PKCθ is required for hemostasis and positive regulation of thrombin-induced platelet aggregation and α-granule secretion

Platelet activation due to vascular injury is essential for hemostatic plug formation, and is mediated by agonists, such as thrombin, which trigger distinct receptor-coupled signaling pathways. Thrombin is a coagulation protease, which activates G protein-coupled protease-activated receptors (PARs) on the surface of platelets. We found that C57BL/6J and BALB/C mice that are deficient in protein kinase C θ (PKCθ), exhibit an impaired hemostasis, and prolonged bleeding following vascular injury. In addition, murine platelets deficient in PKCθ displayed an impaired thrombin-induced platelet activation and aggregation response. Lack of PKCθ also resulted in impaired α-granule secretion, as demonstrated by the low surface expression of CD62P, in thrombin-stimulated platelets. Since PAR4 is the only mouse PAR receptor that delivers thrombin-induced activation signals in platelets, our results suggest that PKCθ is a critical effector molecule in the PAR4-linked signaling pathways and in the regulation of normal hemostasis in mice.     

Acceptance of low-saponin lines of alfalfa with varied phenolic concentrations by pea aphid (Homoptera: Aphididae)

This research aims to examine the effect of phenolics on pea aphid (Acyrthosiphon pisum) (Homoptera: Aphididae) development and feeding behaviour, on leaves of selected low-saponin lines of Radius alfalfa (Medicago sativa). There was a slight, negative correlation (Spearman rank correlation r _s = −0.80) between concentrations of saponins and phenols. Lines with higher concentrations of saponins had less phenolics. Levels of phenolics in low-saponin lines of alfalfa cv. Radius were related to their acceptance by the pea aphid. Our data revealed an inverse relationship between level of phenolics and the aphid abundance and its biology on studied alfalfa lines. Larval development of the pea aphid was longer, reproduction period was shorter, and the fecundity was lower on low-saponin lines with higher level of phenolics. There were observed some tendencies in the pea aphid feeding behaviour on these lines: prolonging the probing of the peripheral tissues (epidermis and mesophyll) and shortening the period of phloem sap ingestion. The better hosts for the pea aphid were low-saponin lines with low levels of phenolic compounds.     

Grazing dynamics in intertidal rockpools: Connectivity of microhabitats

Differences between rockpool and emergent rock communities are often attributed to their contrasting physical conditions. However, differences in grazing pressure between rockpools and open rock could also exert an important structuring role. Greater densities and/or the lack of tidal constraints on foraging may allow grazing intensity to be greater in rockpools. Here, wax discs were deployed to compare grazing intensity between rockpool and emergent rock habitats at each of three tidal heights on a moderately exposed shore in SW England. Grazing intensity was then examined in relation to herbivore density. Grazing intensity in pools was twice that on emergent rock, despite a lower density of herbivores in the rockpools. Of these herbivores, patellid limpets are the dominant grazers on rocky shores throughout the NE Atlantic and are recognised to have a major role in structuring intertidal communities. Thus, subsequent experiments focussed on the influence of limpets in determining the differences in consumer pressure between rockpools and emergent rock. Three alternative explanations were considered: (1) the effect of continuous immersion on grazing intensity in rockpools; (2) differences in limpet species abundance between the two habitats; (3) movement of limpets from emergent rock into pools to feed. The level of grazing pressure exerted by Patella ulyssiponensis (Gmelin), the predominant species living constantly immersed in rockpools, was similar to that of P. vulgata (Linnaeus) which is predominantly found on emergent rock. P. vulgata were observed moving from emergent rock into rockpools during high tide. Manipulative experiments confirmed that these foraging excursions resulted in a 2-fold increase in grazing intensity in the pools. Grazing activity of P. vulgata in rockpools was not consistent between sites and may be influenced by differences in wave exposure and/or the abundance of microbial resources. Elevated consumer pressure in rockpools may be an important factor influencing algal assemblages and probably explains the predominance of grazer resistant-species in these pools.     

Restoring depleted coral‐reef fish populations through recruitment enhancement: a proof of concept

To determine whether enhancing the survival of new recruits is a sensible target for the restorative management of depleted coral‐reef fish populations, settlement‐stage ambon damsel fish Pomacentrus amboinensis were captured, tagged and then either released immediately onto small artificial reefs or held in aquaria for 1 week prior to release. Holding conditions were varied to determine whether they affected survival of fish: half the fish were held in bare tanks (non‐enriched) and the other half in tanks containing coral and sand (enriched). Holding fish for this short period had a significantly positive effect on survivorship relative to the settlement‐stage treatment group that were released immediately. The enrichment of holding conditions made no appreciable difference on the survival of fish once released onto the reef. It did, however, have a positive effect on the survival of fish while in captivity, thus supporting the case for the provision of simple environmental enrichment in fish husbandry. Collecting and holding settlement‐stage fish for at least a week before release appear to increase the short‐term survival of released fish; whether it is an effective method for longer‐term enhancement of locally depleted coral‐reef fish populations will require further study.     

Summer diet of beluga whales inferred by fatty acid analysis of the eastern Beaufort Sea food web

Beluga whales (Delphinapterus leucas) are the most abundant odontocetes in Arctic waters and are thus thought to influence food web structure and function. The diet of the Beaufort Sea beluga population is not well known, partly due to the inherent difficulty of observing feeding behaviour in Arctic marine cetaceans. To determine which prey items are critical to the Beaufort Sea beluga diet we first examine and describe the Mackenzie Delta and Beaufort Sea food web using fatty acid analyses. Fatty acid profiles effectively partitioned prey items into groups associated with their habitat and feeding ecology. Next, the relative contribution of various prey items to beluga diet was investigated using fatty acids. Finally, beluga diet variability was examined as a function of body size, a known correlate of habitat use. Beluga appeared to feed predominantly on Arctic cod (Boreogadus saida) collected from near shore and offshore regions. Size related dietary differences suggested larger sized beluga preferred offshore Arctic cod given the shared high levels of long chain monounsaturates, whereas smaller sized beluga appeared to feed on prey in their near shore habitats that included near shore Arctic cod. The presence of Arctic cod groups in shallow near shore and deep offshore habitats may facilitate the behavioural segregation of beluga habitat use as it relates to their size and resource requirements. Given Arctic cod are a sea ice associated fish combined with the accelerated sea ice loss in this region, beluga whales may need to adapt to new dietary regimes.     

Does predation risk influence habitat use by northern redbelly dace Phoxinus eos at different spatial scales?

This study investigated the relationship between spatial variations in predation risk and abundance of northern redbelly dace Phoxinus eos at both macroscale (littoral v. pelagic zones) and microscale (structured v. open water habitats in the littoral zone) of Canadian Shield lakes. Minnow traps were placed in both structured and open water habitats in the littoral zone of 13 Canadian Shield lakes, and estimates of the relative predation risk of P. eos in both the pelagic and the littoral zones were obtained from tethering experiments. Results showed that (1) the mean abundance of P. eos in the littoral zone was positively correlated with the relative predation risk in the pelagic zone, (2) P. eos preferentially used structured over open water habitats in the littoral zone and (3) this preference was not related to the relative predation risk in the littoral zone but decreased as the relative predation risk increased in the pelagic zone. At the lake level, these results support the hypothesis that P. eos enter the littoral zone to avoid pelagic piscivores. At the littoral zone level, the results do not necessarily contradict the widely accepted view that P. eos preferentially use structured over open habitats to reduce their predation risk, but suggest that flexibility in antipredator tactics ( e.g. shelter use v. shoaling) could explain the spatial distribution of P. eos between structured and open water habitats.     

The reproductive ecology of the southern red tabira bitterling Acheilognathus tabira jordani in Japan

The life history, population and reproductive variables of the southern red tabira bitterling Acheilognathus tabira jordani were investigated in a lowland reach of the River Ohara in Shimane Prefecture, western Honshu, Japan. Acheilognathus t. jordani , like all other species of bitterling, lays its eggs on the gills of freshwater mussels. It was the only species of bitterling present in the study reach, and three species of bivalve mussel were available to it for spawning: Anemina arcaeformis, Anodonta lauta and Corbicula leana . Spawning by A.t. jordani was recorded between early April and early July in 2003 and began at a size of 38· 0 mm standard length ( L _S) in the 1+ age class. Ovipositor length ( L _OP) during oviposition was positively correlated with female L _S, and showed significant seasonal variation, with a mean ± s.d. L _OP of 27· 5 ± 5· 3 mm ranging from 16· 8 to 42· 0 mm during the spawning period, which was shorter than that of a previously studied A. t. tabira population. Eggs of this subspecies are relatively long and elliptic in shape, with a volume of c. 2· 4 mm³. Egg number correlated positively with female L _S and both egg shape and volume changed significantly with season. The population size of adults was estimated to be 850 individuals, and comprised age 0+ to 3+ individuals with L _S ranging from 12· 0 to 72· 2 mm. The population sex ratio was significantly female biased, with seven females: three males. Egg shape and size and L _OP during oviposition in the present A. tabira population may be the result of local adaptations to the mussel species utilized and no competition with other bitterling species for spawning sites.