Harpellales in the digestive tracts of Ephemeroptera and Plecoptera nymphs from Veracruz, Mexico

This is the first report of Harpellales (Zygomycota) from Mexico, including herein only the endosymbiotic species of gut fungi in the digestive tracts or shed exuviae of Plecopteran and Ephemeropteran nymphs. Four new species are described: Allantomyces zopilotei, Bojamyces olmecensis, Gauthier-omyces viviparus and Graminella ophiuroidea. Among previously known Harpellales, Lancisporomyces nemouridarum and Zygopolaris ephemeridarum are southern range extremes and new records for Mexico. All species are illustrated and discussed relating to biogeographic implications of the new reports from Mexico, as well as the particular environmental circumstances of the Harpellales in the tropics.     

Evolution and diversity of clonal bacteria: the paradigm of Mycobacterium tuberculosis

Background

Mycobacterium tuberculosis complex species display relatively static genomes and 99.9% nucleotide sequence identity. Studying the evolutionary history of such monomorphic bacteria is a difficult and challenging task.

Principal Findings

We found that single-nucleotide polymorphism (SNP) analysis of DNA repair, recombination and replication (3R) genes in a comprehensive selection of M. tuberculosis complex strains from across the world, yielded surprisingly high levels of polymorphisms as compared to house-keeping genes, making it possible to distinguish between 80% of clinical isolates analyzed in this study. Bioinformatics analysis suggests that a large number of these polymorphisms are potentially deleterious. Site frequency spectrum comparison of synonymous and non-synonymous variants and Ka/Ks ratio analysis suggest a general negative/purifying selection acting on these sets of genes that may lead to suboptimal 3R system activity. In turn, the relaxed fidelity of 3R genes may allow the occurrence of adaptive variants, some of which will survive. Furthermore, 3R-based phylogenetic trees are a new tool for distinguishing between M. tuberculosis complex strains.

Conclusions/Significance

This situation, and the consequent lack of fidelity in genome maintenance, may serve as a starting point for the evolution of antibiotic resistance, fitness for survival and pathogenicity, possibly conferring a selective advantage in certain stressful situations. These findings suggest that 3R genes may play an important role in the evolution of highly clonal bacteria, such as M. tuberculosis. They also facilitate further epidemiological studies of these bacteria, through the development of high-resolution tools. With many more microbial genomes being sequenced, our results open the door to 3R gene-based studies of adaptation and evolution of other, highly clonal bacteria.     

Lipolysis drives expression of the constitutively active receptor GPR3 to induce adipose thermogenesis

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Diversification and biogeographic history of the Western Palearctic freshwater flatworm genus Schmidtea (Tricladida: Dugesiidae), with a redescription of Schmidtea nova

The freshwater flatworm genus Schmidtea is endemic in the Western Palearctic region, where it is represented by only four species, thus contrasting with the high species diversity of the closely related genus Dugesia within Europe. Although containing an important model species in developmental and regeneration research, viz. Schmidtea mediterranea, no evolutionary studies on the genus Schmidtea have been undertaken. For the first time, we present a well‐resolved molecular phylogenetic tree of the four species of the genus, inferred on the basis of two molecular markers, and provide also the first detailed morphological account of Schmidtea nova. The phylogenetic tree generated corroborates an earlier speciation hypothesis based on karyological data and points to chromosomal rearrangements as the main drivers of speciation in this genus. The high genetic divergence between the four species, in combination with previous dating studies and their current geographic distribution, suggests that Schmidtea could have originated in Laurasia but lost most of its diversity during the Oligocene. Thus, its present distribution pattern may be the result of the expansion of three of its four relictual species over Europe, probably after the Pleistocene glaciations. Our detailed morphological study of S. nova revealed that it shows a number of remarkable features: interconnected testis follicles, parovaria, an ejaculatory duct exiting into the primary as well as the secondary seminal vesicle by means of a nipple, and the wall of the distal section of the ejaculatory duct being sclerotic or chitinized.     

Interannual variations in needle and sapwood traits of Pinus edulis branches under an experimental drought

In the southwestern USA, recent large‐scale die‐offs of conifers raise the question of their resilience and mortality under droughts. To date, little is known about the interannual structural response to droughts. We hypothesized that piñon pines (Pinus edulis) respond to drought by reducing the drop of leaf water potential in branches from year to year through needle morphological adjustments. We tested our hypothesis using a 7‐year experiment in central New Mexico with three watering treatments (irrigated, normal, and rain exclusion). We analyzed how variation in “evaporative structure” (needle length, stomatal diameter, stomatal density, stomatal conductance) responded to watering treatment and interannual climate variability. We further analyzed annual functional adjustments by comparing yearly addition of needle area (LA) with yearly addition of sapwood area (SA) and distance to tip (d), defining the yearly ratios SA:LA and SA:LA/d. Needle length (l) increased with increasing winter and monsoon water supply, and showed more interannual variability when the soil was drier. Stomatal density increased with dryness, while stomatal diameter was reduced. As a result, anatomical maximal stomatal conductance was relatively invariant across treatments. SA:LA and SA:LA/d showed significant differences across treatments and contrary to our expectation were lower with reduced water input. Within average precipitation ranges, the response of these ratios to soil moisture was similar across treatments. However, when extreme soil drought was combined with high VPD, needle length, SA:LA and SA:LA/d became highly nonlinear, emphasizing the existence of a response threshold of combined high VPD and dry soil conditions. In new branch tissues, the response of annual functional ratios to water stress was immediate (same year) and does not attempt to reduce the drop of water potential. We suggest that unfavorable evaporative structural response to drought is compensated by dynamic stomatal control to maximize photosynthesis rates.     

Polygenic analysis of ammonia-oxidizing bacteria using 16S rDNA, amoA, and amoB genes.

Finding a unique molecular marker capable of quickly providing rigorous and useful phylogenetic information would facilitate assessing the diversity of ammonia-oxidizing bacteria in environmental samples. Since only one of several available markers can be used at a time in these kinds of studies, the 16S rDNA, amoA and amoB genes were evaluated individually and then compared in order to identify the one that best fits the information provided by the composite dataset. Distance-based neighbor-joining and maximum parsimony trees generated using the sequences of the three mentioned genes were analyzed with respect to the combined polygenic trees. Maximum parsimony trees were found to be more accurate than distance-based ones, and the polygenic topology was shown to best fit the information contained in the sequences. However, the taxonomic and phylogenetic information provided by the three markers separately was also valid. Therefore, either of the functional markers (amoA or amoB) can be used to trace ammonia oxidizers in environmental studies in which only one gene can be targeted.