. Bonner zoologische Beiträge : Herausgeber: Zoologisches Forschungsinstitut und Museum Alexander Koenig, Bonn. Biology; Zoology. 536 Thorpe tiate between primary and secondary contact zones (as could exist between G g. galloti and G. g. eisentrauti). If the situation is simplified to the case of inter-island dispersal then it is pos- sible to hypothesize a node (branching point) on the tree as an ancestral popu- lations in a specified locality. The locality of the ancestral (nodal) populations can be hypothesized as being in the same geographic locality as the anageni- cally nearest actu
. Bonner zoologische Beiträge : Herausgeber: Zoologisches Forschungsinstitut und Museum Alexander Koenig, Bonn. Biology; Zoology. 536 Thorpe tiate between primary and secondary contact zones (as could exist between G g. galloti and G. g. eisentrauti). If the situation is simplified to the case of inter-island dispersal then it is pos- sible to hypothesize a node (branching point) on the tree as an ancestral popu- lations in a specified locality. The locality of the ancestral (nodal) populations can be hypothesized as being in the same geographic locality as the anageni- cally nearest actual population. This assumes that a 'stay at home' population diverges at a relatively constant rate that is lower (perhaps much lower) than the initial rate in a population that has just colonized an island. In the latter case the initially greater rate of divergence would be expected from the founder effect and the foreign selection regime of the newly colonized island. If the out-group root is used then the nodes can be hypothesized as ancestral populations as in Fig. 2 a. This indicates an origin in La Palma, and a dispersal pattern of La Palma -* Tenerife -» Tenerife -» Gomera -> Hierro (Fig. 2b). out-group Fig. 2 a: Out-group rooted tree. Taxa indicated by squares and the locality of the hypo- thesized ancestral populations (circles) given in brackets. Fig. 2 b: Direction of dispersal hypothesized by a phylogenetic interpretation of the out-group rooted tree. If the mid-point root is used then the nodes can be hypothesized as ancestral populations as in Fig. 3 a. This (Fig. 3 b) indicates the same pattern of intercon- nection between islands as when the out-group root is used (Fig. 2b). However in this case the island of origin is Tenerife ( Tenerife is only marginally clo- ser to the root than S. Tenerife) with colonization of La Palma from Tene- rife and colonization of Gomera from S. Tenerife and subsequent colonization of Hierro from Go
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