Effects of Temperature Variation on Male Behavior and Mating Success in a Montane Beetle

Abstract

Locomotion and mating ability are crucial for male reproductive success yet are energetically costly and susceptible to physiological stress. In the Sierra willow beetle Chrysomela aeneicollis, male mating success depends on locating and mating with as many females as possible. Variation at the glycolytic enzyme locus phosphoglucose isomerase (Pgi) is concordant with a latitudinal temperature gradient in these populations, with Pgi-1 frequent in the cooler north, Pgi-4 in the warmer south, and alleles 1 and 4 in relatively equal frequency in areas intermediate in geography and climate. Beetles experience elevated air temperatures during a mating season that causes differential physiological stress among Pgi genotypes, and running speeds of individuals homozygous for Pgi-4 are more tolerant of repeated thermal stress than individuals possessing Pgi-1. Here the importance of running behavior for male mating activity was examined, and differential effects of thermal stress among Pgi genotypes on male mating activity were measured. In nature, males run more than females, and nearly half of males mate or fight for a mate after running. In the laboratory, mating activity was positively correlated with running speed, and repeated mating did not reduce running speed or subsequent mating activity. Males homozygous for Pgi-4 mated longer and more frequently after heat treatment than 1-1 and 1-4 males. All heat-treated males had lower mating frequencies and higher heat shock protein expression than control males; however, mating frequency of recovering 4-4 males increased throughout mating trials, while treated 1-1 and 1-4 males remained low. These results suggest that effects of stress on mating activity differ between Pgi genotypes, implying a critical role for energy metabolism in organisms' response to stressful temperatures.

Mitochondria and the thermal limits of ectotherms

“…In montane leaf beetles (Chrysomela aeneicollis), there are differences in mitochondrial and nuclear genotypes across latitude that are associated with differences in a variety of performance and fitness traits, including running speed (Dahlhoff et al, 2008;Dick et al, 2013;McMillan et al, 2005;Neargarder et al, 2003;Rank and Dahlhoff, 2002;Rank et al, 2007). In populations where individuals bearing these different nuclear and mitochondrial genotypes interbreed naturally, mitonuclear mismatches (see Glossary) result in reductions in running speed that tend to be amplified by exposure to sub-lethal heat stress (Rank et al, 2020).…”

Getting chased up the mountain: High elevation may limit performance and fitness characters in a montane insect

“…Frequencies of the glycolytic enzyme locus phosphoglucose isomerase ( PGI ) vary with latitude and elevation, differences that have remained stable for decades (Rank, ; Rank & Dahlhoff, ; Roberts, ). Laboratory and field studies show that PGI genotypes vary with respect to components of fitness, and allele frequencies shift in response to climate change (Dahlhoff et al, ; Dick et al, ; Mc Millan, Fearnley, Rank, & Dahlhoff, ; Neargarder, Dahlhoff, & Rank, ; Rank, Smiley, & Köpf, ). Geographic variation at another metabolic gene, mitochondrial cytochrome c oxidase II ( COII ), is concordant with variation at PGI , and interactions between PGI genotype and COII haplotype appear to explain more variation in performance and fitness characters than PGI alone (Fearnley, ; Heidl, ).…”

Climate variability differentially impacts thermal fitness traits in three coprophagic beetle species

“…Deviations from optimal ranges not only affect physiological processes (e.g. metabolic rates), but also key activities such as locomotion [ 12 , 13 ], mating, and reproductive success [ 14 , 15 ] and ultimately survival [ 16 , 17 ]. As such, the ability of organisms to operate within varying magnitudes of temperature fluctuation may be a critical trait in the face of climate change.…”