Lecture 3: Constraints on adaptation

Question 1

evolutionary forces:

Answer 1

• migration
• mutation
• selection
• drift

Question 2

why wouldn’t a species be able to adapt?

Answer 2

1) evolution is slow - environment changes can be quick (eg. climate change)
2) population may end up on a suboptimal adaptive peak
3) lack of variance (behavioural, genetic)
4) Traits can be correlated
5) Plasticity might prevent selection from acting

Question 3

why wouldn’t a species be able to adapt? if the population ends up on a suboptimal peak? example

Answer 3

-Zuk et al 2006
-Hawaii
Ormia ochracea (FLY)
- Teleogryllus oceanicus (cricket)
-usually crickets make chirping noises for mate attraction
-crickets were being used as hosts for fly to lay eggs (1991 30% males parasitised, 2001 almost pop died out)
-Oahu and Kauai crickets became silent (2003 lots but silent)
–silent males piggy back two singing males (get close)
–suboptimal peak = as previous adaptive path was CONSTRAINED

Question 4

why wouldn’t a species be able to adapt? lack of behavioural variation. example

Answer 4

• mockford & marshall 2009
• must be able to adapt or die out
• bird song in urban areas
• freq of great tits increases in urban
• get above urban noise

Question 5

why wouldn’t a species be able to adapt? lack of behavioural variation. 3 options:

Answer 5

1) species that do not have to alter their song to inhabit urban habitats
2) species that have the vocal capacity to adapt their song for urban habitats
3) species that can do neither and therefore not be able to inhabit urban habitats
LACK OF BEHAVIOURAL VARIANCE CAN BE A CONSTRAINT

Question 6

why wouldn’t a species be able to adapt? lack of genetic variation.

Answer 6

greater genetic variance, better chances of adapting
–seen between global pop and tropical pop in drosophila (in cold & desiccation)
-CAN MUTATION CAN SAVE THEM? OVERALL NO, BUT MOSQUITOS
(single base pair mutation)

Question 7

why wouldn’t a species be able to adapt? variance two types

Answer 7

behavioural and genetic

Question 8

why wouldn’t a species be able to adapt? correlated traits 2 mechanisms

Answer 8

• linkage disequilibrium

- pleiotropy

Question 9

linkage disequilibrium:

Answer 9

genes (and the traits they control) appear together often ( low recombination rate)

Question 10

pleiotropy

Answer 10

genes affecting more than one character

Question 11

why wouldn’t a species be able to adapt? correlated traits

Answer 11

Grant & Grant 1986

• G. fortis (finch - darwin)
• bill size
• drought in 1977 = bigger seeds & harder
• bill length does get bigger, even though selection is acting to make it smaller
• because bill length & depth are coded for on the genome v v closely together and depth was really selected for
• individual bill lengthh increase = would decrease fitness

Question 12

evolution of correlated traits; direction of evolution depends on

Answer 12

genetic correlation

-LD and pleiotropy

Question 13

why wouldn’t a species be able to adapt? phenotypic plasticity
example

Answer 13

• squinting bush brown (butterfly)
• same genotype produces different phenotypes in response to environmental conditions
• Morphs depend on temperature during development
• wet season: patterned and ready to attract and find mate
• dry season: camouflaged, more predators, looks like leaf
• HOWEVER, IF ENVIRONMENT CHANGES OUTSIDE THESE TWO OPTIONS, theres little for selection to act on