Evolution, 4th Edition

408 CHAPTER 16

tree. Factors that make ILS more frequent, and thus more problematic for estimat-

ing phylogenies, are short intervals between speciation events and large popula-

tion sizes.

Incomplete lineage sorting can be a problem for resolving relationships not

only in recent radiations but also among lineages that evolved tens or even hun-

dreds of millions of years ago, if the radiation occurred over a short time. FIGURE

16.8 shows a phylogeny of many mammals based on DNA sequences from 14,632

genes, amounting to 20 million nucleotides [10]. Most of the relationships confirm

earlier studies, and are almost certainly correct. But even genomic data of this scale

leave several relationships uncertain (shown by the red circles). For example, the

Chiroptera (bats), Carnivora (cats, bears, etc.), and Perissodactyla (horses, rhinoc-

eroses, etc.) are certainly related to one another, but it is still not certain which two

of them are closest relatives.

But even though some such cases are difficult, phylogenetic relationships can

almost always be resolved with confidence if enough genomic data are used.

The cichlid fishes of Lake Victoria in Africa are one of the most famous adap-

tive radiations. They have the highest speciation rate of any vertebrate group,

with more than 450 species having originated in just the last 15,000 years (see

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

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Evolution4e_16.08.ai Date 02-14-2017

Time (Mya)

Mus (mouse)

Callithrix (marmoset)

Pan (chimpanzee)

Vicugna (alpaca)

Echinops (tenrec)

Dasypus (armadillo)

Procavia (hyrax)

Gorilla (gorilla)

Tarsius (tarsier)

Ochotona (pika)

Canis (dog)

Tupaia (treeshrew)

Homo (human)

Oryctolagus (rabbit)

Tursiops (dolphin)

Erinaceus (hedgehog)

Choloepus (sloth)

Spermophilus (squirrel)

Cavia (guinea pig)

Felis (cat)

Sus (pig)

Pongo (orangutan)

Bos (cow)

Sorex (shrew)

Rattus (rat)

Loxodonta (elephant)

Equus (horse)

Otolemur (galago)

Microcebus (mouse lemur)

Pteropus (ying fox)

Myotis (little brown bat)

Macaca (macaque)

Dipodomys (kangaroo rat)

20406080100 Present

Primates

Scandentia

Rodentia

Lagomorpha

Carnivora

Xenarthra

Perissodactyla

Cetartiodactyla

Chiroptera

Eulipotyphla

Afrotheria

FIGURE 16.8 A phylogeny of many of the higher taxa of mammals, based on 20

million base pairs of genome sequence. Some lineages diverged before the mass

extinction 66 Mya, at the end of the Cretaceous period. The red circles show nodes in

the phylogeny where relationships among the lineages are uncertain, despite the im-

mense amount of data. (After [32], based on [10].)

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