Size-dependent sex allocation in a simultaneous hermaphrodite parasite

doi:10.1046/j.1420-9101.2001.00263.x

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Wiley InterScience

Journal of Evolutionary Biology

Volume 14 Issue 1, Pages 55 - 67

Published Online: 20 Dec 2001

Published on behalf of the European Society for Evolutionary Biology (ESEB)

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Size-dependent sex allocation in a simultaneous hermaphrodite parasite

L. Schärer ¹ , L. M. Karlsson ² , M. Christen ¹ & C. Wedekind1,3

¹ Abteilung Verhaltensökologie, Zoologisches Institut, Universität Bern, Hinterkappelen, Switzerland ² Stereology Unit, Institute of Anatomy, Universität Bern, Bern, Switzerland ³ Institute of Cell, Animal and Population Biology, University of Edinburgh, West Mains Road, Edinburgh, Scotland, UK

Correspondence to: Dr L.Schärer, Université Pierre et Marie Curie, Laboratoire d'Écologie, UMR 7625, 7 quai Saint Bernard – Case 237, 75252 Paris Cedex 05, France. Tel.: +33 1 44 27 32 94; fax: +33 1 44 27 35 16; e-mail: lukas.scharer@snv.jussieu.fr

KEYWORDS

histology • local mate competition • local resource competition • parasite • selfing • sex allocation • simultaneous hermaphroditism • size-dependent sex allocation • stereology • time commitment hypothesis

ABSTRACT

Most models of sex allocation distinguish between sequential and simultaneous hermaphrodites, although an intermediate sexual pattern, size-dependent sex allocation, is widespread in plants. Here we investigated sex allocation in a simultaneous hermaphrodite animal, the tapeworm Schistocephalus solidus, in which adult size is highly variable. Sex allocation was determined using stereological techniques, which allow measuring somatic and reproductive tissues in a common currency, namely volume. We investigated the relationships between individual volume and allocation to different reproductive tissues using an allometric model. One measure of female allocation, yolk gland volume, increased more than proportionally with individual volume. This is in contrast to the measure of male allocation, testis volume, which showed a strong tendency to increase less than proportionally with individual volume. Together these patterns led to sex allocation being strongly related to individual volume, with large individuals being more biased towards female allocation. We discuss these findings in the light of current ideas about size-dependent sex allocation in, primarily, plants and try to extend them to simultaneous hermaphrodite animals.

DIGITAL OBJECT IDENTIFIER (DOI)

10.1046/j.1420-9101.2001.00263.x About DOI