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Sperm competition, mating rate and the evolution of testis and ejaculate sizes: a population model
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| Zeitschriftentitel: | Biology Letters |
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| Personen und Körperschaften: | , |
| In: | Biology Letters, 1, 2005, 2, S. 235-238 |
| Format: | E-Article |
| Sprache: | Englisch |
| veröffentlicht: |
The Royal Society
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| Schlagwörter: |
| Zusammenfassung: | <jats:p> There are various ways to estimate ejaculate expenditure. Ejaculate size or sperm number ( <jats:italic>s</jats:italic> ) is an absolute number of units of ejaculate. Relative ejaculate expenditure ( <jats:italic>E</jats:italic> ) is the expenditure on the ejaculate as the proportion of the total expenditure on all aspects of the mating, including finding and acquiring a female, and so on. Relative testis size or gonadosomatic index ( <jats:italic>σ</jats:italic> ) is testes mass divided by body mass; it is assumed to reflect the product of mating rate ( <jats:italic>M</jats:italic> ) and ejaculate mass ( <jats:italic>s</jats:italic> ). In a new model, where mating rate, sperm competition and sperm allocation interact, and where the female's inter-clutch interval is assumed to be independent of <jats:italic>s</jats:italic> or <jats:italic>M</jats:italic> , we show that <jats:italic>σ</jats:italic> is directly proportional to the mean <jats:italic>E</jats:italic> for a species; across species <jats:italic>σ</jats:italic> and <jats:italic>E</jats:italic> increase monotonically with sperm competition. However, the relation between <jats:italic>s</jats:italic> and sperm competition across species depends on the range of sperm competition (low risk or high intensity): <jats:italic>s</jats:italic> increases with sperm competition at low risk levels, but decreases with sperm competition at high intensity levels. This situation arises because <jats:italic>s</jats:italic> ∝ <jats:italic>E</jats:italic> / <jats:italic>M</jats:italic> ; both <jats:italic>E</jats:italic> and <jats:italic>M</jats:italic> increase with sperm competition, but <jats:italic>E</jats:italic> increases differently with sperm competition in its two ranges. </jats:p> |
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| Umfang: | 235-238 |
| ISSN: |
1744-9561
1744-957X |
| DOI: | 10.1098/rsbl.2004.0273 |