VL 8 Genetics and Genomics of speciation

Question 1

cryptic species

Answer 1

A pair of species that are phenotypically very similar.

Question 2

hybrid zones

Answer 2

A geographical range where the distribution of two divergent populations or species overlap and where hybridization takes place. (contact zones)

• cline: geographic gradient of allele frequencies

They are useful for studying speciation processes, introgression, and divergent selection.

Question 3

different species concepts

Answer 3

1) Typological species: clusterng (genetic or phenotypic) -> good marker have to be found similrity; threshold for “cluster”; huge data sets

2) Biological properties: reproductive isolation, inbreeding, natural populations -> Probelms: hybridization, asexuall reproduction, divergence can happen with gene flow

3) phylogenetic species concept: monophyletic group of common ancetor -> Problems: not all species derive from bifurcation event e.g. italian sparrow

clustering: samples in each group are more similar to each other than they are to samples in another group

Question 4

modes of speciation (allopatric, parapatric, peripatric, sympatric)

Answer 4

allopatric (geographic isolation),
sympatric (same area, different niches),
parapatric (adjacent populations),
and peripatric (small populations isolated from a larger group).

Question 5

What is Haldane’s rule?

Answer 5

Haldane’s rule states that in hybrids, the heterogametic sex (e.g., XY in mammals, ZW in birds) has lower fitness, often due to sterility or inviability. This rule suggests a larger effect of genes on the sex chromosomes in hybrid fitness.

Question 6

What are genomic islands of speciation?

Answer 6

These are regions in the genome with elevated FST, indicating divergent selection and reduced effective migration. They contain barrier loci that contribute to reproductive isolation between populations.

(Genomic islands of speciation are specific regions in the genomes of two diverging species where there is a high level of genetic differentiation compared to the rest of the genome. These regions are thought to contain genes that contribute to reproductive isolation, meaning they help prevent the two species from interbreeding. While most of the genome may still be quite similar between the species, these “islands” show strong differences and are key to the speciation process.)

Question 7

What is hybrid speciation?

Answer 7

Hybrid speciation occurs when two species interbreed, leading to new species. It can involve whole genome duplication (polyploidy) or homoploid hybridization without changes in ploidy level

Question 8

What is polyploid hybrid speciation?

Answer 8

It involves e.g. WGD, resulting in a tetraploid organism. This form of speciation is especially common in plants (self- fertilization is key) and can lead to instant reproductive isolation from diploid ancestors.

• allopolyploidy (one set each from two species)
• autopolyploidy (two sets from the same species)

Question 9

What is subfunctionalization?

Answer 9

After gene duplication, subfunctionalization occurs when duplicate genes lose different functions, complementing each other (Paralogs). This can lead to specialization of gene functions in different tissues or processes.

Question 10

What is the Dobzhansky-Muller model?

Answer 10

The Dobzhansky-Muller model explains hybrid incompatibility through interactions between incompatible genes that evolve in separate populations. When these populations interbreed, the incompatible gene combinations can lead to reduced fitness or sterility in hybrids, contributing to reproductive isolation.