Behavioural evidence for polarisation vision in stomatopods reveals a potential channel for communication

Polarisation sensitivity (PS) - the ability to detect the orientation of po larised light - occurs in a wide variety of invertebrates [1,2] and vertebr ates [3-5], many of which are marine species Mi. Of these, the crustacea ar e particularly well documented in terms of their structural [6] and neural [7,8] adaptations for PS. The few behavioural studies conducted on crustace ans demonstrate orientation to, or local navigation with, polarised sky pat terns [9]. Aside from this, the function of PS in crustaceans, and indeed i n most animals, remains obscure. Where PS can be shown to allow perception of polarised light as a 'special sensory quality' [1], separate from intens ity or colour, it has been termed polarisation vision (PV). Here, within th e remarkable Visual system of the stomatopod crustaceans (mantis shrimps) [ 10], we provide the first demonstration of PV in the crustacea and the firs t convincing evidence for learning the orientation of polarised light in an y animal. Using new polarimetric [11] and photographic methods to examine s tomatopods, we found striking patterns of polarisation on their antennae an d telson, suggesting that one function of PV in stomatopods may be communic ation [12]. PV may also be used for tasks such as navigation [5,9,13], loca tion of reflective water surfaces [14] and contrast enhancement [1,15-18]. It is possible that the stomatopod PV system also contributes to some of th ese functions.