Evidence of Evolution (6)

The oak leaf gall fly lays its eggs on the surface of Oak tree leaves. Larvae feed on the gall that develops around them. The larvae are typically prey to both parasitoid wasps and to birds; wasps selectively prey on larvae inside the smallest galls while birds selectively prey on larvae inside the largest galls. This year a rampant nematode infection has killed all of the parasitoid wasps. The oak leaf gall flies will likely experience:

A. balancing selection

B. stabilizing selection

C. directional selection

D. disruptive selection

E. heterozygote advantage

• C

  • One selective pressure coming from one side --> pressure on only large sized galls --> smaller galls would survive

In a hypothetical population of 1000 crickets, there exists a gene with two alleles. 350 Crickets are homozygous dominant (DD), and 200 are homozygous recessive (dd). What is the frequency of the D allele in the population?

A. 0.475

B. 0.500

C. 0.575

D. The answer cannot be determined from the data provided.

• 350 Dd crickets and 200 dd crickets 

• If 1000 total crickets then 450 must be Dd 

• D alleles in DD.           "D" alleles in Dd = 1150 total "D" alleles 

(350 x 2)               +.         450 

• 1000 diploid indivi... 2 alleles.. = 2 alleles in pop 

• 1150/2000= 0.575 

What was Alfred Russel Wallace’s ideology?

• activism for environmental issues

Which area did Wallace conduct his studies

• Malay Archipelago

• striking pattern in distribution of animals around the archipelago

What was Wallace’s line

biogeographical boundary that divides the fauna of Asia from the fauna of Australasia, running through Indonesia between the islands of Borneo and Sulawesi, and between Bali and Lombok

What conclusion did Wallace and Darwin both get?

Came to conclusion that the fittest individuals survived and reproduced, passing their advantageous characteristics on to their offspring.

What is a theory?

• Well-established, well-supported, well-documented explanations

  for our observations

Theory vs. Law

• Theory and Law are equal

• Law describes

• Theory explains

What is macroevolution?

Changes between species

Theory of Evolution

• Things evolve | populations change over time

• Evolution usually happens gradually | populations change over hundreds to

thousands of years

• Speciation occurs | one species splits into two or more species

• All species share common ancestry | splitting of lineages from one ancestral

form

• Much of evolutionary change caused by natural selection | the sole process

producing adaptation, the ‘appearance’ of design

Where should we see evidence of life beginning in a distant past in evolution theory?

If life originated on Earth in the distant past and then evolved, we should see evidence in the fossil record

What should we see changes in if evolution occurred within lineages (EVT)?

• If evolution occurred within lineages, and those lineages sometimes split then we should see change in species or morphology through the fossil record

What should we see if organisms share common ancestry (EVT)?

If organisms share a common ancestry, then we should see transitional forms

What other evidence should we see ?

• We should see evidence of retrodictions and vestigial

characters

• We should be able to see evidence of natural selection

What process leads to speciation?

Descent with modification --> isolation --> speciation 

What is Daphne Major?

A windswept island with harsh environment

What thesis was being tested on Daphne Major

• study on the heritability of beak size by swapping eggs to control for parental care

• Eggs of parents of big beaks and switch with eggs of small beaks 

  • Inheritability: they would care for smaller beak  

  • Environmental: would slowly have larger beaks? 

Which birds were being studied?

• Geospiza fortis: Medium Ground Finch (smaller beak)

• Geospiza magnirostris: Large Ground Finch (larger beak)

What were the normal conditions for the birds on the island?

• • Most finches eat a preferred 24 types of seeds

• G. fortis and G. magnirostris are near identical in preference

• Usually spend ~50% time foraging on their favourite seven seeds

• High abundance of seeds (10g/m2)

What impactful event occurred on the island

Massive drought

What happened to resources on the island during the drought?

• Food availability decreased by 84%

• Variety decreased by ½

• Remaining seeds were big and tough

• Seed abundance decreased to < 3g/m2

  • typical is 10g/m2

How did the birds foraging behavior change due to the drought?

•  Spent ~0.03% time foraging on favourites (usually 50%)

• Soon after only a few types of seeds left

• Little to no mating opportunities

What did the different sized of fortiz feed on during drought?

• large fortis ate large seeds

• medium fortis ate medium seeds

• small fortis ate small seeds

Which seed were the birds forced to eat due to drought?

• Forced to feed on the dreaded Tribulus

Why did the finches not eat Tribulus (aka Caltrop) before the drought?

• Only fortis and magnirostris can break

open it’s hard spines

• Extremely sharp spines

What strategy did the magnirostris have for eating tribulus?

• Crushes the seeds with its beak

• Requires 200 newtons of force

• Can often eat all the seeds in one mericarp

What strategy did the fortis have for eating tribulus?

• Too small to crush the seeds

• Braces it against a rock to split it open

• Requires only 54 newtons

• Cost = fewer seeds obtained per mericarp

• Some even steal from magnirostris

Which size made it easier to survive during the drought? 

• G. magnirostris gets 2.5x more energy per minute than G. fortis

• But G. magnirostris is larger and needs more food

• Even then Magnirostris come out on top (2.5 – 1 = 1.5x more energy)

What does a fitness disadvantage put on the specie?

severe selective pressure

Which specie has a marked disadvantage?

Small G. fortis

Why did fortis have a marked disadvantage?

couldn’t open tirbulus

What did fortis have to eat instead?

• Had to eat Chamaesyce

  • Herb with small soft seeds

  • But exudes a sticky, milky latex

  • Similar to milkweed

• Gets stuck to their heads —> Feathers on their heads fall off —> Bald birds die in the hot sun

What was the evolutionary response of the G.fortis to selection caused by drought?

• All got larger in size 

• Larger birds survived --> passed to offspring 

Was the change of G. fortis beak depth slow or rapid?

Rapid environemtnal change --> rapid bird change (Offispring inherit the beak size of the parent of the parent that was able to survive)

After the drought, what significant weather event occured?

El Nino

What did the El Nino cause for resource availability?

• brought heavy rains and increased vegetation

• Shift in Food Availability: The increased rainfall changed the available food sources, leading to a scarcity of the larger, harder seeds.

What evolutionary pressures resulted with the increase in smaller seeds?

• Reverse Evolutionary Pressures: Finches with smaller beaks now better suited to exploit the abundant small seeds

What did the reverse of evolutionary pressures cause in offspring?

offspring inherit smaller beaks.

What is rapid NS in response of?

back-and-forth changing conditions.

What kind of competitions are there?

• Interspecific competition

• Infraspecific competition directly between organisms (fighting)

• Fight for resources through small differences (ex: beak sizes)

What is interspecific competition?

Competition between individuals of different species.

What is interspecific competition?

Competition between individuals of the same species.

What the roles of adaptation?

• morphology and behavior

When does the role of adaptations may only be evident?

during times of stress and competition

What happens to species in good years?

• variation fills in 

• less selection on the adaptations

What happens to species in tough years?

• adaptations become important

• increased selection

• reduction in variation

What are the genetics of beak morphology?

• Bmp4

• Candidate gene from chicken

• Known to influence beak depth

• Finches with deeper beaks have stronger

expression of Bmp4