Thamnophis sirtalis garter snakes eat poisonous newts,Taricha granulosa, containing tetrodotoxin. Resistance totetrodotoxin is highly heritable in these snakes. Garter snakesmust also escape predators by moving quickly, and crawling speed isalso highly heritable. Selection on both resistance to tetrodotoxinand crawling speed are strong. Nonetheless, neither trait increasesvery much each generation if both are artificially selected in alab population. Explain this result.
