Lecture 8 - Species, Speciation, Phylogenies

Sexual dimorphism

the systematic differences in physical characteristics between males and females of the same species

EX:

• birds of paradise

• gorillas

• beetles

Can individuals vary within a colony or population?

Yes

Ecophenotypic variation

when morphology changes in different habitats

Taphonomic distortion

the ways that geological and biological processes after an organism's death can alter its remains, potentially leading to misinterpretations of its original form and features

Genetic habitat

the sequence of nucleotides in a gene, acting as a template for replication

• can change through recombination, mutation

Somatic habitat

the physical entity or phenotype

• immediate conditions within which the genes act

• can change through growth and development

Environmental habitat

everything external to the body

• supplies resources to an organism

• can change as external conditions change

Population

Groups of conspecific organisms that occupy a more or less well-defined geographic region and exhibit eproductive continuity from generation to generation

• share a single gene pool

Natural selection

variation exisst among individuals where the advantageous variation is heritable

• increase those gene frequencies that are more “fit” in environment

• most powerful force in changing gene frequencies in LARGE POPULATIONS

Random genetic drift would

change fluctuation in gene frequency

Inbreeding would

reduce genetic variability

Migration would

cause mixing that prevents genetic divergence

Mutation would be

the ultimate source of genetic variation

Species

Groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups

• defined by genetic cohesion

Geographic isolation

individuals occupy different regions

Habitat isolation

live in different habitats, utilize different resources

Seasonal isolation

live in different times of year

Behavioral isolation

a type of reproductive isolation where differences in mating rituals or behaviors prevent different species from interbreeding

Mechanical isolation

no successful mating, different reproductive systems

Gametic mortality

sperm is transferred but no fertilization occurs

Allopatric speciation

geographic barrier introduces variation of species

Parapatric speciation / ring species

speciation occurs in adjacent geographic areas

• gene flow is reduced even thoug individuals are near each other

• gradients form but the end populations are reproductively isolated

Sympatric speciation

Speciation occurs in one geographic area

EX: different mating seasons but both species can live in the same place still

Difficulties with the biological species concept that paleontologists have:

• Reproductive isolation is difficult to identify or verify

• Can’t test reproductive isolation directly in the fossil record

• Reproductive isolation may not be expressed morphologically

• This model ignores evolution (change over time) altogether

Speciation occurs over time!

Anagenesis

• gradual change in fossil populations over time

• arbitrarily divided

Cladogenesis

• splitting of lineages

• barrier to reproduction leads to divergence of each

Visualizing anagenesis versus cladogenesis