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Different phenotypic forms often serve the same functional outcome. A classical textbook example is the evolution of the wing in dinosaurs, birds and bats. This implies that organisms can respond in a variety of comparable ways to selection and that the same selection pressure thus can produce phenotypic diversity. Terry Ord and I have an early view paper in the American Naturalist that shows that an anole-like dewlap has evolved repeatedly in iguanids (Anolis) and agamids (Draco, Sitana, and Otocryptis), but in each case through different modifications to the underlying hyoid, which is the structure that powers the extension of the dewlap. The main point of difference among hyoid morpho-types, and also the component critical for the evolution of an extendible dewlap, is the angle between a short perpendicular structure called the hypohyal (see the figure) and a longer structure called the second ceratobranchial, which runs along the edge of the extended dewlap. There is also significant variation in the relative lengths of the same structures.

Other lizard species have converged around other hyoid morpho-types (our analysis identified a total of eight separate hyoid morpho-types). Interestingly we found evidence for convergence in hyoid morphology among species from distantly related genera, such as Polychrus, Gonocephalus and Trapelus. Species from these genera lack the large dewlap type found in Anolis and Draco, although the hyoid morpho-type of the two groups show some gross similarities. We suggest that the hyoid morpho-type of Polychrus, Gonocephalus and Trapelus might represent what an intermediate step looks like in the evolution of an extendable dewlap. More generally, our study shows that multiple adaptive solutions have been possible in apparent response to a common selection pressure, and that the phenotypic outcome that subsequently evolved in different genera seems to have been contingent on the history of the group in question.

And an Ecuadorian student has studied the use of their horns in intraspecific interactions. Read all about it on BBC Earth.

We’ve seen anole wedding cakes and thesis defense cakes, but here’s a new one. Anole research veteran Natalie Jacewicz reports:

For my bachelorette party, my bridesmaids went to an erotic bakery (quite the business niche) in Boston and brought the shop pictures of Anolis lizards. The bakery evidently usually deals in, er, human encounters, so only had skin-toned frosting, and the store clerks weren’t sure if they could do anything lizard themed. But the shop owner evidently got really into the project, did a lot of independent anole research, and produced the cake below. Yes, that is a bridal veil on the yellow one.

Some weeks ago, a paper I wrote on the display behaviour and morphology of fan-throated lizards was published early online at the Journal of Herpetology. Some unfortunate timing meant that my paper did not incorporate these lizards’ new taxonomy, recently published by V. Deepak and colleagues. In this post, I’m going to summarize my results, and explore them in the context of what we now know about Sitana (Agamidae) systematics.

Male fan-throated lizards (surprise, surprise) have fans under their throats that are displayed in a manner analogous to the Anolis dewlap. The appearance of the throat-fan varies dramatically across this group, from small and mostly white to large and blue, black, and orange. I wanted to answer two broad questions

1. Does display behaviour vary with throat-fan morphology? In other words, if you have different tools with which to communicate, do you communicate differently?
2. Can we examine morphological and environmental variation to deduce anything about how this variation in throat-fan morphology has evolved?

Figure 1 from my paper, showing sampled sites and throat-fan variants.

To address these two questions, I measured the display behaviour, morphology, and environment of eight populations of lizards, from three “throat-fan variants.” I found the following:

1. The main axis of variation in display behaviour differed between the coloured-fan variant and everybody else. Displays were fewer and longer in the coloured-fan variant, and included more head twists. The same axis of display behaviour did not differ between the white-fan and the intermediate-fan variants, though there was variation in the frequency of head-bobs across populations with different-sized throat-fans. These differences in display behaviour make sense in light of morphology. Head twisting was more frequent in the variant with a large blue section on the throat-fan that appears iridescent. Head-bobs, which often co-occur with a fully extended throat-fan, were more frequent in the variant(s) with smaller throat-fans (see Figure 6 in my paper for more).
2. Throat-fan elaboration (both size and colour) was paired with increased male-biased sexual size dimorphism, suggesting sexual selection as a likely selective force driving throat-fan variation.
3. Habitat structure did not co-vary with throat-fan morphology, suggesting that the visual environment is unlikely to play much of a role in the maintenance of this variation in throat-fan morphology. But because these lizards all persist in human-modified landscapes, it is difficult to discern how important the visual environment was for the origin of dewlap diversification in this group.

Figure 2 from Deepak et al. 2016.

Based on geography, I can tell that all three of the coloured-fan variant populations I sampled belong to the newly described Sarada darwinii. The white-fan populations are Sitana laticeps and Sitana spinaecephalus (+ one population I’m not sure about), and the northern and southern intermediate-fan populations are Sitana ponticeriana and Sitana visiri respectively. Recast in terms of these species delimitations, I found that:

1. Display behaviour differs between the genera Sitana and Sarada. It doesn’t vary consistently with species within Sitana, though variation in head-bobbing should be explored further.
2. There are two broad possibilities for throat-fan evolution in the group. One possibility is that throat-fan elaboration and a shift towards male-biased SSD has evolved independently twice, once in Sarada (Clade 1) and once in the South India/Sri Lanka clade (Clade 3 in the phylogeny) in Sitana. The other possibility is the reduction of dewlap size and colour in the west Indian Sitana clade (Clade 2). This question won’t be definitively answerable until we have a phylogeny that includes the remaining north-eastern species of Sitana as well as more species of the sister genus Otocryptis, which also vary in the presence and morphology of the throat-fan.

Before knowing about the phylogeny, I predicted that throat-fan elaboration had evolved twice in fan-throated lizards, based on a suite of differences between the coloured-fan variant (now Sarada) and the intermediate-fan variant (now Sitana Clade 3). The main ones are:

1. Different display behaviour.
2. Different allometric relationships between body size and throat-fan size, suggesting different ways in which throat-fans have gotten big.
3. Different spectral reflectances from the blue and orange patches, plus the presence/absence of black on the throat-fan.
4. The ability of Sitana, but not Sarada, to turn “on” and “off” the blue colour on their throat-fans (more about this in a future post!).

These differences now lead me to favour the first of the two possibilities outlined above: repeated, somewhat parallel evolution of throat-fan elaboration, as opposed to the loss of an elaborate throat-fan. Given that the sister genus Otocryptis has also either evolved or lost a throat-fan (throat-fans are present in O. nigristima and O. wiegmanni but not O. beddomi), this group is positively rife with lability in display evolution, offering all sorts of exciting possibilities for future research!

Anolis garmani. Photo by Janson Jones.

Over on phostracks.com: Florida Wildlife, Ecology and More, Janson Jones reports on a very successful trip to Miami that yielded many anoles, most notably the Jamaican crown-giant, Anolis garmani and the Cuban knight anole, Anolis equestris.

Photo by Janson Jones.

Photo by Janson Jones

Janson Jones is at it again. Actually, he’s been at it for a year, but somehow that slipped below our radar. The former purveyor of Dust Tracks on the Web has a new venue, phosTracks.com: florida wildlife, ecology and more.

Like it’s predecessor, phosTracks is full of keen natural history, engagingly presented and complemented by gorgeous photography. And better yet, anoles are one of Jones’ two favorite animals, neck-and-neck (hard as it may be to believe) with watersnakes.

Check out some of Jones’ recent musings on:

curly-tailed lizards:

Photo by Janson Jones

red-headed agamas:

Photo by Janson Jones

Anolis cristatellus:

Photo by Janson Jones

and more! Stay on these pages for some of his giant anole goodness coming up soon!

Figure1. Saddled anole on a fallen tree trunk, Guana Island of the British Virgin Islands.

De Gao and Gad Perry have recently detected the small island effect (SIE) and nestedness patterns of Anolis Lizards of the West Indies. We applied regression-based analyses, including linear regression and piecewise regressions with two (two-slope function and left-horizontal with one threshold function) and three (three-slope function and left-horizontal with two thresholds function) segments, to detect the SIE and then used the Akaike’s information criterion (AIC) as a criterion to select the best model. We used the NODF (a nestedness metric based on overlap and decreasing fill) to quantify nestedness and employed two null models to determine significance. Moreover, a random sampling effort was made to infer about the degree of nestedness at portions of the entire community.

Figure 2. SAR

Figure 3. Nestedness

We found piecewise regression with three segments performed best, suggesting the species–area relationships (SARs) possess three different patterns that resulted from two area thresholds: a first one, delimiting the SIE, and a second one, delimiting evolutionary processes. Moreover, the traditional two-segment piecewise regression method may cause poor estimations for both slope and threshold value of the SIE. Thereby, we suggest previous SIE detection works that conducted by two-segment piecewise regression method, ignoring the possibility of three segments, need to be reanalyzed. Anti-nestedness occurred in the entire system, whereas high degree of nestedness could still occur in portions within the region. So, nestedness may still be applicable to conservation planning at portions even if it is anti-nested at the regional scale.

One of the few known Anolis roosevelti specimens.

Anole stalwart Greg Mayer gave a wonderful talk discussing the distribution and morphology of the large and maybe-extinct Anolis roosevelti. A. roosevelti, commonly known as the Culebra Island giant anole, was first described in 1931 by Chapman Grant, a US Army Major and practising herpetologist, from a single adult male specimen collected on Culebra. Although Reinhardt and Lutken, in 1863, had already provided an accurate description of A. roosevelti, but under an alternative name of A. velifer.

Reinhardt and Lutken’s specimens were collected from Vieques, Tortola, and St. John, although Greg having the opportunity to study them meant tracking them down to natural history collections in both Copenhagen and Stockholm. In total, this entire species is known from eight specimens, only six of which are still in existence (Greg had the opportunity to study all six, meaning he’s now seen more roosevelti than any other anolologist?). Greg explains that roosevelti based on the limited information provided by Dimas Villanueva, who collected the holotype, and his own investigations, roosevelti can be classified as a “crown-giant” ecomorph. This means that the eastern islands of the Puerto Rico bank had a series of four ecomorphs, with roosevelti being what Ernest Williams termed a climatic vicariant of cuvieri, occuring in (and presumably being adapted to) the more xerophytic forests of the eastern bank islands.

The known distribution of Anolis roosevelti.

Greg went on to describe the morphological features which distinguish A. roosevelti from a A. cuivieri, an ecologically and morphologically similar species from neighbouring Puerto Rico. Roosevelti is a larger, brownish gray rather than green as is seen in cuvieri (although check out these gray cuvieri preveiously mentioned on AA). Roosevelti generally has larger head scales, and a more elongate and deeply grooved head – these differences are confirmed in the ANCOVA analyses below.

So, what chances are there of seeing roosevelti in the wild? Low, probably. No specimens have been collected since 1932, and several researchers, including Greg, have recently scoured both Vieques, St. John and Tortola but with no success. By far the most extensive searches have been conducted by Ava Gaa, who exhaustively searched Culebra (totalling 1500 hours of looking!) as well as short visits to Vieques and St. John all with no success. Tantalising reports of potential candidates turned out to be juvenile green iguanas. Greg concludes by recommending that the long-protected and relatively poorly explored eastern half of Vieques may hold the secret to if any populations remain.

The gold dust day gecko was introduced to Hawaii in the 1980s. It is ecologically similar to the green anole, which was introduced to Hawaii in the 1950s.

Hawaii has no native herpetofauna, aside from sea turtles. Human-mediated introductions between the 1950s and 1980s have created an interesting new guild of arboreal and diurnal lizards: the green anole (Anoles carolinensis), the gold dust day gecko (Phelsuma laticauda) and the brown anole (A. sagrei ).

Amber Wright next to her poster on Saturday

Phelsuma laticauda belongs to a genus that is endemic to Madagascar with almost 50 species, that are known for their incredible color patterns. Anolis carolinensis and P. laticauda are thought to be ecologically similar and thus potential competitors.

Amber Wright’s research investigates whether and how the three species partition their habitat when they occur in sympatry and how that might affect species abundance. Using field observations and morphological data, she found that the three species overlap in body size and habitat use, which suggests that they are potential competitors for food resources and perch sites.

Enclosure experiment.

Preliminary data show that abundance decreases when ecologically similar species are present.

In a pilot study, Amber used seven 10x10m plots to simulate different community scenarios: only one species, two species and all three species. Anolis carolinensis and A. sagrei seem to be interacting similarly to populations outside of Hawaii: coexistence with reduced densities and increased perch heights of A. carolinensis. When all three species were present, P. laticauda perched higher than usual, presumably to avoid competition with A. carolinensis. Future work will focus on long term effects of species composition on resource partitioning and abundance of each species.