Origin of Species: Evolutionary Biology Study Notes

• Study notes on the Origin of Species from an evolutionary biology perspective

Species

• Groups of organisms that share morphological and phenotypic similarities, have a common gene pool, and can produce fertile offspring through interbreeding.
• Functions as the basic unit of taxonomy.

The Species Problem

• Arose as a result of the large number of species concepts

Phenon

• Refers to a group of observable traits within a population, including intrapopulation variants such as form, age, and seasonal differences.

Taxon

• Any group of organisms that taxonomists formally classify and identify to a species level within the hierarchical classification system.
• Organisms are classified based on shared traits and evolutionary relationships.
• Example of a species is Homo sapiens, families like Hominidae

Category

• Refers to a specific level within the taxonomy hierarchical classification system.

Species Concept

• 26 different species concepts exist

Biological Species Concept

• Defines species as groups capable of interbreeding, isolated from other populations, and maintaining a shared gene pool with evolutionary stability.
• Limitations include its applicability to organisms with diverse phenotypes, asexual organisms, and fossils.

Morphospecies Concept

• Defines species based on morphological characteristics, making it easier to observe and applicable to many organisms.
• Limitations include issues with inconsistency in classification, cryptic species, and seasonal differences.

Genetic Species

• Defines species based on inherited characters, sharing a common gene pool, and forming a reproductive community.
• Strengths include accurate data from DNA sequencing and applicability to asexual organisms and fossil records.
• Limitations include being expensive and relying solely on genetic data.

Speciation

• Evolutionary process where distinct species emerge and separate into different lineages, preserving biodiversity and preventing interbreeding.
• Occurs when the same species becomes reproductively isolated.

Reproductive Barrier

• The biological process by which living organisms produce offspring of the same or similar species, crucial for species continuity and survival.
• Mechanisms and factors restrict successful reproduction, allowing the natural process of speciation and evolution.

Types of Reproductive Barriers

Prezygotic Barrier

• Occurs before the formation of a zygote, preventing successful fertilization and gene flow.

Prezygotic Isolation Mechanisms

• Habitat isolation: species live in different habitats
• Temporal isolation: species reproduce at different times of the day, seasons, or years
• Behavioral isolation
• Mechanical isolation
• Gametic isolation

Postzygotic Barrier

• Occurs after the formation of a zygote but prevents the production of viable or fertile offspring.

Types of Postzygotic Barriers

• Hybrid inviability: Reduced viability where a hybrid zygote fails to develop or dies.
• Hybrid sterility: Hybrids are viable but not fertile.
• Hybrid breakdown: First-generation hybrids are viable and fertile, but subsequent generations are not.

Biogeography of Speciation

• Explores how geographical factors and population distributions influence species formation.
• Geographic isolation and environmental differences create reproductive barriers and facilitate new species formation.

Types of Biogeography of Speciation

Allopatric Speciation

• Occurs when populations of a species become geographically isolated by a physical barrier that leads to genetic divergence and new species emergence.
• An example is Darwin's finches in the Galapagos Islands

Sympatric Speciation (without geographic isolation)

• Occurs when populations coexist in the same geographical area, creating new species due to ecological, behavioral, or genetic influence.
• Polyploidy in plants

Genetic Mechanism of Speciation

• Explains how genetic differences arise and generate new species.

Speciation by Divergence

• Populations accumulate genetic differences due to environmental pressures, natural selection, genetic drift, and mutation, leading to reproductive isolation and interbreeding.

Speciation by Peak Shifts

• Describes rapid genetic changes in small, isolated populations due to genetic drift, often occurring in peripatric speciation.

Genetic Changes

• Requires genetic change depending on speciation mechanism and mode.
• Factors influencing genetic change include reproductive isolation mechanisms, population size, and ecological pressures.