Plastic and evolutionary responses to heat stress in a temperate dung fly: negative correlation between basal and induced heat tolerance?

Extreme weather events such as heat waves are becoming more frequent and intense. Populations can cope with elevated heat stress by evolving higher basal heat tolerance (evolutionary response) and/or stronger induced heat tolerance (plastic response). However, there is ongoing debate about whether basal and induced heat tolerance are negatively correlated and whether adaptive potential in heat tolerance is sufficient under ongoing climate warming. To evaluate the evolutionary potential of basal and induced heat tolerance, we performed experimental evolution on a temperate source population of the dung fly Sepsis punctum. Offspring of flies adapted to three thermal selection regimes (Hot, Cold and Reference) were subjected to acute heat stress after having been exposed to either a hot‐acclimation or non‐acclimation pretreatment. As different traits may respond differently to temperature stress, several physiological and life history traits were assessed. Condition dependence of the response was evaluated by exposing juveniles to different levels of developmental (food restriction/rearing density) stress. Heat knockdown times were highest, whereas acclimation effects were lowest in the Hot selection regime, indicating a negative association between basal and induced heat tolerance. However, survival, adult longevity, fecundity and fertility did not show such a pattern. Acclimation had positive effects in heat‐shocked flies, but in the absence of heat stress hot‐acclimated flies had reduced life spans relative to non‐acclimated ones, thereby revealing a potential cost of acclimation. Moreover, body size positively affected heat tolerance and unstressed individuals were less prone to heat stress than stressed flies, offering support for energetic costs associated with heat tolerance. Overall, our results indicate that heat tolerance of temperate insects can evolve under rising temperatures, but this response could be limited by a negative relationship between basal and induced thermotolerance, and may involve some but not other fitness‐related traits.     

Optimal hurricane overwash thickness for maximizing marsh resilience to sea level rise

The interplay between storms and sea level rise, and between ecology and sediment transport governs the behavior of rapidly evolving coastal ecosystems such as marshes and barrier islands. Sediment deposition during hurricanes is thought to increase the resilience of salt marshes to sea level rise by increasing soil elevation and vegetation productivity. We use mesocosms to simulate burial of Spartina alterniflora during hurricane‐induced overwash events of various thickness (0–60 cm), and find that adventitious root growth within the overwash sediment layer increases total biomass by up to 120%. In contrast to most previous work illustrating a simple positive relationship between burial depth and vegetation productivity, our work reveals an optimum burial depth (5–10 cm) beyond which burial leads to plant mortality. The optimum burial depth increases with flooding frequency, indicating that storm deposition ameliorates flooding stress, and that its impact on productivity will become more important under accelerated sea level rise. Our results suggest that frequent, low magnitude storm events associated with naturally migrating islands may increase the resilience of marshes to sea level rise, and in turn, slow island migration rates. Synthesis: We find that burial deeper than the optimum results in reduced growth or mortality of marsh vegetation, which suggests that future increases in overwash thickness associated with more intense storms and artificial heightening of dunes could lead to less resilient marshes.     

Parasites of fishes in the recently inundated ephemeral Lake Liambezi,Namibia

Lake Liambezi forms the periodic connection between the upper Zambezi, Kwando and Okavango rivers. A full parasitological assessment was conducted on 86 fish, representing 14 species in six families sampled in August 2011. Parasite diversity was low and dominated by species with complex life cycles involving intermediate hosts. Most prevalent were larval nematodes (Contracaecum sp.) infecting 12 and Trypanasoma sp. infecting nine of the 14 host species. The intra-erythrocytic parasite Babesiosoma mariae was found in the blood of Coptodon rendalli and Oreochromis andersonii with prevalence of 50% and 60%, respectively. The host-specific monogenean Annulotrema hepseti was recorded only from H. cuvieri with a prevalence of 100%. Notable absences were the copepod and branchiuran parasites that have direct lifecycles and usually occur in high prevalence and abundance in the region. Because parasites with direct life cycles can only be transported into the lake on the host fish, their absence suggests limited immigration of infected fishes into the lake. This suggests that internal recruitment dominates over immigration in the fish population dynamics in Lake Liambezi.     

Diet and trophic interactions of a circumglobally significant gelatinous marine zooplankter,Dolioletta gegenbauri (Uljanin, 1884)

Gelatinous zooplankton play a crucial role in marine planktonic food webs. However, primarily due to methodological challenges, the in situ diet of zooplankton remains poorly investigated and little is known about their trophic interactions including feeding behaviour, prey selection and in situ feeding rates. This is particularly true for gelatinous zooplankton including the marine pelagic tunicate, Dolioletta gegenbauri. In this study, we applied an 18S rRNA amplicon metabarcoding approach to identify the diet of captive‐fed and wild‐caught D. gegenbauri on the midcontinental shelf of the South Atlantic Bight, USA. Sequencing‐based approaches were complimented with targeted quantitative real‐time polymerase chain reaction (PCR) analyses. Captive‐fed D. gegenbauri gut content was dominated by pico‐, nano‐ and micro‐plankton including pico‐dinoflagellates (picozoa) and diatoms. These results suggested that diatoms were concentrated by D. gegenbauri relative to their concentration in the water column. Analysis of wild‐caught doliolids by quantitative real‐time PCR utilizing a group‐specific diatom primer set confirmed that diatoms were concentrated by D. gegenbauri, particularly by the gonozooid life stage associated with actively developing blooms. Sequences derived from larger metazoans were frequently observed in wild‐caught animals but not in captive‐fed animals suggesting experimental bias associated with captive feeding. These studies revealed that the diet of D. gegenbauri is considerably more diverse than previously described, that parasites are common in wild populations, and that prey quality, quantity and parasites are likely all important factors in regulating doliolid population dynamics in continental shelf environments.     

Specificity of machine, barbell, and water-filled log bench press resistance training on measures of strength

The purpose of this study was to compare the effects of 10 weeks of resistance training with an isotonic bench press machine and 2 types of free-weight bench press exercises on several measures bench press strength. Specificity was investigated by comparing the ability to transfer strength gained from a type of training that differed from the mode of testing. Forty-nine men participated in the study. The subjects completed a pretest on the machine (MB), barbell (BB), isokinetic (IB), and log (LB) bench press to determine baseline strength and completed 10 weeks of training on the MB, BB, or LB. The 3 groups were tested to see whether differential training effects occurred from pre- to posttest scores on the BB, MB, LB, and peak force on the IB. By multivariate analysis, the trial-by-group interaction was not statistically significant. The multivariate and subsequent univariate analyses of variance tests indicated statistically significant effects from pre- to posttest for peak force on the IB test and the BB, MB, and LB. Correlations among the strength tests were high (0.92 > or = r < or = 0.97) and moderate between the strength tests and IB peak force (0.62 > or = r < pr = 0.83). Mean 3 repetition maximum MB strength was 8% higher than BB strength, which was 3% higher than LB strength, indicating differences in the amount of stabilization required to control the resistance. The findings of this study showed that all 3 training groups significantly improved in strength during short-term training on the MB, BB, and LB. These data lend evidence that improved strength after training on the MB, BB, and LB equally transfers to strength gains on any of the 4 modes of testing. These results should be considered when including similar exercises varying in stability into the training program to improve strength.     

The SH3 domain of a M7 interacts with its C-terminal proline-rich region

Myosins play essential roles in migration, cytokinesis, endocytosis, and adhesion. They are composed of a large N-terminal motor domain with ATPase and actin binding sites and C-terminal neck and tail regions, whose functional roles and structural context in the protein are less well characterized. The tail regions of myosins I, IV, VII, XII, and XV each contain a putative SH3 domain that may be involved in protein-protein interactions. SH3 domains are reported to bind proline-rich motifs, especially "PxxP" sequences, and such interactions serve regulatory functions. The activity of Src, PI3, and Itk kinases, for example, is regulated by intramolecular interactions between their SH3 domain and internal proline-rich sequences. Here, we use NMR spectroscopy to reveal the structure of a protein construct from Dictyostelium myosin VII (DdM7) spanning A1620-T1706, which contains its SH3 domain and adjacent proline-rich region. The SH3 domain forms the signature beta-barrel architecture found in other SH3 domains, with conserved tryptophan and tyrosine residues forming a hydrophobic pocket known to bind "PxxP" motifs. In addition, acidic residues in the RT or n-Src loops are available to interact with the basic anchoring residues that are typically found in ligands or proteins that bind SH3 domains. The DdM7 SH3 differs in the hydrophobicity of the second pocket formed by the 3(10) helix and following beta-strand, which contains polar rather than hydrophobic side chains. Most unusual, however, is that this domain binds its adjacent proline-rich region at a surface remote from the region previously identified to bind "PxxP" motifs. The interaction may affect the orientation of the tail without sacrificing the availability of the canonical "PxxP"-binding surface.