| 1. |
- Larsdotter Mellström, Helena, 1978-
(författare)
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Life history evolution in a bivoltine butterfly
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Larsdotter Mellström, Helena, 1978-, et al.
(författare)
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Males use sex pheromone assessment to tailor ejaculates to risk of sperm competition in a butterfly
- 2009
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Ingår i: Behavioral Ecology. - CARY, NC 27513 USA : OXFORD UNIV PRESS INC. - 1045-2249 .- 1465-7279. ; 20:5, s. 1147-1151
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Larsdotter Mellström, Helena, 1978-, et al.
(författare)
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Timing of Male Sex Pheromone Biosynthesis in a Butterfly – Different Dynamics under Direct or Diapause Development
- 2012
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Ingår i: Journal of Chemical Ecology. - : Springer Science+Business Media B.V.. - 0098-0331 .- 1573-1561. ; 38:5, s. 584-591
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Larsdotter Mellström, Helena, 1978-, et al.
(författare)
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What affects mating rate? : Polyandry is higher in the directly developing generation of the butterfly Pieris napi
- 2010
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Ingår i: Animal Behaviour. - : Elsevier Ltd.. - 0003-3472 .- 1095-8282. ; 80, s. 413-418
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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