The Enigma of the Respiratory Chain Supercomplex

Respiratory chain dysfunction plays an important role in human disease and aging. It is now well established that the individual respiratory complexes can be organized into supercomplexes, and structures for these macromolecular assemblies, determined by electron cryo-microscopy, have been described recently. Nevertheless, the reason why supercomplexes exist remains an enigma. The widely held view that they enhance catalysis by channeling substrates is challenged by both structural and biophysical information. Here, we evaluate and discuss data and hypotheses on the structures, roles, and assembly of respiratory-chain supercomplexes and propose a future research agenda to address unanswered questions.N.G.L. receives support from the Max Planck Society, the Swedish Research Council (2015-00418), and the Knut and Alice Wallenberg foundation. J.H. and J.N.B. are supported by The Medical Research Council (U105663141 to J.H.)

Species, Diaspore Volume and Body Mass Matter in Gastropod Seed Feeding Behavior

<div><p>Background</p><p>Seed dispersal of ant-dispersed plants (myrmecochores) is a well studied ecosystem function. Recently, slugs have been found to act as seed dispersers of myrmecochores. The aim of our study was to (1) further generalize the finding that gastropods feed on seeds of myrmecochores and hence may act as seed dispersers, (2) to test whether gastropod body mass and the volume of diaspores have an influence on the seed dispersal potential.</p><p>Methodology and Principal Findings</p><p>We assessed the seed dispersal potential of four slug and snail species with a set of seven myrmecochorous plant species from seven different plant families common to Central European beech forests. Diaspores differed in shape and size. Gastropods differed in their readiness to feed on diaspores and in the proportion of seeds that were swallowed as a whole, and this readiness generally decreased with increasing diaspore size. Smaller Arionid slugs (58 mm body length; mean) mostly fed on the elaiosome but also swallowed small diaspores and therefore not only act as elaiosome consumers, a nutrient rich appendage on myrmecochorous diaspores, but may also disperse seeds. Large Arionid slugs (>100 mm body length) swallowed diaspores of all sizes. Diaspores swallowed by gastropods were defecated without damage. Within-species variability in body size also affect seed dispersal potential, as larger individuals of the red slug (<i>Arion rufus</i>) swallowed more diaspores of wood anemone (<i>Anemone nemorosa</i>) than smaller ones.</p><p>Conclusions and Significance</p><p>Our results help to generalize the finding that gastropods consume and potentially disperse seeds of myrmecochores. The dispersal potential of gastropods is strongly influenced by diaspore size in relation to gastropod size.</p></div

Relationship of slug body mass and diaspore swallowing frequency.

<p>Relationship of slug body mass and (A) the proportion of diaspores swallowed, (B) the proportion of diaspore fruit skin area (FS) consumed (a swallowed diaspore was regarded as if 100% of its fruit skin was consumed) and (C) the proportion of fruit skin (FS) that was consumed by swallowing diaspores of the total fruit skin area consumed of all ten diaspores. Least-squares regression lines are given to illustrate the trends. rs, Spearman’s Rank Correlation Coefficient; p, p-value of the correlation.</p

Number of gastropod individuals to which diaspores of certain plant species were offered (No) and proportion of individuals that fed on the diaspores (Nf(%)).

<p>In species where elaiosome damage was visible, feeding included swallowed seeds and seeds with consumed elaiosomes and in species where elaiosome damage was not visible, only swallowed seeds are regarded as fed upon.</p

Comparison of diaspore swallowing and the elaiosome damaging frequency by gastropods among plant species.

<p>Comparison of (A) the diaspore swallowing frequency and (B) of the elaiosome damaging frequency by gastropod species among plant species. Swallowing of diaspores is considered as the potential dispersal ability of gastropods. Lamiastrum galeobdolon was not offered to all gastropod species and is not shown here. Results are given as mean ± standard error (SE). Results of GLMM analyses (Tukey contrasts) are shown for comparisons of diaspore and elaiosome feeding; treatments with different letters differ significantly at least at p<0.05.</p

Different feeding behavior of diaspores by <i>A. rufus individuals.</i>

<p>Relationship of diaspores that were either swallowed or of which elaiosomes were consumed by <i>A. rufus</i> individuals. Each point represents a single feeding trial (N = 89). The sum of both axes may not exceed 100% ( = all diaspores offered were consumed) but may well be less if diaspores remained disregarded by slugs. There are great differences in the feeding behavior among individuals.</p

Relationship of diaspore volume and the dispersal potential.

<p>Relationship between diaspore volume and the dispersal potential of diaspores by gastropods described as the number of diaspores swallowed (Ns) of the number of diaspores offered (No) to all gastropod individuals. Results are given as mean ± standard error (SE).</p

Number of swallowed diaspores (mean±SE) and proportion of total fruit skin area consumed of all 10 diaspores (mean±SE) of <i>A. nemorosa</i> offered to <i>A. rufus</i> individuals within the four body mass classes (N = 14 individuals/class).

<p>Number of swallowed diaspores (mean±SE) and proportion of total fruit skin area consumed of all 10 diaspores (mean±SE) of <i>A. nemorosa</i> offered to <i>A. rufus</i> individuals within the four body mass classes (N = 14 individuals/class).</p

Wing induction of offspring in different colony sizes exposed to alarm pheromone and control under different conditions.

<p>The square root transformed proportion of winged offspring as a function of the number of offspring in the field and in the climate chamber, treated with either EBF or hexane. White circles represent field colonies treated with hexane control (0.2679+0.0025X, r² = 0.058, F_1,25 = 1.525, p = 0.228); black circles are field colonies treated with EBF (−0.420+0.019X, r² = 0.448, F1,26 = 21.08, p<0.01); white triangles are chamber colonies treated with hexane control (1.920+0.011X, r2 = 0.209, F_1,26 = 7.146, p = 0.0126); and black triangles are chamber colonies treated with EBF (9.306-0.00041X, r² = 0.011, F_1,26 = 0.288, p = 0.596).</p

Induction of wing formation in offspring from colonies exposed to alarm pheromone and control under different conditions.

<p>The proportions of winged morphs among offspring were recorded in the field and in the climate chamber, for both the control (white bars) and (E)-β-farnesene (black bars) treatments (F^1,103 = 38.784, p<0.001). Bars with different letters are statistically significant different (p<0.01). The bars show mean values+SE.</p