Anolis
Temporal range:
Green anole (Anolis carolinensis)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Iguania
Family: Dactyloidae
Genus: Anolis
Daudin, 1802
Type species
Anolis punctatus
Daudin, 1802
Species

circa 425 spp., see text

Anolis is a genus of anoles (US: /əˈnoʊ.liz/ ⓘ), iguanian lizards in the family Dactyloidae, native to the Americas. With more than 425 species,[1] it represents the world's most species-rich amniote tetrapod genus, although many of these have been proposed to be moved to other genera, in which case only about 45 Anolis species remain.[2][3] Previously, it was classified under the family Polychrotidae that contained all the anoles, as well as Polychrus, but recent studies place it in the Dactyloidae.[2]

Taxonomy

This very large genus displays considerable paraphyly, but phylogenetic analysis suggests a number of subgroups or clades.[2][4] Whether these clades are best recognized as subgenera within Anolis or separate genera remains a matter of dispute.[2][3][5]

If the clades are recognized as full genera, about 45 species remain in Anolis, with the remaining moved to Audantia (9 species), Chamaelinorops (7 species), Ctenonotus (more than 40 species), Dactyloa (circa 95 species), Deiroptyx (almost 35 species), Norops (about 190 species), and Xiphosurus (around 15 species).[2][3] Some of these can be further subdivided. For example, Phenacosaurus was often listed as a full genus in the past, but it is a subclade within Dactyloa (Dactyloa heteroderma species group).[6] Among the subgroups within Anolis are:

In 2011, the green (or Carolina) anole (Anolis carolinensis) became the first reptile to have its complete genome published.[7]

Closely related, recently diverged anole lizards exhibited more divergence in thermal biology than in morphology. These anole lizards are thought to have the same structural niche and have similarities in their size and shape, but they inhabit different climatic niches with was variability in temperature and openness of the environment. This suggests that thermal physiology is more associated with recently diverged anole lizards.[8][9]

Ecomorphs

Anolis lizards are some of the best examples of both adaptive radiation and convergent evolution. Populations of lizards on isolated islands diverge to occupy separate ecological niches, mostly in terms of the location within the vegetation where they forage (such as in the crown of trees vs. the trunk vs. underlying shrubs).[10] These divergences in habitat are accompanied by morphological changes primarily related to moving on the substrate diameter they most frequently encounter, with twig ecomorphs having short limbs, while trunk ecomorphs have long limbs.

In addition, these patterns repeat on numerous islands, with animals in similar habitats converging on similar body forms repeatedly.[10][11] This demonstrates adaptive radiation can actually be predictable based on habitat encountered, and experimental introductions onto formerly lizard-free islands have proven Anolis evolution can be predicted.[12][13][14][15]

After appearing on each of the four Greater Antillean Islands about 50 million years ago, Anolis lizards spread on each island to occupy niches in the island's trees. Some living in the tree canopy area, others low on the tree trunk near the ground; others in the mid-trunk area, others on twigs. Each new species developed its own distinct body type, called an ecomorph, adapted to the tree niche where it lived. Together, the different species occupied their various niches in the trees as a "community". A study of lizard fossils trapped in amber shows that the lizard communities have existed for about 20 million years or more. Four modern ecomorph body types, trunk-crown, trunk-ground, trunk, and twig, are represented in the amber fossils study. Close comparison of the lizard fossils with their descendants alive today in the Caribbean shows the lizards have changed little in the millions of years.[16][17]

Behavior

As ectotherms, Anolis lizards must regulate their body temperature partly through behavioral changes and bask in the sunlight to gain enough heat to become fully active, but lizards cannot behaviorally warm themselves at night when temperatures drop. Because of this, cold tolerance evolves faster than heat tolerance in these lizards.[18] On the island of Hispaniola, both high-altitude and low-altitude lizard populations exist, and the thermal conditions at high and low elevations differ significantly.[19] High-altitude lizards have shifted their ecological niche to boulder environments, where warming themselves is easier, and they show changes in the shape of limbs and skull that make them better adapted to these environments.

Species

The Anolis lizards that are less susceptible to predation are those with a dewlap in which both the scales and the exposed skin areas between them match the usual pale gray or whitish of the rest of the ventral surface.[20]

Dewlap

The dewlap is a flap of skin found beneath the jaw or throat of Anolis lizards. It can present in a variety of colorations, and is most present in male anoles. The dewlap is extended by means of the hyoid muscles in the throat, and can be flashed in a "pulse" pattern where the flap is extended repeatedly, or a "moving flag" pattern, where the lizard flashes it continuously while bobbing up and down.[21] The coloration of the dewlap is caused by two pigments, pterins and carotenoids. Pterin pigments are compounds synthesized from guanine, whereas carotenoids are pigments acquired from the diet.[22] Both cause the red-yellow hues most commonly found in Anolis lizard dewlaps. The function of the dewlap in Anolis lizards has been a topic of debate for centuries. It is thought that the dewlap is flashed as a visual signal for other competing males, or as a courtship signal for single females. It has also been hypothesized that the dewlap serves as a signal for sex recognition.[23]

Pink dewlap on an Anolis carolinensis lizard

Initial studies

The first study done on dewlap function was by Mertens (1926). The initial assumption was that the dewlap was flashed as a method of sexual selection, and that the males would use it in order to attract females. It is hypothesized that female Anolis lizards are more attracted to males who flash their dewlaps more often, or have more brightly colored dewlaps.[23] This was then challenged by the hypothesis that males flashed their dewlap as a way to threaten other males in the area.[24] During intermale fights, dewlaps are flashed. More currently, many studies have been done on the dewlap as a function for species recognition, with focus on the relationship of the contrast between dewlap color and environment.

Relationship with environment

The dewlap comes in a variety of colors, including yellow, blue, and red. It was previously believed that the color of the dewlap is what mattered most in interlizard interactions, but it has since been found that there exists a relationship between habitat light conditions and dewlap color.[25][21] This means that, rather than the color being of importance, it is the contrast of the dewlap against the background of its environment that best visually signals to other lizards. There have been many methods used to determine this. Persons et. al (1999) found that the probability of a dewlap showing being detected goes up with the contrast of dewlap against the background. They determined this by measuring the amount of times a "positive response" of the lizard's eyes turning towards a flashed dewlap occurred among different background contrasts. Similarly, Leal and Fleishman (2002) found that the light conditions in which a lizard displays its dewlap affects the probability of it being visually detected. They did this by measuring the UV spectral reflectance of dewlaps in Anolis cristatellus lizards using a spectroradiometer, then measuring the spectral sensitivity of the lizards’ retinal responses using electroretinographic (ERG) flicker photometry.[26]

Evolution

Anolis lizards have emerged to be a good example of adaptive radiation. The difference in dewlap morphology among Anolis lizard populations demonstrates this phenomenon. Anolis lizards have the ability to adapt to different areas of the environment in a way where multiple species can coexist effectively. The amount of vegetation in an environment affects the amount of light absorbed. Studies have shown that lighting affects the dewlap’s function as a visual signal. The diversity in vegetation in Anolis lizards’ environments has caused a similar diversity in dewlap morphology, as different species of anoles adapt to the lighting conditions in their environment.[26] The ability for a lizard to signal effectively also means it is able to defend its territory and attract mates more effectively, making it a good competitor.

The relationship between background contrast and visual signals also suggests that there exists a coevolution between the signals and sensory systems of Anolis lizards.[27] The environmental diversity of Anolis habitats causes a diversity in the recognition of individuals. Sensory systems must be able to effectively pick up on dewlap signals, thus coevolving with the changes in dewlap characteristics.

One of the main limitations to these theories is that of gene flow. Population genetic theory says that gene flow can counteract evolutionary adaptations made and prevent signal divergence, due to an influx of abnormal alleles into the new population.[28] This causes a genetic homogenization and challenges the idea that dewlap morphology in Anolis lizards and their sensory systems have coevolved.

References

  1. ↑ Uetz, P.; Hallermann, J. (2018). "Dactyloidae". The Reptile Database. Retrieved 5 November 2018.
  2. 1 2 3 4 5 Nicholson, Kirsten E.; Crother, Brian I.; Guyer, Craig; Savage, Jay M. (2012). "It is time for a new classification of anoles (Squamata: Dactyloidae)" (PDF). Zootaxa. 3477 (1): 1–108, page 38. doi:10.11646/zootaxa.3477.1.1. Archived (PDF) from the original on 30 January 2016. Abstract
  3. 1 2 3 Nicholson, K.A.; B.I. Crother; C. Guyer; J.M. Savage (2018). "Translating a clade based classification into one that is valid under the international code of zoological nomenclature: the case of the lizards of the family Dactyloidae (Order Squamata)". Zootaxa. 4461 (4): 573–586. doi:10.11646/zootaxa.4461.4.7. PMID 30314068. S2CID 52975031.
  4. ↑ Glor, Richard E.; Jonathan, B. Losos; Larson, Allan (2005). "Out of Cuba: overwater dispersal and speciation among lizards in the Anolis carolinensis subgroup" (PDF). Molecular Ecology. 14 (8): 2419–2432. Bibcode:2005MolEc..14.2419G. doi:10.1111/j.1365-294X.2005.02550.x. PMID 15969724. S2CID 20092906.
  5. ↑ Poe; Nieto-Montes de Oca; Torres-Carvajal; Queiroz; Velasco; Truett; Gray; Ryan; Köhler; Ayala-Varela; Latella (2017). "A Phylogenetic, Biogeographic, and Taxonomic study of all Extant Species of Anolis (Squamata; Iguanidae)". Systematic Biology. 66 (5): 663–697. doi:10.1093/sysbio/syx029. PMID 28334227.
  6. ↑ Nicholson 2012, p. 17
  7. ↑ Sweetlove, Lee (2011-08-31). "Lizard genome unveiled". Nature. doi:10.1038/news.2011.512.
  8. ↑ Losos, J. B. (2009). Lizards in an evolutionary tree: ecology and adaptive radiation of anoles. University of California Press, Berkeley, CA.
  9. ↑ Hertz, P.E.; Arima, Y.; Harrison, A.; Huey, R.B.; Losos, J.B.; Glor, R.E. (2012). "Asynchronous evolution of physiology and morphology in Anolis lizards". Org. Evol. 67 (7): 2101–2113. doi:10.1111/evo.12072. PMID 23815663. S2CID 2793493.
  10. 1 2 Losos, J.B. (2007). "Detective work in the West Indies: integrating historical and experimental approaches to study island lizard evolution" (PDF). BioScience. 57 (7): 585–597. doi:10.1641/b570712. S2CID 6869606.
  11. ↑ Losos, J. B.; Jackman, T. R.; Larson, A.; de Queiroz, K.; Rodriguez-Schettino, L. (1998). "Contingency and determinism in replicated adaptive radiations of island lizards". Science. 279 (5359): 2115–2118. Bibcode:1998Sci...279.2115L. doi:10.1126/science.279.5359.2115. PMID 9516114.
  12. ↑ Calsbeek, R (2008). "Experimental evidence that competition and habitat use shape the individual fitness surface". Journal of Evolutionary Biology. 22 (1): 97–108. doi:10.1111/j.1420-9101.2008.01625.x. PMID 19120813. S2CID 25745447.
  13. ↑ Calsbeek, R.; Buermann, W.; Smith, T.B. (2009). "Parallel shifts in ecology and natural selection in an island lizard". BMC Evolutionary Biology. 9: 3. doi:10.1186/1471-2148-9-3. PMC 2630972. PMID 19126226.
  14. ↑ Calsbeek, R.; Cox, R.M. (2010). "Experimentally assessing the relative importance of predation and competition as agents of selection". Nature. 465 (7298): 613–616. Bibcode:2010Natur.465..613C. doi:10.1038/nature09020. PMID 20453837. S2CID 4326027.
  15. ↑ Calsbeek, R.; Smith, T.B. (2007). "Probing the adaptive landscape using experimental islands: density-dependent natural selection on lizard body size". Evolution. 61 (5): 1052–1061. doi:10.1111/j.1558-5646.2007.00093.x. PMID 17492960. S2CID 4643163.
  16. ↑ "Trapped in Amber: Ancient fossils reveal remarkable stability of Caribbean lizard communities". 27 July 2015. Retrieved 2015-07-28.
  17. ↑ Sherratt, Emma; Castañeda, María del Rosario; Garwood, Russell J.; Mahler, D. Luke; Sanger, Thomas J.; Herrel, Anthony; Queiroz, Kevin de; Losos, Jonathan B. (2015-07-27). "Amber fossils demonstrate deep-time stability of Caribbean lizard communities". Proceedings of the National Academy of Sciences. 112 (32): 9961–9966. Bibcode:2015PNAS..112.9961S. doi:10.1073/pnas.1506516112. ISSN 0027-8424. PMC 4538666. PMID 26216976.
  18. ↑ Muñoz, Martha M.; Stimola, Maureen A.; Algar, Adam C.; Conover, Asa; Rodriguez, Anthony J.; Landestoy, Miguel A.; Bakken, George S.; Losos, Jonathan B. (2014-03-07). "Evolutionary stasis and lability in thermal physiology in a group of tropical lizards". Proceedings of the Royal Society B: Biological Sciences. 281 (1778): 20132433. doi:10.1098/rspb.2013.2433. ISSN 0962-8452. PMC 3906933. PMID 24430845.
  19. ↑ Muñoz, Martha M.; Losos, Jonathan B. (January 2018). "Thermoregulatory Behavior Simultaneously Promotes and Forestalls Evolution in a Tropical Lizard". The American Naturalist. 191 (1): E15–E26. doi:10.1086/694779. ISSN 0003-0147. PMID 29244559. S2CID 3918571.
  20. ↑ Fitch, H.S.; Hillis, D.M. (1984). "The anolis dewlap: Interspecific variability and morphological associations with habitat". Copeia. 1984 (2): 315–323. doi:10.2307/1445187. JSTOR 1445187.
  21. 1 2 Persons, M. H.; Fleishman, L. J.; Frye, M. A.; Stimphil, M. E. (1999-07-05). "Sensory response patterns and the evolution of visual signal design in anoline lizards". Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology. Springer Science and Business Media LLC. 184 (6): 585–607. doi:10.1007/s003590050358. ISSN 0340-7594. S2CID 21160410.
  22. ↑ Steffen, John E.; McGraw, Kevin J. (2007). "Contributions of pterin and carotenoid pigments to dewlap coloration in two anole species". Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology. Elsevier BV. 146 (1): 42–46. doi:10.1016/j.cbpb.2006.08.017. ISSN 1096-4959. PMID 17056290.
  23. 1 2 Sigmund, William R. (1983). "Female Preference for Anolis carolinensis Males as a Function of Dewlap Color and Background Coloration". Journal of Herpetology. JSTOR. 17 (2): 137–143. doi:10.2307/1563454. ISSN 0022-1511. JSTOR 1563454.
  24. ↑ NOBLE, G. K.; BRADLEY, H. T. (1933). "The Mating Behavior of Lizards; ITS Bearing on the Theory of Sexual Selection". Annals of the New York Academy of Sciences. Wiley. 35 (1): 25–100. Bibcode:1933NYASA..35...25N. doi:10.1111/j.1749-6632.1933.tb55365.x. ISSN 0077-8923. S2CID 85270929.
  25. ↑ Fleishman, Leo J.; Perez-Martinez, Christian A.; Leal, Manuel (2022-08-01). "Can Sensory Drive Explain the Evolution of Visual Signal Diversity in Terrestrial Species? A Test with Anolis Lizards". The American Naturalist. University of Chicago Press. 200 (2): 236–249. doi:10.1086/720267. ISSN 0003-0147. PMID 35905402. S2CID 247884850.
  26. 1 2 Leal, Manuel; Fleishman, Leo J. (2002-02-22). "Evidence for habitat partitioning based on adaptation to environmental light in a pair of sympatric lizard species". Proceedings of the Royal Society of London. Series B: Biological Sciences. The Royal Society. 269 (1489): 351–359. doi:10.1098/rspb.2001.1904. ISSN 0962-8452. PMC 1690909. PMID 11886622.
  27. ↑ Leal, Manuel; Fleishman, Leo J. (2004). "Differences in Visual Signal Design and Detectability between Allopatric Populations ofAnolisLizards". The American Naturalist. University of Chicago Press. 163 (1): 26–39. doi:10.1086/379794. ISSN 0003-0147. PMID 14767834. S2CID 5650723.
  28. ↑ Dieckmann, Ulf; Doebeli, Michael (1999). "On the origin of species by sympatric speciation" (PDF). Nature. Springer Science and Business Media LLC. 400 (6742): 354–357. Bibcode:1999Natur.400..354D. doi:10.1038/22521. ISSN 0028-0836. PMID 10432112. S2CID 4301325.

Further reading

Wikimedia Commons has media related to Anolis.
Wikispecies has information related to Anolis.
  • Anole Annals, a blog written and edited by scientists who study Anolis lizards
  • Anolis, The Reptile Database
  • Adapting Anolis, short film on adaptations of Cuba's Anolis lizards
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