From pollinating flowers to enabling decomposition and supporting nutrient cycles, insects' abundance and biodiversity are critical for maintaining healthy ecosystems. However, recent studies showing population declines have raised alarm about how insects are coping with the modern world. Understanding whether recent observations are part of longer timescale trends can help inform global conservation efforts, and identify the reasons behind the so-called "Insect Apocalypse".
Published in Science, researchers from the Okinawa Institute of Science and Technology (OIST) used a community genomics approach to explore ant populations in the Fijian archipelago as a model system to understand insect biodiversity trends. By studying the genomics of museum collections, they were able to trace the ants' evolutionary relationships to explore their arrival to the islands and reconstruct the population history of the species.
Global conservation efforts rely on biodiversity monitoring, but often focus on larger photogenic animals, and on easier to monitor areas, like temperate habitats. However, it's widely suspected that many insect species are experiencing rapid population decline. We know that island systems are hotspots of biodiversity, so they are critical to study. Dr. Evan Economo, a Professor at OIST and the University of Maryland, and one of the senior authors on the paper, explains, "It can be difficult to estimate historical changes to insect populations, because with few exceptions, we haven't been directly monitoring populations over time. We take a novel approach to this problem by analyzing the genomes of many species in parallel from museum specimens collected recently. The genomes hold evidence of whether populations are growing or shrinking, allowing us to reconstruct community-wide changes."
What the researchers found is alarming; 79% of the endemic species (species found only in Fiji) are in decline, over a timescale which correlates with the arrival of humans to the islands. Meanwhile, ant species recently brought by humans are exploding in population. The largest proportion of declines are seemingly within the most recent few hundred years, coinciding with European contact, colonization, global trade and the introduction of modern agricultural techniques.
A community-wide approach
By focusing on the Fijian archipelago, a region of long-term interest to the researchers, they were able to get a broad, comprehensive overview of the population changes and colonization history of almost all the different ant species in the region. "Being closed, isolated ecosystems, islands are expected to feel the effects of human impact faster, so they are kind of a canary in the coal mine," notes Dr. Cong Liu, first author on this paper.
However, studying the populations of tropical islands is not without challenges. Often fieldwork can be extremely difficult, and it isn't easy to do continuous surveys. Therefore, instead of relying on real-time field monitoring, here the team used museum collections built across decades of fieldwork, including both the team's previous collection efforts and those by other entomologists.
Museumomics: reconstructing ant colonization
One challenge of using museum collections is that DNA degrades over time. Therefore, the researchers had to use special sequencing methods (museumomics) to compare small fragments of DNA. In this study, they sequenced samples of genomes from thousands of ants from over one hundred different confirmed ant species. Using these data, they identified 65 separate instances (colonization events) where new ant species came to the island. These ranged from natural colonization (i.e. arrival of the ants with no human involvement) millions of years ago, to recent human introduction after Fiji became part of global trade networks.
Building on this history, the researchers were able to use their population genetics models to identify the rise or decline in population of different ant groups throughout the Fijian archipelago, noting the decline of endemic species, as well as dramatic increases in population of non-native species in more recent years.
Island endemic species have often evolved traits that make them sensitive to environmental changes, including the arrival of new damaging species. "Most recorded extinctions have historically been from island systems," adds Dr. Liu.
Going beyond the archipelago
The team hopes that this work can act as inspiration for future work to continue building scientific understanding of insect populations, and to inform conservation efforts. "This study also highlights the importance of biodiversity and museum collections," explains Professor Alexander Mikheyev of the Australian National University, a senior author on this study. "As our scientific toolbox expands, there is more and more information that we are able to capture from biodiversity collections, so it's essential that we continue investing in and maintaining these vital resources."
The team are looking into this locally as well, to measure the biodiversity of Okinawan insect populations in real-time through acoustic monitoring and trapping as part of the Okinawa Environmental Observation Network (OKEON) .
"Insects are essential for the environment," emphasizes Prof. Economo. "As scientists, we need to play our part in their protection, and provide and analyze the relevant data to ensure the long-term integrity of our ecosystems".
