Independently evolving species in asexual bdelloid rotifers

Asexuals are an important test case for theories of why species exist. If asexual clades displayed the same pattern of discrete variation as sexual clades, this would challenge the traditional view that sex is necessary for diversification into species. However, critical evidence has been lacking: all putative examples have involved organisms with recent or ongoing histories of recombination and have relied on visual interpretation of patterns of genetic and phenotypic variation rather than on formal tests of alternative evolutionary scenarios. Here we show that a classic asexual clade, the bdelloid rotifers, has diversified into distinct evolutionary species. Intensive sampling of the genus Rotaria reveals the presence of well-separated genetic clusters indicative of independent evolution. Moreover, combined genetic and morphological analyses reveal divergent selection in feeding morphology, indicative of niche divergence. Some of the morphologically coherent groups experiencing divergent selection contain several genetic clusters, in common with findings of cryptic species in sexual organisms. Our results show that the main causes of speciation in sexual organisms, population isolation and divergent selection, have the same qualitative effects in an asexual clade. The study also demonstrates how combined molecular and morphological analyses can shed new light on the evolutionary nature of species.     

A microcarrier-based cultivation system for expansion of primary mesenchymal stem cells

Microcarrier cultures have been shown to allow extensive cell expansion of tissue engineering relevant cells, such as chondrocytes, while maintaining their phenotype. Our aim was to investigate the in vitro three-dimensional expansion of porcine bone-marrow-derived primary mesenchymal stem cells (MSC) using commercially available Cytodex type 1, type 2, and type 3 microcarriers. In comparison, the Cytodex type 1 microcarriers showed the best results for adherence with over 80% adherent cells after 3 h of incubation, analyzed by the Poisson distribution. Different start cell densities ranging from 1 to 3 x 106 cells per 100 cm2 had only a minor influence on adhesion. The proliferation was examined on Cytodex type 1 microcarriers over a cultivation time of 28 days, which could reveal cell growth and proof of cells recolonizing freshly added microcarriers. Scanning electron microscopy displayed appropriate cell morphology and confirmed cell proliferation. After enzymatic harvest from microcarriers, the osteogenic and chondrogenic differentiation of these cells was induced and shown by relevant histochemistry, such as von Kossa and Alcian blue staining. Totaling the results, we have shown that the three-dimensional expansion of MSC on microcarriers represents a beneficial alternative to the conventional two-dimensional monolayer cultivation method.     

Early queen infection shapes developmental dynamics and induces long-term disease protection in incipient ant colonies

Infections early in life can have enduring effects on an organism's development and immunity. In this study, we show that this equally applies to developing ‘superorganisms’––incipient social insect colonies. When we exposed newly mated Lasius niger ant queens to a low pathogen dose, their colonies grew more slowly than controls before winter, but reached similar sizes afterwards. Independent of exposure, queen hibernation survival improved when the ratio of pupae to workers was small. Queens that reared fewer pupae before worker emergence exhibited lower pathogen levels, indicating that high brood rearing efforts interfere with the ability of the queen's immune system to suppress pathogen proliferation. Early-life queen pathogen exposure also improved the immunocompetence of her worker offspring, as demonstrated by challenging the workers to the same pathogen a year later. Transgenerational transfer of the queen's pathogen experience to her workforce can hence durably reduce the disease susceptibility of the whole superorganism.     

Electrophysiological characterization of Tityus obscurus β toxin 1 (To1) on Na+-channel isoforms

To1, previously named Tc49b, is a peptide neurotoxin isolated from venom of the scorpion Tityus obscurus that is responsible for lethal human poisoning cases in the Brazilian Amazonian region. Previously, To1 was shown to be lethal to mice and to change Na⁺ permeation in cerebellum granular neurons from rat brain. In addition, To1 did not affect Shaker B K⁺ channels. Based on sequence similarities, To1 was described as a β-toxin. In the present work, To1 was purified from T. obscurus venom and submitted to an electrophysiological characterization in human and invertebrate Na_V channels. The analysis of the electrophysiological experiments reveal that To1 enhances the open probability at more negative potentials of human Na_V 1.3 and 1.6, of the insect channel BgNa_V1 and of arachnid VdNa_V1 channel. In addition, To1 reduces the peak of Na⁺ currents in some of the Na_Vs tested. These results support the classification of the To1 as a β-toxin. A structure and functional comparison to other β-toxins that share sequence similarity to To1 is also presented.     

Domain redistribution within ergosterol-containing model membranes in the presence of the antimicrobial compound fengycin

The cyclic lipopeptide fengycin, produced by Bacillus subtilis, exhibits its antimicrobial capabilities by altering the integrity of the cell membrane of plant pathogens. Previous work has correlated fengycin activity with membrane characteristics, such as sterol content. This work focused on the influence of fengycin on supported lipid bilayers containing varying levels of ergosterol. Total internal reflection fluorescence (TIRF) microscopy was used to visualize and distinguish ordered (L_β/L_o) and disordered (L_α/L_d) domains in the model membranes following exposure to low (50 μg) and high (500 μg) fengycin doses. Application of an initial low dose of fengycin to 0% and 3% ergosterol-containing bilayers resulted in redistribution of L_α/L_β and L_o/L_d domains, respectively, which the bilayers compensated and corrected for over time. These membranes were unable to tolerate a second 50 μg dose or a single high fengycin dose. The 6% ergosterol bilayers were able to tolerate sequential low doses of fengycin. Exposure of these bilayers to the high fengycin dose caused a decrease in the number of L_o domains, albeit less than that seen in the 0% and 3% ergosterol bilayers. Bilayers containing 12% ergosterol, exhibited the least amount of change after fengycin exposure. These were the only bilayer to exhibit an increase in area taken up by ordered domains. These results suggest fengycin may preferentially act on the L_β or L_o phase, the area in which ergosterol resides. Bilayers containing low levels of ergosterol appear to be more sensitive to the lipopeptide, suggesting ergosterol plays a role in buffering perturbations caused by fengycin.     

Plastic collective endothermy in a complex animal society (army ant bivouacs: Eciton burchellii parvispinum)

Endothermic animals do not always have a single adaptive internal temperature; some species exhibit plastic homeostasis, adaptively allowing body temperature to drop when thermoregulatory costs are high. Like large‐bodied endotherms, some animal societies exhibit collective thermal homeostasis. We tested for plasticity of thermoregulation in the self‐assembled temporary nests (bivouacs) of army ants. We measured core bivouac temperatures under a range of environmental conditions and at different colony developmental (larval vs pupal brood) stages. Contrary to previous assertions, bivouacs were not perfect thermoregulators in all developmental stages. Instead, bivouacs functioned as superorganismal facultative endotherms, using a combination of site choice and context‐dependent metabolic heating to adjust core temperatures across an elevational cline in ambient temperature. When ambient temperature was low, the magnitude of metabolic heating was dependent on colony developmental stage: pupal bivouacs were warmer than larval bivouacs. At cooler high elevations, bivouacs functioned like some endothermic animals that intermittently lower their body temperatures to conserve energy. Bivouacs potentially conserved energy by investing less metabolic heating in larval brood because the high costs of impaired worker development may require more stringent thermoregulation of pupae. Our data also suggest that site choice played an important role in bivouac cooling under high ambient temperatures at low elevations. Climate warming may expand upper elevational range limits of Eciton burchellii parvispinum, while reducing the availability of cool and moist bivouac sites at lower elevations, potentially leading to future low‐elevation range contraction.     

Quantitative control of gene expression by nucleocytoplasmic interactions in early mouse embryos: Consequence for reprogrammation by nuclear transfer

HSP 70.1 is one of the first genes to be expressed in the mouse embryo at the time of zygotic genome activation. We studied the regulation of this gene, using a transgene associating HSP 70.1 promoter and the firefly luciferase reporter gene, which allows the precise quantification of HSP 70.1 level of expression on individual embryos. In the present work, we show first that the level of HSP 70.1 expression at the two-cell stage is significantly higher (around two-fold) in embryos whose maternal cytoplasm is from C3H strain than with BALB/c strain. We verified that this difference is not an artefact of the use of transgenic embryos, of the time of first cleavage, or of in vitro culture. This regulation of HSP 70.1 level of expression is controlled by strain-specific maternal modifiers and is independent of replication, syngamy, and mitosis. Following nuclear transfer, reactivation of HSP 70.1 is also subjected to the same epigenetic influence. Only the strain-of-origin of the recipient cytoplast modulates the level of HSP 70.1 reprogrammation; the origin of donor nucleus is not significant, demonstrating the reversibility of this strain effect. These results point out the importance of the quality of recipient cytoplast in the intensity of gene reprogrammation, which may be of importance for nuclear transfer efficiency. © 1996 Wiley-Liss, Inc.