Sex differences in metabolic scaling exponents in American cockraoch, Periplaneta americana (L) (Blattodea: Blattidae)

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 con
sumption (VO2
) and carbon dioxide evolution (VCO2
) using manometric and titrimetric 
methods respectively. Least square regression was used to scale Log10
VO2
 with Log10
Mass 
and inferential statistics of analysis of variance, t-test, and coefficient of 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 the 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 dif
ferent (t46 
= 5.75); however, the slopes of regression lines of both sexes combined was not 
significantly different from that of males (t71 
= 0.83). 
Conclusion: The results imply that there is a sexual difference in metabolic scaling expo
nents of cockroaches since their regression models cannot be represented by a single line 
due to differences in their intercept.