Evolutionary innovations refer to the emergence of new traits, functions, or behaviors in organisms and lineages over time. Although research has demonstrated that such innovations can arise gradually or through small steps (Chouard 2010), the mechanisms by which rapid morphological diversification takes place remain poorly understood (Bailey et al. 2019). To explore this question, we used the evolution of sex combs, as a system (Ho et al. 2018). We used this male-specific row of leg bristles, comprising sex combs as a system, because it displays spectacular morphological diversification in a short time (Kopp 2011). Homeotic mutations in the fruit fly, Drosophila melanogaster, are those which create modifications in one part of a fly to resemble another region. Here we describe effects of some of these mutations which transform the D. melanogaster fly sex comb morphology to closely resemble sex comb morphology in other species. These findings support previous research indicating that minor alterations to regulatory elements can play a significant role in explaining morphological evolution (Atallah et al. 2004). Thus, our results suggest that rapid diversification may not require starting from scratch, but rather may require minor modifications to the sex comb ground plan, which may account for its rapid morphological evolution (Lee et al. 2011).
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