Effect of Light Wavelength — Rosen et al. 



99 



Table 1. Paired Student t-test comparisons of mean swimming distances and electrical burst activity of Proterometra 

 macrostoma cercariae under the four tested light conditions. 



Comparisons 



V'tTtiral swimniiiit; c 



listancvs 



Electrical 1 





t (cU) 



F 



t ((10 



p 



Red vs. Blue 



6.866 (22) 



< 0.001* 



3.289 (9) 



0.009* 



Red vs. White 



7.601 (22) 



< 0.001* 



6.232 (9) 



< 0.001* 



Red vs. Green 



6.603 (22) 



< 0.001* 



4.436 (9) 



0.002* 



Blue vs. White 



1.427 (22) 



0.168 



2.613 (9) 



0.028* 



Blue vs. Green 



0.514 (22) 



0.613 



1.456 (9) 



0.179 



White vs. Green 



1.527 (22) 



0.141 



0.140 (9) 



0.0891 



* Significantly different at F < 0.05 



(Cole 1983) and would thus be less likely to 

 reach and activate a possible cercarial light 

 receptor associated with P. macrostoma 

 swimming. Exposure of cercariae to this red 

 light produced significant increases in vertical 

 swimming distances and associated electrical 

 burst duration in the tail of P. macrostoma 

 cercariae when compared to the other tested 

 (and shorter) light wavelengths which pene- 

 trate deeper into the water column. With re- 

 gard to these shorter wavelengths, a graded 

 swimming response to this range of the visible 

 spectrum was unsupported due to the absence 

 of significant differences among the blue, 

 white, or green light regimens. This suggested 

 that any shorter light wavelengths reaching 

 the P. macrostoma cercariae will produce sim- 

 ilar decreases in swimming burst duration. In- 

 tense acetylcholinesterase activity has been lo- 

 calized in the transverse band of the tail, and 

 acetylcholine has been shown to abolish or re- 

 duce electrical burst activity in the tail of P. 

 macrostoma (Uglem and Prior 1983). It is 

 possible that the release of this neurotrans- 

 mitter was triggered by exposure of cercariae 

 to blue, white, or green light as evidenced by 

 the reduced activity of cercariae exposed to 

 these light regimens. 



The maximum swimming burst established 

 for this cercaria when exposed only to red 

 light likely simulates nocturnal conditions due 

 to the diminished penetration of this wave- 

 length in the water column and coincides with 

 the nocturnal shedding of P. macrostoma in 

 nature (Lewis 1988). This extended swim- 

 ming would assist in attracting night-feeding 

 hosts such as warmouth, Lepomis gulosus 

 (Larimore 1957). However, this cercaria can 

 continue swimming up to 14-20 hr (Braham 

 et al. 1996), well into daylight hours in the 



field during spring and summer months. In 

 this regard, it has been found that Schistosoma 

 haematobium (Haas et al. 1994) and Crypto- 

 cotyle lingua (Chapman 1974; Rea and Irwin 

 1992) exhibit an increased swimming re- 

 sponse to brief, dark stimuli known as the 

 "shadow response." Rea and Irwin (1992) 

 found that exposure to shadowed light in- 

 creased the attachment of 12-13 hr C. lingua 

 cercariae to their fish host. Fish casting a 

 shadow during daylight hours on P. macros- 

 toma would trigger greater vertical swimming. 

 Such a response would make P. macrostoma 

 cercariae more obvious for subsequent inges- 

 tion by day-feeding hosts such as longear sun- 

 fish, Lepomis megalotis (Becker 1983). 



ACKNOWLEDGEMENTS 



This study was supported by a grant to 

 Ronald Rosen from the Undergraduate Re- 

 search and Creative Projects Program 

 (URCPP) at Berea College. We acknowledge 

 the late Gary L. Uglem, who provided the first 

 author much insight and support with the P. 

 macrostoma system; Dr. Gene Chao, Depart- 

 ment of Psychology, Berea College, for as- 

 sisting us with our electrophysiology tech- 

 niques; Finally, Dr. Bernard Fried, 

 Department of Biology, Lafayette College, 

 Easton, Pennsylvania, and Dr. Allen Shostak, 

 Department of Biological Sciences, University 

 of Alberta, Edmonton, Alberta, for reviewing 

 this paper. 



LITERATURE CITED 



Becker, G. C. 1983. Fishes of Wisconsin. University of 



Wisconsin Press, Madison. 

 Braham, G. L., M. W. Riley, and G. L. Uglem. 1996. 



Infectivity of the cercarial tail chamber in Proterometra 



macrostoma. J. Helminthol. 70:169-170. 



