Light or Temperature? What Regulates the Emergence of Trematode Cercariae from the Molluscan Hosts and How It Is Done

• Published in: Biology bulletin reviews 2023, Vol.13 (Suppl 2), p.S172-S183
• Main Authors: Prokofiev, V. V., Galaktionov, K. V., Levakin, I. A., Nikolaev, K. E.
• Format: Article
• Language: English
• Subjects: Biochemistry; Biomedical and Life Sciences; Cell Biology; Cercaria; Ecology; Illumination; Life Sciences; Photoreceptors; Temperature; Zoology
• ISSN: 2079-0864; 2079-0872
• DOI: 10.1134/S2079086423080108

We have studied the differential influence of light and temperature on the regulation of daily cercarial emission of ten species of littoral trematodes of the White Sea ( Cryptocotyle lingua , C. concava , Himasthla elongata , H. continua , Cercaria parvicaudata , Levinseniella brachysoma , Maritrema subdolum , Microphallus claviformis , M. similis , and Paramonostomum alveatum ) and two freshwater species from Lake Chudskoe ( Diplostomum pseudospathaceum and Moliniella anceps ). The experiments tested short-term (2 h) exposure to illumination (darkness and light 800 lux) and temperature (10, 20, 25°C) on the intensity of cercariae emission from infected molluscan host. The experimental setup and experimental design made it possible to separate the effects of the studied factors of all gradations. It was found that light plays a significant role in stimulating the emission of cercariae with pigmented eyes and echinostomatoid larvae Moliniella anceps and Himasthla spp., which are expected to have nonpigmented photoreceptors. However, even in these larvae in the dark, the emission was controlled by temperature. For almost all studied species, the high significance of the interaction between temperature and light factors in the regulation of cercariae emission was revealed. With the same values illumination can act as an emission trigger, and at other temperatures it can act as an inhibitor. It has been suggested that the temperature dependence of the rhythm and intensity of daily cercarial emission is especially favorable in polar latitudes, where most of the seasonal window of trematode transmission occurs during the polar day with minor changes illumination during the day.