Adaptive radiations: From field to genomic studies

Abstract

Adaptive radiations were central to Darwin's formation of his theory of natural selection, and today they are still the centerpiece for many studies of adaptation and speciation. Here, we review the advantages of adaptive radiations, especially recent ones, for detecting evolutionary trends and the genetic dissection of adaptive traits. We focus on Aquilegia as a primary example of these advantages and highlight progress in understanding the genetic basis of flower color. Phylogenetic analysis of Aquilegia indicates that flower color transitions proceed by changes in the types of anthocyanin pigments produced or their complete loss. Biochemical, crossing, and gene expression studies have provided a wealth of information about the genetic basis of these transitions in Aquilegia. To obtain both enzymatic and regulatory candidate genes for the entire flavonoid pathway, which produces anthocyanins, we used a combination of sequence searches of the Aquilegia Gene Index, phylogenetic analyses, and the isolation of novel sequences by using degenerate PCR and RACE. In total we identified 34 genes that are likely involved in the flavonoid pathway. A number of these genes appear to be single copy in Aquilegia and thus variation in their expression may have been key for floral color evolution. Future studies will be able to use these sequences along with next-generation sequencing technologies to follow expression and sequence variation at the population level. The genetic dissection of other adaptive traits in Aquilegia should also be possible soon as genomic resources such as whole-genome sequencing become available.anthocyanins ͉ evolutionary trend ͉ flower color ͉ hybrid zone A daptive radiations have played, and continue to play, a central role in the development of evolutionary theory. After his exploration of the Galapagos Islands, Darwin recognized that variants of species were confined to specific islands. In particular, Darwin (1) noted that mockingbirds he collected on different islands represented 3 distinct forms and that all of the forms were similar to mockingbirds from the mainland of South America. He further noted that the different islands were within sight of one another, all quite similar in their habitats, and apparently geologically young. Based on these observations, Darwin (2) began to suspect that species gradually became modified. Thus, began his search for a process that could account for such observations, leading to his formulation of the theory of natural selection.Key to Darwin's suspicion of common ancestry was the close proximity of environmentally-similar islands comprising the Galapagos archipelago. In fact, many classic examples of adaptive radiations involve islands or lakes; notable examples include Darwin's finches of the Galapagos, honeycreeper birds and silversword plants of Hawaii, and cichlid fish of lakes Malawi and Victoria in Africa. The power of these examples for inferring the force of natural selection in evolution stems from the marked diversity in form and function among ...

The MADS-Box Gene Family of the Basal Eudicot and HybridAquilegia coerulea‘Origami' (Ranunculaceae)1

“…These recently by taxon, reflecting independent and relatively recent diversified species have long fascinated researchers gene duplications (Nam et al, 2004;Arora et al, working in the fields of evolution and ecology due to 2007). Second, they are commonly involved in the their association of poor genetic differentiation with development of the female gametophyte and endo-highly divergent pollinator syndromes (Hodges et al, sperm, as confirmed by both forward genetics and 2004; Hodges & Derieg, 2009). More recently, broad expression studies (Bemer et al, 2010b and Aquilegia has become a model for the evolution of references therein).…”

How can an understanding of plant–pollinator interactions contribute to global food security?

“…For example, flower colour is a trait with astonishing lability over evolutionary time and the potential to discriminate between pollinator types. Multiple evolutionary shifts from hummingbird to moth pollination in Aquilegia have been associated with independent losses of anthocyanin production [37]. The molecular basis of many such shifts is attributable to changes in the transcription factors that regulate the pigment synthetic pathway (reviewed by [38]), and similar changes can cause variations in the pattern of floral pigment, generating spots, veins and other nectar guides that are differentially used by different pollinators [39,40*,41].…”

The genomic basis of parallel ecological speciation

“…One biological process that can lead to the evolution of such diverse groups is adaptive radiation. Adaptive radiation refers to the rapid diversification of an ancestral species, producing descendants adapted to a great variety of ecological niches (Gavrilets & Losos 2009;Hodges & Derieg 2009;Losos 2010;. Adaptive radiations can result either from ecological opportunity, where an ancestral species colonizes an environment with underutilized resources like under populated lakes or islands, or from "key innovations" allowing the establishment of novel ways to interact with the environment .…”

“…have not yet fully attained RI are especially profitable resources for dissecting the genetic basis of ecological speciation, because they allow to test the effect of gene flow in speciation and because the ability to make hybrids allows the dissection of the genetic basis of traits (Hodges & Derieg 2009). Additionally, adaptive radiations presenting a diversity of adaptive traits or the repeated evolution of the same traits in different lineages constitute excellent systems for identifying evolutionary trends and estimating whether evolution follows predictable trajectories (Hodges & Derieg 2009 , some environments seem to have been colonized repeatedly as S. lautus populations are grouped according to their geographic location independently of their ecology and morphology.…”

“…Additionally, adaptive radiations presenting a diversity of adaptive traits or the repeated evolution of the same traits in different lineages constitute excellent systems for identifying evolutionary trends and estimating whether evolution follows predictable trajectories (Hodges & Derieg 2009 , some environments seem to have been colonized repeatedly as S. lautus populations are grouped according to their geographic location independently of their ecology and morphology. The evolution of these inter-fertile Melo 2014) but divergent forms has occurred in a very short period of time, which suggest the existence of genetic mechanisms to produce phenotypic variation in a relatively short period of time.…”