Optimizing egg production by trait selection and starvation in Hydra vulgaris

This paper presents a method for reliably inducing egg production in Hydra vulgaris, an effectively immortal freshwater cnidarian widely used as a model organism due to its position as a sister group to Bilateria. Despite over 280 years of research using Hydra, transgenic method development has been limited by its facultative reproduction, since laboratory populations typically default to asexual budding and the conditions that trigger egg development in these hermaphroditic animals were historically unclear.

The researchers addressed this by selecting egg-producing polyps to establish a dedicated “KSO” colony and pairing this selection with a customized starvation protocol designed to rapidly stimulate gametogenesis. Five replicate populations of 100 polyps each, from both the KSO line and a control AEP line, underwent a four-week starvation trial to compare egg production.

Results showed strong evidence that trait selection for egg-producing capability created a significant sexual bias toward egg generation (median difference of -1.023, 95% credible interval: -1.580 to -0.466), supporting earlier theories of distinct stable sexes within Hydra populations. Combining starvation with trait selection produced a fivefold increase in egg generation relative to controls.

This work advances the understanding of sexual reproduction in H. vulgaris and establishes a repeatable, scalable protocol for generating eggs on demand, an important step toward expanding transgenic methodologies in this key model organism.

Recommended citation: Cochran, K. N., DeMartino, J., Alfaro-Córdoba, M., & Macias-Muñoz, A. (2026). "Optimizing egg production by trait selection and starvation in Hydra vulgaris." Frontiers in Ecology and Evolution, 14, 1761812. DOI: 10.3389/fevo.2026.1761812
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