Comparison of the wing polyphenic response of pea aphids (\u3ci\u3eAcyrthosiphon pisum\u3c/i\u3e) to crowding and predator cues

1. Pea aphids (Acyrthosiphon pisum Harris; Hemiptera: Aphididae) exhibit transgenerational wing polyphenism, in which unwinged females produce genetically identical winged offspring in response to environmental cues such as overcrowding and predation risk that indicate poor habitat quality. 2. Laboratory experiments were carried out to explore the intensity of the wing polyphenic response of pea aphids exposed to cues from ladybird predators and crowding, and their response was compared to pea aphids that were not exposed to any cues (control). 3. The study used cues from two different ladybird species: Coccinella septempunctata L. (Coleoptera: Coccinellidae) and Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae) to investigate whether the wing polyphenic response of pea aphids to predator cues can be generalized 4. The intensity of the wing polyphenic response of pea aphids to crowding was found to be much stronger than their response to predator cues. There was no response to H. convergens cues and the response to C. septempunctata cues was mixed

Pea aphid winged and wingless males exhibit reproductive, gene expression, and lipid metabolism differences

Alternative, intraspecific phenotypes offer an opportunity to identify the mechanistic basis of differences asso- ciated with distinctive life history strategies. Wing dimorphic insects, in which both flight-capable and flight- incapable individuals occur in the same population, are particularly well-studied in terms of why and how the morphs trade offflight for reproduction. Yet despite a wealth of studies examining the differences between fe- male morphs, little is known about male differences, which could arise from different causes than those acting on females. Here we examined reproductive, gene expression, and biochemical differences between pea aphid ( Acyrthosiphon pisum ) winged and wingless males. We find that winged males are competitively superior in one- on-one mating circumstances, but wingless males reach reproductive maturity faster and have larger testes. We suggest that males tradeoffincreased local matings with concurrent possible inbreeding for outbreeding and in- creased ability to find mates. At the mechanistic level, differential gene expression between the morphs revealed a possible role for activin and insulin signaling in morph differences; it also highlighted genes not previously identified as being functionally important in wing polymorphism, such as genes likely involved in sperm produc- tion. Further, we find that winged males have higher lipid levels, consistent with their use as flight fuel, but we find no consistent patterns of different levels of activity among five enzymes associated with lipid biosynthesis. Overall, our analyses provide evidence that winged versus wingless males exhibit differences at the reproductive, gene expression, and biochemical levels, expanding the field’s understanding of the functional aspects of morph differences

Investigations into Sensory Ecology and Gene Evolution of the pea aphid (\u3ci\u3eAcyrthosiphon pisum\u3c/i\u3e)

Organisms use environmental cues to gather information required to perform activities that are essential for their survival and reproduction, such as searching for food, avoiding danger, and finding mates. They respond to the acquired information by changing their behavior or physiology, which may result in increased fitness. Due to the fundamental importance of information in an organism’s life, it is important to understand its acquisition, processing, and the organism’s response to it. In the work presented here, we used the pea aphid (Acyrthosiphon pisum), an insect that produces multiple phenotypes, or morphs, that are genetically identical, but differ in morphology, ecology, and behavior, as a model system for investigations into sensory ecology and gene evolution. First, we examined the influence of aphid honeydew, a prey-associated cue, on the interactions between pea aphids and their ladybird predators. We found that the honeydew influenced the foraging behavior of predator larvae, but the larvae were not able to distinguish between the honeydew of high and low nutritional quality prey. Next, we compared the wing polyphenic response of pea aphids to two factors that are potential indicators of poor habitat - predator cues and crowding. The wing polyphenic response occurs when wingless pea aphids produce winged offspring in response to environmental stress. We found that the intensity of the wing polyphenic response of pea aphids to crowding was much stronger than their response to predator cues, suggesting pea aphids acquire and process information from different cues to assess environment quality and differentially respond to it. Thirdly, we compared chemosensory gene expression between different pea aphid morphs to investigate weather the chemosensory system changes with morph specialization. We found distinct chemosensory gene expression profiles of the pea aphid morphs that indicated intraspecific specialization of chemosensory systems. Finally, we compared the rates of evolution of morph-biased genes (genes highly expressed in one morph compared to the other morphs) with unbiased genes to explore the evolutionary consequences of phenotypic plasticity. Our results illustrated that morph-biased genes evolve faster than unbiased genes as a result of relaxed purifying selection. Advisors: Brigitte Tenhumberg and Jennifer A. Brisso

Influence of aphid honeydew on the foraging behavior of \u3ci\u3eHippodamia convergens\u3c/i\u3e larvae

1. Environmental cues associated with prey are known to increase predator foraging efficiency. Ladybird larvae are major predators of aphids. The sugary excretion of aphids (honeydew) has been proposed to serve as a prey-associated cue for ladybird larvae. 2. Ladybird larvae are regularly found on the ground moving between plants or after falling off plants. The use of prey-associated cues would be particularly beneficial for ladybird larvae on the ground in that such cues would help them to decide which plants to climb because aphids are patchily distributed within as well as amongst plants and, as a result, many plants are either not infested with aphids or do not host an aphid species of high nutritional value for ladybird larvae. 3. Laboratory experiments with larvae of Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae) were carried out to explore whether honeydew accumulated on the ground is used as a foraging cue. The study also investigated whether, if honeydew is a foraging cue, larvae show differential responses to honeydew of high-quality prey Acyrthosiphon pisum Harris compared with that of low-quality prey Aphis fabae Scopoli (both: Homoptera: Aphididae). 4. Hippodamia convergens larvae stayed longer in areas containing honeydew but did not engage in longer bouts of searching. Furthermore, larvae did not distinguish between honeydew from high- and low-quality aphid prey

Investigations into sensory ecology and gene evolution of the pea aphid (Acyrthosiphon pisum)

Organisms use environmental cues to gather information required to perform activities that are essential for their survival and reproduction, such as searching for food, avoiding danger, and finding mates. They respond to the acquired information by changing their behavior or physiology, which may result in increased fitness. Due to the fundamental importance of information in an organism’s life, it is important to understand its acquisition, processing, and the organism’s response to it. In the work presented here, we used the pea aphid (Acyrthosiphon pisum), an insect that produces multiple phenotypes, or morphs, that are genetically identical, but differ in morphology, ecology, and behavior, as a model system for investigations into sensory ecology and gene evolution. First, we examined the influence of aphid honeydew, a prey-associated cue, on the interactions between pea aphids and their ladybird predators. We found that the honeydew influenced the foraging behavior of predator larvae, but the larvae were not able to distinguish between the honeydew of high and low nutritional quality prey. Next, we compared the wing polyphenic response of pea aphids to two factors that are potential indicators of poor habitat - predator cues and crowding. The wing polyphenic response occurs when wingless pea aphids produce winged offspring in response to environmental stress. We found that the intensity of the wing polyphenic response of pea aphids to crowding was much stronger than their response to predator cues, suggesting pea aphids acquire and process information from different cues to assess environment quality and differentially respond to it. Thirdly, we compared chemosensory gene expression between different pea aphid morphs to investigate weather the chemosensory system changes with morph specialization. We found distinct chemosensory gene expression profiles of the pea aphid morphs that indicated intraspecific specialization of chemosensory systems. Finally, we compared the rates of evolution of morph-biased genes (genes highly expressed in one morph compared to the other morphs) with unbiased genes to explore the evolutionary consequences of phenotypic plasticity. Our results illustrated that morph-biased genes evolve faster than unbiased genes as a result of relaxed purifying selection

Comparison of the wing polyphenic response of pea aphids (\u3ci\u3eAcyrthosiphon pisum\u3c/i\u3e) to crowding and predator cues

1. Pea aphids (Acyrthosiphon pisum Harris; Hemiptera: Aphididae) exhibit transgenerational wing polyphenism, in which unwinged females produce genetically identical winged offspring in response to environmental cues such as overcrowding and predation risk that indicate poor habitat quality. 2. Laboratory experiments were carried out to explore the intensity of the wing polyphenic response of pea aphids exposed to cues from ladybird predators and crowding, and their response was compared with pea aphids that were not exposed to any cues (control). 3. The study used cues from two different ladybird species—Coccinella septempunctata L. (Coleoptera: Coccinellidae) and Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae)—to investigate whether the wing polyphenic response of pea aphids to predator cues can be generalized. 4. The intensity of the wing polyphenic response of pea aphids to crowding was found to be much stronger than their response to predator cues. There was no response to H. convergens cues and the response to C. septempunctata cues was mixed. Includes 2 supplementary tables

Accelerated Evolution of Morph-Biased Genes in Pea Aphids

International audiencePhenotypic plasticity, the production of alternative phenotypes (or morphs) from the same genotype due to environmental factors, results in some genes being expressed in a morph-biased manner. Theoretically, these morph-biased genes experience relaxed selection, the consequence of which is the buildup of slightly deleterious mutations at these genes. Over time, this is expected to result in increased protein divergence at these genes between species and a signature of relaxed purifying selection within species. Here we test these theoretical expectations using morph-biased genes in the pea aphid, a species that produces multiple morphs via polyphenism. We find that morph-biased genes exhibit faster rates of evolution (in terms of dN/dS) relative to unbiased genes and that divergence generally increases with increasing morph bias. Further, genes with expression biased towards rarer morphs (sexual females and males) show faster rates of evolution than genes expressed in the more common morph (asexual females), demonstrating that the amount of time a gene spends being expressed in a morph is associated with its rate of evolution. And finally, we show that genes expressed in the rarer morphs experience decreased purifying selection relative to unbiased genes, suggesting that it is a relaxation of purifying selection that contributes to their faster rates of evolution. Our results provide an important empirical look at the impact of phenotypic plasticity on gene evolution