What Explains the Genetic Diversity of an Iberian Grasshopper? Ice, Ice, Baby
By Melissa Mayer
The Pleistocene Epoch began 2.6 million years ago and was marked by wild climate swings that caused glaciers to advance and recede—sometimes covering huge swaths of the northern hemisphere and changing important habitats.
A study published last week in Insect Systematics and Diversity looks at the long-lasting effect of the last glacial maximum on a common Iberian grasshopper, Omocestus panteli, that enjoys a wide range of habitats and elevations. It turns out that today’s genetic makeup of O. panteli, sometimes called Pantel’s grasshopper, is best explained by the way populations of the grasshoppers were split up during the last glacial period.
Common Grasshopper, Big Data
The research team was drawn to the O. panteli grasshopper precisely because of its broad range. Most previous genetic research looked at narrowly distributed grasshoppers like alpine grasshoppers, which were driven down to the valleys and lowlands when glaciers covered the mountains. “The consequences of ice ages on species distributed across a wide variety of habitats and climate gradients are less obvious and difficult to predict: This was the main motivation for our study,” says lead author Joaquín Ortego, Ph.D., of the Department of Integrative Ecology at Estación Biológica de Doñana in Seville, Spain. The study is published as part of a new special collection in Insect Systematics and Diversity titled “Advances in Analysis of Spatial Distributions of Intra-Species Genetic Variation in Arthropods.”
The team collected O. panteli grasshoppers by sweep netting and preserved the samples in vials of ethanol. Then, they extracted the DNA for sequencing. While Ortego loves fieldwork—”I am always thinking about the next sampling trip!” he says—he also likes the challenge of analyzing the genomic data. “[It] is something I personally enjoy but often takes a long time given the huge amount of data that we can now generate thanks to high-throughput sequencing technologies developed in the last years,” he says. “The obvious advantage is that a high amount of genomic data allows us to get more resolution and be more confident about our results and inferences.”
The team determined that the grasshopper population has significant genetic subdivisions that can’t be explained by environmental factors or geographic barriers that exist today. Instead, these patterns point to the last glacial maximum—the time when the ice was at its peak about 21,000 years ago. At that time, O. panteli was likely even more common in terms of overall distribution, but swaths of unsuitable habitat broke up populations of the grasshopper and disrupted gene flow for long periods.
Data analysis showed three main clusters for genomic variation, with those populations localized in northwestern, central-southern, and northeastern Iberia. The limits imposed by the glaciers plus the grasshopper’s short generation time appear to explain the clustering.
Those populations can now interbreed and admix in places where they contact each other, but this hasn’t been enough to break down the genetic divisions so far. The grasshopper is very small—females are under 23 millimeters and males are under 17 millimeters—and their size may have played a role in limiting how far they disperse and interbreed. Plus, some of the grasshoppers aren’t great fliers. “Collectively, these factors contribute to speed up the accumulation of genetic differences among isolated populations over time in comparison with organisms presenting long generation times and high capacity to move through large geographical distances,” says Ortego.
Ortego’s study is an intriguing look back at how the last ice age affected the distribution and genomic diversity of O. panteli grasshoppers today. That data is also a helpful tool for looking forward—especially if human-driven climate change disrupts the planet’s normal cycle of ice ages in the future.
“Investigating how species responded to past climate changes can provide us with key information to understand their future dynamics under the ongoing scenario of climate warming,” says Ortego. “This can help to identify which particular species or ecosystems would be more vulnerable to climate change and, thus, should be the focus of conservation actions aimed at preventing the loss of biodiversity and the multiple services that it provides.”
Insect Systematics and Diversity
Melissa Mayer is a freelance science writer based in Portland, Oregon. Email: email@example.com.
Ortego photo by Yolanda De La Calle