Question

The scatter plot of megachiropera bats in the Hosken(1998) study of testes mass and sperm competition showed a strong correlation between the variables Testis size and social group size. However that scatter plot data points needed to be independent of each other for the correlations to have meaning. for example testes size might be an ancestral character rather than an adaptation to group size. what is the name of the method Hosken(1998) use to illustrate independent? give a short description of the method.

Answer 1

Independent contrast comparison

At a species level, testes mass was significantly related to body mass. Therefore to remove body mass effects,residual testes mass was calculated, from a regression of testes mass against body mass, and regressed against roost-group size.

Residual testes mass was significantly positively related to roost-group size at the species level.

Comparing independent contrasts gave a similar result. A significant and positive relationship was found between residual contrasts in testes mass and contrasts in roost-group size. This indicates a significant evolutionary association between testes mass and roost-group size.

In statistics, particularly in analysis of variance and linear regression, a contrast is a linear combination of variables (parameters or statistics) whose coefficients add up to zero, allowing comparison of different treatments