Complex trait differentiation between host-populations of the pea aphid Acyrthosiphon pisum (Harris): implications for the evolution of ecological specialisation

Abstract

Variation in traits affecting preference for, and performance on, new habitats is a key factor in the initiation of ecological specialisation and adaptive speciation. However, habitat and resource use also involves other traits whose influence on ecological and genetic divergence remains poorly understood. In the present study, we investigated the extent of variation of life-history traits among sympatric populations of the pea aphid Acyrthosiphon pisum, which shows several host races that are specialised on various plants of the family Fabaceae plants and is an established model for ecological speciation. First, we assessed the community structure of microbial partners within host populations of the pea aphid. The effect of these microbes on host fitness is uncertain, although there is growing evidence that they may modulate various important adaptive traits of their host such as plant utilisation and resistance against natural enemies. Second, we performed a multivariate analysis on several ecologically relevant features of host populations recorded in the present and previous studies (including microbial composition, colour morph, reproductive mode, and male dispersal phenotype), enabling the identification of correlations between phenotypic traits. We discuss the ecological significance of these associations of traits in relation to the habitat characteristics of pea aphid populations, and their consequences for the evolution of ecological specialisation and sympatric speciatio

Facultative Symbiont Infections Affect Aphid Reproduction

“…For offsetting the high fitness reduction due to loss of male offspring, potential benefits associated with the male-killing phenotype have been investigated both theoretically and empirically, which include increment of available resources through cannibalism, avoidance of inbreeding depression, reduced local mate/resource competition, and others [40]. Previous studies on the pea aphid using molecular markers have shown that populations associated with perennial host plants tend to produce sexual forms and are generally less dispersive, while populations associated with annual host plants tend to produce few sexual forms and are more dispersive [28], [29]. Inbred crosses are thus more likely in the former type of populations than in the latter type of populations, especially after several generations of clonal reproduction on the same plant in the same field.…”

“…Inbred crosses are thus more likely in the former type of populations than in the latter type of populations, especially after several generations of clonal reproduction on the same plant in the same field. It was certainly reported that Spiroplasma infections were higher in populations on perennial host plants (30–40%) than in populations on annual host plants (less than 10%) [29]. It is conceivable, although speculative, that Spiroplasma infection may reduce the risk of inbreeding depression through male-killing in such aphid populations.…”

Symbiont infection affects aphid defensive behaviours

“…The genotypes and the symbiotic status of the sampled aphids were determined (see [10] and [9] for details on genotyping and symbiont detection, respectively). From these analyses, we selected 10 aphid genotypes infected or not infected with H. defensa (table 1).…”

Cover Caption

“…defensa in an aphid line harboring a double infection. Infections with two or more facultative endosymbionts are frequently observed in aphids (Ferrari et al ., ; Frantz et al ., ; Nyabuga et al ., ; Ferrari et al ., ; Russell et al ., ). However, sequencing of its genome revealed that phages were absent (Hansen et al ., ).…”