Speciation and Evolution Lecture Review

These flashcards cover core concepts from the lecture on evolution, speciation, isolating mechanisms, and key examples such as Galápagos finches, Howea palms, and Kangaroo Island kangaroos.

What is the biological definition of evolution?

A change in the genetic composition (allele frequencies) of populations over time.

What is the primary driving force behind evolution?

Natural selection.

How do changing environmental conditions influence allele frequencies in a population?

They alter selective pressures, favouring some alleles over others and shifting allele frequencies through natural selection.

At what point is a new species considered to have formed?

When populations can no longer interbreed to produce viable, fertile offspring.

Define ‘species’ according to the biological species concept.

A group of individuals able to breed with one another and produce viable, fertile offspring.

What is speciation?

The process by which populations genetically diverge until they become distinct species.

Name four evolutionary mechanisms that can lead to speciation.

Mutations, natural selection, genetic drift and gene flow.

What are the two main categories of speciation?

Allopatric speciation and sympatric speciation.

Besides breeding tests, how can scientists recognise speciation?

Through molecular comparisons (DNA or amino-acid sequences) and analysis of structural/phenotypic features.

Differentiate pre-reproductive and post-reproductive isolating mechanisms.

Pre-reproductive mechanisms prevent mating or fertilisation; post-reproductive mechanisms act after fertilisation, reducing hybrid viability or fertility.

Give two examples of pre-reproductive isolating mechanisms.

Habitat isolation and behavioural isolation (other correct answers: temporal, mechanical, gametic).

Give two examples of post-reproductive isolating mechanisms.

Zygote mortality and hybrid sterility (another example: hybrid inviability).

What is habitat isolation?

When populations occupy different ecological niches, preventing them from encountering one another to mate.

What is temporal isolation?

When populations breed at different times of the day or year, preventing interbreeding.

What key feature characterises allopatric speciation?

Geographical separation that prevents gene flow between populations.

Why are Galápagos finches an example of allopatric speciation?

The islands’ oceans act as geographical barriers, isolating finch populations and preventing gene flow, leading to divergence.

Approximately how many distinct finch species exist on the Galápagos Islands?

Eighteen species.

What has driven the beak diversity seen among Galápagos finches?

Different food sources on each island imposing distinct selection pressures.

What key feature characterises sympatric speciation?

New species arise within the same geographical area due to divergent selection pressures or genetic abnormalities.

Define polyploidy and its relevance to sympatric speciation.

Polyploidy is the possession of more than two sets of chromosomes; it can instantly create reproductive isolation and new species, especially in plants.

Why is polyploidy often fatal in animals but survivable in some plants?

Complex animal developmental systems are highly dosage-sensitive, whereas many plants can tolerate and even benefit from additional chromosome sets.

Why are Howea palms on Lord Howe Island considered an example of sympatric speciation?

Two palm species diverged in the same geographic area, likely due to differing soil pH preferences rather than physical separation.

Contrast the soil preferences of Howea belmoreana and Howea forsteriana.

H. belmoreana prefers neutral to acidic soils (low pH), while H. forsteriana prefers alkaline soils (high pH).

What is a biological consequence of changing allele frequencies within a population?

It can increase or decrease genetic diversity, affecting the population’s adaptive potential.

Explain how rising sea levels after the last ice age led to divergence of Kangaroo Island kangaroos.

Sea water created a geographical barrier isolating the island population, preventing gene flow and allowing distinct genetic and morphological traits to evolve.

Why doesn’t the slower movement of Kangaroo Island kangaroos greatly reduce their fitness?

The island lacks major predators, so slower speed does not diminish survival or reproductive success.

Why might conservationists introduce mainland Western Grey kangaroos to Kangaroo Island?

To increase genetic diversity and reduce the risks associated with a small, isolated gene pool.

What is genetic drift?

Random changes in allele frequencies, especially significant in small populations, which can lead to divergence.

How can reduced gene flow contribute to speciation?

Without gene flow, isolated populations accumulate genetic differences until they become reproductively incompatible.