Abstract
We examined the roles of wing melanisation, weight, and basking posture in thermoregulation in Polyommatus Icarus, a phenotypically variable and protandrous member of the diverse Polyommatinae (Lycaenidae). Under controlled experimental conditions, approximating to marginal environmental conditions for activity in the field (= infrequent flight, long duration basking periods), warming rates are maximised with fully open wings and maximum body temperatures are dependent on weight. Variation in wing melanisation within and between sexes has no effect on warming rates; males and females which differ in melanisation had similar warming rates. Posture also affected cooling rates, consistent with cooling being dependent on convective heat loss. We hypothesise that for this small sized butterfly, melanisation has little or no effect on thermoregulation. This may be a factor contributing to the diversity of wing colours in the Polyommatinae. Because of the importance of size for thermoregulation in this small butterfly, requirements for attaining a suitable size to confer thermal stability in adults may also be a factor influencing larval feeding rates, development time and patterns of voltinism. Our findings indicate that commonly accepted views of the importance of melanisation, posture and size to thermoregulation, developed using medium and large sized butterflies, are not necessarily applicable to small sized butterflies.
Highlights
The colour and pattern of butterfly wings has been described as being shaped by three major selective forces: thermoregulation, apparency to conspecifics and reduction of predation risk [1,2,3,4,5,6,7,8,9,10,11]
These requirements can conflict [12] as apparency may promote more brightly coloured butterflies [2], [10], [13]-[14], but these individuals may be more visible to predators [9], PLOS ONE | DOI:10.1371/journal.pone
Our results indicate that variation in wing melanisation only plays a minor role in heating rates or in the maximum achieved body temperature in the small sized butterfly, P. icarus under radiation and temperature conditions approximating to those which are marginal for activity in the field
Summary
The colour and pattern of butterfly wings has been described as being shaped by three major selective forces: thermoregulation, apparency to conspecifics and reduction of predation risk [1,2,3,4,5,6,7,8,9,10,11]. These requirements can conflict [12] as apparency may promote more brightly coloured butterflies [2], [10], [13]-[14], but these individuals may be more visible to predators [9], PLOS ONE | DOI:10.1371/journal.pone.0122623. Heating and cooling rates are partly dependent on microclimate and the interaction of this with wing colouration, basking posture, basking method and body size [1], [3], [23]-[24]; wing melanisation has been demonstrated to have a significant role in thermoregulation by medium and large sized butterflies (>c. 60 mg and >c. 45 mm wingspan)
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