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SPECIES & SPECIATION

SPECIES & SPECIATION. (a) In your own words define what is the species? (b) What is speciation?. SPECIES & SPECIATION. The term " species " is used simultaneously for the unit of evolution & the unit of classification. It is a taxonomic category below genus. Species Classification.

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SPECIES & SPECIATION

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  1. SPECIES & SPECIATION (a) In your own words define what is the species? (b) What is speciation?

  2. SPECIES & SPECIATION • The term "species" is used simultaneously for the unit of evolution & the unit of classification. • It is a taxonomic category below genus

  3. Species Classification • There are seven main taxa: Kingdom, Phylum, Class, Order, Family, Genus, & Species. • Lets examine Humans and the black mamba (snake) classification in the next slide:

  4. Classification Levels Man Black mamba (snake) Kingdom: Animalia, ???????? Phylum: ????????, Vertebrata, Class: Mammalia, ??????? Order: ???????, Squamata Family: Hominidae, Elapidae Genus: ?????, Dendroaspis Species: H. sapiens. D. polylepis.

  5. Classification Levels Man Black mamba (snake) Kingdom: Animalia, Animalia, Phylum: Vertebrata, Vertebrata, Class: Mammalia, Reptilia Order: Primate, Squamata Family: Hominidae, Elapidae Genus: Homo, Dendroaspis Species: H. sapiens. D. polylepis.

  6. The Concept of a Species: Historical (a) Typological Species Concept In this concept a species is just a 'type' of organism. Linnaeus (1758) asserts "Species are as many as were created in the beginning….“

  7. The Concept of a Species: Historical (b) Nominalistic Species Concept species are named “Just” for convenience. Darwin (1859) says “I look at the term species, as one arbitrarily given for the sake of convenienceto a set of individuals closely resembling each other....". E.g., Class Amphibia = tetrapods without scales. Homo sapiens = "featherless bipeds". Taxonomic categories are arbitrary: Ex.: "bats + birds" are flying animals, "whales + fish" are swimming animals etc

  8. The Concept of a Species: Modern (a) Biological Species Concept (BSC). Species are defined as groups of interbreeding natural populations that are reproductively isolated from other such groups. This is the most widely used concept among ecologists. There are three key points under BSC: (i) Interbreeding, meaning that species are gene pools. (ii) Natural Populations. It means species are an ecological unit and must be understood with their environment. (iii) Reproductively isolated. Species is a reproductive unit.

  9. Reproductively isolated… • In this case there are • Species Reproductive Isolating Mechanisms (RIMs) that prevent mating outside the species as well as • Species Recognition Mechanisms (SRMs) that allow recognition of potential mates.

  10. The Concept of a Species: Modern (b) Evolutionary Species Concept (EvSC) • An evolutionary species is a single lineage of ancestor-descendant populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate. • This is the most popular concept among paleontologists.

  11. So what is the best definition of a species? • Most scientists feel that the biological species concept should be kept, but with some qualifications. • It can only be used with living species, • The real test applies to species that have the potential to interbreed.

  12. The Process of Speciation • One of the biggest questions among biologists has been how do species arise? • Members of species differ genetically,ecologically, and in their behavior and morphology from other species. • There is fair agreement that the crucial event, for the origin of a new species, is reproductive isolation. • The major isolating mechanisms are outlined below

  13. Major Isolating Mechanisms • Premating or prezygotic (prevent hybrid zygote) • Ecological or habitat isolation, • Seasonal or temporal isolation, • Sexual or ethological isolation, • Mechanical isolation, • Gametic isolation.

  14. Major Isolating Mechanisms • Postmating or zygotic isolating mechanisms • Hybrid inviability, meaning that hybrids have reduced viability • Hybrid sterility. In this case F1 hybrids fail to produce functional gametes e.g a mule • Hybrid breakdown. Here the F2 hybrids have reduced viability or fertility.

  15. Types of Species Formation 1. AllopatricSpeciation • Two populations should be separated by a physical, geographic barrier, • The separated populations then undergo independent evolution, • Isolating mechanisms also evolve to reduce chances of interbreeding, • If the barrier is removed and the two separated populations fails to interbreed then the process of speciation is complete

  16. Types of Species Formation • This is the most widely accepted hypothesis of species formation. • The most popular example of allopatric speciation is the Darwin finches in the Galapagos Islands. • Since Darwin's time, these birds have provided a case study of how a single species reached the Galapagos from Central or South America gave rise to the 13 species that live there today.

  17. Types of Species Formation 2. Parapatric speciation • A new species arise in the absence of geographical barrier. • If a population range occurs over vast area and can disperse over only a small portion of this range, then gene flow across these great distances would be reduced. • This situation is likely to occur in organisms that move very little, such as plants, moles, reptiles and flightless insects. • Genetic isolation arising simply from distance separating subpopulations could thus lead to "parapatric" speciation. • It is thought that the enormous species diversity of the rainforests e.g., arise from parapatric speciation.

  18. Types of Species Formation 3. Sympatric Speciation • Formation of two or more species from a single ancestral species all occupying same geographic location. • Some evolutionary biologists don't believe that it ever occurs. • They feel that interbreeding would soon eliminate any genetic differences that might appear. • But Dolph Schluter provide evidence for sympatric speciation,

  19. Types of Species Formation: Sympatric • Two separate species of freshwater sticklebacks fishes were studied on five different lakes. • In each lake, there existed two separate species (i) a large benthic species with a large mouth that feeds on large prey, (ii) a smaller limnetic species with a smaller mouth that feeds on the small planktons in open water

  20. Types of Species Formation: Sympatric • DNA analysis showed that the two species in each lake were more closely related to each other than they are to any of the species in the other lakes. • Nevertheless, the two species in each lake were reproductively isolated; neither mates with the other.

  21. Types of Species Formation: Sympatric • Their conclusion was that in each lake, what began as a single population faced such competition for limited resources that disruptive selection occurred and competition favoring fishes at either extreme of body size and mouth size over those nearer the mean • That was coupled with assortative mating — each size preferred to mate with its own-sized individuals. • That way it favored a divergence into two subpopulations exploiting different food in different parts of the lake

  22. Types of Species Formation: Sympatric The fact that this pattern of speciation occurred the same way on the five lakes suggests strongly that ecological factors in a sympatric population can cause speciation.

  23. Type of Speciation 4) Speciation by Hybridization (Polyploid) • Hybridization between related angiosperm is sometimes followed by a doubling of the chromosome number. • This normally happens during mitosis and meiosis • The resulting polyploids become fully fertile with each other although unable to breed with either parental type. • Nevertheless a new species has been created. • This appears to have been a frequent mechanism of speciation in angiosperms.

  24. Type of Speciation • Even without forming a polyploid, interspecific hybridization can occasionally lead to a new species of angiosperm. • Two species of sunflower, the common sunflower, Helianthus annuus, and the prairie sunflower, H. petiolaris, grow widely over the western half of the United States. • They can interbreed, but only rarely are fertile offspring produced.

  25. Species geographical variation • In ecology, an ecocline or simply cline (=gradient) describes an ecotone in which a series of biocommunities display a continuous gradient. • More technically, clines consist of ecotypes or form of species that exhibit gradual phenotypic and/or genetic differences over a geographical area,

  26. Species geographical variation • Typically this is a result of environmental heterogeneity. • Genetically, clines result from the change of allele frequencies within the gene pool of the group of taxa in question.

  27. Ring species • Ring species: distinct type of cline where geographical distribution is circular in shape, • Two ends of the cline overlap with one another, giving two adjacent populations that rarely interbreed • The populations elsewhere along the cline interbreed with their geographically adjacent populations as in a standard cline.

  28. The Larus gulls interbreed in a ring around the arctic Larus argentatus vegae, Larus argentatus smithsonianus Larus argentatus birulai Larus fuscus heuglini Larus argentatus argenteus Larus fuscus fuscus Larus argentatus argentatus

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