- Email: [email protected]
Butterflies evolve to thwart male killers
DR SYLVAIN CHARLAT
This week– THIS WEEK 34 YEARS AGO
Butterflies evolve to thwart male killers
16 | NewScientist | 26 August 2006
060826_N_p16_p17.indd 16
AT
males have likely appeared on numerous occasions. Hornett’s team were studying a strain of male-killing Wolbachia that infects a widespread species of tropical butterfly, Hypolimnas bolina, when they discovered an unusual pattern: the strain killed all the male offspring of infected Polynesian butterflies, but butterflies from south-east Asia infected with the same strain produced male and female offspring in equal numbers. To understand why, the team carried out controlled breeding experiments between butterflies from the two regions. They found that Wolbachia from Polynesia, which usually kill males, did not do so in hybrid butterflies. The normally ineffectual Wolbachia from south-east Asia also failed
IST
NT
“It may be that male-killing bacteria have had a fairly significant part in the evolution of many insect species”
CELEBR
A BACTERIUM that slaughters the male offspring of its insect hosts has now provided a clear example of natural selection in action. The male-killing bacterium is a strain of Wolbachia, a widespread species that passes from one generation to the next in eggs but not sperm. Wolbachia strains infect an estimated 20 per cent of all insect species. Since males represent a dead end for the bacteria, they have evolved a variety of tricks to favour the females of their host species, including converting males into females, preventing males from being born and even killing male offspring outright (New Scientist, 16 October 1999, p 44). This presents a clear challenge to the insects, and Emily Hornett, an evolutionary biologist at University College London, and her colleagues have shown that they are able to develop evasive strategies very quickly. The findings also imply that bacterial strategies for dispatching
No drugs, no sports teams “If we were informed that we could not select an athlete taking steroids, we simply wouldn’t have a team.” This recent comment by Dr Pat O’Shea, an exercise physiologist and member of the US Olympic Weightlifting Committee, summarises the considerable increase in the use of anabolic steroids by athletes in recent years. Athletes now either take them, or desist and feel frustrated about possible unfair competition with those who do. Many other drugs are now used, openly or secretively, in the dressing room and on the sports field. A recent report states that a spot check of the Delaware State University football –Genes for the boys– team showed that about a fifth of the players had been taking drugs. to kill male hybrid butterflies. The pressures of modern professional However, when these infected sport make it likely that such hybrids were repeatedly medication will increase further. backcrossed with Polynesian As the games in Munich draw closer, butterflies, progressively diluting is the Olympic ideal of unfettered the contribution of Asian genes, competition between natural skills the crosses produced fewer and realistic any more? Total fairness is fewer male offspring (PLoS an illusory goal which would restrict Biology, vol 4, p e283). events to competitors with similar The pattern suggests that genomes, environmental background, Wolbachia retains its male-killing coaches and opportunities. That being potential in both regions, but the so, why ban drugs any more than Asian butterflies have evolved a special diet or training methods? single, dominant gene to suppress Governments and doctors have a this. What is not known is exactly responsibility to discourage people how Wolbachia kills males, how from consuming dangerous the butterfly’s suppressor gene substances. But beyond that, need works, or indeed what the gene is. there be any restrictions on the use of A study in the 1960s drugs taken to promote athletic skill? documented male-killing in Asian As things are, we face the ludicrous Hypolimnas, which suggests that spectacle of scientists devising ever this suppressor gene must have more sensitive monitoring tests to spread through the population in detect drugs while others play the 40 years since. “It’s a very nice molecular roulette to devise new drugs example of how quickly natural that escape detection. selection can act,” says co-author Greg Hurst. From New Scientist, 24 August 1972 This means many insects might have gone through a YEARS phase in which Wolbachia killed G 50 IN its males. “It may be that male-killers have had a fairly significant part in the evolution of many insect species,” says IE OF N E W S C Mike Majerus of the University of Cambridge. Bob Holmes ● www.newscientist.com
22/8/06 12:02:30 pm
This week– THIS WEEK 34 YEARS AGO
Butterflies evolve to thwart male killers
16 | NewScientist | 26 August 2006
060826_N_p16_p17.indd 16
AT
males have likely appeared on numerous occasions. Hornett’s team were studying a strain of male-killing Wolbachia that infects a widespread species of tropical butterfly, Hypolimnas bolina, when they discovered an unusual pattern: the strain killed all the male offspring of infected Polynesian butterflies, but butterflies from south-east Asia infected with the same strain produced male and female offspring in equal numbers. To understand why, the team carried out controlled breeding experiments between butterflies from the two regions. They found that Wolbachia from Polynesia, which usually kill males, did not do so in hybrid butterflies. The normally ineffectual Wolbachia from south-east Asia also failed
IST
NT
“It may be that male-killing bacteria have had a fairly significant part in the evolution of many insect species”
CELEBR
A BACTERIUM that slaughters the male offspring of its insect hosts has now provided a clear example of natural selection in action. The male-killing bacterium is a strain of Wolbachia, a widespread species that passes from one generation to the next in eggs but not sperm. Wolbachia strains infect an estimated 20 per cent of all insect species. Since males represent a dead end for the bacteria, they have evolved a variety of tricks to favour the females of their host species, including converting males into females, preventing males from being born and even killing male offspring outright (New Scientist, 16 October 1999, p 44). This presents a clear challenge to the insects, and Emily Hornett, an evolutionary biologist at University College London, and her colleagues have shown that they are able to develop evasive strategies very quickly. The findings also imply that bacterial strategies for dispatching
No drugs, no sports teams “If we were informed that we could not select an athlete taking steroids, we simply wouldn’t have a team.” This recent comment by Dr Pat O’Shea, an exercise physiologist and member of the US Olympic Weightlifting Committee, summarises the considerable increase in the use of anabolic steroids by athletes in recent years. Athletes now either take them, or desist and feel frustrated about possible unfair competition with those who do. Many other drugs are now used, openly or secretively, in the dressing room and on the sports field. A recent report states that a spot check of the Delaware State University football –Genes for the boys– team showed that about a fifth of the players had been taking drugs. to kill male hybrid butterflies. The pressures of modern professional However, when these infected sport make it likely that such hybrids were repeatedly medication will increase further. backcrossed with Polynesian As the games in Munich draw closer, butterflies, progressively diluting is the Olympic ideal of unfettered the contribution of Asian genes, competition between natural skills the crosses produced fewer and realistic any more? Total fairness is fewer male offspring (PLoS an illusory goal which would restrict Biology, vol 4, p e283). events to competitors with similar The pattern suggests that genomes, environmental background, Wolbachia retains its male-killing coaches and opportunities. That being potential in both regions, but the so, why ban drugs any more than Asian butterflies have evolved a special diet or training methods? single, dominant gene to suppress Governments and doctors have a this. What is not known is exactly responsibility to discourage people how Wolbachia kills males, how from consuming dangerous the butterfly’s suppressor gene substances. But beyond that, need works, or indeed what the gene is. there be any restrictions on the use of A study in the 1960s drugs taken to promote athletic skill? documented male-killing in Asian As things are, we face the ludicrous Hypolimnas, which suggests that spectacle of scientists devising ever this suppressor gene must have more sensitive monitoring tests to spread through the population in detect drugs while others play the 40 years since. “It’s a very nice molecular roulette to devise new drugs example of how quickly natural that escape detection. selection can act,” says co-author Greg Hurst. From New Scientist, 24 August 1972 This means many insects might have gone through a YEARS phase in which Wolbachia killed G 50 IN its males. “It may be that male-killers have had a fairly significant part in the evolution of many insect species,” says IE OF N E W S C Mike Majerus of the University of Cambridge. Bob Holmes ● www.newscientist.com
22/8/06 12:02:30 pm