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Different mating expenditure in response to sperm competition risk between generations in the bivoltine butterfly Pieris napi
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0001-7104-1406
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0003-4719-487X
2015 (English)In: Behavioral Ecology and Sociobiology, ISSN 0340-5443, E-ISSN 1432-0762, Vol. 69, no 7, 1067-1074 p.Article in journal (Refereed) Published
Abstract [en]

Examining how the response to sperm competition risk varies in a population is essential in order to understand variation in reproductive success and mating system. In polyandrous butterflies, males transfer a large spermatophore at mating that delays female remating and confers an advantage in sperm competition. However, as large ejaculates are costly to produce—male expenditure on ejaculate size should be selected to vary with risk of sperm competition, as previously shown in the butterfly Pieris napi. In P. napi, adults can either emerge after winter diapause, or they can emerge as a directly developing generation later in the summer. Post-diapause adults have fewer developmental constraints because direct developers have to grow, develop, emerge, mate, and reproduce during a more limited seasonal timeframe, and as a result are more time-stressed. The two generations show polyphenisms in a variety of traits including polyandry, pheromone production, mating propensity, and sexual maturity at eclosion. Using these within-species, between generation differences in ecology, we generated three important findings: (1) that both generations respond to an immediate risk of elevated sperm competition and significantly raise ejaculate investment, (2) that the diapausing generation raises this investment by a far greater 65 % increase compared with the direct generation males’ 28 %, and (3) that males show a graded response relative to sperm competition risk and increase their ejaculate investment in relation to the actual level of mate competition. The difference in male mating allocation between generations may help explain life history evolution and geographic differences in mating patterns.

Place, publisher, year, edition, pages
2015. Vol. 69, no 7, 1067-1074 p.
Keyword [en]
Ejaculate, Mating investment, Nuptial gift, Paternal investment, Resource allocation, Spermatophore
National Category
Ecology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-81398DOI: 10.1007/s00265-015-1919-8ISI: 000356044700001OAI: oai:DiVA.org:su-81398DiVA: diva2:561398
Available from: 2012-10-18 Created: 2012-10-18 Last updated: 2017-12-07Bibliographically 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.
Keyword
Bivoltine, Diapause, Lepidoptera, Life history, Mating system, Pheromone, Polyphenism, Population density, Sexual selection, Sperm competition
National Category
Ecology
Research subject
Animal Ecology
Identifiers
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)
Opponent
Supervisors
Note

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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