Allometry of proboscis architecture of painted lady butterflies, Vanessa cardui, in relation to butterfly mass and fluid uptake rates

The butterfly proboscis is composed of hydrophilic and hydrophobic structures that act together as a functional unit for fluid uptake. We studied the structural configurations of proboscises among Painted lady butterflies, Vanessa cardui, of different body masses. We employed the allometric growth equation and linear regression analysis to acquire the slopes of log10-transformed data of six different proboscis characters in relation to fluid uptake rates and proboscis length. Slopes were tested for significant differences from isometry (slope b = 1). We found negative allometry (0 < b < 1) among measured characters when proboscis length and butterfly mass were the independent variables. Fluid uptake rates, however, indicated an isometric relationship to measured characters. Our study indicated that proboscis architecture does not change proportionally in relation to changes in butterfly mass. We suggest that intense selection pressures, such as floral shapes and sizes, act to maintain a particular proboscis configuration.