Biology - Story Archives: Speciation of Anoles - The Mysterious Dewlap

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Speciation of Anoles:
    The Mysterious Dewlap

    (Assistant Professor Rich Glor, Biology)

     by Katie Shaw & Lois. H. Gresh

February 6, 2007: Assistant Professor Richard Glor of the University of Rochester Biology Department travels to exotic locations all over the world to study the speciation and habits of genus Anolis lizards.  The small Anolis lizards, though unprepossessing at first glance, are one of the most biologically diverse genera in the world, with over 350 recognized species.  The genome of Anolis carolinensis, commonly called the Green Anole, is currently being sequenced at the Broad Institute in Cambridge--the first reptile genome ever to be completely sequenced.  Dr. Glor’s work focuses on speciation and diversification of anoles, with particular focus on the anoles' spectacular adaptive radiation -- the proliferation and ecological diversification of species -- and how distinctive features like the dewlap, or throat fan, have contributed to their success.

Anolis lizards have two unusual features:  their dewlaps, which are flaps of skin beneath their necks, and their adhesive foot pads, which allow them to scale vertical surfaces and which are composed of millions of tiny hairs called lamelli. 

The dewlap is an important structure because it is an integral component of anole communication. Anoles use their dewlaps to defend their territory against other males, warn away other species, and communicate with the opposite sex. Though almost all species of anole have dewlaps, the colors and displays associated with each species are vastly different. Anoles will combine several behaviors like pulsing their dewlaps out, doing pushups of varying heights, and curling their tails in a variety of ways, with each species having its own distinct pattern of communication.

Images -- A few Anolis dewlap variations (from:  "Schwartz, Albert, Geographic Variation in Anolis distichus Cope (Lacertilia, Iguanidae) in the Bahama Islands and Hispaniola," Bulletin of the Museum of Comparative Zoology, Volume 137, Number 2, Cambridge, MA:  Harvard University, September 27, 1868)

	Anolis d. ocior, Port Nelson, Rum Cay, Bahama Islands	Anolis d. juliae, western end, Ile-à-Vache, Haiti	Anolis d. biminiensis, western end, South Bimini Island, Bahama Islands	Anolis d. favillarum, 3 km NE Las Auyamas, 3300 feet, Barahona Province, República Dominicana

Currently, Dr. Glor is investigating if dewlap variations have given rise to the diversity of anoles. Because the dewlap displays limit each species to mating with its own type, a change in the dewlap could lead to species divergence.

One of the intriguing facts about anoles is that they are cryptic--that is, some species are morphologically the same, but may exhibit molecular or behavioral differences. Therefore, it is very possible that what is thought to be only one species of anole is in actuality several.

To study this problem, Dr. Glor extensively sampled Anolis distichus, a species that shows differing dewlap coloration across the island of Hispaniola, which lies between Cuba and Puerto Rico.  Glor captured lizards at a variety of locations on the island and recorded the locations using a GPS device.  Then, each sample was plotted on a map of the island and coded according to the color of dewlap.  In one area, dewlap colors changed from yellow to orange over an eight mile transect.

Next, Glor performed a molecular analysis of mitochondrial DNA to determine how related the lizards are to each other.  Samples with more similar DNA diverged more recently.  Using the molecular data, a phylogenetic tree can be drawn, which shows the divergences in the lineage of this species.  Preliminary data shows that the split between orange and yellow dewlaps occurred long ago, even though the populations are geographically close to each other. 

Another part of Glor’s research relates to niche modeling, in specific, whether particular subspecies are characterized by particular climatic requirements. First, grids of climate data for the modeling area are assembled.  Temperature, precipitation, and mean annual rainfall during the driest season are just a few of the sets of data available for every square kilometer of the globe.  Glor tries to determine whether particular dewlaps are associated with particular climates. If they are associated, then the predicted ranges of subspecies are expected to correspond fairly closely with some environmental variables. If subspecies and their associated dewlaps are not restricted to particular climatic conditions, then Glor will have gone some way toward rejecting the idea that a particular dewlap phenotype diverged in response to selection.

Speciation is an integral part of understanding invasion ecology, which occurs when a non-native species colonizes an area and becomes a pest.

In fact, the Brown Anole is invasive in Florida, where it has driven out native populations of the Green Anole, our genome sequencing candidate. While the loss of the Green Anole may not affect the daily lives of Floridians, other invasive species such as the Brown Tree Snake in Guam not only have wreaked havoc with ecosystems, they have caused problems for human residents as well. Understanding the mechanisms of speciation and adaptive radiation is critical to the fields of evolution and ecology.

Additional Details

For further details, see:

Jonathan B. Losos, Richard E. Glor, Jason J. Kolbe, and Kirsten Nicholson, "Adaptation, Speciation, and Convergence:  A Hierarchical Analysis of Adaptive Radiation in Caribbean Anolis Lizards," Annals of the Missouri Botanical Garden, 93:  24-33, October 2006.

Jason H. Knouft, Jonathan B. Losos, Richard E. Glor, and Jason J. Kolbe, "Phylogenetic Analysis of the Evolution of the Niche in Lizards of the Anolis Sagrei Group," Ecology, 87(7) Supplement, 2006, pp. S29-S38.

Richard E. Glor, Jonathan B. Losos, and Allan Larson, "Out of Cuba:  overwater dispersal and speciation among lizards in the Anolis carolinensis subgroup," Molecular Ecology (2005), 14, 2419-2432.

Richard E. Glor, Matthew E. Gifford, Allan Larson, Jonathan B. Losos, Lourdes Rodriguez Schettino, Ada R. Chamizo Lara, and Todd R. Jackman, "Partial island submergence and speciation in an adaptive radiation:  a multilocus analysis of the Cuban green anoles," Procedures of the Royal Society of London (2004), 271, 2257-2265.

For more information, please contact:
   Assistant Professor Richard Glor
   Email: rglor@mail.rochester.edu
   Faculty Webpage: http://www.rochester.edu/College/BIO/professors/glor.html

This article was co-authored by Katie Shaw as part of the curriculum of PHY 396, Supervised Science Writing I, Spring 2007. Katie is a junior Biology undergraduate.

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