The Origin of Species

Chapter 24

Basics

Speciation Macroevolution Two basic patterns of

evolution: Anagenesis Cladogenesis

Species

Biological species concept: a population/group of whose members can potentially reproduce & create fertile offspring, but are unable to do so with other populations

Reproductive isolation is the key! Often this is a combination of several types of

barriers

Reproductive Isolation

Prezygotic barriers Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation

Postzygotic barriers Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown

Reproductive Isolation Charades

Your group will be assigned one of the reproductive isolation mechanisms

Your job is to create a silent skit to teach this to the class…remember, you’re at school so this needs to be appropriate Your skit doesn’t have to be very long

You have ten minutes before we start the presentations. GO!

Limitations to Biological Species Concept

Reproductive isolation is difficult to determine for extinct species & those that are asexually reproducing which limit the use of bsc

These definitions focus on the unity found within species: Morphological species concept Paleontological species concept Ecological species concept Phylogenetic species concept

SpeciationAllopatric speciation

Gene flow of a population is prevented due to geographic isolation creating two distinct subspecies

The size of the geographic barrier is dependent on the species & their motility

Example: antelope squirrels at the Grand Canyon

Speciation

Sympatric speciation Populations with geographic overlap become

isolated leading to speciation Driven by chromosomal changes & nonrandom

mating that reduce gene flow Polyploidy (changes in the number of sets of

chromosomes during meiosis) in plants Habitat differentiation Sexual selection

• Example: cichilids with coloration preference

Sympatric Speciation

Autopolyploidy

Sympatric Speciation

Allopolyploidy: A hybrid plant that is infertile may reproduce asexually

& eventually mutate to become fertile polyploid

Sympatric Speciation

Habitat Differentiation Genetic factors allow new generations to exploit a

resource that was unused by previous generations (the parent population)

Example: apple maggot flies had speciation as new generation inhabited European introduced apple trees with different apple production season

Allopatric vs Sympatric Speciation

Adaptive Radiation

The evolution of many diverse species from a common ancestor after introduction to new environments Usually results from new populations being established

in distant areas

This is what happened to mammals after the dinosaurs went extinct!

This can be seen in the Hawaiian islands as species invaded the naked islands & then had allopatric & sympatric speciation events occur

Silversword Alliance in Hawaii

The Tempo of Speciation

Gradualism Punctuated

Equilibrium

Evolution & Developmental Biology (Evo-devo)

Slight genetic differences can can lead to major morphological differences Especially for genes that control the rate,

timing, & spatial pattern of an organism’s form as it develops

Rate & Timing: Heterochrony (general

term) Allometric growth

(proportioning that gives a body its specific form)

Paedomorphosis (sexually mature species with juvenile characters because sexual development was faster than somatic development)

Spatial Pattern: Homeotic genes

(determine where a pair of appendages will be located)

Does evolution have a goal?

NOPE! There is no specific direction that a species is trying to follow & that’s why you see so many evolutionary branches that end Think about species selection: the species that

survives the longest will determine the next evolutionary trend

Stanley compares species to an individual (speciation is birth, extinction is death, & new species created from this one are the offspring)