Experimental breeding reveals mating patterns and F1 phenotypic diversification in the cosmopolitan diatom Cylindrotheca

Diatom mating activity contributes to their enormous phenotypic and genetic diversity, yet little is known about patterns in diatom reproductive compatibility across genetically diverse strains, nor the effects on offspring phenotypes that may confer adaptive evolution, niche partitioning, or trait improvement. Here a panel of 38 Arctic Cylindrotheca sp. isolates were crossed pairwise to detect mating compatibility. Positive mating patterns were identified in multiple clades, including amongst crosses of different parental rbcL genotypes. F1 isolated from three different crosses presented phenotypic variation in growth rate, plastid traits, and associated photo-physiological responses to blue and green actinic light. Offspring gliding speed and behaviour also varied, providing insights into complex motility traits that link cell morphology, bioenergetics and sensory adaptation with emergent movement patterns. Exploratory analysis of the F1 trait landscape identified a varaible mixture of individual-level and cross-dependent effects, including substantial variation in growth rate between individuals and strong effects of different crosses on morphology and motility. Experimental diatom breeding may offer a unique strategy to study ocean protist evolution and phenotypic diversification and could complement other biotechnological innovations to enhance cultivation yields and crop resilience in mass cultivation.