Last day talking about macroevolution, ended on

1
Last day talking about macroevolution, ended on
topic of adaptive radiations (including mass
extinction, contingency)
2
Extinctions are likely a major source of
contingency in evolution (outcome depends on
chance events)
Controversy over importance of contingency if
start over from scratch, would results be same?
Much evidence that parts of the story would be
the same... Cases of convergent evolution
indicate that similar traits have been favored
more than once
Klingon
3
- Old World New World vultures - hummingbirds
sunbirds
4

• crocodiles, phytosaurs,
• champsosaurs, etc.

Nile Crocodile
May not have produced humans, but some
organisms likely to look familiar
phytosaur
champsosaur
5
Organisms may converge on particular forms, but
is there any consistent direction to evolution?
Not much?
Some trends exhibited by particular taxa, rarely
general
e.g. Copes rule suggests animals increase
in size within a lineage
6

• must be a weak trend from origin of life, but
  debated
• on finer scale
• - late Cretaceous molluscs found decreases
  as frequent
• as increases
• fossil mammals new spp. average 9.1 larger
• than old spp. in same genus
• - trend may exist in some taxa, but likely weak

7
If there are trends, it still does not mean that
evolution is goal-oriented - evolution acts
by favoring those forms that have a
competitive advantage in particular
environment at particular time, NO foresight
8
Speciation Darwin explained evolution, but
didnt do so well with speciation Natural
selection causes change in a pop., but what
causes pop. to split? - had idea of
diversification, but not of gene pool
What is a species?
9
Most popular idea (still?) is Biological Species
Concept (Ernst Mayr)
- pop. or group of pops. whose members have
potential to interbreed produce fertile
offspring

• largest interbreeding unit, genetically isolated
  from
• other pops.

1904-2005
10
Species usually look different, but may be very
hard to distinguish (or a species may be very
variable)
Eastern Meadowlark
Western Meadowlark
Polymita
11
In practice, many species hybridize if only
rare, generally considered distinct spp.
Blue-winged Warbler
Golden-winged Warbler
Lawrences Warbler
Liger
12
Hard to classify if - disjunct range
- asexual reproduction
- fossils
13
Can have ring species dont interbreed in 1
zone of contact, but connected by interbreeding
pops
14
Difficulties expected if species arise by gradual
divergence of pops.
15

• other species concepts proposed, but they have
• difficulties too

Morphological Species Concept based on similar
structure appearance - scientists may not
agree on what differences define a sp.
Phylogenetic Species Concept species is
smallest group of related organisms that share
a defining feature - could greatly increase of
species
16
Reproductive isolation important to speciation
can be achieved in various ways
A Prezygotic barriers 1) Habitat isolation
(flycatchers)
Dusky Flycatcher
Hammonds Flycatcher
17
2) Behavioral isolation (fireflies)
18
3) Temporal isolation (spotted skunks)

Eastern Spotted Skunk
Western Spotted Skunk
19
4) Mechanical isolation (flowers, insects)
20
5) Gametic isolation (marine animals, flowers)