1. Ecological Speciation- Sticklebacks

2. Outline: Introduction: Speciation Articles: Three Spine Stickleback
Evolutionary diversitfication in stickleback affects ecosystem functioning
Evidence for ecology’s role in speciation

3. Types of Specieation: Allopatric:
speciation mediated by geographic separation causes reproductive isolation

4. Types of Specieation: Sympatric:
reproductive isolation occurs among individuals living in the same geographic area mediated by intrinsic factors

5. Three Spine Stickleback
Gasterosteus aculeatus
Native to North America, Europe and Asia
Common in coastal marine ecosystems of the Northern Hemisphere
Colonized and adapted into freshwater habitats in coastal areas
There are sticklebacks that are marine, anadromous and those that remain in freshwater systems

6. Introduction
In 7 lakes of British Columbia sympatric species pairs of sticklebacks have evolved independently (10,000 years)
Species pairs: are ecologically and genetically distinct populations found in sympatry that behave as real biological species, but are classified under the same latin binomial
One Limnetic: occupying open surface waters, away from the shore
One Benthic: occupying the bottom layers
of water

7. Evidence for ecology’s role in speciation
Parallel speciation or assortative mating by environmental selection
Build up of incompatibilities between stickleback populations largely account for assortative mating

8. Terms to know:
Assortative mating: when sexually reproducing organisms tend to mate with individuals that are like themselves in some respect (positive assortative mating) or dissimilar (negative assortative mating)
Parallel speciation: is when reproductive incompatibility in closely related populations is determined by traits that independently evolve due to adaptation to differing environments.
Ecotype: genetically distinct geographic population within species
In the case of this study they are: anadromous and stream resident sticklebacks

9. hypothesis
Reproductive isolation of sticklebacks may be accounted for by non-random mating based on:
Body Size
= Speciation was cause by ecological differences and divergent selection

10. Experiments conducted
1) To test for reproductive capability between ecotypes and fish from genetically distinct populations
fish of varying geographic areas were brought into the lab for mating trials
2) Reproductive capability was compared to body size differences
Mating trials were conducted between males and females of varying size

11. Experiments conducted
3) Reproductive capability was compared to body size differences this time female size was manipulated
Female fish where raised with fish from both ecotypes and then their mating patterns where tested against an assortment of males

12. Methods
Both freshwater stream (small) and anadromous (large) forms of sticklebacks where used in this study
Fish for mating trials were collected from distinct regions: Alaska, British Columbia, Iceland, Scotland, Norway and Japan.

13. Results (1) Courtship was 2X more successful with in ecotypes
freshwater and anadromous females preferred males of their own ecotype (with and between regions)
Within: species from the same geographic area
Between: species that are physically seperated by geography

14. Results (2)
Mating compatibility decreased with increasing body length difference
Small stream fish
Anadromous fish larger
Both preferred to mate with fish similarly sized to themselves

15. Results (3)
Females preferred a body size of males of ecotype that she was raised with

16. Conclusions
Reproductive isolation was brought on by adaptations to different environments
Speciation arised largely as a by product of ecological differences and divergent selection on a small # of phenotypic traits (ex. Size)
Stream and anadromous size differences are ecological in origin and can product reproductive isolation only when coupled with size-assortative mating

17. Future work
Body size is not a simple genetic outcome, there could be many variables that together determine it.
Phenotypic plasticity might contribute to large size in anadromous fish

18. Ecology affects speciation and
Speciation and specialization affects ecology ...

19. Evolutionary divesification in stickleback affects ecosystem functioning
Looks at:
the short term effect of speciation and specialization of sticklebacks on pond ecosystems
Consequences of evolutionary diversitfication on ecosystems mediated by trophic cascades

20. Hypotheses
1) Sticklebacks would cause the strongest cascades in their preferred foraging habitats, leading to higher levels of primary productivity with increasing predator specialization
G < B, L < B L
2)Distinct types of sticklebacks might differ in their engineering effect on ecosystems

21. Methods
Experimental ponds were set up and tested with different combinations of forms of Sticklebacks
Generalist (G)
Only benthics (B)
Only limnetics (L)
Species Pair with both benthics and limnetics (BL)

22. Methods Invertebrate Biomass
the amount of Chl-A in benthic and pelagic zones
Primary productivity
Net primary productivity
Respiration
Ecosystem properties (DOC)
Where all tested to see if they differed among stickleback treatments

23. Results
Examples:
Significant difference between zooplankton species total biomass G and BL treatments
Stickleback diversification affected the community composition of organisms

24. Results
Pelagic Prey communities with species pair (BL) were significantly different then those only with B but not with only L
Calanoid copepods population where desimated in the presence of L

25. Results
Primary productivity and algal biomass, differed greatly between G and BL treatments
G had the highest level of primary productivity

26. Results
Effected the DOC composition and therefore the physical light environment
Supporting hypothesis two that sticklebacks act as ecosystem engineers

27. Conclusions
Both specialization and speciation effect how an ecosystem functions
Sticklebacks effect both trophic and non-trophic interactions in an pond ecosystem
Therefore in a relativity short time (10,000 yrs) adaptive radiation can potentially change the form and function of freshwater ecosystems

28. Future work
To test the effect of a higher predator on these systems to see how predators might effect evolution of ecosystem engineering and trophic interactions ecosystem

29. Final thoughts Ecology can both cause specialization and speciation
specialization can influence ecology