Avian Speciation and Species Limits Review

Practice questions covering the Biological Species Concept, reproductive isolating mechanisms, genomic analysis, and the complexities of delimiting avian species based on Kevin Winker's review.

How does Ernst Mayr define species under the Biological Species Concept (BSC)?

Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.

What is the 'yardstick method' in avian taxonomy?

A comparative framework that uses the degree of difference found between sympatric species (known distinct species) to infer whether isolated allopatric populations have achieved species-level divergence.

According to the transcript, what is the predominant driver of speciation in birds?

Selection.

What are the two main axes used to visualize the 'speciation process space'?

The phenomic axis (largely adaptive attributes) and the genomic axis (largely neutral attributes).

What is the neutral 'inflection point' described by Wright (1943) regarding gene flow and population differentiation?

The point at which populations switch from diverging to converging, which occurs at approximately one migrant per generation ($Ne m = 1.0$).

Why is mitochondrial DNA (mtDNA) distance considered an unreliable indicator of species limits?

Because speciation (driven by selection) and neutral genetic divergence are not tightly coupled, and substantial mtDNA splits (e.g., $14.8\%$ in Greater Honeyguides) can exist within a single biological species.

Define 'lineage sorting' in the context of speciation.

A population genetics phenomenon where variants of a genetic locus (alleles) become partitioned between populations through genetic drift, eventually tracking the speciation event.

What is the difference between ecological speciation and mutation-order speciation?

Ecological speciation is driven by divergent selection between different environments, whereas mutation-order speciation occurs when different advantageous mutations fix in populations experiencing similar environments.

What term does the author use for lineages that are phenotypically distinct but remain 'evolutionarily glued' by gene flow for long periods?

Evolutionary trysts (or stable adaptive partial reproductive isolation).

What are Dobzhansky–Muller (DM) incompatibilities?

Gene combinations between two populations with different evolutionary histories that result in lowered fitness when they are combined in hybrids.

What is the 'large-Z effect' in avian speciation?

The observation that incompatibilities in hybrids can be disproportionately caused by differences in sex chromosomes ($Z$ being the sex chromosome for which female birds are heterogametic).

How do chromosomal inversions function as reproductive isolating mechanisms?

They prevent recombination within the inverted segment, inhibiting the transfer of adaptive loci between divergent populations and maintaining linkage disequilibrium.

Why is assortative mating alone often an inadequate criterion for determining species limits?

It is common within species (non-speciating), can be a nongenetic consequence of ecology, and does not represent the total effect of all reproductive isolating mechanisms (e.g., postzygotic factors).

What is the primary risk of using coalescent-based species delimitation programs alone?

They often focus on 'lineage delimitation' rather than speciation, potentially leading to 'oversplitting' by diagnosing structure that does not represent essential reproductive isolation.

What is 'character displacement' in the context of the yardstick method?

A phenomenon where two species become more dissimilar in areas of sympatry to avoid competitive exclusion, which can make allopatric populations of the same species appear more similar than they 'should' be based on their status.

Why are Blue-winged ($Vermivora cyanoptera$) and Golden-winged ($V. chrysoptera$) warblers cited as a taxonomic challenge?

Because they have largely undifferentiated genomes and high gene flow despite striking phenotypic (plumage) differences, raising questions about whether they represent adaptation or true speciation.