If a tight host association exists, closely related species tend to attack closely related hosts; host associations are less stable if associations are determined by more plastic traits like parasitoid searching and oviposition behaviour.
Helminth parasites are generally well-adapted to their definitive hosts, yet closely related host species, and certain genotypes of their normal host organism, can be resistant to infection.
In nearly any local assemblage of potential plant hosts, there will be few pairs of closely related host genera, and many more combinations of genera that are more distantly related.
Generally, host-plant switches can occur between distantly [ 41- 45] or more closely related host lineages [ 20, 46, 47].
This finding suggests that myzostomids (which have a free-living planktonic stage) are limited to one or a few closely related hosts, despite most hosts co-occurring on the same reefs, many within physical contact of each other.
A spokesman for the American Embassy, Tim Moore, said the United States had sought on security issues to "work very closely with host country authorities".
The rabies virus, the researchers said, needed a "closely related host" to be able to jump species.
It was a common observation in molecular phylogenetic studies on DM that near-terminal clades (subtrees) within the trees were comprised of collections from identical or closely related host plants [40] [44], [67], [68], [70], [72].
This substantial proportion of shared genes indicates that the independent processes of reduction that occurred in these closely related host species led to similar gene contents, which may reflect some kind of "core" plastid genes.
Thus, clustering optimization can be used to define DM species as monophyletic units that are characterized by a specific set of (almost always) closely related host plants and by a comparable genetic diversity, thus deserving the same taxonomic rank.
