Habitat variability does not generally promote metabolic network modularity in flies and mammals

TL;DR

This study tests the hypothesis that habitat variability promotes metabolic network modularity in higher organisms, finding limited support and suggesting gene duplication as a more significant factor.

Contribution

It provides the first direct test of the habitat variability-modularity hypothesis in flies and mammals, challenging previous assumptions.

Findings

No consistent positive correlation between habitat variability and network modularity.

Gene duplication frequency is a key factor influencing network modularity.

Habitat variability's role in network modularity may be limited or context-dependent.

Abstract

The evolution of species habitat range is an important topic over a wide range of research fields. In higher organisms, habitat range evolution is generally associated with genetic events such as gene duplication. However, the specific factors that determine habitat variability remain unclear at higher levels of biological organization (e.g., biochemical networks). One widely accepted hypothesis developed from both theoretical and empirical analyses is that habitat variability promotes network modularity; however, this relationship has not yet been directly tested in higher organisms. Therefore, I investigated the relationship between habitat variability and metabolic network modularity using compound and enzymatic networks in flies and mammals. Contrary to expectation, there was no clear positive correlation between habitat variability and network modularity. As an exception, the network modularity increased with habitat variability in the enzymatic networks of flies. However, the observed association was likely an artifact, and the frequency of gene duplication appears to be the main factor contributing to network modularity. These findings raise the question of whether or not there is a general mechanism for habitat range expansion at a higher level (i.e., above the gene scale). This study suggests that the currently widely accepted hypothesis for habitat variability should be reconsidered.