Monday, August 19, 2013

Colour variation in captive Onchestus rentzi

For a while now we have been captive breeding a genetic population of 'lichen-form' Crowned Stick Insects (Onchestus rentzi). Although these insects are somewhat variable in colour, the most common colour form is brown. Over recent years we have noticed some individuals within our main breeding colony exhibiting a lichen-like trait. Last year we decided to experiment with a few of those to see if the trait was genetic or the result of environmental influences including lighting and food plant.

We separated three young lichen-form females and let them mature in isolation, but kept them under the same conditions as our main group. The three females matured and began to lay eggs without being mated. The species is believed to be parthenogenetic but we had never tested it, so we were quite interested to see if the eggs they laid were even fertile. Those eggs are now hatching and the resultant offspring are indeed the same colouration as the females that produced them.

Two or the original three females are still alive and laying eggs on a daily basis. Recently though, the eggs that they are producing are different in appearance than previously. Normally the eggs are uniform brown, ranging from tan through to a chocolate colour - exactly what these individuals have been producing until now. These recent eggs are two-tone like the insects themselves, with a splash of white across the posterior end. We are not sure why this is occurring but will continue to observe and document these insects with interest.

One of the original 'lichen-form' females.

The eggs laid recently exhibiting an unusual colour trait.

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