EVOLUTIONARY REDUCTION OF COMPLEX LIFE CYCLES: LOSS OF HOST‐ALTERNATION IN PEMPHIGUS (HOMOPTERA: APHIDIDAE)

Abstract

Abstract. -In a Utah canyon, the aphid, Pemphigus betae, exhibits two life cycles: a cycle involving host-alternation between cottonwood trees and roots of herbaceous plants and a secondarily reduced cycle, in which the cottonwood generations are eliminated so that wingless forms live year round on roots. Relative frequencies of the two life-cycle types vary along a 30-km stretch of the canyon, with the reduced cycle predominating at upper sites. Factors underlying this life-cycle variation were examined with common-garden and transfer experiments. Results showed 1) a facultative increase in production of alternating forms in response to crowding in root colonies, 2) a genetic component to both within-and between-site variation in tendency to produce alternating morphs, and 3) site-specific environmental effects on level of investment in the reduced versus alternating life cycles. Thus, the variation in frequency of life-cycle reduction in this aphid is dependent on a complex of interdependent factors. These include adaptive phenotypic plasticity, microgeographically variable cues affecting mechanisms ofmorph determination, and genetically based variation in tendency to show reduction versus alternation.Genetic variation between sites corresponds to microgeographic variation in success oflife-cycle phases. Where cottonwood hosts are absent (lower elevations) or where the cottonwood phase has low survival (upper elevations), clones tend to produce fewer migrating morphs, as compared to clones from middle elevations, where the cottonwood phase is relatively favorable. Such independence between conditions in alternate phases is a general feature of complex life cycles and can generate strong site-specific selection for permanent life-cycle reduction. Such life-cycle shifts have sometimes been followed by extensive radiations in aphids and other groups.

The Effects of Host‐plant Genotype, Hybridization, and Environment on Gall‐aphid Attack and Survival in Cottonwood: The Importance of Genetic Studies and the Utility of RFLPS

“…An alternative hypothesis for the increase in resistance as one proceeds higher in elevation contends that aphids are directly affected by elevational differences in environment (e.g., temperature). Environmental differences, such as temperature, are known to effect patterns of aphid host-alternation (Moran and Whitham, 1988). Such environmental differences may also result in increased mortality as well (aphids were collected from a single source tree and transferred, therefore results are not confounded by potential genotypic effects of site).…”

Seed Germination Ecology of Chenopodium album and Chenopodium murale

“…Along with various indirect losses, both species can result in direct crop losses through the release of several allelochemicals, and their allelopathic effects have been reported on sunflower, tomato, mustard, and a few other crop species [ 7 , 10 , 11 ]. Furthermore, C. album also serves as an alternate host for plentiful plant pathogens ( Stagonospora atriplicis, Polymyxa betae, Yellow Vein Virus, Beet Yellows Virus, Peanut Stunt Cucumovirus, Prunus Necrotic Ring Spot Virus), insects ( Pemphigus betae ), and nematodes ( Ditylenchus destructor, Meloidogyne incognita ) [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. Besides crop fields, both species propagate luxuriantly on wastelands, pastures, and uncultivated lands.…”

Host Plants Influence the Symbiont Diversity of Eriosomatinae (Hemiptera: Aphididae)

“…Eriosomatinae is an extraordinary aphid group exhibiting very diverse life history traits and is widely distributed in the Holarctic and Oriental regions [63]. Most eriosomatine species show a heteroecious holocyclic life history, i.e., seasonal switching between primary and secondary host plants [64][65][66]. Eriosomatinae aphids have strong primary host specificity, with different patterns of host association among tribes.…”