Mating opportunity and the evolution of sex-specific mortality rates in a butterfly |
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Authors: | K Gotthard Sören Nylin Christer Wiklund |
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Institution: | (1) Department of Zoology, Stockholm University, S-10691 Stockholm, Sweden e-mail: karl.gotthard@zoologi.su.se Fax: +46-8-167715, SE |
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Abstract: | Life history theory predicts that organisms should only invest resources into intrinsic components of life span to the degree
that it pays off in terms of reproductive success. Here, we investigate if the temporal distribution of mating opportunities
may have influenced the evolution of intrinsic mortality rates in the butterfly Pararge aegeria (Satyrinae). In this species, females mate only once and the frequency of male mating opportunities depends on the temporal
emergence pattern of virgin females. As expected, in a population from Madeira where females emerge continuously throughout
the year, there was no sex difference in adult life span, while in a Swedish population with synchronised female emergence,
males had significantly shorter life spans compared to females. A logistic mortality model provided the best fit to the observed
change in age-specific mortality and all categories reached an asymptotic mortality rate of a similar magnitude. However,
the Swedish males reached this mortality plateau more rapidly than the other categories. External mortality, due to water
and food limitation, affected the pattern of sex-specific mortality but males from Sweden still had higher rates of mortality
compared to all other categories. We argue that selection on male longevity is likely to be weaker in Sweden because under
synchronised emergence, all females emerge and mate within a short period of time, after which male reproductive value will
quickly approach zero. On Madeira, however, male reproductive value decrease more slowly with age since the probability of
finding a receptive female is constant over the year.
Received: 29 July 1999 / Accepted: 23 August 1999 |
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Keywords: | Life history theory Longevity Ageing Mortality rate Lepidoptera |
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