Impacts of artificial light at night on interactions between four trematode parasites and their marine invertebrate hosts: species-specific effects?

Parasitism is influenced by anthropogenic stressors, among which artificial light at night (ALAN) remains understudied. With the expansion of urban areas and the development of lighting technology, the range and intensity of ALAN's effects on host-parasite interactions are increasing. Trematodes, with their complex life cycles, are particularly sensitive to anthropogenic stressors, especially during the transmission of motile cercariae (infective stages) from the first to the second intermediate host while exposed to external conditions. We examined how three types of ALAN (warm white LED, cold white LED, ultraviolet fluorescent light) affect: (1) the cercarial output of four trematode species (Acanthoparyphium sp., Galactosomum otepotiense, Maritrema novaezealandense, and Philophthalmus attenuatus) from snail hosts; (2) the light attraction of snails infected by different trematode species; (3) the light attraction of cercariae of the four trematodes; and (4) the transmission of M. novaezealandense cercariae from snails to amphipod second intermediate hosts. We observed strong species-specific differences in cercarial output among ALAN treatments. Snails consistently avoided light containing UV radiation, while their responses to other light types varied depending on the trematode species infecting them. Cercariae of different species differed in their attraction to light. Transmission success of M. novaezealandense to amphipods was highest under UV light and lowest under cold white light. The interspecific differences observed can be explained by divergence among the phylogenetically-unrelated trematodes, whereas impacts on M. novaezealandense transmission success may reflect the amphipods' susceptibility under different ALAN conditions. Light pollution represents an underestimated anthropogenic stressor whose effects on host-parasite interactions demand greater recognition.