Adaptive Radiation

Cambrian Explosion

Cambrian Explosion

Fig. 25-10

Spon

ges

LateProterozoiceon

EarlyPaleozoicera(Cambrianperiod)

Cnid

aria

ns

Anne

lids

Brac

hiop

ods

Echi

node

rms

Chor

date

s

Mill

ions

of y

ears

ago

500

542

Arth

ropo

ds

Mol

lusc

s

Fig. 25-18

Close North American relative,the tarweed Carlquistia muirii

Argyroxiphium sandwicense

Dubautia linearisDubautia scabra

Dubautia waialealae

Dubautia laxa

HAWAII0.4

millionyears

OAHU3.7

millionyears

KAUAI5.1

millionyears

1.3millionyears

MOLOKAIMAUI

LANAI

Dawkins on Hawaiian Drosophila

Studying Hawaiian Drosophila

Melawi eye biter

Scale-eatingcichlid

Placental and marsupial mammals radiated soon after dinosaur extinction,AND after many other mammal lineages also went extinct (see next slide)

Radiation due to key character evolution?

Russell 1968

4 genera appeared over a 2 my period

Pappogeomys, Cratogeomys, and Orthogeomys diverged over 800,000 years

Molecular data also support a relatively rapid radiation…

From Korth 1994Tertiary Record of Rodents of North America

•The fossil record indicates rapid radiation leading to modern pocket gopher genera in the Blancan•Radiation corresponds with increase in hypsodonty and expansion of grassland

Maybe expansion of Blancan grasslands was responsible for pocket gopher radiation?

Replicated sister-group comparisons:

allow a more refined approach to assessing “key characters” as causes of adaptive radiations

Both clades of herbivorous insects are more taxonomically diverse than their sister groupsThis pattern was seen in 11 of 13 sister group comparisons of herbivorous vs. other

Example radiation: Land plants are a monophyletic group that has evolved fit many ecological niches

Waxy cuticle prevents water loss

Stomata allow gas exchangethrough the waxy cuticle