What defines an adaptive radiation? Macroevolutionary diversification dynamics of an exceptionally species-rich continental lizard radiation

Liolaemus have diversified under a density-dependent procedure with slightly pronounced apparent episodic pulses of descent collection, which are compatible with the expected episodic ecological opportunity created by gradual uplifts of the Andes over the last ~25My. We argue that ecological opportunity can be solid and a crucial driver of adaptive radiations in continents, but may emerge less frequently ( compared to islands ) when major events ( for example, climatic, geographic ) significantly modify environments. In contrast, body size diversification conforms to an Ornstein-Uhlenbeck model with multiple trait optimum. Despite this asymmetrical diversification between both lineages and phenotype, links are expected to exist between the two processes, as shown by our trait-dependent analyses of diversification. We finally suggest that the definition of adaptive radiation should not be conditioned by the universe of early-bursts of diversification, and should alternatively be generalized to lineages in which species and ecological diversity have evolved from a single ancestor. Our phylogenetic analyses lend support to a density-dependent lineage diversification model. however, the linage through-time diversification curve does not provide hard confirm for an early break. In contrast, the development of phenotypical ( body size ) relative disparity is eminent, significantly different from a Brownian mannequin during approximately the last 5 million years of Liolaemus evolution. Model-fitting analyses besides reject the ‘ early-burst ’ model of phenotypical development, and rather favour stabilizing choice ( Ornstein-Uhlenbeck, with three peaks identified ) as the best mannequin for consistency size diversification. finally, diversification rates tend to increase with smaller soundbox size. adaptive radiation theory posits that ecological opportunity promotes rapid proliferation of phylogenetic and ecological diverseness. Given that adaptive radiotherapy proceeds via occupation of available niche space in newly accessed ecological zones, hypothesis predicts that : ( iodine ) evolutionary diversification follows an ‘ early-burst ’ work, i.e., it accelerates early in the history of a clade ( when available recess space facilitates speciation ), and subsequently slows down vitamin a niche outer space becomes saturated by fresh species ; and ( two ) phylogenetic branch is accompanied by diversification of ecologically relevant phenotypical traits among newly evolving species. here, we employ macroevolutionary phylogenetic model-selection analyses to address these two predictions about evolutionary diversification using one of the most exceptionally species-rich and ecologically divers lineages of living vertebrates, the south american lounge lizard genus Liolaemus .

Background

adaptive radiation theory predicts that the proliferation of phylogenetic and ecological diversity within a linage results from the exposition of a single ancestor to multiple episodes of divergent natural choice [ 1, 2 ]. A fundamental part of this process is the emergence of ‘ ecological opportunity ’, which provides the conditions that allow speciation through adaptation to unlike niches [ 3, 4 ]. ecological opportunity arises when spatial and/or ecological dispersion ( i, access to novel recess dimensions facilitated by adaptive innovations ) expose a species to a new set of abundant ecological resources [ 2 – 7 ]. For exercise, spatial and/or ecological dispersion can be driven by the egress of modern habitats ( for example, islands, mountains ), by modifications of existing environments via climatic changes, or by the vacate of niches following extinctions [ 1 – 3 ]. As diversification proceeds, the extent of ecological opportunity declines as a function of increasing saturation of niche outer space by newly evolving species. consequently, a core prediction based on the above scenario is that adaptively radiating lineages will show early bursts of rapid diversification followed by asymptotic decreases in diversification rates over time [ 2, 8 – 10 ].

In addition, phenotypical traits with ecological significance play a fundamental role in the process of recess construction, and hence, in the way diversifying lineages saturate niches over prison term [ 2, 11 ]. As a solution, analyses of macroevolutionary models of lineage accretion have been complemented with studies of tempo and manner of diversification of ecologically relevant phenotypes during adaptive radiations [ 2, 8, 12, 13 ]. Based on the model of adaptively radiating lineages expounded above, we may predict that phenotypical diversification is high early in a group ’ s history, when ancestors enter an adaptive zone with abundant resources [ 3, 10 ]. As natural selection promotes impregnation of ecological space via phenotypical diversification, opportunities for recess occupation refuse, therefore causing a slowdown in the rates of diversification of ecologically functional traits [ 2, 8 – 10 ]. consequently, if the radiotherapy of a ancestry has been adaptive, then the diversifications of both the linage and the phenotype are expected to display alike patterns, which would be driven by changes in niche filling over time ( for example, [ 2, 14 ] ). For exemplify, if the rapid early emergence of raw species causes a decrease in recess space, then the opportunities for adaptive speciation decline, and slowdowns in ecological trait development would be expected given the boil down opportunities for adaptive recess expansions.

evidence for coupled patterns of ancestry and phenotype diversification is not coherent. While some studies reveal a link between these two components of diversity, others fail to identify such links. For example, Harmon et alabama. [ 12 ] showed that ‘ bursts ’ of descent accretion in the radiation of iguanian lizards are reproducible with pulses of phenotypical disparity during their phylogenetic history. similarly, the radiation of Caribbean Anolis lizards has been shown to partition ecological morphospace more finely as the numbers of competing lineages present on an island increase [ 15 ]. In contrast, the radiation of cetaceans show signals of diversity-dependent development of ecological phenotypes, while their net diversification fails to support a model of early-bursts of speciation followed by slowdowns [ 13 ]. last, although net linage diversification has been rapid and described by a diversity-dependent trajectory in the exceptionally explosive radiation of Rattus rats, the extent of interspecies geomorphologic diversification has been minimal [ 16 ]. A number of hypotheses have been formulated to explain such disjoint patterns between descent and phenotype diversity. For example, it has been suggested that the signatures of early burst adaptive radiations can be retained in phenotypical traits, while high extinction or fluctuations in net diversifications can erase them from the structure of the evolution [ 13, 17 ]. besides, non-adaptive radiations are expected to diversify taxonomically but not a lot phenotypically [ 16, 18 – 20 ]. last, a longstanding argue focuses on whether macroevolutionary processes differ between island and continental radiations. Given that islands are spatially limited and have simpler ecological backgrounds compared to continents, both diversification processes and cladogenesis-phenotype links may follow different trajectories mediated by their intrinsic differences in ecological opportunity, which is expected to be more common on islands [ 1, 21 – 23 ]. In fact, although most biodiversity resides on continents [ 24 ], stream cognition on adaptive radiations derives chiefly from island models. therefore, studies of diversification dynamics in both lineages and phenotypes in continental radiations remain both a critical empiric and conceptual necessitate and a promise research venue. In holocene years, the exceptionally diverse radiotherapy of south american lizards of the genus Liolaemus has emerged as a promise model to investigate adaptiveradiations on continents. Consisting of 240+ species, Liolaemus is the world ’ s second gear rich genus of extant amniotes [ 25 ]. signally, since their origin ( estimated ~22 Mya, [ 25, 26 ] ), these lizards have adapted to the widest range of ecological and climatic conditions known among reptiles [ 6, 25, 27, 28 ], including extreme point environments ranging from the Atacama Desert ( the driest position on land ) to Tierra del Fuego ( the southernmost stead where a reptile has been found ), along both the Pacific and Atlantic coasts, and reaching up to 5,000 + thousand altitudes in the Andes [ 27, 29 – 34 ]. importantly, late studies suggest that this radiation may have been accelerated by the enormous ecological opportunity created by the Andes upheaval [ 6, 35 ]. This mind besides suggests that the evolution of viviparity ( viviparous replica ) provided the samara initiation that unlocked the harsh Andean environments for early Liolaemus colonization and subsequent diversification [ 6, 35, 36 ]. thus, this linage offers a unique model to investigate the causes and trajectories of evolutionary radiations on continents. here, we study the tempo and mode of macroevolutionary diversification in descent affluence and torso size in the Liolaemus radiation, and discuss our findings in the context of radiations triggered by continental ecological opportunity. A central prediction derived from adaptive radiation theory is that both diverseness dimensions will show signals of diversity-dependent diversification over time .

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