Cannibalistic tadpoles that pose the greatest threat to kin are most likely to discriminate kin

Inclusive fitness theory predicts that altruism should often be directed to wards reproductive relatives, but it is unclear whether individuals that ar e most likely to help or harm relatives are also most likely to identify ki n in the first place. Here I show that species and sibships of spadefoot to ad tadpoles (Spea bombifrons and S. multiplicata) that were most likely to produce an environmentally induced cannibalistic morph were also most likel y to avoid eating kin. Moreover, tadpoles avoided eating kin when they expr essed the cannibal phenotype, but not when these same individuals reverted to the non-cannibalistic morph. Thus, individual tadpoles facultatively adj ust their level of discrimination according to how likely they are to harm kin. In general, sensory systems and/or decision rules enabling recognition may be especially likely to evolve among those individuals that are most o ften faced with the problem of discrimination.