Hybridization

Dobzhansky-Muller Incompatibilities

1. Alleles and genomes that can change over time in populations and may not be able to produce viable offspring because of mutation. 2. The more distantly related the phylogenies, the more unlikely they are to produce offspring. Ex: One population possesses an allele that makes the animals good swimmers; the other population possesses an allele that makes the animals good runners. These two populations mate, and the combination of *allele from the swimmers* + *allele from the runners* proves deleterious for the hybrid, which, because of the combination of alleles, is neither suited for running nor swimming because it possesses two alleles that are incompatible. Model attributes hybrid incompatibility to the interactions between two or more genes that have evolved independently in two isolated populations. These independently evolving genes diverge functionally, and the interactions of these a functionally divergent genes in a hybrid individual are responsible for the defective phenotypes observes (either inviability or sterility). If this is the case, the alleles, or versions, of the gene causing hybrid incompatibility should have distinct phenotypes in the two species.

General outcomes

1. Reinforcement 2. Fusion 3. Stability 4. Introgression

Fusion

2 populations come back together (populations of same species freely interbreed)

Hybrid zone

A zone where two species (come into sympatry) and there exists the opportunity to interbreed and they produce viable and healthy offspring.

Known rates of hybridization and introgression

Birds 10% Eukaryotes 10-25% Plants 10-30% Just know roughly 10-20% of creatures in a species normally hybridize. Introgression rates not known as well

Introgression

Gene flow from one species/ population into another species/population

Introgression

Happens when gene flow occurs between one species and another, but only happens when hybridization is in place. The flow of genes from one species or population to another.

Hybrid speciation

Happens when hybrids mate with differing species.

The relationship between hybrids/introgression and novel environments

Hybridization is required for introgression to happen. Hybrids have unique set of alleles that help them thrive in environments that neither parent could survive in

Reinforcement

Individuals are hybridized that have low fitness pass on genes that prevent interbreeding between populations through the subsequent generations (natural selection favors the prevention of interbreeding) Reinforcement is the process, in which traits that increase pre‐zygotic isolation between two differentiated populations are favoured due to natural selection against the production of unfit hybrids or otherwise maladaptive interbreeding. Reinforcement is the process by which natural selection increases reproductive isolation

Hybridization

Occurs and has different outcomes

Transgressive segregation/hybridization

Species looks completely different from two parent offspring Can be positive or negative in terms of fitness. Formation of extreme phenotypes; species looks completely different from two parent offspring- can be positive or negative in terms of fitness

Stability

When the hybrid zones are very clear cut and they stay stable for years