Sex for reproduction of a species requires a male and female, but now biologists believe they have found the reason that males exist in most complex life forms. Researchers examined beetles over the course of 50 generations to study how they chose mates.
Sexual reproduction is a highly inefficient way of producing offspring, as only half of all children (daughters) will be able to reproduce. Also, in many species, males contribute little, if anything, to raising the young. Together, these facts led many biologists to question why most species produce so many males, or any at all.
"We wanted to understand how Darwinian selection can allow this widespread and seemingly wasteful reproductive system to persist, when a system where all individuals produce offspring without sex - as in all-female asexual populations - would be a far more effective route to reproduce greater numbers of offspring," Matt Gage of the University of East Anglia (UEA) said.
Tribolium flour beetles were examined in various mating scenarios, from just two beetles held together providing zero competition, to collections where males outnumbered females nine to one. Following six to seven years of study, the health of the various populations were examined through their genetic record. Controlled inbreeding was then used on the insects to measure the effect of genetic defects on the populations.
Researchers found that beetles raised in environments where males greatly outnumbered females were better than other groups at withstanding genetic damage. Within 10 generations, groups of beetles born from populations with little or no sexual competition all went extinct. The situation was even worse for the monogamous beetles, who were all wiped out within just eight generations.
The study revealed that sexual selection, in which males compete with one another for access to females, plays an important role in maintaining the health of populations. Healthier males tend to win such contests over their rivals, spreading their genetic material more often. This results in better health for the species as a whole over time.
"To be good at out-competing rivals and attracting partners in the struggle to reproduce, an individual has to be good at most things, so sexual selection provides an important and effective filter to maintain and improve population genetic health," Gage said.
Without males, genetic errors would continually build up until a species no longer existed, investigators determined. With sexual selection maximized, groups of beetles were able to withstand 20 generations of inbreeding.
Research into sexual selection as a means of explaining the existence of males was detailed in the journal Nature.
Photo: Tony Alter | Flickr
