Prey targeting by the infrared-imaging snake Python: effects of experimental and congenital visual deprivation

Bold and crotaline snakes possess two distinct types of organ evolved to im age radiant electromagnetic energy: the lateral eye, which responds to visi ble light, and the pit organ, which responds to infrared radiation. While i nfrared imaging may allow accurate predatory targeting in complete absence of visual information, both infrared and visual information are probably no rmally involved in prey targeting. We examined the roles of vision and infr ared imaging in Python molurus predatory performance under conditions of (1 ) high visual contrast; (2) very low visual contrast; (3) complete blinding ; (4) experimental monocular occlusion; and (5) congenital monocularity. No rmally sighted pythons were equally successful at targeting white (BALB/c) and black (C57BL6/J) mice (Mus domesticus) against a black background. Bino cularly occluded snakes exhibited strike angles and distances similar to no n-occluded snakes, but exhibited lower strike success, suggesting that high visible contrast is not required for accurate targeting, but that precise targeting depends to some degree upon visual information. Strike angles, di stances and latencies were indistinguishable between snakes subjected to ex perimental monocular occlusion and normally sighted snakes. However, snakes congenitally lacking one eye preferentially targeted on the sighted side. Thus, accurate targeting of highly mobile homeothermic prey by Python can b e accomplished with little or no visual information, but performance can be affected by complete visual deprivation or by alteration of visual input d uring development. The developmental effects of early visual deprivation in this system provide a novel opportunity to investigate the neural integrat ion of two electromagnetic radiation-imaging systems in a single animal. (C ) 2001 Elsevier Science B.V. All rights reserved.