Red eyed tree frog

The red eyed tree frog, Agalychnis callidryas, is one of the most famous denizens of the Central American forests, recorded by photographers and eco-warriors almost as an advert for conservation; Credit: © Earth Times

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When a dead frog’s egg is used as food by fly larvae, that is an important part of the decomposition of living material. The flies tend to choose dead eggs but can lay on others that are healthy nearby. Spatial contagion is a term reserved for this kind of colonisation where good areas may be ignored while unsuitable ones are actually colonised.

Myra C. Hughey of Boston University and her three colleagues publish today in the journal Biology Letters, describing how they found specialist flies colonising all damaged egg clutches and some intact eggs. They were 3.3x more likely to colonise the intact clutch if they were next to a damaged one. Strangely there was no impact from overcrowding, as intact eggs were often ignored even when they were not very far from damaged clutches.

The key points of this project are to discover how accurately the flies evaluate the quality of their potential food (for the larvae.) Risk avoidance behaviour could contribute to the flies’ decision making processes (risk contagion.) Reward contagion involves the colonisation of non-preferred patches close to the preferred ones. Together they make up the study’s “spatial contagion.”

Frogflies are Phorid flies that lay eggs on the Agalychnis callidryas (red-eyed tree frog frogspawn). These clutches of spawn may be several metres apart, and affected by predation (by wasps).

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