Credit: BANANASTOCK

Gene duplication followed by the emergence of a new function in one copy is an important source of evolutionary novelty. However, little is known about the effects that a new function can have on the evolution of other genes. A recent study in honeybees addresses this question, showing that neofunctionalization in one gene of a paralogous pair can restrict the evolution of its sister copy.

In the honeybee (Apis) lineage a tandem duplication of the feminizer (fem) gene has given rise to the paralogous gene complementary sex determiner (csd). Whereas fem has maintained its original function in sex determination, csd has evolved a new function to become an initiating signal in the sex determination pathway.

Hasselmann and colleagues compared the ratio of non-synonymous (n) to synonymous (s) mutations in fem in two contexts: in Apis species, which have both fem and csd, and in other bee species that have fem only. The n/s ratio was significantly lower in the Apis lineage, which suggests that fem has been subject to increased purifying selection — that is, mutations that affect the function of fem have been selected against. Hasselmann and colleagues ruled out the alternative possibilities that the rate of synonymous substitution had increased in fem genes of Apis bees, or that the genetic linkage between fem and csd caused the reduced rate of fem evolution.

Because fem and csd function in the same pathway, an attractive explanation for the limited evolution of fem when csd is present is that changes in the FEM protein would disrupt the function of CSD. As well as prompting similar investigations of other paralogous gene pairs, this study highlights more generally the need to look at the effects of newly evolved functions on the evolution of other genes.