Reproductive success of Tree Pipits Anthus trivialis in relation to habitat selection in conifer plantations

Aspects of the reproductive success of Tree Pipits Anthus trivialis were examined in relation to broad‐scale habitat and nest‐site selection in Thetford Forest, a coniferous plantation forest in eastern England. Three habitat classes were defined corresponding to previously reported densities of Tree Pipits: clearfell and recently planted stands (habitat class A: low density), stands 2–5 years old (B: high density) and stands 6 years or older (C: low density). The preference for 2–5‐year‐old stands indicated by higher densities was supported by the timing of territory settlement. Tree Pipits also showed distinct preferences for nest‐site characteristics that were relatively consistent across habitat classes and throughout the breeding season. At the ‘habitat scale’, results were consistent with the predictions of the ideal despotic distribution model. First clutches were laid significantly earlier in the preferred habitat class B. Overall nesting success (i.e. the proportion of nests producing fledglings), but not clutch size, also varied between habitats, being greater in habitat classes B and C than in habitat class A. The variation in overall nesting success between habitats was primarily driven by low nest survival rates during the laying/incubation period in clearfell and recently planted stands. Nest survival rates during the nestling period were lower in the preferred 2–5‐year‐old (and older) stands and declined over the course of the study. Preferences for nest‐site characteristics (at least for those that were measured) provided no apparent benefit to nest survival rates. Overall nesting success thus appeared to be determined at the habitat scale, perhaps because the broad differences in cover between habitats affected the likelihood of nest predation (the main cause of nest failure). It is suggested that the very low nesting success experienced by Tree Pipits in clearfell and new stands may be one factor in the species’ relative avoidance of this habitat and preference for 2–5‐year‐old stands.     

Survival and metabolism of <Emphasis Type="Italic">Rana arvali</Emphasis>s during freezing

Freeze tolerance and changes in metabolism during freezing were investigated in the moor frog (Rana arvalis) under laboratory conditions. The data show for the first time a well-developed freeze tolerance in juveniles of a European frog capable of surviving a freezing exposure of about 72 h with a final body temperature of −3°C. A biochemical analysis showed an increase in liver and muscle glucose in response to freezing (respectively, 14-fold and 4-fold between 4 and −1°C). Lactate accumulation was only observed in the liver (4.1 ± 0.8 against 16.6 ± 2.4 μmol g⁻¹ fresh weight (FW) between 4 and −1°C). The quantification of the respiratory metabolism of frozen frogs showed that the aerobic metabolism persists under freezing conditions (1.4 ± 0.7 μl O₂ g⁻¹ FW h⁻¹ at −4°C) and decreases with body temperature. After thawing, the oxygen consumption rose rapidly during the first hour (6-fold to 16-fold) and continued to increase for 24 h, but at a lower rate. In early winter, juvenile R. arvalis held in an outdoor enclosure were observed to emerge from ponds and hibernate in the upper soil and litter layers. Temperature recordings in the substratum of the enclosure suggested that the hibernacula of these juvenile frogs provided sheltering from sub-zero air temperatures and reduced the time spent in a frozen state corresponding well with the observed freeze tolerance of the juveniles. This study strongly suggests that freeze tolerance of R. arvalis is an adaptive trait necessary for winter survival.     

SLP‐2 is required for stress‐induced mitochondrial hyperfusion

Mitochondria are dynamic organelles, the morphology of which results from an equilibrium between two opposing processes, fusion and fission. Mitochondrial fusion relies on dynamin‐related GTPases, the mitofusins (MFN1 and 2) in the outer mitochondrial membrane and OPA1 (optic atrophy 1) in the inner mitochondrial membrane. Apart from a role in the maintenance of mitochondrial DNA, little is known about the physiological role of mitochondrial fusion. Here we report that mitochondria hyperfuse and form a highly interconnected network in cells exposed to selective stresses. This process precedes mitochondrial fission when it is triggered by apoptotic stimuli such as UV irradiation or actinomycin D. Stress‐induced mitochondrial hyperfusion (SIMH) is independent of MFN2, BAX/BAK, and prohibitins, but requires L‐OPA1, MFN1, and the mitochondrial inner membrane protein SLP‐2. In the absence of SLP‐2, L‐OPA1 is lost and SIMH is prevented. SIMH is accompanied by increased mitochondrial ATP production and represents a novel adaptive pro‐survival response against stress.     

Intestinal epithelial cancer cell anoikis resistance: EGFR‐mediated sustained activation of Src overrides Fak‐dependent signaling to MEK/Erk and/or PI3‐K/Akt‐1

Herein, we investigated the survival roles of Fak, Src, MEK/Erk, and PI3‐K/Akt‐1 in intestinal epithelial cancer cells (HCT116, HT29, and T84), in comparison to undifferentiated and differentiated intestinal epithelial cells (IECs). We report that: (1) cancer cells display striking anoikis resistance, as opposed to undifferentiated/differentiated IECs; (2) under anoikis conditions and consequent Fak down‐activation, cancer cells nevertheless exhibit sustained Fak–Src interactions and Src/MEK/Erk activation, unlike undifferentiated/differentiated IECs; however, HCT116 and HT29 cells exhibit a PI3‐K/Akt‐1 down‐activation, as undifferentiated/differentiated IECs, whereas T84 cells do not; (3) cancer cells require MEK/Erk for survival, as differentiated (but not undifferentiated) IECs; however, T84 cells do not require Fak and HCT116 cells do not require PI3‐K/Akt‐1, in contrast to the other cells studied; (4) Src acts as a cornerstone in Fak‐mediated signaling to MEK/Erk and PI3‐K/Akt‐1 in T84 cells, as in undifferentiated IECs, whereas PI3‐K/Akt‐1 is Src‐independent in HCT116, HT29 cells, as in differentiated IECs; and (5) EGFR activity inhibition abrogates anoikis resistance in cancer cells through a loss of Fak–Src interactions and down‐activation of Src/MEK/Erk (T84, HCT116, HT29 cells) and PI3‐K/Akt‐1 (T84 cells). Hence, despite distinctions in signaling behavior not necessarily related to undifferentiated or differentiated IECs, intestinal epithelial cancer cells commonly display an EGFR‐mediated sustained activation of Src under anoikis conditions. Furthermore, such sustained Src activation confers anoikis resistance at least in part through a consequent sustenance of Fak–Src interactions and MEK/Erk activation, thus not only overriding Fak‐mediated signaling to MEK/Erk and/or PI3‐K/Akt‐1, but also the requirement of Fak and/or PI3‐K/Akt‐1 for survival. J. Cell. Biochem. 107: 639–654, 2009. © 2009 Wiley‐Liss, Inc.     

Studies on the susceptibility of different culture morphotypes of Listeria monocytogenes to uptake and survival in human polymorphonuclear leukocytes

This study demonstrated that atypical virulent filaments of Listeria monocytogenes (rough variant type II and designated FR for this study), isolated from clinical specimens or generated during exposure to pulsed-plasma gas discharge in liquids, were shown to be capable of survival when engulfed by human polymorphonuclear leukocytes (PMNLs). Factors shown to significantly influence the maximal respiratory burst response in PMNLs and survival of different internalized cell or filament forms of L. monocytogenes were bacterial strain, culture form, degree of opsonization (with and without the use of 10% serum) and composition of the bacterial growth media used before uptake by PMNLs. Opsonized regular-sized L. monocytogenes cells grown on blood agar (BA) elicited the greatest respiratory burst response and survived best in PMNLs. The filamentous (FR) and multiple cell chain (MCR) rough variants were significantly less susceptible to uptake and survival in PMNLs. Supplementation of tryptone soya agar with hemin resulted in significantly reduced chemiluminescence responses in phagocytosing PMNLs compared with the maximal levels observed from prior bacterial growth on BA or brain heart infusion agar that also contained a source of iron. The MCR variants secreting decreased levels of a peptidoglycan hydrolase CwhA protein exhibited the lowest percentage survival when internalized in PMNLs compared with wild-type smooth or FR culture variants as determined by the macrophage-killing assay.     

Lifespan, lifetime reproductive performance and paternity loss of within-pair and extra-pair offspring in the coal tit Periparus ater

The hypothesis that females of socially monogamous species obtain indirect benefits (good or compatible genes) from extra-pair mating behaviour has received enormous attention but much less generally accepted support. Here we ask whether selection for adult survival and fecundity or sexual selection contribute to indirect selection of the extra-pair mating behaviour in socially monogamous coal tits (Periparus ater). We tracked locally recruited individuals with known paternity status through their lives predicting that the extra-pair offspring (EPO) would outperform the within-pair offspring (WPO). No differences between the WPO and EPO recruits were detected in lifespan or age of first reproduction. However, the male WPO had a higher lifetime number of broods and higher lifetime number of social offspring compared with male EPO recruits, while no such differences were evident for female recruits. Male EPO recruits did not compensate for their lower social reproductive success by higher fertilization success within their social pair bonds. Thus, our results do not support the idea that enhanced adult survival, fecundity or within-pair fertilization success are manifestations of the genetic benefits of extra-pair matings. But we emphasize that a crucial fitness component, the extra-pair fertilization success of male recruits, has yet     

Taphonomy of the early Miocene flora, Hiwegi Formation, Rusinga Island, Kenya

A fossil flora was collected in situ from early Miocene deposits at site R117 in the Hiwegi Formation of Rusinga Island contemporaneous with and in close proximity to the sites from where the anthropoid primates were recovered. The flora exhibits a spatially and temporally patchy distribution of fruits and seeds, mixed with twigs of various sizes, fragments of wood, bark, and leaves, all with random orientations and very low depositional dips. There has been minimal transport and the flora evidently accumulated as in situ litter beneath local vegetation. Based on Nearest Living Relatives (NLR) of fruits and seeds, the vegetation represented is a deciduous broad-leaved woodland with continuous canopy, with trees, shrubs, lianas, and climbers, reminiscent of the structure of the modern vegetation in the steep-sided protected valleys in the Laetoli-Endulen area. The interpretation of the vegetation is supported by the presence of twigs, wood, and bark fragments from larger diameter axes. Climbers are represented by twining stem fragments as well as by a wide variety of distinctive fruits and seeds. The proportion of fossilised thorny twigs represents only 3% of the twig collections, and there are no unequivocal forest trees amongst the NLR. No grasses were present; monocotyledons are only represented by a single date palm stone. No conifer seeds or cones have been recovered, and there are no coniferous leafy shoots.     

Stress-induced activation of Nox contributes to cell survival signalling via production of hydrogen peroxide

Reactive oxygen species (ROS) have traditionally been viewed as a toxic group of molecules; however, recent publications have shown that these molecules, including H₂O₂, can also strongly promote cell survival. Even though the retina has a large capacity to produce ROS, little is known about its non-mitochondrial sources of these molecules, in particular the expression and function of NADPH oxidase (Nox) proteins which are involved in the direct generation of superoxide and indirectly H₂O₂. This study demonstrated that 661W cells, a retina-derived cell line, and mouse retinal explants express Nox2, Nox4 and certain of their well-established regulators. The roles of Nox2 and Nox4 in producing pro-survival H₂O₂ were determined using 661W cells and some of the controlling factors were identified. To ascertain if this phenomenon could have physiological relevance, the novel technique of time-lapse imaging of dichlorofluorescein fluorescence (generated upon H₂O₂ production) in retinal explants was established and it showed that explants also produce a burst of H₂O₂. The increase in H₂O₂ production was partly blocked by an inhibitor of Nox proteins. Overall, this study demonstrates a pro-survival role of Nox2 and Nox4 in retina-derived cells, elucidates some of the regulatory mechanisms and reveals that a similar phenomenon exists in retinal tissue as a whole.