Siepielski Adam M, Benkman Craig W
Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
Proc Biol Sci. 2008 Aug 22;275(1645):1917-25. doi: 10.1098/rspb.2008.0451.
Although antagonists are hypothesized to impede the evolution of mutualisms, they may simultaneously exert selection favouring the evolution of alternative mutualistic interactions. We found that increases in limber pine (Pinus flexilis) seed defences arising from selection exerted by a pre-dispersal seed predator (red squirrel Tamiasciurus hudsonicus) reduced the efficacy of limber pine's primary seed disperser (Clark's nutcracker Nucifraga columbiana) while enhancing seed dispersal by ground-foraging scatter-hoarding rodents (Peromyscus). Thus, there is a shift from relying on primary seed dispersal by birds in areas without red squirrels, to an increasing reliance on secondary seed dispersal by scatter-hoarding rodents in areas with red squirrels. Seed predators can therefore drive the evolution of seed defences, which in turn favour alternative seed dispersal mutualisms that lead to major changes in the mode of seed dispersal. Given that adaptive evolution in response to antagonists frequently impedes one kind of mutualistic interaction, the evolution of alternative mutualistic interactions may be a common by-product.
尽管拮抗剂被认为会阻碍互利共生关系的进化，但它们可能同时施加选择压力，有利于替代互利共生相互作用的进化。我们发现，由一种传播前种子捕食者（红松鼠Tamiasciurus hudsonicus）施加的选择导致扭叶松（Pinus flexilis）种子防御增加，这降低了扭叶松主要种子传播者（北美星鸦Nucifraga columbiana）的传播效率，同时提高了地面觅食、分散贮藏种子的啮齿动物（鹿鼠属）的种子传播效率。因此，在没有红松鼠的地区，从依赖鸟类进行主要种子传播，转变为在有红松鼠的地区越来越依赖分散贮藏种子的啮齿动物进行二次种子传播。种子捕食者因此可以推动种子防御的进化，这反过来又有利于替代种子传播的互利共生关系，从而导致种子传播方式的重大变化。鉴于对拮抗剂的适应性进化经常会阻碍一种互利共生相互作用，替代互利共生相互作用的进化可能是一种常见的副产品。
