Download species selection

Last day… were talking about macroevolution…
- ended on topic of punctuated equilibrium
Some debate just about frequency of patterns details
of patterns
Real question – is macroevolution just more natural
selection, or something else?
Some versions of P.E. suggest hard to change a species,
likely to happen only at speciation
Suggests major trends in evolution are not due to
natural selection acting on population, but rather
due to species selection
- new species may vary in any direction, but certain types
of species may be more likely to speciate again, or
less likely to go extinct, & thus create trends
Quite controversial, & not much evidence to support these
extensions of P.E. theory?
Punctuated Equilibrium suggests species evolve quickly
– current evidence?
e.g. African cichlids
- L. Victoria - > 500 endemic spp.
- appears that ‘species flocks’ are monophyletic groups
- suggests that speciation took place in same lake
How
long dosurveys
you think
would take
for >
species to
- geological
- L.itVictoria
largely
or500
completely
(??)
evolve
fromyears
a common
dry
~15,000
ago ancestor?
15,000numerous
years
-A)
implies
speciation events in lake in 15,000
B) 40,000
years, &years
tremendous morphological diversity generated
C) 4 million years
D) 15 million years
Genetic
evidence
suggests that
E) 40 million
years
process took longer - start
4 MY to 100,000 years ago?
- but much speciation in last
15,000 yrs and still
exceptionally fast!
On other hand: tadpole shrimp (Triops)
- no morphological change since Triassic (>200 MYA)!
Cichlid case an example of adaptive radiation:
evolution of many new spp. from a common
ancestor when exposed to new environment
Other examples:
- Galapagos (Darwin’s) finches – 15 spp.
- Hawaiian honeycreepers – ~32 recent spp. (many extinct)
Iiwi
Akiapolaau
Carlquistia muirii
Hawaiian silverswords radiation
- 28 spp. in ~5.2 MY
- likely ancestor a tarweed from s. California
- South American mammals – 75-100 genera in
15-20 million yrs.
Pyrotherium
Doedicurus, a glyptodont
Toxodon
What causes radiations?
Evolutionary novelties
- e.g. wings on insects
 feedback on flowering plants
- origin of skeletons & exoskeletons
 change predator-prey relationships
Cloudina
Vacancies
a) colonizing new area
- islands or continents
b) extinction of other groups
Mass extinctions an important recurring pattern in
fossil record
- about 12 events, marking boundary of many
geological periods, & especially eras
Some extinctions ‘all’ of the time (2 - 4.6 families per
million years)
Mass extinctions have higher extinction rate (up to 19.3
families per M.Y.)
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
- Old World & New World vultures
- hummingbirds & sunbirds
- crocodiles, phytosaurs,
champsosaurs, etc.
Nile Crocodile
May not have produced
humans, but some
organisms likely
to look familiar…
phytosaur
champsosaur
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. ‘Cope’s rule’ suggests
animals increase in size
within a lineage
- 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
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
Pakicetus
In a population of skunks, some of the skunks are found to
have an unusual variation, in that they smell sweet and
pleasant instead of the usual terrible smelly defensive odor.
A study finds that the new ‘Sweet’ mutation is a dominant
allele, and also that 95% of the population is made up of
normal ‘stinky’ skunks. If the population is in HardyWeinberg equilibrium, what is the frequency of the dominant
allele? What is the frequency of heterozygotes?
First – what is the H-W equation?
Second – what does the value (95%) represent?
A) p
B) q
C) p2
D) 2pq
E) q2