Darwin's finches Flashcards
What are Darwin’s finches?
A group of 14 closely related passerine birds found on the Galapagos islands
What family do Darwin’s finches belong to?
Fringillidae
Who has extensively studied Darwin’s finches? Why?
Peter and Rosemary Grant of Princeton University
They are a major model for adaptive evolution
What is adaptive evolution?
Evolution that occurs in response to a changing environment
What is the adaptive trait in finches? What does it correlate to?
Beak morphology, correlates to ecological niche filled by each species
What kind of beaks do Ground finches have?
Crushing bills for eating seeds
What kind of beaks do Warbler and Cactus finches have?
Probing bills
What kind of beaks do Tree finches have?
Grasping bills for eating invertebrates
What kind of beak does the Vegetarian tree finch have and why?
What is its latin name?
P. crassirostris
A parrot-like bill for eating buds of trees
Why is diversity in finch beak shape important in the Galapagos?
All 14 species are very similar and must diversify to exploit different niches and thus avoid competitive exclusion
What is it about the Galapagos islands that drives such morphological diversity? Why?
The harsh environmental conditions.
In unforgiving conditions selection is stronger, producing more drastic and rapid patterns of change.
Fluctuations in environmental conditions are mirrored by…
fluctuations in trait value that evolve in response
Who described the results of a comparative 30-year study on the medium ground finch (G. fortis) and the cactus finch (G. scandens)?
Grant and Grant, 2002
Grant and Grant, 2002;
What did the authors find?
Both G. fortis and G. scandens underwent fluctuations in body size, beak shape and beak size over the 30-year period.
Grant and Grant, 2002;
What happened to body size in G. fortis and G. scandens?
They had become smaller
Grant and Grant, 2002;
What happened to the beak of G. fortis?
It became more pointed
Grant and Grant, 2002;
What happened to the beak of G. scandens?
It became blunter
Grant and Grant, 2002;
Over the 30 years of the study, environmental conditions were particularly difficult on the Galapagos. Why, what happened?
Due to ENSO effects;
Trade winds slow, causing an accumulation of warm surface water in the Eastern Pacific, resulting in extreme rainfall due to increased evaporation.
Who documented some of the wettest years on record? Which years were these?
Grant and Grant (1993)
1983 and 1987
Grant and Grant (1993):
The extreme rains of 1983 and 1987 coincided with beak changes in…
G. scandens, its beak became blunter during this period
Why would beak morph change due to environmental harshness?
Because it is even more difficult to secure food. Specialisation can increase the chance of securing a particular food, thus saving the animal from starvation.
There are two major genes controlling beak shape. What are they?
Bmp4 and CaM
Who described Bmp4 in beak evolution? How did they find this?
Abzhanov et al., 2004
They injected chick embryos with viruses containing Bmp4. This upregulation of expression caused the chick to develop a deep, wide beak
Abzhanov et al., 2004:
Injecting Bmp4 caused the chick’s beak to resemble that of…
G. magnirostris, or the large ground finch
What shape does a) high and b) low Bmp4 produce?
a) a deep, wide beak
b) a shallow, narrow beak
Who described CaM in beak evolution?
How did they select CaM as a candidate gene?
What did they then do?
What did they find?
Abzhanov et al., 2006;
Microarrays were used to study gene expression, CaM selected as a candidate.
Upregulated CaM in the frontonasal prominence
Upregulation produced a long beak
Abzhanov et al., 2006;
Upregulating CaM produced a beak similar in morphology to…
cactus finches
What shape does a) high and b) low CaM produce?
a) long beak
b) short
What is Bmp4 implicated in?
Bone and cartilage development in birds, tooth development in non-aves
What is CaM?
A Ca2+ signalling protein
How are these two genes controlled?
Via a trans-regulatory mechanism
How do trans-regulatory elements (TREs) work?
They encode TSFs, and so modify the expression of distant genes
How do cis-regulatory elements (CREs) work?
They encode binding sites for TSFs and so modify the expression of local genes
How found beak morphology was attributable to TREs?
What did they do?
Lamichhaney et al., 2015
They compared the diversity of genomic regions between species and phenotypes (ZFst) in Darwin’s finches.
Lamichhaney et al., 2015:
What does high ZFst show?
What did ZFst show for Bmp4 and CaM? What does this mean?
High ZFst = organisms are under differential selection as selection favour polymorphism, producing genomic diversity
(assume this indicates cis-regulation)
There was low ZFst for Bmp4 and CaM as there was little variation around the coding sequences, meaning changes in morphology had to be attributable to trans-regulation
Lamichhaney et al., 2015:
Trans-regulation of Bmp4 and CaM have since been attributed to which gene?
Why?
Why is this unsurprising?
ALX1
It was identified as divergent between pointed and blunt beaked individuals
It is known to be integral to craniofacial development in vertebrates
They are not sure, but it COULD be this
