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From UVATODAY

Yes, Lizards Have Their Own Holiday. Learn Why They Add Color to Our World

Wait, you didn’t know that Monday is World Lizard Day? What rock have you been living under?

To celebrate, two University of Virginia lizard-ologists want you to see these tiny reptiles’ true colors shining through.

There almost aren’t enough crayons in the box to capture the scale of their scaly vibrance. Add to that their amazing ability to sometimes change colors, and you can see how it’s easy to become a fan of the fan-throated lizard, or geek-out over the crested gecko.

Christopher Robinson, a doctoral candidate in the lab of biology professor Robert Cox, is one such devotee. He’s currently a Doffermyre Family Jefferson Dissertation-Year Fellow.

“Lizards are such wonderful organisms to study,” Robinson said. “They can be stunningly beautiful, exhibiting vibrant colors and fascinating patterns that are useful for investigating principles in evolutionary biology.”

Robinson and Cox decoded for UVA Today some of the many colorful mysteries behind lizards’ pigmentation.

Q. Why do lizards around the world vary so much in their colors?

Robinson: The evolution of color is driven by the selective pressures an animal encounters in their environment, and the way that they can be seen in it. For example, the coloration of a lizard in a deeply shaded forest and a species in a bright desert are usually quite different.

Similarly, lizards that are only active at night use color differently than lizards that are active during the day.

Two of the biggest drivers of color evolution are predation and social interactions, such as finding a mate or protecting a resource.

All of these selective pressures interact to produce the stunning variation we see in lizard colors around the world.

Q. Is predation the primary driver of why the colors have evolved?

Robinson: For some species, yes, but for others, probably not. While predation is a strong selective pressure, the ability to find a mate is just as important as not being eaten.

Many species of lizards have sexually dimorphic coloration, meaning males and females have different colors. Often, females are less colorful than males. The female coloration allows them to be cryptic and avoid predators, while the vibrant male colors act as signals to mates and rivals.

Q. Does more intense color indicate they’ll taste bad to a predator?

Robinson: In Virginia, we don’t have any lizards that are unpalatable to predators, although we do have amphibians, such as the red-spotted newt, which are bright red as juveniles to warn predators that they contain lethal toxins, which are potent enough to kill humans if they are consumed.

Cox: Bright warning colors that signal toxic or unpalatable prey are common in insects and amphibians, but not in lizards or other reptiles. However, bright color can be a warning that a species is venomous.

Gila monsters and beaded lizards of the southwestern United States and Mexico are the only truly venomous lizards, and they are strikingly colored orange and black as a warning.

Q. How does color help with mating?

Robinson: Male lizards often use coloration and colorful ornaments to signal to mates, and in some species, variation in coloration is associated with individual quality. This might mean that the individual is healthy and free from parasites, able to secure food easily, or strong.

In theory, a female can then use coloration to assess whether the offspring she has with a male are likely to be successful themselves.

Q. What are the most colorful lizards we can see in Virginia?

Robinson: The lizard most people contact me about is the common five-lined skink. Juvenile skinks have dark backs with bright yellow stripes and a vibrant blue tail. But as they mature, the blue color in their tail fades, and they tend to lose their yellow stripes.

Cox: Eastern fence lizards, which we study, are also very colorful, but you might not know it at first glance.

Juveniles and adult females have subtle brown and black patterns on their backs that help them blend in with tree bark and avoid predators. Even adult males are not particularly colorful from above.

But, if you look at the underside of a male, you will see vibrant blue patches that they display to rival males or potential mates – by doing push-ups.

Q. Why do some lizards’ bodies seem to be segmented into two or more distinct colors?

Robinson: There are several reasons why this can occur, but if we revisit the example of the common five-lined skink, with a striped body and a blue tail, it is primarily an anti-predator tactic.

When the lizard moves quickly, the stripes running down its back are disorienting and make it hard for a predator to focus on the body. The blue tail serves as a visual attractant, so that predators are encouraged to attack an expendable body part.

The tail, as you may know can break off, allowing the lizard to escape and live another day while the tail regenerates.

Cox: In other species, the distinct colors may be a way of generating a contrasting pattern that stands out during visual communication with other individuals. Lizards generally do not vocalize, so most of their social communication occurs through visual displays or chemical signals.

Many lizards also have ornaments that are brightly colored and stand out from their background color. For example, we study anole lizards that use an extendable throat fan called a dewlap to communicate with one another. The color and pattern of the dewlap is highly specific to the particular species of anole.

Q. What is color-changing used for?

Robinson: Color change is often used as a social signal to indicate something about an individual’s current state. If a male lizard has just won an aggressive interaction with a rival, it may signal this by changing its color to help attract a mate, or to advertise its victory.

Because lizards do not produce their own body heat like birds or mammals, many species also use color change to thermoregulate and control their body temperature.

A lizard that is cold can darken its skin to help absorb more solar radiation and quickly warm up. Once it has reached its optimal body temperature, it can lighten its skin to slow the rate of solar absorption and maintain its preferred temperature.

Contrary to popular belief, there is much less evidence that rapid color changes are used for background matching and camouflage.

Q. What are the biological mechanisms that create the color changes?

Robinson: Different cell types contain different pigments and structures that contribute to color. For example, melanin pigment absorbs light and appears brown or black. Lizards can darken their color by dispersing melanin throughout the cells that contain it, or lighten their color by concentrating the same melanin into a small area of each cell.

Color change often involves several cell types. In the green anole, cells that reflect blue light interact with other cells that contain yellow pigment to produce their green color.

Cells containing melanin sit beneath these blue and yellow cells, but they have arms that extend above the other cells to the surface of the skin. When the lizard darkens, melanin disperses to the tips of these arms, covering the other pigment cells and producing a brown color.

Q. How will you be celebrating World Lizard Day?

Robinson: I will be working on my next lizard-based paper and likely watching “Rango” in the evening.

Cox: I’ll use it as an opportunity to read a few recent papers on lizard evolution to find some new material to incorporate into my teaching.

 

Cannibalism is widely known to occur in anoles (also here). We can now add the Central American Anolis limifrons to the list.

We are saddened to note the passing of Skip Lazell, who made seminal contributions to the understanding of anole diversity, biogeography and many other topics. We will especially miss his regular commentary, always in a very supportive way, on many Anole Annal posts.

According to Numi Mitchell at the Conservation Agency, “Skip died on Friday, 30 June 2023. He had Parkinson’s and died quietly of pneumonia after many happy years of retirement and tender care from Wenhua Lu, his wife.  There will likely be a memorial service at some point, but nothing is planned at the moment.”

 

Research can be a formative experience for undergraduate students interested in STEM fields. Unfortunately, research opportunities can be difficult to identify and engage in for many students, particularly students from underserved communities. Designing courses to include a class research component, commonly referred to as Course-based Undergraduate Research Experiences (CUREs), has been suggested as a means of alleviating some of the inequities that can result from missed research opportunities. By implementing discovery-based research projects in undergraduate courses, students that may not have the time or financial stability to be involved in the more traditional model of mentored research are able to engage in the complete process of scientific research, from the conception of the research project through its publication. With these benefits in mind, we sought to integrate a research project on anoles into a Herpetology class (taught by Christian Cox, with help from myself and Noah Gripshover) at Florida International University (FIU).

The Modesto A. Madique campus of FIU hosts a diverse and novel lizard community of non-native species. In general, the lizard communities of South Florida are dominated by introduced species that are native to tropical and subtropical regions around the globe. Anoles from the Greater Antilles are especially common in these novel communities, and despite their ubiquity in the region, relatively little is known about the behavioral interactions that structure these emerging lizard communities. Undergraduate students taking the herpetology class were interested in how behavioral interactions among species might impact the lizard community on campus. First, we conducted surveys that revealed brown anoles (Anolis sagrei) and bark anoles (A. distichus) were the most common species on campus. With that information in hand, we decided to develop a study to investigate both inter- and intraspecific interactions between brown and bark anoles as part of their semester-long CURE.

Throughout the semester, we simulated territorial intrusions by presenting resident brown and bark anoles with unknown male or female brown anole intruders. Note that we did not do the reciprocal experiment (bark anoles intruding on bark and brown anoles) because of time and logistical constraints. This allowed us to compare behavioral responses between these two different species and between the sexes to better understand how behavior mediates community structuring. We also made behavioral observations during these interactions to investigate the role of behavioral displays in escalating aggression.

Our research, published recently in Journal of Zoology, showed that brown anoles were consistently more likely to attack intruders than bark anoles, and that female brown anoles were more likely to attack female intruders and flee from male intruders. In contrast, bark anoles were far more likely to flee when they encountered intruder brown anoles, regardless of the intruder’s sex. We also found that behavioral displays had little bearing on whether brown anoles escalated to combat or bark anoles fled. That is to say, resident brown anoles attacked intruders and bark anoles fled from intruders regardless of whether or not they displayed signs of aggression.

Overall, brown anoles appear to be much more combative than the smaller, (slightly) less abundant bark anoles, and this may, at least in part, explain why brown anoles are often found in such high densities in South Florida. Our work here reveals a likely mechanism underlying the establishment and stabilization of novel communities in highly modified landscapes.

The mechanisms underlying the development of stable communities are often unclear and must be inferred from the observation of contemporary interactions and dynamics. However, the recent introductions of various lizard species in South Florida provides an excellent opportunity to explore these mechanisms as they occur in emerging communities. FIU’s location in the region not only makes it an ideal location to investigate the mechanisms underlying community stabilization, but it facilities the direct involvement and engagement of undergraduate investigators in ecological research.

We also found that this was a fun and effective addition to the laboratory of the Herpetology course. Students told us that they enjoyed the hands-on experience, and seeing how research is planned and implemented. After the course, students were fully engaged as collaborators, providing feedback on analyses and manuscript drafts. Because of this, all students in this class were co-authors on the manuscript, and now have a coauthored manuscript to add to their CV or resume. Of course, we don’t anticipate that these research experiences will always result in a scientific publication (sometimes projects don’t work!), but our goal is to continue developing feasible projects that can be conducted as part of the Herpetology class. We hope to continue these and similar projects to engage undergraduate students in rigorous field ecology that provides valuable and authentic research experiences.

 

Greetings from the Land of Enchantment, folks! I’m down here in Albuquerque, New Mexico, on the Anolis beat at the Evolution 2023 conference covering all things anole lizards. We’ve got several great presentations lined up, so if you’re at #Evolution2023, be sure to check em’ out and say hi!

 

New community science reports show that the Peters’s Rock Agama (Agama picticauda) is spreading from Florida and has reached the Bahamas and the British Virgin Islands, undoubtedly carried as stowaways on outbound vessels. A group of Caribbean-based biologists and conservationists are expressing their deep concern because this region is a biodiversity hotpot with thousands of unique, endemic species, over 1,500 of which are already at high risk of extinction.

In their letter to the journal Animal Conservation, the authors identify nearly 50 native reptile species (among which many species of Anolis) that could be impacted if the agama becomes established across the Eastern Caribbean. Given that it is known to capture prey up to at least 5 cm snout-vent length, many species are at risk of being eaten by the agamas; even large native lizards are likely to experience competition and displacement given the agama’s aggressive behaviours.

The authors advise scientists, conservationists, policy makers, veterinarians and border control agencies to be on high alert for incursions by Peters’s Rock Agamas and other non-native reptiles. They further urge the transport sector – especially those operating out of Florida – to be on the lookout for the agama and to take swift measures to remove them.

The letter has been published in Animal Conservation: M.P. van den Burg et al.: The threat of Peters’s Rock Agama (Agama picticauda) to reptile diversity across the Lesser Antilles. Animal Conservation 2023, 12889. https://doi.org/10.1111/acv.12889

I was recently reminded of the paper by Estrada and Silva Rodriguez on the ecological morphology of Cuban anoles. It was one of the first papers to quantitatively examine differences in morphology among a large and ecomorphologically diverse set of species. It was published in Ciencias Biológicas which can be hard to access, probably accounting for the fact that it hasn’t received the attention it deserves.

The picture and caption say it all. Read the paper by Felipe Espinoza De Janon and Mario Yánez-Muñoz.