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The Nature of Species: Understanding Species Distinctiveness and Connection

This informative text explores the concept of species, focusing on the uniqueness of populations within a locale and the relationships between different populations of the same species. It delves into the biological species concept coined by Ernst Mayr, speciation processes, and reproductive isolation mechanisms. The text also discusses prezygotic and post-zygotic isolating mechanisms such as geographic, ecological, behavioral, temporal, mechanical, gamete fusion, and hybridization. Through examples like the Eastern and Western Meadowlark songs, readers can grasp the intricacies of species differentiation and the barriers to interbreeding.

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The Nature of Species: Understanding Species Distinctiveness and Connection

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  1. The Origin of Species Chapter 22

  2. The Nature of Species “Species” must account for 2 things: • distinctiveness of sp. (populations) together at a single locale

  3. The Nature of Species • connection that exists among diff. pop. belonging to the same sp. • Subspecies • ind. in sp. that occur in diff. areas and are distinct from one another

  4. The Nature of Species Biological species concept: • defined by Ernst Mayr • population whose members can interbreed & produce viable, fertile offspring • reproductively compatible Distinct species:songs & behaviors are different enough to prevent interbreeding Eastern Meadowlark Western Meadowlark

  5. Song Comparisons Eastern Meadowlark http://www.youtube.com/watch?v=Th4T4YrtR2o Western Meadowlark http://www.youtube.com/watch?v=lvAUgFb1cLY

  6. The Nature of Species Darwin never actually tackled how new species arose… “Both in space and time, we seem to be brought somewhat near to that great fact—that mystery of mysteries—the first appearance of new beings on this Earth.” -Charles Darwin

  7. The Nature of Species Speciation • the process by which new sp. arise by: • transformation of 1 sp. into another (anagenesis) • splitting of 1 ancestral sp. into 2 descendant sp. (cladogenesis)

  8. Reproductive Isolation Reproductive isolation • pop. whose members don’t mate with each other or who can’t produce fertile offspring • isolating mechanisms: • Geographic • Ecological • Behavioral • Temporal • Mechanical • Gamete fusion • Hybridization

  9. Isolating Mech. Poster • Name mechanism • Is mechanism prezygotic or postzygotic? • Define/Describe how mechanism works • Give 3 examples of mechanism

  10. Prezygotic Isolation • Geographic Isolation • sp. occur in different areas • physical barrier Harris’s antelope squirrel inhabits the canyon’s south rim (L). Just a few miles away on the north rim (R) lives the closely related white-tailed antelope squirrel

  11. GeographyIsolation Two different types of geographic isolation: • Allopatric speciation • result of geo. isolation • Sympatric speciation • occurs without geo. iso. (in the same geo.)

  12. Prezygotic Isolation • Ecological Isolation • Species occur in same region, but occupy different habitats so rarely encounter each other 2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial • lions & tigers could hybridize, but they live in different habitats: • lions in grasslands • tigers in rainforest Tiglon: Cross between a male tiger and a female lion

  13. Prezygotic Isolation • Behavioral Isolation • Unique behavioral patterns & rituals isolate species • identifies members of species • attract mates of same species • courtship rituals, mating calls Blue footed boobies mate only after a courtship display unique to their species http://www.youtube.com/watch?v=LLdC-8nqPog&feature=related

  14. Prezygotic Isolation 4. Temporal Isolation • Species that breed during different times of day, different seasons, or different years cannot mix gametes Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

  15. Prezygotic Isolation Plants 5. Mechanical Isolation • Morphological differences can prevent successful mating Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen.

  16. Prezygotic Isolation Animals • For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer • lack of “fit” between sexual organs: hard to imagine for us… but a big issue for insects with different shaped genitals! Damsel fly penises

  17. Prezygotic Isolation 6. Gametic isolation • Sperm of one species may not be able to fertilize eggs of another species • Mechanisms: • biochemical barrier so sperm cannot penetrate egg • Sperm cannot penetrate egg • chemical incompatibility • sperm cannot survive in female reproductive tract Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

  18. Post-zygotic Isolation Hybridization • Hybrid offspring don’t develop into a viable, fertile adult • reduced hybrid viability zebroid Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.

  19. Post-zygotic Isolation • reduced hybrid fertility • Even if hybrids are vigorous they may be sterile • chromosomes of parents differ in number or structure & meiosis in hybrids fail to produce normal gametes Mules are vigorous, but sterile Horses have 64 chromosomes (32 pairs) Donkeys have 62 chromosomes (31 pairs) Mules have 63 chromosomes!

  20. Post-zygotic Isolation • hybrid breakdown • Hybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterile In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species.

  21. Adaptive Radiation Adaptive radiation • closely related sp. ev. from a com. ancestor by adapting to different parts of the env. • caused by OR results in geographic isolation

  22. The Pace of Speciation Punctuated Equilibrium Gradualism • Does speciation happen gradually or rapidly? gradual accumulation of small changes over long time • rapid bursts of change mixed with long periods of little or no change Charles Darwin Charles Lyell Stephen Jay GouldNiles Eldredge

  23. The Pace of Evolution Evolution most likely includes both!

  24. Speciation and Extinction Speciation, through time, has surpassed extinction • 5 mass extinctions have occurred • not all groups of organisms are affected equally during extinctions

  25. Speciation and Extinction Consequence of extinction • previously dom. groups may perish, changing the course of ev.

  26. Speciation and Extinction 6th extinction is underway • Estimates: • 1/4th of all species will become extinct in the near future • rebound in sp. diversity may be slower than following previous mass extinction events • large proportion of the world’s resources will be taken up by human activities

  27. The Future of Evolution Human influences on the environment affect the evolutionary processes • changing patterns of NS • global climate change • decreased pop. sizes increase the likelihood of genetic drift • geographic isolation removes effect of gene flow • chemicals and radiation could increase mutation rate • introduction of sp. into areas they aren’t naturally found

  28. The Future of Evolution Tigers now exist in geographically isolated populations

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