Two developmental switch points for the wing polymorphisms in the pea aphid Acyrthosiphon pisum

Kota Ogawa,Toru Miura

doi:10.1186/2041-9139-4-30

Abstract

BackgroundIn many insect taxa, wing polymorphism is known to be a consequence of tradeoffs between flight and other life-history traits. The pea aphid Acyrthosiphon pisum exhibits various morphs with or without wings associated with their complex life cycle including wing polyphenism in viviparous females, genetic wing polymorphism in males, and a monomorphic wingless phenotype in oviparous females and fundatrices. While wing differentiation has been investigated in some detail in viviparous females and males, these processes have not yet been elucidated in monomorphic morphs. The ontological development of the flight apparatus, including wings and flight muscles, was therefore carefully examined in oviparous females and fundatrices and compared with other morphs.ResultsThe extensive histological examinations showed that flight-apparatus primordia were not at all produced throughout their postembryonic development in oviparous females and fundatrices, suggesting that during the embryonic stages the primordia are degenerated or not developed. In contrast, in viviparous females and males, the differentiation points to winged or wingless morphs occurred at the early postembryonic instars (first or second instar).ConclusionsBased on the above observations together with previous studies, we propose that there are two developmental switch points (embryonic and postembryonic) for the flight-apparatus development in A. pisum. Since there are multiple developmental trajectories for four wingless phenotypes (wingless viviparous females, oviparous females, fandatrices, wingless males), it is suggested that the developmental pathways leading to various morphs were evolutionarily acquired independently under selective pressures specific to each morph. Especially in viviparous females, the delay of determination is thought to contribute to the condition-dependent expressions of alternative phenotypes, that is, phenotypic plasticity.

Highlights

In many insect taxa, wing polymorphism is known to be a consequence of tradeoffs between flight and other life-history traits
Flight-apparatus development during postembryonic development 1: males and viviparous females To compare the processes associated with flightapparatus development among all morphs, the internal structures of the thoracic segments were observed throughout the postembryonic development
As previously reported [11], the flight muscles of wingless males consist of three components, that is, dorsoventral muscle, dorsal longitudinal muscle, and oblique dorsal muscle, as seen in winged males, despite the degree of flight muscle development differs

Summary

Introduction

In many insect taxa, wing polymorphism is known to be a consequence of tradeoffs between flight and other life-history traits. The pea aphid Acyrthosiphon pisum exhibits various morphs with or without wings associated with their complex life cycle including wing polyphenism in viviparous females, genetic wing polymorphism in males, and a monomorphic wingless phenotype in oviparous females and fundatrices. The ability of insects to fly, which is considered to have arisen only once in the insect class, has contributed enormously to their diversity and evolutionary success [1,2]. Genetic wing polymorphisms and environmental polyphenisms are both observed, sometimes even within a single species [7,8]. Most aphid species exhibit a variety of phenotypes during their life cycle, wing polymorphisms, including wing polyphenism, are the most prevalent of these phenotypic changes [9]. Since the acquisition of wingless morphs appears to have contributed to the evolutionary success of aphids [7,8,13], the evolutionary transition and the acquisition of developmental mechanisms for producing wingless phenotypes are fascinating study foci

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