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◦ Until recently, over 500 species of cichlid fishes lived in East Africa’s Lake Victoria Copyright © 2009 Pearson Education, Inc.

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Presentation on theme: "◦ Until recently, over 500 species of cichlid fishes lived in East Africa’s Lake Victoria Copyright © 2009 Pearson Education, Inc."— Presentation transcript:

1 ◦ Until recently, over 500 species of cichlid fishes lived in East Africa’s Lake Victoria Copyright © 2009 Pearson Education, Inc.

2 Lake Tanganyika Africa Tanzania Kenya Uganda Lake Victoria Lake Malawi

3 ◦ Lake Victoria’s cichlids diversified 100,000 years ago (young species!) ◦ Why?? –Specialized mouthparts that allow them to specialize on different food sources –Bright colors of the males vary with species, as females chose males with specific colors ◦ Groups isolated by diet or female mate choice may have lost the ability to interbreed Copyright © 2009 Pearson Education, Inc.

4  Species: a group of organisms whose members can breed and produce fertile offspring, but who do not produce fertile offspring with members of other groups

5 Copyright © 2009 Pearson Education, Inc. ◦ Over the last 30 years, 200 species of cichlids have disappeared from Lake Victoria –Introduced predator (perch) eats them up –Pollution makes it difficult for females to see colors

6 Copyright © 2009 Pearson Education, Inc.  Speciation is the emergence of new species and increases diversity  Millions of species all arose from ancestor that lived 3.6 billion years ago

7 Copyright © 2009 Pearson Education, Inc. ◦ Taxonomy is the field of biology that names and classifies species and groups them into broader categories ◦ Binomial system gives every organism a genus and species name  Example: Homo sapien, Escherichia coli

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9 Order Genus Family Felis Felidae Mephitis Mustelidae Lutra Carnivora Canidae Canis Species Felis catus (domestic cat) Mephitis mephitis (striped skunk) Lutra lutra (European otter) Canis latrans (coyote) Canis lupus (wolf)

10 Copyright © 2009 Pearson Education, Inc. But how do we decide what is actually a species??

11 Copyright © 2009 Pearson Education, Inc. ◦ The biological species concept  Species is a population or group of populations whose members have the potential to interbreed in nature and produce fertile offspring ◦ Reproductive isolation prevents gene flow and maintains separate species

12 Copyright © 2009 Pearson Education, Inc. ◦ Can the biological species concept always distinguish species from each other?

13 Copyright © 2009 Pearson Education, Inc. ◦ The morphological species concept :  classifies organisms based on observable phenotypic traits  It can be applied to asexual organisms, fossils, and when we don’t know about inbreeding

14 Copyright © 2009 Pearson Education, Inc.  The ecological species concept:  Defines a species by its ecological role or niche –Consider the cichlids, which are similar in appearance but feed at different depths in the lake

15 Copyright © 2009 Pearson Education, Inc. ◦ The phylogenetic species concept:  Species as a set of organisms representing a specific evolutionary lineage –Morphological or DNA similarities or differences can be used to define a species –Defining the amount of difference required to distinguish separate species is a problem

16 Copyright © 2009 Pearson Education, Inc. ◦ Reproductive barriers serve to isolate a species gene pool and prevent interbreeding 1. Prezygotic (before sex) 2. Postzygotic (after sex)

17 ◦ Prezygotic Barriers: prevent mating or fertilization between species 1. Temporal isolation- two species breed at different times (seasons, times of day, years) Copyright © 2009 Pearson Education, Inc.

18 ◦ Prezygotic Barriers: prevent mating or fertilization between species 2. Habitat isolation: two species live in the same general area but not in the same kind of place Copyright © 2009 Pearson Education, Inc.

19 ◦ Prezygotic Barriers: prevent mating or fertilization between species 3. Behavioral isolation: there is little or no sexual attraction between species, due to specific behaviors Reproductive barriers keep species separate Copyright © 2009 Pearson Education, Inc.

20 ◦ Prezygotic Barriers: prevent mating or fertilization between species 4. Mechanical isolation: female and male sex organs are not compatible Reproductive barriers keep separate Reproductive barriers keep species separate Copyright © 2009 Pearson Education, Inc.

21 ◦ Prezygotic Barriers: prevent mating or fertilization between species 5. Gametic isolation: female and male gametes are not compatible Reproductive barriers keep species separate Copyright © 2009 Pearson Education, Inc.

22 ◦ Postzygotic Barriers : operate after hybrid zygotes are formed 1. Zyogotic mortality 2. Reduced hybrid viability most hybrid offspring do not survive 3. Reduced hybrid fertility hybrid offspring are vigorous but sterile 4. Hybrid breakdown- first generation hybrid fertile, loss in second generation Reproductive barriers keep species separate

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24 Copyright © 2009 Pearson Education, Inc. ◦ If two related species live in the same area, would natural selection favor the evolution of prezygotic or postzygotic reproductive isolating mechanisms?

25 Copyright © 2009 Pearson Education, Inc. MECHANISMS OF SPECIATION

26 Copyright © 2009 Pearson Education, Inc. ◦ In allopatric speciation, populations of the same species are geographically separated, separating their gene pools ◦ Changes in the allele frequencies of each population may be caused by __________?????

27 Copyright © 2009 Pearson Education, Inc. ◦ Gene flow between populations is initially prevented by a geographic barrier –The Grand Canyon and Colorado River separate two species of antelope squirrels A. leucurus A. harrisi South North

28 Copyright © 2009 Pearson Education, Inc. ◦ In sympatric speciation, new species may arise within the same geographic area as a parent species ◦ Gene flow between populations may be reduced by: 1. Polyploidy: multiplication of the chromosome number due to errors in cell division (plants) 2. Habitat differentiation (animals) 3. Sexual selection (animals) In sympatric speciation, speciation takes place without geographic isolation

29 a.b.

30 Copyright © 2009 Pearson Education, Inc. ◦ Hybrid zones: regions in which members of different species meet and mate producing some hybrid offspring How do you know if two species are reproductively isolated? Ancestral species 2 1 Gene flow Population (five individuals are shown) Barrier to gene flow New species Hybrid zone Hybrid Gene flow 3 4

31 Reinforcement Stability Fusion Outcomes of hybrid zones

32 Copyright © 2009 Pearson Education, Inc. ◦ What is the total length of time between speciation events (between formation of a species and subsequent divergence of that species)? –In a survey of 84 groups of plants and animals, the time ranged from 4,000 to 40 million years –Overall, the time between speciation events averaged 6.5 million years and rarely took less than 50,000 years

33 Prezygotic barriers Temporal isolation Habitat isolation Behavioral isolation Mechanical isolation Gametic isolation Zygote Gametes Postzygotic barriers Viable, fertile offspring Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown


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