Biomedical subjects
Publications and source records attributed to R Happel.
The dynamics of a network of autocatalytically replicating species in a continuously stirred tank reactor can be described by a replicator equation in the limit of small flux rates.
Novel species are introduced into a network of interacting replicators either (i) as mutants of members of the network (ii) as unrelated immigrants. We consider the meta-population dynamics of such a system. In the first case the appearance of mutants leads to a slow growth of the replicator network, proportional to the logarithm of the number of mutation events. Surprisingly, replicators evolved by mutant incorporation are always permanent, despite the fact that permanence is in general a very rare phenomenon. In the second case, on the other hand, immigrants lead to frequent break-downs on the entire network and hence to complete extinction. In both cases individual species are short-lived and the distribution of survival times is exponential.
A class of autocatalytic reaction networks based on template-dependent replication and specific catalysis is considered. Trimolecular "elementary steps" of simple replicator dynamics are resolved into two consecutive irreversible reactions. The extreme cases, competition for common resources and hypercycle-like cooperative feedback, were analyzed in some detail. Although the dynamics of the extended networks resembles corresponding replicator dynamics in general, there are significant differences. Most notably, the interior fixed points in the cooperative model turned out to be asymptotically stable for an arbitrary number of species, whereas simple replicator dynamic predicts an asymptotically stable periodic orbit fixed for four species and fewer and a stable periodic orbit for all other cases.
Numerical experiments suggest that cooperation is a very rare phenomenon in autocatalytic networks with more than about five interacting species. There is strong evidence that the probability for cooperative behavior in random networks decreases at least exponentially and at most as an2 with the number n of interacting species. The evolution of larger persistent networks by subsequent incorporation of additional species into a cooperative network is shown to be even less probable. This leads to the conclusion that hypercycle-type interactions alone are not sufficient to maintain the genetic information of more than a few interacting species in a pure RNA world.
Data on tooth use in eating fruits and seeds were collected on 12 West African monkeys representing five species of cercopithecines, Cercopithecus aethiops, Cercopithecus campbelli, Cercocebus atys, Erythrocebus patas, and Papio papio. Field observations and information in the published literature were used to select fruits for captive feeding trials. A total of over 27,000 tests were conducted to determine the preferences of the monkeys for 78 fruits. Data were collected on the selection of fruit parts, as well as tooth use, in eating 88 fruit species. All five monkey species had remarkably similar fruit part preferences. Seeds were eaten in 86% of the tested fruits and represent the fruit part most frequently eaten by all the tested monkeys. With few exceptions, molars were used to puncture and crush the seeds. It is suggested that the development of bilophodont molars might be an adaptation by Old World monkeys to seed predation. Given their large size relative to other arboreal frugivores, seed predation could provide a dietary niche for Old World monkeys.