Profiles

Helena Mellström

Helena Mellström

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Arbetar vid Zoologiska institutionen
E-post helena.mellstrom@zoologi.su.se
Besöksadress Svante Arrheniusväg 18 B
Rum D 544b
Postadress Zoologiska institutionen: Ekologi 106 91 Stockholm

Publikationer

I urval från Stockholms universitets publikationsdatabas
  • 2017. Peter Pruisscher (et al.). Physiological entomology (Print) 42 (3), 257-265

    Many temperate insects survive harsh environmental conditions, such as winter, by entering a state of developmental arrest. This diapause state is predominantly induced by photoperiod. The photoperiod varies with latitude and has led to local adaptation in the photoperiodic induction of diapause in many insects. To understand the rapid evolution of the photoperiodic threshold, it is important to investigate and understand the underlying genetic mechanisms. In the present study, the genetic basis of photoperiodic diapause induction is investigated in the green-veined white butterfly Pieris napi (Lepidoptera, Pieridae) by assaying diapause induction in a range of conditions for a Swedish and Spanish population. Furthermore, the inheritance of diapause induction is assessed in reciprocal F1 hybrids and backcrosses between the two populations. The southern population shows a clear photoperiodic threshold determining diapause or direct development, whereas the northern populations show a high incidence of diapause, regardless of photoperiod. The hybrid crosses reveal that the inheritance of diapause induction is strongly sex-linked, and that diapause incidence in the genetic crosses is highly dependent on photoperiod. This emphasizes the importance of assaying a range of conditions in diapause inheritance studies. The results indicate a strongly heritable diapause induction with a major component on the Z-chromosome, as well as a minor effect of the autosomal background.

  • 2016. Helena Larsdotter-Mellström (et al.). Functional Ecology 30 (2), 255-261

    When females mate with multiple partners, the risk of sperm competition depends on female mating history. To maximize fitness, males should adjust their mating investment according to this risk. In polyandrous butterflies, males transfer a large, nutritious ejaculate at mating. Larger ejaculates delay female remating and confer an advantage in sperm competition. We test whether male ejaculate size in the butterfly Pieris napi (Lepidoptera) varies with female mating history and thus sperm competition, and whether males assess sperm competition using the male-transferred anti-aphrodisiac methyl salicylate (MeS) as a cue. Both sexes responded physiologically to MeS in a dose-dependent manner. Males, however, were more sensitive to MeS than females. Ejaculates transferred by males mating with previously mated females were on average 26% larger than ejaculates transferred by males mating with virgin females, which conforms to sperm competition theory and indicates that males tailored their reproductive investment in response to sperm competition. Furthermore, ejaculates transferred by males mating with virgin females with artificially added MeS were also 26% larger than ejaculates transferred to control virgin females. Male-transferred anti-aphrodisiac pheromone not only functions as a male deterrent, but also carries information on female mating history and thus allows males to assess sperm competition.

  • 2016. Helena Larsdotter-Mellström (et al.). Frontiers in Physiology 7

    Among insects, sexual pheromones are typically mixtures of two to several components, all of which are generally required to elicit a behavioural response. Here we show for the first time that a complete blend of sexual pheromone components is needed to elicit a response also in a butterfly. Males of the Green-veined White, Pieris napi, emit an aphrodisiac pheromone, citral, from wing glands. This pheromone is requisite for females to accept mating with a courting male. Citral is a mixture of the two geometric isomers geranial (E-isomer) and neral (Z-isomer) in an approximate 1:1 ratio. We found that both these compounds are required to elicit acceptance behaviour, which indicates synergistic interaction between processing of the isomers. Using functional Ca2+ imaging we found that geranial and neral evoke significantly different but overlapping glomerular activity patterns in the antennal lobe, which suggests receptors with different affinity for the two isomers. However, these glomeruli were intermingled with glomeruli responding to ,for example, plant-related compounds, i.e. no distinct subpopulation of pheromone-responding glomeruli as in moths and other insects. In addition, these glomeruli showed lower specificity than pheromone-activated glomeruli in moths. We could, however, not detect any mixture interactions among four identified glomeruli, indicating that the synergistic effect may be generated at a higher processing level. Furthermore, correlations between glomerular activity patterns evoked by the single isomers and the blend did not change over time.

  • 2015. Helena Larsdotter Mellström, Christer Wiklund. Behavioral Ecology and Sociobiology 69 (7), 1067-1074

    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.

  • 2009. Helena Larsdotter Mellström, Christer Wiklund. Behavioral Ecology 20 (5), 1147-1151

    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.

Visa alla publikationer av Helena Mellström vid Stockholms universitet

Senast uppdaterad: 23 mars 2018

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