Due to the very emergent properties involved in the evolution of these life styles; these cases are interesting models for thinking about the value of Developmental System Theory or Evolution by Means of Natural Drift as explanatory backgrounds.
Previously in this blog, we have seen comments about the relevance of the “incomplete isolation” of the multicellulars systems processes as a way to understand certain kinds of dynamic changes in the ontogenetic niche. This “epigenetic permeability”, could be suggested as a property that may help to understand why it is not always necessarily an “Internalization” (i.e incorporation of adaptative traits in the genome of the evolving species) for the development of new life styles or lineage changes in order to get an idea of the points when this “epigenetic permeability” may help to explain the establishment and conservation of these life styles, lets compare the steps of the parasite-host interactions.
In avian brood parasites, the female lays the egg in the host nest, which has been recognized by some authors as the only interaction between the parasite and host species. I would suggest to add a second step that is performed by the parasite chick: the expulsion from the nest of the host offspring (this does not always happen though). For the realization of step one of the interaction, the parasite mother had to find the appropriate host nest and the host parents have to be fooled to keep believing that the extra egg belongs to them. Some parasites species present similar egg pigmentation with their main host, but it is not clear, as far as I´ve read, that this is genetically determined and that this trait can vary inter and intraspecies. The second step is very similar to other kind of parasitic interaction where the allocation of resources is diverted to feed the growing parasite (See Sacculina barnacles post in this blog as an example).
In ant nest usurpation species, the first step involves the usurpation of the queen host throne by the parasite ant. The female searching for nest, sneaking in the nest without being detected as alien by the colony, and (as similar as the avian parasite chick) the diversion towards the reproducing parasite.
In the second step, the parasite queen offspring will search for new host colonies, raid them and kidnap host worker’s larvae. Experiments have demonstrated that when two alternative host are available for the queen and she picks one of them in the first step, the parasite sons will also choose that one for collecting more workers.
This two examples suggest to me that the Developmental System is more than the niche variables and the inheritable organism material, and cannot be reduced to the somatic and germinal part as a satisfactory explanatory background but also the construction of these parasitic life styles due to epigenetic permeability are possible thanks to crucial behavioral operations (“conducta” in Maturana’s approach) that allow the emergence of these very externalized and dependent systems.