Measurement of parental investment and sex allocation in the European beewolf Philanthus triangulum F. (Hymenoptera: Sphecidae) |
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Authors: | E Strohm K Eduard Linsenmair |
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Institution: | (1) Theodor-Boveri-Institut für Biowissenschaften, Zoologie III Biozentrum, Am Hubland, D-97074 Würzburg, Germany e-mail: strohm@biozentrum.uni-wuerzburg.de Tel.: +49-931-8884373, Fax: +49-931-8884352, DE |
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Abstract: | Fisher’s 1930 theory of sex allocation predicts a population-wide 1:1 ratio of parental investment. We tested this prediction
in the European beewolf, a sphecid wasp that hunts for honeybees as larval food. Because the method to quantify parental investment
is of crucial importance, we compared the suitability of several different investment measures. Female/male cost ratios were
determined from a sample and the total investment in sons and daughters was calculated. In addition, the actual number of
prey items for sons and daughters was directly determined by excavating nests and counting the cuticle remains of the prey.
Though mortality was high (70%), it had only a weak effect on the estimate of the investment ratio. Based on commonly used
measures like fresh and dry weight of emerged adults, the investment ratio did not deviate from Fisher’s prediction of equal
investment. However, progeny weight considerably underestimates investment in males and investment in large progeny. Measures
that reflect the allocation of resources more directly (amount of provisions, brood cell volume) revealed a significant male
bias and thus contradicted Fisher’s theory. Three kinds of explanation are discussed. First, non-adaptive explanations are
unlikely. Second, from the spectrum of alternative adaptive theories, only models that assume a non-linear relationship between
amount of investment and progeny fitness seem to be relevant for the study species. Third, though the number of prey in a
brood cell seems to be a rather good measure of parental investment in European beewolves, some problems in measuring parental
investment remain. These problems are of broad significance.
Received: 17 June 1999 / Received in revised form: 6 July 1999 / Accepted: 11 July 1999 |
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Keywords: | Fisher Investment measure Cost ratio Male bias Sex ratio |
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