Quantifying selection on standard metabolic rate and body mass in Drosophila melanogaster

Standard metabolic rate (SMR), defined as the minimal energy expenditure required for self-maintenance, is a key physiological trait. Few studies have estimated its relationship with fitness, most notably in insects. This is presumably due to the difficulty of measuring SMR in a large number of very small individuals. Using high-throughput flow-through respirometry and a Drosophila melanogaster laboratory population adapted to a life-cycle that facilitates fitness measures, we quantified SMR, body mass, and fitness in 515 female and 522 male adults. We used a novel multivariate approach to estimate linear and non-linear selection differentials and gradients from the variance-covariance matrix of fitness, SMR, and body mass, allowing traits specific covariates to be accommodated within a single model. In males, linear selection differentials for mass and SMR were positive and individually significant. Selection gradients were also positive but, despite substantial sample sizes, were non-..., Methods are described in Videlier, M., V. Careau, A.J. Wilson, and H.D. Rundle. Quantifying selection on standard metabolic rate and body mass in Drosophila melanogaster. Evolution: in press.
, Each row corresponds to an individual fly (total: 1060 individuals, 532 females and 528 males). Columns are as follows:

BLOCK: Experimental block, a categorical variable with six levels (1 to 6) corresponding to the 6 temporal blocks over which the experiment was performed.
Sspop: Day of adult emergence, a categorical variable with three levels (1 to 3) corresponding to flies that ecolosed 8, 9 or 10 days after eggs were laid.
B_S: A combination of block (six levels) and day of emergence (three levels).
ID: A categorical variable corresponding to a unique individual identifier.
SEX: A categorical variable with 2 levels (0 for female, 1 for male).
MASS: A continuous variable representing the wet body mass (g) of the individual.
TEMP: A continuous variable consisting of the average temperature (Celcius) during the 20 sec measurement of standard metabolic rate (i.e. SMR).
WV: A continuous variable representing the average water vapor  (ppt) during the 20 sec SMR measurement.
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