Catechin–metal interactions as a mechanism for conditional allelopathy by the invasive plant Centaurea maculosa

1. Evaluating variation, or 'conditionality', in plant interactions is crucial to understanding their ecological importance and predicting where they might be at play. Much is known about conditionality for competition, facilitation and herbivory, but not for allelopathy, which likely contributes to the equivocal nature of reports on this topic. Centaurea maculosa (spotted knapweed) is an invasive species in North America, whose success has been attributed, at least in part, to the allelochemical root exudate (±)-catechin.
2. Understanding the ecological relevance of (±)-catechin necessitates determining how it interacts with various soil components. We found that some metals caused rapid declines in measurable (±)-catechin, while calcium impeded its auto-oxidation, maintaining concentrations higher than for (±)-catechin alone. Certain (±)-catechin–metal complexes were more phytotoxic than (±)-catechin alone, while others showed lower toxicity.
3. The variable phytotoxicity of these complexes suggests that (±)-catechin effects are enhanced, mitigated or otherwise affected by complexation with different metals and perhaps other soil components.
4.  Synthesis . These findings serve to illustrate that the precise chemical forms, interactions and effects of catechin in the environment are highly variable and that further examination is warranted to increase our understanding of its role in invasion and allelopathy. The conditional effects observed for catechin detection and phytotoxicity likely extend to related allelopathic compounds, other root exudates and potentially other systems involving chemically complex and spatially heterogeneous environments.     

Seasonal structuring of a benthic community exposed to regular hypoxic events

The Western Trough of the Lough Hyne Marine Reserve in southern Ireland features annual episodes of profound hypoxia beneath an oxy-thermocline that develops each summer. Previous work had indicated that the hypoxia caused mass mortality of the sessile benthic fauna, but information about the winter fauna, or about mobile species was lacking. Here we report on a combined remote-operated vehicle, SCUBA and baited trap study, backed by regular oxygen-temperature-depth monitoring of the Trough. Our results show that there is community of resident benthic and mobile species during the oxic winter months that disappears in the summer. Mobile fish and crustaceans avoid the hypoxic areas of the Trough, though the prawn Palaemon serratus will venture into the hypoxic zone to scavenge on baits. At the oxy-thermocline itself, burrows of benthic fauna remain evident in summer, but their inhabitants show much reduced activity or death. Regular hypoxic episodes clearly structure the benthic community of the Trough, but this is not a simple matter of alternating mass mortality and recolonization; mobile species are clearly capable of avoiding the hypoxic zone in summer, but benefit from its productivity in winter and spring.     

Low peripheral progesterone and late embryonic/early fetal loss in suckled beef and lactating dairy cows

Pregnancy failure during placentation in lactating dairy cows was associated with low concentrations of serum progesterone. Beef cows have greater serum progesterone and less pregnancy failure. Experiment 1 determined that reduction of serum progesterone affected late embryonic/early fetal loss in suckled beef cows. Cows (n = 40) received progesterone from two new or used controlled internal drug releasing devices, replaced every 5 d, beginning on Day 28 of gestation (mating = Day 0); CL were enucleated on Day 29. Retention of pregnancy was 77% in treated cows and 97% in 78 control cows (P < 0.05). Experiment 2 determined how pregnant, lactating dairy cows with high or low progesterone concentrations during Days 28-34 differed in luteal function or in serum progesterone during replacement therapy. Luteal tissue from such cows was assayed for progesterone and expression of mRNA for genes of endothelin and prostaglandin (PG) systems. Secretion of progesterone and prostaglandins by dispersed luteal cells was determined during incubation with LH, endothelin-1, or arachidonic acid. Neither luteal progesterone nor mRNAs for endothelin or prostaglandin systems differed. Endothelin-1 inhibited secretion of progesterone more (P < 0.05) in luteal cells from cows with low versus high serum progesterone, when incubated with arachidonic acid. Secretion of prostaglandin F₂α was increased and that of 6-keto-PGF₁α decreased by endothelin-1 in vitro. Serum progesterone during replacement was lower (P < 0.05) for cows with low than high serum progesterone at lutectomy. Thus, clearance, more than luteal production, determined peripheral progesterone in pregnant, lactating dairy cows.     

Risk factors for perinatal mortality in dairy cattle: Cow and foetal factors, calving process

It was the aim of this study to identify risk factors of perinatal mortality (PM) on a large dairy farm in Germany. Four hundred and sixty-three cows were observed continuously around calving. Data such as the lactation number, body condition score, pelvic measurements, duration of second stage of labour (SSL), degree of abdominal press (AP), presentation/position/posture of the calf, calving classification, various measurements of the calves and every action of the barn staff were documented. Calves born dead and those that died within 24 h were classified as cases of PM. Logistic regression was performed to identify risk factors for the dependent variables PM, SSL and AP. 9.7% of all calves born (n = 483) were classified as PM. In the logistic regression model, only SSL and presentation/position/posture of the foetus remained as significant effects for PM. The odds ratio for PM was 0.20, when SSL was ≤120 min, and 0.33, when the calves were born in anterior presentation, upper position and normal posture. With regard to SSL, primipara, insufficient AP, assisted calvings and as a trend, work shift changeover, these were risk factors for a prolonged SSL beyond 120 min. The risk for insufficient AP was lower when the calves were born spontaneously, in anterior presentation and as single calves. In conclusion, the duration of SSL and presentation/position/posture of the calf seemed to be key risk factors for PM. Interventions should be considered when SSL lasts longer than 2 h. Insufficient monitoring around parturition had a negative effect on the duration of SSL and thereby, indirectly on PM.     

Functions of canopy-stored seeds in the dune ecosystem: conclusions from Agriophyllum squarrosum and Artemisia wudanica

Delay in seed release is found in the dune ecosystem. However, its functions have been rarely reported. We studied delayed seed release in the Agrio-phyllum squarrosum (Chenopodiaceae), an annual psam-mophyte, and the Artemisia wudanica (Asteraceae), a psammophilous subshrub in an active sand dune field in Inner Mongolia, China, to get insights into its functions in dealing with sand movement. We concluded that delay in seed release in the dune ecosystem are as follows: (1) postponing dispersal of a portion of seeds until the end of windy season and the start of growing season; (2) regulating the spatiotemporal pattern of seed bank; (3) helping psammophytes adapt to wind erosion on the active sand dune; and (4) helping psammophytes realize long-distance dispersal.     

Relationship between the behaviour of sows at 6 months old and the behaviour and performance at farrowing

Piglet crushing remains a major problem in pig production. Reduced crushing might be obtained through genetic selection on sow behavioural traits. The aim of the study was to assess the relationship between behavioural responses at 6 months of age, around farrowing, and sows' reproductive performance including crushing levels. At 6 months of age, behavioural responses of 75 nulliparous sows were observed both during behavioural tests to human presence and to the presence of a novel object in their home pen, and their responses when placed in a weighing device. At first farrowing, nervousness of the sows was observed when placed in the farrowing crate 1 week before and the day of farrowing, as well as their fear responses when approached by a human from behind or at the front of the farrowing crate. At 6 months of age, escape from a human tended to be correlated with the reactivity in the weighing device (rs = 0.21, P = 0.09). Around first farrowing, the withdrawal reaction when a human approached at the front was correlated with the fear response when approached from behind and the nervousness of the sow in the crate (rs = 0.29, P < 0.05; rs = 0.37, P < 0.01). The fear response when approached from behind was correlated with nervousness in the crate and around farrowing (rs = 0.70, P < 0.001; rs = 0.25, P < 0.05), and nervousness in the crate was significantly correlated with the nervousness around farrowing (rs = 0.34, P < 0.01). The escape from a human at 6 months was correlated with withdrawal when approached from the front before farrowing (rs = 0.38, P < 0.01) and with nervousness of the sow in the crate (rs = 0.24, P < 0.05). The number of piglets crushed at first farrowing was correlated with the latency to approach a novel object at 6 months and nervousness around farrowing (rs = -0.27, P < 0.05; rs = 0.28, P < 0.05), and tended to be correlated with the escape behaviour from human at 6 months and withdrawal away from human presence before farrowing (rs = 0.21, P = 0.09; rs = 0.22, P = 0.08). These results suggest that behavioural responses to humans and during management practices of nulliparous sows at 6 months of age are, to some extent, related with their behaviour around farrowing and crushing levels of piglets at farrowing.     

Drying and warming immediately after birth may reduce piglet mortality in loose-housed sows

The aim of the present experiment was to investigate the effects of placing newborn piglets under the heat lamp or both drying and placing them under the heat lamp on piglet mortality. Sixty-seven healthy (Landrace × Yorkshire) sows were divided equally into three different experimental groups: a control group where the farrowings occurred without supervision from the farmer (C; n = 23 litters), another group where the piglets were placed under the heat lamp in the creep area immediately after birth (HL; n = 22 litters) and a third group where the piglets were dried with straw and paper towels followed by placing them under the heat lamp in the creep area immediately after birth (DHL; n = 22 litters). The sows were individually loose-housed in farrowing pens during farrowing and lactation. The piglets were not closed inside the creep area, but were free to move around in the pen. The routines in the experimental groups required the stock person to attend the farrowings from the onset of birth of the first piglet until the last piglet was born. All the dead piglets were weighed and subjected to a post mortem examination at the farm to ascertain the causes of death. Postnatal mortality (% of live born) was significantly lower in the HL and DHL groups than in the control group (P < 0.0001). This was significant concerning all causes of mortality. Compared to the control group, crushing occurred in significantly fewer litters when the piglets were both dried and placed under the heat lamp (P < 0.05). In the DHL treatment, crushing of one or more piglets by the sow occurred in only 13.6% of the litters, whereas this was increased to 34.8% in the HL and to 47.9% in the control group, respectively. All causes of death, except the proportion of stillborn piglets, increased significantly with increasing litter size. Because of the relatively large potential that these rather simple routines may have to improve piglet survival, different types of management or human interference around the time of farrowing should be compared on a larger scale, both experimentally and on commercial farms.     

Lifetime productivity of dairy cows in smallholder farming systems of the Central highlands of Kenya

Evaluation of lifetime productivity is sensible to target interventions for improving productivity of smallholder dairy systems in the highlands of East Africa, because cows are normally not disposed of based on productive reasons. Feeding strategies and involuntary culling may have long-term effects on productive (and therefore economic) performance of dairy systems. Because of the temporal scale needed to evaluate lifetime productivity, experimentation with feedstuffs in single lactations is not enough to assess improvements in productivity. A dynamic modelling approach was used to explore the effect of feeding strategies on the lifetime productivity of dairy cattle. We used LIVSIM (LIVestock SIMulator), an individual-based, dynamic model in which performance depends on genetic potential of the breed and feeding. We tested the model for the highlands of Central Kenya, and simulated individual animals throughout their lifetime using scenarios with different diets based on common feedstuffs used in these systems (Napier grass, maize stover and dairy concentrates), with and without imposing random mortality on different age classes. The simulations showed that it is possible to maximise lifetime productivity by supplementing concentrates to meet the nutrient requirements of cattle during lactation, and during early development to reduce age at first calving and extend productive life. Avoiding undernutrition during the dry period by supplementing the diet with 0.5 kg of concentrates per day helped to increase productivity and productive life, but in practice farmers may not perceive the immediate economic benefits because the results of this practice are manifested through a cumulative, long-term effect. Survival analyses indicated that unsupplemented diets prolong calving intervals and therefore, reduce lifetime productivity. The simulations with imposed random mortality showed a reduction of 43% to 65% in all productivity indicators. Milk production may be increased on average by 1400 kg per lactation by supplementing the diet with 5 kg of concentrates during early lactation and 1 kg during late lactation, although the optimal supplementation may change according to milk and concentrate prices. Reducing involuntary culling must be included as a key goal when designing interventions to improve productivity and sustainability of smallholder dairy systems, because increasing lifetime productivity may have a larger impact on smallholders’ income than interventions targeted to only improving daily milk yields through feeding strategies.     

Conflicting selection on diaspore traits limits the evolutionary potential of seed dispersal by ants

Conflicts of selection on diaspore traits throughout the dispersal cycle can limit the evolutionary consequences of seed dispersal. However, these conflicts have never been investigated in directed dispersal systems. We explored conflicts of selection through life stages of dispersal in the myrmecochorous herb Helleborus foetidus. Seeds are subject to two contrasting partial selective scenarios. Undispersed seeds are subject to positive directional selection on seed size characters, whereas seeds dispersed are subject to stabilizing selection for size. In both scenarios, seedling establishment determined the magnitude and direction of selection. This does not reflect ant preferences for seed size. However, total selection still depends largely on ant activity, as ants control the relative importance of each selective scenario. We advocate the use of analytical approaches combining multiplicative fitness and microenvironment‐specific selection to more realistically estimate the realized selection on traits functional during several life stages. This approach may be extended to any organism dispersing offspring to different environments.