Chapter 18B Formation of New Species PDF

Chapter 18B Formation of New Species The bridge between micro and macroevolution A common definition of species – a group (of organisms) whose members possess similar anatomical characteristics and have the ability to interbreed Other definitions: bi...

Chapter 18B Formation of New Species The bridge between micro and macroevolution A common definition of species – a group (of organisms) whose members possess similar anatomical characteristics and have the ability to interbreed Other definitions: biological species concept – a group of populations whose members have the potential to interbreed in nature and to produce viable and fertile offspring with each other, but not with members of other such groups morphological species concept – defining species by measurable anatomical criteria paleontological species concept – based on morphological differences known only from the fossil record ecological species concept – defining species in terms of ecological roles (niches) phylogenetic species concept – a set of organisms with a unique genetic history—that is, as one branch on the tree of life allopatric speciation sympatric speciation ancestral population radical change in segregated by genome of geographic barrier subpopulation (divided into two or reproductively more geographically isolates it from the isolated populations) parent population common rare in nature “allo” = other “sym” = together Allopatric speciation and isolation by distance Genetic incompatibility https://www.pbs.org/video/nova-evolution-in-action/ Ensatina salamanders “Rassenkreis” (group of races)  Prezygotic barriers Postzygotic barriers are evolutionary adaptations are biological accidents that prevent hybridization that can result in decreased before fertilization or zero fitness different habitats minimize contact distinct body structural color and differences in courtship genitalia may display can prevent prevent accidental active at different hybridization sperm transfer times of day, year, (many birds, (many plants, or breeding season frogs, insects) insects, spiders)  hybrid offspring does not inability of hybrid F1 offspring future generations develop sperm to fuse may be healthy but are less viable properly (most with ovum of cannot reproduce (some ornamental organisms) other species as easily as their garden flowers, (e.g., chemical parents (or at all) crops: cotton, rice) barrier as in sea urchins)  s r de o h hil o + c d r r r ste ce ty u b po edu tili = or r fer ) f rid le b u hy (m My diploid karyotype is 62 chromosomes. Þ Can’t take half of 63!!!... Mine is 64. there’ll be no meiosis for me!  When prezygotic barriers fail... male mallards are conspicuously different speculum (wing ornament) is blue for mallards & purple for black duck American Mallard Duck American Black Duck (occasional hybrid accidents are a waste of genes)  Sympatric speciation adaptive radiation – emergence of numerous species from a common ancestor (in an environment that presents a diversity of new opportunities and problems) ecological niche – the unique environmental role of a species (every resource that it uses, and all aspects of its habitat that allow it to thrive) http://media.hhmi.org/biointeractive/films/OriginSpecies-Lizards.html “Empty” niches provide the potential for diversification; where (or when) would such opportunities arise?  A mechanism for sympatric speciation: polyploidy – mutational change (meiotic failure resulting in diploid gametes) may produce an offspring with more than two sets of chromosomes Sexual selection – natural selection arising through preference by one sex for certain characteristics in individuals of the other sex. Habitat differentiation – Sympatric speciation scheme in which mutations in a population allow individuals to exploit different conditions within the same environment.  A mechanism for sympatric speciation: some plant species have their origins in an accident of cell division polyploidy – mutational change (meiotic failure resulting in diploid gametes) may produce an offspring with more than two sets of chromosomes, all derived from a single species “poly” = many “ploidy” = # chromosomes  Types of Polyploidy Autopolyploidy Allopolyploidy Polyploid plants clothe and feed us oats, potatoes, bananas, peanuts, barley, plums, apples, sugarcane, coffee, cotton, tobacco... wheat: 20 species, including bread wheat  Polyploidy produces cryptic species; this happens (rarely) in animals too! Cope’s gray treefrog Common gray treefrog Hyla chrysoscelis Hyla versicolor diploid (24 chromosomes) tetraploid (48 chromosomes) both are native to Eastern North America where their ranges overlap, they are distinguishable only by the male mating call (speed) at a given temperature  A mechanism for sympatric speciation: Sexual selection – natural selection arising through preference by one sex for certain characteristics in individuals of the other sex.  A mechanism for sympatric speciation: Habitat differentiation – Sympatric speciation scheme in which mutations in a population allow individuals to exploit different conditions within the same environment. The three outcomes of hybridization  The three outcomes of hybridization collared (Ficedula albicollis) and pied flycatchers (Ficedula hypoleuca) Reinforcement The three outcomes of hybridization Fussion  Hybrid zones and reproductive isolation Bombina bombina X variegata Stability How many changes to create a new species? How often do they speciate? How fast?  The time course of speciation Punctuated equilibria (Niles Eldredge and Stephen Jay Gould) Gradualism Hyla chrysoscelis 2n=24 Hyla versicolor Hybrid, 4n=48 Hyla cinerea 2n=24