Recently, authors including Safeguard researcher Viktor Szigeti from the Centre for Ecological Research (OK) have published the first study documenting phenotypic senescence in a natural butterfly population, using in vivo measurements. The paper published in the Ecology and Evolution journal and titled “Phenotypic senescence in a natural insect population” sheds light on the body mass and thorax width changes, that happen with age in a natural population of the univoltine Clouded Apollo butterfly (Parnassius mnemosyne, Lepidoptera: Papilionidae). Another focus of investigation is the relationship of this change with sex and wing length.
Over a span of six years, from 2014 to 2020, the team studied a population using mark-recapture during the whole flight period each year. By repeatedly measuring body mass and thorax width, as well as taking single measurements of wing length, the scientists were able to investigate how these traits changed with age.
Interestingly enough, the results revealed that as individuals aged, both body mass and thorax width declined nonlinearly. Butterflies appearing earlier in the flight period exhibited higher initial body mass and thorax width, but their body mass declined at a faster rate compared to those appearing later. Furthermore, it was discovered that, compared to male individuals, females had larger initial body sizes, which also decreased faster, indicating that differential selection influences phenotypic senescence.
Based on their findings, the authors recommend that future laboratory studies should explore the effects of weather conditions and resource availability on the rates of larval growth and adult senescence. Understanding these relationships will be crucial for predicting the effects of global environmental changes on the viability of insect populations.
Read the full article here.
Figure 1. from article: Body mass (a) and thorax width (b) change with age. Symbols represent the individuals' measurements (red + = females; blue × = males). Dots are slightly jittered along the x-axis for better visibility. Lines represent the estimated relationship between age and body size for the two sexes and of an individual with average wing length (31.4 mm), with first capture = 0th day (solid lines) or first capture = 14th day (dashed lines) of the flight period.