Evolution of offspring desertion in a stickleback fish

Parental care is expected to evolve when its principal benefit, increased survival of offspring, outweighs the cost of diminished future reproduction of the care giver(s). All sticklebacks (Gasterosteidae) show male parental care, but the males of a newly described form with iridescent white sexual colors ("white" stickleback) are here shown to be emancipated; they actively remove embryos from the nest after fertilization and disperse them over plumes of filamentous algae. Experiments show that the emancipation behaviors are heritable and that desertion apparently imposes little cost in environments with abundant filamentous algae. This evolutionary reversal from paternal care to desertion is the first reported for fishes. It is consistent with models of the adaptive evolution of parental care, and it illustrates that traits which exhibit a long phylogenetic stasis may nevertheless retain sufficient underlying variance to permit adaptive evolution under appropriate ecological conditions.