1. Biological Species Concept Chapter 24 Section 1 Pgs. 488 – 492 Objective: I can describe multiple ways in which we define distinct species, so that I can participate in the debates surrounding it. Eastern meadowlark (Sturnella magna) Western meadowlark (Sturnella neglecta)

2. Definition of Species (Biological Concept) A group of organisms that can successfully breed within the group but are reproductively isolated from others Successful breeding = produce viable, fertile offspring Reproductively isolated = will not mate OR will not produce (viable, fertile) offspring Lots of debate and controversy today  “species problem”…

3. Reproductive Isolation Different organisms exist as different species due to reproductive isolation HOW they are isolated can be different A) Prezygotic Barriers (Isolating Mechanisms) A1) Habitat Isolation A2) Temporal Isolation A3) Behavioral Isolation A4) Mechanical Isolation A5) Gametic Isolation B) Postzygotic Barriers (Isolating Mechanisms) Can mate and produce offspring, but something “wrong” with offspring Won’t even try to mate Will try to mate, but can’t produce zygote/offspring

4. A) Prezygotic Barriers Isolate reproduction BEFORE making zygote (before fertilization/syngamy) A1) Habitat Isolation –live in different area Different habitats (different niches) No natural encounters Cannot try to mate, unless forced to “unnaturally”

5. “Geographic Isolation” If two organisms live apart (opposite ends of the world) in different areas and would never naturally meet together to even try to reproduce, should you consider them different species? If you brought them together, and they could reproduce, should you consider them different species? BIG Debate… THIS Book does not consider geographic isolation its own barrier to reproduction (includes it under habitat isolation)

6. A) Prezygotic Isolating Mechanisms A2) Temporal Isolation Separated by time (season/day) Different mating/breeding/brooding times Cannot even try to mate, unless forced to unnaturally

7. A) Prezygotic Barriers A3) Behavioral Isolation Will only mate if follow correct mating/courtship behavior Note: Predatory/competitive behavior prevents mating

8. A) Prezygotic Isolating Mechanisms A4) Mechanical Isolation Morphological differences prevent mating (i.e. structural differences, differences in size of sexual organs)

9. A) Prezygotic Barriers A5) Gametic Isolation Prevention of Gamete Fusion Sperm can only fertilize correct egg Usually chemically-based (protein receptors on cell membranes)

10. B) Postzygotic Isolating Mechanisms Capable of mating and producing offspring (performed fertilization), but reproduction NOT successful in some way… (successful reproduction = viable, fertile offspring) Hybrid = offspring of 2 different species

11. B) Postzygotic Barriers: 3 Types B1) Reduced hybrid viability Hybrid does not survive birth/born weak & won’t survive in environment (nat. selec.) B2) Reduced hybrid fertility Hybrid offspring is sterile/infertile B3) Hybrid breakdown Hybrid will not be able to produce offspring that can sustain species

12. Examples Won’t even try to mate ELEPHANT MOUSE Same or Different species Behavioral Isolation Mechanical Isolation If DID try to mate, then…

13. Examples Won’t even try to mate – maybe kill each other for resources RAT MOUSE Same or Different species Behavioral Isolation

14. Examples Same speciesSame or Different species

15. Examples Can attempt to mate, but no fertile, viable offspring produced Same or Different species Gametic Isolation

16. Examples Can attempt to mate, but no fertile, viable offspring produced Same or Different species Gametic Isolation In fact, dogs are pretty crazy…(spay/neuter!) But it ain’t just dogs…

17. Examples HORSE DONKEYMULE Same or Different species Mule is born sterile/infertile Postzygotic Isolation Reduced hybrid fertilityWhat type of postzygotic?

18. Examples HORSE Same or Different species Zorse is born sterile/infertile Postzygotic Isolation Reduced hybrid fertility ZEBRA ZORSE HEBRA What type of postzygotic?

19. Examples LIGER TIGLON Same or Different species Mating does not occur naturally (different habitats/niches) Habitat Isolation Postzygotic Isolation Reduced Hybrid fertility Hybrid breakdown Hybrids cannot mate together (or can they…?) What type of postzygotic?

20. Examples CHIHUAHUALABRADOR Same or Different species Can successfully breed together CHIHUAHUA/LAB MIX But they are different Same species breeds

21. Examples Same or different species But they are different Can successfully breed together Same species races

22. Examples Same or Different species Mating does not occur naturally (different habitats/niches)…or does it? Habitat Isolation Need more data on hybrid mating… Is there postzygotic? GROLAR BEAR PIZZLY BEAR

23. Criticisms of Bio. Species Con. Based on reproductive isolation Viable, fertile hybrids violate this Most common in plants, some animals Based on natural reproductive isolation Should it? If can reproduce unnaturally… And what about…(2 problem situations) Asexually reproducing organisms? Reproductive isolation does not apply to prokaryotes! Extinct Organisms (Fossils/dinosaurs) Can’t see which dinosaurs have sex…

24. Other Definitions of Species Morphological species concept Species should be defined on how they look  actually, their phenotype Great for prokaryotes (structures, reactions to chemicals/medicines) But what if male/female of species look different…? This is called sexual dimorphism…remember? Paleontological species concept Based on fossils (how we define and differentiate different species of dinosaurs) Type of morphological species concept It’s the best we got for extinct species…

25. Other Definitions of Species Ecological species concept Species should be defined by natural selection – what type of niche it fills Two finches that look alike and live in same island eat different foods entirely… Takes care of lion/tiger debate …but grolar Phylogenetic species concept Species should be defined based on its evolutionary history (phylogeny) Eats cactus only Eats insects only species = immediate family

26. Summarizing the Controversy Scientists argue about whether two organisms are in the same species or not ALL THE TIME Have arguments because our definition of species is faulty Maybe, there is no single, universal definition of species Maybe just make judgment call made on case-by-case basis Or maybe cop-out with “subspecies”