Category: All Posts Page 78 of 148

Species divergence is driven by a wide variety of forces, but two of the strongest predictors of speciation are the amount of time a lineage has persisted in a landscape, and the ability of lineages to move through a landscape. Lineages are more likely to diverge when they have occupied a landscape for a long time, and/or if their ability to move is restricted, thus limiting gene flow.

In his talk titled “Geographical factors promoting diversification of the northern Andes and Brazilian Cerrado regions: the case of frogs and Anole lizard species,” Carlos Guarnizo described his efforts to test whether these patterns hold true in both different landscapes and different taxa. He surveyed two herpetofaunal communities in two diversity hotspots in South America: frogs in the northern Andes mountain range and Anolis lizards in the Brazilian Cerrado. The montane Andean landscape is structurally complex and covers a range of altitudes, while the Cerrado region is a more uniform savannah-like environment, with intermediate structural complexity. Guarnizo used species distributions and genetic data to look at patterns of diversification across these landscapes to explore which landscape characteristics lead to higher levels of divergence and speciation.

He found that in both areas, topography was a strong predictor of divergence; specifically, more structurally complex landscapes led to higher levels of genetic divergence between sister lineages. These genetic breaks are also often deeper than previously realized, likely representing cryptic species. Despite these strong genetic splits, the niches occupied by sister taxa are generally well-conserved, lending support to the conclusion that landscape structure – rather than adaptive divergence – is responsible for the genetic divergence observed. Interestingly, in Andean frogs, Guarnizo found that the strongest genetic breaks did not occur across mountain peaks as previously thought. Instead, valleys appear to be the strongest geographic barrier to dispersal.

These cases show that landscape topography is a strong factor determining genetic divergence across different landscapes and taxa (including anoles), and may lead to high levels of cryptic speciation.

Photo by Nsimean

It’s true, they’re not anoles, but lizards of the genus Liolaemus form another extremely diverse clade, occupying one of the broadest climatic and elevational niche ranges of any vertebrate. Whether the ecological and phenotypic diversity of this genus are correlated, as is the case in adaptive radiation, remains an open question. Studies of the whole genus have shown that body size diversification is consistent with expansion into different ecophysiological niches, but other morphological traits don’t show the same pattern. Yet much of the ecology of the genus is unknown, so it is difficult to draw any definite conclusions.

In her talk “Evolution of niche and ecomorphological traits in a phylogenetic context in lizards of the Liolaemus bibroni complex,” Dan Edwards sought to address this gap in understanding of Liolaemus by focusing on one species complex within the genus, L. bibroni. The L. bibroni species group is composed of 26 species that occupy a broad range of habitats representative of those occupied by the genus as a whole. To explore their history of genetic and morphological diversification, Edwards constructed a phylogeny of the group, characterized rates of diversification, and measured a suite of relevant morphological traits. She found that there has been an increase in trait diversification over time, consistent with the colonization of new habitat types. In addition, she found that ecology and body size are significantly correlated, supporting previous results from studies of the genus as a whole. Other morphological traits were not as clearly associated with habitat type, but there do appear to be possible patterns of ecomorphological divergence in response to divergence in habitat. Edwards plans to further characterize the evolutionary relationships and explore more ecomorphological traits of Liolaemus species to resolve this question.

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.