The Origin of Species Chapter 24

Lunch Thursday Speaker from Hawai'i Institute of Marine Biology!!

Biological species concept A population whose members have the potential to interbreed with one another in nature to produce viable, fertile offspring, but who cannot produce viable, fertile offspring with members of other species

Reproductive Isolation Barriers that prevent two species from producing viable fertile hybrids

Pre-zygotic barriers Do not allow species to mate Does not allow fertilization of eggs

Habitat Isolation Species living in different locations may never meet and thus will never mate.

Behavioral Isolation If mating behaviors are dissimilar among species, mating may not occur Unique behaviors allow own species recognition

Temporal Isolation When species mate at different times of year and are not able to breed with one another

Mechanical Isolation The reproductive organs of two species are incompatible

Gametic Isolation Gametes of 2 species may not meet due to chemical barriers preventing survival of sperm Important to aquatic species

Postzygotic Barriers Barriers that prevent the hybrid zygote from becoming an adult (or producing offspring).

Reduced hybrid viability Genetic incompatibility may force miscarriage of hybrid embryo

Reduced hybrid fertility Adult hybrid organisms can be sterile

Hybrid Breakdown 1st generation hybrids are viable and fertile but subsequent generations are not (may be sterile and feeble)

Limitations to the BSC Does not account for asexually reproducing organisms, like bacteria Does not account for interbreeding that may have happened in fossil species

Mode of speciation: Allopatric Two species are separated by a physical barrier that causes them to be isolated Over time, gene frequencies diverge due to selection, mutation, or genetic drift

Mode of speciation: sympatric New species arise within parent population in geographically overlapping populations In plants: Allopolyploidy (getting an extra set of chromosomes in cell division) In animals: less common; subset of population becomes reproductively isolated b/c of switch to a habitat or food source not used by parent population OR sexual selection

Adaptive Radiation Rapid evolution of many species from single ancestor when that ancestral species colonizes a new area or environmental changes cause extinctions and new ecological niches open up (Changing to survive new habitations)- example: Hawaiian honeycreepers

Gradualism vs. Punctuated equilibrium Gradualism: Gradual accumulation of small changes over time Punctuated Equilibrium: long periods of stasis punctuated by rapid changes

Phylogeny and Systematics Chapter 25

Cladistics and Phylogeny Cladistics: study of relationships among organisms shown by common characteristics not found in ancestral group Cladogram: diagram showing relationships among organisms

Cladogram