Soldier differentiation during embryogenesis of a social aphid, Pseudoregma bambucicola

Authors


Dr Takema Fukatsu, Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, 305-8566 Japan. Email: t-fukatsu@aist.go.jp

Abstract

To understand the developmental process of aphid soldier differentiation, we investigated the morphological characters of normal nymphs, soldier nymphs and developing embryos of Pseudoregma bambucicola. Results of morphometric analyses showed that normal and soldier nymphs formed discrete clusters on the basis of several morphological characters, although a small number of intermediate individuals, termed ‘intercaste nymphs’, were present. In late embryonic stages, normal and soldier embryos were morphologically distinguishable. The earlier the embryonic stage, the smaller the morphological differences between them. In early embryos less than 1000 µm in length, normal and soldier embryos were not morphologically distinguishable, suggesting that the onset of soldier differentiation occurs at an early embryonic stage. Throughout embryonic development, morphological differentiation of the soldier caste proceeded gradually. Notably, several morphological characters of soldiers grew remarkably upon larviposition. Observation of embryonic leg cuticle revealed a characteristic folding structure, indicating that  some  morphological  traits  of  the  soldier  are  exaggerated  upon  larviposition  through  expansion  of the folded cuticle. We suggest that morphological differentiation of the soldier caste in P. bambucicola comprises two phases: gradual growth during embryogenesis and rapid growth upon larviposition.

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