The interacting effects of total light intensity and chromatic contrast on visual signal visibility in an Anolis lizard
In Animal Behaviour
Fleishman, Wadman, and Maximov
Abstract
The sensory drive hypothesis states that selection acts on signals to make them more detectable in the habitat conditions in which they occur, resulting in signal divergence for species occupying different habitats. For colour signals, visibility depends on the luminance contrast and the chromatic contrast between the signal and the viewing background. Sensory drive has been tested in studies of the colourful dewlaps of anolines occupying different habitats. These studies found that red or orange dewlaps were more visible than yellow or white dewlaps across all habitat types, counter to the predictions of sensory drive that a species’ signal should be more visible in its own habitat than in habitats of other species. However, in these, and other sensory drive studies, chromatic contrast was calculated with a visual perception model that assumed that total light intensity has little or no effect on chromatic contrast perception. We carried out behavioural experiments testing the probability of detection of green, yellow and red stimuli presented against luminance-matched green backgrounds, at low and high light intensity typical of shaded and unshaded habitats. We found that the red stimulus was most detectable in the high light condition, while in low light, yellow and red stimuli were equally detectable. We modelled the stimuli with a receptor noise model that takes total light intensity into account. The model predictions were consistent with the behaviour results. We conclude that there is an important interaction between total light intensity and chromatic contrast in determining the visibility of colour signals, which should be taken into account in visual ecology studies. For animals with small eyes, shade level, which strongly influences total light intensity, may be as important as, or more important than habitat spectral quality in the evolution of signal colour diversity through sensory drive.
Consumer Responses to Experimental Pulses Subsidies in Isolated versus Connected Habitats
In The American Naturalist
Wright, Yang, Piovia-Scott, Spiller, and Schoener
Abstract
Increases in consumer abundance following a resource pulse can be driven by diet shifts, aggregation, and reproductive responses, with combined responses expected to result in faster response times and larger numerical increases. Previous work in plots on large Bahamian islands has shown that lizards (Anolis sagrei) increased in abundance following pulses of seaweed deposition, which provide additional prey (i.e., seaweed detritivores). Numerical responses were associated with rapid diet shifts and aggregation, followed by increased reproduction. These dynamics are likely different on isolated small islands, where lizards cannot readily immigrate or emigrate. To test this, we manipulated the frequency and magnitude of seaweed resource pulses on whole small islands and in plots within large islands, and we monitored lizard diet and numerical responses over 4 years. We found that seaweed addition caused persistent increases in lizard abundance on small islands regardless of pulse frequency or magnitude. Increased abundance may have occurred because the initial pulse facilitated population establishment, possibly via enhanced overwinter survival. In contrast with a previous experiment, we did not detect numerical responses in plots on large islands, despite lizards consuming more marine resources in subsidized plots. This lack of a numerical response may be due to rapid aggregation followed by disaggregation or to stronger suppression of A. sagrei by their predators on the large islands in this study. Our results highlight the importance of habitat connectivity in governing ecological responses to resource pulses and suggest that disaggregation and changes in survivorship may be underappreciated drivers of pulse-associated dynamics.
A morphometric assessment of species boundaries in a widespread anole lizard (Squamata: Dactyloidae)
In Biological Journal of the Linnean Society
Myers, de Mello, and Glor
Abstract
Cryptic species – genetically distinct species that are morphologically difficult to distinguish – present challenges to systematists. Operationally, cryptic species are very difficult to identify and sole use of genetic data or morphological data can fail to recognize evolutionarily isolated lineages. We use morphometric data to test species boundaries hypothesized with genetic data in the North Caribbean bark anole (Anolis distichus), a suspected species complex. We use univariate and multivariate analyses to test if candidate species based on genetic data can be accurately diagnosed. We also test alternative species delimitation scenarios with a model fitting approach that evaluates normal mixture models capable of identifying morphological clusters. Our analyses reject the hypothesis that the candidate species are diagnosable. Neither uni- nor multivariate morphometric data distinguish candidate species. The best-supported model included two morphological clusters; however, these clusters were uneven and did not align with a plausible species divergence scenario. After removing two related traits driving this result, only one cluster was supported. Despite substantial differentiation revealed by genetic data, we recover no new evidence to delimit species and refrain from taxonomic revision. This study highlights the importance of considering other types of data along with molecular data when delimiting species.
In Annals of Anatomy
Tinius, Russell, Jamniczky, and Anderson
Summary
External morphological metrics have featured prominently in comparative studies examining the morphological convergence that characterizes anoline ecomorphs. To what degree the appendicular-skeletal morphology of Greater Antillean island Anolis lizards tracks their diversity and ecological adaptation, however, remains relatively unexplored. Here we employ computed tomographic scanning techniques to visualise in situ the scapulocoracoid of ecomorph representatives (trunk-ground, trunk-crown, crown-giant, twig) from three islands (Jamaica, Hispaniola, and Puerto Rico), and compare its three-dimensional geometry using qualitative-descriptive and quantitative-morphometric techniques. In contrast to our previous, similarly-conducted study of the pelvic girdle of these same species, the form of the scapulocoracoid varies markedly both within and between species, with much of the variation relating to phylogenetic relationship, specimen size, and assigned ecomorph category. Morphometric variation that correlates with size and/or phylogenetic signal varies between species and cannot be eliminated from the data set without markedly reducing its overall variability. The discovered patterns of skeletal variation are consistent with the demands of locomotor mechanics imposed by the structural configuration of the microhabitat of these ecomorphs. Most pertinently the ecomorphs differ in the anteroposterior length of the coracoid, the dorsoventral height of the scapulocoracoid, the dorsoventral height of the scapula in relation to the height of the suprascapula, and the relative positioning of the borders of the scapulocoracoid fenestra. In the examined ecomorph categories these skeletal differences likely relate to microhabitat usage by permitting different degrees of tilting and displacement of the scapulocoracoid in the parasagittal plane and influencing the sizes of muscle origins and the vectors of their actions. These differences relate to the amount of humeral adduction applied during its protraction, and to the structural stability of the shoulder girdle during acrobatic maneuvers, thus influencing the perch diameter that can be effectively negotiated, a critical factor in the microhabitat structure of Anolis ecomorphs.
In Journal of Helminthology
dos Santos Mesquita, de Oliveira, Perez, and Ávila
Abstract
Helminthological studies may contribute with valuable information on host biology and conservation. Herein, we provide new data on helminths infecting the lizard Norops fuscoauratus, testing one of the factors considered most important in parasitic ecology: host size. We analysed 25 specimens of N. fuscoauratus from three highland marshes in the Brazilian semi-arid. Eight taxa of helminths belonging to Nematoda, Trematoda and Acanthocephala were found. Physaloptera sp. showed the higher prevalence (40%), with a mean intensity of infection of 3.3 ± 1.46 (1–16) and mean abundance 1.32 ± 0.65 (0–16). Norops fuscoauratus represents four new host records for the helminths Cyrtosomum sp., Pharyngodon travassosi, Strongyloides sp. and Centrorhynchus sp. There is no relationship of host body size (P = 0.79) and mass (P = 0.50) with parasite richness. In addition, the present study contributes to the knowledge of the parasitic fauna of N. fuscoauratus and the Neotropical region.
Learn about how you can landscape for lizards! We will cover many of the species you may see in Northeast Florida, the many benefits to having them around, and what you can do you in landscape and garden to support and protect them.
This is a free online course but registration through Eventbrite is required and the class is limited in size to 80 participants.
The cover photo for the event features a green anole (Anolis carolinensis, also pictured above), so expect some discussion of our beloved anoles. If you attend, please comment below and let us know what you learned!
When I hear or read Salmonella, I think of my mom explaining to my 7-year-old self why I shouldn’t eat raw chicken (to be clear, I never expressed interest in doing this, but lesson learned nonetheless). According to the U.S. Centers for Disease Control and Prevention, most instances of Salmonella bacteria making people sick do in fact result from transmission by food. But Salmonella infection can come from other sources, including direct contact with living animals, particularly reptiles (including birds which, in case you haven’t heard, are reptiles). So I was only a little surprised when I came across a recent paper in the Journal of Veterinary Medical Science, based in Japan, documenting the prevalence of Salmonella in the green anole, Anolis carolinensis, on Okinawa Island, Japan.
Of the 706 green anoles from Okinawa Island whose intestinal contents were analyzed for Salmonella presence between 2009 and 2014, only 2.1% tested positive. That number is low compared with published results for green anole populations in Florida (7.5%), Chichi Island in Japan (34.2% – this study was highlighted here on Anole Annals when it came out in 2013), and Guam (76.2%). I’m struck by how much these percentages vary. Green anoles have been in Florida for millions of years, whereas populations in the other locations have only been established for tens of years. The authors hypothesize that infection rate in recently introduced populations should correlate with how long the population has been established. Testing this hypothesis will require data from more populations. It also appears that we know little about whether anoles are affected by carrying Salmonella, although a quick search did reveal this study involving the brown anole, Anolis sagrei.
All told, we have a lot to learn about anoles and Salmonella. In the meantime, please protect yourself from Salmonella infection by following basic food safety precautions: refrigerate foods adequately, wash fruits and vegetables and cook meat and eggs thoroughly, and clean potentially contaminated cookware and utensils with soap and water. Most importantly, WASH YOUR HANDS, although I assume that like me, you are already doing this approximately a hundred times per day (for those of you reading this in the future, I’m not a weirdo. We’re in the middle of a pandemic).
For those who may be interested, green anoles became established in and around Japan several decades ago and are considered an ecologically disruptive pest. If you want to read more, here are links to some old Anole Annals posts on various topics related to the region’s green anoles: trapping efforts, population age structure, range expansion. Enjoy!
Interactions between native Anolis carolinensis (green anoles) and invasive Anolis sagrei (brown anoles) in the United States are discussed often here on Anole Annals. Most recently, this blog featured a local news broadcast from Louisiana and newspaper article from Florida, both of which describe a pattern that is repeated across the southern United States: When brown anoles invade a habitat, green anoles begin perching higher off the ground and thus become more difficult for anole enthusiasts to find.
Why do green anoles and brown anoles tend to occupy different perch heights in areas where they co-occur? By far the most popular explanation is that these species partition space as a means of partitioning resources, namely arthropod food. In simpler terms, they are competitors. But competition itself is not always simple. To better understand and study competition, biologists often classify competition as one of two types. Species can compete directly via aggressive encounters (termed “interference competition”) or indirectly through their shared use of a limited resource (termed “exploitative competition”). We know that green and brown anoles eat similar prey, suggesting that their competition is at least partly exploitative. Do they also engage in direct interference?
In a recently published paper in Oecologia, Katherine Culbertson (Harvard ESPP ‘18, former undergrad researcher in the Losos lab) and I tested the hypothesis that interference competition between native green anoles and invasive brown anoles occurs in the field. More specifically, we wondered if an asymmetry in interference competition might contribute to the vertical displacement of green anoles by brown anoles. To test for competitive asymmetries between the species, we used a classic method in behavioral ecology: tethered intruder trials. We presented adult male intruders to previously undisturbed focal individuals of the opposite species and videotaped the interactions. Intruders were tied around the waist with string at the end of a fishing pole with enough slack to move freely. We analyzed several aspects of the behavior of the focal lizards to evaluate asymmetries in interspecific aggression between the species: how often they attacked, how often they displayed (throat fan extensions, headbobs, and pushups), how often they retreated, and in what direction they retreated. (Disclaimer: Whenever an attack occurred, we ended the trial immediately so no lizards were harmed.)
As anticipated, we found that interference competition is asymmetric in favor of brown anoles, which are more likely to display and less likely to retreat from interactions than green anoles. In line with their arboreal tendencies, male green anoles also trend toward retreating upward more often than expected by chance. Somewhat surprisingly, these asymmetries are prevalent despite the almost complete absence of physical attacks (there were only two attacks in nearly one hundred trials, both by brown anoles). All told, our results suggest that signaling between the species and avoidance behavior by green anoles resolve most potential conflicts before they escalate to combat.
Figure 2 from our paper, which displays posterior predictions for the (a) probability of display, (b) display rate, and (c) probability of retreat of male Anolis sagrei (brown anoles, “SA”) and male Anolis carolinensis (green anoles, “CA”) when presented with a male intruder of the opposite species. Brown anoles were more likely to display and less likely to retreat than green anoles.
Many Floridians I’ve met in the course of my fieldwork have described brown anoles as bullies. Although anecdotal observations of animal behavior do not always reliably represent biological truths, in this case, the collective of observations made the residents I’ve spoken with are concordant with our data. Kudos to the many local naturalists who’ve shared their stories!
In closing, I’ll attempt to refine the metaphor of brown anoles as bullies, in acknowledgement that metaphors are often imperfect and with apologies to those who bristle at any attempt to anthropomorphize non-human animals. First, what makes a bully effective? On the playground, a bully might gain a reputation as such by initiating and winning a fight. Afterward, the mere threat of physical combat is often enough for the bully to exert his or her will on others. At our study sites, where green anoles and brown anoles have co-existed for several generations, brown anoles tend to dominate interactions with green anoles without attacking them. Perhaps physical combat is more common during the incipient stages of brown anole invasion, a hypothesis which could be tested by applying our methods across sites that vary in their invasion history.
Second, what’s the best way to deal with a bully? Many children learn to ignore bullies, a strategy rendered possible by the existence of alternative space to play or activities to engage in. Green anoles appear to find refuge in the canopy, where brown anoles seldom venture. Anecdotally, areas where no such canopy exists (i.e. areas with few plants or with only short, shrubby vegetation) are the areas where green anoles are most likely to disappear entirely following brown anole invasion. This hypothesis deserves a formal test.
Special thanks to the Aquatic Preserve Program run by the Florida Department of Environmental Protection for making this work possible. Check out the paper to learn more about our methods, results, and the implications of our findings.
Katherine Culbertson marking the location of a captured green anole in the field.
Yesterday afternoon Kristin Winchell successfully defended her Ph.D. dissertation at UMass Boston…during a nor’easter! The university was officially closed due to the inclement weather (I myself got stuck in a stairwell for several minutes because I didn’t have card swipe access), but that didn’t stop Kristin from delivering a fabulous talk about her work on urban evolution in anoles.
Congratulations Kristin!! And can you believe this cake?!?!
Anolis oxylophus at La Selva Biological Station (left, photo by Christian Perez) and Anolis aquaticus at Las Cruces Biological Station (right, posed).
Among anoles, West Indian ecomorphs are the best known microhabitat specialists, but they are not the only ones. Semiaquatic anoles, of which there are 11 described species, live exclusively near streams and will sometimes enter water to feed or to escape a threat. The Central American species Anolis aquaticus appears to be specialized for climbing on rocks, particularly relative to other Central American semiaquatic anoles (Muñoz et al. 2015). Recent posts on A. aquaticus have addressed sleep site fidelity,dewlaps and trait scaling, and underwater foraging.
During a field ecology course with the Organization for Tropical Studies last winter, I compared patterns of substrate use between A. aquaticus and another Central American semiaquatic anole, Anolis oxylophus. Unlike A. aquaticus, A. oxylophus perches predominantly on woody and leafy substrates (Table 1). I wondered what was driving the differences in substrate use between these two species that appear broadly similar in morphology and lifestyle. Some Caribbean anoles alter their behavior to use only a narrow subset of available substrates in their habitat, whereas others have a greater breadth of substrate use that more closely reflects habitat-wide availability (Irschick and Losos, 1999; Mattingly and Jayne, 2004; Johnson et al., 2006). To evaluate whether substrate use differences between A. aquaticus and A. oxylophus are driven by substrate availability, species-specific selectivity, or both, I simultaneously quantified lizard substrate use and substrate availability within their streamside habitats.
