As insect populations dwindle globally — in what some refer to as an “insect disaster” — biologists are striving to comprehend how these six-legged organisms are reacting to a warming climate and to forecast the long-term victors and victims.

A recent investigation into grasshoppers in Colorado’s mountainous regions illustrates that, although the solutions are complex, biologists possess much of the information required to make these forecasts and prepare for the repercussions. The research, released on Jan. 30 in PLOS Biology, evaluates thousands of grasshoppers gathered in Colorado between 1958 and 1960 against contemporary samples.

“Gaining insight into which species are likely to thrive or decline due to climate change has been particularly complicated,” stated corresponding author Lauren Buckley, a biology professor at the University of Washington. “We hope that this research helps clarify some principles which could enhance predictions and allow us to devise appropriate responses to ecological shifts induced by climate change.”

By juxtaposing museum specimens with newly gathered insects, the research group evaluated the effects of 65 years of climate alteration on the sizes of six grasshopper species. Since insects are ectothermic and do not produce their own heat, their body temperatures, developmental rates, and growth are more responsive to environmental warming.

Despite considerable speculation that animals will shrink in size to counteract heat stress amid climate change, the research revealed that certain grasshopper species actually became larger over the years, capitalizing on an earlier spring to nourish themselves on vegetation.

Growth was observed only in species that spent the winter as juveniles and thus could gain an advantage by feeding early in the spring. Conversely, species that hatched in spring from autumn-laid eggs lacked this benefit and decreased in size over the years, presumably due to the vegetation wilting earlier in the summer.

“This study underscores that there will undoubtedly be species that emerge as winners and others as losers, but sub-groups within those species’ populations, based on their ecological or environmental circumstances, will exhibit varying responses,” remarked co-author Monica Sheffer, a postdoctoral researcher at both UW and the University of California, Berkeley.

The authors of the current study predicted much of this based on the life cycles of grasshoppers and the site’s environmental conditions.

“We reviewed everything that was understood about the system, including elevation gradients and how these could influence responses, as well as how different grasshoppers might react, leveraging our extensive understanding of their natural histories. While not every prediction was validated, many were indeed confirmed,” elucidated co-author Caroline Williams from the University of California, Berkeley.

The 65-year-old grasshopper collection was initially assembled over three summers by the late entomologist Gordon Alexander from the University of Colorado Boulder. He not only gathered and mounted specimens from Rocky Mountain plots close to Boulder but also chronicled the timing of six different life stages of the grasshoppers. His tragic passing in a plane crash in 1973 left the neatly pinned specimens in 250 wooden boxes in a state of uncertainty.

The collection lay dormant until 2005, when César Nufio, then a postdoctoral fellow at CU Boulder, undertook the curation of the collection and initiated a re-examination of the same sites to gather additional grasshoppers.

Nufio and several others eventually acquired approximately 17,000 new grasshopper specimens from identical or similar locations. While this paper marks the first report on grasshopper size variations between 1960 and 2015, the authors conducted additional studies to clarify these patterns.

The insects belonged to a large category of inconspicuous grasshoppers from the Acrididae family known as short-horned grasshoppers. Most feed on a variety of plant types, although some have specialized diets in grasses. Two species (Eritettix simplex and Xanthippus corallipes) reach maturity as early as May; two others (Aeropedellus clavatus and Melanoplus boulderensis) reach maturity in mid-June; and the final two (Camnula pellucida and Melanoplus sanguinipes) mature in late July.

The researchers discovered that the grasshopper species that reach adulthood in May increased in size at lower altitudes, around 6,000 feet, while the early and late-emerging species at these altitudes diminished in size over the decades.

“The data support the notion that grasshoppers may either capitalize on warming by growing larger and emerging sooner or conversely, experience stress and become smaller,” Buckley remarked.

“We would anticipate similar trends for grasshoppers residing in the mountains of Washington, although variations in seasonal timing due to late snowmelt in Washington state could affect their responses,” she further added.

Other experiments conducted by Buckley on butterflies in Colorado reflect similar patterns.

“We observe a quite comparable trend with butterflies, which gives me hope, as if we can apply fundamental biological principles, we substantially enhance our predictive capabilities regarding climate change responses,” Buckley stated.

At UW, Buckley’s research group is replicating surveys initiated in 1995 of cabbage white butterflies in Seattle and western white butterflies in central Washington to ascertain how these insects may have evolved over the past 30 years.

Buckley has also recently taken on the role of adjunct curator of entomology at the Burke Museum, where she intends to continue utilizing museum collections for ecological investigations.

Additional co-authors of this new study include Julia Smith, a biology graduate student at UW; Simran Bawa from UC Berkeley; and Ebony Taylor, Michael Troutman, and Sean Schoville from the University of Wisconsin, Madison. This research was supported by the National Science Foundation.

 

For additional information, contact Buckley at [email protected], Williams at [email protected], and Sheffer at [email protected].

This piece is derived from a UC Berkeley press announcement.

NSF funding: DEB-1951356, DEB-1951588, DEB-1951364