Snuggled warmly beneath mum, chicks within their eggshells have no need to generate their own heat. However, during the first few days after hatching, the tiny defenceless animals have to ramp up their inner furnaces and begin generating their own warmth in readiness for fledging. ‘There is a hypothesis that SERCA is part of a mechanism for heat generation in birds’, says Edwin Price, from the University of North Texas, USA, who explains that SERCA [sarco(endo)plasmic reticulum Ca2+-ATPase] is a specialised protein found in muscles that usually pumps calcium ions to drive contractions. However, it may also be involved in heat generation and, if so, Price and PI Edward Dzialowski wondered how the levels of SERCA protein found in the largest muscle (the pectoral muscle) in the bodies and the hearts of red-winged blackbirds (Agelaius phoeniceus) might alter during the first days of life.
‘Red-winged blackbirds usually nest in marshes’, says Price, who recalls wading through the Lewisville marshes with colleagues Tushar and Sarah Sirsat, visiting the nests to monitor chick development. After collecting heart and pectoral muscles from 1- to 9-day-old hatchlings, Price recorded the amount of SERCA protein found in both tissues back in the lab. As he had thought, the SERCA levels in the chicks’ pectoral muscles increased as the tiny birds developed until they were ready to fledge, likely to increase heat generation, but declined after fledging. ‘The decline is an effect we attribute to remodelling of the muscle from a primarily heat-generating organ to a primarily force-generating organ’, says Price. He suspects that when the muscle switches from producing warmth to powering flight, the calcium storage structure – the sarcoplasmic reticulum, in which the SERCA proteins are located in the muscle – shrinks, and additional muscle filaments fill the vacated space. However, when Price compared the quantities of SERCA located in the chicks’ heart muscles, it continued increasing into adulthood – with a dramatic increase just prior to fledging – probably to provide the fledglings with the increased blood flow that they require to power flight.
Price also wondered whether oils in the chicks’ diet may affect the activity of the SERCA protein. ‘Recent studies have suggested that omega-6s are important for increasing SERCA activity in the hearts of hibernating mammals’, says Price, adding that an omega-6-rich diet seems to increase the metabolism of red-winged blackbirds. Could the oil benefit the developing chicks’ SERCA to increase their metabolism? Price and Tushar and Sarah Sirsat supplemented the diets of some of the chicks with a daily dose of omega-3-rich fish oil, while others were fed a dose of omega-6-rich sunflower oil. However, when Price compared the activity of the SERCA protein in both groups of chicks, the omega-6 supplement had little effect. ‘This was a surprise’, says Price, who admits that he is now unsure how omega-6 oils increase the chicks’ metabolism, but it certainly isn't through the SERCA protein pump.