Meeting Abstract
Evolutionary innovations frequently promote diversification by allowing access to ecological opportunity but also often result in performance trade-offs. Adaptive simplification ─ the secondary loss or reduction of these innovations ─ can alleviate functional constraints, but evidence that this process can stimulate new adaptive radiation is lacking. Using phylogenetic comparative methods across a phylogeny of 500 caudate amphibians we show that the loss of lungs in plethodontid salamanders (Caudata: Plethodontidae) was associated with an increased rate of species diversification. Adaptive simplification of the lung appears to have led to reduced energetic constraints as more than half of the mitochondrial genome ─ encoding proteins critical for oxidative phosphorylation ─ exhibited significantly relaxed selection compared to species with lungs. The macroevolutionary adaptive landscape exhibited a complex pattern of evolution. Analysis of the climatic niche indicated more adaptive peaks in lungless salamanders and that most peaks were unique to the lungless group. Overall the results are consistent with previous studies suggesting some degree of niche conservatism in temperate lungless lineages, but increased divergence in tropical lineages. However, a macroevolutionary perspective of diversification indicates that the loss of lungs is associated with increased rates of ecological diversification as expected of an adaptive radiation. The loss of key evolutionary innovations may therefore be an underappreciated mechanism of species and functional diversification.
