There are 21 new papers on PLoS ONE published this week. Here are some titles that got my personal attention:
Climate Change, Genetics or Human Choice: Why Were the Shells of Mankind's Earliest Ornament Larger in the Pleistocene Than in the Holocene? by Peter R. Teske, Isabelle Papadopoulos, Christopher D. McQuaid, Brent K. Newman and Nigel P. Barker:
The southern African tick shell, Nassarius kraussianus, is the earliest ornament known to be used by humans, dating back ~75,000 years. This study investigates why beads made from these shells in more recent times are smaller. It is likely due to increased temperatures produced by climate change at the beginning of the present interglacial period, making N. kraussianus fossil shells a possible biomonitor of climatic conditions.
Cortical Modulations Increase in Early Sessions with Brain-Machine Interface by Miriam Zacksenhouse, Mikhail A. Lebedev, Jose M. Carmena, Joseph E. O'Doherty, Craig Henriquez and Miguel A.L. Nicolelis:
Brain-machine interfaces (BMIs) use the activity of cortical motor neurons to control external actuators, such as robot limbs. This study investigates the effects of the BMI itself on neuronal activity. Monkeys showed characteristic changes when they first starting training on BMIs that decreased as they gained experience, alluding to the formation of an internal model of the external actuator.
Do You See What I Mean? Corticospinal Excitability During Observation of Culture-Specific Gestures by Istvan Molnar-Szakacs, Allan D. Wu, Francisco J. Robles and Marco Iacoboni:
People all over the world use their hands to communicate expressively. Autonomous gestures, also known as emblems, are highly social in nature, and convey conventionalized meaning without accompanying speech. To study the neural bases of cross-cultural social communication, we used single pulse transcranial magnetic stimulation (TMS) to measure corticospinal excitability (CSE) during observation of culture-specific emblems. Foreign Nicaraguan and familiar American emblems as well as meaningless control gestures were performed by both a Euro-American and a Nicaraguan actor. Euro-American participants demonstrated higher CSE during observation of the American compared to the Nicaraguan actor. This motor resonance phenomenon may reflect ethnic and cultural ingroup familiarity effects. However, participants also demonstrated a nearly significant (p = 0.053) actor by emblem interaction whereby both Nicaraguan and American emblems performed by the American actor elicited similar CSE, whereas Nicaraguan emblems performed by the Nicaraguan actor yielded higher CSE than American emblems. The latter result cannot be interpreted simply as an effect of ethnic ingroup familiarity. Thus, a likely explanation of these findings is that motor resonance is modulated by interacting biological and cultural factors.
Although there is growing evidence that males tend to suffer higher levels of parasitism than females, the implications of this for the population dynamics of the host population are not yet understood. Here we build on an established 'two-sex' model and investigate how increased susceptibility to infection in males affects the dynamics, under different mating systems. We investigate the effect of pathogenic disease at different case mortalities, under both monogamous and polygynous mating systems. If the case mortality is low, then male-biased parasitism appears similar to unbiased parasitism in terms of its effect on the population dynamics. At higher case mortalities, we identified significant differences between male-biased and unbiased parasitism. A host population may therefore be differentially affected by male-biased and unbiased parasitism. The dynamical outcome is likely to depend on a complex interaction between the host's mating system and demography, and the parasite virulence.
The population genetics and structure of P. falciparum determine the rate at which malaria evolves in response to interventions such as drugs and vaccines. This has been the source of considerable recent controversy, but here we demonstrate the organism to be essentially sexual, in an area of moderately high transmission in the Lower Shire Valley, Malawi. Seven thousand mosquitoes were collected and dissected, and genetic data were obtained on 190 oocysts from 56 infected midguts. The oocysts were genotyped at three microsatellite loci and the MSP1 locus. Selfing rate was estimated as 50% and there was significant genotypic linkage disequilibrium (LD) in the pooled oocysts. A more appropriate analysis searching for genotypic LD in outcrossed oocysts and/or haplotypic LD in the selfed oocysts found no evidence for LD, indicating that the population was effectively sexual. Inbreeding estimates at MSP1 were higher than at the microsatellites, possibly indicative of immune action against MSP1, but the effect was confounded by the probable presence of null mutations. Mating appeared to occur at random in mosquitoes and evidence regarding whether malaria clones in the same host were related (presumably through simultaneous inoculation in the same mosquito bite) was ambiguous. This is the most detailed genetic analysis yet of P. falciparum sexual stages, and shows P. falciparum to be a sexual organism whose genomes are in linkage equilibrium, which acts to slow the emergence of drug resistance and vaccine insensitivity, extending the likely useful therapeutic lifespan of drugs and vaccines.
Tried to add an annotation, didn't work. Tried to start a discussion, didn't work. So I'm commenting on the article in question here.
The authors do note that humans did exploit the animal as a source of beads, but do not take into consideration that this exploitation may help to explain the reduction in size. Animals do tend to a reduction in adult size when over-exploited. Selection pressure is placed upon the species for earlier esxual maturation. A pressure seen in over-exploited fish populations for example.
For this reason I must find the study incomplete, and the findings unsupported.
ItÂ´s intriguing to think of a Middle Stone Age industry of Nassarius beads that may have been the cause of a decrease in shell sizes on the south coast. However, have you considered the following: On the west coast, there is much evidence for human settlement throughout the Middle- and Late Stone Age (see e.g. Dietl et al. 2005: J Afr Archaeol 3:233-244). If the pressure of collecting beads has resulted in a reduction of Nassarius shell sizes along the south coast, why didnÂ´t the same happen on the west coast? Also, much time has passed since these shells were collected, so wouldnÂ´t you expect the south coast populations to have recovered by now?