Definitions
What are the key steps to speciation in order?
Isolation, divergence, reproductive isolation
What is the location of interest?
Daphne Major, a small Galapagos island.
How was the new finch lineage established?
A new finch lineage was established by the hybridization between an immigrant G. conirostris male and resident G. fortis female on Daphne Major island.
Despite close inbreeding, members of the lineage experience [higher/lower] fitness. Explain your answer.
Higher. Bill morphology allowed the finches to efficiently exploit the large woody fruits of Tribulus cistoides.
Although homoploid hybrid speciation is believed to be a generally slow process extending over hundreds of generations, what did the study show? Hint: how long did the process take?
The study showed that reproductive isolation can be established in only three generations, which is much faster than previously thought.
What was the final stage in speciation, according to the paper?
Reproductive isolation from the parent population. In Darwin’s finches, a premating barrier to interbreeding is established by a difference in song and morphology.
What is the nickname for the new finch lineage that are conspicuously large?
Big Bird Lineage
How did the researchers investigate the genetic basis for the relatively large bills of the Big Birds? Hint: what were the names of the genotype loci?
They examined the genotypes at HMGA2 and ALX1, two closely linked loci shown to be associated with variation in bill morphology in Darwin’s finches.
Besides morphology, describe another factor that contributed to the success of inbreeding. Hint: think behaviorally.
Finch species imprint on features of their parents early in life and discriminate between members of their own and other species on the basis of unique song patterns that are critical for mate attraction in finches.
What evolutionary factors may have changed the frequency of polygenic traits, such as bill dimension of the finches (could list one of several things)?
Natural selection, transgressive segregation, epistasis
Describe how isolation occurred in the lineage.
An immigrant male finch from another island mated with a female from a different species of Daphne Major, creating a hybrid lineage that was isolated from both parent species due to the unique combination of its genetic makeup.
What were the cues used in finch mate choice that typically result in the avoidance of interspecific mating?
Song and morphology
What did the researchers discover at the HMGA2 locus?
The frequency of the allele associated with large bill size was 60.8% in generations 4 to 6.
What caused the ecological success and reproductive isolation of the Big Bird Lineage (3 major things)?
Large bill, body size, and distinctive song
How does this study provide an example of homoploid hybrid speciation?
The Big Bird lineage demonstrated reproductive isolation from both parental species within a few generations, facilitated by morphological, ecological, and behavior distinctions.
Describe how divergence occurred in the lineage.
Genetically, the hybrids possessed a mix of traits from both species. Ecologically, they exploited resources in a manner distinct from both parents. Behaviorally, divergence was marked by differences in bird song and mating behaviors.
What did the phylogenetic tree show the founder male to be a hybrid of? In other words, what are the parental species?
G. fortis x G. conirostris
What did the researchers discover at the ALX1 B alleles?
From generation 3 onward, all Big Birds were homozygous for these alleles associated with blunt bills.
After what generation did the lineage behave as an independent species relative to other birds on the island?
Generation 2
Explain the possible scenario as to why there was an increase in bill depth independent of body size AND why bill length did not change in the population.
Transgressive segregation produced genotype combinations that have been favored by natural selection, causing the shift in beak morphology. The net result was morphologically based ecological segregation from the three sympatric competitor species.
What is homoploid hybrid speciation?
Rare occurrence of hybrid speciation without chromosomal doubling, aka the process by which a new species arises from the hybridization of two different species without a change in chromosome number.
Why was G. conirostris immigration from Espanola noteworthy and unexpected?
Espanola is located more than 100km from Daphne Major and a large island lies between them.
Describe the individual that started the research following its survival and breeding for six generations.
An immature male finch that resembled the medium ground finch G. fortis, but was 70% larger and sang a distinctive song.
What were the two variants of the B allele and what was the difference between them?
B1 and B2. B1 originated from the founder male that was genotyped as P/B1, whereas the B2 allele originated from G.fortis. They differ by nine nucleotide substitutions within the 240-kb, showing a strong association with bill shape.
According to the paper, what is the most important component of bill size? Explain why (2 reasons).
Bill depth. (1) Increase in bill depth was independent of body size. However, in G. fortis, the genetic correlation between bill depth and body mass was strongly positive. (2) Bill length did not change in population and only grew larger and blunter.