Lo4- Speciation

What is speciation?

Speciation is the process by which new species form from preexisting species. It occurs when populations become genetically isolated from one another, leading to the evolution of distinct species.

What is the Biological Species Concept?

The Biological Species Concept defines a species as a group of populations whose members can interbreed in nature and produce fertile offspring, while being reproductively isolated from other populations.

What are the limitations of the Biological Species Concept?

• It cannot be applied to fossils or asexual organisms.

• Gene flow sometimes occurs between distinct species (e.g., grizzly bears and polar bears can produce "grolar bears")

What is the Morphological Species Concept?

The Morphological Species Concept defines a species based on structural features (morphology). It applies to both sexual and asexual species but relies on subjective criteria.

What is the Phylogenetic Species Concept?

The Phylogenetic Species Concept defines a species as a single line of descent (lineage) with a unique genetic history that maintains its identity from other lineages. It applies to both sexual and asexual species and fossils.

What is the Ecological Species Concept?

The Ecological Species Concept defines a species based on its ecological niche, emphasizing the role of disruptive selection. It applies to both sexual and asexual species.

What is reproductive isolation?

Reproductive isolation refers to biological barriers that prevent members of two species from producing viable, fertile offspring. It can occur before or after fertilization.

What are prezygotic barriers?

Prezygotic barriers prevent fertilization from occurring. Examples include:

1. Habitat isolation

2. Temporal isolation

3. Behavioral isolation

4. Mechanical isolation

5. Gametic isolation

Habitat isolation

Species live in different habitats (e.g., maggot flies).

Temporal isolation

Species breed at different times (e.g., skunks).

Behavioral isolation

Species have different courtship rituals (e.g., blue-footed boobies).

Mechanical isolation

Physical differences prevent mating (e.g., snails with different shell spirals).

Gametic isolation

Gametes are incompatible (e.g., sea urchins).

What are postzygotic barriers?

Postzygotic barriers prevent hybrid zygotes from developing into viable, fertile adults. Examples include:

1. Reduced hybrid viability

2. Reduced hybrid fertility

3. Hybrid breakdown

Reduced hybrid viability

Hybrids die early

Reduced hybrid fertility

Hybrids are sterile

Hybrid breakdown

Hybrids are fertile, but their offspring are less fit

What is allopatric speciation?

Allopatric speciation occurs when populations are geographically isolated, leading to genetic divergence due to mutation, natural selection, and genetic drift. Example: Mosquitofish in different ponds.

What is sympatric speciation?

Sympatric speciation occurs when new species form without geographic separation. Mechanisms include polyploidy, habitat differentiation, and sexual selection. Example: Cichlid fish in Lake Victoria.

What is polyploidy?

Polyploidy is the presence of extra sets of chromosomes due to errors in cell division. It is a major factor in sympatric speciation, especially in plants. Types include:

1. Autopolyploidy: Extra chromosomes from the same species.

2. Allopolyploidy: Extra chromosomes from different species.

What is autopolyploidy?

Autopolyploidy occurs when an individual has more than two chromosome sets derived from one species. Example: Tetraploid plants (4n) that can self-pollinate or mate with other tetraploids.

What is allopolyploidy?

Allopolyploidy occurs when a species has multiple sets of chromosomes derived from different species. Example: Wheat (Triticum aestivum) is an allohexaploid (6n).

How does habitat differentiation lead to sympatric speciation?

Habitat differentiation occurs when new ecological niches appear, leading to reproductive isolation. Example: Apple maggot flies that live on hawthorn trees vs. apple trees.

How does sexual selection drive sympatric speciation?

Sexual selection can lead to reproductive isolation when individuals prefer mates with specific traits. Example: Cichlid fish in Lake Victoria that mate based on color.

What is anagenic speciation?

Anagenic speciation is the gradual transformation of one species into a new species over time without branching.

What is cladogenic speciation?

Cladogenic speciation is the branching off of a new species from a common ancestor. It includes allopatric and sympatric speciation.

What is the difference between allopatric and sympatric speciation?

• Allopatric speciation: Geographic isolation leads to genetic divergence.

• Sympatric speciation: New species form without geographic separation, often due to polyploidy, habitat differentiation, or sexual selection.

What are the key mechanisms of sympatric speciation?

1. Polyploidy: Extra sets of chromosomes.

2. Habitat differentiation: New ecological niches.

3. Sexual selection: Mate choice based on specific traits.

What is hybrid breakdown?

Hybrid breakdown occurs when first-generation hybrids are fertile, but their offspring (F2 generation) are sterile or have reduced fitness. Example: Some cultivated rice strains.

What is the role of natural selection in speciation?

Natural selection can lead to genetic divergence in isolated populations, resulting in reproductive isolation and the formation of new species.

What is the role of genetic drift in speciation?

Genetic drift can cause random changes in allele frequencies, especially in small, isolated populations, leading to reproductive isolation and speciation.

What is the significance of polyploidy in agriculture?

Many important crops (e.g., wheat, oats, cotton) are polyploids. Polyploidy increases genetic diversity and can lead to new species with desirable traits.

What is the experimental evidence for sympatric speciation?

Experiments with cichlid fish in Lake Victoria show that sexual selection for mates of different colors can lead to reproductive isolation and speciation.