ECOL 182R 1st Edition Lecture 2 Outline of Last Lecture I Alleles A Frequencies over time II Four mechanisms of evolution A Natural selection B Genetic drif C Gene flow D Mutation Outline of Current Lecture I Population species A Problems of interbreeding II How new species form A Isolation B Divergence III Speciation rates Current Lecture Quick review from last lecture What two evolutionary processes were required to see the increase in the number of white lizards in the sand dunes Mutation Natural Selection Of the 4 processes which 1 Tend to reduce genetic variation Genetic drif 2 Tends to increase genetic variation Gene flow mutation 3 Makes organisms more adapted to its environment Natural selection Population group of potentially interbreeding individuals of the same species coexisting in the same place and time Species capable of interbreeding and reproductively isolated from other groups III Capability potential of interbreeding is called the biological species concept IV By capable of interbreeding explanation Species may consist of several populations all capable of interbreeding but rarely or never actually have the opportunity like the two different populations of Agelaius phoeniceus birds V Reproductively Isolated explanation two species in same genus they re related but they VI VII VIII IX X don t breed with each other So who actually interbreeds The first problem of not knowing is that we re rarely actually out in nature watching it happen and ofen we use clues from morphology but it can still be tricky Paleontologists rely on morphology and date when they found species to see if they were even alive in the same period They look for areas in morphology that are discontinuous Second problem is that people can force interbreeding that would never normally happen Ex Liger cama camel and llama Should they be considered species Third problem is that some organisms never have sex to begin with like some bacteria protists and fungi Scientists use DNA to find where the breakpoints are If they re looking at 100 different species they can see what the distance is between different organisms and how alike they are The more we know about organisms the more we know about morphology genetic information and behavior the more confident we can be that they re assigned tot the correct species How do new species form They diverge from existing species but how Isolation separation separating over time Genetic divergence and reproductive isolation they diverge over time by becoming reproductively isolated Speciation occurs at the nodes of phylogenetic trees One way species form One species is separated into two populations by a barrier they become physically separated Then each population adapts to the new habitat so they diverge genetically Then when if the populations overlap again they no longer interbreed So one interbreeding group is isolated in 2 subgroups Become more and more different Then they don t interbreed if brought back together How can a population break into 2 though Allopatric speciation a physical barrier arises that prevents interbreeding different countries Is thought to be the usual start to speciation Involves distances and a geographic barrier Ex allopatric speciation in the grand canyon or the Galapagos finches lost contact with each other and diverged so they look different have different beaks etc Sympatric speciation same country No physical barrier arises but interbreeding stops for some other reason There are two types of this Autopolyploidy multiplication of chromosome number Due to spontaneous duplication of chromosomes or the combination of parents chromosome number in offspring when 2 species successfully mate There s a meiotic error so they make diploid instead of haploid Triploid hybrid is ofen sterile Consequence If polyploid offspring can mate with each other but not with their diploid parents they have become a different species Autopolyploidy is very common in angiosperms specifically the coffee plant Different species have different numbers of chromosomes Some are large in size and successful Temporal Isolation separation in time Example hawthorn fruit fly They re native to US attracted to fruit smell and lay eggs in fruit Mutation in these flies at some point made them attracted to apples so they began laying eggs in apples Hawthorn and apples fruit at different times causing immediate separation in time SO these flies are separated in time The ones that like hawthorn mate with each other and the ones that like apples mate with each other which is where speciation begins You can make them breed but they re already genetically disinct A How does isolation occur b afer initial separation groups become reproductively isolated from each other They don t mate or make fertile offspring when they do B What prevents them from interbreeding Prezygotic barriers occur before zygote is formed Examples There s a barrier in space or time so these individuals never meet Behavioral isolation they recognize each other they meet but females won t accept mating Many animal species have elaborate courtship rituals where the evaluate the mates but discriminate against the wrong species Postzygotic the mating occurs but something goes wrong afer that Barriers afer zygote forms Hybrid inviability hybrid zygotes don t develop or die before birth Hybrid sterility hybrids survive but are sterile Ex Mule XI DIVERGENCE Why do they diverge so much A 1 Natural selection may reinforce reproductive isolating mechanisms Ex Closely related jumping spiders Ofen behaviors that keep species apart courtship are more different when the species are in sympatry Why In allopatry they re pretty similar Because they re trying to differentiate themselves because the cost of mating with the wrong species might be huge Hybrids are produced that are not as fit as either pure species They may even be inviable Therefore there is selection for even more reproductive isolation B 2 Once isolated species adapt to local conditions Ex Those galapagos finches adapting to different food Speciation Rates What factors drive speciation Why are the rates different We don t really know but we can see that specialization has something to do with it Ex True bugs can be plant feeders or predators In these bugs the lineages of the specialist herbivores tend to have many more species than the generalist predator lineages Sexual selection is another thing that drives speciation It can lead to a quicker rate of