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Genetic Basis of Sexual Conflict in Lake Malawi Cichlid Fishes

Genetic Basis of Sexual Conflict in Lake Malawi Cichlid Fishes. Thomas D. Kocher Department of Biology. Vertebrate sex determination. SRY. Ezaz et al. 2006. Tilapia. (Genomar). A Genetic Linkage Map of Tilapia. Lee et al. 2005, Genetics. Sex-linked markers in Oreochromis niloticus: LG1.

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Genetic Basis of Sexual Conflict in Lake Malawi Cichlid Fishes

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  1. Genetic Basis of Sexual Conflict in Lake Malawi Cichlid Fishes Thomas D. Kocher Department of Biology

  2. Vertebrate sex determination SRY Ezaz et al. 2006

  3. Tilapia (Genomar)

  4. A Genetic Linkage Map of Tilapia Lee et al. 2005, Genetics

  5. Sex-linked markers in Oreochromis niloticus: LG1 (Lee 2003)

  6. X/X X/Y LG 1 W/Z LG 3 Z/Z Epistasis in O. aureus (Lee 2004)

  7. LG1 and LG3 are distinct chromosomes (Cnaani 2007)

  8. Sex-linked markers in tilapia

  9. Sex determination in other cichlids? ? Sex determination and speciation?

  10. Cichlid mtDNA Phylogeny

  11. Lake Malawi cichlids: textbook example of adaptive radiation http://www.malawicichlids.com/

  12. Three Stages of the Malawi Radiation Rock Sand Danley and Kocher, Mol Ecol (2001)

  13. Sex determination in Malawi cichlids • Survey of 19 species in five genera • 94 families (2066 offspring) • Sex ratios • Genotypes for microsatellite markers • Focused on LG 5 and 7

  14. Metriaclima phaeos - XY on LG7

  15. Metriaclima phaeos - WZ on LG5

  16. M. fainzilberi - WZ and XY

  17. Grand summary…

  18. Sex determiners in African cichlidsTilapia Malawi

  19. Hidden complexity of genetic interactions LG5 WZ (OB species) LG? WZ M. pyrsonotus LG7 XY (widespread) LG? XY M. kompakt LG? M. callainos LG? WZ M. lombardoi

  20. Metriaclima lombardoi 44 chromosomes + B chromosome (some females) Inversion in largest pair (some males) Irani Ferreira

  21. Sexual selection and sexual dimorphism M. zebra Nakantenga Male M. zebra masinje Female

  22. Is sexual selection the whole answer? QTL Normal ‘BB’ female Orange-blotch ‘OB’ female

  23. Alternative models

  24. Orange blotch (OB) • OB acts in a dominant manner, and results in a binary phenotype. • The OB phenotype is one of the few exceptions to drab female coloration. • OB is found in multiple genera across the Lake Malawi cichlid radiation. • Range of OB phenotypes suggests additional genetic interactions.

  25. How many fish do you see?

  26. OB is cryptic against some backgrounds

  27. OB males are ugly! Females Males BB OB

  28. Family mapping

  29. M.zebraMakonde L.trewavasae Thumbi West A D A 100 km LOD LOD B B E M.zebra‘blaze’ Manda Tropheops sp. Thumbi West LOD LOD Lake-wide mapping panel M.xanstomachus Nankoma C LOD LOD C E D Tetraodon Chr11 (Mb) Tetraodon Chr11 (Mb) F

  30. SingleOBhaplotypeinMalawi

  31. Association in populations Pax7

  32. PAX3/7 genes encodetranscription factors which modulate neural crest and pigment cell differentiation Pax3Sp/+ mouse Waardenburg Syndrome

  33. Differences in Pax7 expression

  34. What about the sex phenotype? Not easy to identify a function of Pax7 in gonad development, but there is a difference in expression in the gonad… 3 month old fish

  35. Other nearby candidates… Pax7 DJ-1 (aka Park7) Mig6 (EGFR inhibitor)

  36. +/+ Ob/+ Ob/Ob p = 0.32 DJ-1 DJ-1 tailfin Androgen receptor DAXX male sex development? apoptosis

  37. DJ-1 is also differentially expressed in the gonad… but not in the expected direction 3 month old fish

  38. Hard work ahead • Mapping work is done! • No coding differences • No major deletions • Tantalizing differences in expression • Needs difficult functional analysis • Let’s not race to conclusions

  39. Implications for speciation • New male colors may evolve to facilitate territoriality • Sexually antagonistic selection may recruit new sex determiners linked to color genes • Differences in sex determining mechanism may contribute to reproductive isolation • What other conflicts might contribute to evolution of sex determiners?

  40. Tilapia linkage map Woo-Jai Lee Bo-Young Lee Aimee Howe BAC physical map Takayuki Katagiri Celeste Kidd Informatics Justin Stern Charles Bancroft Shalabh Sharma Matt Conte Sex determination Bo-Young Lee Avner Cnaani Jennifer Ser OB color morph Todd Streelman Reade Roberts Gene expression Jianzhou Cui Transgenics Koji Fujimura People

  41. Collaborators • Gideon Hulata (ARO, Israel) • Jean-Francois Baroiller & Helena D’Cotta (CIRAD, Montpellier) • Catherine Ozouf (MHN, Paris) • Cesar Martins, Andreia Poletto, Irani Ferreira (UNESP, Brazil)

  42. Funding • National Institutes of Health (R01HD058635) • National Science Foundation (DEB-0445212) • USDA National Research Initiative (#2003-03561) • US-Israeli BARD (IS-3561-04, IS-3995-07C)

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