Abstract

Background: Sexual differences in physiologies could results in significant variation in energy generation, allocation and utilization among males and females organisms. Metabolic scaling exponents could as well be dimorphically varied in insects in which females are less active due to reproductive demands. This study investigated into the metabolic-mass scaling patterns of male and female American cockroach, Periplaneta americana.
Methods: Metabolic rate was measured indirectly by estimating the rate of oxygen consumption (VO2) and carbon dioxide evolution (VCO2) using manometric and titrimetric methods respectively. Least Square Regression (LSR) was used to scale Log10VO2 with Log10Mass and inferential statistics of ANOVA, t-test and coefficient determinant (R2) were used to test the goodness of regression slopes, compare slopes of regression lines and test significance of the variance accounted for by each regression model respectively at P < 0.05.
Results: The results show that metabolic rate was significantly correlated with body mass for males (t24=67.8), females (t24=37.6) and both sexes combined (t49=22.4). Each regression model was also significant; males (F1, 48=69.7), females (F1, 48=261.4) and both sexes combined (F1, 98=88.9). The slopes of males and females lines were significantly different (t46=5.75), however the slopes of regression lines of both sexes combined was not significantly different from that of males (t71=0.83).
Conclusions: The results imply that there is a sexual difference in metabolic scaling exponents of cockroaches since their regression models cannot be represented by a single line due to differences in their intercept.

Key words: Metabolic Scaling, Physiologies, Sexual dimorphism, titrimetric