![]() ![]() However, molecular decay may be prevented if the underlying genes are involved in the development of multiple traits beyond the trait that was lost. This process is expected to occur over the span of 0.5 to 6 million years and has been documented in association with many instances of trait loss, such as the loss of eyes in cavefish and teeth in edentulous mammals. One possible outcome is the gradual erosion of pathway genes through the accumulation of inactivating mutations, leading to pseudogenization or even gene loss. Trait losses may lead to a range of outcomes for genes in pathways underlying those traits. ), this type of transition provides a powerful tool for understanding the predictability of genetic changes following phenotypic evolution. īecause trait losses occur relatively frequently across the tree of life (e.g. Despite having strong expectations about the genetic changes that are likely to follow many types of phenotypic transitions, relatively few studies have tested these predictions at macroevolutionary scales. Predictable molecular patterns are also seen at the protein level, where substitutions that cause changes in function may be followed by compensatory mutations to offset fitness declines, or by mutations to optimize the derived activity and/or increase stability of the new conformation. Even genes which are conserved for other functions may experience an increase in evolutionary rate if the trait transition is associated with reduced breath or level of expression. ![]() For example, transitions to a parasitic or symbiotic habit are often followed by pseudogenization and molecular decay in particular functional gene categories. In addition to predictability in the mutations that cause phenotypic transitions, the genetic changes that follow phenotypic transitions can also be predictable. Indeed, for many traits, the mutations responsible for convergent phenotypes are concentrated in a small set of “hotspot” loci and are restricted to particular classes of mutations (e.g. These patterns suggest that the causes of phenotypic evolution may often be predictable at the molecular level, given knowledge of the genetic basis for the trait. In some cases, this molecular convergence extends not only to the locus but also to the type of mutation and even its nucleotide position. Evolutionary genetic studies across a wide range of organisms and traits have revealed that repeated phenotypic transitions are often caused by similar changes at the genetic level. Understanding the predictability of the molecular changes associated with phenotypic transitions is a major goal in evolutionary biology. Moreover, this conservation maintains the potential for regain of flower color, and indicates that evolutionary losses of floral pigmentation may be readily reversible. The broad conservation of anthocyanin pathway genes across lineages with and without floral anthocyanins is consistent with the growing consensus that losses of pigmentation are largely achieved by changes in gene expression as opposed to structural mutations. Despite the increase, the values for dN/dS in both pigmented and unpigmented lineages were consistent overall with purifying selection acting on these loci. Maximum likelihood analyses suggest that this increase is due to relaxed constraint on anthocyanin genes in the unpigmented lineages as opposed to positive selection. However, two of the three genes ( Chi, F3h) show significantly elevated dN/dS ratios in lineages without floral pigmentation. We recovered intact coding regions for the three genes in all of the lineages that have lost floral pigmentation, suggesting that molecular decay is not associated with these flower color transitions. Focusing on the Iochrominae clade (Solanaceae), we examine how repeated losses of floral anthocyanin pigmentation associated with flower color transitions have affected the molecular evolution of three anthocyanin pathway genes ( Chi, F3h, and Dfr). For example, trait losses can result in molecular decay of the pathways underlying the trait. Phenotypic transitions, such as trait gain or loss, are predicted to carry evolutionary consequences for the genes that control their development. ![]()
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