A lack of sex may be the first step toward extinction for a species, according to recent research from Imperial College London.
The researchers studied Penicillium marneffei, a fungus that is found in only certain areas of Southeast Asia. They discovered that despite P. marneffei's ability to spread widely on air currents, it is unable to establish a foothold in new areas. This, researchers say, may ultimately be due to its sexual habits.
'We believe the failure of P. marneffei to adapt to new environments is because the fungus has largely dispensed with sexual reproduction. Without sex, you will not have the mixing of genes it causes, something all organisms need in order to be able to adapt to new environments,' explained researcher Matthew Fisher, a lecturer in molecular epidemiology, the study of disease in groups of organisms.
Instead, P. marneffei has found itself in the genetically unenviable position of reproducing by creating clones of itself via 'asexual' reproduction. This involves a single organism producing a genetically identical offspring through mitosis, the cell-copying process that is more commonly used to grow and repair an organism's tissues. Sexual reproduction, by comparison, uses half the genes from each parent to create a genetically novel offspring through a type of cell replication called meiosis.
Mitosis enables the severed arm of a starfish to grow into another, independent starfish. Normally, however, starfish reserve this cloning method for emergencies and practice sexual reproduction for everyday species propagation.
The ability to use either sexual or asexual reproduction can be quite an advantage for organisms, according to Christina Hull, assistant professor of biomolecular chemistry at UW-Madison.
'Many organisms can go both ways, although some might not want to undergo sexual reproduction due to the energy expenditure involved; asexual reproduction is very simple in comparison, much more so than sexually,' Hull said. 'For microbes especially, it is quite hard. They have to find a partner and undergo sexual reproduction, bringing their genetic material together; it is a huge undertaking.'
The inherent difficulties in sex, and the obvious advantages of asexual reproduction, have caused scientists to wonder at the overwhelming prevalence of sexual species on Earth.
Every living organism exists with a drive to pass on its own genes. Given this drive, asexual reproduction appears ideal'the population grows much more quickly and all the genes of every individual are passed on. A study conducted at the University of California-Santa Barbara sought to identify why sexual species out-survive their asexual brethren in spite of these benefits to this mode of reproduction.
The researchers studied two populations of fruit flies'one that was genetically modified to be asexual and one that was left sexual. They then tracked the adoption of a beneficial red eye mutation in each population. The asexual fruit flies adopted the red eye mutation at a slow rate that eventually tapered off. In contrast, the sexual fruit flies quickly adopted the useful trait until the entire population was red-eyed.
These results led the researchers to conclude that sexual reproduction allows for faster evolution. Asexual reproduction, however, as the Imperial College London team concluded for the unfortunate P. marneffei, seems to lead only to stagnation and eventual extinction.
