A green gecko in the Auckland area has the unusual habit of throwing off yellow progeny. Herpetologists describe the yellow offspring as a colour morph—a genetic variant which lacks the ability to produce blue pigment.
There are seven varieties of green tree gecko in New Zealand. Opinions vary as to whether they are seven separate species or all members of the same species, but only the Auckland geckos are known to have had yellow offspring.
New Zealand Herpetological Society president Brian Humberstone says the Auckland variety Naultinus elegans is found south to Taupo and north to Hokianga and the Bay of Islands. The geckos can grow up to 20 cm long, and vary from dark to light green. Some have distinctive white markings in stripes or patterns, others have none at all.
Humberstone says it is thought the yellow offspring occur at a rate of between one in 500 births to one in 2000. The “yellows” as they are known to lizard lovers, vary in colour from pale to dark yellow, with or without markings, with some a bright sulphur.
The yellows have a low survival rate in the wild because their bright colouring makes them easier targets than their naturally camouflaged green parents. Their prime habitat is manuka scrubland, a habitat which is a permanent state in some areas of New Zealand and a transitional nursery stage for native forest regeneration in others. The geckos are most often found on manuka trees between 1.8 and 3m high.
Diurnal creatures, they eat flying insects like flies, beetles and moths, but will not touch ants, Humberstone says. They rely on a claw and use a prehensile tail as a fifth leg to climb, sometimes to the top of manuka 8m high.
There are five major sites for the green tree gecko around Auckland and three rescue areas where society members are pulling out the creatures to save them from subdivision-prompted land clearances. The main area known for the yellow forms has been Manuka Rd in Glenfield, where about 30 yellows have been found in the last 15 years. That area has been completely destroyed with the last of the scrub cleared about two years ago.
Former Heritage Park natureworld assistant supervisor and former herpetological society secretary Bob Porter, who has just left New Zealand for the larger reptiles of Australia, says colour morphs are not unusual in the animal kingdom, but are more often found in birds rather than reptiles. Budgerigars are naturally green, their other colours having been bred in captivity, while goldfish are brown in the wild and are selectively bred through to their bright aquarium gold.
Porter says he has only ever heard reports of the yellow geckos occurring in Auckland and says the phenomenon could be the result of a restricted breeding pool after large numbers of geckos were wiped out by development.