Supraorbital ridge and masticatory apparatus I: Primates

The supraorbital ridge formation in apes is a result of the traction of the masticatory force exerted by the anterior part of the temporalis muscle. This force varies inversely with the ratio of the power arm to the load arm of the mandible. The smaller this ratio, the greater the anterior part of the temporalis muscle and the larger the supraorbital ridge. The size of the ridge is independent of the actual size of the skull. The orang has a larger skull but the smallest brow ridge of the three species studied: gorilla, chimpanzee and orang. Pearson’s correlation coefficient shows a positive correlation between the anterior temporalis muscle and the ridge as well as between the ridge/sinus and anterior/whole temporalis muscle. The correlation is negative between the power/load arms and anterior/whole muscle and also between the power/load arms and the ridge/sinus ratio.     

A novel type of colistin resistance genes selected from random sequence space

Antibiotic resistance is a rapidly increasing medical problem that severely limits the success of antibiotic treatments, and the identification of resistance determinants is key for surveillance and control of resistance dissemination. Horizontal transfer is the dominant mechanism for spread of resistance genes between bacteria but little is known about the original emergence of resistance genes. Here, we examined experimentally if random sequences can generate novel antibiotic resistance determinants de novo. By utilizing highly diverse expression libraries encoding random sequences to select for open reading frames that confer resistance to the last-resort antibiotic colistin in Escherichia coli, six de novo colistin resistance conferring peptides (Dcr) were identified. The peptides act via direct interactions with the sensor kinase PmrB (also termed BasS in E. coli), causing an activation of the PmrAB two-component system (TCS), modification of the lipid A domain of lipopolysaccharide and subsequent colistin resistance. This kinase-activation was extended to other TCS by generation of chimeric sensor kinases. Our results demonstrate that peptides with novel activities mediated via specific peptide-protein interactions in the transmembrane domain of a sensory transducer can be selected de novo, suggesting that the origination of such peptides from non-coding regions is conceivable. In addition, we identified a novel class of resistance determinants for a key antibiotic that is used as a last resort treatment for several significant pathogens. The high-level resistance provided at low expression levels, absence of significant growth defects and the functionality of Dcr peptides across different genera suggest that this class of peptides could potentially evolve as bona fide resistance determinants in natura.     

Individual bee foragers are less-efficient transporters of pollen for plants from which they collect the most pollen in their scopae

Premise

Bees provision most of the pollen removed from anthers to their larvae and transport only a small proportion to stigmas, which can negatively affect plant fitness. Though most bee species collect pollen from multiple plant species, we know little about how the efficiency of bees' pollen transport varies among host plant species or how it relates to other aspects of generalist bee foraging behavior that benefit plant fitness, such as specialization on individual foraging bouts.

Methods

We compared the pollen collected and transported by three bee species for 46 co-occurring plant species. Specifically, we compared the relative abundance of pollen taxa in the individual bees' scopae, structures where bees store pollen to provision larvae, with the relative abundance of pollen taxa on the rest of bees' bodies, which is more likely to be transferred to stigmas.

Results

Bees carried five times more pollen grains in their scopae than elsewhere on their bodies. Within foraging bouts, bees were relatively specialized in their pollen collection, but transported proportionally less pollen for the host plants on which they specialized. Across foraging bouts, two bee species transported proportionally less pollen for some of their host plants than for others, though differences didn't consistently follow the same trend as at the foraging bout scale.

Conclusions

Our results suggest that foraging-bout specialization, which is known to reduce heterospecific pollen transfer, also results in less-efficient pollen transport. Thus, bee foragers that visit predominantly one plant species may have contrasting effects on that plant's fitness.