ECOLOGICAL RELEASE ANALYZED AMONG INDIVIDUALS, ACROSS TWO GENERATIONS, AND ALONG MULTIPLE NICHE AXES IN ANOLIS CAROLINENSIS

Impacts of an invasive species (Anolis sagrei) on social and spatial behaviours of a native congener (Anolis carolinensis)

Sleeping site selection of Brookesia decaryi was investigated in a dry forest of northwestern Madagascar from mid-October 2004 to the beginning of May 2005. Sleeping site characteristics were recorded for 304 individuals. This chameleon species is diurnal, dwelling on the ground in the daytime, but at night all individuals were found perching on small plants, shrubs, dead fallen branches, or liana. Eighty percent of adult males, 73% of adult females, 85% of juveniles, and 82% of hatchlings slept on small plants. Approximately 70% of individuals chose a sprig or branch as a support during the sleeping time; the others selected a leaf or trunk. The preferred sleeping orientation was horizontal or oblique with head up. No tendency to sleep at the tip of support was observed. There were no sexual differences in sleeping site selection (perch diameter, perch height, and vegetation height), but there were significant differences in these variables among age classes. Body size was significantly positively correlated with perch diameter and perch height, but not with vegetation height. The primary factor that determines the sleeping site and position of B. decaryi may be predation avoidance, but other factors, such as morphological constraint and climate condition, cannot be excluded.

The positive relationship between hind-limb length and perch diameter is well established in Anolis lizards, both among populations of some species and among species. Interspecific comparisons indicate that longer legs confer an advantage for increased running speed on broad substrates, whereas shorter limbs provide greater maneuverability on narrow surfaces. In this light, phenotypic plasticity for hind-limb length previously detected in Anolis sagrei may be adaptive because hatchlings exposed to only broad substrates developed relatively longer hind limbs for their body size compared to hatchlings exposed to only narrow substrates. We tested the generality of hind-limb length plasticity in Anolis by conducting a hatchling growth experiment on Anolis carolinensis, a distant relative of A. sagrei and a different type of habitat specialist. Similar to A. sagrei, A. carolinensis grown in cages with different sized perches showed hind-limb length plasticity, but the magnitude of difference between treatments and sexes was less for A. carolinensis than for A. sagrei. This finding suggests either hind-limb plasticity is widespread within the genus Anolis or that it has evolved independently at least twice.

Arboreal animals often move in habitats with dense vegetation, narrow perches and variable inclines, but effects of arboreal habitat structure on locomotor function are poorly understood for most animals. Several species of Anolis lizards, which have served as a model group for relating locomotor performance to morphology, have decreased maximal sprinting speeds when perch diameter decreases. However, the effects of perch diameter on the limb movements of Anolis have not been previously studied. Hence, we quantified the hindlimb movements of Anolis sagrei, which naturally occurs on a wide variety of perch diameters and inclines. We analyzed similar speeds of steady locomotion for combinations of flat surfaces and round perches with diameters of 1, 3, 6 and 10 cm and inclines of 0 degrees and uphill 45 degrees and 90 degrees. Diameter significantly affected more kinematic variables than incline, but many kinematic variables changed little with increases in diameter beyond 6 cm. As surface diameter increased, the limb posture of A. sagrei became progressively more sprawled. Significantly greater knee flexion during stance was important for locating the foot more medially during movement on narrow perches. Stride length increased and femur depression, femur retraction and long-axis femur rotation decreased significantly as the surface diameter increased. The low hip heights on the vertical incline and the narrowest perches suggest that bringing the center of mass closer to the locomotor surface is important in these circumstances for reducing the tendency to topple backwards or sideways. Most of the kinematic changes of A. sagrei with decreased perch diameter were opposite those correlated with increased speeds of locomotion for terrestrial lizards. The foot was most lateral to the hip during the swing phase and maximal lateral displacements decreased with decreased perch diameter. Consequently, the width required to accommodate limb movement also decreased as perch diameter decreased.

Native species can coexist with invasive congeners by partitioning niche space; however, impacts from invasive species often occur alongside other disturbances. Native species' responses to the interactions of multiple disturbances remain poorly understood. Here we study the impacts of urbanization and an invasive congener on a native species. Using abundance (catch-per-unit effort) and vertical distribution of native green anoles (Anolis carolinensis) and invasive brown anoles (Anolis sagrei) across a gradient of natural-to-urban forests, we ask if niche shifting (lability) is occurring, and if it can mitigate impacts from one or both disturbances. We use generalized linear models to relate species abundances across the landscape to urbanization, forest structural complexity, and congener abundances (i.e., A. sagrei); and test for an interaction between urbanization and congener abundance. Our data show that A. sagrei presence results in a 17-fold upward shift in vertical niche of A. carolinensis-an 8.3m shift in median perch height, and models reveal urbanization also drives an increase in A. carolinensis perch height. A. carolinensis and A. sagrei abundances negatively and positively correlate with urbanization, respectively, and neither species' abundance correlate with congener abundance. Despite a positive correlation between A. sagrei abundance and urbanization, our results do not show evidence of this interaction affecting A. carolinensis. Instead, niche lability appears to enable the native species to mitigate the impact of one driver of decline (invasive competition) while our data suggest it declines with the second (urbanization).

The major histocompatibility complex (MHC) is an important genomic region for adaptive immunity and has long been studied in ecological and evolutionary contexts, such as disease resistance and mate and kin selection. The MHC has been investigated extensively in mammals and birds but far less so in squamate reptiles, the third major radiation of amniotes. We localized the core MHC genomic region in two squamate species, the green anole (Anolis carolinensis) and brown anole (A. sagrei), and provide the first detailed characterization of the squamate MHC, including the presence and ordering of known MHC genes in these species and comparative assessments of genomic structure and composition in MHC regions. We find that the Anolis MHC, located on chromosome 2 in both species, contains homologs of many previously-identified mammalian MHC genes in a single core MHC region. The repetitive element composition in anole MHC regions was similar to those observed in mammals but had important distinctions, such as higher proportions of DNA transposons. Moreover, longer introns and intergenic regions result in a much larger squamate MHC region (11.7 Mb and 24.6 Mb in the green and brown anole, respectively). Evolutionary analyses of MHC homologs of anoles and other representative amniotes uncovered generally monophyletic relationships between species-specific homologs and a loss of the peptide-binding domain exon 2 in one of two mhc2β gene homologs of each anole species. Signals of diversifying selection in each anole species was evident across codons of mhc1, many of which appear functionally relevant given known structures of this protein from the green anole, chicken, and human. Altogether, our investigation fills a major gap in understanding of amniote MHC diversity and evolution and provides an important foundation for future squamate-specific or vertebrate-wide investigations of the MHC.

We artificially invaded a set of small islands with the large lizard Leioce- phalus carinatus to determine effects on food-web elements including an intermediate predator, the lizard Anolis sagrei; the latter was previously found to have major, mostly direct effects on web spiders, as well as detectable indirect effects on aerial arthropods (including parasitoids) and leaf damage. In addition to these food-web elements, we mon- itored ground-surface arthropods; they are expected to be affected directly, as well as indirectly via A. sagrei ,b yL. carinatus. Five islands were randomly selected for invasion while six others served as controls. In addition, four islands without A. sagrei were mon- itored to determine the natural state of the sagrei-free food web. We also monitored a variety of A. sagrei's traits, from behavioral through physiological and demographic to morphological, to elucidate the mechanisms whereby L. carinatus might affect the smaller lizard and to evaluate trait-mediated as well as density-mediated effects. Comparison of unmanipulated islands with and without A. sagrei showed that A. sagrei appeared to be affecting web-spider density and diversity, numbers of small aerial arthro- pods, number of large ground-surface arthropods, and two types of leaf damage, scars and mines. All effects were negative save one: Small aerial arthropods were more abundant with A. sagrei; this variable and parasitoid abundance were negatively related to web-spider density, implicating an indirect effect pathway from A. sagrei via web spiders. Introduction of L. carinatus had major and immediate effects on A. sagrei density and perch height; effects on perch diameter, percentage hatchlings, and the width of the body- size distribution followed over time. Behavioral shifts in habitat use continued to the end of the experiment, after changes in population density had mostly leveled off. Adult-male body condition became poorer after introduction of L. carinatus. Among islands, percentage use of the ground was correlated negatively with percentage vegetated area of the island and positively with premanipulation relative hindlimb length. We hypothesize that longer- legged individuals do better on the ground because they are faster there. Conditional ev- idence for an increase in adult-male relative hindlimb length suggested that, when the ground-inhabiting L. carinatus was introduced, such individuals were differentially able to escape predation. Introduction of L. carinatus significantly reversedA. sagrei's effect on number of species and density of web spiders but had no other major effects on lower level food-web elements. Thus, a relatively short-chained (two links) effect, with a relatively strong second link ( A. sagrei on spiders), showed the greatest indirect effect of the manipulation. Another poten- tially strong indirect effect, that on large ground-surface arthropods, did not occur, possibly because of compensatory (direct) predation by L. carinatus. Thus presence of omnivory may also be relevant to whether reversal of effects occurs. Although most A. sagrei effects were not reversed in the time available for the experiment, this may be typical, as natural L. carinatus colonizations can dwindle away to extinction over about the same time span, producing at best only short-term indirect effects. Population-density estimates from other sites and comparisons to other experimental studies suggest that, in general, predators on Anolis may have erratic effects in space and time.

Influence of microhabitat use on morphology traits of three species of the Anolis sericeus complex (Squamata: Dactyloidae) in Mexico

Calcium oscillations increase the efficiency and specificity of gene expression: Dolmetsch RE, Xu K, Lewis RS: Nature 1998. 392:933–936

The range of inclines and perch diameters in arboreal habitats poses a number of functional challenges for locomotion. To effectively overcome these challenges, arboreal lizards execute complex locomotor behaviors involving both the forelimbs and the hindlimbs. However, few studies have examined the role of forelimbs in lizard locomotion. To characterize how the forelimbs and hindlimbs differentially respond to changes in substrate diameter and incline, we obtained three-dimensional high-speed video of green anoles (Anolis carolinensis) running on flat (9 cm wide) and narrow (1.3 cm) perches inclined at 0, 45 and 90 deg. Changes in perch diameter had a greater effect on kinematics than changes in incline, and proximal limb variables were primarily responsible for these kinematic changes. In addition, a number of joint angles exhibited greater excursions on the 45 deg incline compared with the other inclines. Anolis carolinensis adopted strategies to maintain stability similar to those of other arboreal vertebrates, increasing limb flexion, stride frequency and duty factor. However, the humerus and femur exhibited several opposite kinematic trends with changes in perch diameter. Further, the humerus exhibited a greater range of motion than the femur. A combination of anatomy and behavior resulted in differential kinematics between the forelimb and the hindlimb, and also a potential shift in the propulsive mechanism with changes in external demand. This suggests that a better understanding of single limb function comes from an assessment of both forelimbs and hindlimbs. Characterizing forelimb and hindlimb movements may reveal interesting functional differences between Anolis ecomorphs. Investigations into the physiological mechanisms underlying the functional differences between the forelimb and the hindlimb are needed to fully understand how arboreal animals move in complex habitats.

In a meta-analysis, we examined the behavioral portfolio of invasive brown anoles (Anolis sagrei) and native green anoles (Anolis carolinensis) in urban and non-urban environments. We hypothesized that invasive anoles would display more agonistic and bold signals (head bobbing, dewlap extensions, and pushups) than their native-range counterparts and their native competitors. We found that in urban settings, anoles of both species signaled more with dewlap extensions than with head bobs. Brown anoles displayed significantly more in non-urban habitats and their native range compared to urban habitats and invasive ranges. The outcome of our analysis suggests that brown anoles have plastic behavioral portfolios, whereas green anoles have relatively balanced preferences for head bobbing, irrespective of the habitat in which the populations were collected. We attribute the success of the brown anole invasion to the flexible strategy in the face of higher mate competition, higher predation risks, and less resource competition in both urban and invasive ranges. Lastly, we observed publication biases. More studies were conducted with urban and invasive brown anoles and specifically in manipulative mesocosm experimental settings—transplanting populations from native field settings. We show this altered the display rates across all studied signals.

Competition takes place not only between species but also within them. Intersexual competition for resources may increase sexual dimorphism in body size to minimise ecological niche overlap. Change in the level of sexual dimorphism in a species is a common feature of island radiations. This is often interpreted as ecological release from interspecific competitors absent from small islands, allowing niche expansion by both sexes of a dimorphic species. The Olive-backed Sunbird (Cinnyris jugularis) is a widespread island-colonising species found throughout the Indo-West Pacific. Here we investigate sexual dimorphism in morphological niche of Olive-backed Sunbird populations in South-east Sulawesi, Indonesia. We found decreased overlap in morphological niche between females and males on the species-depauperate Wakatobi Islands, in comparison to mainland Sulawesi and its larger continental islands, indicating greater sexual dimorphism on the small islands. This change in sexual dimorphism was associated with a decrease in the morphological niche hypervolume of females, but no change in males. Therefore there was no indication of expansion of morphological niche space in the absence of mainland competitors. These morphological differences were associated with the significantly higher population density of Wakatobi Olive-backed Sunbirds. Therefore this increased sexual dimorphism may serve to alleviate intraspecific competition for resources.

Biological invasions are both a pressing environmental challenge and an opportunity to investigate fundamental ecological processes, such as the role of top predators in regulating biodiversity and food-web structure. In whole-ecosystem manipulations of small Caribbean islands on which brown anole lizards (Anolis sagrei) were the native top predator, we experimentally staged invasions by competitors (green anoles, Anolis smaragdinus) and/or new top predators (curly-tailed lizards, Leiocephalus carinatus). We show that curly-tailed lizards destabilized the coexistence of competing prey species, contrary to the classic idea of keystone predation. Fear-driven avoidance of predators collapsed the spatial and dietary niche structure that otherwise stabilized coexistence, which intensified interspecific competition within predator-free refuges and contributed to the extinction of green-anole populations on two islands. Moreover, whereas adding either green anoles or curly-tailed lizards lengthened food chainson the islands, adding both species reversed this effect-in part because the apex predators were trophic omnivores. Our results underscore the importance of top-down control in ecological communities, but show that its outcomes depend on prey behaviour, spatial structure, and omnivory. Diversity-enhancing effects of top predators cannot be assumed, and non-consumptive effects of predation risk may be a widespread constraint on species coexistence.

Since its introduction ten years ago, Anolis sagrei has spread over much of Grand Cayman and is now more common in some habitats than the native anole, A. conspersus. Interspecific differences in body size, perch height, and microclimatic preference may have facilitated the colonization. Nonetheless, competition may be occurring between the species; comparisons with studies of habitat use prior to the arrival of A. sagrei indicate that in open habitats, where A. sagrei is now abundant, A. conspersus perches higher, but in closed habitats, where A. sagrei is absent, no change in perch height is evident. Review of data concerning 23 Anolis introductions indicates that the presence or absence of an ecologically similar native species may be an important determinant of colonization success or failure.

Effects of age- and sex-specific density on behaviour and survival in a territorial lizard (Anolis sagrei)