When the breeding season comes around, American green tree frogs get calling, boasting to the ladies and letting other males know not to mess with them. But what effect does this racket have on their sensitivity to signals from other green tree frogs? ‘Much of the previous work on the significance of repeated exposure to social signals has focused on neural habituation and diminished behavioural responses to individual signals’, explain Megan Gall and Walter Wilczynski from Georgia State University, USA, adding that short-term exposure to calls clearly diminishes the responses of some species to subsequent communication signals. However, they explain that it is less clear how an animal's ability to respond to communication signals is affected by long-term exposure to social signals. Gall and Wilczynski decided to focus on a region of the brain – the midbrain – in American green tree frogs that is known to process social signals in order to find out how it responds to communication signals after lengthy exposures to either a chorus of tree frogs or random sounds (p. ).
Monitoring expression of a gene, the immediate early gene egr-1 – which indicates cellular activity and is used as a proxy for neural excitation in brain tissue – the duo found that listening to sounds for 10 days increased the sensitivity of the amphibian's midbrain to calls from their own species. And when they compared the effects of the random sounds with those of the frog chorus, the tree frogs that had been listening to calls from their own species were more sensitive to the calls of other tree frogs than animals that had been listening to random sounds.
Gall and Wilczynski say, ‘We believe that this is the first report of stimulation with an assemblage of mate attraction signals enhancing future sensory processing in anurans.’ They also point out that the study raises various questions, including how the frogs alter their acoustic responses and the significance of this modification, which we hope to find out soon.
