Rising Temperatures Could Stunt Growth, Threaten Survival of Common Damselfly
By Andrew Porterfield
Current climate change projections show that air temperature in the Great Plains of North America could rise between 1.4 and 7.2 degrees Celsius by 2090 and that a very likely scenario could involve an average temperature 2-4 degrees higher than today.
These numbers, based on models that recent research has been shown to be quite accurate, may not bode well for ecosystems, plants, and animals living in the Great Plains.
One geographic feature in that region that could be acutely affected is the playa—a massive wetland unique to Texas and the southern plains that is home to diverse flora and fauna. The playas, individual lakes that intermittently dry up and recharge with rainfall, number 80,000 in the southern plains states and about 18,000 in Texas, and they supply the Ogallala aquifer, the country’s largest. If temperatures increase enough, the playas could permanently dry up or become so hot that they no longer support life.
One insect that calls the playas home is Enallagma civile, a narrowwinged damselfly sometimes known as the familiar bluet. This insect is a generalist (living in a variety of habitats and on a variety of food) and predatory. Its ability to survive in the face of rising temperatures could provide an indicator of the effects of climate change in this area.
In one of the first studies to look at climate change effects on the common damselfly, Scott Starr, Ph.D., then a doctoral student at Texas Tech University (and now an instructor of biology at South Plains College) and Nancy McIntyre, Ph.D., professor of landscape and community ecology at Texas Tech, measured the survival of eggs and nymphs, adult morphology, stadia, days for egg hatching, and time taken from egg to adult in water at increasing temperatures. Their results, which showed both positive and negative implications for the damselfly, was published in December in Environmental Entomology.
Starr and McIntyre collected 77 adult E. civile females from a public park in Lubbock, Texas, and placed them in chambers that contained about 2.5 centimeters of water. Eggs were collected and reared at various water temperatures—26, 32, 38, or 41 degrees Celsius—and following natural day/night heating and cooling cycles. Of those 77 females, 16 laid a total of 2,402 eggs.
Significantly fewer eggs hatched at 41 degrees than at 26, 32, or 38 degrees. Egg survivorship at 41 degrees was 25 percent, versus 60 to 65 percent for other temperatures. Eggs in cooler temperatures (26 and 32 degrees) took longer to hatch.
For nymphs, those reared in hotter temperatures showed greater mortality. Nymphs raised in 41-degree water showed 100 percent mortality by the experiment’s fourth day, and nymphs raised at 38 degrees showed 15 percent survival by day 8. Nymphs raised at 26 degrees had 38 percent survival, and 32 degrees had 31 percent survival.
Adults raised at 26 and 32 degrees had longer bodies and wider heads than those raised at 38 degrees (none of the 41 degree-nymphs survived).
On the other hand, ontogenetic development was increased in warmer waters. At 32 degrees, emergence occurred at about 26 days after hatching, while emergence at 26 degrees occurred at day 33.
These results provide vital information on how an umbrella species like E. civile could indicate the changes in ecological systems and how biodiversity could change due to warmer climates overall. While Starr and the researchers suspected that results would be negative, the positive effects of ontogenetic development were surprising. “This means that there may be more generations of E. civile possible,” says McIntyre.
Since E. civile is a more generalist insect and produces several generations a year, it could possibly adapt to changes in climate, if those changes aren’t very sudden and if water temperatures don’t approach 41 degrees. “E. civile has a better chance of adapting because of its current life history,” says Starr. “Because it is so broadly found across North America, there is a good likelihood that some populations of the species may be able to adapt as long as there is still water available and the changes do not happen too quickly.”
While their study made significant inroads into understanding insect adaption to climate, much more needs to be studied, the researchers note. “If there are more generations per year, there are opportunities for evolutionary change to take place (via mutation or natural selection),” Starr says. “As always, the more data we can collect about different species and the impact that climate warming is having on them, the better.”
Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.