When is overkill optimal? Tritrophic interactions reveal new insights into venom evolution

Organisms embedded within food webs must balance arms races with their predators and prey. For venom users, venom may mediate each arms race, but the dynamical evolutionary changes in venom production in response to the two arms races are still poorly understood. Here, we use a simple model to evaluate the evolutionary response of a venomous consumer to the presence of an apex generalist predator and evolution of the consumer’s prey. We find that introduction of the apex predator can weaken the arms race between the two lower trophic levels. In addition, when consumer prey capture and predator defense venoms functionally overlap, a reduced evolutionary response in the prey population can drive investment in venom used for prey capture going beyond what is optimal for subduing prey. These dynamics suggest that interactions with multiple trophic levels can substantially alter the venom complexity in predatory venomous animals and may explain the paradox of the overkill hypothesis.     

Acid-base Balance in Acute Gastrointestinal Bleeding

Acid-base balance has been studied in 21 patients with acute upper gastrointestinal bleeding. A low plasma bicarbonate concentration was found in nine patients, accompanied in each case by a base deficit of more than 3 mEq/litre, indicating a metabolic acidosis. Three patients had a low blood pH. Hyperlactataemia appeared to be a major cause of the acidosis. This was not accompanied by a raised blood pyruvate concentration. The hyperlactataemia could not be accounted for on the basis of hyperventilation, intravenous infusion of dextrose, or arterial hypoxaemia. Before blood transfusion it was most pronounced in patients who were clinically shocked, suggesting that it may have resulted from poor tissue perfusion and anaerobic glycolysis. Blood transfusion resulted in a rise in lactate concentration in seven patients who were not clinically shocked, and failed to reverse a severe uncompensated acidosis in a patient who was clinically shocked. These effects of blood transfusion are probably due to the fact that red blood cells in stored bank blood, with added acid-citrate-dextrose solution, metabolize the dextrose anaerobically to lactic acid. Monitoring of acid-base balance is recommended in patients with acute gastrointestinal bleeding who are clinically shocked. A metabolic acidosis can then be corrected with intravenous sodium bicarbonate.     

A novel application of the Price equation reveals that landscape diversity promotes the response of bees to regionally rare plant species

Bees are ecosystem service providers that are globally threatened by losses of plant diversity. However, effects of multi‐species floral displays on bees in agro‐ecosystems with variable landscape context remain poorly understood, hindering pollinator conservation tactics. We addressed this knowledge gap through a novel application of the modified Price equation to evaluate responses of bees to diverse floral communities on 36 farms in Washington, USA, over 3 years. We found that floral richness, not floral identity, was the best predictor of floral visits by bees. However, the benefits of regionally rare floral species (i.e. plants found at relatively few sites) were only fully realised when farms were embedded in diverse landscapes. Our analysis used the modified Price equation to demonstrate that plant diversity, rather than specific plant species, promotes pollinator visitation, and that diverse landscapes promote the response of pollinators to regionally rare plant species.