Predicting evolution remains difficult. We studied the evolution of cryptic body coloration and pattern in a stick insect using 25 years of field data, experiments, and genomics. We found that evolution is more difficult to predict when it involves a balance between multiple selective factors and uncertainty in environmental conditions than when it involves feedback loops that cause consistent back-and-forth fluctuations. Specifically, changes in color-morph frequencies are modestly predictable through time ( = 0.14) and driven by complex selective regimes and yearly fluctuations in climate. In contrast, temporal changes in pattern-morph frequencies are highly predictable due to negative frequency-dependent selection ( = 0.86). For both traits, however, natural selection drives evolution around a dynamic equilibrium, providing some predictability to the process.
potentially more complex, as the homogenising effects of gene flow must be countered [1][2][3] . The 49 genic model of speciation proposes that specific genetic regions subject to strong divergent 50
The types of mutations affecting
adaptation in the wild are only beginning to be
understood. In particular, whether structural
changes shape adaptation by suppressing
recombination or by creating new mutations is
unresolved. Here, we show that multiple linked but
recombining loci underlie cryptic color morphs of
Timema chumash stick
insects. In a related species, these loci are
found in a region of suppressed recombination,
forming a supergene. However, in seven species of
Timema, we found that a
megabase-size “supermutation” has deleted color
loci in green morphs. Moreover, we found that
balancing selection likely contributes more to
maintaining this mutation than does introgression.
Our results show how suppressed recombination and
large-scale mutation can help to package gene
complexes into discrete units of diversity such as
morphs, ecotypes, or species.
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