Figure 12.9 A telesymbiosis between a photoautotroph and a heterotroph separated from one another by an environment through which matter and energy flow.

times before being lost to the sink. Fortunately, the carbon can be re-mobilized fairly easily. Other atoms, like nitrogen, seem to be even more avidly kept in play: the global cycling ratio for nitrogen is estimated to be between 500 and 1,200 to 1. These ratios are maintained by guilds of organisms each with complementary metabolisms: nitrogen, for example, must be cycled through complicated communities of bacteria before it can be used by plants or animals for proteins, and the nitrogen in proteins must in turn be converted by other bacteria back into nitrogen gas. The high fidelity with which nitrogen is passed from one "metabolic guild" to another speaks strongly for a highly coordinated superorganismal physiology.

"Tuning" a symbiosis presumably is easier if matter and energy can be transferred directly between the symbionts. This may be one reason why conventional symbioses are so intimate. The problem with a telesymbiosis is that matter and energy must pass through the environment that separates the putative telesymbionts. If this environment is fickle or unstable, tuning the telesymbiosis might be difficult. We can express this in a systems diagram (Fig. 12.9) representing the flows between organisms by environmental trans fer functions. For example, a transfer function governs flow from the photoautotroph to the environment, and another, governs it from the environment to the heterotroph. The transfers obviously are more complicated, but the requirement for matching them does not change. A successful telesymbiosis, like a conventional symbiosis, still must keep matter "in play." Again, this can be done only if all the transfer functions of the loop are matched. Telesymbioses in which the matching is better will work at greater power and will have greater fitness than those whose loops are less well tuned.

In telesymbiosis, adaptation is not simply the response of organisms to the environment: it also involves the environment adapting to organism. Let us illustrate this concept with another model world, one that includes two heterotrophs, HA and HB, and one photoautotroph, P (Fig. 12.10). Assume that HA and P have adapted well to the environmental transfers that separate them and that they form a well-tuned telesymbiosis;HB and P do not. Carbon should cycle preferentially between HA and P and do more work for them than it will between HB and P.How can HB successfully compete? One option would be for HB to modify its internal transfer functions, probably through conventional genetic selection of its internal physiology. The other option, though, and one per-

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