The expanded phenotype is explained at genetic level

The caterpillar killed by a virus nuclear polyhedrosis. Caterpillar fabrics became liquid and if the rain goes, virus particles will get on leaves and the branches located below. A photo from a site wikipedia.org

Many parasites manipulate behaviour of the owners, however genetic bases of such manipulations are studied poorly. The American biologists managed to reveal a gene with which help the virus nuclear polyhedrosis forces to climb up the infected caterpillars of an unpaired silkworm tops of trees that promotes virus distribution. As it was found out, the virus achieves it, influencing system of hormonal regulation of moults and food behaviour of a caterpillar.

Manipulations to which parasites of the owners subject, at times remind scenes from a horror film (see: Charles Tsimmer.«Parasites. The secret world»). Some parasites manage to take over the control of behaviour of the owner and actually transform it into "the zombie" which acts henceforth serve only to one purpose: to provide to a parasite the best chances of reproduction and infection of other owners. The virus nuclear polyhedrosis (nuclear polyhedrosis virus, NPV) forces to creep the infected caterpillars of an unpaired silkworm before death all above on branches. As a result the caterpillar dies somewhere highly in a tree crone, having clung to a branch or sheet. Its fabrics larded by virus particles, become liquid and spread, drip downwards together with a rain that as it is easy to guess, promotes infection of new caterpillars. Similar manipulations visually illustrate idea of "the expanded phenotype», the developed R.Dokinzom in the book with the same name. If as a phenotype to understand everything, on what genes of the given organism (and it, apparently, the most logical way of treatment of the term "phenotype") it turns out essentially influence that the changed behaviour of the owner-zombie is phenotypic a sign of a parasite. Clearly that it is adaptation of a parasite, instead of the owner, and that this behaviour has been created by the selection operating on genes of a parasite. However, genetic bases similar "expanded" phenotypic signs in most cases while are unknown. Biologists from several American centres of science have managed to decipher in general the genetic mechanism by means of which virus NPV forces to climb up dying caterpillars tops of trees. They have shown that for this manipulation the gene egt — one of 164 squirrels-coding of the genes containing in rather big ( 161 046 steams nucleotide)genome virus NPV answers. Suspicions have fallen on a gene egt not casually. Earlier it has been established that fiber EGT coded by this gene (enzyme ecdysteroid-uridine 5'-diphosphate-glycosyl), puts out of action one of the major hormones operating life of a caterpillar, — 20-gidroksiekdizon (20Е). The hormone 20Е provides timely moults. Before each moult the caterpillar for some time ceases to eat and goes down from branches where she searches for edible leaves, somewhere more low to hide in cracks of a bark or in soil at tree roots. Besides, healthy caterpillars creep upwards in search of food only at night, and with approach of day aspire downwards, in shelters, escaping from insectivorous birds. At a late stage of a virus infection fiber EGT produced by viruses, blocks hormone action 20Е. As a result the caterpillar ceases to fade and starts to eat constantly, without breaks. Probably, this changed food behaviour also leads finally to that the caterpillar appears at tree top because movement upwards is characteristic just for the caterpillars actively searching for a forage. To check up a hypothesis about a key role egt in the changed behaviour of a caterpillar, authors have designed two lines (strain) genetically modified viruses at which the gene egt has been put in two different ways out of action. As control two lines of "wild" viruses from natural populations of an unpaired silkworm were used. Caterpillars infected with one of virus strains and put in high plastic bottles where the forage was at the bottom, but there was a possibility to climb up on walls. At early stages of development of an infection all caterpillars behaved approximately equally: crept upwards-downwards and kept mainly in the bottom part of a bottle. At late stages, shortly before  destruction, the caterpillars infected with wild viruses, started to clamber purposefully upwards and died, having clung to a bottle wall highly it is necessary a bottom. The caterpillars infected with genno-modified viruses without a gene egt, too died, but is not high on a wall, and nearby to a bottle bottom ( drawing see).

A - gypsy moth caterpillar killed by the virus NPV; B - height, which killed the caterpillars infected with different strains of the virus. Two left column - the wild virus taken from wild populations and two secondary - with the virus genome incapacitated egt; two right - the virus that instead of a spoiled egt gene inserted another acting. The image of the article under discussion in the journal Science

Definitively to be convinced that has put in a gene egt, instead of in any casual damages which could receive viruses as a result of genno-engineering procedures, authors have inserted to the modified viruses new, working, a gene egt instead of the spoilt. The caterpillars infected with these repeatedly modified viruses, before death climbed up walls in the same way, as well as in case of infection with wild viruses. Hence, the agonal behaviour of the infected caterpillars is really defined by a virus gene egt.

Thus, a virus, blocking by means of fiber EGT hormonal regulation of life cycle of the owner, reaches simultaneously two purposes. First, it forces a caterpillar to eat and not to waste time more actively both energy on moults and other actions useful to a caterpillar, but not to a virus. So very many parasites arrive with the owners. Secondly, constantly included instinctive program of search of tasty leaves exhausts a dying caterpillar on tree top, whence it is more convenient to virus to infect other caterpillars.

Source: Kelli Hoover, Michael Grove, Matthew Gardner, David P. Hughes, James McNeil, James Slavicek. A Gene for an Extended Phenotype//Science. 2011 V. 333. P. 1401.

See also:
1) Richard Dokinz. The expanded phenotype: a long hand of a gene. М: CORPUS, 2010.
2) Charles Tsimmer. Parasites. The secret world. М: Alpina non-fikshn, 2011.
3) Toksoplazma — a parasite manipulating human culture, "Elements", 9/5/2006.
4) Young parasites protect the owner, mature exhaust to its predator in a mouth, "Elements", 6/6/2011.
5) Strategy of parasites: to kill it is impossible to pardon (under article: V.N.Mikheyev. Monoksennye and geteroksennye parasites of fishes differently manipulate behaviour of owners//Magazine of the general biology. 2011. Т. 72. №3. With. 183–197).