Sex and speciation in marine fishes

  • Gage, Matthew (Principal Investigator)
  • Emerson, Brent (Co-Investigator)

Project Details


There are millions of types of animals, plants, and microbes on earth, and we call this rich variety of life 'biodiversity'. This biodiversity is essential for biologists to understand and maintain, because all forms of life depend on each other for their existence. Each type of animal, plant or microbe is called a 'species'. This classification is very important to understand, because it is species number that combines to make up biodiversity. A species is a group of organisms that are more similar to each other than by comparison with members of another species. The key definition of a species is a group of organisms that reproduce with one another to produce fertile offspring: within a species, therefore, individuals are suited to produce offspring.

How is a new species produced? Evolution, which is the process responsible for all forms of life on our planet, allows species to change and fill up new niches as they become available through time. Species can change, because it is only the most successful individuals within a species that survive against a struggle to reproduce and produce offspring. When the opportunity to fill a new niche arises, individuals more suited to that new niche will more efficiently fill that niche and reproduce within it, they then evolve to fit within the niche. Eventually they can evolve to become so different from their original species, that they no longer can reproduce successfully with their original species, and they have then become a new species.

Biologists are particularly interested in how exactly a species becomes reproductively isolated, and what forces drive this isolation to occur. This level of evolution is important and poorly understood. In this project, we plan to use one animal model, a flour beetle, to examine what specific reproductive features change before different groups become reproductively isolated, and whether the competition to reproduce can also play an important role. In this beetle (a very important food pest), many different strains have been isolated by humans in laboratories for up to 60 years. Tests between different strains shows that they have started to become reproductively isolated, even though they seem very similar from the outside to their original ancestor species. We will measure sperm, egg, and male and female reproductive tract features to see which traits cause reproductive isolation, and therefore play a key role in 'speciation'. Males deposit sperm in the female tract, but then the sperm from many different males are stored by the female for many weeks in a special storage organ, while she uses them to fertilize her eggs. The storage organ is especially variable between strains, and therefore likely to play a key role because different males' sperm must be perfectly adapted to living in this organ, and going on to successfully fertilize her eggs. We know from preliminary microdissections that there is much variation in all these reproductive traits, but not in non-reproductive traits, so there is a good possibility that we will be able to identify the precise mechanism of reproductive isolation.

In addition to these reproductive trait measures, we will examine whether the universal competition to reproduce (which all individuals must go through) causes an even faster rate of reproductive isolation, and therefore greater differences between strains in reproductive traits. This competition, known as 'sexual selection', is a key force because it controls which individuals get their genes in the next generation. We will keep different populations under different levels of sexual selection (by changing the levels of competitions between males to have offspring) and then examine how they have evolved after 20 generations. Our project will therefore hopefully identify which reproductive traits lead to reproductive isolation, and therefore a new species, and also examine whether sexual selection can drive this speciation even faster.
Effective start/end date1/05/0430/09/08


  • Natural Environment Research Council: £240,059.00