Conservation and divergence of meiotic DNA double strand break forming mechanisms in Arabidopsis thaliana

In the current meiotic recombination initiation model, the SPO11 catalytic subunits associate with MTOPVIB to form a Topoisomerase VI-like complex that generates DNA double strand breaks (DSBs). Four additional proteins, PRD1/AtMEI1, PRD2/AtMEI4, PRD3/AtMER2 and the plant specific DFO are required for meiotic DSB formation. Here we show that (i) MTOPVIB and PRD1 provide the link between the catalytic sub-complex and the other DSB proteins, (ii) PRD3/AtMER2, while localized to the axis, does not assemble a canonical pre-DSB complex but establishes a direct link between the DSB-forming and resection machineries, (iii) DFO controls MTOPVIB foci formation and is part of a divergent RMM-like complex including PHS1/AtREC114 and PRD2/AtMEI4 but not PRD3/AtMER2, (iv) PHS1/AtREC114 is absolutely unnecessary for DSB formation despite having a conserved position within the DSB protein network and (v) MTOPVIB and PRD2/AtMEI4 interact directly with chromosome axis proteins to anchor the meiotic DSB machinery to the axis.     

A genomic snapshot of Salmonella enterica serovar Typhi in Colombia

Little is known about the genetic diversity of Salmonella enterica serovar Typhi (S. Typhi) circulating in Latin America. It has been observed that typhoid fever is still endemic in this part of the world; however, a lack of standardized blood culture surveillance across Latin American makes estimating the true disease burden problematic. The Colombian National Health Service established a surveillance system for tracking bacterial pathogens, including S. Typhi, in 2006. Here, we characterized 77 representative Colombian S. Typhi isolates collected between 1997 and 2018 using pulse field gel electrophoresis (PFGE; the accepted genotyping method in Latin America) and whole genome sequencing (WGS). We found that the main S. Typhi clades circulating in Colombia were clades 2.5 and 3.5. Notably, the sequenced S. Typhi isolates from Colombia were closely related in a global phylogeny. Consequently, these data suggest that these are endemic clades circulating in Colombia. We found that AMR in S. Typhi in Colombia was uncommon, with a small subset of organisms exhibiting mutations associated with reduced susceptibility to fluoroquinolones. This is the first time that S. Typhi isolated from Colombia have been characterized by WGS, and after comparing these data with those generated using PFGE, we conclude that PFGE is unsuitable for tracking S. Typhi clones and mapping transmission. The genetic diversity of pathogens such as S. Typhi is limited in Latin America and should be targeted for future surveillance studies incorporating WGS.     

Litter Decomposition of Scirpus maritimus L. in a Mediterranean Coastal Marsh: Importance of the Meiofauna during the Initial Phases of Detached Leaves Decomposition

Growth, senescence and decomposition rates of Scirpus maritimus were studied in a Mediterranean brackish wetland. Plant tussocks were tagged in March, 2002 and were totally dead by September, 2002. Decomposition rates were determined over 360 days using litter bag technique and mass loss, nutrient dynamics, fungal biomass, meiofauna and macroorganisms were determined. Decomposition rate of detached S. maritimus litter was 0.00196 (k, day^–1) with a 54% of mass lost observed in 1 year. The pattern of mass loss was characterized by an initial phase of fast loss of organic matter with high density of meiofauna and a decrease of oxygen content, followed by two slower phases, with no significant losses from 50 to 180 days and with 21% of mass lost from 180 to 360 days. Nitrogen (N) and phosphorus (P) content of plant litter increased during decomposition process whereas atomic C:N and C:P ratios decreased, suggesting a nutrient immobilization on plant detritus. Fungal biomass measured as ergosterol content decreased after submersion of leaves, indicating that their importance in litter decomoposition decreases in submerged leaves during the first days of decomposition. An inverse relationship (r = –0.79, P < 0.005) was observed between ergosterol content and nematodes density on S. maritimus litter. Our results suggest that in Mediterranean brackish marshes, where large amounts of dead organic matter is accumulated over the sediment surface, decomposition process is greatly affected by extremely high temperatures in summer that, if water is available, accelerates microbial activity decreasing oxygen content thus slowing decomposition. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Food Preferences and Nutrient Composition in Captive Spider Monkeys,Ateles geoffroyi

We assessed the occurrence of food preferences in captive spider monkeys and analyzed whether their preferences correlate with nutrient composition. Using a two-alternative choice test, we repeatedly presented 7 Ateles geoffroyi with all possible binary combinations of 12 types of food that are part of their diet in captivity. They exhibited the following rank order of preference: avocado > sapodilla > pineapple > mango > papaya > melon > banana > apple > tomato > orange > carrot > cucumber. Correlational analyses revealed that this preference ranking is significantly positively correlated with total energy content, irrespective of the source of energy as neither total carbohydrate content nor protein or lipid content is significantly correlated with food preference. Further, food preferences are significantly negatively correlated with water content and positively correlated with the content of magnesium, copper and manganese. These results suggest that despite their high degree of frugivory and high taste sensitivity for soluble carbohydrates, spider monkeys are opportunistic feeders with regard to maximizing net gain of energy.     

Competition for Milk in the Domestic Rabbit: Survivors Benefit from Littermate Deaths

We sought evidence for postnatal resource limitation among littermates of the domestic rabbit Oryctolagus cuniculus , and asked whether deaths of indi~vidual pups benefit survivors by increasing their share of milk. Milk ingestion, growth and mortality of 10 chinchilla-breed captive litters were recorded between birth and age 21 d. That milk limits growth and survival was indicated by larger litters showing lower weight gain and higher mortality, and by a significant positive correlation between milk ingested by individual pups and weight increase. Within litters, pups with higher birth weights grew faster, and weight hierarchies became increasingly stable over the 3 weeks, suggesting that advantages accrued during gestation were progressively consolidated during lactation. After individual pups died, the total daily milk weight obtained by the litter was generally unaffected but per capita milk consumption and growth of surviving pups increased, and increases in per capita consumption were greater in smaller litters. The most successful competitors for milk apparently benefit from the deaths of their littermates by obtaining an increased share of an undiminished daily food supply. This relationship has not previously been demonstrated in any vertebrate.     

Multiple matings modify the estrous length,the moment of ovulation,and the estradiol and LH patterns in ewes

In several species, mating reduces the estrous length and advances ovulation. The aim of this study was to determine if multiple matings reduces the estrous length and modifies the moment of ovulation, as well as the estradiol and LH patterns in ewes. The estrous cycle of Corriedale ewes was synchronized, and the onset of receptivity was monitored every 3 h with rams, avoiding mating. At the estrous onset, ewes were assigned to two experimental groups (n=10 each): 1) estrous was monitored every 3 h with a ram avoiding mating (group CON), and 2) a ram was allowed to mate and ejaculate once every 3 h (group MAT). The ovaries were scanned with transrectal ultrasonography and blood samples were collected for measuring 17β-estradiol and LH concentrations every 3 h until ovulation. Estrus was shorter in MAT than CON ewes (24.7 ± 1.5 h vs. 30.4 ± 1.5 h, respectively; P=0.02); the proportion of animals that ovulated before the end of estrus was greater in CON ewes: (9/10 vs. 3/10, P=0.009). The area under the LH curve (AUC) was greater in MAT than CON ewes (36.1 ± 3.5 ng.h^-1.mL^-1 vs 24.9 ± 3.5 ng.h^-1.mL^-1 P=0.03). However, MAT ewes had a lower 17β-estradiol AUC than CON ewes (41.0 ± 4.9 pg.h^-1.mL^-1 vs 59.4 ± 4.9 pg.h^-1.mL^-1 P=0.01). Mating reduced the estrous length, induced a greater secretion of LH but less total 17β-estradiol secreted and, additionally, ovulation occurred more frequently after the end of estrus in mated ewes.     

Glypican 4 mediates Wnt transport between germ layers via signaling filopodia

Glypicans influence signaling pathways by regulating morphogen trafficking and reception. However, the underlying mechanisms in vertebrates are poorly understood. In zebrafish, Glypican 4 (Gpc4) is required for convergence and extension (C&E) of both the mesoderm and endoderm. Here, we show that transgenic expression of GFP-Gpc4 in the endoderm of gpc4 mutants rescued C&E defects in all germ layers. The rescue of mesoderm was likely mediated by Wnt5b and Wnt11f2 and depended on signaling filopodia rather than on cleavage of the Gpc4 GPI anchor. Gpc4 bound both Wnt5b and Wnt11f2 and regulated formation of the filopodia that transport Wnt5b and Wnt11f2 to neighboring cells. Moreover, this rescue was suppressed by blocking signaling filopodia that extend from endodermal cells. Thus, GFP-Gpc4–labeled protrusions that emanated from endodermal cells transported Wnt5b and Wnt11f2 to other germ layers, rescuing the C&E defects caused by a gpc4 deficiency. Our study reveals a new mechanism that could explain in vivo morphogen distribution involving Gpc4.     

Effect of climatic variation on the relative abundance of the red alga Gelidium robustum in Baja California Sur, Mexico

The red alga Gelidium robustum is important,because of its commercial exploitation in Mexico as araw material for the agar industry, providing 10% ofthe world production of agarophytes. In recent years,its annual harvest in Mexico has shownobvious,variations partly because of an increasedharvesting effort, but also because of environmentalchanges. An analysis is presented of the effect thatinterannual variability of the sea surfacetemperature, wind speed, and upwelling index had onthe relative abundance of this alga from 1980 to 1990.The results indicate a close relation betweenenvironmental fluctuations and the relative abundanceof this species. The response of G. robustum tothe different environmental conditions has not alwaysbeen equal. During El Niño 1982–84, the seasurface temperature was the most important factor andthere was a high negative correlation with therelative abundance. A lag period of three monthsshowed a positive correlation with upwelling index andwind speed. Under normal conditions and during LaNiña, the relative abundance of the alga showed apositive correlation with the sea surface temperature. For the upwelling index and wind speed, therelationship was similar to that during El Niño.