| In nature,more than 80%of angiosperms rely on biotic vectors for successful pollination,but pollen limitation caused by lacking of pollinators is widespread,resulting in the failure of the normal development of fruits or seeds.The phenomenon of florivory is also very common in nature.Damages done to flowers often directly or indirectly affect the reproductive fitness of plants.When pollinators and florivores are in the same system,floral traits may evolve in complex ways to cope with the combined selection pressures imposed by pollinators and florivores in order to achieve higher reproductive fitness.However,until now,research on integration of pollination and florivory is still limitedHere we studies Iris bulleyana,a perennial herbaceous plant of Iris,Iridaceae.This hermaphroditic and protandrous species relies on specific pollinators for successful pollen transfer,and its sexual reproduction can be affected by the feeding behavior of the florivory sawfly(Tenthredo spp.).To understand the role of pollinator and florivore on evolution of floral traits,we conducted a large-scale comparative study on wild populations of I.bulleyana,in the Hengduan Mountains of southwest China in 2017 and2018.The results are as follows:Under natural conditions,the number of seeds produced by single flower is(22.84±1.91)(n=293).The number of seeds of supplementary pollinated flowers(48.91±2.35,n=276)was significantly higher than that of the natural flowers(P<0.001),indicating that pollen limitation is prevalent in natural populations of this species.After artificial damage treatment of corolla tube,the number of seeds(14.21±1.25,n=275)also decreased significantly,in comparison with natural controls(P<0.001).However,there was no significant difference in seed number between the two treatments with supplementary pollination(P>0.05).This indicates that damage of corolla tube by sawfly can indirectly affect the reproduction of plants through its influence on pollination process.In general,the diversity and abundance of pollinators decrease as the elevation rises,and plants tend to evolve larger flowers to increase their pollinator attractiveness.Our large-scale survey shows that,with the increase of the population altitude,the visitation frequency of pollinators is indeed significantly reduced(R~2=0.7954,P<0.001),and the visual size of flowers is significantly increased(R~2=0.5707,P<0.01),but the total sugar content in nectar shows a downward trend(R~2=0.2926,P<0.05).This may be due to the large overall yield of the nectar,which is enough to be the reward for pollinators in the short flowering period of a single flower,and does not contribute as much as the visual signal of flowers to attract pollinators.In order to improve pollination,plants will allocate the limited resources of flower organs to improve visual attractiveness,rather than to raise the yield of reward.Although the florivory incidence was not correlated with elevation(R~2=0.1474,P=0.1192),it was significantly negatively correlated with the average thickness of corolla tube(R~2=0.33,P<0.05).This is because a thinner corolla tube is beneficial for the sawfly to obtain the nutrient-rich tissue and nectar in the corolla tube.However,we have not found the defense strategy that I.bulleyana evolved in response to the florivory,which may be due to a lack of effective revelation of the chemical defense mechanism in this study,or it may be because the sawfly has not appeared in this system for a long time,and plants has not undergone adaptive evolution. |
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