2017), suggesting the pattern of radiation along genetic lines of least resistance may be common in nature, even when considering evolution over tens of millions of years. We compare adaptive radiation models within Anolis and in the Anolis clade and a potential sister lineage, the Corytophanidae. We then explore whether the major axes of genetic variation for each species share orientation in multivariate space (Krzanowski common subspace analysis). Biol. If you do not receive an email within 10 minutes, your email address may not be registered, B. Ecomorphology, performance capability, and scaling of West Indian Anolis lizards: An evolutionary analysis. The lizards are situated across multiple Caribbean islands known as the Greater Antilles with 154 of the 300 species being located on these islands, all from two colonizing species (Knox et al., 2001). On the scale of a few generations, the interactions between these factors are well understood. 2002; Arnold et al. Anolis. and E.D.B. (2017). King for advice on analyses; and L. Harmon, J. Kolbe, B. Langerhans, S. Gavrilets and D. Simberloff for critical review of the manuscript. When we compared the estimated ancestral G matrix (Ganc) to the divergence matrix D in a common subspace, we found a strong relationship between within‐species genetic variance (G) in a given direction and divergence in species means (D) in the same direction (Fig. 1998; Mahler et al. Because eigenvalues may be negative, the eighth eigenvector within an eigentensor sometimes explains a large amount of divergence in G (Table S5). Learn about our remote access options, Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, 24061, Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, Minnesota, 55108, Computing Community Consortium, Computing Research Association, Washington, District of Columbia, 20036, Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 3B2 Canada, Department of Biological Sciences, University of Rhode Island, Kingston, Rhode Island, 02881, Department of Biology, Washington University, Saint Louis, Missouri, 63130, Department of Biology and Mountain Lake Biological Station, University of Virginia, Charlottesville, Virginia, 22904. 25, 241–286 (2000), Duong, T. ks: Kernal Smoothing, version 1.3.4. 2002; Rabinowitz and Vokes 2012). Campbell, B. G.) 180–230 (Aldine, Chicago, 1972), Hedrick, A. V. & Temeles, E. J. 2013). Substituting these eigenvectors for hi in our subsequent analyses did not change our results. (2021), Biological Journal of the Linnean Society Studying their movement across the islands in the Greater Antilles, it is apparent that new species have diversified, specializing to different parts of the structural habitat (e.g., twigs, grass, canopy). (2020). Using estimated intercepts, slopes from the regression of ln‐transformed trait values on ln‐transformed SVL, and the grand mean SVL across all seven species (34.81 mm; Table S2), we calculated size‐corrected species means for each trait. In all species, the axis of greatest genetic variance (gmax) was strongly associated with genetic variance in limb traits, which consistently showed strong positive loadings (Table S1). Genetic covariance tensor analysis showed that nearly half of the divergence in G could be accounted for by the first eigentensor (E1), which was highly correlated with the overall genetic variance. We thank J. Higa, L.-R. Chu and C. K. Wang for assistance in the field; T. Duong and A. To obtain We found that the major axis of morphological evolution was well aligned with a major axis of genetic variance shared by all species despite separation times of 20–40 million years, suggesting that divergence occurred along a conserved genetic line of least resistance. Size‐corrected species means and divergence matrix. Caribbean Anolis lizards are a classic case of adaptive radiation, repeated four times across islands of the Greater Antilles. They have become a textbook example of adaptive radiation and have contributed greatly to our understanding of … Further research is needed to determine whether the patterns demonstrated here are general and to dissect the mechanisms responsible for their persistence. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate. 72, 541–559 (2002), Losos, J. This project tests the hypothesis that developmental responses to mechanical stress drive adaptive diversification in Anolis lizard limb length. Second, multivariate nonlinear selection may further contribute to the stability of G by conforming its orientation to the adaptive landscape (Cheverud 1982; Jones et al. On each island, very similar patterns of evolutionary divergence have occurred, resulting in the evolution of the same set of ecological specialists—termed ecomorphs—on each island. In drosophild flies, Houle et al. Further, this signal persisted even as G itself evolved, apparently because the largest evolutionary changes in G were themselves aligned with the line of genetic least resistance. Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily. Berkeley: University of California Press, 528 pp. In the short run, features of genetic architecture such as limited genetic variation or strong genetic correlations may lead to constraints that bias evolutionary response to selection toward certain directions, while slowing or prohibiting evolution in other directions (Arnold 1992; Blows and Hoffmann 2005; Walsh and Blows 2009). Similarly, ecological and evolutionary factors governing community-level diversity are rarely invoked to explain the degree to which the sexes can differ. Zool. 1998; Losos 2009; Mahler et al. Adaptive radiation, which results when a single ancestral species gives rise to many descendants, each adapted to a different part of the environment, is possibly the single most important source of biological diversity in the living world. Google Scholar, Andersson, M. B. We were unable to estimate M in anoles, but the combination of traits represented within e11 suggests that the generation of pleiotropic mutations may indeed play a role in how G diverges. Most tests of evolution along genetic lines of least resistance follow Schluter (1996), comparing divergence of species means to a single estimate of G. We used a different approach that allows us to capture information from all of estimates of G within the radiation. 2010; Bolstad et al. To visualize species differences in multivariate genetic variance, we projected each of these eigenvectors through each species‐specific G matrix to calculate genetic variance in a common set of orthogonal trait combinations. Some of our observations, such as relative stability of orientation and more divergence of trait combinations with greater genetic variance, are consistent with a G matrix constrained by mutation. Article  Dozens of undergraduates at the University of Virginia provided animal care and assistance with data collection; special thanks are due to Margo Adler, Tyler Cassidy, Brian Duggar, Maridel Fredericksen, Casey Furr, Jessie Handy, Bryan Hendrick, Uma Pendem, Jeff Wright, and Elizabeth Zipperle. Alignment of eij with di would suggest that G‐matrix evolution was influenced by the same factors that led to divergence in species means. S2). 2019. 2004, 2012). Evolution of lizard congeners in a complex island fauna: a trial analysis, Combining phylogenomic and supermatrix approaches, and a time‐calibrated phylogeny for squamate reptiles (lizards and snakes) based on 52 genes and 4162 species, The additive genetic variance‐covariance matrix. In addition, within each island, trunk‐ground species had slightly higher scores for d1 than did trunk‐crown species. Although we cannot definitively distinguish between genetic constraint, drift, and selection as the cause of this pattern, the alternatives lead to equally compelling conclusions about the evolutionary process. J. Evol. The second axis of divergence (d2) was nearly orthogonal to h1 (Table 4) and was significantly but weakly aligned with the next axis of available genetic variation (h2; Table 4). On microevolutionary timescales, adaptive evolution depends upon both natural selection and the underlying genetic architecture of traits under selection, which may constrain evolutionary outcomes. In this view, there are many potential evolutionary optima available to anoles, but divergence tends to occur more often in certain directions with more available genetic variance. Parameters from our animal models were used to quantify species divergence in morphology. The coordinates of each species within each eigentensor can be calculated to determine the extent to which species differ in a particular subspace (Hine et al. III conceived the study; J.W.M. We tested for evidence of this signal in West Indian Anolis lizards, an iconic example of adaptive radiation. Trends Ecol. As an additional measure of orientation, we calculated all pairwise angles between species‐specific estimates of gmax. Alternative estimates of divergence (see Additional Methods) had similar eigenstructure to D (Tables S2, S3; Fig. Present address: Present address: Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138, USA., Department of Zoology, University of Hawaii at Manoa, 2538 McCarthy Mall, Edmonson 152, Honolulu, Hawaii 96822, USA, Department of Mathematics, Campus Box 1146, Department of Biology, Campus Box 1137, Washington University, St Louis, Missouri 63130, USA, You can also search for this author in This axis primarily described genetic variance in body and head width. Drift should also cause population means to diverge in directions with more genetic variance, resulting in divergence along gmax and thus alignment between d1 and the direction of most change in G. Although this scenario is theoretically plausible, the well‐established role of selection in the evolution of Anolis ecomorphs (Losos 2009) suggests that neutral processes are highly unlikely to be the only factor explaining such alignment. Both Bahamian species are from lineages that originated in Cuba and colonized the Bahamas naturally (Kolbe et al. Similarly, divergence in G (DG) was also predicted by within‐species genetic variance (slope = 1.83 ± 0.105; P < 0.0001, R2 = 0.98), with the trait combinations with the greatest genetic variance also showing the greatest divergence in variance across species (Fig. behavioral convergence and adaptive radiation: effects of habitat use on territorial behavior in anolis lizards Michele A. Johnson, 1 , 2 , 3 Liam J. Revell, 4 , 5 and Jonathan B. Losos 4 Leleña Avila, Brian Falk, Chris Feldman, Vince Formica, José Luis Herrera, Tonia Hsieh, Melissa Losos, Ashli Moore, Liam Revell, and Matt Sanford provided assistance with field collections. 1). One of the best-studied examples involves Caribbean Anolis… Conversely, if sexual dimorphism and interspecific divergence are alternative means of ecological diversification, then the degree of sexual dimorphism may be negatively related to the extent of adaptive radiation. 64, 419–461 (1989), Schoener, T. W. in Biology of the Reptilia Vol. and J.J.K. contributed to study design; J.W.M., J.J.K., D.L.M., J.B.L., and E.D.B. Species coordinates in the first eigentensor (E1), which explained 48% of divergence in G, were highly correlated with the trace of G (total genetic variance), suggesting that the largest changes in G were changes in size (Fig. 2017). 2003). Depending on what mechanisms are ultimately responsible for these patterns, our results may have one of two equally exciting implications. Convergent evolution is a process in which a specific hereditary traits become developed in organisms that did not have such. 2008), potentially altering the genetic lines of least resistance to reflect the adaptive landscape (Arnold et al. We also thank J. David Aguirre, Robert Cox, Tamara Fetters, Sarah Foltz, Angela Hornsby, and Josef Uyeda for helpful discussions and/or comments on the manuscript. We demonstrate that the Puerto Rican Anolis adaptive radiation is accompanied by physiological divergence in both heat tolerance and sensitivity to sub-lethal temperature variability. 1). Statistical significance of alignment was assessed by comparison to a null distribution of randomly generated pairs of vectors (see Methods); Understanding the evolution and stability of the, The adaptive landscape as a conceptual bridge between micro‐ and macroevolution, From micro‐ to macroevolution through quantitative genetic variation: positive evidence from field crickets, Ecological morphology of Caribbean anoles, Genetic constraints on the evolution of mate recognition under natural selection, A reassessment of genetic limits to evolutionary change, Genetic constraints predict evolutionary divergence in, Evolution of the additive genetic variance‐covariance matrix under continuous directional selection on a complex behavioural phenotype, The contribution of selection and genetic constraints to phenotypic divergence, Phenotypic, genetic, and environmental morphological integration in the cranium, ASReml User Guide Release 3.0. The vector explaining the largest proportion of divergence in G (e11) was well aligned with the major axes of both morphological divergence (d1) and conserved genetic variance (h1; Table 4). Science 279, 2115–2118 (1998), Stamps, J. 2004) (Table S1). (2021), Integrative Organismal Biology Nature 447, 202–205 (2007). Relationship between log‐transformed genetic variance (G) and four different estimates of divergence in a set of eight orthogonal trait combinations. Phenotypic evolution, constant covariances, and the maintenance of additive variance, Abundant genetic variation plus strong selection = multivariate genetic constraints: a geometric view of adaptation, Evolution of genetic variance during adaptive radiation, The origin of faunas. In our analyses, these eigenvalues could range from 0 to 7, the number of species. This approach allowed us to determine how species had diverged in shape while controlling for species differences in overall size. Caribbean Anolis lizards are a classic case of adaptive radiation, repeated four times across islands of the Greater Antilles. Both natural selection and genetic architecture play important roles in determining the direction and magnitude of evolutionary change (Lande 1976, 1979). Stanley A Sawyer Evolution 54, 259–272 (2000), CAS  Perhaps even more surprising than the correspondence between genetic variation and divergence is the fact that this alignment occurred despite evolutionary changes in the G matrix. Adaptive radiation, which results when a single ancestral species gives rise to many descendants, each adapted to a different part of the environment, is possibly the single most important source of biological diversity in the living world. S1). Article  On the one hand, elaborate adaptive radiations like the one seen in West Indian anoles may be possible even when genetic constraints persist for millions of years. 2014; but see Houle et al. Because the direction of eigenvectors is arbitrary, we reversed the sign of one of the vectors if the calculated angle was above 90°. The first of these axes (h1) explained between 46 and 61% of genetic variance within each species and was similar (but not identical) to each species‐specific gmax (Table S4) as well as to an ancestral reconstruction of gmax (θ = 10.7°). The percent variance explained by gmax (the axis of greatest additive genetic variance) was used as an index of G matrix shape, which indicates a population's potential to respond to selection aligned with gmax relative to other directions. Two other axes (h3 and h4) were less similar across species (P = 5.89 and 4.32, respectively) and captured a smaller amount of genetic variance within each species (5–14% and 3–15%, respectively). Quantitative genetic theory predicts that G should eventually conform to the contours of the adaptive landscape (Cheverud 1982; Arnold et al. Such a process should not only stabilize the orientation of gmax but also cause changes in the magnitude of genetic variance explained by gmax. 2017). Among other traits, ecomorphs differ notably in relative limb length, which allows different ecomorphs to perform well in different microhabitats. Together, these findings suggest that groups of species may diverge along lines of genetic least resistance for millions of years and that this pattern is unlikely to be disrupted by concomitant changes in underlying genetic architecture. Examination of first ten e vectors showed that divergence in G was more closely aligned with axes of conserved genetic variance (h1 and h2) than with axes of morphological divergence (d1 and d2; two‐tailed sign test, P = 0.04; Table S5). Genetic drift is predicted to primarily influence G‐matrix size, with smaller populations retaining less genetic variance (Jones et al. It is surprising, then, that such a pervasive source of biological diversity has not been integrated into studies of adaptive radiation, despite extensive and growing attention to both phenomena1,3,4,5,6,7. Second, we asked whether the divergence of G itself occurred in directions predicted by either morphological divergence or conserved axes of genetic variance by calculating the angles between the largest ten eigenvectors (eij) from the tensor analysis and di and hi vectors, respectively. Marguerite A. Butler. Ecological character displacement: glass half full or half empty? Relationship between log‐transformed genetic variance (, I have read and accept the Wiley Online Library Terms and Conditions of Use. the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in In the study of adaptive radiation, few organisms serve as a better model than Caribbean . The classification of Anolis: conflict between genetic and osteological interpretation as exemplified by Anolis cybotes. However, the well‐established adaptive basis of morphological divergence in the Anolis radiation suggests that selection likely plays a role in generating this pattern. Taken together, these results suggest that the alignment of phenotypic divergence and G‐matrix evolution may be a general phenomenon.
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