Host Specificity Of Acorn Weevils And Their Parasitic Relationships With Fagaceae Species In Zhoushan Archipelago

Habitat fragmentation is one of the major threats to biodiversity.The biodiversity loss could alter the interspecific relationships.The balance of interspecific relationship between plants and insects contributes to the stability of forest community.For the plants-insects system,plants tend to adjust defence mechanism when suffering parasitism.And the infestation and host specificity of parasitic insects may be greatly influenced by habitat fragmentation.Here,we collected Fagaceae seeds and sampled acorn weevils inside the seeds in Zhoushan Archipelago,Zhejiang,China.We measured traits of the seeds and recorded the parasitism rate to test whether parasitism of acorn weevils and the plants physical defense varied among islands.Also we wondered whether specificity of acorn weevils were influenced by habitat fragmentation.Finally,results were obtained as following:1)Habitat fragmentation had significant influence on the parasitism rate of different Fagaceae species.We detected significant interactions among the distance to mainland and plant species,i.e.parasitism rates responded differentially to fragmentation in different plant species.2)Evidence of induced defense was found in the present study.Generally,seed coat thickness increased with increasing parasitism rate,while such trends did not vary among Fagaceae species,indicating that parasitism of weevils induced strengthened physical defense of host trees.3)We however failed to detect the alteration of host specificity of acorn weevils in fragmented habitats.Using two genes from mitochondrial DNA and one gene from nuclear DNA,all sampled acorn weevils were clustered into 5 distinct clades,three of which were identical to the clades revealed by previous study with the other two clades being new species.Furthermore,the host specificity of acorn weevils was not changed on islands with different degrees of fragmentation.Limitations in resources and dispersal capability of acorns weevils were likely to cause the significant influence of habitat fragmentation on their parasitism relationships with their host trees.Nonetheless,the unchanged host specificity of acorn weevils in fragmented habitats was probably the consequence of the relatively small samples.Our findings highlighted that plant-animal interactions could be important and it is of great necessity for further studies focusing on the mechanisms stabilizing interspecific relationships and maintaining biodiversity in island ecosystems.