African Pygmy Mouse Upgrades Mitochondria to Compensate for Size

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African pygmy mouse upgrades mitochondria to compensate for size

used by most researchers to collect sufficient mitochondria from the minute (0.3 g) muscles.

Sure enough, the mitochondria of the bulkier house mice and one of the pygmy mice (M. minutoides) performed exactly as they expected based on the animals’ respective sizes; the mitochondria of M. minutoides were relatively inefficient compared with those of the house mice. However, when Boël analysed the mitochondria of the smallest mouse on the planet (M. mattheyi), the team was astonished. The muscle and liver mitochondria were as efficient as those of the house mice. Instead of generating large amounts of waste heat while producing ATP, the mitochondria of M. mattheyi African pygmy mice Mus mattheyi. Photo credit: Laurana Serres-Giardi were able to produce as licensed under the Creative Commons Attribution-Share Alike 3.0 much ATP per molecule of oxygen as the Unported. house mice. ‘The hypothesis of a mitochondrial adaptation, by which There’s a reason why so few warm First, Boël recorded the animals’ oxygen extremely small species could avoid … blooded (endothermic) animals are super consumption and carbon dioxide associated energy wastage in order to tiny. It’s simply too costly for them to production rate for 4 days to calculate maintain their cellular energy keep their internal central heating turned their metabolic rate as they scampered homeostasis, is thus verified in two tissues up. This is because the tiny powerhouses around their individual cages. Not of M. mattheyi’, says Boël. (mitochondria) that produce the energy surprisingly, the heavyweight house mice (ATP) required for warmth and activity had the lowest active metabolic rate Even though minute M. mattheyi can become less efficient as animals scale (∼0.03 W g−1) compared with those of hibernate to conserve energy, they have down and their metabolic rates increase. the pygmy mice, which tipped the scales also improved the efficiency of their The few mammals that have miniaturised at ∼0.04 W g−1 (M. minutoides) and mitochondria to reduce energy tend to conserve energy by hibernating ∼0.06 W g−1 (M. mattheyi). But would expenditure. And, Boël is eager to discover and dropping their body temperature their mitochondria prove to be as whether this minuscule titan is unique, ‘in while inactive. However, Mélanie Boël, inefficient as those of other diminutive order to know if the improvement of Damien Roussel and Yann Voituron from warm-blooded creatures? mitochondrial efficiency in species below the Université de Lyon, France, wondered 7 g is a physiological adaptation limiting whether the mitochondria of these minute After collecting samples of the animals’ the high energy cost to maintain their body mammals could have improved their foreleg muscles, Boël measured the temperature’, she says. efficiency, by producing less waste heat to respiration rate of muscle fibres before augment their ATP supply. The team painstakingly collecting mitochondria 10.1242/jeb.223693 decided to compare the performance of from the muscles and liver, which mitochondria from three species of mice – together account for almost half of an Boël, M., Romestaing, C., Duchamp, C., two members of the smallest mouse animal’s basal metabolic rate. Then, she Veyrunes, F., Renaud, S., Roussel, D. and Mus Voituron, Y. (2020). Improved mitochondrial family, African pygmy mice recorded their oxygen consumption and coupling as a response to high mass-specific mattheyi (∼5 g) and Mus minutoides determined how much ATP and waste metabolic rate in extremely small mammals. (∼7 g), and larger house mice, Mus heat the mitochondria produce. ‘To J. Exp. Biol. 223, jeb215558. doi:10.1242/jeb. musculus (∼22 g) – to find out whether perform our study, we needed quite a 215558 any of the minuscule mammals benefit large amount of isolated mitochondria’, Kathryn Knight from boosted mitochondria. says Boël, who had to alter the method [email protected]

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