Ecological Speciation- Sticklebacks

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

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