Not all cicadas increase thermal tolerance in response to a temperature gradient in metropolitan Seoul

Abstract

Rapid anthropogenic alterations caused by urbanization are increasing temperatures in urban cores, a phenomenon known as the urban heat island (UHI) effect. Two cicada species, Cryptotympana atrata and Hyalessa fuscata (Hemiptera: cicadidae), are abundant in metropolitan Seoul where their population densities correlate strongly with UHI intensities. Such a positive correlation between cicada density and UHI intensity may be possible if cicada abundance is linked to a certain thermal tolerance. We tested this hypothesis by investigating variation in morphology and thermal responses of two cicada species along a thermal gradient in Seoul and surrounding areas. The morphological responses were measured by metrics such as length, thorax width and depth, and mass. The thermal responses were measured in terms of minimum flight temperature, maximum voluntary temperature and heat torpor temperature. First, we observed a species-specific variation in thermal responses, in which C. atrata displayed a higher thermal threshold for maximum voluntary and heat torpor temperatures than H. fuscata. Second, a positive association between temperature conditions and body sizes were displayed in females H. fuscata, but not in either conspecific males or C. atrata individuals. Third, C. atrata exhibited similar thermal responses regardless of habitat temperature, while H. fuscata in warmer areas showed an increase in heat tolerance. In addition, H. fuscata individuals with bigger thorax sizes were more heat-tolerant than those with smaller thoraxes. Overall, our research is the first to detect a variation in thermal responses and body size of H. fuscata individuals at a local scale. More investigations would be needed to better understand the adaptation mechanisms of insects linked to UHI effects.Temperature is one of the most important abiotic factors affecting daily activities and the life history of cicadas 1-6 . As temperature directly dictates chemical rates and metabolic processes in vivo, a habitat with fluctuating temperatures could drive insects to manage the high energy costs of maintaining body temperature, T b , within a certain range to coordinate reproductive activity 4 . The surrounding conditions may also have an effect on reproductive success and mortality 7-10 . If so, cicadas should select favorable thermal conditions to obtain optimal body temperatures via behavioral-or physiological mechanisms 4,11 .The urban heat island (UHI) effect, in which increased temperatures are associated with urban areas, is a ubiquitous consequence of microclimatic perturbation 12 due to human activities and energy consumption, along with modification of landscapes and urban geometry [13][14][15][16][17] . Elevated temperatures in urban environments are regarded as detrimental as they reduce plant photosynthesis capability 18 and biological diversity 19,20 . Nevertheless, for urban herbivorous insects such as cicadas, such warm habitats may prove advantageous. First, post-morphogenesis development of cicada eggs require a large degree o...

De Novo Transcriptome Analysis Reveals Potential Thermal Adaptation Mechanisms in the Cicada Hyalessa fuscata

“…As a result, those individuals who cannot cope with thermal stress may experience irreversible cell death, or at least lower fertility. In contrast, the positive association between the localized thermal regime and thermal responses of cicadas inhabiting warm areas in metropolitan Seoul showed that those individuals could increase their heat endurance as the temperature conditions of their habitat increased [45]. Furthermore, bigger body sizes, which is an indicator of higher reproducibility, were also observed in females living in warm areas, which indicated a possible close relationship between female fecundity and thermal tolerance.…”

“…This was attributed to the urban heat island (UHI) effect, which is a phenomenon that occurs when urban cores become hotter than the surroundings [44]. A positive relationship between the thermal responses of cicadas and the intensity of the urban heat island effect was documented [45]. This finding suggests the potential adaptation of this cicada species to warm urban cores in Seoul.…”

“…Here, only adult H. fuscata cicadas were chosen as study samples. Three sampling areas representing high-UHI, low-UHI, and suburban areas of metropolitan Seoul were selected: Seocho (127 • 1 13.7994 E, 37 • [45]. From 1 June 2010 to 31 August 2016, the average maximum ambient temperatures in summer in these areas followed a descending thermal gradient, decreasing gradually from 30.97 • C in the high-UHI area to 29.02 • C in the suburban area.…”

“…We hypothesized that under exposure to heat stress, a greater extent of gene expressions that are likely involved in facilitating thermal tolerance would be observed in high-UHI cicadas than those from cooler areas. Examination of the thermal responses exhibited by H. fuscata from various thermal conditions revealed that the local thermal regime was strongly associated with the cicadas' heat torpor temperatures, but not with the minimum body temperature during fully coordinated activities or the upper thermoregulatory point for shade-seeking behavior [45]. For these reasons, we predicted that: (1) no transcriptional differences under unheated conditions would be exhibited across cicadas sampled from different thermal areas; (2) no significant transcriptional changes would be observed in response to acute heat stress, where no thermoregulating behaviors were present; and (3) cicadas that were sampled from warmer urban areas would show greater transcriptome changes related to heat endurance under heat torpor than cicadas that were sampled from cooler urban areas.…”

Automated Applications of Acoustics for Stored Product Insect Detection, Monitoring, and Management

“…Such studies include on termites and other tree-boring insects that produce feeding sounds that have spectral and temporal patterns like those of stored product insects [ 94 , 95 , 142 , 143 , 235 ]. Others describe effects of temperature on rates of activity [ 60 ]. Others incorporate optical sensors in traps [ 150 , 275 ] with similarities to pitfall traps used for monitoring stored product insects [ 236 ].…”