Abstract
Insect populations feeding on different plant species are under selection pressure to adapt to these differences. A study integrating elements of the ecology, behavior, and gene expression of aphids on different host plants has not yet been well-explored. The present study explores the relationship between host fitness and survival, feeding behavior, and salivary gland gene expression of a pea (Pisum sativum) host race of Acyrthosiphon pisum feeding on a common host Vicia faba and on three genetically-related hosts (Vicia villosa, Medicago truncatula, and Medicago sativa). Life table data indicated that aphids on non-favored hosts exhibited small size, low reproduction rate, slow population increase and individual development, and long lifespan. Electrical penetration graph results showed that the aphids spent significantly less time in passive ingestion of phloem sap on all non-preferred host plants before acclimation. After a period of acclimation on M. truncatula and V. villosa, pea host race individuals showed improved feeding behavior. No individuals of the pea host race completed its life history on M. sativa. Interestingly, the number of host-specific differentially-expressed salivary gland genes was negatively correlated with the fitness of aphids on this host plant. This study provided important cues in host plant specialization in aphids.
Highlights
Bean, V. faba, is an universal host for all pea aphid genotypes[14]
Remarkable decreases in the net reproductive rate, intrinsic rate of increase, and finite rate of increase were observed during the short-term shift to the three host plants, especially in M. sativa, on which the YYC clone showed the lowest net reproductive rate (R0 = 14 offspring), intrinsic rate of increase, and finite rate of increase (λ = 1.19 d−1) (Table 1)
The degree of gene expression change when the YYC clone was transferred to the two Medicago plants was more similar than when the YYC clone was transferred to V. villosa (Fig. 5A)
Summary
Bean, V. faba, is an universal host for all pea aphid genotypes[14]. In North America, pea aphid populations feeding on two important legumes, alfalfa (M. sativa) and red clover (Trifolium pratense), are highly specialized and reproductively isolated[13,15]. Watery saliva is composed of a more complex mixture of enzymes and other components, which highly differ between aphid species and within the same species based on their diet[18,19,20,21,22,23,24,25,26,27,28,29] These studies imply that the aphid adaptation range of host plants is largely linked to the variations of watery saliva composition. We maintain the clone in the laboratory on the neutral host V. faba, compare its survival, feeding behavior, and salivary gland gene expression on three additional plants (V. villosa, Medicago truncatula, and M. sativa) representing preferred hosts for closely related host races[11]. We measure the performance of the YYC clone on each host plant before any acclimation to the new host has occurred, and again once the clone has had the opportunity to “adapt” to the new host plant
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