A high-throughput assay shows that DNase-I binds actin monomers and polymers with similar affinity

Previous conflicting reports suggest that DNase-I binds F-actin with either equal or drastically different K(D) values compared to G-actin. We developed a high-throughput DNase-I inhibition assay to determine the K(D) of DNase-I for F-actin. We confirmed that phalloidin-stabilized F-actin is protected from depolymerization by DNase-I and that the critical concentration at the pointed end of phalloidin-F-actin is 45.5+/-13.9 nM. We found that DNase-I inhibition by actin follows ultrasensitive mechanics. Using varying lengths of gelsolin-capped phalloidin-F-actin, we concluded that the affinities of DNase-I for G- and the pointed end subunits of F-actin are almost indistinguishable, such that DNase-I may not distinguish between G- and F-actin conformations.     

Hepatocyte growth factor-induced Ras activation requires ERM proteins linked to both CD44v6 and F-actin

In several types of cells, the activation of the receptor tyrosine kinase c-Met by its ligand hepatocyte growth factor (HGF) requires the coreceptor CD44v6. The CD44 extracellular domain is necessary for c-Met autophosphorylation, whereas the intracellular domain is required for signal transduction. We have already shown that the CD44 cytoplasmic tail recruits ezrin, radixin and moesin (ERM) proteins to the complex of CD44v6, c-Met, and HGF. We have now defined the function of the ERM proteins and the step they promote in the signaling cascade. The association of ERM proteins to the coreceptor is absolutely required to mediate the HGF-dependent activation of Ras by the guanine nucleotide exchange factor Sos. The ERM proteins need, in addition, to be linked to the actin cytoskeleton to catalyze the activation of Ras. Thus, we describe here a new function of the cytoskeleton. It is part of a "signalosome" complex that organizes the activation of Ras by Sos. So far the cytoskeleton has mainly been identified as a "responder" to signal transduction. Here, we show now that F-actin acts as an "inducer" that actively organizes the signaling cascade.     

Growth and reproductive characteristics of rarely observed resident female Dolly Varden (Salvelinus malma malma) in North America

The replacement of native species by invasive species is one of the most critical threats to the biodiversity of aquatic systems today. However, little is known about potential effects of species invasions on the genetic diversity of indigenous species in cases where the latter coexist with the invader. Here we present an example of the indigenous amphipod Gammarus roeselii, which has been partly replaced by the invasive Dikerogammarus villosus in Lake Constance (C-Europe) and now mostly exists in small, isolated populations. We compared the genetic diversity, population structure, indicators for bottlenecks and migrations rates of G. roeselii before and after the invasion event from samples collected between 1999 and 2013. We expected a genetic impoverishment in the reduced and segregated populations of G. roeselii. However, no genetic measure on G. roeselii differed temporally or spatially over the investigated period, which indicates that D. villosus has not yet had an impact on G. roeselii at the genetic scale. Hence, even though a decline in population size of G. roeselii was found in Lake Constance, our results on the genetic scale contribute to recent findings that the overall impact of D. villosus on native species is not as strong as often discussed.

     

Spatial scale affects novel and disappeared climate change projections in Alaska

The formation of novel and disappeared climates between the last glacial maximum (LGM) and the present is important to consider to understand the expansion and contraction of species niches and distributions, as well as the formation and loss of communities and ecological interactions over time. Our choice in climate data resolution has the potential to complicate predictions of the ecological impacts of climate change, since climate varies from local to global scales and this spatial variation is reflected in climate data. To address this issue, we downscaled LGM and modern (1975–2005) 30‐year averaged climate data to 60‐m resolution for the entire state of Alaska for 10 different climate variables, and then upsampled each variable to coarser resolutions (60 m to 12 km). We modeled the distributions of novel and disappeared climates to evaluate the locations and fractional area of novel and disappeared climates for each of our climate variables and resolutions. Generally, novel and disappeared climates were located in southern Alaska, although there were cases where some disappeared climates existed within coastal and interior Alaska. Climate resolution affected the fractional area of novel and disappeared climates in three patterns: As the spatial resolution of climate became coarser, the fractional area of novel and disappeared climates (a) increased, (b) decreased, or (c) had no explainable relationship. Overall, we found the use of coarser climate data increased the fractional area of novel and disappeared climates due to decreased environmental variability and removal of climate extremes. Our results reinforce the importance of downscaling coarse climate data and suggest that studies analyzing the effects of climate change on ecosystems may overestimate or underestimate their conclusions when utilizing coarse climate data.     

Why do earlier‐arriving migratory birds have better breeding success?

In migratory birds, early arrival on breeding sites is typically associated with greater breeding success, but the mechanisms driving these benefits are rarely known. One mechanism through which greater breeding success among early arrivers can potentially be achieved is the increased time available for replacement clutches following nest loss. However, the contribution of replacement clutches to breeding success will depend on seasonal variation in nest survival rates, and the consequences for juvenile recruitment of hatching at different times in the season. In particular, lower recruitment rates of late‐hatched chicks could offset the benefits to early arrivers of being able to lay replacement clutches, which would reduce the likelihood of replacement clutch opportunities influencing selection on migratory timings. Using a simulation model of time‐constrained capacity for replacement clutches, paramaterized with empirically‐derived estimates from avian migratory systems, we show that greater reproductive success among early‐arriving individuals can arise solely through the greater time capacity for replacement clutches among early arrivers, even when later renesting attempts contribute fewer recruits to the population. However, these relationships vary depending on the seasonal pattern of nest survival. The benefits of early arrival are greatest when nest survival rates are constant or decline seasonally, and early arrival is least beneficial when nest success rates increase over the breeding season, although replacement clutches can mitigate this effect. The time benefits of early arrival facilitating replacement clutches following nest loss may therefore be an important but overlooked source of selection on migratory timings. Empirical measures of seasonal variation in nest survival, renesting, and juvenile recruitment rates are therefore needed in order to identify the costs and benefits associated with individual migration phenology, the selection pressures influencing migratory timings, and the implications for ongoing shifts in migration and breeding phenology.     

Quantifying the robustness of first arrival dates as a measure of avian migratory phenology

As the climate changes, many long‐term studies have shown that the timing of bird migration is shifting, increasing the need for reliable measures of migratory phenology. Ideally, daily counts of birds at a site are used to calculate the mean arrival date (MAD) but, as this approach is not always possible and is very labour‐intensive, simpler metrics such as first arrival date (FAD) have commonly been used. Here, we examine the relationship between FAD and MAD in 28 summer migrant bird species over a 42‐year period (1970–2011) at Portland Bird Observatory, UK. Although significant correlations between FAD and MAD were detected, relationships were weak, particularly in long‐distance migrants. We suggest that FAD, although a simple and straightforward measure, is not particularly robust as a proxy for overall migratory phenology at a population level.     

Flexibility in the timing of post‐breeding moult in passerines in the UK

Higher temperatures resulting from climate change have led to predictions that the duration of the breeding season of many temperate bird species may be changing. However, the extent to which breeding seasons can be altered will also depend on the degree of flexibility in processes occurring at other points in the annual cycle. In particular, plasticity in the timing of post‐breeding moult (PBM) could facilitate changes in the timing of key events throughout the annual cycle, but little is known about the level of within‐ and between‐species plasticity in PBM. As part of the British Trust for Ornithology (BTO) Ringing Scheme, many ringers routinely record moult scores of flight feathers, and these can be used to provide information on the annual progression of PBM for a range of species. Here we use ringing data to investigate patterns of PBM in 15 passerines, as well as data from the BTO Nest Record Scheme to relate these differences to the timing of breeding of these species across the UK. We find considerable variation in both the mean start (19 May–29 July) and duration (66–111 days) of PBM between species, but find no evidence that species starting PBM later in the season complete it any faster. However, there is considerable within‐species variation in PBM, particularly for multi‐brooded species; PBM starts later and is completed in less time when the duration of the breeding season (difference between first and last nests) is longer. This implies that a later end to breeding can be compensated for by faster PBM, and that advances in breeding could lead to earlier and slower PBM. Our findings suggest that adaptation of PBM in response to climate‐mediated changes in the timing and duration of the breeding season is possible. However, the requirement to complete PBM prior to migration or the onset of winter might constrain the extent to which breeding seasons can lengthen, especially for later nesting species.