Some researchers in biology believe that as global temperatures rise, animals may shrink in size to handle heat better. This reduction in size could apply to warm-blooded animals, but what about cold-blooded ones like insects? Thanks to a collection of grasshoppers gathered 65 years ago, scientists found that certain species, especially those that survive winter as young nymphs, have actually increased in size over the years, aided by the sooner arrival of spring. Conversely, other grasshopper species have gotten smaller.
With insect populations dwindling globally, often referred to as an “insect apocalypse,” scientists are eager to understand how these small creatures are adapting to a warming climate and to forecast the future winners and losers in this scenario.
A recent examination of grasshoppers in Colorado indicates that the situation is complex, but biologists have much of the insight necessary to make informed predictions and prepare for the repercussions.
This research, published on January 30 in the journal PLOS Biology, stemmed from the unexpected discovery of 13,000 grasshoppers collected from a single Colorado location between 1958 and 1960 by a University of Colorado Boulder biologist. After the biologist’s unexpected passing in 1973, his son saved the collection from neglect and contributed it to the CU Museum. It remained untouched until César Nufio, a postdoctoral researcher, found it again in 2005 and began curating it alongside conducting new surveys to gather more grasshoppers.
The new specimens enabled Nufio and his team — which includes Caroline Williams from the University of California, Berkeley; Lauren Buckley from the University of Washington in Seattle; and postdoctoral fellow Monica Sheffer, affiliated with both institutions — to evaluate how climate change has influenced the sizes of six grasshopper species over the past 65 years. Since insects are cold-blooded and do not self-generate heat, they are more reactive to environmental temperature changes, which affects their growth and development rates.
Despite various theories suggesting that animals might shrink in size due to rising temperatures, the researchers found that some grasshopper species have actually increased in size over the decades. These species have benefited from an earlier spring and increased food availability. However, this advantage is mainly seen in those that survive winter as juveniles (known as nymphal diapause); species that emerge from eggs in spring (egg diapausers) did not experience the same benefits and, as a result, have become smaller over time, likely due to dwindling vegetation.
“This research highlights that while certain species may thrive, others will struggle; moreover, subgroups within a species will respond differently based on their environmental situation,” Sheffer explained.
The team was able to anticipate many of these outcomes by examining the grasshoppers’ life cycles and the ecological conditions of their environment.
“We reviewed everything known about the area, including altitude effects and potential responses of different grasshopper species, drawing on our extensive understanding of their life histories. Though not all predictions were confirmed, many were,” remarked Williams, the John L. and Margaret B. Gompertz Chair in Integrative Biology at UC Berkeley.
“Identifying which species are likely to persevere or decline in a changing climate has been quite complex,” Buckley noted. “We hope this research offers insights that can enhance our predictive capabilities and allow us to better address ecosystem changes due to climate change.”
Rescued grasshoppers
The grasshopper collection, now 65 years old, was put together by entomologist Gordon Alexander from CU Boulder over three summers. He meticulously collected and mounted specimens from multiple sites in the Rocky Mountains near Boulder while documenting the timing of six life stages of the grasshoppers. Following Alexander’s tragic plane crash in 1973, the specimens remained stored in 250 neatly organized wooden boxes until Nufio discovered them in 2005 and realized their potential if compared against contemporary specimens.
Museum collections are proving vital for research into climate change over time, as demonstrated by a survey of mammals, birds, reptiles, and amphibians conducted between 1904 and 1940 by Joseph Grinnell of UC Berkeley’s Museum of Vertebrate Zoology. More recent surveys revisiting Grinnell’s sites a century later have helped biologists document the impacts of climate change on wildlife in California.
Nufio and his colleagues eventually gathered approximately 17,000 new grasshopper specimens from the same or similar locations around Boulder. While this paper is the first to document the size changes of grasshoppers from 1960 to 2015, the authors also drew upon previous experimental studies to comprehend the observed patterns.
The grasshoppers belong to the Acrididae family, commonly known as short-horned grasshoppers. Most are general grazers, though some are specialized for specific types of grasses. Two species (Eritettix simplex and Xanthippus corallipes) undergo nymphal diapause, maturing as early as May. Two others (Aeropedellus clavatus and Melanoplus boulderensis) are early season egg diapausers, maturing in mid-June, while the remaining two (Camnula pellucida and Melanoplus sanguinipes) are late season egg diapausers, maturing in late July.
The researchers observed that nymphal diapausers showed size increases at lower elevations, around 6,000 feet, while both early and late season emergers from overwintering eggs shrank in size over the decades at these elevations.
“For those that emerge in late August, when conditions are very dry and hot, we observed significant negative effects due to climate change,” Williams mentioned.
However, the researchers were surprised to find that none of the species increased in size at higher elevations up to approximately 13,000 feet, despite higher summer temperatures associated with climate change in these areas. This might be due to snow inhibiting early vegetation growth at higher elevations, leading to diminished food sources. The results align with earlier experiments where grasshoppers were confined at various elevations to evaluate their adaptability to changes in heat and dryness.
“The data support the notion that grasshoppers can either capitalize on warming by growing larger and emerging earlier or suffer stress and shrink,” Buckley stated.
Similar trends have been observed in other studies by Buckley focusing on butterflies.
“We find a comparable trend with butterflies, which is encouraging because by understanding basic biological principles, we can significantly enhance our ability to predict responses to climate change,” she explained.
The research team continues to collaborate to better understand the metabolic, biochemical, and genetic changes so crucial for the observed alterations in growth size.
“Utilizing these museum collections allowed us to compare the exact same sites over time — there were no changes in land use during this 60-year warming period, and we employed identical methodologies,” Williams remarked. “Having access to these unique historical specimens has enabled us to examine changes over time.”
Other contributors to the study include Julia Smith from the University of Washington, Simran Bawa from UC Berkeley, and Ebony Taylor, Michael Troutman, and Sean Schoville from the University of Wisconsin, Madison. The research received support from the National Science Foundation (DEB-1951356, DEB-1951588, DEB-1951364).
