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Populations Widely separated populations have less opportunity to share gene pools Observable differences among populations occur and are maintained Groups.

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Presentation on theme: "Populations Widely separated populations have less opportunity to share gene pools Observable differences among populations occur and are maintained Groups."— Presentation transcript:

1 Populations Widely separated populations have less opportunity to share gene pools Observable differences among populations occur and are maintained Groups –Subspecies, varieties, subpopulations

2 Fig 24.1 pg 611 Fig 24.2 pg 612 (Adapted from Clausen et al., 1948)

3 Phylogeography Study of evolutionary processes regulating the geographic distributions of lineages/groups –Using reconstruction of genealogies of individual genes, groups of genes or populations –Reveal patters of migration, population bottlenecks, and founder effects Human blood types –Genetic distance African, Caucasian, Greater Asian, Amerindian, Australoid Fig 24.3 pg 616 (Adapted from Nei and Roychoudhury.)

4 Adaptational Patterns Forces producing differences within a population are often adaptive, selective forces of environment Ecogeographical rules –Bergmann's rule Relates endothermic vertebrate body size, to average environmental temperature –Gloger's Rule Individuals more heavily pigmented in warm, humid areas than in cool, dry areas

5 Fig 24.6 pg 620 Fig 24.5 pg 619 (From "The Distribution of Man," by William W. Howells, Scientific American, September © 1960 Eric Mose. Reprinted with permission.)

6 Behavioral Adaptations and Strategies Innate Behaviors –No prior learning or experience –Growth patters, plants, fungi sessile animals Instincts –Complex innate behaviors –Genetically controlled –Drosophila courtship behavior Learned behavior –Flexible, often more complex –Learn and practice Genetic contribution Social relationships –Evolutionary stable strategies Reciprocal altruism Fig 24.7 pg 621

7 Mating Systems: Sexual Competition and Selection Males and females often differ in cost of reproduction –Female investment in producing eggs Female choice –Seek parental investment from male Males –Genes benefit from little discrimination Competitive armaments –Polygynous species –One male mates with many females

8 Fig 24.8 pg 621 (From Darwin.)

9 Origin of Species Barriers to gene flow between populations accelerate formation of distinctive groups Speciation –A qualitative change accompanied by reproductive separation or isolation, leads to population differences and species differences Isolating Mechanisms –Allopatric, vicariance speciation E.g. natural physical barrier –Peripatric speciation Budding off of "founder" colony –Parapatric Gene flow remains possible

10 Fig 24.9 pg 624 VicariancePeripatricParapatric

11 Isolating Mechanisms Prezygotic –Seasonal or Habitat Isolation –Behavioral or Sexual Isolation –Mechanical Isolation Postzygotic –Gamete mortality –Zygote Mortality, hybrid inviability –Hybrid Sterility

12 Modes of Speciation Sequential Allopatry and Sympatry Fig pg 626 (From Genetics Third Edition by Monroe W. Strickberger. Copyright © 1985 by Monroe W. Strickberger. Reprinted by permission of Prentice Hall, Inc., Upper Saddle River, NJ.)

13 Bottlenecks and the Founder Effect Small, isolated population –Exposed to genetic drift, increased homozygosity from inbreeding, and changes in adaptive landscape Radical change in selection pressure Resulting in coadapted gene combinations "Picture-winged" Drosophilidae, Hawaii

14 Genes and Speciation "Speciation genes" –Sexual traits Exhibit greater variation between species Less variation within species –Changes is sexual traits correlating with speciation events

15 Hybridization Viable, fertile hybrids between two species, zones of hybridization –Hybrids better adapted than parents may become isolated Introgressive hybridization –Fertile hybrids act as intermediaries –Introduce genes from one species into another Frequency of hybridization –Difficult to estimate, perhaps 10% –Impact may be greater than frequency

16 Can Species Differences Originate Sympatrically? Is geographic isolation required for speciation? Polymorphism, for habitats within location Cichlids –Aggressive behavior –Territoriatlity –Specialized diets –Phenotypic plasticity Fig pg 274

17 Rates of Speciation Difficulties –Palaeontological data "Lumpers" versus "splitters" Taxonomic levels Generation times –Molecular Which genes, and how many Studies demonstrate rates vary Quantum evolution Microevolution

18 Evolutionary rates (Adapted from Simpson.) Fig pg 631

19 Rates of Evolution Differences in rates –Structure of Populations Evolution can occur faster in population divided into demes –Adaptive and Developmental Constraints –Changes in Selection Direction Intensity Different times and groups Darwin Units (D) –Difference in character's average dimensions Punctuated or Gradual? Continuous or Discontinuous?


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