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Males use sex pheromone assessment to tailor ejaculates to risk of sperm competition in a butterfly
Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.ORCID iD: 0000-0001-7104-1406
Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.ORCID iD: 0000-0003-4719-487X
2009 (English)In: Behavioral Ecology, ISSN 1045-2249, E-ISSN 1465-7279, Vol. 20, no 5, 1147-1151 p.Article in journal (Refereed) Published
Abstract [en]

In polyandrous butterflies males transfer a large, nutritious ejaculate at mating. Larger ejaculates delay female remating and confer an advantage in sperm competition. However, large ejaculates are costly, potentially selecting for male adjustment of ejaculate size to the risk of sperm competition. Here, we test if male ejaculate size in the butterfly Pieris napi varies with male density, and whether males assess sperm competition risk using the male sex pheromone citral as a cue. The results conform to sperm competition theory and showed that male P. napi tailored their reproductive investment in response to the risk of sperm competition; ejaculates transferred by males in the high male density treatments were on average 23% larger than ejaculates transferred at low male densities. The results also show for the first time, that the sex pheromone citral was used by males to assess male density; ejaculates transferred by males in presence of added male sex-pheromone were 19% larger than ejaculates transferred in the control. In conclusion, the study shows how the sex pheromone not only facilitates female acceptance when dispensed by courting males, but also allows males to assess the degree of male competition for matings.

Place, publisher, year, edition, pages
CARY, NC 27513 USA: OXFORD UNIV PRESS INC , 2009. Vol. 20, no 5, 1147-1151 p.
National Category
Ecology Zoology
URN: urn:nbn:se:su:diva-31061DOI: 10.1093/beheco/arp109ISI: 000269956400033OAI: diva2:275115

Author count: 2;

Available from: 2009-11-05 Created: 2009-11-03 Last updated: 2014-10-28Bibliographically approved
In thesis
1. Life history evolution in a bivoltine butterfly
Open this publication in new window or tab >>Life history evolution in a bivoltine butterfly
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Evolution is not always straight-forward, as selection pressures may differ between different generations of the same species. This thesis focuses on the evolution of life history of the model species, the Green-veined White butterfly Pieris napi. In central Sweden P. napi has two generations per year. The directly developing summer generation is short-lived and time stressed, compared to the diapausing generation.

In paper I polyandry, defined as female mating rate, was shown to differ between generations but was unaffected by environmental factors. In paper II both males and females of the direct developing generation were shown to eclose more immature than the diapausing generation, indicating larval time constraints. Consistent with this, diapausing males mated sooner than direct developers. Directly developing females, however, mated sooner after eclosion than diapausing females, even though they are more immature. This was shown to negatively affect fecundity, but can pay off when the season is short.

Paper III shows that directly developing males have less sex pheromones at eclosion than diapausers, and the differences in sex pheromone production is consistent with developmental time constraints and the differences in mating system.

In P. napi and other polyandrous butterflies, males transfer a large, nutritious ejaculate at mating. Large ejaculates confer advantages under sperm competition, but as they are costly, males should adjust ejaculate size to the risk of sperm competition. In paper IV we found that males transfer on average 20% larger spermatophores under high male competition than at low competition. The same effect could be observed if we added male sex pheromone to the air in a mating cage without male-male competition. Paper V shows that males of the two generations respond differently to an increase in male-male competition, with diapausing males transferring larger spermatophores than direct developers at high male competition risk.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2012. 24 p.
Bivoltine, Diapause, Lepidoptera, Life history, Mating system, Pheromone, Polyphenism, Population density, Sexual selection, Sperm competition
National Category
Research subject
Animal Ecology
urn:nbn:se:su:diva-81399 (URN)978-91-7447-592-0 (ISBN)
Public defence
2012-12-07, Magnelisalen,Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)

At the time of the doctoral defence the following paper was unpublished and had a status as follows: Paper 5: Submitted manuscript.

Available from: 2012-11-15 Created: 2012-10-18 Last updated: 2014-10-28Bibliographically approved

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Larsdotter Mellström, HelenaWiklund, Christer
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