Upgrade to Pro — share decks privately, control downloads, hide ads and more …

Natural selection and diversification in the th...

Avatar for Kieran Samuk Kieran Samuk
October 13, 2016

Natural selection and diversification in the threespine stickleback

Delivered at the Duke PopBio Seminar in October 2016.

Avatar for Kieran Samuk

Kieran Samuk

October 13, 2016
Tweet

More Decks by Kieran Samuk

Other Decks in Research

Transcript

  1. Natural selection and diversification in the threespine stickleback Kieran Samuk

    Postdoc, Noor Lab Department of Biology Duke University Photo: Nicole Bedford
  2. An incipient species of marine threespine stickleback from Nova Scotia,

    Canada Kieran Samuk* Hannah Visty Dolph Schluter
  3. Trophic divergence is a major ecological barrier in a wide

    variety of animal species Freed et al. 1994
  4. When animals speciate without geographic isolation, trophic divergence is a

    key initial barrier …but is it, really? Coyne & Orr 2004, Schluter 2008, Feder et al. 2011
  5. When animals speciate without geographic isolation, trophic divergence is a

    key initial barrier …but is it, really? Coyne & Orr 2004, Schluter 2008, Feder et al. 2011
  6. Every described stickleback species pair differs in trophic niche BENTHIC

    Macroinverts LIMNETIC Copepods LAKE Zooplankton STREAM Macroinverts MARINE Copepods RIVER Macroinverts
  7. Most stickleback species pairs are not in the earliest stages

    of speciation Single population Complete reproductive isolation Lake Stream Benthic Limnetic Japan Sea Pacific Marine
  8. Most stickleback species pairs are not in the earliest stages

    of speciation Single population Complete reproductive isolation Lake Stream Benthic Limnetic Japan Sea Pacific Marine Need to look here!
  9. Approach • Find stickleback species pair in very early stages

    of speciation • Test for divergence in trophic characters
  10. Approach • Find stickleback species pair in very early stages

    of speciation • Test for divergence in trophic characters
  11. In the 90s, biologists working in Nova Scotia observed odd

    “white” stickleback Photo: Max Blouw
  12. Approach • Find stickleback species pair in very early stages

    of speciation • Test for divergence in ecological and sexual traits
  13. Approach • Find stickleback species pair in very early stages

    of speciation • Test for divergence in ecological and sexual traits ?
  14. Approach • Find stickleback species pair in very early stages

    of speciation • Test for divergence in trophic characters
  15. Approach • Find stickleback species pair in very early stages

    of speciation • Test for divergence in trophic characters
  16. Whites and commons do not differ at “classic” ecologically linked

    traits Trait Whites are/have… Body shape Not different Dorsal spine length Not different Gill raker number Not different Armor plates Not different Egg weight Not different Body size Smaller Pigmentation Lighter (♂) Testes weight Larger testes (♂)
  17. Whites and commons do not differ at “classic” ecologically linked

    traits Trait Whites are/have… Body shape Not different Dorsal spine length Not different Gill raker number Not different Armor plates Not different Egg weight Not different Body size Smaller Pigmentation Lighter (♂) Testes weight Larger testes (♂)
  18. Summary • White sticklebacks are the least diverged incipient species

    of stickleback described to date • No detectable difference in trophic niche
  19. In the absence of geographic isolation, is trophic divergence necessary

    for speciation in sticklebacks? Not in this case!
  20. The earliest stages of speciation do not require trophic divergence

    Single population Complete reproductive isolation Lake Stream Benthic Limnetic Japan Sea Pacific Marine
  21. Summary • White sticklebacks are the least diverged incipient species

    of stickleback described to date • No detectable difference in trophic niche • Male sexual traits seem to be playing a key role in reproductive isolation
  22. Experimental evidence for the role of predation in the evolution

    of brain size Jan Xue* Kieran Samuk* Diana Rennison
  23. Brains are thought to be involved in energetic tradeoffs with

    other tissues Brain Energy Gut Gonads Fat Stores + –
  24. Comparative work suggests that ecology correlates with brain size LIGHT

    STRUCTURE PREDATION SOCIALITY Moran et al. 2015 Watts 2009 Wikipedia Wikipedia
  25. Many studies suggest that predation favors larger brains in prey

    species Prey species have larger brains Large-brain fish better survive predation Kotrschal et al. (2013) Kondoh (2010)
  26. X 5 F1 hybrid families Benthic Limnetic 1/2 of each

    family 1/2 of each family POND F2 F3 Measure brains Each family split into two ponds (ten ponds total) F1 TROUT! POND POND F2 F3 POND Measure brains
  27. Lab-reared benthics have larger olfactory lobes and telencephla than limnetics

    OLFACTORY LOBE TELENCEPHALON Larger in benthics Park et al. (2012), Park (2010), Keagy (2014)
  28. We dissected brains of experimental fish and measured the lobes

    Area = πxy OLFACTORY LOBE TELENCEPHALON OPTIC LOBE CEREBELLUM
  29. We assessed plasticity by raising offspring of experimental fish in

    the lab F4 Measure brains TROUT POND CONTROL POND Common environment Offspring of 10 random matings Offspring of 10 random matings
  30. Predators force prey into hiding, limiting their interactions with the

    environment %$@*! PREDATION NO PREDATION Miller et al. 2014
  31. The addition of trout also causes a variety of other

    ecological changes Lower phytoplankton biomass Lower zooplankton biomass Greater abundance of large zooplankton Rudman et al. 2016
  32. We are working on assessing if brain size is independent

    from other traits Correlated selection QTL Brain Size
  33. Summary • Contrary to previous results, predation selected for smaller-brained

    individuals • How predation affects brain evolution is likely highly context dependent – bigger not always better! • Selection experiments are a viable method for exploring the evolutionary ecology of the vertebrate brain
  34. Natural selection and gene flow shape the genomic architecture of

    adaptation in threespine stickleback Kieran Samuk* Greg Owens Sara Miller Kira Delmore Diana Rennison Dolph Schluter
  35. We know that signatures of selection are ubiquitous in the

    genome Seehausen et al. Nat Rev. Gen. 2014
  36. Why do we see adaptation in some regions of the

    genome and not others? ? ? Seehausen et al. Nat Rev. Gen. 2014
  37. Are there general constraints on where adaptation can occur in

    the genome? …or can it happen anywhere that adaptive variation is available?
  38. Recent theory suggests that gene flow can constrain where adaptation

    occurs in the genome. Bürger & Akerman 2011 (Theor Popul Biol) Yeaman & Whitlock 2011 (Evolution)
  39. Goal: Test this prediction! Divergent selection + gene flow favors

    tightly linked clusters of locally-adapted alleles Bürger & Akerman 2011 (Theor Popul Biol) Yeaman & Whitlock 2011 (Evolution)
  40. Goal: Test this prediction! Divergent selection + gene flow favors

    tightly linked clusters of locally-adapted alleles Bürger & Akerman 2011 (Theor Popul Biol) Yeaman & Whitlock 2011 (Evolution)
  41. Approach • Classify pairs of populations based on presence of

    selection and/or gene flow • Find loci that are adaptively differentiated between each pair of populations • Quantify the degree of clustering of adaptive loci in the genome, controlling for mutation + gene density
  42. Approach • Classify pairs of populations based on presence of

    selection and/or gene flow • Find loci that are adaptively differentiated between each pair of populations • Quantify the degree of clustering of adaptive loci in the genome, controlling for mutation + gene density
  43. We used morphological differences as a proxy for divergent selection

    Divergent Parallel Benthic vs. Limnetic Alaska Marine vs. Oregon Marine
  44. We used geographic distance + barriers as a proxy for

    gene flow 1. No physical barriers 2. < 500 km apart All pairs of stickleback populations with evidence of recent gene flow
  45. Approach • Classify pairs of populations based on presence of

    selection and/or gene flow • Find loci that are adaptively differentiated between each pair of populations • Quantify the degree of clustering of adaptive loci in the genome, controlling for mutation + gene density
  46. Parallel Selection Divergent Selection Gene flow Allopatry We performed FST

    scans for selection for population pairs in each category
  47. Approach • Classify pairs of populations based on presence of

    selection and/or gene flow • Find loci that are adaptively differentiated between each pair of populations • Quantify the degree of clustering of adaptive loci in the genome, controlling for mutation + gene density
  48. DS+GF favors tightly linked clusters of locally-adapted alleles Bürger &

    Akerman 2011 (Theor Popul Biol) Yeaman & Whitlock 2011 (Evolution)
  49. As predicted, adaptive alleles are more tightly linked in DS-GF

    comparisons What does this actually look like in the genome?
  50. Outliers occurred more often in regions of low recombination in

    DS-GF pairs Outlier Recombination Bias More biased toward Low recombination Less biased toward Low recombination
  51. Smaller set of genes = More re-use of same genes

    DS+GF = more parallelism? Less variation available overall Novel effect of gene flow?
  52. Summary • Gene flow favors the clustering of adaptive alleles

    in regions of low recombination • May be an important and general constraint on adaptive evolution
  53. Acknowledgements Kate Ostevik Marius Roesti Sam Yeaman Armando Geraldes Mark

    Ravinets Anne-Laure Ferchaud Jun Kitano Thor Veen Seth Rudman Baocheng Guo Semiahmoo First Nation Waycobah First Nation Funding Committee Dolph Schluter Mike Whitlock Trish Schulte Loren Rieseberg