Written by: Ken Estrellas
Original Article: Franke et al. BMC Evolutionary Biology 2019
The Gist of It
As winter turns to spring and the temperatures warm in more temperate climates, many humans adapt in some way – changing the clothes we wear, outdoor activities we participate in, and possibly even our sleeping patterns. But what about the other creatures around us – bacteria, mammals, and insects like the butterfly? Although the effects of worldwide temperature warming on butterflies’ migratory patterns have been well-studied, a recent report from Franke and colleagues looks at a more fundamental change – the effect of temperatures on butterflies’ bodies themselves. In this study, male and female butterflies raised in the same environment were subjected to different temperatures (19°C and 27°C) and different diets (food restriction and unlimited food availability). The researchers observed that varying temperatures had significant effects on the body composition of both male and female butterflies in terms of their mass distribution between the thorax and abdomen (butterflies at cooler temperatures tended to have heavier thoraces but lighter abdomen), as well as their body fat content. Activity of the important protective enzyme lysozyme was reduced with elevated temperature and food restriction, which indicates potentially compromised immune system function. Interestingly, food restriction was not associated with significant effects on overall body mass or fat content but did appear to have effects on thorax/abdomen mass distribution and lysozyme activity. To determine the mechanisms that drive each of these changes, patterns of genetic expression under each of these conditions were analyzed using RNAseq, a technique that sequences the RNA transcripts made from DNA to determine how much of each transcript is present. A total of 659 transcripts were found less often at the elevated temperature, while 430 transcripts were found more often. Many of the genes that were found more often at higher temperatures, such as peroxidase/oxygenase and the cytochrome P450 family, are involved in stress responses and may play a role in tolerance of increased temperatures. These results demonstrate that elevated temperatures can have specific effects on an organism’s gene expression and body composition; while these results are interesting in butterflies, future research in other organisms could potentially provide insights into how all of us might adapt to a constantly warming world.
The Nitty Gritty
In this study, Franke et al utilized the tropical butterfly Bicyclus anyanna to study the effects of elevated temperature, diet, and gender on body composition and genetic expression. Four treatment groups were used: 19°C with food available ad libitum, 19°C with food restrictions, 27°C with unlimited food, and 27°C with food restrictions. The butterflies were monitored over the course of 8 days, then shock frozen at −80°C for further analysis. Statistically significant differences were associated with temperature alone in thorax mass, abdomen mass, thorax/abdomen ratio, fat content, and lysozyme activity. Food restriction alone was associated with significant variations in thorax/abdomen ratio and lysozyme activity. Whole abdomens were used for RNA extraction and subsequent analysis via RNAseq with a de novo assembly process, since a reference genome for B. anyanna is not available. A total of 659 transcripts were shown to be upregulated due to temperature, including those that encode vacuolar H+-ATPase V1 sector, aldehyde dehydrogenase, and trypsin along with genes associated with oxidative defense. In contrast, 430 transcripts were downregulated at elevated temperatures, including those that encode dyneins, aspartyl beta-hydroxylase, a synaptic vesicle transporter SVOP, the chromatin remodeling protein HARP/SMARCAL1, a CUB domain-containing protein, and a chaperonin complex component. Notably, no association was found between components of the heat shock response in this study, likely because the elevated temperature condition of 27°C was still within the range of generally tolerated temperatures for this species. These variances in body composition and gene expression are potentially reflective of differences in energy expenditure, immune function, and oxidative stress responses as a result of elevated temperature. Future studies in organisms could elucidate the effects that overall warming climates might have on influential insect species such as bees, socioeconomically crucial animals such as livestock, and potentially humans.