Examining the influence of temperature on the sex ratio of Nereocystis luetkeana gametophytes

The canopy-forming kelp, Nereocystis luetkeana, provides important biogenic habitat and numerous ecosystem services. There has been a documented decline of this foundation species in the Salish Sea due to increasing temperatures and nutrient limitation, among other stressors. The early, microscopic life stages of the species are particularly vulnerable to environmental stressors such as temperature. Past work has demonstrated that temperature significantly affects gametophyte growth, density, and survivorship in Nereocystis luetkeana, and sex-expressed genes in Saccharina latissima. However, the impact of temperature on the sex ratio of Nereocystis luetkeana gametophytes is unknown. This study explored how temperature affects the gametophyte sex ratio, the relative proportion of female to male gametophytes, of Nereocystis luetkeana through a temperature-controlled experiment. Zoospores were grown in treatments across their thermal tolerance (10-18℃) for 12 days, then cultures were imaged and categorically scored by their sex. We observed no difference in the mean ratio of female to male gametophytes between temperature treatments (p=0.13). However, we found that the observed gametophyte sex ratio was not the expected proportion of 0.5 to 0.5 and male gametophytes were consistently more abundant in the samples. These results suggest that warming water temperatures anticipated in response to climate change will not significantly bias the development of male and female Nereocystis gametophytes within their thermal tolerance. Furthermore, this study highlights the need for further research on the effects of environmental stressors on the microscopic, haploid phases of kelp to better understand population dynamics under future conditions