Abstract

The European map butterfly (Araschnia levana) is a classic example of seasonal polyphenism because the spring and summer imagoes display two distinct morphological phenotypes. The light regime and temperature during larval and prepupal development determine whether or not the pupae commit to diapause and overwintering and thus whether spring or summer imagoes emerge. We used suppression subtractive hybridization to experimentally screen for genes that are differentially expressed in prepupae committed either to accelerated metamorphosis and egg production or diapause and overwintering. The range and ontology of the differentially expressed genes in prepupae developing from larvae exposed either to long‐day (LD) or short‐day (SD) conditions revealed fundamental differences. The SD prepupae preferentially expressed genes related to cuticle formation and immunity, reflecting the formation of a robust pupal exoskeleton and the upregulation of antimicrobial peptides as preparations for overwintering. One protein preferentially expressed in SD prepupae has a counterpart in Bombyx mori that functions as a diapause duration clock. The differentially expressed genes in LD prepupae included several members of the dusky and osiris families. We also observed the strong induction of different yellow‐like genes under SD and LD conditions which suggest a role in the developmental choice between seasonal phenotypes. Our transcriptomic data will facilitate the more detailed analysis of molecular mechanisms underlying seasonal polyphenism.

Highlights

  • Seasonal polyphenism is a phenomenon observed in species that respond to seasonally changing environmental parameters by expressing distinct phenotypes (Shapiro 1976; Simpson et al 2011)

  • We investigated the molecular basis of seasonal polyphenism in A. levana by screening for genes that are differentially expressed in prepupae developing from larvae exposed either to LD (18-h photoperiod) or SD (8-h photoperiod) conditions

  • We investigated differences in gene expression between A. levana prepupae derived from larvae exposed to LD or SD conditions to identify candidate genes involved in seasonal polyphenism

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Summary

Introduction

Seasonal polyphenism is a phenomenon observed in species that respond to seasonally changing environmental parameters by expressing distinct phenotypes (Shapiro 1976; Simpson et al 2011). The caterpillars developing into either the spring or the summer phenotype of the imagoes are exposed to distinct biotic and abiotic environments. Caterpillars encountering longday (LD) conditions develop rapidly into adult butterflies of the summer generation (Reinhardt 1984) Their offspring are exposed to short-day (SD) conditions, and the resulting pupae enter a dormant state known as diapause characterized by enhanced stress tolerance, which is necessary to survive winter temperatures and prolonged exposure to pathogens (MacRae 2010). Both the day length a 2016 The Authors.

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