Photosymbiosis in green algae: Diversity and its impacts on host and symbiont fitness

Photosymbiosis is a symbiotic relationship between microalgae and non-photosynthetic eukaryotes. Such associations have independently evolved multiple times across a wide range of eukaryotic lineages. In some photosymbiotic relationships, photosymbionts supply photosynthetic products to the host, and, on the other hand, host organisms supply some nutrients. Considering these trophic interactions, photosymbiosis appears to be mutualistic, but the balance between benefits and costs is highly dependent on environmental conditions. In this article, we focus on photosymbioses in green algae, which show particularly high diversity in both symbiont and host species, and discuss how these symbiotic relationships affect the fitness of symbionts and their hosts.