Seasonal ecosystem linkages contribute to the maintenance of migratory polymorphism in a salmonid population

<p><span>The influence of resource subsidies on animal </span><span>growth, survival, and reproduction </span><span>is well understood</span><span>, but their ultimate effects on life</span> <span>history</span> <span>have been </span><span>less</span><span> explored.</span> <span>Some wild species</span><span> have </span><span>a</span><span> partially migratory life</span> <span>history</span><span>, wherein migration is dictated based upon </span><span>threshold </span><span>traits</span><span> regulated </span><span>in part </span><span>by </span><span>the </span><span>seasonal </span><span>availability of resources. We conducted</span><span> a large-scale </span><span>field </span><span>manipulation</span><span> experiment</span><span> where</span><span> we </span><span>provided a</span><span> terrestrial invertebrate subsidy</span><span> to </span><span>red-spotted masu salmon</span><span>. Individuals in stream</span><span> reaches </span><span>that received a subsidy had, on average, a 53% increase in growth rate relative to those</span><span> in control reaches. </span><span>This increased</span><span> growth </span><span>resulted in a greater proportion of</span><span> individuals </span><span>reaching</span><span> the threshold body size </span><span>and smolting</span><span> in </span><span>the </span><span>autumn. Consequently, 19</span><span>–</span><span>55% of females </span><span>in subsidized</span><span> reaches</span><span> became migratory</span><span>, whereas 0</span><span>–</span><span>14% </span><span>became migratory </span><span>in the control reaches. Our findings highlight seasonal ecosystem linkage </span><span>as</span><span> a key ecosystem </span><span>property for maintaining</span><span> migratory polymorphism in partially</span> <span>migratory animals</span><span>.</span></p>