Why do ants shift their foraging from extrafloral nectar to aphid honeydew?
Why do ants shift their foraging from extrafloral nectar to aphid honeydew?
复制标题
为什么蚂蚁的觅食方式从花外花蜜转向蚜虫蜜露？
作者：
N. Katayama;David H. Hembry;M. Hojo;N. Suzuki
当蚜虫寄生在花外蜜腺（EFNs）植物上且蚜虫群体较小时，蚂蚁经常使用花外蜜腺（EFNs）而不倾向于蚜虫。然而，随着蚜虫群体规模的增加，蚂蚁停止使用efn并加强与蚜虫的联系。虽然蚂蚁行为的转变对于确定蚂蚁-植物-蚜虫相互作用的动力学很重要，但尚不清楚为什么会发生这种转变。在此，我们检验了两种假说来解释这种行为转变的机制：(1)花外花蜜分泌随着蚜虫的食草性而改变，或者(2)植物不改变花外花蜜分泌，但蚜虫对蚂蚁的总回报会超过一定蚜虫群体大小以上的efn。为了判断哪种机制是合理的，我们研究了有蚜虫和没有蚜虫的植物的花外花蜜分泌模式，比较了efn和蚜虫提供的糖量，并研究了花外花蜜和蜜露对蚂蚁的吸引力。结果表明，蚜虫对花外分泌没有诱导作用，但花外花蜜中的糖浓度高于蜜露，并且人工花外花蜜溶液比人工蚜虫蜜露溶液更能吸引工蚁。这些结果表明，单位体积的花外花蜜比蚜虫蜜露更具吸引力。然而，即使一个只有两个个体的蚜虫群体也能比efn给蚂蚁提供更大的奖励。这表明蚂蚁行为的转变可以用第二个假设来解释。
When aphids parasitize plants with extrafloral nectaries (EFNs) and aphid colony size is small, ants frequently use EFNs but hardly tend aphids. However, as the aphid colony size increases, ants stop using EFNs and strengthen their associations with aphids. Although the shift in ant behavior is important for determining the dynamics of the ant–plant–aphid interaction, it is not known why this shift occurs. Here, we test two hypotheses to explain the mechanism responsible for this behavioral shift: (1) Extrafloral nectar secretion changes in response to aphid herbivory, or (2) plants do not change extrafloral nectar secretion, but the total reward to ants from aphids will exceed that from EFNs above a certain aphid colony size. To judge which mechanism is plausible, we investigated secretion patterns of extrafloral nectar produced by plants with and without aphids, compared the amount of sugar supplied by EFNs and aphids, and examined whether extrafloral nectar or honeydew was more attractive to ants. Our results show that there was no inducible extrafloral secretion in response to aphid herbivory, but the sugar concentration in extrafloral nectar was higher than in honeydew, and more ant workers were attracted to an artificial extrafloral nectar solution than to an artificial aphid honeydew solution. These results indicate that extrafloral nectar is a more attractive reward than aphid honeydew per unit volume. However, even an aphid colony containing only two individuals can supply a greater reward to ants than EFNs. This suggests that the ant behavioral shift may be explained by the second hypothesis.