Abundant Citizen Science Data Reveal That the Peacock Butterfly Aglais io Recently Became Bivoltine in Belgium.

Marc Herremans,Karin Gielen,Pieter Vanormelingen,Kristijn R.R Swinnen,Dirk Maes,Jos Van Kerckhoven,Wim Veraghtert

doi:10.3390/insects12080683

Abstract

Simple SummaryThe peacock butterfly is abundant and widespread in Europe. It used to have a single generation per year: adults born in summer overwintered and reappeared in spring to reproduce. However, recent flight patterns in western Europe show three peaks during the year: a first one in spring (overwintering butterflies), a second one in early summer (offspring of the spring generation), and a third one in autumn. Hitherto, it was unclear whether this third autumn flight peak was a second new generation or consisted of butterflies flying again in autumn after a summer rest. Based on hundreds of thousands of observations and thousands of pictures submitted by naturalists from the public to the online portal ‘observation’ in Belgium, we demonstrate that Peacocks shifted towards two new generations per year in recent decades. Mass citizen science data has become increasingly important in tracking the response of biodiversity to rapid environmental changes (e.g., climate change).The peacock butterfly is abundant and widespread in Europe. It is generally believed to be univoltine (one generation per year): adults born in summer overwinter and reappear again in spring to reproduce. However, recent flight patterns in western Europe mostly show three peaks during the year: a first one in spring (overwintering butterflies), a second one in early summer (offspring of the spring generation), and a third one in autumn. It was thus far unclear whether this autumn flight peak was a second new generation or consisted of butterflies flying again in autumn after a summer rest (aestivation). The life cycle of one of Europe’s most common butterflies is therefore still surprisingly inadequately understood. We used hundreds of thousands of observations and thousands of pictures submitted by naturalists from the public to the online portal observation.orgin Belgium and analyzed relations between flight patterns, condition (wear), reproductive cycles, peak abundances, and phenology to clarify the current life history. We demonstrate that peacocks have shifted towards two new generations per year in recent decades. Mass citizen science data in online portals has become increasingly important in tracking the response of biodiversity to rapid environmental changes such as climate change.

Highlights

Many aspects of the life of ectotherms such as biochemistry and development speed depend on environmental temperatures [1,2,3]
We correlate the abundance of each generation with the abundance of year’s spring peak to check which generation contributes most to the year. This way, we demonstrate that the peacock recently had two generations in Belgium, one in early summer and one in late summer, the latter one reappearing the following spring: it is bivoltine rather than having a single generation
With three flight peaks per year, usually of growing importance, appropriately spaced (Figures 2 and 3), reproduction documented at the right time in between (Figure 6), large numbers of fresh butterflies suddenly emerging at the onset of the second and third flight peak (Figures 3 and 4), and with the second generation constituting at least the bulk of the overwintering population, there is no doubt that peacock butterflies were fully bivoltine in Belgium recently

Summary

Introduction

Many aspects of the life of ectotherms such as biochemistry and development speed depend on environmental temperatures [1,2,3]. The extent of the second generation is said to be variable, dependent on region, year, or weather conditions [33,34,37,39,41,46,47,50,52] Whether this third flight peak in autumn represents a genuine second generation is obscured by the possibility that peacocks of the second flight peak may soon after hatching go into diapause early in summer (i.e., aestivation), and may reappear later in autumn to top up fat stores before winter, causing two flight peaks in one year from the same butterflies [37,52]. The life cycle of one of Europe’s most common butterflies is surprisingly inadequately understood

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