Studies should be wary when pooling male and female data

Understanding sex differences in the cost of terrestrial locomotion

John J. Lees,Robert L. Nudds,Lars P. Folkow,Karl-Arne Stokkan,and Jonathan R. Codd

Published online before print August 17, 2011, doi:10.1098/rspb.2011.1334Proc. R. Soc. B

Here is an interesting piece of research done on birds that could be of great relevance for future research.

We know very little about the physiological consequences of the behavioural and morphological differences that result from sexual selection in birds. 

Here the research was done on Svalbard rock ptarmigans (Lagopus muta hyperborea). Svalbard rock ptarmigans exhibit distinctive behavioural differences during the breeding season. Males continuously compete for and defend territories in order to breed successfully. This in turn places large demands on their locomotor system. 

In this piece of research the researchers show that male birds have improved locomotor performance compared with females, showing both a lower cost of locomotion (CoL) and a higher top speed. They suggest that sex differences in locomotor capability may be due to sexual selection for improved male performance.

The researchers sign off with these words” While the mechanisms underlying these energetic differences are unclear, future studies should be wary when pooling male and female data”.