Data for: Phenotypic senescence in a natural insect population

Senescence seems to be universal in living organisms and plays a major role in life-history strategies. Phenotypic senescence, the decline of body condition and/or performance with age, is a largely understudied component of senescence in natural insect populations, although it would be important to understand how and why insects age under natural conditions.

We aimed (i) to investigate how body mass and thorax width change with age in a natural population of the univoltine Clouded Apollo butterfly (Parnassius mnemosyne, Lepidoptera: Papilionidae) and (ii) to assess the relationship of this change with sex and wing length.

We studied a population between 2014 and 2020 using mark-recapture during the whole flight period each year. Repeated measurements of body mass and thorax width and single measurements of wing length were performed on marked individuals. We analysed body mass and thorax width change with age (days since marking), wing length and the date of the first capture.

Both body mass and thorax width declined non-linearly with age. Individuals appearing earlier in the flight period had significantly higher initial body mass and thorax width and their body mass declined faster than later ones. Initial body sizes of females were higher, but males’ body sizes decreased slower. Initial thorax width showed higher annual variation than body mass.

To our best knowledge, this is the first study that revealed phenotypic senescence in a natural butterfly population, using in vivo measurements. We found sexual differences in the rate of phenotypic senescence. Despite the annual variation of initial body sizes, the rate of senescence did not vary considerably across the years.

Methods
- single univoltine population of Clouded Apollo (Parnassius mnemosyne)
- 2014–2020, Europe, Hungary,Visegrádi-hegység
- mark-release-recapture
- in situ measurements on the field:
   - body mass (analytical scale)
   - thorax width (calipers)
   - wing length (ruler)

age: no. of days since an individual’s 1st measurement
time: no. of days since the first day of the flight period
mean(age): average of all age data at the time of measurements of an individual
first capture: the day of the flight period when an individual was captured for the first time
‘mean(first capture)’: the annual average of the days of first captures
mean(age) and mean(age2): the averages of all age and age2, respectively, data at the time of measurements of an individual. These ‘mean variables’ enabled us to distinguish the within-subject and between-subject effects.
log(body mass) or thorax width ~ sex*(age + mean age + age2 + mean_age2 + first capture + mean first capture + wing) + (age:wing) + (age:first capture) | individual ID/year 
both random intercept & random slope; LMM, R 3.6.1

N/A values in the input files mean that we could not measure every butterfly the same number of times.