QUESTION-353: Across real symbioses, does the partner with the larger and faster-growing population become obligate first more often than chance, and does the other partner's dependence follow the balance of births and deaths inside the collective, as Athreya, Czuppon and Gokhale's model predicts?

Why it is a question

THEORY-1051 holds what Athreya, Czuppon and Gokhale’s model shows. No growth parameters, carrying capacities or within-collective rates are measured in any real symbiosis, and the authors call measuring births and deaths inside the collective “imperative”. CASE-173 and NOTE-1236 report none for Buchnera.

What would answer it

Comparative or experimental evidence relating the partners’ population growth parameters to which becomes obligate first, across independent symbioses, with the faster-evolving partner (larger population, faster growth) found obligate first more often than chance; and, for at least one symbiosis, measured rates of partner birth and death inside the collective, with the host’s dependence matching the model’s prediction from their balance (deaths dominating: host fully dependent; births dominating: host independent). The model’s own simulations, or the observation that symbionts are often more obligate than hosts, cannot settle it, since symbionts live inside hosts for other reasons. It is refuted if slower-evolving partners are as often obligate first, or if host dependence is unrelated to within-collective demography.