Paper alert! New preprint out by Jordan A. Gault, Nils Rädecker, Iliana B. Baums, and Thilo Gross that offers mechanistic insights into photosymbiotic stability by analyzing the role of nitrogen competition in corals.
https://arxiv.org/abs/2609.37826
How do cnidarian-algal symbioses maintain ecological stability without relying on host sanctions? Using a generalized modeling framework we show that host-symbiont competition for inorganic nitrogen (ammonium) is sufficient on its own to dynamically stabilize symbiont population.
Nitrogen competition acts as an autonomous negative feedback loop, regulating symbiont density without requiring external density-dependent mechanisms.
At low host nitrogen assimilation rates, stability is driven primarily by intraspecific symbiont competition for ammonium. As host assimilation increases, the system transitions toward interspecific host-symbiont competition.
To maintain dynamic stability under strong interspecific competition, symbiont density must positively couple to host ammonium assimilation via photosynthate translocation.
Bifurcation analyses show that an unregulated influx of external nitrogen can destabilize the interaction, leading to population oscillations or system collapse.
This metabolic feedback loop offers a general ecological mechanism explaining both the maintenance of partner abundance and the repeated evolutionary origin of photosymbiosis across diverse taxa.
