J. Ky. Acad. Sci. 66(2):94-100. 2005. 



Effect of Light Wavelength and Osmolahty on the Swimming of 

 Cercariae of Proterometra macrostoma (Digenea: Azygiidae) 



Ronald Rosen, Andy Ammons, Ayisa Boswell, Amanda Roberts, Amanda Schell, Marcia 

 Watkins, Jonathan Fleming, Bojana Jovanovic, Aishe Sarshad, Emilie Throop, 



and Fady Zaki 

 Department of Biology, Berea College, Berea, Kentucky 40404 



ABSTRACT 



The objectives of this study were to describe the effect of light wavelength and osmolality on the vertical 

 swimming distance of the cercaria of Proterometra macrostoma. Significant differences were found in the 

 average swimming distances and electrical burst activity in the tail of cercariae exposed to red vs. blue, 

 green or white light, but no difference was observed when the last three colors were compared to one another 

 with one exception. Cercarial swimming decreased slightly after 12 hr PE (post-exposure) in artificial pond 

 water (15 mOsm) and artificial snail water (102 mOsm). By contrast, a significant reduction in swimming 

 distance was observed in distilled water (0 mOsm) and artificial snail water with two different concentrations 

 of mannitol (180 and 267 mOsm). 



INTRODUCTION 



Production of the furcocystocercous cercar- 

 ia of Proterometra macrostoma is 100-1000 

 fold less than most other digeneans (Lewis et 

 al. 1989). However, this cercaria possesses 

 several adaptations that increase the probabil- 

 ity that it will remain infective and be ingested 

 by centrarchid fish definitive hosts. The re- 

 traction of the cercarial body into its tail prior 

 to emergence from the snail host serves to 

 protect the body from osmotic stress subse- 

 quently encountered in a freshwater environ- 

 ment (Braham et al. 1996). In addition, the 

 conspicuous swimming behavior and size (4- 

 5 mm) of this cercaria serve to attract appro- 

 priate fish definitive hosts. 



Infectivity of P. macrostoma cercariae is re- 

 tained over 14 hr in hypotonic artificial pond 

 water as long as the cercarial body remains in 

 the tail chamber (Braham et al. 1996). The 

 primary source of this protection has been 

 linked to a continuous barrier provided by the 

 basal membrane associated with the tegument 

 of the cercarial tail (Braham and Uglem 

 2000). Such protection is likely essential for 

 the perpetuation of P. macrostoma, as snails 

 infected with this species release only one or 

 two cercariae at a time often separated by sev- 

 eral days without releasing cercariae. The bas- 

 al membrane may be able to withstand even 

 more extreme hypotonic and hypertonic os- 

 molalities than naturally encountered, given 

 the limited reproductive capacity of this spe- 



cies. Such protection may be evaluated indi- 

 rectly within the initial 12 hr PEm (post-emer- 

 gence) of the cercaria from its snail 

 intermediate host by placing cercariae in a 

 broad range of osmolalities and observing 

 temporal changes in cercarial swimming burst 

 length and infectivity. The latter may be as- 

 sessed by the activation and emergence of the 

 cercarial body from its tail when exposed to 

 low pH, which simulates conditions found in 

 the stomach of the fish definitive host (Hors- 

 fall 1934; Rosen et al. 2000). 



According to Prior and Uglem (1979), the 

 tail of this cercaria is an autonomous loco- 

 motor organ, and the vertical swimming phase 

 is initiated through tactile stimulation of the 

 tail. Following such stimulation, the regular, 

 alternating pattern of the swim-sink cycle in 

 P. macrostoma cercariae has been linked to a 

 possible endogenous oscillator system located 

 in the transverse band of the tail. Electrical 

 potentials are generated from this region and 

 spread to the anterior end of the tail. This elec- 

 trical activity can be modulated by light in- 

 tensity. Lewis (1988) found an inverse rela- 

 tionship between light intensity and electrical 

 burst activity in the tail of P. macrostoma. In- 

 creases in light intensity resulted in shortened 

 electrical burst durations (BD) and longer in- 

 terburst intervals (IBI), while the opposite was 

 true for sudden decreases in intensity. How- 

 ever, no effort was made to evaluate individ- 

 ual components of the visible spectrum (con- 



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