When the Asian tiger mosquito ( Aedes albopictus ) arrived in the US in the 1980s, the invasive bloodsucker only took a year to spread out of Houston St. Louis. New research from the Washington University in St. Louis shows that the mosquitoes at the northern border of their current range successfully use time capsule-like eggs to survive conditions colder than those in their home area.
The northern mosquitoes have adapted to colder winters compared to their southern ones. This new indication of rapid local adaptation may have an impact on efforts to curb the spread of this invasive species, which is considered to be the "competent vector" of many human-related pathogens, including Zika, Chikungunya, and Dengue viruses. The work was published in the August 21 issue of the Journal of Applied Ecology .
"All of this happened within 30 years," said biologist Kim Medley, director of the Tyson Research Center and first author of the new study. "This disease vector has developed rapidly to adapt to the United States, and the fact that this has occurred at an area boundary may indicate that the species may be crawling further north."
Mosquitoes respond to the shortened days Winter's onset is signaled by the laying of diapause eggs – literally delayed development eggs. These special eggs contain a fertilized embryo that is almost hibernating and has a very slow metabolism. The result is almost like a mosquito capsule.
The ability to produce eggs that can wait until hatching is nothing new. This technique helps mosquitoes to survive the winter cold, but also works in dry conditions. All mosquitoes lay their eggs in or near stagnant water, and the larvae hatch in stagnant water. In between, however, they can survive the drying out.
Diapause eggs, however, are different from normal eggs. Previous studies had shown that northern mosquitoes lay more diapause eggs than their southern relatives. What the researchers did not know was how these eggs actually behave in the conditions they are prepared for.
For this new field experiment, Medley and her team, including Katie M. Westby, a postdoctoral fellow at Tyson Research Center, collected live mosquito eggs and larvae from cities near the habitat center they invaded (Huntsville, Ala Macon, Ga.; Beaufort, SC), as well as from the approximate northern edge of their US distribution area (Peoria, Illinois); Columbus, Ohio; and Harrisburg, PA.) The researchers hatched and bred these mosquitoes and their subsequent generations in batches in the laboratory.
Then it was time to catch a cold. The researchers exposed the mosquitoes to shorter light periods to signal the onset of winter. They collected the diapause eggs that produced the mosquitoes and then sent a lot of eggs to survive real winters in four different locations: field sites on the northern edge and at the core of their current range; in an air-conditioned laboratory site, which represented the "optimal" winter conditions in the homelands of mosquitoes in Japan; and in a location in the far north of Wisconsin, which is well outside the current range of mosquitoes.
After this real winter was over, the researchers took the eggs back to the lab and incubated them.
"We counted all the eggs to see how many survived winter in all these places," said Medley. "We've learned that the northern mosquito's diapause eggs survived the winters in the north much better than the eggs of the southern mosquitoes."
"In the winter in the southern area, they all did not object," she said, as did those in the chamber As for Wisconsin, well …
"No one has survived this Wisconsin winter," said Medley.
While the Wisconsin conditions are too harsh for these mosquitoes – at least now – Medley is special Interested in the changes she observes at the very edge of survival.
"These northern mosquitoes produce much more diapause eggs," Medley said, "now we know that these eggs cut much better in winter too. "
What Medley and her team have learned is not only important for this species, but also for ecologists who are studying how animals adapt to new conditions and shift the boundaries of their historical realms.
Based on theory "We expect the populations at the boundaries of the range to be small, fragmented and of low genetic diversity," she said. "It is thought that these populations do not have the demographic and genetic robustness to adapt, and thus remain in that state of mismatch.
" This may not be the case with this species, "Medley said.
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Mosquitoes hit the northern border with time capsule eggs to survive the winter (2019, 21st August)
August 21, 2019 retrieved
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