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

Lake Victoria Lake Tanganyika
Africa Uganda Kenya Lake Victoria Lake Tanganyika Tanzania Map of Lake Victoria and surrounding area. Lake Malawi

Speciation and the loss of species
Speciation and the loss of species 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.

What is a species? 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 Copyright © 2009 Pearson Education, Inc.

What happened to the cichlids?
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 Ask students whether two cichlid species that fused into one were previously separate species. If the two species continued to hybridize with each other, and did so extensively as the environment changed, were they actually separate species? Explain that students will be better able to discuss this question by the end of the lecture. Copyright © 2009 Pearson Education, Inc.

The origin of species is the source of biological diversity
Speciation is the emergence of new species and increases diversity Millions of species all arose from ancestor that lived 3.6 billion years ago Student Misconceptions and Concerns 1. Students might not realize that evolutionary change includes both (a) linear events, in which a species changes over time, and (b) branching events, which produce new species and diversity. Some students simply expect that whenever new species evolve, they replace their ancestors. Teaching Tips 1. Challenge your students to explain why the field of paleontology has largely been concerned with macroevolution. The broader perspective of evolutionary change studied by paleontologists rarely permits an examination of change within a species. Copyright © 2009 Pearson Education, Inc.

How do we categorize all these species?
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 Student Misconceptions and Concerns 1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species. Copyright © 2009 Pearson Education, Inc.

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

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

For many eukaryotic organisms, we use …
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 Members of different species do not usually mate with each other. If members of one species do mate with members of another species, the offspring will probably not be fertile. Student Misconceptions and Concerns 1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species. Copyright © 2009 Pearson Education, Inc.

Can the biological species concept always distinguish species from each other?
What about species (like the cichlids) that can hybridize with each other and produce fertile offspring? What about extinct organisms like Neanderthal and Cro-Magnon? What about organisms (like the amoeba) that are asexual in their reproduction? Student Misconceptions and Concerns 1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species. Copyright © 2009 Pearson Education, Inc.

Other options for defining species…
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 Point out that this is the concept actually used by most field biologists, who recognize their species by morphological traits. Student Misconceptions and Concerns 1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species. Copyright © 2009 Pearson Education, Inc.

Other options for defining species… 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 Student Misconceptions and Concerns 1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species. Copyright © 2009 Pearson Education, Inc.

Other options for defining species… 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 Students may find the large number of species concepts puzzling. It is important to discuss the strengths and limitations of each species concept. Clarify for students that (1) a particular species concept may or may not be appropriate in considering whether a specific set of populations represents different species, and (2) a specific set of populations may or may not be considered separate species, depending on the species concept that is used. Student Misconceptions and Concerns 1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species. Copyright © 2009 Pearson Education, Inc.

Why do species stay separate?
Why do species stay separate? Reproductive barriers serve to isolate a species gene pool and prevent interbreeding 1. Prezygotic (before sex) 2. Postzygotic (after sex) Student Misconceptions and Concerns 1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home. Copyright © 2009 Pearson Education, Inc.

Reproductive barriers keep species separate
Prezygotic Barriers: prevent mating or fertilization between species 1. Temporal isolation- two species breed at different times (seasons, times of day, years) Student Misconceptions and Concerns 1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home. Copyright © 2009 Pearson Education, Inc.

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 Student Misconceptions and Concerns 1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home. Copyright © 2009 Pearson Education, Inc.

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

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

Reproductive barriers keep species separate 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 Student Misconceptions and Concerns 1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home. Copyright © 2009 Pearson Education, Inc.

Test yourself If two related species live in the same area, would natural selection favor the evolution of prezygotic or postzygotic reproductive isolating mechanisms? Prezygotic reproductive isolating mechanisms are much less costly than postzygotic reproductive isolating mechanisms, which lead to provisioning and (in some species) care of an offspring that is an evolutionary dead end. Student Misconceptions and Concerns 1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home. Copyright © 2009 Pearson Education, Inc.

In allopatric speciation, geographic isolation leads to speciation
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 __________????? Student Misconceptions and Concerns 1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this. 2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60 × 60 × 24 × = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day). 3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips 1. The isolation of a few individuals from a parent population may result from a catastrophic weather or geological event. Ask your students to think back to news footage of torrential rains, massive debris rocketing down a river, and the struggles of animals to haul themselves onto these rafts. Better yet, show them a short news clip of such events. Dramatic weather and geological events may be rare in our lifetimes but are frequent enough to play a role in speciation. Copyright © 2009 Pearson Education, Inc.

In allopatric speciation, geographic isolation leads to speciation
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 Student Misconceptions and Concerns 1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this. 2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60 × 60 × 24 × = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day). 3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips 1. The isolation of a few individuals from a parent population may result from a catastrophic weather or geological event. Ask your students to think back to news footage of torrential rains, massive debris rocketing down a river, and the struggles of animals to haul themselves onto these rafts. Better yet, show them a short news clip of such events. Dramatic weather and geological events may be rare in our lifetimes but are frequent enough to play a role in speciation. Copyright © 2009 Pearson Education, Inc.

Gene flow between populations may be reduced by:
In sympatric speciation, speciation takes place without geographic isolation 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) Copyright © 2009 Pearson Education, Inc.

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

Outcomes of hybrid zones
Reinforcement Stability Fusion

Speciation may occur rapidly or slowly
Speciation may occur rapidly or slowly 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 Student Misconceptions and Concerns 1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this. 2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60 × 60 × 24 × = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day). 3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. 4. The concept of rarity is likely to be misunderstood when applied to geologic time. Events such as major floods, earthquakes, or asteroid impacts, which might be so rare as to occur every 1,000 years, are actually common in geological terms. Students might not realize that 1,000 such events would be expected to occur over a million years. Teaching Tips 1. Have your students think of analogous examples of punctuated equilibrium in our culture. One such example is the switch from vinyl records to compact discs, with the brief transitional form of cassette tapes (which students currently entering college may barely remember). Between the years 1900 and 2000, there were both long periods of stasis (vinyl records) and a relatively short period of transition to CDs and now to digital music files (who knows how long they will last?) Similarly, high-definition television is a new technology replacing more than 50 years’ worth of older technology. Debating the validity of analogies can itself be instructive as students articulate the biological principles and compare them to the analogies. Copyright © 2009 Pearson Education, Inc.

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

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

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

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