Fuel for the pace of life: Baseline blood glucose concentration co-evolves with life-history traits in songbirds
Abstrakt
It has been proposed that life histories have co-evolved with a suite of physiological and behavioural adaptations, termed pace-of-life syndromes. Here, we hypothesise that basal concentration of blood glucose (G(0)), a major source of energy circulating in blood, may constitute a key component of pace-of-life syndromes.
To test this hypothesis, we measured G(0) in 30 passerine species and tested its covariation with body mass and other life-history traits. Importantly, body mass is a major life-history determinant and, when its effect is controlled for, there may be no single fast-slow life-history continuum in birds comprising both fecundity and life span.
Hence, we used individual life-history traits, rather than principal component analysis, to characterise life-history variation in our analysis. In support of G(0)-life-history co-evolution, we found G(0) to be negatively correlated with body mass and positively with reproductive investment in a single clutch across 30passerine species.
Higher G(0) in females suggests that the energy demands of clutch production and incubation may be an important selection force driving co-evolution of G(0) with reproductive output. In contrast, G(0) was not associated with maximum life span, suggesting that high G(0) may not constrain evolution of longevity.
This implies that long-lived species can evolve physiological adaptations preventing harmful effects of high glucose concentrations, known to cause pathologies and accelerate ageing. In addition, G(0), but not basal metabolic rate (BMR), was negatively correlated with migration distance, attesting to evolutionary changes in energy metabolism in long-distance migrants.
Our results further suggest that the links between body mass, reproduction and G(0) are not mediated by BMR and that G(0) is associated with fast-slow life-history variation more closely than available BMR data. A species life history is determined to a great extent by body mass.
When this effect is controlled for, only those traits related to reproduction (but not life span) constitute the principal axis of life-history variation in birds. Hence, the co-evolution of G(0) with body mass and reproductive output evidenced in our study indicates that G(0) constitutes an important physiological component of pace-of-life syndromes.