Speciation and Evolution Concepts

Speciation Overview

Species Definition: A species is a group of individuals that can interbreed under natural conditions.
Example: Happy face spiders (Theridion grallator) show morphological differences but belong to the same species due to interbreeding potential.

Appearance is not the sole criterion for species classification.
Example: Western meadowlark vs. Eastern meadowlark: both appear identical but have different songs leading to reproductive isolation.

The interbreeding definition becomes complex with asexual organisms, complicating species definition.

Refers to different stages of evolution within the same lineage in the fossil record.
Example: Distinguishing between different trilobite species over time presents challenges in defining species boundaries.

Example: Ensatina salamanders in California show gradual morphological and genetic differences across their range.
They interbreed except at extremes where two ends of the range do not, but they are considered the same species due to intermediate forms.

A species is considered to be a tip on a phylogenetic tree—essentially the smallest group of organisms sharing an ancestor, distinct from others.

Speciation: A lineage-splitting event resulting in two or more separate species.
Example organisms include Drosophila species (D. dentissima, D. melanogaster, D. obscura).

Geographic Isolation: Initial step for speciation; leads to divergence of populations in different environments.
Reduction of Gene Flow: Different selective pressures across geographic ranges contribute to speciation.

Allopatric Speciation: Speciation occurring due to geographic isolation.
Peripatric Speciation: Takes place when a small population is isolated at the edge of a larger population.
Parapatric Speciation: A continuous population with disparate mating preferences leads to speciation.
Sympatric Speciation: Speciation without geographic isolation, often due to niche exploitation.

Considered the most straightforward mode: A population gets divided by geographic barriers, leading to evolutionary divergence.

Involves small isolated populations, often influenced by the founder effect where a few initial individuals establish a new population
This small size accelerates evolutionary changes due to limited gene flow and genetic drift.

Occur when new populations are started by a small number of individuals.
Can lead to reduced genetic variety and fixation of rare alleles, impacting evolution.

No explicit barrier to gene flow; populations exist in proximity but tend to mate with neighbors more frequently.
Example: Metal-tolerant and intolerant plants show divergence despite being geographically continuous.

Occurs when populations exploit different niches within the same geographic range leading to reduced gene flow.
Example: Apple maggot flies evolved from hawthorn flies, resulting in host-associated mating preferences.

Polyploidy occurs when chromosome numbers increase due to meiotic failure, leading to reproductive isolation from diploid ancestors.
Example: Formation of Tremblay’s salamander from hybridization.

Plants exhibit diverse reproductive strategies include hybridization and changes in ploidy levels.

Describes random changes in allele frequencies in small populations; not driven by natural selection.
Bottleneck Effect: Reduces genetic variation and poses risks for long-term adaptability.

Example: Southern elephant seals underwent a bottleneck due to hunting, reducing genetic variation.
Cospeciation: Close associations between species can lead to parallel speciation events.

Hurricane effects on iguanas showcased how geographic disturbances can initiate speciation events.
Different subspecies of spotted owls demonstrate geographical differentiation leading to speciation.

Evolution can produce significant features enhancing survival.
Examples include:
1. Winged mammals (bats) for improved feeding.
2. C4 and CAM photosynthesis for drought resilience.
3. Diversified wing morphology among treehoppers for various adaptations.

Kea: An intelligent parrot adapted to mountainous environments with unique feeding and behavioral traits.
Palm Nut Vulture: A raptor with a specialized diet, showing adaption towards a unique ecological niche.
Pill Bug and Millipede: Example of convergent evolution demonstrating similar adaptations in different lineages.
Pronghorn Antelope: Misclassified as an antelope; it belongs to a unique evolutionary lineage related to giraffes.
Hoatzin: A primitive bird with unique traits that reflect ancient evolutionary characteristics.