Exhaustive exercise training enhances aerobic capacity in American alligator (Alligator mississippiensis)

Abstract

The oxygen transport system in mammals is extensively remodelled in response to repeated bouts of activity, but many reptiles appear to be 'metabolically inflexible' in response to exercise training. A recent report showed that estuarine crocodiles (Crocodylus porosus) increase their maximum metabolic rate in response to exhaustive treadmill training, and in the present study, we confirm this response in another crocodilian, American alligator (Alligator mississippiensis). We further specify the nature of the crocodilian training response by analysing effects of training on aerobic [citrate synthase (CS)] and anaerobic [lactate dehydrogenase (LDH)] enzyme activities in selected skeletal muscles, ventricular and skeletal muscle masses and haematocrit. Compared to sedentary control animals, alligators regularly trained for 15 months on a treadmill (run group) or in a flume (swim group) exhibited peak oxygen consumption rates higher by 27 and 16%, respectively. Run and swim exercise training significantly increased ventricular mass (*11%) and haematocrit (*11%), but not the mass of skeletal muscles. However, exercise training did not alter CS or LDH activities of skeletal muscles. Similar to mammals, alligators respond to exercise training by increasing convective oxygen transport mechanisms, specifically heart size (potentially greater stroke volume) and haematocrit (increased oxygen carrying-capacity of the blood). Unlike mammals, but similar to squamate reptiles, alligators do not also increase citrate synthase activity of the skeletal muscles in response to exercise.

Making Olympic lizards: the effects of specialised exercise training on performance

“…However, our knowledge about exercise effects does not extend far beyond humans, and not much beyond mammals. In conclusion, our results, combined with perspectives from studies of exercise in fishes (Davison, 1997;He et al, 2013;Palstra and Planas, 2013), amphibians (Cummings, 1979;Miller and Camilliere, 1981), crocodilians (Owerkowicz and Baudinette, 2008;Eme et al, 2009), and birds (e.g. Gaunt et al, 1990) …”

“…Our results cannot conclusively determine the precise mechanisms leading to increased endurance capacity, but the differences in endurance were associated with corresponding differences in haematocrit and SO fibre CSA in two key locomotor muscles. The higher haematocrit in endurance-trained lizards is consistent in its directional change to studies of humans and other mammals (reviewed in Bexfield et al, 2009;Connes et al, 2013), as well as birds (Riera et al, 1983), crocodilians (Eme et al, 2009) and fishes (Beamish, 1978), and locomotor endurance in lizards is related to haematocrit (Garland, 1984;. The increased oxygen-carrying capacity that comes with higher haematocrit may explain a significant portion of the increase in endurance.…”

“…In humans, both endurance running and sprint training can result in dramatic changes to skeletal muscle organisation, from gene expression (Wang et al, 2004;Wilson, 2013) to contractile properties, hypertrophy and power output (Trappe et al, 2006;Harber and Trappe, 2008;Lundberg et al, 2013). There are several studies on the effects of exercise in non-mammalian tetrapods, demonstrating that exercise training can enhance endurance capacity in amphibians (Cummings, 1979;Miller and Camilliere, 1981), crocodilians (Owerkowicz and Baudinette, 2008;Eme et al, 2009) and birds (Gaunt et al, 1990), but such studies have been conducted on only a few very distantly related species. This, combined with equivocal results in some studies, makes it difficult to understand the origin and adaptive significance of skeletal muscle plasticity.…”

Cross-training in birds: cold and exercise training produce similar changes in maximal metabolic output, muscle masses and myostatin expression in house sparrows,Passer domesticus

“…Exercise training generally increases mammalian MMR by 4-23% (Holloszy and Booth, 1976;Pica and Brooks, 1982;Gleeson et al, 1983;Evans and Rose, 1988;Carter et al, 2000). Similarly, exercise training produces increases of 16-28% in reptiles (Owerkowicz and Baudinette, 2008;Eme et al, 2009)…”

Beyond body size: muscle biochemistry and body shape explain ontogenetic variation of anti-predatory behaviour in the lizard Salvator merianae (Squamata: Teiidae)

“…Biochemical properties of hindlimb and head muscles were assessed based on maximum activity of two metabolic enzymes: lactate dehydrogenase (LDH) was used as an indicator of oxygenindependent pathways, whereas citrate synthase (CS) represented the muscle aerobic metabolism (Eme et al, 2009;Fields et al, 2008;Kirkton et al, 2011;Kohlsdorf et al, 2004;Norton et al, 2000;Rosa et al, 2009;Seibel et al, 1998;de Souza et al, 2004;Vetter and Lynn, 1997). Enzyme activities were measured using a Beckman DU-70 spectrophotometer under saturating and noninhibitory substrate conditions, following de Souza et al (2004), as further detailed.…”