Speciation
What is the term for the speciation process in which a new species forms through hybridization between two parental species without a change in chromosome number, as demonstrated by the Big Bird lineage?
Homoploid hybrid speciation.
How many generations did researchers follow to study the development of the Big Bird lineage?
six generations
What genetic technique did the researchers use to analyze the genetic makeup of the Big Bird lineage?
Whole genome sequencing
What is reproductive isolation?
the prevention of gene flow between populations, leading to the formation of distinct species
According to Figure 1, what is the earliest generation where only endogamous (within-lineage) mating occurred?
F2
In the study, how many generations did it take for the Big Bird lineage to establish reproductive isolation from other species?
Three generations
Which two genetic loci were associated with the variation in bill morphology in the Big Bird lineage, contributing to its ecological success
ALX1 and HMGA2
What primary ecological advantage does the large bill size confer to the Big Bird lineage, according to the study?
It allows the birds to efficiently exploit large woody fruits—specifically those of Tribulus cistoides—during dry seasons and periods of food scarcity.
How does bill morphology affect mate choice in Darwin’s finches?
finches choose mates based on bill size and shape
Figure 2B illustrates the geographic origin of the founder male, who traveled over 100 kilometers from Española to Daphne Major. How might the geographic isolation of islands like these influence speciation?
It can influence speciation by limiting gene flow, promoting local adaptation, and increasing the likelihood of reproductive isolation.
What primary factors caused reproductive isolation between the Big Bird lineage and its parental species?
differences in song and morphology
Which evolutionary concept explains the development of extreme traits in the Big Bird lineage that were not observed in the parental species?
transgressive segregation
The Big Bird lineage showed an increase in homozygosity over generations. What caused this increase, and why is it significant for understanding the lineage’s genetic makeup?
The increase in homozygosity was due to inbreeding and genetic drift from the small population size. This is significant as it reflects reduced genetic diversity, yet the lineage maintained ecological success.
Why did the Big Bird lineage develop a unique song that contributed to its reproductive isolation?
the founder male’s song was different, and the offspring learned and passed down this distinct song
Figure 2D shows a steady increase in the inbreeding coefficient (F) over generations. Based on this trend, what mechanisms besides inbreeding could be contributing to the observed rise in homozygosity?
genetic drift due to a small population size, leading to the loss of genetic diversity and increased homozygosity
What is the term for the geographic separation of populations that can lead to speciation?
allopatric speciation
What evidence did researchers use to confirm that the Big Bird lineage was reproductively isolated from its parental species?
endogamous breeding, and differences in song and morphology
At the HMGA2 locus, the allele for large bill size became more frequent in the Big Bird lineage. What evolutionary mechanism likely drove this change, and what evidence supports this?
Natural selection likely drove the increase in the large bill allele frequency, as individuals with larger bills had higher survival rates, especially during food scarcity.
Why is song divergence particularly effective in establishing reproductive isolation in Darwin’s finches, as demonstrated in the Big Bird lineage?
Songs are used in mate recognition. Since male finches learn songs from their fathers, the unique song of the Big Bird lineage acted as a strong reproductive barrier.
Figure 3B shows an increase in bill depth over generations while body size remains stable (Figure 3C). What evolutionary force is most likely responsible for this change, and how does it benefit the Big Bird lineage?
Natural selection. The increased bill depth enhances the birds’ ability to feed on large woody fruits during periods of limited food availability, thereby providing a significant ecological advantage.
The Big Bird lineage developed reproductive isolation within just three generations. How does this challenge traditional views on the time required for speciation, and what factors might have contributed to its rapid success?
Classic speciation models emphasize prolonged genetic divergence through mutation and natural selection over long timescales.
Factors that contribute to success: Assortative Mating, Ecological Niche Differentiation, Strong Selection Pressures
What evidence suggests that natural selection, rather than genetic drift alone, played a significant role in the morphological evolution of the Big Bird lineage?
the consistent increase in bill size across generations and higher survival of large-billed individuals during environmental stress
Why was it surprising that the Big Bird lineage exhibited high fitness despite a decrease in genetic diversity? What factors in the study explain this apparent contradiction?
High fitness despite low genetic diversity was surprising because inbreeding usually reduces adaptability. However, the Big Bird lineage’s large bill size and specialized diet allowed it to exploit a niche with reduced competition, enhancing its survival and reproduction.
The study suggested that the Big Bird lineage likely developed reproductive isolation from its parental species in just three generations. How does this challenge traditional views of speciation?
Traditional views suggest speciation takes hundreds or thousands of generations, but this case shows it can occur rapidly under strong ecological and behavioral selection.
Figure 3B illustrates variation in bill depth over time. If the environment on Daphne Major were to change and smaller seeds became more prevalent, how might this affect the Big Bird Lineage?
We might see the detrimental effects of inbreeding because the fitness benefit of the bigger bills no longer exists, because selection is likely to favor individuals with smaller, more slender bills.