science (IISc), Bengaluru, studied how this seasonality affects the breeding of Peninsular rock agama (a tropical lizard found across rocky habitats in peninsular India) at Rishi Valley. The backs of male agamas turn a bright yellow–orange during the breeding season, while the bulging bellies of females are a sign that they are carrying eggs. Identifying these breeding characteristics of 205 tagged lizards across three years, the team also took physical measurements by recapturing some of these individuals and collated daily temperature and rainfall data from a local weather station.

Most males began displaying breeding colouration in May, when temperatures peaked, and lasted till September. The breeding season ended around September.

Meanwhile, the females began laying the first eggs in June–July, only after the first rains of the year. This could be possibly because the rains loosen the soil, helping them dig holes to lay their eggs. Juvenile lizards began emerging from September to December, mid-way into the monsoon when food resources are abundant. Censuses conducted by the team to arrive at lizard numbers in the area show the highest number of juveniles during November.

“The current year’s juveniles were the breeding males the next year, hinting at a rapid growth to attain reproductive maturity,” says Shreekant Deodhar, the lead author of the study published in Current Science . “But after that, they just disappeared. This annual pattern was unexpected because you would expect these large lizards to live longer than a year.”

Though the team sampled all males of the population they studied, only very few were re-sighted and re-captured across breeding seasons; the species do not hibernate or migrate to other sites.

“Climatic changes could affect these cold-blooded reptiles faster, giving us an inkling of what could be happening with changes in global weather patterns,” he adds.

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