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December 31, 2009

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Mosquito lovers “sing” in harmony

Dec. 31, 2009
Courtesy Cell Press
and World Science staff

The mos­qui­toes re­spon­si­ble for most ma­lar­ia deaths find mates by us­ing their wing­beats to pro­duce tones that har­mo­nize with those of their part­ners, a study has found.

The in­sect lovers can’t find each oth­er with­out “sing­ing” in per­fect har­mo­ny, ac­cord­ing to the re­port, pub­lished on­line Dec. 31 in the re­search jour­nal Cur­rent Bi­ol­o­gy.

An Anoph­e­les gam­biae mosquito. (Image courtesy WHO/TDR/Stam­mers)
“Ev­ery­one must be fa­mil­iar with the mad­den­ing whine a mos­qui­to makes as it hones in for a bite,” said Ga­bri­el­la Gib­son of the Uni­vers­ity of Green­wich at Med­way in the U.K., an au­thor of the report.

“Many of us have won­dered why it makes its pres­ence so ob­vi­ous,” she added, but it’s probably be­cause the ad­van­tages in terms of mate at­trac­tion out­weigh “the risk of be­ing squashed by the rare host that is still awake at feed­ing time.”

The main ma­lar­i­a-trans­mit­ting mos­qui­tos form a group known as An­o­ph­e­les gam­biae. Al­though its mem­bers look es­sen­tially id­ent­i­cal, they ac­tu­ally com­prise sev­en spe­cies and sev­er­al forms of chro­mo­somes sets, Gib­son added, a di­vers­ity that gives the in­sects a re­mark­a­ble adapt­abil­ity.

The new find­ings help to ex­plain how each spe­cies avoids mat­ing with mem­bers of oth­er spe­cies, the re­search­ers said. This oc­curs even as some mos­qui­to groups, in­clud­ing the “M” and “S” forms found in Burk­ina Faso that were the sub­ject of the new stu­dy, trav­el to­geth­er in the same swarms.

Gib­son and col­leagues found that male and female mos­qui­toes har­mo­nize with each oth­er. Gib­son said that this is anal­o­gous to two par­tially deaf singer­s—one al­to and the oth­er so­pra­no—who can hear low tones, but per­haps not their own or each oth­er’s songs. In­stead, they lis­ten to the dis­so­nance if one or the oth­er goes a bit sharp or flat, which they can get rid of by ad­just­ing their re­spec­tive tones un­til the dis­so­nance di­min­ishes to noth­ing.

“They can do this even if they each sing a dif­fer­ent note, say a ‘mid­dle C’ and a ‘G’ four tones high­er,” said co-author Ian Rus­sell of the Un­ivers­ity of Sus­sex, U.K. “By lis­tening and subtly al­ter­ing their pitch to min­i­mize the dis­so­nance, they achieve their goal of ‘sing­ing’ in a per­fect har­mo­ny that we, but not they, can hear.”

The re­search­ers found that two mos­qui­toes don’t har­mo­nize suc­cess­fully if they are of the same sex or if they are not the same type of mos­qui­to. They might try for a while, Gib­son ex­plained, but they eventually give up. 

“Even the most ‘lowly crea­tures,’ such as mos­qui­toes, have highly evolved neu­ro­sen­sory sys­tems,” not­ed Gib­son. These en­a­ble them to dis­tin­guish “oth­er types of mos­qui­to that are so closely re­lat­ed we need to an­a­lyze their DNA to tell them apart.”

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The mosquitoes responsible for the vast majority of malaria deaths find mates by using their wingbeats to produce tones that harmonize with their partners’, a study has found. The insect lovers can’t find each other without “singing” in perfect harmony, according to the report, published online Dec. 31 in the research journal Current Biology. “Everyone must be familiar with the maddening whine a mosquito makes as it hones in for a bite,” said Gabriella Gibson of the University of Greenwich at Medway in the U.K. “Many of us have wondered why it makes its presence so obvious,” she added, but it’s probably because the advantages in terms of mate attraction outweigh “the risk of being squashed by the rare host that is still awake at feeding time.” The predominant malaria-transmitting mosquitos form a group known as Anopheles gambiae. Although members of this group look essentially the same, they actually comprise seven species and several forms of chromosomes sets, Gibson added, a diversity that gives the insects a remarkable adaptability. The new findings help to explain how each species avoids mating with members of other species, the researchers said. This occurs even as some mosquito groups, including the “M” and “S” forms found in Burkina Faso that were the subject of the new study, travel together in the same swarms. Gibson and colleagues found that male and female mosquitoes harmonize with each other. Gibson said that this is analogous to two partially deaf singers—one alto and the other soprano—who can hear low tones, but perhaps not their own or each other’s songs. Instead, they listen to the dissonance if one or the other goes a bit sharp or flat, which they can get rid of by adjusting their respective tones until the dissonance diminishes to nothing. “They can do this even if they each sing a different note, say a ‘middle C’ and a ‘G’ four tones higher,” said co-author Ian Russell of the University of Sussex, U.K. “By listening and subtly altering their pitch to minimize the dissonance, they achieve their goal of ‘singing’ in a perfect harmony that we, but not they, can hear.” The researchers found that two mosquitoes don’t harmonize successfully if they are of the same sex or if they are not the same type of mosquito. They might try for a while, Gibson explained, but they never find that harmony and eventually give up trying. “Even the most ‘lowly creatures,’ such as mosquitoes, have highly evolved neurosensory systems,” noted Gibson. These enable them to distinguish “other types of mosquito that are so closely related we need to analyze their DNA to tell them apart.”