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Träfflista för sökning "WFRF:(Walters Richard) srt2:(2006-2009)"

Sökning: WFRF:(Walters Richard) > (2006-2009)

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1.
  • Baba, Yuki G., et al. (författare)
  • Host-dependent differences in prey acquisition between populations of a kleptoparasitic spider Argyrodes kumadai (Araneae: Theridiidae)
  • 2007
  • Ingår i: Ecological Entomology. - : Wiley. - 0307-6946 .- 1365-2311. ; 32:1, s. 38-44
  • Tidskriftsartikel (refereegranskat)abstract
    • 1. A kleptoparasitic spider, Argyrodes kumadai, is known to use phylogenetically unrelated host species in different regions - Cyrtophora moluccensis (Araneidae) in south-west Japan and Agelena silvatica (Agelenidae) in north-east Japan. The work reported here examined whether differences in host characters affect prey acquisition of A. kumadai. 2. Field surveys showed that prey-biomass capture rate of Argyrodes was significantly higher in populations parasitising Cyrtophora than in populations parasitising Agelena. Although Argyrodes appeared to catch fewer prey within Cyrtophora webs, they were able to feed upon substantially larger prey. 3. Differences in prey-biomass capture rate were found to reflect differences in host traits rather than regional differences in potential prey availability. Individuals in populations parasitising Cyrtophora were observed to acquire prey via a number of foraging tactics that included stealing wrapped food bundles, feeding upon prey remains and, in the case of large prey items, feeding together with the host. In contrast, individuals in populations parasitising Agelena were only ever observed to feed upon small prey items ignored by its host. 4. This variability in prey acquisition between kleptoparasite populations reflected different opportunities for feeding within their respective host webs - opportunities that were primarily determined by the foraging behaviour of the host. One key trait associated with host foraging behaviour was host-web structure, namely the presence/absence of a retreat.
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2.
  • Berger, David, et al. (författare)
  • What keeps insects small? - Size dependent predation on two species of butterfly larvae
  • 2006
  • Ingår i: Evolutionary Ecology. - : Springer Science and Business Media LLC. - 0269-7653 .- 1573-8477. ; 20:6, s. 575-589
  • Tidskriftsartikel (refereegranskat)abstract
    • Insect size usually increases greatly in the latter stages of development, while reproductive value increases strongly with adult size. Mechanisms that can balance the benefits associated with increased growth are poorly understood, raising the question: what keeps insects from becoming larger? If predation risk was to increase with juvenile size, it would make an extension of development very risky, favouring smaller final sizes. But field measures of juvenile mortality seldom show any general patterns of size dependence. We here therefore try to estimate a mechanistic relationship between juvenile size and predation risk by exposing the larvae of two closely related butterflies to a generalist invertebrate predator in a laboratory experiment. Predation risk increased with larval size but was not affected by the species-specific growth rate differences. These results indicate that predation risk may increase with the size of the juvenile even when predators are relatively small. By basing a model simulation on our data we also show that size dependent predation of the kind found in this study has potential to stabilise selection on body size in these species. Thus, these findings suggest that more detailed studies of the size dependence of predation risk on juvenile instars will increase the understanding of what it is that keeps insects small.
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3.
  • Berger, David, et al. (författare)
  • What limits insect fecundity? Body size- and temperature-dependent egg maturation and oviposition in a butterfly
  • 2008
  • Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 22:3, s. 523-529
  • Tidskriftsartikel (refereegranskat)abstract
    • 1. Large female insects usually have high potential fecundity. Therefore selection should favour an increase in body size given that these females get opportunities to realize their potential advantage by maturing and laying more eggs. However, ectotherm physiology is strongly temperature-dependent, and activities are carried out sufficiently only within certain temperature ranges. Thus it remains unclear if the fecundity advantage of a large size is fully realized in natural environments, where thermal conditions are limiting.2. Insect fecundity might be limited by temperature at two levels; first eggs need to mature, and then the female needs time for strategic ovipositing of the egg. Since a female cannot foresee the number of oviposition opportunities that she will encounter on a given day, the optimal rate of egg maturation will be governed by trade-offs associated with egg- and time-limited oviposition. As females of different sizes will have different amounts of body reserves, size-dependent allocation trade-offs between the mother's condition and her egg production might be expected.3. In the temperate butterfly Pararge aegeria, the time and temperature dependence of oviposition and egg maturation, and the interrelatedness of these two processes were investigated in a series of laboratory experiments, allowing a decoupling of the time budgets for the respective processes.4. The results show that realized fecundity of this species can be limited by both the temperature dependence of egg maturation and oviposition under certain thermal regimes. Furthermore, rates of oviposition and egg maturation seemed to have regulatory effects upon each other. Early reproductive output was correlated with short life span, indicating a cost of reproduction. Finally, large females matured more eggs than small females when deprived of oviposition opportunities. Thus, the optimal allocation of resources to egg production seems dependent on female size.5. This study highlights the complexity of processes underlying rates of egg maturation and oviposition in ectotherms under natural conditions. We further discuss the importance of temperature variation for egg- vs. time-limited fecundity and the consequences for the evolution of female body size in insects.
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4.
  • Lindgren, Cecilia M, et al. (författare)
  • Genome-wide association scan meta-analysis identifies three Loci influencing adiposity and fat distribution.
  • 2009
  • Ingår i: PLoS genetics. - : Public Library of Science (PLoS). - 1553-7404. ; 5:6, s. e1000508-
  • Tidskriftsartikel (refereegranskat)abstract
    • To identify genetic loci influencing central obesity and fat distribution, we performed a meta-analysis of 16 genome-wide association studies (GWAS, N = 38,580) informative for adult waist circumference (WC) and waist-hip ratio (WHR). We selected 26 SNPs for follow-up, for which the evidence of association with measures of central adiposity (WC and/or WHR) was strong and disproportionate to that for overall adiposity or height. Follow-up studies in a maximum of 70,689 individuals identified two loci strongly associated with measures of central adiposity; these map near TFAP2B (WC, P = 1.9x10(-11)) and MSRA (WC, P = 8.9x10(-9)). A third locus, near LYPLAL1, was associated with WHR in women only (P = 2.6x10(-8)). The variants near TFAP2B appear to influence central adiposity through an effect on overall obesity/fat-mass, whereas LYPLAL1 displays a strong female-only association with fat distribution. By focusing on anthropometric measures of central obesity and fat distribution, we have identified three loci implicated in the regulation of human adiposity.
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5.
  • Lyon, Helen N., et al. (författare)
  • The association of a SNP upstream of INSIG2 with body mass index is reproduced in several but not all cohorts
  • 2007
  • Ingår i: PLoS Genetics. - : Public Library of Science (PLoS). - 1553-7404. ; 3:4
  • Tidskriftsartikel (refereegranskat)abstract
    • A SNP upstream of the INSIG2 gene, rs7566605, was recently found to be associated with obesity as measured by body mass index (BMI) by Herbert and colleagues. The association between increased BMI and homozygosity for the minor allele was first observed in data from a genome-wide association scan of 86,604 SNPs in 923 related individuals from the Framingham Heart Study offspring cohort. The association was reproduced in four additional cohorts, but was not seen in a fifth cohort. To further assess the general reproducibility of this association, we genotyped rs7566605 in nine large cohorts from eight populations across multiple ethnicities (total n = 16,969). We tested this variant for association with BMI in each sample under a recessive model using family-based, population-based, and case-control designs. We observed a significant (p < 0.05) association in five cohorts but saw no association in three other cohorts. There was variability in the strength of association evidence across examination cycles in longitudinal data from unrelated individuals in the Framingham Heart Study Offspring cohort. A combined analysis revealed significant independent validation of this association in both unrelated (p = 0.046) and family-based (p = 0.004) samples. The estimated risk conferred by this allele is small, and could easily be masked by small sample size, population stratification, or other confounders. These validation studies suggest that the original association is less likely to be spurious, but the failure to observe an association in every data set suggests that the effect of SNP rs7566605 on BMI may be heterogeneous across population samples.
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6.
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