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

Vertebrate sex determination Ezaz et al SRY

Tilapia (Genomar)

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

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

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

LG1 and LG3 are distinct chromosomes (Cnaani 2007)

Sex-linked markers in tilapia

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

Cichlid mtDNA Phylogeny

Lake Malawi cichlids: textbook example of adaptive radiation

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

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

Metriaclima phaeos - XY on LG7

Metriaclima phaeos - WZ on LG5

M. fainzilberi - WZ and XY

Grand summary…

Sex determiners in African cichlids Tilapia Malawi

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

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

Sexual selection and sexual dimorphism M. zebra masinjeM. zebra Nakantenga Male Female

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

Alternative models

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.

How many fish do you see?

OB is cryptic against some backgrounds

OB males are ugly! Females Males BB OB

Family mapping

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

Single OB haplotype in Malawi

Association in populations Pax7

PAX3/7 genes encode transcription factors which modulate neural crest and pigment cell differentiation Pax3 Sp /+ mouse Waardenburg Syndrome

Differences in Pax7 expression

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

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

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

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

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

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?

People 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

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)

Funding National Institutes of Health (R01HD058635) National Science Foundation (DEB ) USDA National Research Initiative (# ) US-Israeli BARD (IS , IS C)