Lecture 13. - September 24, 2008 Speciation. 1. What are species?

Lecture 13. - September 24, 2008

Speciation.

1. What are species?2. Do species exist, and, if so, what is the evidence?3. How does speciation occur?

a) How does genetic differentiation arise?b) How does reproductive isolation occur?

____________________________________________________________Note: two extra-credit opportunities on Friday. Location: the new I-Hotel, 1900 S. 1st Street

11:10 - noon two fish speakers: John Chick (Illinois Natural History SurveyRiver Station at St. Louis) and Larry Page (University of Florida - previous director of INHS collections)

3:25 - 3:50 - Dave Phillipp - INHS _____________________________________________________________

Note: The review questions are up on the website. We covered a lot of material.Don’t wait until the last minute to study. Test on October 1.________________________________________________________________

What is a species?

Cyprinella galactura had its distribution cut intwo by glaciers millions of years ago. When willthese two subspecies become their own separatespecies and how would we know?

L. gooeilonger (25-40 mm) shorter (22-39 mm)

slender (5-8 mm) thicker (6-10 mm)

two rows of teeth one row of teeth

freshwater* brackish*

L. goodei L. parva

Hybridization between L. goodei and L. parvais low in sympatry (<1%). How much hybridization can occur and still maintain species?

Amazon molly -

What to do with clonal species if you use the biological species concept?

E. spectabile has been split into several different species based on coloration.

Is this variation in coloration an effect of genetics, environment or both?

If it’s largely environmental, then this is meaningless taxonomy.

Amazon molly -

If you use phylogenetic species concept - is each individual a separate species?

A1 A2 A3 B1

A1 A2 A3 B1

A1 A2 A3 B1

Which definition is best - biological species concept or phylogenetic species concept?

Are species real?

H1: Species are “real” in that there are discrete groups of interbreeding fish.

H2: There is continuous variation between types. Humans have a need to categorize everything, and we’ve divided the living world up into manageableunits.

This question is important because poop heads who want to build a golf courseand ruin the last spawning site for some little obscure fish will claim that there are no such things as species.

What evidence do we have for or against these hypotheses?

green sunfish(L. cyanellus)vs. hybridsvs. bluegill(L. macrochirus)

in size (x-axis)versus shape (y-axis)

How does speciation occur?

Gasterosteiformes

• Sympatric speciation

Gasterosteiformes

• Sympatric speciation

• Two “ecomorphs” or species

limnetic

benthic

Body depthGill rakers





L. goodei L. parva

species *salinity – X2 = 15.39, df = 1, p < 0.0001

0

0.2

0.4

0.6

0.8

1

salinity (ppt)

surv

ival

0 2 4 8

L. goodeiL. parva

Aquatic Environments and Fishes

• Fishes live in almost every conceivable aquatic environment– thermal extremes from Antarctica (-2oC) to desert Southwest US (>40oC).– depth extremes from 8000 m to 5200 m above sea level!

• Freshwater - 41.2% Primary Freshwater 33.1%Secondary Freshwater 8.1%

• Marine- 58.2% Shallow-warm 39.9%Shallow-cold 5.6%Epipelagic 1.3%Deep-pelagic 5.0%Deep-benthic 6.4%

• Diadromous- 0.6%

-- but by volume only ~1% of all water on earth is fresh

Why are there so many more species per unit area in freshwater?





L. goodei L. parva

Bolnick & Near. 2005. Evolution.

Sperm & egg fertilization does get messed up with increasing divergence, but thisdoesn’t seem to be important for speciation in Centrarchids because it doesn’t happen until a long time after speciation has occurred. Also indicates that F1s (at least for the early stages) do not show evidence of hybrid inviability for closely related species.

Crosses between close relatives have relativelyhigh hatching success.

Crosses between moredistant relatives (i.e. betweengenera) have much lowerhatching success.





L. goodei L. parva

Crosses

control Lg ♀ x Lg ♂ Lp ♀ x Lp ♂

Crosses


F2 HyA ♀ x HyB ♂ HyB ♀x HyA ♂

Crosses



Back Lg ♀ x HyA ♂ Lg ♀ x HyB ♂Crosses Lp ♀ x HyA ♂ Lp ♀ x HyB ♂

HyA ♀ x Lg ♂ HyA ♀ x Lp ♂HyB ♀ x Lg ♂ HyB ♀ x Lp ♂

Crosses





Crosses

Salinity Treatment0, 2, 4, 8 ppt





Crosses

Salinity Treatment0, 2, 4, 8 ppt

Dependent Variables: % hatching, % fry eating

parental control

F2 crosses

parental crosses

parental control

parental crossesF1 female backcross

parental control

F1 female backcross F1 male backcross

hybrid A

hybrid b

When there is a difference in hybrid fitness between the sexes, the heterogametic sex is the one with lowered fitness.

Review Questions Set 1.

1. What is the biological species concept (BSC)? What is the phylogenetic species concept (PSC)? How do the two differ? What are the difficulties with defining species with the BSC? with the PSC? Under what conditions do the two species concepts result in different outcomes? Why will some species be “paraphyletic” in the early stages of speciation?

2. Are species real? Give two lines of evidence that species really do exist?

4. In general, how does speciation occur for sexually reproducing organisms?

5. What types of phenomena can cause genetic differentiation? Is genetic differentiation more likely when two groups are in allopatry or sympatry? Why?

6. What data did Bolnick & Near produce regarding hybridization between various Centrarchid species? What is the interpretation of their data? Are there any caveats to this work? List two caveats to this study.

Review Questions, Cont’d.

6. Explain how hybrids might experience decreased fitness due to extrinsic factors. Name at least two different stages where F1 hybrids might have decreased fitness.

7. Explain what types of intrinsic genetic factors might decrease hybrid fitness. Specifically, what would have to happen for F1 hybrids to experience lower fitness? What would have to happen for F2 hybrids to experience lower fitness? For backcross animals to experience lower fitness?

8. What is reinforcement? Why does reinforcement occur?

Cyprinella spiloptera vs. C. whipplei vs. their hybrids.

They are different sizes & shapes.

C. spiloptera

C. whipplei

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Lecture 13. - September 24, 2008 Speciation. 1. What are species?