Evolution repeats itself in replicate long-term studies in the wild

The extent to which evolution is repeatable remains debated. Here we study
changes over time in the frequency of cryptic color-pattern morphs in 10
replicate long-term field studies of a stick-insect, each spanning at
least a decade (across 30 years of total data). We find predictable
‘up-and-down’ fluctuations in stripe frequency in all populations,
representing repeatable evolutionary dynamics based on standing genetic
variation. A field experiment demonstrates that these fluctuations involve
negative frequency-dependent natural selection (NFDS). These fluctuations
rely on demographic and selective variability that pushes populations away
from equilibrium, such that they can reliably move back towards it via
NFDS. Finally, we show that the origin of new cryptic forms is associated
with multiple structural genomic variants such that which mutations arise
affects evolution at larger temporal scales. Thus, evolution from existing
variation is predictable and repeatable, but mutation adds complexity even
for traits evolving deterministically under natural selection.