Incipient speciation without trophic specialization in the white stickleback

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1. Incipient speciation without trophic specialization in the white stickleback Kieran Samuk1, Hannah Visty2 & Dolph Schluter3 1Department of Biology, Duke University 2Department of Forestry, University of British Columbia 3Department of Zoology, University of British Columbia Photo: Max Blouw
2. Speciation with gene flow often favors ecologically-mediated barriers TROPHIC NICHE IMMIGRANT INVIABILITY POLLINATORS ©The McGraw Hill Company ©AAAS ©Biodiversity Heritage Library
3. Speciation with gene flow often favors ecologically-mediated barriers TROPHIC NICHE IMMIGRANT INVIABILITY POLLINATORS ©The McGraw Hill Company ©AAAS ©Biodiversity Heritage Library
4. Sister species often differ in trophic niche Images: ©The McGraw Hill Company Image: © Dr. Douglas Pratt; Freed et al. 1994
5. Sticklebacks are a poster-child for speciation via trophic niche divergence BENTHIC LIMNETIC LAKE STREAM MARINE RIVER Image: © TREE, McKinnon & Rundle 2002
6. Trophic divergence occurs across the stickleback speciation continuum Single population Complete reproductive isolation Lake Stream Benthic Limnetic Japan Sea Pacific Marine Hendry + Bolnick et al. McPhail + Taylor + Schluter Kitano + Ravinet et al.
7. Question Is trophic specialization an essential first step for stickleback speciation with gene flow?
8. Lake Stream Benthic Limnetic Japan Sea Pacific Marine Hendry + Bolnick et al. McPhail + Taylor + Schluter Kitano + Ravinet et al. Need data at earliest stages
9. Approach • Find stickleback species pair in the very early stages of speciation + gene flow • Test for divergence in trophic characters
10. Approach • Find stickleback species pair in the very early stages of speciation + gene flow • Test for divergence in trophic characters
12. Photos: Max Blouw Max Blouw
13. Photo: Max Blouw
14. Allozyme studies in the 90s found no genetic differences
15. I sampled white and common stickleback at 12 sites in Nova Scotia
16. ~15K SNPs
17. ~15K SNPs
18. FST = 0.02
21. Best fit demographic model: Isolation with migration (Best of four models fit using ∂a∂i)
22. Approach • Find stickleback species pair in very early stages of speciation • Test for divergence in trophic characters
23. Approach • Find stickleback species pair in very early stages of speciation • Test for divergence in trophic characters – Morphological traits – Stable isotopes
24. Divergence along a benthic-limnetic trophic axis is extremely common in fish BENTHIC LIMNETIC Deeper body Fewer gill rakers Thinner body More gill rakers Schluter 1993
25. TRAIT 1 Body shape
26. Bell et al. 1978
27. Bell et al. 1978
29. No difference in body shape between white and common sticklebacks (Procrustes MANOVA, P = 0.42)
30. TRAIT 2 Gill rakers
33. No difference in gill raker number between white and common sticklebacks (t-test, P = 0.38, 0.33)
34. Abundances of 13C and 15N can detect fine-scale differences in trophic niche
35. Kaeuffer et al. 2011 Lake Stream
37. No difference in stable isotope profile between white and common sticklebacks (MANOVA, P = 0.15)
38. Summary • White sticklebacks are one of the least diverged incipient species of stickleback • No detectable differences in trophic niche • Although obviously important, trophic divergence is not a necessary first step for speciation in sticklebacks
39. If not trophic divergence, what traits do differ between white and common sticklebacks?
40. Trait Different? Body shape No Gill raker number No Stable isotopes No
41. Trait Different? Body shape No Gill raker number No Stable isotopes No Spines / Armor No
42. Trait Different? Body shape No Gill raker number No Stable isotopes No Spines / Armor No Body size Smaller
43. Trait Different? Body shape No Gill raker number No Stable isotopes No Spines / Armor No Body size Smaller Pigmentation Lighter (♂)
44. Trait Different? Body shape No Gill raker number No Stable isotopes No Spines / Armor No Body size Smaller Pigmentation Lighter (♂) Testes weight Larger testes (♂)
45. Trait Different? Body shape No Gill raker number No Stable isotopes No Spines / Armor No Body size Smaller Pigmentation Lighter (♂) Testes weight Larger testes (♂) Nest substrate Filamentous algae (♂)
46. Trait Different? Body shape No Gill raker number No Stable isotopes No Spines / Armor No Body size Smaller Pigmentation Lighter (♂) Testes weight Larger testes (♂) Nest substrate Filamentous algae (♂) Parental care No parental care! (♂)
47. Trait Different? Body shape No Gill raker number No Stable isotopes No Spines / Armor No Body size Smaller Pigmentation Lighter (♂) Testes weight Larger testes (♂) Nest substrate Filamentous algae (♂) Parental care No parental care! (♂)
48. Trait Different? Body shape No Gill raker number No Stable isotopes No Spines / Armor No Body size Smaller Pigmentation Lighter (♂) Testes weight Larger testes (♂) Nest substrate Filamentous algae (♂) Parental care No parental care! (♂) “Male-biased” traits
49. Is there a connection between male-biased traits and reproductive isolation?
50. We compiled a list of all the genes in outlier + non-outlier regions
51. We used previous data to assign degree of sex-biased expression to each gene Leder et al. 2015
53. Working hypothesis White sticklebacks are a “sexual ecotype” maintained by ecologically-mediated sexual selection
54. Filamentous algae “niche” Sand/rocks “niche” -No parental care -Males constantly courting -High male-male competition Selection favors: Mating rate over parental care -Parental care -No courting during care -Low male-male competition Selection favors: Parental care over mating rate “Sexy dad” “Good dad” (White stickleback) (Common stickleback)
55. Ecologically-mediated sexual selection may maintain species by acting against hybrids (White stickleback) (Common stickleback) (Hybrid) Fitness Phenotype (PC1)
56. THANKS FOR LISTENING
57. Acknowledgements Waycobah First Nation Max Blouw Jeff Hutchings Bill Marshall Kate Ostevik Noor Lab Diana Rennison Sara Miller Davis Iritani Thor Veen Seth Rudman Alex Kotrschal Funding PhD Committee Dolph Schluter (advisor) Mike Whitlock Trish Schulte Loren Rieseberg