The relative level of each protein was measured by determining their mean spot volumes under each of the growth conditions in three independent replicate experiments.
The average spot volumes of identified spots ranged from 112 to 121 for the six samples.
Firstly, the spot intensities were corrected for local background (mean spot intensity minus mean spot background intensity).
To achieve this, we related population specific mean values of those reproductive phenotypes that differed significantly across populations with the population specific mean normalized spot volumes of those SFPs whose relative abundance differed significantly across populations.
Ratios of mean normalized spot volumes were calculated.
Mean value of spot volume (dpi) from all three replicate were using to describe the spot density and for further comparison of protein expression, taking into account spots with relative volume equal to or bigger than 0.1 dpi.
In the multivariate analysis (PCA and PLS-DA) the spot volume ratios were mean centred and scaled for unified variance.
Spot volume was estimated by means of its optical density (sum of the spot pixels) normalized as a percentage of total spot optical density in the gel image (Pattini et al., 2008).
Mean spot signal was used as intensity measure.
