Evolution, 4th Edition

480 CHAPTER 18

occur if species successively dispersed to new islands as they were formed, did not

disperse from younger to older islands, and did not suffer extinction. A phyloge-

netic analysis of trees in the genus Psychotria revealed just this pattern (FIGURE

18.12B) [34]. A similar pattern has been found for other Hawaiian taxa, such as the

cricket genus Laupala [27].

Phylogeography

Phylogeography is the description and analysis of the processes that govern

the geographic distribution of lineages of genes, especially within species and

among closely related species [1, 16, 21]. These processes include the dispersal of

the organisms that carry the genes, so phylogeography provides insight into the

past movements of species—including humans (see Chapter 21)—and the history

by which dispersal and vicariance have determined their present distributions.

Phylogeographic studies find the phylogenetic relationships among populations,

and can be used to infer their history of spread. For example, the tree Symphonia

globulifera was shown to have dispersed from West Africa to South America more

than 15 Mya, after which it crossed the Andes and spread through western South

America to Central America (FIGURE 18.13).

Phylogeographic studies have traced the expansion of species from Pleistocene

refugia after glacial periods, and have shown how Pleistocene events such as sea

level changes have shaped some geographic patterns of genetic variation. For

example, the genetic differences among populations of many species of freshwater

fishes and other species in the coastal plain of the southeastern United States show

that they were separated into western and eastern populations in the past (FIGURE

18.14), probably by high sea level during interglacial episodes.

Futuyma Kirkpatrick Evolution, 4e

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Evolution4e_18.12.ai Date 12-07-2016

(A)

Kauai (~5 Mya)

Oahu (~2.5 Mya)

Hawaii (<0.5 Mya)

Maui Nui (~1 Mya)

(B)

P. mariniana

P. hawaiiensis

P. mauiensis

P. fauriei

P. mauiensis

P. hawaiiensis

P. hathewayi

P. kaduana

P. kaduana

P. greenwelliae

P. mariniana

P. wawrae

P. grandiora

P. mariniana

P. hobdyi

P. hexandra

P. hexandra

M

M

M

M

M

O

O

OO

O

O

K K K K K K

H

FIGURE 18.12 Dispersal accounts for the distribution of species in the Hawaiian

Islands. (A) The present Hawaiian archipelago, showing the approximate dates of

each island’s formation. (B) A phylogeny of Hawaiian species of Psychotria trees shows

successive shifts from older islands to younger islands, as expected if younger islands

were colonized after they formed. (After [34].)

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