Understanding the variations in the rate of molecular evolution among lineages may provide clues on the processes that molded extant biodiversity. Here, we report the high rate of molecular evolution in Lycaenidae and Riodinidae compared to other families of butterflies (Papilionoidea). We assembled a phylogeny of butterflies using eight molecular markers and comprising 4891 species. We found that the rate of molecular evolution is higher in Lycaenidae and Riodinidae compared to the other families, but only the nuclear gene Wingless showed a marked difference, while Elongation factor 1-alpha showed a more moderate difference. In contrast, the gene Cytochrome Oxidase subunit 1 showed no difference between lycaenids as well as riodinids, and other butterflies. In parallel, we calculated the rates of diversification in all subfamilies of the Papilionoidea using the method-of-moments estimator for stem-group ages, which does not require a fully solved phylogeny for the target clades. We found that the Nemeobiinae and Lycaeninae, from the Riodinidae and Lycaenidae families, respectively, had the highest rate of diversification among all subfamilies. Among the life-history traits that could explain differences in molecular evolution and diversification rate, lycaenids display mutualistic or antagonistic interactions with ants, a higher level of host plant specialization and reduced dispersal abilities compared to other butterfly families. Since the current study is limited by the unique event of apparition of myrmecophily analyzed, the relationship with traits cannot be evaluated statistically. Future studies should measure myrmecophily and dispersal abilities quantitatively across a more detailed phylogeny of lycaenids to test for an association between shifts in the strength of mutualism, rates of molecular evolution and the diversification of lineages.
Oceans, or other wide expanses of inhospitable environment, interrupt present day distributions of many plant groups. Using molecular dating techniques, generally incorporating fossil evidence, we can estimate when such distributions originated. Numerous dating analyses have recently precipitated a paradigm shift in the general explanations for the phenomenon, away from older geological causes, such as continental drift, in favour of more recent, long-distance dispersal (LDD). For example, the ‘Gondwanan vicariance’ scenario has been dismissed in various studies of Indian Ocean disjunct distributions. We used the gentian tribe Exaceae to reassess this scenario using molecular dating with minimum (fossil), maximum (geological), secondary (from wider analyses) and hypothesis-driven age constraints. Our results indicate that ancient vicariance cannot be ruled out as an explanation for the early origins of Exaceae across Africa, Madagascar and the Indian subcontinent unless a strong assumption is made about the maximum age of Gentianales. However, both the Gondwanan scenario and the available evidence suggest that there were also several, more recent, intercontinental dispersals during the diversification of the group.
Abstract Aim Macroevolutionary patterns and processes change substantially depending on levels of taxonomic and ecological organization, and the resolution of environmental and spatial variability. In comparative methods, the resolution of environmental and spatial variability often defines the number of selective regimes used to test whether phenotypic characteristics are adaptively correlated with the environment. Here, we examine how investigator choice of the number of selective regimes, determined by varying the resolution of among‐species variability in the species climatic niche (hereafter called ‘ecological scale’), influences trait morphological diversification among Eriogonoideae species. We assess whether adaptive or neutral processes drive the evolution of several morphological traits in these species. Location South‐western North America. Methods We applied a phylogenetic framework of three evolutionary models to four morphological traits and the climatic niches of Eriogonoideae (in the buckwheat family, Polygonaceae). We tested whether morphological traits evolve in relation to climate by adaptive or neutral process, and whether the resulting patterns of morphological variability are conserved or convergent across the clade. We inspected adaptive models of evolution under different levels of resolution of among‐species variability of the climatic niche. Results We show that morphological traits and climate niches of Eriogonoideae species are not phylogenetically conserved. Further, adaptive evolution of phenotypic traits is specific to climatic niche occupancy across this clade. Finally, the likely evolutionary process and the level of detectable niche conservatism change depending on the resolution of environmental variability of the climatic niche. Main conclusions Our study demonstrates the need to consider both the resolution of environmental variability and alternative evolutionary models to understand the morphological diversification that accompanies divergent adaptive evolution of lineages to climatic conditions.
Macroevolutionary and microevolutionary studies provide complementary explanations of the processes shaping the evolution of niche breadth. Macroevolutionary approaches scrutinize factors such as the temporal and spatial environmental heterogeneities that drive differentiation among species. Microevolutionary studies, in contrast, focus on the processes that affect intraspecific variability. We combine these perspectives by using macroevolutionary models in a comparative study of intraspecific variability. We address potential differences in rates of evolution of niche breadth and position in annual and perennial plants of the Eriogonoideae subfamily of the Polygonaceae. We anticipated higher rates of evolution in annuals than in perennials owing to differences in generation time that are paralleled by rates of molecular evolution. Instead, we found that perennial eriogonoid species present greater environmental tolerance (wider climate niche) than annual species. Niche breadth of perennial species has evolved two to four times faster than in annuals, while niche optimum has diversified more rapidly among annual species than among perennials. Niche breadth and average elevation of species are correlated. Moreover, niche breadth increases more rapidly with mean species elevation in perennials than in annuals. Our results suggest that both environmental gradients and life-history strategy influence rates and patterns of niche breadth evolution.
Summary Given the dual role of many plant traits to tolerate both herbivore attack and abiotic stress, the climatic niche of a species should be integrated into the study of plant defense strategies. Here we investigate the impact of plant reproductive strategy and components of species' climatic niche on the rate of chemical defense evolution in the milkweeds using a common garden experiment of 49 species. We found that across Asclepias species, clonal reproduction repeatedly evolved in lower temperature conditions, in species generally producing low concentrations of a toxic defense (cardenolides). Additionally, we found that rates of cardenolide evolution were lower for clonal than for nonclonal species. We thus conclude that because the clonal strategy is based on survival, long generation times, and is associated with tolerance of herbivory, it may be an alternative to toxicity in colder ecosystems. Taken together, these results indicate that the rate of chemical defense evolution is influenced by the intersection of life‐history strategy and climatic niches into which plants radiate.
Abstract Aim The study of adaptive radiations provides an evolutionary perspective on the interactions between organisms and their environment, and is necessary to understand global biodiversity. Adaptive radiations can sometimes be replicated over several disjunct geographical entities, but most examples are found on island or in lakes. Here, we investigated the biogeographical history of the clownfishes, a clade of coral reef fish with ranges that now span most of the Indo‐Pacific Ocean, in order to explore the geographical structure of an unusual adaptive radiation. Location Indian Ocean, Indo‐Australian Archipelago ( IAA ) and Central Pacific Ocean. Methods We generated DNA sequence data comprising seven nuclear markers for 27 of the 30 clownfish species. We then inferred a Bayesian phylogeny and reconstructed the biogeographical history of the group using three different methods. Finally, we applied a biogeographical model of diversification to assess whether diversification patterns differ between the Indian and Pacific Oceans. Results The phylogenetic tree is highly supported and allows reconstruction of the biogeographical history of the clade. While most species arose in the IAA , one clade colonized the eastern shores of Africa and diversified there. We found that the diversification rate of clownfishes does not differ between the main radiation and the African clade. Main conclusions The clownfishes first appeared and diversified in the IAA . Following a colonization event, a geographically independent radiation occurred in the Indian Ocean off East Africa. This rare example of replicated adaptive radiation in the marine realm provides intriguing possibilities for further research on ecological speciation in the sea.
In severe and variable conditions, specialized resource selection strategies should be less frequent because extinction risks increase for species that depend on a single and unstable resource. Psithyrus (Bombus subgenus Psithyrus) are bumblebee parasites that usurp Bombus nests and display inter‐specific variation in the number of hosts they parasitize. Using a phylogenetic comparative framework, we show that Psithyrus species at higher elevations display a higher number of hosts species compared with species restricted to lower elevations. Species inhabiting high elevations also cover a larger temperature range, suggesting that species able to occur in colder conditions may benefit from recruitment from populations occurring in warmer conditions. Our results provide evidence for an ‘altitudinal niche breadth hypothesis’ in parasitic species, showing a decrease in the parasites’ specialization along the elevational gradient, and also suggesting that Rapoport’s rule might apply to Psithyrus.
Abstract Aim Specialized mutualistic clades may revert and thus increase their autonomy and generalist characteristics. However, our understanding of the drivers that trigger reductions in mutualistic traits and of the consequences for the tolerance of these species to various environmental conditions remains limited. This study investigates the relationship between the environmental niche and the degree of myrmecophily (i.e. the ability to interact with ants) among members of the Lycaenidae. Location The western Swiss Alps. Methods We measured the tolerance of Lycaenidae species to low temperatures by comparing observations from a random stratified field sampling with climatic maps. We then compared the species‐specific degree of myrmecophily with the species range limits at colder temperatures while controlling for phylogenetic dependence. We further evaluated whether the community‐averaged degree of myrmecophily increases with temperature, as would be expected in the case of environmental filters acting on myrmecophilous species. Results Twenty‐nine Lycaenidae species were found during sampling. Ancestral state reconstruction indicated that the 24 species of Polyommatinae displayed both strong myrmecophily and secondary loss of mutualism; these species were used in the subsequent statistical analyses. Species with a higher degree of ant interaction were, on average, more likely to inhabit warmer sites. Species inhabiting the coldest environments displayed little or no interaction with ants. Main conclusions Colder climates at high elevations filter out species with a high degree of myrmecophily and may have been the direct evolutionary force that promoted the loss of mutualism. A larger taxon sampling across the Holarctic may help to distinguish between the ecological and evolutionary effects of climate.
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