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Insects, such as flies, play a crucial role in their ecosystems but are heavily influenced by environmental temperature due to their cold-blooded nature. As such, they serve as effective indicators for assessing the effects of climate change on various animal behaviors and distributions. However, the mechanisms by which insects sense and react to temperature remain largely unexplored.
A recent study conducted by scientists at Northwestern University examined two distinct species of flies, each originating from varying climatic conditions. One species is found in the cool, high-altitude forests of Northern California, while the other thrives in the hot, arid deserts of the Southwest. Both species are relatives of the common laboratory fly, Drosophila melanogaster. The research revealed interesting differences in how these two flies perceive and respond to temperature.
The forest-dwelling flies exhibited a heightened avoidance of heat, potentially due to increased sensitivity in the molecular heat receptors located within their antennae. Conversely, desert flies were found to be attracted to heat, which may be linked to variations in the neural circuitry in their brains that processes sensory information related to temperature. This divergence in response is believed to reflect the evolutionary adaptations of each species to their specific thermal environments, tracing back to a shared ancestor that lived approximately 40 million years ago, shortly after the extinction of dinosaurs.
Published in the journal Nature, these findings enhance our understanding of how different species develop preferences for temperature and could offer insight into how climate change may affect animal behaviors and distributions across the globe.
‘Insufficient Awareness of Insect Issues’
Marco Gallio, a neurobiologist at Northwestern, emphasized the critical threat that climate change poses to insects. “Behavior is the primary interface between animals and their surroundings,” he explained. “Before grappling with survival, animals can react to climate shifts by migrating or altering their habitat range. We’re witnessing significant declines in insect populations worldwide, affecting even the vectors of diseases such as Zika and malaria as they spread to new territories.”
As a professor in neurobiology and an advocate for insects, Gallio pointed out the alarming decline in insect populations over the past two to five decades, despite the lack of widespread concern for these vital organisms. He highlighted that insects are fundamental to the structure of terrestrial food webs and are responsible for pollinating around 70% of global crops. A reduction in insect diversity and numbers could have dire implications for ecosystems and human welfare alike.
Deciphering Brain Responses to Temperature
Previous research from Gallio’s lab has specifically investigated how small insects, like the common fruit fly, respond to varying temperatures, both benign and harmful.
The fruit fly is particularly advantageous for such studies due to extensive research conducted on its genetics and neurological structures, allowing for detailed mappings of its brain that are unmatched in other species.
In their recent study, Gallio and his colleagues probed the neural circuits and behaviors of sympatric fly species that differ primarily in their thermal habitat preferences.
Utilizing advanced genetic techniques, including CRISPR, the researchers were able to deactivate specific genes and swap genetic material between species. Through this, they aimed to isolate and understand the molecular and neurological mechanisms responsible for their differing temperature preferences.
Matthew Capek, a Ph.D. student and lead author, noted initial findings indicated distinct heat-detecting molecules that activate at different temperature thresholds. While this activation variation accounted for the forest flies’ cooler temperature preference, it did not sufficiently explain the behavior of the desert flies.
“Desert flies seem actively drawn to warmer temperatures—around 90 degrees Fahrenheit—contrasting with forest flies, which prefer just below 70 degrees,” Capek stated. “The heat detection mechanisms in their antennae align more with their favored temperature range, prompting them to seek warmth rather than avoid it.”
High Costs and Benefits of Temperature Preference
Initially, Gallio found it perplexing that desert flies would seek heat, considering their extremely high daytime temperatures. However, a research trip to Anza Borrego Desert in Southern California provided clarity.
“In this desert, temperatures soar during the day but can plummet rapidly overnight,” explained Alessia Para, a key author and research associate professor in neurobiology. “Desert flies must continually adapt to these swift temperature shifts, searching for cool shade during the day and finding warmth in cacti at night.”
Flies in less extreme environments, however, may only react to rapid temperature changes. While constant temperature monitoring demands considerable energy, for desert flies, it is necessary for survival.
Gallio further discussed the comparative nature of this research, highlighting its dual benefits. “When an animal is born, it intuitively understands what stimuli are beneficial or harmful to it. We still lack insight into how this cognitive programming occurs,” he noted. “These fly species present a unique opportunity for studying the adaptive strategies that have evolved in response to temperature fluctuations. Understanding their responses could significantly inform predictions on how various species might adapt to ongoing climate change. Our aim is to foster a greater appreciation for insects and to inform conservation efforts.”
The study, titled “Evolution of temperature preference behavior in flies of the genus Drosophila,” received funding from the National Institutes of Health and the PEW Scholars Program. Gallio is also affiliated with the National Science Foundation’s Simons National Institute for Theory and Mathematics in Biology in Chicago.
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