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Ch18.speciation tb and lect.docx

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BIOL 1000
Tamara Kelly

Chapter 18- Speciation – quiz 5 Ch. 18 (Speciation). These include: Sections 18.1, 18.2, 18.3, 18.6 (intro, 18.6a, 18.6b), 18.7 (intro, 18.7a, 18.7b), and 18.8 (intro, 18.8a, 18.8b, 18.8c). 18.1 What’s in the name ? speciation is known as the process of species formation. - in this chapter- the concept of species is explored and the mechanisms involved in speciation and appreciate the importance of names of organisms in biology. - communication can affect both inter- and intraspecifc behaviour 18.2 Definition of species what are species defined as? it can be described many different ways 1. Biological Species Concept (BSC)- group of species that can successfully interbreed together and produce fertile offspring. 2. Phylogenetic Species Concept (PSC)- group of species bound by a unique ancestry, 3. Ecological Species Concept - defines species as a group of organisms that share a distinct ecological niche. NSERT- definition of niche. Problems with the Biological Species Concept - the definition seems to work for species that reproduce sexually but it doesn't make sense for species that reproduce asexually. -scientific names?? - doesn't address species that hybridize Androdioesous species: composed of males and hermaphrodites (which produce both egg and sperm. Gynogenetic Species - species of only females that go through internal fertilization but still need sperm. They need mechanical stimulation by sperm donated by other male species. Therefore, they have to mate with other species. This goes against what the BSC definition. Hybridization: when species interbreed and produce fertile offspring. When sterile offspring are produced, it doesn't put them outside the definition of BSC. Recombination- is a principle advantage of sexual reproduction = explains it's prevalence among living organism. Sexual reproduction involves genetic recombination. 18.3 One size does not fit all - More than one definition of species in biology. - The diversity of species and their lifestyles partly reflects the mechanisms underlying the processes of speciation. - Gene flow among individuals in a population of conspecfics mixes their genetic material and is suppose to be like glue holding the species together. - Individuals of different species are genetically isolated but spp that produce fertile hybrids may not be naturally isolated. ( are they spp ??) - The BSC explains why individuals of a species generally look alike = the phenotype reflects the genotype = therefore individuals share similar genetic info. Biologists use the similarities and differences in morphological traits as convenient markers. - According to the MSC- individuals of the same spp share measurable traits that distinguish them from individuals of other species. - Paleonlogists use morphology to identify fossil to spp but also depend on info of the fossils' age. 18.6 Geographic Variation - subspecies: geographically separated pops of a species show a dramatic yet noticeable phenotypic variation. - Individuals from different spp usually interbreed where their geographic distributions meet and their offspring often exhibit intermediate phenotypes. 18.6a Ring Species: Genes Flowing between Some Populations - ring shaped geographic distribution that surrounds inhabitable terrain: pops next to the ring species can still exchange material directly, but gene flow b/w distant pops occurs only through intermediate pops. 18.b Clinal variation - Clinal changes are smooth patterns of variation along a geographic gradient. - Clines: when there is gene flow b/w adjacent pops that are adapting to slightly different conditions 18.7 reproductive Isolation - important to BSC** - reproductive isolating mechanism: biological characteristic that prevents the gene pools of two species from mixing even when they are sympatric. ( note: sympatric: occupying the same space at the same time. - 2 ways to achieve reproductive isolation : 1. prezygotic isolation: exert their effects before the production of a zygote or fertilized gag. 2. postzygotic isolation: operate after zygote formation Time relative to fertilization Mechanism Mode of action Prezygotic (pre mating) Ecological isolation Spp live in different habitats mechanism Temporal isolation Spp breed @ diff times Behaviourial isolation Spp can’t communicate Mechanical isolation Spp can’t physically mate Genetic isolation Spp have non-matching receptors on gametes Postzygotic (post mating) Hybrid inviability Hybrid offspring do not mechanism complete development Hybrid sterility Hybrid offspring can’t produce gametes Hybrid breakdown Hybrid offspring have reduced survival or fertility 18.7a Prezygotic Isolating Mechanisms: Isolation before fertilization - 5 mechanisms can prevent interspecific mating sot fertilizations and the production of hybrid( mixed spp) offspring 1. Ecological isolation - spp tht may share the same geographic region but in th different habitats. (ex. lions and tigers in the 19 century: lions in open grasslands and tigers in dense forest.) 2. Temporal isolation - spp tht may live in the same habitat but they mate at different times of the day or different seasons of the year. 3. Mechanical isolation- differences in the structure of copulatory organs prevent successful mating b/w two different spp. 4. Genetic isolation- refer to table 18.7b Postzygotic Isolating Mechanisms: Barriers after fertilization - refer to table above for summary 18.8 Geography of Speciation - Gepgraphy has a huge impact on whether gene pools have an opportunity to mix. - 3 modes of speciation 1. Allopatric= different homeland 2. Parapatric = para: beside 3. Sympatric = sym: together 18.8a Allopatric speciation: new spp develop from isolated pops - Allopatric speciationmost common) physical barriers subdivides a larger pop or when a small pop becomes separated from a spp’ main geographic distribution. - 2 stages 1. two pops become geographically separated preventing gene flow b/w them. 2. As the pops experience distinct mutations as well as different patterns of natural selection and genetic drift, they may have genetic differences tht isolate them reproductively. - Geographic separation: occurs when a barrier divides a large pop in two or more units. - In some cases, small pops become isolated at the edge of species’ geographic distribution .( ex. oceanic pops ) - A spp cluster results from after founding pop colonize an island or isolated land mass. - AP (allopatric pop) may reestablish contact when a geographic barrier is eliminated. - The secondary contact provides a test whether or not the pop have diverged into separate spp. If their gene pools did not differentiate much during their geographic separation, the pops will interbreed and merge. If they are different enough then they have become reproductively isolated. - Hybrid zones can be created when individuals of one pop mates with an ini from another pop. - If hybrid offspring have lower fitness than those produced from those who mated from the same pop. Natural selection(NS) will favour the ones produced from ini from the same pop. 18.8b Parapatric Speciation: new spp develop when pops span a barrier - Parapatric isolation : speciation arising from adjacent pops may occur if hybrid offspring’s have low relative fitness. - PS occurs when a spp is distributed across a discontinuity in environment conditions so tht NS favours different alleles and phenotypes on either side of
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