A new mechanistic model for individual growth suggests upregulated maintenance costs when food is scarce in an insect

In order to calibrate and evaluate a recently developed growth model, the Maintenance-Growth Model (MGM), for the case of growth under food restriction, empirical data for house crickets (Acheta domesticus) were collected and analysed. This data set contains data for individually reared crickets growing under two different regimes of controlled food limitation as well as data for food-limited cohorts of growing house crickets. The sets include temporal data for body mass and ingestion as well as age and size at maturation (imago emergence). The data for food-limited cohorts were collected prior to this study and parts of it have previously been analysed and presented in a publication on animal self-thinning.  

Methods
Data for individually reared house crickets

81 newly hatched nymphs of house crickets (Acheta domesticus) were collected, weighted and reared individually in plastic boxes at an ambient temperature of 28.6 °C for 72 days. A controlled amount of food (an equal mixture of pellets for rats and guinea pigs) was provided twice a week (every 4th or 3rd day). Each cricket was exposed to one of two different treatments; 1) moderate food restriction or 2) strong food restriction, see the table below. At each feeding occasion, the weight of the cricket and remaining food and faecal material were measured. Sex and age at imago emergence was recorded for each individual. At some occasions, faeces were separated from remaining food and weighted separately (in order to estimate relative egestion rate). See the related manuscript for a detailed description of the experimental setup.

Treatment
Food supply
at day 1 [mg]
Food supply
at day 4 [mg]

Resulting average 
food supply [mg/day]

Number of
male replicates

Number of
female replicates

Moderate food restriction
90
120
5
25
16

Strong food restriction
15
20
30
21
19

Data for cohorts of house crickets

Newly hatched nymphs of house crickets (Acheta domesticus) were collected, weighted and reared in cohorts at a temperature of 30.5 °C. A fixed amount of food (an equal mixture of pellets for rats and guinea pigs) was provided at regular time intervals (1200 mg each week). The initial number of individuals in each cohort varied according to the table below. Surviving individuals were regularly counted and weighed. The data were collected prior to this study and parts of it have previously been analysed and presented in a publication on animal self-thinning (Jonsson 2017). See this and the current manuscript for more details of the experimental setup. 

Starting density
5
10
20
40
80

Number of cohorts
30
18
12
6
5

The average mass of all individuals in a cohort was calculated and used as juvenile growth data for both sexes. When the sex could be identified for at least some individuals, sex-specific average masses were calculated based on these and used to represent the cohort (though individuals that could not be identified by sex were excluded). Sex-specific average growth data were thereby obtained for each cohort. 

Reference

Jonsson T (2017) Metabolic theory predicts animal self-thinning. Journal of Animal Ecology 86:645-653. https://doi.org/10.1111/1365-2656.12638