While leucophores are widespread in cephalopods, this is the first time switchable leucophores have been identified in D. opalescens squid. What's more, these leucophores are predominantly made up of reflectin subtypes that have only ever been found in adaptive iridocytes before. In iridocytes, these adaptive reflectins contract and change their refractive properties in response to the neurotransmitter acetylcholine, allowing them to fine-tune colour of the reflected light. But are they also adaptive in a leucophores? Sure enough, when DeMartini treated the female squid with acetylcholine the white region became brighter. 'This discovery reveals a fundamental relationship between the switchable leucophores and the tunable colour-producing iridocytes, suggesting they share a mechanism at the molecular level', says DeMartini.
So what is the purpose of these markings in females? In short, DeMartini doesn't know, but he points out that the white stripe looks remarkably similar to the white testes seen in male squid. He speculates that the iridescent stripes might give a 3D perspective to the white strip: 'You could orient the iridocyte's reflection at some specific angle so it'll look brighter from certain positions, instead of white scattering which is always going to be uniformly bright in all directions.' As male squid are notoriously aggressive towards females, DeMartini suspects that these adaptable iridocytes and leucophores could help females mimic males to escape unwanted attention.
|Contact: Nicola Stead|
The Company of Biologists