After completing a Bsc(Hons) in Zoology here at
The University of Sheffield
Molecular evolution is an area of evolutionary and molecular biology which is currently generating a lot of interest. Genes involved in different functions undergo evolutionary change at different rates. Recent research has shown that many genes involved in reproduction are evolving up to twice as fast as genes not involved in reproduction (Civetta & Singh 1995). This phenomenon has been observed across a wide variety of taxonomic groups including; Protozoa, Insects, Birds and Mammals.
Some of the best studied rapidly evolving reproductive genes are those which encode the accessory gland proteins (Acps) produced by male fruit flies, known as Drosophila. Acps have been particularly well studied in a species fruit fly called Drosophila melanogaster. Males are thought to produce as many as 70-106 different Acps, with functions in several important reproductive processes.
Acps are produced, along with other seminal fluid components, in male reproductive organs known as the accessory glands (Figure 1). They are then transferred, along with sperm, to the female reproductive tract during copulation.
Figure 1. A photograph of the reproductive
system of a male Drosophila pseudoobscura.
Once the Acps have been transferred to the female they can alter her physiology and behaviour, in a number of ways to increase the males’ reproductive success. For example, an Acp known as Acp70A has been found to increase ovulation (egg-production) and oviposition (egg-laying) rates in females upon transfer. This particular Acp also induces rejection behaviour towards subsequent males by the female. Being able to exert these kinds of effects on females can dramatically increase the number of offspring a male can sire in his lifetime. It is thought that because they play such key roles in determining the reproductive success of males, Acps are subject to strong selective pressures leading to the high rates of evolution observed.
It has been suggested that sexual selection (the component of natural selection associated with reproductive success) is responsible for this rapid rate of evolutionary change. However, whilst evidence collected to date does appear to suggest this could be the case, as yet there is no direct experimental evidence in support of this idea. This leaves the selective mechanisms driving the rapid evolution unclear. Therefore, using our D.pseudoobscura selection lines to determine whether, and the extent to which, sexual selection is responsible for the rapid evolution of Acps is the primary focus of my PhD.
research investigating the evolutionary responses to such varying levels of
sexual selection has shown that E males;
1) are better able to induce rejection behaviour towards subsequent male partners in females than M males
2) are capable of a greater number of sequential matings than M males
3) have evolved larger accessory glands than M males.
Because re-mating patterns in both male and female Drosophila are known to be related to Acp function and/or quantity these findings provide priliminary evidence that Acps produced by males from the different selection lines may have altered as a result of sexual selection.
In order to test this we will compare expression levels and allele frequencies between the selection line treatments in order to detect any changes that may have occurred.
we have determined whether sexual selection is responsible for driving rapid
evolution in Acps, this knowledge can then be applied to gaining a better
a) How sexual selection influences gene evolution and the rate of evolutionary change
b) The molecular basis of sperm competition and cryptic female choice
c) Underlying mechanisms of sexual conflict.