Abstract
Interspecific interaction with host plants have important consequences for the host race formation of herbivorous insects. Plant secondary metabolites, particularly those that are involved in host races specializing on plants, warrant the theory of host specialization. Acyrthosiphon pisum comprises various host races that adapt to different Fabaceae plants, which provides an ideal system for determining the behavioral and physiological mechanisms underlying host-adaptive diversification. The current study evaluated the effects of host transfer on population fitness, feeding behavior and the transcriptome-wide gene expression of the two host races of A. pisum, one of which was originally from Medicago sativa and the other from Pisum sativum. The results showed that the Pisum host race of A. pisum had a lower population abundance and feeding efficiency than the Medicago host race in terms of a longer penetration time and shorter duration times of phloem ingestion when fed on M. sativa. In contrast, few differences were found in the population abundance and feeding behavior of A. pisum between the two host races when fed on P. sativum. Meanwhile, of the nine candidate phenolic compounds, only genistein was significantly affected by aphid infestation; higher levels of genistein were detected in M. sativa after feeding by the Pisum host race, but these levels were reduced relative to uninfested controls after feeding by the Medicago host race, which suggested that genistein may be involved in the specialization of the aphid host race on M. sativa. Further exogenous application of genistein in artificial diets showed that the increase in genistein reduced the survival rate of the Pisum host race but had little effect on that of the Medicago host race. The transcriptomic profiles indicated that the transcripts of six genes with functions related to detoxification were up-regulated in the Pisum host race relative to the Medicago host race of A. pisum. These results suggested that the inducible plant phenolics and associated metabolic process in aphids resulted in their differential adaptations to their Fabaceae host.
Highlights
Host race is considered to be one of several intermediates in the continuum between polymorphisms and the full species [1]
The present study aimed (1) to compare the feeding behavior and population abundance of the Medicago and Pisum host races of A. pisum on their specialized and non-specialized legume hosts; (2) to determine whether the levels of defensive phenolic contents, such as phenols and flavonoids, change in response to aphid feeding and have detrimental effects on the performance of the two host races; and (3) to quantify the transcriptome-wide gene expression of the two host races of A. pisum when fed on M. sativa and to further screen the candidate genes that are involved in the differential host adaptation between the two host races of A. pisum
The field-collected colonies (Medicago host race and Pisum host race) were individually established from a single parthenogenetic female. We verified that these two populations are specialized on different host plants by investigating the aphid population abundance and detecting the aphid feeding behavior using the electrical penetration graph (EPG) technique when fed on their own host plant and the alternative plant
Summary
Host race is considered to be one of several intermediates in the continuum between polymorphisms and the full species [1]. Given that the different host races of aphids have enormous variations in saliva composition, their specialized responses to host defenses are of paramount importance in host transformation These effectors could interfere with the defense-signaling pathway [12,13,14] and alter plant secondary metabolite levels [15]. The present study aimed (1) to compare the feeding behavior and population abundance of the Medicago and Pisum host races of A. pisum on their specialized and non-specialized legume hosts; (2) to determine whether the levels of defensive phenolic contents, such as phenols and flavonoids, change in response to aphid feeding and have detrimental effects on the performance of the two host races; and (3) to quantify the transcriptome-wide gene expression of the two host races of A. pisum when fed on M. sativa and to further screen the candidate genes that are involved in the differential host adaptation between the two host races of A. pisum
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