Assortative mating by an obliquely transmitted local cultural trait promotes divergence Justin Yeh University of North Carolina at Chapel Hill Do learned birdsong dialects lead to speciation? • Molecular similarity might correlate with dialect similarity (Baker 1975; Baker & Thompson 1982; Zink & Barrowclough 1984) • Genetic cline overlap with cultural cline, but at lower steepness, and the birdsong does not predict genotype (Kenyon et al. 2016) • Bird lineage with song learning has more species than that without (Lachlan & Servedio 2004) Justin Yeh 2 correlation ⇏ causation no correlation ⇏ no causation Justin Yeh 3 Oblique learning: from unrelated individual of the previous generation • Juvenile songbirds learn from adult neighbors • Obliquely transmitted traits are immune to sexual selection (Yeh & Servedio 2015) • If any juvenile can learn from any adult, there should not be correlation between gene and culture Justin Yeh 4 Spatial structure creates gene- culture association • Learning is spatially restricted • Cultural traits can be locally adapted – High-freq vocal signals in cities (Luther & Derryberry 2012) – Tonal languages in humid environment (Everett et al. 2014) Justin Yeh 5 Hypothesis Local genes & Local song & local local oblique reproduction learning Justin Yeh 6 Hypothesis Local genes & Local song & local local oblique reproduction learning Gene-culture association Justin Yeh 7 Hypothesis Local genes & Local song & local local oblique reproduction learning Divergent selection Gene-culture & sexual selection association on song Genetic divergence Justin Yeh 8 Hypothesis Local genes & Local song & local local oblique reproduction learning Divergent selection Gene-culture & sexual selection association on song Genetic divergence Justin Yeh 9 Population genetic model m Justin Yeh 10 Population genetic model m A B a b Justin Yeh 11 Population genetic model m A B a b s H sH Justin Yeh 12 Population genetic model C1 C2 m A B a b s H sH Justin Yeh 13 Population genetic model sD , α sD , α C1 C2 m A B a b s H sH Justin Yeh 14 Population genetic model sD , α sD , α C1 C2 m A B a b s H sH Justin Yeh 15 Population genetic model sD , α, μ sD , α , μ N C1 C2 m N A B a b s H sH Justin Yeh 16 Simulation conditions • All genes and cultural traits start diverged – Contact zone • 5000 generations Justin Yeh 17 Both sexual and divergent selection promote LD Local gene Local song Gene-culture Selection on association song (α, sD) Genetic divergence (LD) Justin Yeh 18 Both sexual and divergent selection promote LD m=0.01, sH=0.09, μ=0, no drift Local gene Local song LD s Gene-culture Selection on D association song (α, sD) 0.01 0.1 1 10 100 Female preference strength (α) Genetic divergence (LD) Note: Intermediate α maximizes sexual selection in phenotype-matching models (Servedio 2011) Justin Yeh 19 Drift and mutation just make things messy Drift & mutation Local gene Local song Gene-culture Selection on association song (sD, α) Genetic divergence (LD) Justin Yeh 20 Drift and mutation just make things messy -3 Drift & mutation m=0.01; sH=0.1; α=1; μ=10 ; N=1000 Local gene Local song LD Gene-culture Selection on sD association song (sD, α) Cultural trait divergence (calculated like Nei’s genetic distance) Genetic divergence (LD) Justin Yeh 21 Mate choice and viability give better evidence than gene-culture correlation • Correlation can be caused by geography • Correlation can be difficult to observe – Oblique learning temporarily and locally removes gene-culture association – Stochastic process may lead to high cultural variation within patches Justin Yeh 22 Why should cultural evolution care about speciation? • group formation, ideological divide, radicalization, etc. • Reduced genetic exchange <--> reduced memetic exchange • Genetic divergence <--> cultural divergence Justin Yeh 23 Acknowledgement • Maria Servedio • Marc Feldman • Courtney Fitzpatrick • National Science Foundation (USA) Justin Yeh 24 Life cycle Drift Oblique learning with Migration cultural mutation Viability Sexual selection selection & reproduction Justin Yeh 25 Drift Migration Oblique learning w/ cultural mutation Sexual selection & Viability selection reproduction • D-M incompatibility for A and B (sH) • Divergent selection on C (sD) Genotype Culture Patch 1 Patch 2 AB & ab C1, C3… 1 1-sD Ab & aB C1, C3… 1-sH (1-sH)(1-sD) AB & ab C2, C4… 1-sD 1 Ab & aB C2, C4… (1-sH)(1-sD) 1-sH Justin Yeh 26 Drift Migration Oblique learning w/ cultural mutation Viability Sexual selection & selection reproduction • Polygyny (sexual selection on males) • Preference (α) to mate with individuals of the same cultural trait (phenotype-matching) ♂ ♀ C1 C2 C3 … C1 1+α 1 1 1 C2 1 1+α 1 1 C3 1 1 1+α 1 … 1 1 1 … 27 Drift Oblique learning w/ Migration cultural mutation Viability Sexual selection selection & reproduction • From the previous generation in the same patch f(ABC1)juvenile=f(AB)juvenile((1- μ) f(C1)adult + μ f(C2)adult) • Gene-culture association becomes 0 within each patch! Justin Yeh 28 Life cycle order & number of possible cultural traits -3 m=0.01; sH=0.1; α=1; μ=10 ; N=1000 m=0.01; sH=0.1; sD=0-0.5; α=1 # of C alleles LD sD Cultural trait divergence Drift Viability Oblique learning selection Migration Sexual selection 29 sD selection Local gene Local song Local gene Local song migration migration Gene-culture Gene-culture α, s α association D association selection Genetic divergence (LD) Genetic divergence (LD) Justin Yeh 30 Scientific Empirical Proof-of-concept method research models Observe nature and build hypothesis Choose Design protocol Gather evidence assumptions and gather data and build model Analyze evidence Analyze data Analyze model Evaluate hypothesis and propose new directions Servedio et al. (2014) Not Just a Theory—The Utility of Mathematical Models in Evolutionary Biology. PLoS Biol 12(12): e1002017.