Sacrificial males: the potential role of copulation and predation in contributing to copepod sex‐skewed ratios

Predation is thought to play a selective role in the emergence of behavioural traits in prey. Differences in behaviour between prey demographics may, therefore, be driven by predation with select components of the population being less vulnerable to predators. While under controlled conditions prey demography has been shown to have consequences for predation success, investigations linking these implications to natural prey population demographics are scarce. Here we assess predator–prey dynamics between notonectid predators (backswimmers) and Lovenula raynerae (Copepoda), key faunal groups in temperate ephemeral pond ecosystems. Using a combination of field and experimental approaches we test for the development and mechanism of predation‐induced sex‐skewed ratios. A natural population of L. raynerae was tracked over time in relation to their predator (notonectid) and prey (Cladocera) numbers. In the laboratory, L. raynerae sex ratios were also assessed over time but in the absence of predation pressure. Predation success and prey performance experiments evaluating differences between L. raynerae male, female, gravid female and copulating pairs exposed to notonectid predation were then examined. Under natural conditions, a female dominated copepod population developed over time and was correlated to predation pressure, while under predator‐free conditions non sex‐skewed prey population demographics persisted. Predator–prey laboratory trials showed no difference in vulnerability and escape performance for male, female and gravid female copepods, but pairs in copula were significantly more vulnerable to predation. This vulnerability was not shared by both sexes, with only female copepods ultimately escaping from successful predation on a mating pair. These results suggest that contact periods during copula may contribute to the development of sex‐skewed copepod ratios over time in ecosystems dominated by hexapod predators. This is discussed within the context of vertebrate and invertebrate predation and how these dissimilar types of predation are likely to have acted as selective pressures for copepod mating systems.     

Influence of intra‐ and interspecific variation in predator–prey body size ratios on trophic interaction strengths

1. Predation is a pervasive force that structures food webs and directly influences ecosystem functioning. The relative body sizes of predators and prey may be an important determinant of interaction strengths. However, studies quantifying the combined influence of intra‐ and interspecific variation in predator–prey body size ratios are lacking.
2. We use a comparative functional response approach to examine interaction strengths between three size classes of invasive bluegill and largemouth bass toward three scaled size classes of their tilapia prey. We then quantify the influence of intra‐ and interspecific predator–prey body mass ratios on the scaling of attack rates and handling times.
3. Type II functional responses were displayed by both predators across all predator and prey size classes. Largemouth bass consumed more than bluegill at small and intermediate predator size classes, while large predators of both species were more similar. Small prey were most vulnerable overall; however, differential attack rates among prey were emergent across predator sizes. For both bluegill and largemouth bass, small predators exhibited higher attack rates toward small and intermediate prey sizes, while larger predators exhibited greater attack rates toward large prey. Conversely, handling times increased with prey size, with small bluegill exhibiting particularly low feeding rates toward medium–large prey types. Attack rates for both predators peaked unimodally at intermediate predator–prey body mass ratios, while handling times generally shortened across increasing body mass ratios.
4. We thus demonstrate effects of body size ratios on predator–prey interaction strengths between key fish species, with attack rates and handling times dependent on the relative sizes of predator–prey participants.
5. Considerations for intra‐ and interspecific body size ratio effects are critical for predicting the strengths of interactions within ecosystems and may drive differential ecological impacts among invasive species as size ratios shift.

     

Ecological Assessment of Two Species of Potamonautid Freshwater Crabs from the Eastern Highlands of Zimbabwe,with Implications for Their Conservation

The spatial ecology of freshwater crabs and their conservation status is largely understudied in Africa. An ecological assessment was conducted at 104 localities in 51 rivers and/or streams in the Eastern Highlands of Zimbabwe whereby the distribution and abundances of freshwater crab species were mapped and the possible drivers of the observed trends in population structure explored. In addition, information on crab utilisation as a food resource by local communities was assessed via face to face interviews across the region. Finally, the conservation status of each species was assessed using the IUCN Red List criteria. Only two crab species Potamonautes mutareensis and Potamonautes unispinus were recorded within the region of study. Potamonautes mutareensis was largely restricted to less impacted environments in the high mountainous river system, whereas P. unispinus was found in low laying areas. In stretches of river where both species were found to co-occur, the species were never sampled from the same site, with P. mutareensis occurring in shallower, faster flowing environments and P. unispinus in deeper, slow flowing sites. Interview results revealed that the local communities, particularly in the southern part of the Eastern Highlands around the Chipinge area, had a considerable level of utilisation (55% of households) on the harvesting of crabs for household consumption during the non-agricultural season (May to September). Results from the IUCN Red List assessment indicate that both species should be considered as “Least Concern”. Threats to freshwater crabs in the Eastern Highlands, however, include widespread anthropogenic impacts such as habitat destruction associated with gold and diamond mining, inorganic and organic pollution and possibly exploitation for human consumption. The current study provides important information and insight towards the possible development of a freshwater crab conservation action plan within the region.     

Plasma Concentrations of Hepcidin in Anemic Zimbabwean Infants

Objective

Anemia in infancy is a global public health problem. We evaluated the relative contributions of iron deficiency and inflammation to infant anemia.

Methods

We measured plasma hepcidin, ferritin, soluble transferrin receptor (sTfR), alpha-1-acid glycoprotein and C-reactive protein (CRP) by ELISA on archived plasma from 289 HIV-unexposed anemic or non-anemic Zimbabwean infants at ages 3mo, 6mo and 12mo. Among anemic infants, we determined the proportion with iron-deficiency anemia (IDA) and anemia of inflammation (AI). We undertook regression analyses of plasma hepcidin and anemia status, adjusting for sex, age and birthweight.

Results

Anemic infants at 3mo were more stunted and had higher CRP (median 0.45 vs 0.21mg/L; P = 0.037) and hepcidin (median 14.7 vs 9.7ng/mL; P = 0.022) than non-anemic infants, but similar levels of ferritin and sTfR; 11% infants had IDA and 15% had AI. Anemic infants at 6mo had higher hepcidin (median 7.9 vs 4.5ng/mL; P = 0.016) and CRP (median 2.33 vs 0.32mg/L; P<0.001), but lower ferritin (median 13.2 vs 25.1μg/L; P<0.001) than non-anemic infants; 56% infants had IDA and 12% had AI. Anemic infants at 12mo had lower ferritin (median 3.2 vs 22.2μg/L; P<0.001) and hepcidin (median 0.9 vs 1.9ng/mL; P = 0.019), but similar CRP levels; 48% infants had IDA and 8% had AI. Comparing anemic with non-anemic infants, plasma hepcidin was 568% higher, 405% higher and 64% lower at 3mo, 6mo and 12mo, respectively, after adjusting for sex and birthweight (all p<0.01). Plasma hepcidin declined significantly with age among anemic but not non-anemic infants. Girls had 61% higher hepcidin than boys, after adjusting for age, anemia and birthweight (p<0.001).

Conclusion

Anemia is driven partly by inflammation early in infancy, and by iron deficiency later in infancy, with plasma hepcidin concentrations reflecting the relative contribution of each. However, there is need to better characterize the drivers of hepcidin during infancy in developing countries.     

Robust,tunable genetic memory from protein sequestration combined with positive feedback

Natural regulatory networks contain many interacting components that allow for fine-tuning of switching and memory properties. Building simple bistable switches, synthetic biologists have learned the design principles of complex natural regulatory networks. However, most switches constructed so far are so simple (e.g. comprising two regulators) that they are functional only within a limited parameter range. Here, we report the construction of robust, tunable bistable switches in Escherichia coli using three heterologous protein regulators (ExsADC) that are sequestered into an inactive complex through a partner swapping mechanism. On the basis of mathematical modeling, we accurately predict and experimentally verify that the hysteretic region can be fine-tuned by controlling the interactions of the ExsADC regulatory cascade using the third member ExsC as a tuning knob. Additionally, we confirm that a dual-positive feedback switch can markedly increase the hysteretic region, compared to its single-positive feedback counterpart. The dual-positive feedback switch displays bistability over a 10⁶-fold range of inducer concentrations, to our knowledge, the largest range reported so far. This work demonstrates the successful interlocking of sequestration-based ultrasensitivity and positive feedback, a design principle that can be applied to the construction of robust, tunable, and predictable genetic programs to achieve increasingly sophisticated biological behaviors.     

Origin and evolution of HIV-1 in breast milk determined by single-genome amplification and sequencing

HIV transmission via breastfeeding accounts for a considerable proportion of infant HIV acquisition. However, the origin and evolution of the virus population in breast milk, the likely reservoir of transmitted virus variants, are not well characterized. In this study, HIV envelope (env) genes were sequenced from virus variants amplified by single-genome amplification from plasmas and milk of 12 chronically HIV-infected, lactating Malawian women. Maximum likelihood trees and statistical tests of compartmentalization revealed interspersion of plasma and milk HIV env sequences in the majority of subjects, indicating limited or no compartmentalization of milk virus variants. However, phylogenetic tree analysis further revealed monotypic virus variants that were significantly more frequent in milk (median proportion of identical viruses, 29.5%; range, 0 to 61%) than in plasma (median proportion of identical viruses, 0%; range, 0 to 26%) (P = 0.002), suggesting local virus replication in the breast milk compartment. Moreover, clonally amplified virus env genes in milk produced functional virus Envs that were all CCR5 tropic. Milk and plasma virus Envs had similar predicted phenotypes and neutralization sensitivities to broadly neutralizing antibodies in both transmitting and nontransmitting mothers. Finally, phylogenetic comparison of longitudinal milk and plasma virus env sequences revealed synchronous virus evolution and new clonal amplification of evolved virus env genes in milk. The limited compartmentalization and the clonal amplification of evolving, functional viruses in milk indicate continual seeding of the mammary gland by blood virus variants, followed by transient local replication of these variants in the breast milk compartment.     

Evidence of spatial and temporal changes in sources of organic matter in estuarine sediments: stable isotope and fatty acid analyses

We investigated spatial and temporal changes in sources of organic matter in sediments within an estuarine environment in South Africa using fatty acids (FA) and stable isotopes (SI). Samples of sediments and sources of organic matter [i.e., particulate organic matter, microphytobenthos (MPB), macrophytes, salt marsh plants, and terrestrial leaves] were collected during spring and summer 2012, and autumn and winter 2013 from the upper, middle, and lower reaches. A Stable Isotope Analysis in R (SIAR) mixing model was used to identify the organic matter sources contributing to sediments in each estuarine reach and season. We found that diatom-associated fatty acids (20:5ω3; 16:1ω7) increased toward the upper reaches, while long-chained terrigenous fatty acids (24:0) tended to be more prevalent in lower reach sediments. In support of the FA results, the SI mixing model showed a substantial contribution from the marsh grass Spartina maritima in sediments of the lower estuary during periods of low-freshwater discharge (autumn and winter), while MPB was the main component in sediments from the upper and middle reaches during all seasons. Our results have implications for evaluating estuarine food webs since the spatial and seasonal variability in the organic matter deposited can influence estuarine community structure.     

An Assessment of the Effect of Rotenone on Selected Non-Target Aquatic Fauna

Rotenone, a naturally occurring ketone, is widely employed for the management of invasive fish species. The use of rotenone poses serious challenges to conservation practitioners due to its impacts on non-target organisms including amphibians and macroinvertebrates. Using laboratory studies, we investigated the effects of different rotenone concentrations (0, 12.5, 25, 37.5, 50, 100 μg L^-1) on selected invertebrate groups; Aeshnidae, Belostomatids, Decapods, Ephemeroptera, Pulmonata and zooplankton over a period of 18 hours. Based on field observations and body size, we hypothesized that Ephemeropterans and zooplankton would be more susceptible to rotenone than Decapods, Belostomatids and snails. Experimental results supported this hypothesis and mortality and behaviour effects varied considerably between taxa, ranging from no effect (crab Potamonuates sidneyi) to 100% mortality (Daphnia pulex and Paradiaptomus lamellatus). Planktonic invertebrates were particularly sensitive to rotenone even at very low concentrations. Future research should investigate the recovery time of invertebrate communities after the application of rotenone and conduct field assessments assessing the longer term effects of rotenone exposure on the population dynamics of those less sensitive organisms.     

Human umbilical cord mesenchymal stromal cells as an adjunct therapy with therapeutic hypothermia in a piglet model of perinatal asphyxia

Background: With therapeutic hypothermia (HT) for neonatal encephalopathy, disability rates are reduced, but not all babies benefit. Pre-clinical rodent studies suggest mesenchymal stromal cells (MSCs) augment HT protection. Aims:The authors studied the efficacy of intravenous (IV) or intranasal (IN) human umbilical cord-derived MSCs (huMSCs) as adjunct therapy to HT in a piglet model. Methods:A total of 17 newborn piglets underwent transient cerebral hypoxia-ischemia (HI) and were then randomized to (i) HT at 33.5°C 1–13 h after HI (n = 7), (ii) HT+IV huMSCs (30 × 10⁶ cells) at 24 h and 48 h after HI (n = 5) or (iii) HT+IN huMSCs (30 × 10⁶ cells) at 24 h and 48 h after HI (n = 5). Phosphorus-31 and hydrogen-1 magnetic resonance spectroscopy (MRS) was performed at 30 h and 72 h and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells and oligodendrocytes quantified. In two further piglets, 30 × 10⁶ IN PKH-labeled huMSCs were administered. Results:HI severity was similar between groups. Amplitude-integrated electroencephalogram (aEEG) recovery was more rapid for HT+IN huMSCs compared with HT from 25 h to 42 h and 49 h to 54 h (P ≤ 0.05). MRS phosphocreatine/inorganic phosphate was higher on day 2 in HT+IN huMSCs than HT (P = 0.035). Comparing HT+IN huMSCs with HT and HT+IV huMSCs, there were increased OLIG2 counts in hippocampus (P = 0.011 and 0.018, respectively), internal capsule (P = 0.013 and 0.037, respectively) and periventricular white matter (P = 0.15 for IN versus IV huMSCs). Reduced TUNEL-positive cells were seen in internal capsule with HT+IN huMSCs versus HT (P = 0.05). PKH-labeled huMSCs were detected in the brain 12 h after IN administration. Conclusions:After global HI, compared with HT alone, the authors saw beneficial effects of HT+IN huMSCs administered at 24 h and 48 h (30 × 10⁶ cells/kg total dose) based on more rapid aEEG recovery, improved ³¹P MRS brain energy metabolism and increased oligodendrocyte survival at 72 h.