Reduction of a nymphal instar in a dampwood termite: heterochronic shift in the caste differentiation pathways

EvoDevo

Toru Miura¹  Junpei Shinji¹  Kohei Oguchi¹  Shigeyuki Koshikawa²  Ryotaro Nii³ 

[1] 0000 0001 2151 536X, grid.26999.3d, Misaki Marine Biological Station, School of Science, The University of Tokyo, 238-0225, Miura, Kanagawa, Japan;0000 0001 2173 7691, grid.39158.36, Faculty of Environmental Earth Science, Hokkaido University, 060-0810, Sapporo, Hokkaido, Japan;0000 0001 2173 7691, grid.39158.36, Graduate School of Environmental Science, Hokkaido University, 060-0810, Sapporo, Hokkaido, Japan;

关键词: Termites;    Alate differentiation;    Caste differentiation;    Nymphal instar;    Wing formation;    Gene expression;    Heterochrony;   

DOI  :  10.1186/s13227-019-0123-8

来源: publisher

【 摘 要 】

BackgroundGenerally in termites, alates differentiate through multiple nymphal instars which gradually develop wing buds. However, in a dampwood termite, Hodotermopsis sjostedti, alates molt directly from a single nymphal instar with short wing buds. In this study, to examine the mechanism underlying the wing formation during the alate differentiation in H. sjostedti, histological and morphological observations were carried out on the developmental process of wing formation during the nymphal instar, in comparison with those in Zootermopsis nevadensis, which has two nymphal instars. Furthermore, the expression patterns of genes that are thought to be responsible for wing formation, i.e., wing-patterning genes and genes encoding hormone-related factors, were quantified during alate differentiation and compared between the two species.ResultsThe results showed that, in H. sjostedti, wings were formed in a complicatedly folded shape, not only inside the wing buds as seen in Z. nevadensis, but also under the dorsal thoracic cuticle, where the wing tips shifted toward the median thoracic part. Accordingly, the wing expansion pattern also differed from that in Z. nevadensis. Furthermore, the results of real-time qRT-PCR on overall expression profiles of wing-patterning genes and hormone-related genes suggest that the single nymphal instar in H. sjostedti well resembles to the second nymphal instar in Z. nevadensis. In particular, significant upregulation of vestigial (vg) and downregulation of Krüppel homolog 1 (Kr-h1) that were observed at the second nymphal instar in Z. nevadensis apparently occurred during the single nymphal instar in H. sjostedti.ConclusionThe developmental events for wing formation are compacted into a single nymphal instar in H. sjostedti, and as a result, the unique wing formation is seen to compensate for the spatial restriction inside small wing buds, leading to the completion of functional wings.

【 授权许可】

CC BY