Data Sheet 1_Optimizing egg production by trait selection and starvation in Hydra vulgaris.pdf

Hydra vulgaris is considered an effectively immortal freshwater cnidarian. As a sister group to all Bilateria, studies of cnidarian genomes offer valuable evolutionary insight into a range of genetic mechanisms. Over 280 years of interdisciplinary study have paved the way for the use of Hydra as a model organism; however, the development of transgenic methods has been inhibited by their facultative reproduction. Hydra default to asexual reproduction in a lab setting, and despite being understood as hermaphroditic, the conditions to induce egg production were famously cryptic. We overcame this limitation by selecting for and isolating polyps capable of producing eggs and fostering those individuals into a large “KSO” colony, and designing a starvation care protocol to rapidly induce gametogenesis. To validate that this approach led to increased egg production, we set up five replicate populations (100 polyps each) of KSO and a control AEP group and then conducted a 4-week-long starvation trial. We found overwhelming evidence (−1.023 median difference, 95% credible interval: −1.580 to −0.466) that selection for “egg-bearing” as a trait resulted in significant sexual bias toward egg production in a population, supporting previous claims of distinct stable sexes. Overall, the combined effect of starvation and selection resulted in a 5-fold increase in egg production over the control AEP. Our study not only strengthens our understanding of H. vulgaris sexual reproduction but also provides a repeatable, effective approach for establishing stable egg-producing populations for the advancement of transgenic methodology.