Abstract
In butterflies, life span often increases only at the expense of fecundity. Prolonged life span, on the other hand, provides more opportunities for oviposition. Here, we studied the association between life span and summer dormancy in two closely related species of Palearctic Meadow Brown butterflies, the endemic Maniola nurag and the widespread M. jurtina, from two climatic provenances, a Mediterranean and a Central European site, and tested the relationships between longevity, body size and fecundity. We experimentally induced summer dormancy and hence prolonged the butterflies’ life in order to study the effects of such a prolonged life. We were able to modulate longevity only in Mediterranean females by rearing them under summer photoperiodic conditions (light 16 h : dark 8 h), thereby more than doubling their natural life span, to up to 246 days. Central European individuals kept their natural average live span under all treatments, as did Mediterranean individuals under autumn treatment (light 11: dark 13). Body size only had a significant effect in the smaller species, M. nurag, where it affected the duration of dormancy and lifetime fecundity. In the larger species, M. jurtina, a prolonged adult life span did, surprisingly, not convey any fecundity loss. In M. nurag, which generally deposited fewer eggs, extended life had a fecundity cost. We conclude that Mediterranen M. jurtina butterflies have an extraordinary plasticity in aging which allows them to extend life span in response to adverse environmental conditions and relieve the time limitation on egg-laying while maintaining egg production at equal levels.
Highlights
Why some animals grow very old and others do not is still a challenge to biological science, despite massive ongoing research especially on humans [1,2,3,4,5], other vertebrates [6,7,8,9,10] and on some invertebrate groups like Drosophila and butterflies [11,12,13,14,15,16]
Our aims are to test if (1) we can experimentally induce summer dormancy in Meadow Brown butterflies that do not normally conduct a summer dormancy, (2) if the adult lifespan of the animals can be prolonged by keeping them under constant summer conditions, (3) if the two co-occurring species M. nurag and M. jurtina react concomittantly to constant summer conditions, and (4) if body-size plays a role for compensating the trade-offs for such a prolonged life?
As representatives from a Mediterranean climate, expected to undergo an extended reproductive dormancy [31], we collected females of the endemic M. nurag and the widespread M. jurtina (‘‘jurtina from Sardinia (JM)’’, 54 individuals) between 29.5. – 12.6.2012 at different sites in the mountains of Sardinia, Italy, from the following locations: N 39.261972/E 9.412333, N 39.261528/E 9.411778, N 39.233694/E 9.39575, N 39.238972/ E 9.385806. Both species co-occur in partial sympatry at elevations between 500 and 950 m a.s.l [29]. To contrast these insects with Meadow Browns of Central European provenance, expected to show no or much shorter summer dormancy, 34 M. jurtina females were captured in a lowland habitat (150 m a.s.l.) in eastern Austria (20.6. –3.7.2012; abbreviated ‘‘jurtina from Austria (JA)’’ hereafter)
Summary
Why some animals grow very old and others do not is still a challenge to biological science, despite massive ongoing research especially on humans [1,2,3,4,5], other vertebrates [6,7,8,9,10] and on some invertebrate groups like Drosophila and butterflies [11,12,13,14,15,16]. Life span differences within and among species are generally linked to differences in life-history strategies or resource availability. We attempt to investigate intraspecific variation in life span ‘senescence plasticity’ ( = phenotypic plasticity affecting life span) within a context of its potential evolutionary benefit. Such intraspecific plasticity in live-history and concomitantly life span is advantageous when organisms have to cope with temporally heterogeneous environmental conditions [14], as herbivorous insects in temperate regions, and are obliged to synchronize their growth and reproduction with seasonal variation of the availability of hosts plants
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