potentially more complex, as the homogenising effects of gene flow must be countered [1][2][3] . The 49 genic model of speciation proposes that specific genetic regions subject to strong divergent 50

Rapid adaptation of invasive species to novel habitats has puzzled evolutionary biologists for decades, especially as this often occurs in the face of limited genetic variability. Although some ecological traits common to invasive species have been identified, little is known about the possible genomic/genetic mechanisms that may underlie their success. A common scenario in many introductions is that small founder population sizes will often lead to reduced genetic diversity, but that invading populations experience large environmental perturbations, such as changes in habitat and environmental stress. Although sudden and intense stress is usually considered in a negative context, these perturbations may actually facilitate rapid adaptation by affecting genome structure, organization and function via interactions with transposable elements (TEs), especially in populations with low genetic diversity. Stress-induced changes in TE activity can alter gene action and can promote structural variation that may facilitate the rapid adaptation observed in new environments. We focus here on the adaptive potential of TEs in relation to invasive species and highlight their role as powerful mutational forces that can rapidly create genetic diversity. We hypothesize that activity of transposable elements can explain rapid adaptation despite low genetic variation (the genetic paradox of invasive species), and provide a framework under which this hypothesis can be tested using recently developed and emerging genomic technologies.

How polymorphisms are maintained within populations over long periods of time remains debated, because genetic drift and various forms of selection are expected to reduce variation. Here, we study the genetic architecture and maintenance of phenotypic morphs that confer crypsis in Timema cristinae stick insects, combining phenotypic information and genotyping-by-sequencing data from 1,360 samples across 21 populations. We find two highly divergent chromosomal variants that span megabases of sequence and are associated with colour polymorphism. We show that these variants exhibit strongly reduced effective recombination, are geographically widespread and probably diverged millions of generations ago. We detect heterokaryotype excess and signs of balancing selection acting on these variants through the species' history. A third chromosomal variant in the same genomic region likely evolved more recently from one of the two colour variants and is associated with dorsal pattern polymorphism. Our results suggest that large-scale genetic variation associated with crypsis has been maintained for long periods of time by potentially complex processes of balancing selection.

Summary1. Two major theories underpin our understanding of how predation risk shapes life history. The first is centred around predator induced changes in activity that subsequently reduce food intake and thus growth. The second is centred around size selective, predator induced changes in development. 2. Here, we challenge these theories using experiments and probabilistic models of maturation reaction norms to investigate predator induced life history in the water flea Daphnia pulex facing two different predators. 3. We combine this reaction norm investigation with an assessment of growth rate, development rate, moult number and moult duration to uncover the mechanisms controlling predator induced life history plasticity when D. pulex face either large or small size selective predators. 4. The probabilistic reaction norms reveal predator specific norms of reaction in size and age along a food gradient. Fish cues reduce age and size, with a bias in age, and do so by reducing moult number and duration. Midge cues increase age and size, with a bias in size, and do so by fine scale modulation of early growth rates. 5. These data contribute towards developing a unified view of how predation risk from multiple predators shapes life history evolution.

A long-standing question in ecology is whether phenotypic plasticity, rather than selection per se, is responsible for phenotypic variation among populations. Plasticity can increase or decrease variation, but most previous studies have been limited to single populations, single traits and a small number of environments assessed using univariate reaction norms. Here, examining two genetically distinct populations of Daphnia pulex with different predation histories, we quantified predator-induced plasticity among 11 traits along a fine-scale gradient of predation risk by a predator (Chaoborus) common to both populations. We test the hypothesis that plasticity can be responsible for convergence in phenotypes among different populations by experimentally characterizing multivariate reaction norms with phenotypic trajectory analysis (PTA). Univariate analyses showed that all genotypes increased age and size at maturity, and invested in defensive spikes (neckteeth), but failed to quantitatively describe whole-organism response. In contrast, PTA quantified and qualified the phenotypic strategy the organism mobilized against the selection pressure. We demonstrate, at the whole-organism level, that the two populations occupy different areas of phenotypic space in the absence of predation but converge in phenotypic space as predation threat increases.

No abstract

Squamates include all lizards and snakes, and display some of the most diverse and extreme morphological adaptations among vertebrates. However, compared with birds and mammals, relatively few resources exist for comparative genomic analyses of squamates, hampering efforts to understand the molecular bases of phenotypic diversification in such a speciose clade. In particular, the ∼400 species of anole lizard represent an extensive squamate radiation. Here, we sequence and assemble the draft genomes of three anole species—Anolis frenatus, Anolis auratus, and Anolis apletophallus—for comparison with the available reference genome of Anolis carolinensis. Comparative analyses reveal a rapid background rate of molecular evolution consistent with a model of punctuated equilibrium, and strong purifying selection on functional genomic elements in anoles. We find evidence for accelerated evolution in genes involved in behavior, sensory perception, and reproduction, as well as in genes regulating limb bud development and hindlimb specification. Morphometric analyses of anole fore and hindlimbs corroborated these findings. We detect signatures of positive selection across several genes related to the development and regulation of the forebrain, hormones, and the iguanian lizard dewlap, suggesting molecular changes underlying behavioral adaptations known to reinforce species boundaries were a key component in the diversification of anole lizards.

Ecology and genetics are both of general interest to evolutionary biologists as they can influence the phenotypic and genetic response to selection. The stick insects Timema podura and Timema cristinae exhibit a green/melanistic body color polymorphism that is subject to different ecologically based selective regimes in the two species. Here, we describe aspects of the genetics of this color polymorphism in T. podura, and compare this to previous results in T. cristinae. We first show that similar color phenotypes of the two species cluster in phenotypic space. We then use genome‐wide association mapping to show that in both species, color is controlled by few loci, dominance relationships between color alleles are the same, and SNPs associated with color phenotypes colocalize to the same linkage group. Regions within this linkage group that harbor genetic variants associated with color exhibit elevated linkage disequilibrium relative to genome wide expectations, but more strongly so in T. cristinae. We use these results to discuss predictions regarding how the genetics of color could influence levels of phenotypic and genetic variation that segregate within and between populations of T. podura and T. cristinae, drawing parallels with other organisms.