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Life history evolution in a bivoltine butterfly
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0001-7104-1406
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 [en]
Bivoltine, Diapause, Lepidoptera, Life history, Mating system, Pheromone, Polyphenism, Population density, Sexual selection, Sperm competition
National Category
Ecology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-81399ISBN: 978-91-7447-592-0 (print)OAI: oai:DiVA.org:su-81399DiVA: diva2:561572
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
List of papers
1. What affects mating rate?: Polyandry is higher in the directly developing generation of the butterfly Pieris napi
Open this publication in new window or tab >>What affects mating rate?: Polyandry is higher in the directly developing generation of the butterfly Pieris napi
2010 (English)In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 80, 413-418 p.Article in journal (Refereed) Published
Abstract [en]

Polyandry is common among insects and female insects in general gain directly from mating multiply in terms of increased lifetime reproductive success. Nevertheless, polyandry is not rampant, suggesting that realized polyandry is the outcome of costs and benefits associated with multiple matings. In the bivoltine green-veined white butterfly Pieris napi, females gain from mating multiply as males transfer a substantial nuptial gift along with the sperm at mating. Nonetheless, lifetime number of matings varies between 1 and 6 and 12 % of females mate only once. Here, we explore the reason for this variation and test (1) whether female polyandry is contingent on environmental conditions, specifically whether females can compensate for adverse conditions by mating more often, and (2) whether the level of polyandry differs between the diapausing generation that flies after pupal hibernation, and the directly developing generation, specifically whether females in the more time-constrained summer generation are more polyandrous, possibly as a result of selection for early high mating propensity and thereby shorter pre-reproductive period. Results showed that (1) females do not compensate for adverse conditions by mating more often, and (2) the level of polyandry was higher in the directly developing generation than in the diapause generation. Hence, we argue that differences in time stress and mating propensity between generations interplay in shaping mating frequency, and that the difference in polyandry between generations highlights the importance of integrating developmental pathway and life history.

Place, publisher, year, edition, pages
Elsevier Ltd., 2010
National Category
Zoology
Identifiers
urn:nbn:se:su:diva-41287 (URN)10.1016/j.anbehav.2010.05.025 (DOI)000280846800009 ()
Note

Author count:2;

Available from: 2010-07-09 Created: 2010-07-09 Last updated: 2014-10-28Bibliographically approved
2. Seasonal polyphenism in life history traits: Time costs of direct development in a butterfly
Open this publication in new window or tab >>Seasonal polyphenism in life history traits: Time costs of direct development in a butterfly
Show others...
2010 (English)In: Behavioral Ecology and Sociobiology, ISSN 0340-5443, E-ISSN 1432-0762, Vol. 64, 1377-1383 p.Article in journal (Refereed) Published
Abstract [en]

Insects with two or more generations per year will generally experience different selection regimes depending on the season, and accordingly show seasonal polyphenisms. In butterflies, seasonal polyphenism has been shown with respect to morphology, life history characteristics and behaviour. In temperate bivoltine species, the directly developing generation is more time-constrained than the diapause generation and this may affect various life history traits, such as mating propensity (time from eclosion to mating). Here we test whether mating propensity differs between generations in Pieris napi, along with several physiological parameters, for males sex pheromone synthesis, and for females ovigeny index and fecundity.

As predicted, individuals of the directly developing generation – who have shorter time for pupal development - are more immature at eclosion; males take longer to synthesize the male sex pheromone after eclosion and also take longer to mate than diapause generation males. Females show the same physiological pattern, the directly developing females lay fewer eggs than diapausing females during the first days of their life. Nevertheless, the directly developing females mate faster after eclosion than diapausing females, indicating substantial adult time stress in this generation and possibly an adaptive value of shortening the pre-reproductive period.

Our study highlights how time-stress can be predictably different between generations, affecting both life history and behaviour. By analyzing several life history traits simultaneously we adopt a multi-trait approach to examining how adaptations and developmental constraints likely interplay to shape these seasonal polyphenisms.

Place, publisher, year, edition, pages
Springer, 2010
National Category
Zoology
Identifiers
urn:nbn:se:su:diva-38148 (URN)10.1007/s00265-010-0952-x (DOI)000280842600002 ()
Note

Author count:6;

Available from: 2010-03-29 Created: 2010-03-29 Last updated: 2014-10-28Bibliographically approved
3. Timing of Male Sex Pheromone Biosynthesis in a Butterfly –  Different Dynamics under Direct or Diapause Development
Open this publication in new window or tab >>Timing of Male Sex Pheromone Biosynthesis in a Butterfly –  Different Dynamics under Direct or Diapause Development
2012 (English)In: Journal of Chemical Ecology, ISSN 0098-0331, E-ISSN 1573-1561, Vol. 38, no 5, 584-591 p.Article in journal (Refereed) Published
Abstract [en]

The life history traits and behavior of the butterfly are well-known, as the species is often used as a model organism for evolutionary and ecological studies. The species has two or more generations per year in the major part of its temperate distribution, and as different selection pressures affect the different generations, both behavioral and physiological seasonal polyphenisms have been shown previously. Here, we explored the dynamics of male sex pheromone production. The two generations are shown to have significantly different scent compositions early in life; the direct developers-who have shorter time for pupal development-need the first 24 hr of adult life after eclosion to synthesize the sex pheromone citral (geranial and neral 1:1)-whereas the diapausing individuals who have spent several months in the pupal stage eclose with adult scent composition. Resource allocation and biosynthesis also were studied in greater detail by feeding butterflies C-13 labeled glucose either in the larval or adult stage, and recording incorporation into geranial, neral, and other volatiles produced. Results demonstrate that the pheromone synthesized by newly eclosed adult males is based on materials ingested in the larval stage, and that adult butterflies are able to synthesize the pheromone components geranial and neral and the related alcohols also from adult intake of glucose. In summary, our study shows that time-stress changes the timing in biosynthesis of the complete pheromone between generations, and underpins the importance of understanding resource allocation and the physiological basis of life history traits.

Place, publisher, year, edition, pages
Springer Science+Business Media B.V., 2012
Keyword
Aphrodisiac, Citral, Green-veined white butterfly, Polyphenism, Sex pheromone
National Category
Ecology Biochemistry and Molecular Biology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-75700 (URN)10.1007/s10886-012-0126-6 (DOI)000304208300016 ()
Note

Author count: 4;

Available from: 2012-04-25 Created: 2012-04-25 Last updated: 2017-12-07Bibliographically approved
4. Males use sex pheromone assessment to tailor ejaculates to risk of sperm competition in a butterfly
Open this publication in new window or tab >>Males use sex pheromone assessment to tailor ejaculates to risk of sperm competition in a butterfly
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
National Category
Ecology Zoology
Identifiers
urn:nbn:se:su:diva-31061 (URN)10.1093/beheco/arp109 (DOI)000269956400033 ()
Note

Author count: 2;

Available from: 2009-11-05 Created: 2009-11-03 Last updated: 2014-10-28Bibliographically approved
5. Different mating expenditure in response to sperm competition risk between generations in the bivoltine butterfly Pieris napi
Open this publication in new window or tab >>Different mating expenditure in response to sperm competition risk between generations in the bivoltine butterfly Pieris napi
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.

Keyword
Ejaculate, Mating investment, Nuptial gift, Paternal investment, Resource allocation, Spermatophore
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-81398 (URN)10.1007/s00265-015-1919-8 (DOI)000356044700001 ()
Available from: 2012-10-18 Created: 2012-10-18 Last updated: 2017-12-07Bibliographically approved

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