Species richness and trait composition of butterfly assemblages change along an altitudinal gradient

Species richness patterns along altitudinal gradients are well-documented ecological phenomena, yet very little data are available on how environmental filtering processes influence the composition and traits of butterfly assemblages at high altitudes. We have studied the diversity patterns of butterfly species at 34 sites along an altitudinal gradient ranging from 600 to 2,000 m a.s.l. in the National Park Berchtesgaden (Germany) and analysed traits of butterfly assemblages associated with dispersal capacity, reproductive strategies and developmental time from lowlands to highlands, including phylogenetic analyses. We found a linear decline in butterfly species richness along the altitudinal gradient, but the phylogenetic relatedness of the butterfly assemblages did not increase with altitude. Compared to butterfly assemblages at lower altitudes, those at higher altitudes were composed of species with larger wings (on average 9 %) which laid an average of 68 % more eggs. In contrast, egg maturation time in butterfly assemblages decreased by about 22 % along the altitudinal gradient. Further, butterfly assemblages at higher altitudes were increasingly dominated by less widespread species. Based on our abundance data, but not on data in the literature, population density increased with altitude, suggesting a reversed density–distribution relationship, with higher population densities of habitat specialists in harsh environments. In conclusion, our data provide evidence for significant shifts in the composition of butterfly assemblages and for the dominance of different traits along the altitudinal gradient. In our study, these changes were mainly driven by environmental factors, whereas phylogenetic filtering played a minor role along the studied altitudinal range.     

Complex Coacervation and Precipitation Between Soluble Pea Proteins and Apple Pectin

Complex formation (leading to either coacervation or precipitation) offers a tool to generate plant-based novel food structures and textures. This study investigated the formation of complexes between soluble pea proteins and apple pectin upon varying the protein-to-pectin ratio (r?=?2:1 to 10:1), pH (3–7), and temperature (25 and 85 °C) with a total biopolymer concentration set to 1% (w/w). The results showed that predominantly soluble biopolymer complexes were formed at pH 5, and at low ratio (r?=?2:1), whereas lowering the pH to more acidic condition, and to higher ratios (r?=?4:1–10:1) induced the formation of more insoluble biopolymer complexes. In general, the mean particle sizes of the biopolymer complexes ranged between approximately 20 and 100 μm. Upon heating to 85 °C, the amount of insoluble biopolymer complexes increased at pH 3–5 at all ratios, except at r?=?2:1. In addition, the complex sizes became somewhat larger at r?=?2:1 to 6:1 upon heat treatment, whereas only trivial size changes were observed at higher ratios (r?=?8:1 to 10:1). Overall, electrostatic and hydrophobic interactions played a major role in the complex formation between the soluble pea proteins and apple pectin. These findings are important for designing solely plant-based food structures.

     

Societies Drifting Apart? Behavioural,Genetic and Chemical Differentiation between Supercolonies in the Yellow Crazy Ant Anoplolepis gracilipes

Background

In populations of most social insects, gene flow is maintained through mating between reproductive individuals from different colonies in periodic nuptial flights followed by dispersal of the fertilized foundresses. Some ant species, however, form large polygynous supercolonies, in which mating takes place within the maternal nest (intranidal mating) and fertilized queens disperse within or along the boundary of the supercolony, leading to supercolony growth (colony budding). As a consequence, gene flow is largely confined within supercolonies. Over time, such supercolonies may diverge genetically and, thus, also in recognition cues (cuticular hydrocarbons, CHC''s) by a combination of genetic drift and accumulation of colony-specific, neutral mutations.

Methodology/Principal Findings

We tested this hypothesis for six supercolonies of the invasive ant Anoplolepis gracilipes in north-east Borneo. Within supercolonies, workers from different nests tolerated each other, were closely related and showed highly similar CHC profiles. Between supercolonies, aggression ranged from tolerance to mortal encounters and was negatively correlated with relatedness and CHC profile similarity. Supercolonies were genetically and chemically distinct, with mutually aggressive supercolony pairs sharing only 33.1%±17.5% (mean ± SD) of their alleles across six microsatellite loci and 73.8%±11.6% of the compounds in their CHC profile. Moreover, the proportion of alleles that differed between supercolony pairs was positively correlated to the proportion of qualitatively different CHC compounds. These qualitatively differing CHC compounds were found across various substance classes including alkanes, alkenes and mono-, di- and trimethyl-branched alkanes.

Conclusions

We conclude that positive feedback between genetic, chemical and behavioural traits may further enhance supercolony differentiation through genetic drift and neutral evolution, and may drive colonies towards different evolutionary pathways, possibly including speciation.     

Disentangling Woodland Caribou Movements in Response to Clearcuts and Roads across Temporal Scales

Although prey species typically respond to the most limiting factors at coarse spatiotemporal scales while addressing biological requirements at finer scales, such behaviour may become challenging for species inhabiting human altered landscapes. We investigated how woodland caribou, a threatened species inhabiting North-American boreal forests, modified their fine-scale movements when confronted with forest management features (i.e. clearcuts and roads). We used GPS telemetry data collected between 2004 and 2010 on 49 female caribou in a managed area in Québec, Canada. Movements were studied using a use – availability design contrasting observed steps (i.e. line connecting two consecutive locations) with random steps (i.e. proxy of immediate habitat availability). Although caribou mostly avoided disturbances, individuals nonetheless modulated their fine-scale response to disturbances on a daily and annual basis, potentially compromising between risk avoidance in periods of higher vulnerability (i.e. calving, early and late winter) during the day and foraging activities in periods of higher energy requirements (i.e. spring, summer and rut) during dusk/dawn and at night. The local context in which females moved was shown to influence their decision to cross clearcut edges and roads. Indeed, although females typically avoided crossing clearcut edges and roads at low densities, crossing rates were found to rapidly increase in greater disturbance densities. In some instance, however, females were less likely to cross edges and roads as densities increased. Females may then be trapped and forced to use disturbed habitats, known to be associated with higher predation risk. We believe that further increases in anthropogenic disturbances could exacerbate such behavioural responses and ultimately lead to population level consequences.     

Identification of a beta-secretase activity,which truncates amyloid beta-peptide after its presenilin-dependent generation

The beta-amyloid precursor protein (beta APP) is proteolytically processed by two secretase activities to produce the pathogenic amyloid beta-peptide (A beta). N-terminal cleavage is mediated by beta-secretase (BACE) whereas C-terminal intramembraneous cleavage is exerted by the presenilin (PS) gamma-secretase complex. The A beta-generating gamma-secretase cleavage principally occurs after amino acid 40 or 42 and results in secretion of A beta-(1-40) or A beta-(1-42). Upon overexpression of BACE in cultured cells we unexpectedly noticed a reduction of secreted A beta-(1-40/42). However, mass spectrometry revealed a truncated A beta species, which terminates at amino acid 34 (A beta-(1-34)) suggesting an alternative gamma-secretase cut. Indeed, expression of a loss-of-function variant of PS1 inhibited not only the production of A beta-(1-40) and A beta-(1-42) but also that of A beta-(1-34). However, expression levels of BACE correlate with the amount of A beta-(1-34), and A beta-(1-34) is produced at the expense of A beta-(1-40) and A beta-(1-42). Since this suggested that BACE is involved in a C-terminal truncation of A beta, we incubated purified BACE with A beta-(1-40) in vitro. Under these conditions A beta-(1-34) was generated. Moreover, when conditioned media containing Abeta-(1-40) and A beta-(1-42) were incubated with cells expressing a loss-of-function PS1 variant together with BACE, A beta-(1-34) was efficiently produced in vivo. These data demonstrate that an apparently gamma-secretase-dependent A beta derivative is produced after the generation of the non-truncated A beta via an additional and unexpected activity of BACE.     

NGF controls dendrite development in hippocampal neurons by binding to p75NTR and modulating the cellular targets of Notch

Notch and neurotrophins control neuronal shape, but it is not known whether their signaling pathways intersect. Here we report results from hippocampal neuronal cultures that are in support of this possibility. We found that low cell density or blockade of Notch signaling by a soluble Delta-Fc ligand decreased the mRNA levels of the nuclear targets of Notch, the homologues of enhancer-of-split 1 and 5 (Hes1/5). This effect was associated with enhanced sprouting of new dendrites or dendrite branches. In contrast, high cell density or exposure of low-density cultures to NGF increased the Hes1/5 mRNA, reduced the number of primary dendrites and promoted dendrite elongation. The NGF effects on both Hes1/5 expression and dendrite morphology were prevented by p75-antibody (a p75NTR-blocking antibody) or transfection with enhancer-of-split 6 (Hes6), a condition known to suppress Hes activity. Nuclear translocation of NF-kappaB was identified as a link between p75NTR and Hes1/5 because it was required for the up-regulation of these two genes. The convergence of the Notch and p75NTR signaling pathways at the level of Hes1/5 illuminates an unexpected mechanism through which a diffusible factor (NGF) could regulate dendrite growth when cell-cell interaction via Notch is not in action.