Showing papers by "Jonathan B. Losos published in 2010"

Early bursts of body size and shape evolution are rare in comparative data.

Abstract: George Gaylord Simpson famously postulated that much of life's diversity originated as adaptive radiations-more or less simultaneous divergences of numerous lines from a single ancestral adaptive type. However, identifying adaptive radiations has proven difficult due to a lack of broad-scale comparative datasets. Here, we use phylogenetic comparative data on body size and shape in a diversity of animal clades to test a key model of adaptive radiation, in which initially rapid morphological evolution is followed by relative stasis. We compared the fit of this model to both single selective peak and random walk models. We found little support for the early-burst model of adaptive radiation, whereas both other models, particularly that of selective peaks, were commonly supported. In addition, we found that the net rate of morphological evolution varied inversely with clade age. The youngest clades appear to evolve most rapidly because long-term change typically does not attain the amount of divergence predicted from rates measured over short time scales. Across our entire analysis, the dominant pattern was one of constraints shaping evolution continually through time rather than rapid evolution followed by stasis. We suggest that the classical model of adaptive radiation, where morphological evolution is initially rapid and slows through time, may be rare in comparative data.

Adaptive Radiation, Ecological Opportunity, and Evolutionary Determinism

Abstract: Adaptive radiation refers to diversification from an ancestral species that produces descendants adapted to use a great variety of distinct ecological niches. In this review, I examine two aspects of adaptive radiation: first, that it results from ecological opportunity and, second, that it is deterministic in terms of its outcome and evolutionary trajectory. Ecological opportunity is usually a prerequisite for adaptive radiation, although in some cases, radiation can occur in the absence of preexisting opportunity. Nonetheless, many clades fail to radiate although seemingly in the presence of ecological opportunity; until methods are developed to identify and quantify ecological opportunity, the concept will have little predictive utility in understanding a priori when a clade might be expected to radiate. Although predicted by theory, replicated adaptive radiations occur only rarely, usually in closely related and poorly dispersing taxa found in the same region on islands or in lakes. Continge...

Ecological opportunity and the rate of morphological evolution in the diversification of Greater Antillean anoles.

Abstract: The pace of phenotypic diversification during adaptive radiation should decrease as ecological opportunity declines. We test this prediction using phylogenetic comparative analyses of a wide range of morphological traits in Greater Antillean Anolis lizards. We find that the rate of diversification along two important axes of Anolis radiation—body size and limb dimensions—decreased as opportunity declined, with opportunity quantified either as time elapsed in the radiation or as the diversity of competing anole lineages inferred to have been present on an island at different times in the past. Most previous studies of the ecological opportunity hypothesis have focused on the rate of species diversification; our results provide a complementary perspective, indicating that the rate of phenotypic diversification declines with decreasing opportunity in an adaptive radiation.

Favorable climate change response explains non-native species' success in Thoreau's woods.

Abstract: Invasive species have tremendous detrimental ecological and economic impacts. Climate change may exacerbate species invasions across communities if non-native species are better able to respond to climate changes than native species. Recent evidence indicates that species that respond to climate change by adjusting their phenology (i.e., the timing of seasonal activities, such as flowering) have historically increased in abundance. The extent to which non-native species success is similarly linked to a favorable climate change response, however, remains untested. We analyzed a dataset initiated by the conservationist Henry David Thoreau that documents the long-term phenological response of native and non-native plant species over the last 150 years from Concord, Massachusetts (USA). Our results demonstrate that non-native species, and invasive species in particular, have been far better able to respond to recent climate change by adjusting their flowering time. This demonstrates that climate change has likely played, and may continue to play, an important role in facilitating non-native species naturalization and invasion at the community level.

Are Lizards Toast

Abstract: Lizards should be relatively invulnerable to warming: They are very good at evading thermal stress, tolerate high body temperatures, and resist water loss. Nevertheless, on page 894 of this issue, Sinervo et al. ( 1 ) document extinctions of lizard populations on five continents and argue that global warming is responsible. They use a simple biological model, validated against observed extinctions, to predict that warming will drive almost 40% of all global lizard populations extinct by 2080. If their prediction is even close to correct, lizards may be “the new amphibians” ( 2 ) in a race toward extinction.

Habitat use affects morphological diversification in dragon lizards

Abstract: Habitat use may lead to variation in diversity among evolutionary lineages because habitats differ in the variety of ways they allow for species to make a living. Here, we show that structural habitats contribute to differential diversification of limb and body form in dragon lizards (Agamidae). Based on phylogenetic analysis and ancestral state reconstructions for 90 species, we find that multiple lineages have independently adopted each of four habitat use types: rock-dwelling, terrestriality, semi-arboreality and arboreality. Given these reconstructions, we fit models of evolution to species’ morphological trait values and find that rock-dwelling and arboreality limit diversification relative to terrestriality and semi-arboreality. Models preferred by Akaike information criterion infer slower rates of size and shape evolution in lineages inferred to occupy rocks and trees, and model-averaged rate estimates are slowest for these habitat types. These results suggest that ground-dwelling facilitates ecomorphological differentiation and that use of trees or rocks impedes diversification.

Adaptation and plasticity of animal communication in fluctuating environments.

Abstract: Adaptations that facilitate the reception of long-range signals under challenging conditions are expected to generate signal diversity when species communicate in different habitats. Although we have a general understanding of how individual communicating animals cope with conditions influencing signal detection, the extent to which plasticity and evolutionary changes in signal characteristics contribute to interspecific differences in signaling behavior is unclear. We quantified the visual displays of free-living lizards and environmental variables known to influence display detection for multiple species from two separate island radiations. We found evidence of both adaptive evolution and adaptive plasticity in display characteristics as a function of environmental conditions, but plasticity accounted for most of the observed differences in display behavior across species. At the same time, prominent differences between the two island radiations existed in aspects of signaling behavior, unrelated to the environment. Past evolutionary events have therefore played an important role in shaping the way lizards adjust their signals to challenges in present-day environments. In addition to showing how plasticity contributes to interspecific differences in communication signals, our findings suggest the vagaries of evolution can in itself lead to signal variation between species.

The Anoles of Soroa: Aspects of Their Ecological Relationships

Abstract: Most lizard communities are characterized by having one or two dominant species and a handful of other species that occur at relatively low densities. However, Soroa, a site in the Sierra del Rosario of western Cuba, is home to 11 sympatric species of Anolis, of which nine are found in high abundance. In this study, we evaluate how interspecific differences in structural niche, thermal niche, body size, and behavior might allow the extraordinarily high anole species diversity at this site. We found that all pairs of species differ in at least one of the following niche axes: vegetation types occupied, substrates used, perch height, irradiance at occupied perch sites, and body temperature. Interspecific differences across these axes might serve to reduce competition, allowing the 11 species to live sympatrically within a relatively small geographic area.

Nonlinear selection and the evolution of variances and covariances for continuous characters in an anole.

Abstract: The pattern of genetic variances and covariances among characters, summarized in the additive genetic variance-covariance matrix, G, determines how a population will respond to linear natural selection. However, G itself also evolves in response to selection. In particular, we expect that, over time, G will evolve correspondence with the pattern of multivariate nonlinear natural selection. In this study, we substitute the phenotypic variance-covariance matrix (P) for G to determine if the pattern of multivariate nonlinear selection in a natural population of Anolis cristatellus, an arboreal lizard from Puerto Rico, has influenced the evolution of genetic variances and covariances in this species. Although results varied among our estimates of P and fitness, and among our analytic techniques, we find significant evidence for congruence between nonlinear selection and P, suggesting that natural selection may have influenced the evolution of genetic constraint in this species.

Cruise foraging of invasive chameleon (chamaeleo jacksonii xantholophus) in hawai'i

Abstract: We quantified the foraging behavior of the Jackson's chameleon (Chamaeleo jacksonii xantholophus), an invasive insectivorous lizard species in Hawai'i. Using video taken in the field, we focused on percent time moving, moves per minute, and movement speeds. Our results supported previous findings that chameleons are “cruise foragers” (sensu Butler, 2005), a foraging behavior unlike almost all other species of lizards.

Evolutionary biology: Communication and speciation

Abstract: An electrifying evolutionary radiation has evidently occurred among elephant fish in Africa's Ivindo basin. An implication is that open niches for communication can result in species diversification.