Evolution, 4th Edition

T HE EvoluTion of BiologiCAl DivERsiTy 503

The immense diversity of flowering plants (angiosperms), compared with that

of other vascular plants, has been ascribed to features such as animal-mediated

pollination, closed carpels that protect the developing seeds, and more efficient

water-conducting vasculature of angiosperm leaves [40]. But the angiosperms

reveal a problem: from among the several distinctive features of a diverse clade,

any of which might have enhanced speciation or reduced the likelihood of extinc-

tion, how can we identify the characteristic that was the key to the group’s high

diversity? Demonstrating the cause of a single event is always difficult. Stronger

evidence is provided if the rate of diversification is consistently associated (corre-

lated) with a particular character that has evolved independently in several differ-

ent clades. Such tests have been applied mostly to living organisms. The diversity

of several clades that independently evolved a similar novel character can be com-

pared with the diversity of their sister groups that retain the ancestral character

state. Since sister taxa are equally old, the difference between them in number of

species cannot be ascribed to age. If the convergently evolved character is consis-

tently associated with high diversity, we have support for the hypothesis that it has

caused a higher rate of origination or has lowered the extinction rate, by allowing a

greater number of species to coexist (as in Figure 19.3A and B).

Charles Mitter and colleagues applied this method, called replicated sister-

group comparison, to herbivorous insects and plants [16, 45]. The habit of feeding

on the vegetative tissues of green plants has evolved at least 50 times in insects,

usually from predatory or detritus-feeding ancestors. Phylogenetic studies identi-

fied the nonherbivorous sister groups of 13 herbivorous clades. In 11 of these cases,

the herbivorous lineage has more species than its sister group (FIGURE 19.13). T his

Futuyma Kirkpatrick Evolution, 4e

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Evolution4e_19.12.ai Date 12-12-2016

Q: Suggestions from Mark: Add pictures of the extinct groups.

“Pictures of the extinct groups may be hard to nd --Doug”

CS: I did a quick search in SA books and didn’t nd anything. LG

Note: Art left as found in pu les. OK as is?

BothriocideroidaEchinocystitoidaPalechinoidaCidaroidaDiademataceaEchinacea Gnathostomata Atelostomata

Cenozoic

Mesozoic

Paleozoic

Time

FIGURE 19.12 Changes in the

diversity of several groups of

echinoid echinoderms over

time. The width of the symmet-

rical profile of each group rep-

resents the number of families

in that group. The diversity of

sea urchins (order Echinacea),

sand dollars (Gnathostomata),

and heart urchins (Atelosto-

mata) greatly increased during

the Mesozoic and Cenozoic,

probably because of the key

adaptations described in the

text. (After [3].)

Futuyma Kirkpatrick Evolution, 4e

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Evolution4e_19.13.ai Date 12-12-2016

Herbivory Herbivory

< 10,000 species 130,000 species 140,000 species 7000 species

Cucujoid beetles Weevils, leaf beetles,

and kin

Moths and butteries Caddisies

FIGURE 19.13 Two replicated sister-

group comparisons of herbivorous

clades of insects with their sister

clades that feed on animals, fungi,

or detritus. Herbivorous clades are

consistently more diverse, demon-

strating higher rates of diversifica-

tion. (Data from [45].)

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