Outstanding Origin of Species Chapter 24

Vocabulary Macroevolution- broad pattern of evolution over long time spans Speciation-process where one species splits into two or more species Anagenesis (phyletic evolution)-accumulation of changes associated with the transformation of one species into another

Vocabulary (cont.) Cladogenesis (branching evolution) - budding of one or more new species from a parent species that continues to exist *Promotes biological diversity by increasing number of species

Vocabulary Biological Species Concept- a population or group of populations whose members have the potential to interbreed with one another in nature to produce viable, fertile offspring *Hinges on Reproductive Isolation- the existence of biological factors that prevent two species from producing fertile offspring

Pre-Zygotic Barriers to Reproduction “Before the zygote”, Block fertilization Habitat Isolation-two species that live in different habitats within the same area may never encounter each other Behavioral Isolation-sexual signals that attract mates and elaborate behavior unique to a species (songs, mating dances, etc)

Pre-Zygotic Barriers to Reproduction Temporal Isolation - two species that breed during different times of day, different seasons or different years can’t mate Mechanical Isolation - anatomical differences might prevent closely related species from mating

Pre-Zygotic Barriers to Reproduction Gametic Isolation - even if gametes from different species meet, they rarely fuse to make a zygote

Post-Zygotic Barries to Reproduction Prevents a hybrid zygote from developing into fertile adult Reduced Hybrid Viability - genetic incompatibility may abort development of hybrid during embryonic development Reduced Hybrid Fertility - if two different species do mate and produce a hybrid, many hybrids are sterile and cannot produce offspring

Post-Zygotic Barries to Reproduction Hybrid Breakdown - occasionally, first generation hybrids are viable and fertile, but when hybrids mate the next generation is often feeble or sterile

Biological Species Ecological Niche Concept - species is defined in terms of their niche (role in the environment) Morphological species concept - relies on structural features to distinguish species Phylogenetic species concept - defines a species as a set of organisms with a unique genetic history

Modes of Speciation Allopatric Speciation - Geologic processes can fragment a population (ex. Mountain emerges) Amount that geography separates organisms depends on their ability to move (fly, swim) Allopatric speciation increases when population becomes small and isolated from others Ring species can be studied to see allopatric speciation in progress Adaptive radiation - evolution of many diversely adapted species from a common ancestor (ex. Finches on Galapagos)

How do reproductive barriers evolve? Must be intrinsic to organism and prevent interbreeding even when species are brought back together Most likely coincidental-not that organism is trying to make a barrier to reproduction Fruit fly experiment shows formation of pre-zygotic barrier due to different mating ritual When trying to mate same plant from diffeent areas of US, those that were close together could interbreed while farther apart were unable to interbreed

Sympatric Speciation Speciation takes place in geographically overlapping populations. Biological factors such as chromosomal changes and non-random mating reduce gene flow Polyploidy: cell division that results in extra sets of chromosomes Autopolyploid: individual that has more than two sets of chromosomes derived from a single species

Allopolyploid: two different species interbreed, combine chromosomes and produce a hybrid. Hybrid only mates with other hybrid

Punctuated Equilibrium Species diverge in spurts of relatively rapid change (thousands of years) followed by long periods of stasis (unchanging) – based on fossil evidence