Optimal-foraging predator favors commensalistic Batesian mimicry

Background

Mimicry, in which one prey species (the Mimic) imitates the aposematic signals of another prey (the Model) to deceive their predators, has attracted the general interest of evolutionary biologists. Predator psychology, especially how the predator learns and forgets, has recently been recognized as an important factor in a predator–prey system. This idea is supported by both theoretical and experimental evidence, but is also the source of a good deal of controversy because of its novel prediction that in a Model/Mimic relationship even a moderately unpalatable Mimic increases the risk of the Model (quasi-Batesian mimicry).

Methodology/Principal Findings

We developed a psychology-based Monte Carlo model simulation of mimicry that incorporates a “Pavlovian” predator that practices an optimal foraging strategy, and examined how various ecological and psychological factors affect the relationships between a Model prey species and its Mimic. The behavior of the predator in our model is consistent with that reported by experimental studies, but our simulation''s predictions differed markedly from those of previous models of mimicry because a more abundant Mimic did not increase the predation risk of the Model when alternative prey were abundant. Moreover, a quasi-Batesian relationship emerges only when no or very few alternative prey items were available. Therefore, the availability of alternative prey rather than the precise method of predator learning critically determines the relationship between Model and Mimic. Moreover, the predation risk to the Model and Mimic is determined by the absolute density of the Model rather than by its density relative to that of the Mimic.

Conclusions/Significance

Although these predictions are counterintuitive, they can explain various kinds of data that have been offered in support of competitive theories. Our model results suggest that to understand mimicry in nature it is important to consider the likely presence of alternative prey and the possibility that predation pressure is not constant.     

Relationship between BMI and all-cause mortality in Japan: NIPPON DATA80

As body composition in Asian populations is largely different from Western populations, a healthy BMI could also differ between the two populations. Thus, further study is needed to determine whether a healthy BMI in Asians should be lower than Western populations, as recommended by the World Health Organization (WHO). We investigated the relationship between BMI and mortality in a sample of 8,924 Japanese men and women without stroke or heart disease. During 19 years of follow-up, 1,718 deaths were observed. We found a U-shaped relationship between BMI and fatal events. Risk of total mortality was highest in participants with BMI <18.5 kg/m(2) and lowest in participants with BMI 23.0-24.9 kg/m(2). These findings persisted even after excluding the first 5 years of follow-up with a focus on healthy participants who never smoked, were aged <70 years, and had total cholesterol (TC) levels >or=4.1 mmol/l (N=3712). For both the full sample and healthy participants, all-cause mortality risk did not differ between BMI ranges 21.0-22.9 and 23.0-24.9 kg/m(2). Our findings do not support the recent WHO implications that BMIs <23.0 kg/m(2) is healthy for Asians. Therefore, further studies are needed to identify an optimal BMI range for Asia.     

mKikGR,a Monomeric Photoswitchable Fluorescent Protein

The recent demonstration and utilization of fluorescent proteins whose fluorescence can be switched on and off has greatly expanded the toolkit of molecular and cell biology. These photoswitchable proteins have facilitated the characterization of specifically tagged molecular species in the cell and have enabled fluorescence imaging of intracellular structures with a resolution far below the classical diffraction limit of light. Applications are limited, however, by the fast photobleaching, slow photoswitching, and oligomerization typical for photoswitchable proteins currently available. Here, we report the molecular cloning and spectroscopic characterization of mKikGR, a monomeric version of the previously reported KikGR that displays high photostability and switching rates. Furthermore, we present single-molecule imaging experiments that demonstrate that individual mKikGR proteins can be localized with a precision of better than 10 nanometers, suggesting their suitability for super-resolution imaging.     

Mycolyltransferase-mediated glycolipid exchange in Mycobacteria

Trehalose dimycolate (TDM), also known as cord factor, is a major surface glycolipid of the cell wall of mycobacteria. Because of its potent biological functions in models of infection, adjuvancy, and immunotherapy, it is important to determine how its biosynthesis is regulated. Here we show that glucose, a host-derived product that is not readily available in the environment, causes Mycobacterium avium to down-regulate TDM expression while up-regulating production of another major glycolipid with immunological roles in T cell activation, glucose monomycolate (GMM). In vitro, the mechanism of reciprocal regulation of TDM and GMM involves competitive substrate selection by antigen 85A. The switch from TDM to GMM biosynthesis occurs near the physiological concentration of glucose present in mammalian hosts. We further demonstrate that GMM is produced in vivo by mycobacteria growing in mouse lung. These results establish an enzymatic pathway for GMM production. More generally, these observations provide a specific enzymatic mechanism for dynamic alterations of cell wall glycolipid remodeling in response to the transition from noncellular to cellular growth environments, including factors that are monitored by the host immune system.     

Crystal structure of MutS2 endonuclease domain and the mechanism of homologous recombination suppression

DNA recombination events need to be strictly regulated, because an increase in the recombinational frequency causes unfavorable alteration of genetic information. Recent studies revealed the existence of a novel anti-recombination enzyme, MutS2. However, the mechanism by which MutS2 inhibits homologous recombination has been unknown. Previously, we found that Thermus thermophilus MutS2 (ttMutS2) harbors an endonuclease activity and that this activity is confined to the C-terminal domain, whose amino acid sequence is widely conserved in a variety of proteins with unknown function from almost all organisms ranging from bacteria to man. In this study, we determined the crystal structure of the ttMutS2 endonuclease domain at 1.7-angstroms resolution, which resembles the structure of the DNase I-like catalytic domain of Escherichia coli RNase E, a sequence-nonspecific endonuclease. The N-terminal domain of ttMutS2, however, recognized branched DNA structures, including the Holliday junction and D-loop structure, a primary intermediate in homologous recombination. The full-length of ttMutS2 digested the branched DNA structures at the junction. These results indicate that ttMutS2 suppresses homologous recombination through a novel mechanism involving resolution of early intermediates.     

Successions of bacterial community in composting cow dung wastes with or without hyperthermophilic pre-treatment

Comparative analyses of bacterial community successions in the composting materials were done for a conventional windrow post-treatment (WPOT) process with the hyperthermophilic pre-treatment (HTPRT) and simple windrow composting (SWC; without the HTPRT). Multidimensional scaling profiles based on data of terminal restriction fragment length polymorphisms of the bacterial population in the samples of every 7 days composting material and analyses of the 16S rRNA gene-based clone library of the 7 and 21 days composting materials suggested that bacterial communities of the composting materials differed much between these two processes until the 35 days of composting, whereas that they were closely related to each other at the final composting stage (42 days of composting). Detailed phylogenetic analysis clarified that all WPOT clone libraries contained many clones of the lineages of aerobic bacteria (for example, bacilli). However, the most abundant clones retrieved from all SWC materials were affiliated with a clone cluster closely related to identified and classified members of the phylum Firmicutes that have strictly anaerobic metabolism pathways. From these results, we conclude that the HTPRT process contributed to easily establish an aerobic ecosystem from the early stage to the final stage of WPOT composting with plowing the materials only once a week.