What is meant by "introgressed-types"

[Hugh Harries]

One member has written directly to me to explain the terms "introgressed-wild-type" and "introgressed-domestic-type" that I used in a recent e-mail about coconut evolution (extract shown at the end). But I am replying via the group to explain why I favour these complicated-sounding categories in the hope that someone else will provide a clearer explanation..

Introgression, or  introgressive hybridization, can happen when two forms that  look different but can cross pollinate grow in one location. The first generation progeny would be quite uniform but uncontrolled pollination at each subsequent  generation would give rise to more variable, populations. In each population  one of the original forms would predominate and individuals  showing the contrasting form  would tend to disappear unless retained by intentional selection.

So, for example, the common coconut (typica) on the Indian mainland has thick husk (but is not wild), in Thailand the preferred varieties have less husk and more water (domestic characteristics), while in Samoa individually extreme Niu kafa and Niu vai palms coexist  because the original Polynesian settlers valued both types and looked after them in every generation (palm and human),

In summary, virtually all present day coconut populations are introgressed but which characteristics predominate will depend on which ancestral parent was most numerous when they came into contact and to what extent directed selection was more important than chance,  when seednuts were selected for germination.

Finally, keep in mind that I am talking about phenotypes - what the palms look like. My guess is that genetic differences will be much less. For instance the extreme types in Samoa may have DNA fingerprints that are more similar to one another than to comparable types in either India or Thailand.
.
Hugh
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Extract from previous email:

Before domestication the wild-type coconut had a natural coastal range within the tropics  all around the Indian Ocean and halfway across the Pacific without human assistance because it evolved by floating. The domestic-type was selected for drinking and was carried by people to inland and upland sites, and to coastlines that could not be reached by floating. Wherever the wild and domestic coconuts came into contact uncontrolled cross-pollination produced introgressed-types with intermediate characteristics.

Ancestors of the Polynesians took the introgressed-domestic-type eastwards into the Pacific - and also westwards to Madagascar - but it was not until the 16th century that coconut completed its global circumnavigation when Europeans took the introgressed-domestic-type to the Pacific coast of America and  introgressed-wild-type to the Atlantic coasts of America and Africa and to the Caribbean. 

[Severino Magat]

Dr Hugh (Harries), Thanks a lot for your effort to explain the subject terms which to people who are not familiar with uncommon plant breeding and genetics terminologies could lead to ignoring the message the author wishes to convey. I like the way you explain deep technical or scientific knowledge as you usually relates to your significant experience and research work in many tropical countries. You're a blessing to this e-forum, indeed. More Power ! Good Day ! Sev Magat --- On Wed, 11/4/09, Hugh Harries <hugh.h...@gmail.com> wrote:

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