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Many exaggerated phenotypic traits, such as the large and colorful dewlaps of male anoles, increase fitness of individuals who possess them. But these traits are often energetically costly. Too high an investment in showy or extreme traits can come at the cost of an individual’s health and performance. Such traits are therefore said to be condition-dependent; that is, individuals will not develop them unless they are already in a healthy condition.

John David Curlis and colleagues explored  several potential condition-dependent traits in two closely related Central American Anolis species, A. limifrons and A. humilis. He quantified a number of sexually and naturally selected traits and tested whether they varied by body condition to see whether any of them were condition dependent, and whether the degree of condition dependence varied between two closely related species. None of the traits he tested were condition dependent in A. limifrons, but two traits – jaw width and dewlap size – were condition dependent in A. humilis. He therefore concluded that the degree of condition dependence of these traits is evolutionarily labile. In addition, A. humilis dewlaps are generally larger than A. limifrons, which suggests that condition dependence may be a more important force affecting traits that are subjected to stronger sexual selection. Taken together, these results suggest that condition-dependence of sexually-selected traits may be playing a role in dewlap diversity (and perhaps other phenotypic traits) throughout Anolis lizards.

Studies of adaptive radiation often focus on two main axes of divergence: the structural niche (e.g., where a species lives) and resource niche (e.g., what a species eats). In his SSE Symposium talk titled “The physiology of adaptive radiation,” Alex Gunderson explained the importance of a third, under-appreciated axis of species diversification: the thermal niche. Gunderson and colleagues tested whether different approaches to estimate the rates of evolution of the thermal niche lead to different conclusions, and whether thermal traits evolve at similar rates to classic ecomorphological traits like body size and limb length.

Scientists generally use three main approaches to quantify the thermal niche and estimate rates of thermal niche evolution: ecological niche modeling (ENM), organismal body temperatures, and physiological data (tolerance/sensitivity to different temperatures). Different studies use different approaches, but few use all three. Each of these metrics addresses a different scale of thermal biology, from broad environmental variables (ENM) to individual organisms (physiology). Gunderson and colleagues therefore predicted that estimated rates of evolution would vary based on the metrics used, and they used data from a number of Anolis species to test this prediction.

Specifically, the authors predicted that: a) ecological niche modeling approaches would estimate greater rates of thermal niche evolution, because environmental factors like temperature and precipitation used in ENM are very broad metrics, and are not necessarily directly correlated with individual thermal niche; b) organismal temperature data would estimate intermediate rates of thermal niche evolution, while it is a measure of individual thermal niche, it is also quite plastic; c) physiological measures would estimate the most conservative/low  rates of evolution, because measures of thermal maxima and minima most accurately reflect the possible tolerance and sensitivity of individuals to thermal environments. They found that physiological data does indeed produce the most conservative estimates of thermal trait evolution, but their predictions about the performance of ENM and body temperature differed. Estimates of thermal niche evolution were highest when using body temperature data, and were intermediate when based on ENM. The fact that body temperature-based estimates of evolution rates were higher than ENM-based estimates suggests that researchers are generally underestimating error in body temperature measurements in the field.

After evaluating the results of these three different approaches in relation to thermal niche evolution, the researchers then compared rates of evolution of thermal traits to those of classical ecomorphological traits. When they used ENM, thermal traits seemed to evolve much more rapidly than morphological traits. In contrast, when they used physiological data, they found the opposite. Clearly, different metrics of climatic niche lead to different conclusions about evolutionary patterns. Gunderson therefore recommends incorporating aspects of multiple ecological and physiological scales when studying divergence of the thermal niche.

Tereza Jezkova helped kick off the anole festivities at Evolution 2016 with her talk entitled: “A peculiar case of hybridization with advantageous mtDNA introgression and lack of nuclear introgression in Caribbean anoles.” Along with a string of co-authors (Todd Castoe; Manuel Leal; Daren Card; Drew Schield; David Elzinga; Javier Rodríguez-Robles), Tereza has discovered that completely normal looking Anolis pulchellus populations in western Puerto Rico (and a bit elsewhere) harbor the DNA of the closely related A. krugi.

What’s going on? Detailed examination revealed two interesting findings. First, this appears to be the result not of a single hybridization event, but minimally of 15 such events, all of them apparently quite recent. The krugi mtDNA has completely displaced the pulchellus mtDNA in these populations, and population genetic analyses rule out genetic drift as the cause. Puzzlingly, genomic analyses find absolutely no krugi nuclear DNA in these populations. The mtDNA is getting in, but not the nuclear genes. Natural selection must be at work, but how? Tereza suggested some sort of genetic mechanism that excludes the nuclear DNA of the introgressing species, somehow kicking it out, likening it to a phenomenon reported in frogs and some insects, but not in any amniotes.

Hello,

A friend sent me some photos of this female anole he found in Limón Indanza, in the Morona-Santiago Province of Ecuador.

Any ideas on a possible species? I know it is not as easy as with a photo of a male.

It’s not anoles but at least it’s about convergent evolution!

A recent study by Damien Esquerre and Scott Keogh published in Ecology Letters found that pythons and boas, the two famous constrictor snake families, have evolved convergent head shapes. The study was based on over 1,000 specimens and including most of the species. Pythons and boas that occupy the same micro-habitat or ecology (i.e. arboreal, terrestrial, semi-aquatic, semi-fossorial) look more like each other than to other snakes in their own family. This is exciting because it highlights how important ecology and adaptation is in shaping biological diversity.

Abstract:

Pythons and boas are globally distributed and distantly related radiations with remarkable phenotypic and ecological diversity. We tested whether pythons, boas and their relatives have evolved convergent phenotypes when they display similar ecology. We collected geometric morphometric data on head shape for 1073 specimens representing over 80% of species. We show that these two groups display strong and widespread convergence when they occupy equivalent ecological niches and that the history of phenotypic evolution strongly matches the history of ecological diversification, suggesting that both processes are strongly coupled. These results are consistent with replicated adaptive radiation in both groups. We argue that strong selective pressures related to habitat-use have driven this convergence. Pythons and boas provide a new model system for the study of macro-evolutionary patterns of morphological and ecological evolution and they do so at a deeper level of divergence and global scale than any well-established adaptive radiation model systems.

Reference:

Esquerré, D & J S Keogh. 2016. Parallel selective pressures drive convergent diversification of phenotypes in pythons and boas. Ecology Letters, 19(7): 800-809.

While doing some local herping for fun this weekend with a couple of friends visiting from out of town (Janson Jones of previous AA fame; 1,2,3,4,5), we happened upon this Cuban knight anole (Anolis equestris) with a fairly conspicuous hole in its dewlap. Despite this, the lizard appeared in prime condition. Other reports of strange dewlaps have been documented on AA before, such as these grey-dewlapped Puerto Rican crested anoles (A. cristatellus) and American green anoles (A. carolinensis), but has anyone ever seen any individuals with tissue missing from the core region of the dewlap (as opposed to injuries sustained on the peripheries, such as this Cuban brown anole (A. sagrei), which aren’t generally that uncommon)?

Here’s one example, from an AA post from four years ago.

Christian Perez is currently studying anoles at La Selva Biological Station in Costa Rica. Recently, he found a vine snake. Here’s his report:

As I reached towards the snake, I startled an anole (Anolis limifrons) that was hiding nearby. The snake turned rapidly, looked at the anole, and made movements synchronized with the wind to remain inconspicuous among surrounding vegetation. I stayed with them for a while, and after one failed strike, the snake successfully stalked and caught the anole. The snake took under a minute to consume the lizard, and it was very friendly after its meal.

Over at Lizards and Friends, Amy Payne from Michele Johnson’s lab reports on her first field experience studying green anoles. Fear not–they kept an eagle eye out for snakes.

On a fleeting one-night stopover in Miami last week, Anthony Geneva had the chance to pop in and say hello at Fairchild Tropical Botanical Gardens and take a morning stroll to view some of the resident anoles (see others posts about Fairchild anoles here: 1,2,3,4). While waiting to be joined by fellow local anolologist and distichus aficionado Winter Beckles (University of Miami), Anthony and I noticed some commotion by the edge of a nearby pond. Upon closer inspection, we realized that a tricolored heron (Egretta tricolor) appeared to be juggling a large anole in it’s mouth! In my morning rush, I had managed to forget not just my anole-catching noose pole, but alas, also my camera. Fortunately, Anthony was on hand to fill the David Bailey role.

After re-positioning the lizard a few times, the heron appeared to do something peculiar – it repeatedly dunked the lizard in and out of the water. This happened perhaps 5-6 times. Was this an attempt to expedite a fatality prior to consumption, or perhaps a neat trick to help lubricate such a large prey item?

In all, the process of ingestion took less than 10 seconds, following a couple of minutes of dunking and repositioning.

This observation follows a recent hot post reporting the predation of anoles by reintroduced whooping cranes (Grus americana) in Louisiana, which itself was preceded by various observations of avian-fuelled anolivory in South Florida (1, 2, 3, 4). Even more recently, while showing Thom Sanger and Bonnie Kircher around Fairchild Gardens a few weeks back, we observed a Cooper’s hawk (Accipiter cooperii), a widely-regarded bird specialist, snatch an American green anole (A. carolinensis) from the frond of a towering Royal Palm (Roystonea regia) – an event Rob Heathcote and I had observed the previous year with an adult male A. cristatellus in nearby Matheson Hammock. Unfortunately none of us were privileged with Anthony’s camera reflexes to capture any of those events.

So, why’s this interesting? (Excluding the obvious natural history enlightenment of revealing, at least personally, a previously unclear predator-prey interaction). Well, tricolored herons are a widespread breeding resident throughout much of the US Gulf states and as far south through the Caribbean to central Brazil and Peru. Therefore, the consumption of crested anoles (A. cristatellus) isn’t necessarily a novel interspecific interaction – it’s possible that this occurs in the native range of A. cristatellus, Puerto Rico, where both exist. However, although tricolored herons are natural residents of South Florida, it would be a tough sell to argue that crested anoles would be naturally on the menu. Crested anoles were first introduced to South Miami in the 1970s – the original site of introduction being a mere stone’s throw from this observation (for a review of the subsequent dispersal patterns of A. cristatellus in Miami see Kolbe et al. 2016; pdf here). So although crested anoles are being exposed to many novel biotic interactions in Miami, it seems they can’t escape some.

Have any Puerto Rico anolophiles observed this interaction before?

A smug bird.