Origin of Species The term species refers to individuals in a population that are free to breed and that produce viable offspring, without outside intervention, that can carry on the lineage. Speciation, or how species arise, can be further broken down using the concepts of micro and macroevolution. – microevolution - species arise through a divergence of breeding populations that subsequently change the gene frequencies in a gene pool – macroevolution - evolutionary change above the species level such as the evolution of birds from dinosaurs

Biological Species A biological species cannot (or does not) breed with members of a different population. The concept hinges on the concept of reproductive isolation or the existence of biological factors that inhibit or prevent reproduction.

Prezygotic Barriers prezygotic barriers - factors that prevent mating or inhibit fertilization – habitat isolation - species that rarely come into contact due to occupation different habitats – temporal isolation - time of day – behavioral isolation - courtship rituals that attract mates are different – mechanical isolation - morphological differences (parts don't fit) – gametic isolation - sperm of one species cannot penetrate egg of another

Postzygotic Barrier postzygotic barrier - prevents a hybrid from developing or to become fertile as an adult – reduced hybrid viability - genes of the different parents impair the development and viability of the offspring – reduced hybrid fertility - adult hybrid is sterile (mule) – hybrid breakdown - fertility is decreased with each subsequent generation (more common in plants)

Factors that lead to speciation allopatric speciation - occurs when a population becomes geographically isolated over a long period of time.

Factors that lead to speciation sympatric speciation - occurs between members in a breeding population. Mechanisms include chromosomal changes and non- random mating that changes gene flow within a population. – polyploidy having more than 1 set of chromosomes autopolyploildy - more than 2 sets of chromosomes from a single species. More common in plants. allopolyploidy - two different species interbreed creating a hybrid with an odd # of chromosomes. The offspring then can mate with each other but not with the parental generation forming a new species – Parapatric or habitat differentiation - occurs when a portion of a populations starts to exploit a resource in the habitat which the parent generation cannot use. This can lead to differential sexual selection and speciation.

Factors that lead to speciation Adaptive radiation - the evolution of many diversely adapted species from a common ancestor upon introduction to a new environment (founder effect). Ex: HI islands and introductions of species. Displays the model of gradualism.

Changes that lead to macroevolution. shows model of punctuated equilibrium - new species is formed from parent then is stable (stasis) for many years evolutionary novelties through genes that control development - heterochromy – allometric growth changes - affected by genes that control body proportioning by affecting rate and timing – paedomorphosis - an alteration in the timing of juvenile and adult characteristics (especially in species that have distinct morphological periods) – homeotic gene changes - alter body plan (where wings or appendages form)