Photo credit: www.sciencedaily.com
The fragrances of blooming plants during spring aren’t merely a delightful sensory experience; they play a significant role in the survival and evolution of butterflies and moths. New research conducted by scientists at Penn State has unveiled connections between the daily variations in plant scents and the dietary preferences and evolutionary pathways of these insects, collectively referred to as Lepidoptera.
A recent study featured in the journal Proceedings of the Royal Society B presents a new hypothesis regarding the dietary habits of Lepidoptera—specifically, why some species restrict their diets to a select few plant types, while others exhibit more generalized eating patterns.
This novel concept, termed the Salient Aroma Hypothesis, posits that plant-emitted aromas significantly influence the dietary specialization of butterflies and moths. Researchers discovered that the abundance of plant scents available during daylight hours offers essential chemical cues for diurnal insects, helping them identify and specialize in specific host plants. Conversely, the reduction of these aromatic signals at night forces nocturnal Lepidoptera to adapt to a more varied diet.
“This theory provides fresh insights into the dietary preferences of different Lepidoptera,” stated Po-An Lin, an assistant professor at the National Taiwan University, who initiated the research while pursuing his doctorate at Penn State and continued it as a postdoctoral researcher in Taiwan. “It underscores the vital importance of plant scents in shaping interactions between insects and plants as well as influencing evolutionary adaptations.”
To explore plant scents’ potential impact on evolutionary adaptations, researchers examined the primary olfactory organs of these insects—the antennae. They compared the antennal dimensions of 582 specimens spanning 94 butterfly and moth species.
Collaboration with a Harvard research team revealed that female Lepidoptera active during the day tend to possess larger antennae in proportion to their body size compared to their nighttime counterparts. This suggests that enhanced olfactory capabilities are advantageous when there is a wider range of scents to detect, as explained by Gary Felton, the Ralph O. Mumma Professor of Entomology at Penn State and co-author of the study. Moreover, specialist female Lepidoptera, which feed exclusively on a limited number of plant species, often have larger antennae than their generalist counterparts, indicating the need for acute detection of the specific aromas from their host plants.
“The relationship between antennal size and the breadth of host plant diet is quite strong,” Felton remarked. “Larger antennae are generally equipped with a greater number of sensilla, which are sensory structures linked to olfaction, increasing the surface area available for sensory receptors. This enhanced olfactory capacity may represent a crucial adaptation for certain Lepidoptera that have evolved dietary specialization.”
The study’s results indicate a possible association between the daytime availability of plant aromas and evolutionary enhancements in the insects’ olfactory structures, particularly among females who need to select suitable host plants for egg-laying, according to Lin.
“This research highlights how the presence of chemical signals influences the evolution of sensory organs in insects,” he stated. “It serves as a compelling illustration of how plants, through their chemical emissions, can directly shape the evolutionary trajectory of dependent insect species.”
The Penn State team employed various methodologies to investigate the interplay between plant scents and Lepidoptera diets. Initially, they conducted a meta-analysis of the existing scientific literature, confirming that plants generally emit a broader array of volatile organic compounds during daylight when compared to the night. Subsequently, they analyzed the evolutionary relationships within the Lepidoptera family tree to study the connection between the insects’ activity patterns—either diurnal or nocturnal—and their preferred host plants, using statistical models to factor in evolutionary relationships.
“Our analysis identified a significant correlation between the diurnal or nocturnal activity patterns of Lepidoptera and the diversity of host plant species they consume,” observed Naomi Pierce, a biology professor at Harvard University and co-author of the study.
The findings showed that diurnal Lepidoptera, such as the monarch butterfly, have more opportunities to detect plant aromas and have developed specialized organs for this purpose, leading to a tendency to be selective in their feeding habits. In contrast, nocturnal species, like the Polyphemus Moth, encounter fewer and less diverse plant aromas, which may hinder their ability to be selective and result in more generalized diets that include a wider range of plants.
“For insect herbivores like butterflies and moths, selecting the right plants for feeding and, in the case of females, laying eggs is vital,” Lin emphasized. “This decision is crucial because the caterpillars depend solely on the chosen plant for their survival. Unlike humans, who can consume various foods for nutritional balance, many insect herbivores are highly specialized, feeding on only a few plant species. The Salient Aroma Hypothesis clarifies why some insects exhibit high dietary specialization while others maintain flexibility.”
The research team also included Wei-Ping Chan and Even Dankowicz from Harvard University; Liming Cai from the University of Texas at Austin; Yun Hsiao from National Taiwan University; and Kadeem Gilbert from Michigan State University.
This study received funding from the U.S. National Science Foundation, Taiwan’s National Science and Technology Council, and the Yushan Fellowship Program administered by the Ministry of Education of Taiwan.
Source
www.sciencedaily.com