Selection
Since phenotyping consisted of extracting the sex pheromone gland
invasively, selection was performed post-mating. Each generation, we
continued with those families that had a maternal phenotype satisfying
an increasingly stringent threshold. Initially, a so-called “high” and
“low” line were started with offspring from females with a relative
amount of acetates above 22% or below 16%, respectively. These values
were based on the distribution of the relative amounts of acetates in
the starting population, representing the 1st and 3rd quantile. These
thresholds were kept for the first 3 generations. In subsequent
generations, we increased these thresholds to >24% or
<14% (generation 4 – 5), and >26% or
<12% (generation 6 – 9). The high line consisted of a total
of 2,236 breeding females across nine generations, ranging from 189 –
295 matings per generation. After outlier removal, a total of 1,234 high
line females were phenotyped, or between 89 and 171 per generation
during the selection phase. The low line consisted of 2,250 breeding
females (189 – 296 per generation) and, after outlier removal,
phenotypes were measured for a total of 1,180 females (57 – 169 per
generation). We stopped selecting in generation 10, but continued to
phenotype ~25 females per line and per generation until
generation 13. Throughout the selection experiment, we also maintained a
control line from which we phenotyped between 6 and 111 females (median
20 females) per generation. For detailed sample sizes see Table S1.