GEE Journal Club


Eutrophication causes speciation reversal in whitefish adaptive radiations

Posted in Uncategorized by Journal Club Chair on 28/02/2012

Nature

DOI: 10.1038/nature10824

Author(s):

Vonlanthen, P; Bittner, D; Hudson, A G; Young, K A; Muller, R; Lundsgaard-Hansen, B; Roy, D; Di Piazza, S; Largiader, C R; Seehausen, O

Abstract:

Species diversity can be lost through two different but potentially interacting extinction processes: demographic decline and speciation reversal through introgressive hybridization. To investigate the relative contribution of these processes, we analysed historical and contemporary data of replicate whitefish radiationsfrom 17 pre-alpine European lakes and reconstructed changes in genetic species differentiation through time using historical samples. Here we provide evidence that species diversity evolved in response to ecological opportunity, and that eutrophication, by diminishing this opportunity, has driven extinctions through speciationreversal and demographic decline. Across the radiations, the magnitude of eutrophication explains the pattern of species loss and levels of genetic and functional distinctiveness among remaining species. We argue that extinction by speciation reversal may be more widespread than currently appreciated. Preventing such extinctions will require that conservation efforts not only target existing species but identify and protect the ecological and evolutionary processes that generate and maintain species.

 

Presented by James Howie

Blackawton Bees

Posted in Uncategorized by Journal Club Chair on 22/02/2012

Biology Letters

 

DOI: 10.1098/rsbl.2010.1056

 

Authors:

P. S. Blackawton, S. Airzee, A. Allen, S. Baker, A. Berrow, C. Blair, M. Churchill,J. Coles, R. F.-J. Cumming, L. Fraquelli, C. Hackford, A. Hinton Mellor,M. Hutchcroft, B. Ireland, D. Jewsbury, A. Littlejohns, G. M. Littlejohns, M. Lotto,J. McKeown, A. O’Toole, H. Richards, L. Robbins-Davey, S. Roblyn,H. Rodwell-Lynn, D. Schenck, J. Springer, A. Wishy, T. Rodwell-Lynn, D. Strudwick, and R. B. Lotto

 

Abstract:

Background Real science has the potential to not only amaze, but also transform the way one thinks of the world and oneself. This is because the process of science is little different from the deeply resonant, natural processes of play. Play enables humans (and other mammals) to discover (and create) relationships and patterns. When one adds rules to play, a game is created. This is science: the process of playing with rules that enables one to reveal previously unseen patterns of relationships that extend our collective understanding of nature and human nature. When thought of in this way, science education becomes a more enlightened and intuitive process of asking questions and devising games to address those questions. But, because the outcome of all game-playing is unpredictable, supporting this ‘messyness’, which is the engine of science, is critical to good science education (and indeed creative education generally). Indeed, we have learned that doing ‘real’ science in public spaces can stimulate tremendous interest in children and adults in understanding the processes by which we make sense of the world. The present study (on the vision of bumble-bees) goes even further, since it was not only performed outside my laboratory (in a Norman church in the southwest of England), but the ‘games’ were themselves devised in collaboration with 25 8- to 10-year-old children. Theyasked the questions, hypothesized the answers, designed the games (in other words, the experiments) to test these hypotheses and analysed the data. They also drew the figures (in coloured pencil) and wrote the paper. Their headteacher (Dave Strudwick) and I devised the educational programme (we call ‘i,scientist’), and I trained the bees and transcribed the childrens’ words into text (which was done with smaller groups of children at the school’s local village pub). So what follows is a novel study (scientifically and conceptually) in ‘kids speak’ without references to past literature, which is a challenge. Although the historical context of any study is of course important, including references in this instance would be disingenuous for two reasons. First, given the way scientific data are naturally reported, the relevant information is simply inaccessible to the literate ability of 8- to 10-year-old children, and second, the true motivation for any scientific study (at least one of integrity) is one’s own curiousity, which for the children was not inspired by the scientific literature, but their own observations of the world. This lack of historical, scientific context does not diminish the resulting data, scientific methodology or merit of the discovery for the scientific and ‘non-scientific’ audience. On the contrary, it reveals science in its truest (most naive) form, and in this way makes explicit the commonality between science, art and indeed all creative activities.

Principal finding ‘We discovered that bumble-bees can use a combination of colour and spatial relationships in deciding which colour of flower to forage from. We also discovered that science is cool and fun because you get to do stuff that no one has ever done before. (Children fromBlackawton)’.

 

Presented by Andrew Higgins

Evolution and speciation on holey adaptive landscapes

Posted in Uncategorized by Journal Club Chair on 14/02/2012

TREE

DOI: 10.1016/S0169-5347(97)01098-7

Author

Gavrilets, S.

Abstract

Sewall Wright’s powerful metaphor of rugged adaptive landscapes has formed the basis for discussing evolution and speciation for more than 60 years. However, this metaphor, with its emphasis on adaptive peaks and valleys, is to a large degree a reflection of our three-dimensional experience. Both genotypes and phenotypes of biological organisms differ in numerous characteristics, and, thus, the dimension of ‘real’ adaptive landscapes is much larger than three. Properties of multidimensional adaptive landscapes are very different from those of low dimension. Consequently, something that is seen as a theoretical challenge in a low-dimensional case might be a trivial problem in a multidimensional context and vice versa. In particular, the problem of how a population crosses an adaptive valley on its way from one adaptive peak to another, which Wright attempted to solve with his shifting balance theory, may be non-existent. A new framework is emerging for deepening our understanding of evolution and speciation, which provides a plausible multidimensional alternative to the conventional view of rugged adaptive landscapes.

Presented by Dr. Sam Tazzyman

Genetic drift in antagonistic genes leads to divergence in sex-specific fitness between experimental populations of Drosophila melanogaster

Posted in Uncategorized by Journal Club Chair on 07/02/2012

Authors

Jack Hesketh, Kevin Fowler & Max Reuter

Abstract

Males and females differ in their reproductive roles and as a consequence are often under diverging selection pressures on shared phenotypic traits. Theory predicts that divergent selection can favour the invasion of sexually antagonistic alleles, which increase the fitness of one sex at the detriment of the other. Sexual antagonism can be subsequently resolved through the evolution of sex-specific gene expression, allowing the sexes to diverge phenotypically. While sexual dimorphism is very common, recent evidence also shows that antagonistic genetic variation continues to segregate in populations of many organisms. Here we present empirical data on the interaction between sexual antagonism and genetic drift in populations that have independently evolved under standardised conditions. We demonstrate that small experimental populations of Drosophila melanogaster have diverged in male and female fitness, with some populations showing increased male, but decreased female fitness, while other populations show the reverse pattern. This pattern of divergence between populations is accompanied by a degree of homogenisation within populations, where we find neither genetic variation for sex-specific fitness nor an association between male and female fitness. The between- and within-population patterns are consistent with the differentiation in reproductive fitness being driven by genetic drift in sexually antagonistic alleles. We discuss the implications of our results with respect to the maintenance of antagonistic variation in subdivided populations and consider the wider implications of drift in fitness-related genes.

Presented by Jack Hesketh

Experimental Evolution of Multicellularity

Posted in Uncategorized by Journal Club Chair on 31/01/2012

PNAS

DOI: 10.1073/pnas.1115323109

Authors:

Ratcliff, W. C., Denisona, R. F., Borrelloa, M., and Travisano, M.

Abstract:

Multicellularity was one of the most significant innovations in the history of life, but its initial evolution remains poorly understood. Using experimental evolution, we show that key steps in this transition could have occurred quickly. We subjected the unicellular yeast Saccharomyces cerevisiae to an environment in which we expected multicellularity to be adaptive. We observed the rapid evolution of clustering genotypes that display a novel multicellular life history characterized by reproduction via multicellular propagules, a juvenile phase, and determinate growth. The multicellular clusters are uniclonal, minimizing within-cluster genetic conflicts of interest. Simple among-cell division of labor rapidly evolved. Early multicellular strains were composed of physiologically similar cells, but these subsequently evolved higher rates of programmed cell death (apoptosis), an adaptation that increases propagule production. These results show that key aspects of multicellular complexity, a subject of central importance to biology, can readily evolve from unicellular eukaryotes.

 

Presented by Zena Hadjivasiliou

Strong reproductive isolation between humans and Neanderthals inferred from observed patterns of introgression

Posted in Uncategorized by Journal Club Chair on 23/01/2012

PNAS

DOI: 10.1073/pnas.1107450108

Authors

Currata, M. and Excoffier, L.

Abstract

Recent studies have revealed that 2-3% of the genome of non-Africans might come from Neanderthals, suggesting a more complex scenario of modern human evolution than previously anticipated. In this paper, we use a model of admixture during a spatial expansion to study the hybridization of Neanderthals with modern humans during their spread out of Africa. We find that observed low levels of Neanderthal ancestry in Eurasians are compatible with a very low rate ofinterbreeding (<2%), potentially attributable to a very strong avoidance of interspecific matings, a low fitness of hybrids, or both. These results suggesting the presence of very effective barriers to gene flow between the two species are robust to uncertainties about the exact demography of the Paleolithic populations, and they are also found to be compatible with the observed lack of mtDNA introgression. Our model additionally suggests that similarly low levels of introgression in Europe and Asia may result from distinct admixture events having occurred beyond the Middle East, after the split of Europeans and Asians. This hypothesis could be tested because it predicts that different components of Neanderthal ancestry should be present in Europeans and in Asians.

Presented by Pascale Gerbault

Shame and honour drive cooperation

Posted in Uncategorized by Journal Club Chair on 17/01/2012

Biology Letters (2011)

DOI: 10.1098/rsbl.2011.0367

Authors

Jacquet, JHauert, C; Traulsen, A; Milinski, M

Abstract

Can the threat of being shamed or the prospect of being honoured lead to greater cooperation? We test this hypothesis with anonymous six-player public goods experiments, an experimental paradigm used to investigate problems related to overusing common resources. We instructed the players that the two individuals who were least generous after 10 rounds would be exposed to the group. As the natural antithesis, we also test the effects of honour by revealing the identities of the two players who were most generous. The non-monetary, reputational effects induced by shame and honour each led to approximately 50 per cent higher donations to the public good when compared with the control, demonstrating that both shame and honour can drive cooperation and can help alleviate the tragedy of the commons.

Presented by Dr. Julie Collet

Worthless donations: male deception and female counter play in a nuptial gift-giving spider

Posted in Journal Club paper by Journal Club Chair on 10/01/2012

BMC Evolutionary Biology

DOI: 10.1186/1471-2148-11-329

Authors:

Albo, MJ; Winther, G; Tuni, C; Toft, S; Bilde, T

Abstract:

Background: In nuptial gift-giving species, benefits of
acquiring a mate may select for male deception by donation of worthless
gifts. We investigated the effect of worthless gifts on mating success in
the spider Pisaura mirabilis. Males usually offer an insect prey wrapped
in silk; however, worthless gifts containing inedible items are reported.
We tested male mating success in the following experimental groups:
protein enriched fly gift (PG), regular fly gift (FG), worthless gift
(WG), or no gift (NG).

Results: Males that offered worthless gifts acquired similar mating
success as males offering nutritional gifts, while males with no gift
experienced reduced mating success. The results suggest that strong
selection on the nuptial gift-giving trait facilitates male deception by
donation of worthless gifts. Females terminated matings faster when males
offered worthless donations; this demonstrate a cost of deception for the
males as shorter matings lead to reduced sperm transfer and thus give the
deceiving males a disadvantage in sperm competition.

Conclusion: We propose that the gift wrapping trait allows males to
exploit female foraging preference by disguising the gift content thus
deceiving females into mating without acquiring direct benefits. Female
preference for a genuine prey gift combined with control over mating
duration, however, counteracts the male deception.

Presented by Liz Harley on 12.01.2012

‘Visuoauditory mappings between high luminance and high pitch are shared by chimpanzees (Pan troglodytes) and humans’

PNAS (2011) In press

doi: 10.1073/pnas.1112605108

Authors:

Ludwiga, V.U., Adachid, I. and Matsuzawad, T.

Abstract:

Humans share implicit preferences for certain cross-sensory combinations; for example, they consistently associate higher-pitched sounds with lighter colours, smaller size, and spikier shapes. In the condition of synesthesia, people may experience such cross-modal correspondences to a perceptual degree (e.g., literally seeing sounds). So far, no study has addressed the question whether nonhuman animals share cross-modal correspondences as well. To establish the evolutionary origins of cross-modal mappings, we tested whether chimpanzees (Pan troglodytes) also associate higher pitch with higher luminance. Thirty-three humans and six chimpanzees were required to classify black and white squares according to their colour while hearing irrelevant background sounds that were either high-pitched or low-pitched. Both species performed better when the background sound was congruent (high-pitched for white, low-pitched for black) than when it was incongruent (low-pitched for white, high-pitched for black). An inherent tendency to pair high pitch with high luminance hence evolved before the human lineage split from that of chimpanzees. Rather than being a culturally learned or a linguistic phenomenon, this mapping constitutes a basic feature of the primate sensory system.

Presented by James Howie on 08/12/2011.

‘Effect of Tigecycline on Normal Oropharyngeal and Intestinal Microflora’

Antimicrob. Agents Chemother. (2006) 50(10): 3375-3380

doi: 10.1128/AAC.00373-06

Authors:

Nord, C.E., Sillerström, E. and Wahlund, E.

Abstract:

Antibacterial agents disrupt the ecological balance of the normal human microflora. Tigecycline, a member of a new class of antibiotics (glycylcyclines), has been shown to have a potent broad-spectrum activity against most gram-positive and gram-negative aerobic and anaerobic bacteria. The aim of the study was to investigate the ecological effects of tigecycline on the normal oropharyngeal and intestinal microflora of healthy subjects. Thirteen healthy white subjects (six females and seven males) between 20 and 31 years of age received 100 mg of tigecycline in the morning on day 1 as a 30-min intravenous infusion followed by a 50-mg dose of tigecycline every 12 h as a 30-minute infusion for 10 days. One subject was withdrawn on day 2 because of an adverse event (urticaria). Serum, saliva, and fecal samples were collected before, during, and after administration for microbiological cultivation and for assays of tigecycline. All new colonizing bacteria were tested for susceptibility (resistance of ≥8 mg/liter) during the investigation period. The fecal concentrations on day 8 were from 3.0 to 14.1 mg/kg, with a mean value of 6.0 mg/kg and a median value of 5.6 mg/kg. The saliva concentrations were generally low (0 to 0.12 mg/liter). A minor effect on the oropharyngeal microflora was observed. The numbers of enterococci and Escherichia coli cells in the intestinal microflora were reduced at day 8 (P < 0.05), while those of other enterobacteria and yeasts increased. There was a marked reduction of lactobacilli and bifidobacteria (P < 0.05) but no impact on bacteroides. No Clostridium difficile strains were isolated. Two Klebsiella pneumoniae strains and five Enterobacter cloacae strains resistant to tigecycline were found on day 8.

Presented by Fraser Murdoch on 01/12/2011.

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