Seasonal temperature extremes drive shifts in reproductive strategy in Cassiopea xamachana

Abstract

Large observable densities of jellyfish (Scyphozoa) can seemingly appear out of nowhere but can often be explained by life-history transitions triggered by temperature and host associations with microorganisms. Using a globally distributed scyphozoan, we demonstrate that seasonal temperature extremes trigger polyps to differentially allocate effort in growth and reproductive output and strategy mostly independent of their microbiomes. Cassiopea xamachana polyps were reared under winter (20{degrees}C), ambient (28{degrees}C), and summer (33{degrees}C) temperatures with either antibiotic-treated (ABS) or microbe-exposed (MES) communities. At 20{degrees}C, polyps grew and reproduced through budding but did not strobilate. At 28{degrees}C, polyps sustained the greatest ephyra production, whereas 33{degrees}C accelerated first ephyra release but subsequently truncated strobilation and yielded smaller ephyrae with poorer condition and survival. These patterns indicate that plasticity induced by seasonal temperature extremes may optimize differential allocation towards asexual and sexual propagation. Microbial depletion restructured polyp-associated communities, yet only minimally altered growth and reproduction. Taken together, C. xamachana polyps are likely to overwinter, where they maximize growth and asexual reproduction. As temperatures warm, it triggers a shift in resource allocation towards strobilation. However, the warmest summer temperatures reduced polyp and ephyra fitness, with the magnitude of effect modified by their microbiome.