Anole Annals

Over the last few months, there’s been a slow-boiling battle underway between Holly Dunsworth and Jerry Coyne about the evolution of sexual dimorphism in humans, surrounding the question of why male and female humans, on average, differ in size. The battlefield ranged from blogposts to twitter to magazine articles. In a nutshell, Coyne argued that “sexual dimorphism for body size (difference between men and women) in humans is most likely explained by sexual selection” because “males compete for females, and greater size and strength give males an advantage.” His whole argument was motivated by this notion that certain Leftists ignore facts about the biology of sex differences because of their ideological fears, and are therefore being unscientific.

Dunsworth’s response to Coyne’s position was that “it’s not that Jerry Coyne’s facts aren’t necessarily facts, or whatever. It’s that this point of view is too simple and is obviously biased toward some stories, ignoring others. And this particular one he shares…has been the same old story for a long long time.” Dunsworth went on to propose, seemingly off the cuff, alternative hypotheses for sexual dimorphism in body size in humans that were focussed not on men but on women, as examples of the kind of hypothesis that is relatively rarely considered or tested in this field.

Though on the surface this battle may seem to be about specific biological facts (Coyne certainly tries to win by treating it that way), in reality this disagreement is, as Dunsworth argues, about the process by which hypotheses are tested and about how knowledge comes into existence. About which hypotheses are considered for testing in the first place. As a result, the two ended up arguing past each other quite a bit.

As I followed this whole exchange, I shook my head at the timing–I had a paper in preparation that was SO RELEVANT to the centre of this debate! That paper is now available as a preprint, so I can try to outline why I think that Dunsworth is right, and Coyne is being short-sighted. My argument has *nothing* to do with humans, however–I don’t know the human sexual selection literature well enough to weigh in on that. Instead, my argument is by analogy with our knowledge of mating systems in Anolis lizards.

Cuban Anolis – Request for Help with ID

By Valentin Moser

On March 14, 2017

In All Posts

Hello everybody!

I am a biology Student from Switzerland and together with my travel mate Demian, I visited Cuba for 3.5 weeks in January and February 2017. We are birders, but pretty much interested in everything that moves! We were taking pictures of lizards whenever we could, but without specifically looking for them. Back home, I was surprised how difficult the identification can be and so I would be happy if you can confirm, correct or help me with the ID. There are a lot of pictures…
I will report every safely identified lizard, probably with observado.org, together with the name of the expert, who is helping us out.
We will also put a comprehensive trip report on cloudbirders, including the herp list.

Early Breeding Season Injuries through Aggressive Interactions in Miami, FL

By James T. Stroud

On March 12, 2017

In All Posts

It’s currently dewlapping mayhem down here at the moment, with all species except the late-rising Cuban knight anoles (A. equestris) out and showing off!

An adult male Puerto Rican crested anole (A. cristatellus) performing dewlap extension displays in Miami FL

Visual displays such as dewlap extensions are often used to mediate physical interactions by acting as an indication of the relative size, strength, and fitness of each individual. This is beneficial for both parties; dominant individuals do not have to waste energy that a physical interaction would require, and weaker individuals avert the risk of physical injury (of course, both reasons are reciprocal to both individuals also).

However, when two individuals cannot determine dominance through visual communication, for example if two individuals are equally matched in size, then an aggressive and physical confrontation may occur (read a previous account of one such interaction between two equally-sized males here). The results of these interactions are apparent in many injurious forms, for example through extensive bite marks to the body (as previously discussed here and here), or perhaps even to the extent of tail loss (as discussed here).

Yesterday (9 March 2017) I observed this male Puerto Rican crested anole (A. cristatellus) below that looks like another male had taken a good bite at him!

Of course, there are many avenues through which such an injury may appear. However, the presence of a still-erect nuchal crest paired with how fresh the wound looks (and the time of year!) gives me the impression that this was probably the result of an intraspecific male-male interaction.

Ecomorph Line of Watches on Sale Now

By Jonathan Losos

On March 10, 2017

In All Posts

Note: the watch on the bottom right is not one of ours!

Celebrate Daylight’s Savings time with 40% off the Ecomorph line of watches on Zazzle.com. Sale Code: DAYLIGHTDEAL

And we’re open to suggestions for new species to feature on a lovely wrist fob. Suggest away!

City Lizards Are Hesitant Feeders

By Joshua Hall

On March 4, 2017

In New Research

Figure 1. Anolis cristatellus male in survey position.

Foraging behavior reflects a trade-off between the benefits of obtaining vital resources and the potential costs of energy expenditure, missed mating opportunities, and predation. Through time, selection should canalize foraging behaviors that optimize fitness within a given environment, but novel habitats, like urban landscapes, may require behavior to change. For example, human-landscape modification often results in significant reductions in structural complexity of habitat as compared to natural areas, potentially leaving individuals with a greater sense of perceived vulnerability as they venture out to feed. Moreover, these landscapes can alter the diversity and density of predators in ways that might leave prey with a greater sense of perceived predation risk.

In a recent paper in Urban Ecosystems, Chejanovski et al (2017) sought to quantify differences in foraging behavior between anoles from urban areas and those from more natural, forested locations. They utilized two trunk-ground anoles: Anolis sagrei in Florida and A. cristatellus in Puerto Rico. In both urban and natural habitats, they located male lizards in survey posture (Fig 1), which indicates an individual is likely searching for food, and placed a tray with mealworms on the ground at a fixed distance from the perch. They measured each lizard’s latency to feed which was the time it took to the lizard to descend from its perch and capture a mealworm.

Because the availability of complex habitat structure and the proximity of predators might both influence foraging behavior, they experimentally manipulated perch availability for A. sagrei and predator presence for A. cristatellus in both urban and natural habitats. For A. sagrei, they provided half the individuals with two extra perches between the lizard’s original position and the food tray. For A. cristatellus, they manipulated perceived predation risk by placing a static bird model on the opposite side of the feeding tray from half the lizards.

Additionally, they measured several other factors that might influence foraging behavior: the number of available perches within a fixed radius of each lizard – increased habitat complexity might result in lower perceived predation risk; perch height of each individual – those that perch lower to the ground may be more motivated to feed and those that perch higher may be satiated; estimates of body temperature by placing a copper model at the original position of each lizard – body temperature can influence locomotor function and this may have consequences for how easily a lizard can escape predation and play a role in its perceived risk. They also measured the density of conspecifics in the immediate vicinity and noted when conspecific individuals captured mealworms from the feeding tray.

Finally, they measured SVL and mass for a representative sample of each population (urban and natural) in order to calculate body condition. Trade-offs between costs and benefits of foraging decisions can be influenced by satiation of hunger, and body condition, which increases with food consumption, may indicate the extent to which individuals are well-fed.

For both species, lizards from urban areas had a longer latency to feed and demonstrated lower overall response rates to food trays; many individuals never attempted to capture a mealworm in the allotted time (20 minutes). For A. sagrei, habitat (urban vs. natural) best explained feeding latency, but perch height and the presence of conspecifics were also important determinants of feeding latency for A. cristatellus. Individuals perching lower had shorter latency, and latency was shorter when a conspecific attempted to feed from the tray. Neither experimental perch availability nor perceived predation risk (bird model) had any influence on foraging behavior. In both species, individuals from the forest were smaller (SVL) and less massive than those from the city. Body condition was higher for urban A. sagrei but did not differ between natural and urban habitats for A. cristatellus.

Differences in foraging behavior for male A. cristatellus between natural and urban habitats.

Because of the reduced availability of perches and structural complexity in urban habitats, urban lizards could have generally higher perceived predation risk and this might explain their reluctance to feed; however, experimental perch availability did not influence foraging behavior for A. sagrei and an artificial predator had no effect on A. cristatellis. The latter may simply reflect that the experimental predator was stationary and a moving predator may have elicited different results.

It is possible that foraging differences reflect food availability in urban vs natural habitats, and thus motivation to forage. Urban anoles had higher body condition and may be generally better fed than those from the forest; however, the authors found no significant correlation between individual body condition and latency to feed. It is also possible that mealworms represent a novel food source for urban anoles, and this resulted in a hesitance to initiate feeding since many animals are reluctant to approach novel objects/ food (neophobia).

In summary, this study demonstrates that differences do exist in foraging behavior for two distantly related species of anoles between urban and forested habitats. The increased latency to feed observed in urban anoles could be due to perceived predation risk, foraging motivation, neophobia, or some combination. What is left to be determined is the extent to which these behavioral differences might be adaptive in their respective habitats.

Seeking Field Active Body Temperature Data for Anolis chlorocyanus

By Chris Anderson

On March 2, 2017

In All Posts

Photo by Rich Glor

Hello everyone,

As part of some ongoing work comparing muscle physiology and performance among Anolis species, I am in search of data on the Field Active Body Temperature (Tb) of Anolis chlorocyanus so that I am sure to perform data collection at relevant temperatures. Unfortunately I have been unable to locate Tb data for this species in the literature, so I hoped one of you might have this information and be willing to share it with me. Any help would be greatly appreciated!

Gliding Lizards Use the Position of the Sun to Enhance Social Display

By Danielle Klomp

On February 26, 2017

In All Posts

Along with Devi Stuart-Fox, Indraneil Das and Terry Ord, I recently published a paper in Biology Letters showing that arboreal Draco sumatranus lizards orient themselves on the tree trunk perpendicular to the position of the sun during broadcast signalling. This presumably increases the radiance of the translucent dewlap, and likely it’s conspicuousness.

Figure 1. (a) Draco sumatranus male displaying, showing the transmission of sunlight through the dewlap (photo: T. J. Ord). (b) Perch angle for displaying males, and (c) perch angle for non-displaying males, measured in relation to the sun. Both perpendicular angles (90° and 270°) have been transformed to equal 180°.

Draco lizards are ecologically analogous to the anoles and share similar signalling behaviour (see this recent Draco clip from the BBC’s Planet Earth II). They too possess extendable dewlaps that differ in colour and size between sex / species groups, and they also live in many different habitat types throughout Southeast Asia. I’ve written about my Draco research on Anole Annals before, here and here, if you’re interested – I hope they’re now well accepted as honorary anoles!

Like the anoles, the skin of the dewlap for many Draco species is stretched thin when extended and allows light to pass through. Leo Fleishman published a Functional Ecology paper in 2015 measuring how the dewlap of Anolis lineatopis appears to glow when positioned with the sun behind them, and how this might improve signalling efficacy. Contrary to expectation, they found the transmission of light through the dewlap doesn’t improve the luminance contrast of the dewlap against the background. The radiance of the dewlap is increased by light transmission (radiance is the sum of the light reflected by the dewlap and any transmitted through the dewlap) – but patches of high radiance are very common in Anolis lineatopis forest shade environment, due to many the little shafts of light shining between gaps in the leaves. Instead they showed that due to the higher total intensity of the dewlap colour (thanks to light transmission) it’s probably easier for a conspecific to discriminate the signal from the natural background colours.

Given this and the similarity between anole and Draco dewlaps, I wondered whether Draco lizards might behaviourally adapt their position on the trunk relative to the position of the sun, to maximise the exposure of the extended dewlap to sunlight. To look at this, I just observed the position of the lizard relative to the sun upon first sighting, and noted whether the lizard was displaying, and if so, whether was it directly to a neighbouring conspecific, or whether it was a territorial broadcast display. We found males were significantly more likely to be oriented perpendicular to the sun when displaying, but not when not displaying (fig. 1).

Of course, signals intended for specific individuals in close-range encounters require the signaller to position themselves such that the receiver is in line of sight – but Draco lizards (and anoles) also give these ‘broadcast signals’ which are not intended for any specific individual, but just as territorial display. For these signals, where there is not another lizard around, they seem to orient themselves perpendicular to the sun, so their extended dewlap is exposed to the most light.

Female D. sumatranus also have dewlaps, but they are small in size and females only very occasionally engage in broadcast display. I had not expected to see this orientation behaviour in females, as their dewlaps appear opaque and so don’t benefit from light transmission. However, I found the same orientation pattern for females as for males: perpendicular to the sun when displaying, but not when not displaying. This is perhaps because their dewlap reflects UV light (fig. 2) and direct sunlight is richer in UV and shorter wavelengths than light reflected off objects in the surrounding scene. Males have yellow dewlaps, and they too reflect a little UV (though much less than females). Of course, the transmission of light is unidirectional and only increases the radiance of the dewlap for those viewing the dewlap from the opposite side to that of illumination, so the benefit of direct sunlight hitting the UV/yellow male dewlap likely plays a role in this orientation behaviour for males as well.

Figure 2. a) Draco sumatranus male yellow dewlap colour reflectance;
(b) Draco sumatranus female blue dewlap colour reflectance.

Funky Bone Fusion in the Metatarsals of an Anole Foot

By Jonathan Losos

On February 24, 2017

In All Posts

Of Rats and Reptiles: An Expedition to Redonda

By Colin Donihue

On February 21, 2017

In New Research

Anolis nubilus male and female from The Anoles of the Lesser Antilles.

In 1972, James “Skip” Lazell published a monograph on the Anoles of the Lesser Antilles including the species description of Anolis nubilus, an endemic anole restricted to the island of Redonda. His description of the animal and island, like the rest of the monograph, is colorful and evocative:

“The tiny islet is exceedingly steep-to, and rises nearly 1000 feet out of the sea. There is virtually no surrounding bank, and the full swell of the western North Atlantic pounds Redonda’s cliffs. A tiny, nearly vertical gut on the leeward side provides the only access to the top of the islet up the cliffs; great blocks of basalt lie at the foot of this gut and one’s original entrance to Redonda is made by jumping onto these blocks as the boat goes past them. It is about like jumping from a moving elevator onto a card table, except that elevators give more notice of directional reversals… but getting on is just the beginning. …

The top of Redonda is a rolling wold and a favorite place of innumerable nesting sea birds; the gut provides a route for their guano to descend the cliffs, and it dries to a thick powder there. Because of its lee-ward location, a chimney effect is produced in the gut, and the guano dust, mixed with the volcanic sand weathered from the parent rock, tends to rise when disturbed. As one toils up the gut under the tropical sun, one is accompanied by a cloud of this dust, which soon mingles with one’s own sweat to produce a wondrously aromatic and abrasive, though rather gluey, bath. At the top, jumbles of rocks and clumps of prickly pear rise gently to the old ruins, complete with a hedge of bougainvillea and a single tree. This is the home of Anolis nubilus. …

Surely Redonda once supported more vegetation, and presumably Anolis nubilus then had an easier life. The feral goats should be extirpated on this remarkable island, whose only known nonflying vertebrates are species found nowhere else on earth.”

Now, 45 years, 1 week, and 4 days later, I’m headed to Redonda to gather baseline lizard data on exactly such a goat extirpation.

Skip did miss one nonflying vertebrate in his account; Rattus rattus has taken up residence en masse on Redonda. The black rats are so plentiful now that they’ve taken to stalking the lizards on the island in daytime—“tiger rats,” according to Dr. Jenny Daltry, one of the researchers leading the island restoration effort. And so, the government of Antigua and Barbuda, in conjunction with numerous conservation NGOs including Flora and Fauna International, has decided to remove the goats and rats from Redonda in an attempt to restore the island and help its three endemic lizard species to recover.

Redonda is home to not just A. nubilus but also a jet black ground lizard, Ameiva atrata and an as-yet unnamed dwarf gecko, Sphaerodactylus sp. Presumably, A. nubilus would be perched high in vegetation avoiding the roving A. atrata; however, after centuries of goat grazing on Redonda, that vegetation has been reduced to a single Cassuarina tree. So, while that tree is likely swarming with anoles, most of the A. nubilus are spending their time hopping around the boulders of Redonda. Normally this would put them in range of the roving ground lizards, but it sounds as though both lizards should be more worried about those hungry black rats.

Fortunately for all of Redonda’s reptiles, as of a few weeks ago the goats on the island took a one-way ferry ride to new pastures (not a euphemism) and, well, starting soon the rats will be making their way to the great big garbage heap in the sky (definitely a euphemism). My goal is to get to Redonda and gather as much baseline data on the lizards as possible to see whether and how the lizard community changes on a goat-less, rat-free Redonda.

That’s no easy task, though. Here’s a picture of Redonda:

Photo credit: Dr. Jenny Daltry. I’m reasonably sure that’s the gut there, in the foreground of the image.

Believe it or not, that’s the pleasant side of the island. Here’s the other:

Photo credit: TopTenz.net

We decided that hauling a week’s worth of research and camping gear up Lazell’s gut (let alone jumping to that card-table basalt) was out of the question, so I’m going to be arriving by helicopter. As if the rats weren’t enough, Redonda has no source of fresh water so we’ll be carrying in food and drink for the 8 days on the island. No power either, so I’ve been putting together solar kits to try to get enough juice to run a computer and spectrophotometer.

All in all, it’s going to be an adventure! I’ll update Anole Annals when I return, but I’ll also be posting more frequent updates to my personal blog and twitter. I’d love to hear from you, especially if you have any tips for rat-proofing tents (seems more efficient to just bait the other ones, right?).

Citation: Lazell, J.D. 1972. The Anoles (Sauria, Iguanidae) of the Lesser Antilles. Bulletin of the Museum of Comparative Zoology. 143(1).