「首发」沃邦名师3月10日亚太SAT考试考情速递(11)

exploited by parasites, they are alsobetter able to ? ght back, helping cooperation to persist ( 8). Feeney et al. ?nd that superior anticuckoo defenses in larger groups account for 0.2 moreyoung ? edged per season on average than smaller groups—a substantial boostgiven the fairy-wrens’ low annual fecundity. These results show convincinglythat defense against brood parasites augments the bene? ts of helping, promotingthe persistence of cooperation. But as the authors note, they cannot revealwhat caused cooperation to evolve initially. Brood parasitism alone cannotresolve the question of why some birds breed cooperatively. For example,cooperative king? shers and bee-eaters are heavily parasitized in Africa butnot in Australasia, showing that other advantages of helping behavior are suf?cient for cooperation to persist. But we should take parasitism seriously as animportant force in a cooperative life. Indeed, it may provide a mechanismcontributing to the previously discovered global correlates of cooperation (4–6). Some insight into the likely order of evolution might come from furthercomparative predictions. For instance, if cooperation arose fi rst as a defenseagainst parasitism, cooperators may be most prevalent among hosts that relyheavily on repelling adult parasites, rather than on antiparasite strategies atlater reproductive stages, such as egg or chick discrimination ( 9). Incontrast, if parasites target existing cooperators because they providesuperior care, this should be especially true of parasites whose chicks havethe most pressing needs—for instance, those in parasitic families with largebody size relative to their hosts or those whose chicks do not kill host youngand therefore must share their foster parents’ care. Could there be a similarassociation between cooperation and parasitism among other highly socialanimals? Cooperation in mammals clearly persists irrespective of parasitism, giventhat there are no known brood-parasitic mammals (perhaps because it would bediffi cult for a mammal to insert live young into another’s care). Butrepelling parasitic egg-laying intrusions is crucial to many hosts of sociallyparasitic insects and has shaped sophisticated adaptations and counterdefensesfor and against brute force and secrecy ( 10). It will be fascinating toexplore how selection for antiparasitic defense has interacted with monogamyand defensible resources as forces favoring kin-selected cooperation ininvertebrates, touching on an active debate in evolutionary biology. Answers tosuch comparative questions will ultimately be limited by our knowledge ofnatural history. The work by Feeney et al. is testament to the evolutionaryinsights enabled by careful long-term fi eld studies, together with thecumulative legacy of those naturalists who made the unglamorous effort torecord and publish observations of real animals in real places.