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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.
