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Behaviors and interactions of wild green anoles (Anolis carolinensis) in a large and small artificial enclosure
The Green Anole (Anolis Carolinensis) is a small, green, arboreal lizard with a light colored throat and long tail that is native to North America and prevalent in the southeastern United States. Green anoles inhabit many parts of Texas, including the Rio Grande Valley, and can be found perched on trees, fences, and buildings (LaDuc, 2014). Green anole lizards are best known for flaring their dewlaps and doing pushups, but because they have been studied extensively for over a century, literature documenting many other aspects of their behavior have also been published (Lovern, Holmes, & Wade, 2004). The richness in green anole literature allows these lizards to be effective models for studying animal behavior. In addition, these lizards are easy to obtain from the wild, less expensive than other animals to maintain in a laboratory setting, and can be used in evolutionary studies because of their common ancestry with birds (Lovern et al., 2004). In fact, the green anole was the first non-avian reptile to have its genome sequenced in 2011, and in a comparative analysis with birds
and mammals, it was discovered that, unlike birds who possess ZW sex chromosomes, green anoles lizards have
XY sex chromosomes (Alföldi et al., 2011).
Even different populations of green anoles have diverged in morphology and behavior. Male anoles from habitats with a high density of males displayed different behaviors than anoles from habitats with fewer males, and they displayed their behaviors much more frequently (Bloch & Irschick, 2006). An anole population that spent more time perched on smooth surfaces had larger toepads and the ability to cling to surfaces better than
the population that primarily perched on rough surfaces. In the same study, male and female anoles from both populations behaved differently when perceiving a threat; females fled from an approaching threat at a greater distance than males in both populations (Irschick et al., 2005)
Individuals of the same species, and even population, can vary greatly in behavior and morphology. Some anoles find it rewarding to display aggressive behaviors and will frequent the location where they have behaved aggressively, while other anoles do not (Farrell & Wilczynski, 2006). There are also small, male anoles that will rival larger, stronger males that will likely beat them, to protect their territory (Jenssen, Decourcy, & Congdon, 2005).
Life experiences also shape behavior, contributing to the variance in individual behavior. Many anoles
that have lost a fight will perceive their loss as a lack of ability, and will lose subsequent battles due to decreased aggressive effort. Alternately, contest winners have augmented perceptions of their ability to fight, and will increase aggression in later battles even though their actual aptitude has not changed (Garcia, Murphree, Wilson, & Earley, 2014). Before establishing a dominant-subordinate relationship with another lizard, anoles placed in a stressful environment turned brown and formed an eyespot, both indicators of stress.
When anoles were paired together, and one experienced being the dominant lizard and the other the subordinate, their reactions to the same stressful stimuli changed. After becoming the dominant lizard, the anole's response to stress decreased, while the now subordinate individual's stress response increased (Plavicki, Yang, &
Green anoles exhibit great variation in same-species inter- and intrasexual interactions, as well as varied relationships to the environment and other species. The purpose of this study was to observe the behaviors and interactions of wild green anoles (Anolis carolinensis) in a large and small artificial enclosure, and identify different factors that contribute to anole behaviors.
Seven wild, green anole lizards, six males and one female, were collected from a Brownsville garden, however, one male lizard escaped during the acclimation period prior to conducting any behavioral observations. During the first phase of the experiment, the six lizards were held in a large, 1256-liter cage [244 (L) x 71.5 (W) x 72 (H) cm] for three days, two days of acclimation, and one day of behavioral observations. During the second phase of the study, all six lizards were moved to a smaller, 23.4-L aquarium [ 41.1 (L) x 21.3 (W) x 26.7 (H) cm] where they were allowed to adjust for one day, and were then observed for the following three days. Both the large cage and small aquarium held a water dish, heating lamp, and peat moss. The lizards
were fed crickets every two days while in captivity, and at the end of the week-long experiment, the green anole lizards were released to their garden in Brownsville.
Before collecting the green anole lizards, the large cage was built using lumber [4 (5x5x244 cm)-boards and 10 (5x5x72 cm)-boards], 6.32-mm wire mesh (226 m2), and a brown, king-sized bed sheet (Fig 1). On day 1
(D1), a drop of different colored nail polish was placed on the backs and tails of each lizard to identify the subjects. The lizards were also measured with a ruler from the tip of the premaxilla to the tip of the tail (full length) and from the tip of the premaxilla to the end of the sacrum (body length; Table 1). The measurements were taken in inches, but converted to cenitmeters. The subjects were subsequently placed in the large, 1256- liter cage [244 (L) x 71.5 (W) x 72 (H) cm], fed crickets, and allowed to acclimate to their new environment.
On D2, the lizards continued to adjust to the large cage, while improvements to the cage were made by covering small gaps with clear tape because a male lizard had escaped. Behavioral observations commenced at noon on D3, and continued for three consecutive hours. The six lizards were concurrently observed for any noticeable actions or behaviors, and all was documented in a notebook. On D4, lizards were transferred to the small, 23.4- L aquarium, but behavioral documentation did not resume until D5. Two-hour, midday, behavioral observation periods were conducted on D5, D6, and D7. Again, all lizards were observed concurrently, and all perceivable actions and behaviors were written in a notebook. Following the two-hour observation on D7, the lizards were set free.
Frequency of behaviors were tallied for each lizard, without regard to the amount of time spent exhibiting the behavior. The attempt was to record every single action of the six lizards at the same time, however, only the most repetitive and obvious behaviors were transposed to tables for analysis (Table 2 & 3). Some of the repetitive, observable behaviors in the large cage and small aquarium were different, therefore, the tables of documented behaviors are also unalike. Due to the low activity in the large cage, estimated time was determined by observing if the lizards were together the entire time (=2), if they spent some time together (=1), or no time at all together (=0).
The Kruskal Wallis test and Spearman correlation coefficients were used to evaluate the relationships of the independent variables to the ordinal dependent variables, with a p-value less than 0.05 considered significant. SPSS 21 was utilized to carry out the statistical analyses.
Table 1. Green anole characteristics
Table 2. Green anole behaviors
Table 3. Green anole behaviors
measured in the large cage.
measured in the small aquarium.
Green F 15.24 5.08
Red M 11.43 6.033
Sky M 16.828 6.985
Blue M 19.05 6.668
Holding head up/looking around
Holding head up/looking around
Pinky M 20.003 6.668
Walking Turning brown
Running Being alone
Walking Turning brown
Running Being alone
Being approached Approaching
Estimated time near Red
Estimated time near Blue
Estimated time near female
Estimated time near Sky
Being knocked over by someone else
Knocking somebody else over
Estimated time near Pinky
Estimated time near Yellow
The most frequent behavior in the large cage was “walking” (Fig. 2), and the most frequent behavior in the small aquarium was “falling” (Fig. 3). Males with greater full lengths (FL) were alone more often than shorter males in the small aquarium (rho= 0.926, p=0.008; Figure 2), but no significant relationship was found in the large cage or when combining data from both enclosures. Larger FL males displayed aggressive behaviors, pushups and dewlap flares, significantly more frequently than smaller males when combining data
from the small aquarium and large cage (rho=0.703, p=0.023; Figure 3), although the only male lizard to exhibit
aggressive behaviors was Pinky. The female lizard, Green, spent more time with larger BL males than smaller BL males in the large cage (rho= 0.913, sig 0.03; Figure 4). Males with shorter BL approached the female more often than other males in the small cage (rho= -0.892, p= 0.042; Figure 5). There was much greater overall activity in the small aquarium compared to the large cage (chi-square= 4.035, p=0.045, df=1; Figure 6), however cage size did not effect the number of times individuals turned brown (chi-square= 0.489, p= 0.484, df= 1; Figure 7). Contradictory to the literature, lizards with broken tails did not fall significantly more than lizards with intact tails when jumping (chi-square= 2.206, p= 0.137, df= 1; Figure 8).
Figure 2. Total frequency of green anole behaviors in large cage.
Figure 3. Total frequency of green anole behaviors in small aquarium.
Figure 4. Number of times spent alone in small aquarium by full lizard length.
Figure 5. Total frequency of aggressive behaviors in both large and small containers by lizard length.
Figure 6. The estimated time [entire (=2), some (=1), none (=0)] near female in large cage by average male body length.
Figure 7. Average number of times male lizards of different body lengths approached the female lizard.
Figure 8. Total activity in the small aquarium compared to the large cage.
Figure 9. The number of times any of the six lizards turned brown while in the small aquarium and large cage.
Walking was the most frequent behavior in the large cage, and was done most by the same individual, Red (Fig. 2). The large cage had more space to explore than the small aquarium, and two other lizards had previously escaped from a small opening in the cage (though, one was caught). Red had attempted to escape during the observational period, and was possibly searching for another opportunity.
The most frequent behavior in the small aquarium was “falling” (Fig. 3), and was also accomplished most by Red. Red's tail was severed, and lizards with missing tails have less stability when jumping (Figure 10; Kuo, Gillis, & Irschick, 2012). Although there was a relationship between having a broken tail and falling (Fig.
10), the relationship was not significant in this study. It is likely that there were not enough individuals with severed tails to establish a statistical relationship.
This study found that male lizards with greater full lengths were alone more often than shorter males in the small aquarium (Fig. 4). In nature, larger males typically have larger territories with excellent resources compared to smaller males (Crawford, 2011). It is possible that the larger lizards had established their territories within the aquarium. In the large cage, larger males were not alone more often than smaller males, however, larger-bodied males did spend more time with the female lizard (Fig. 6). Female lizards are not typically known to have a preference for male characteristics, but a 2010 study found that they did prefer larger males (Stellar & White, 2010). It was postulated that females may not actually prefer larger males, but that females prefer better quality territories, and male size can indicate territory quality. In addition, males with
shorter bodies approached the female lizard more times than larger males (Fig. 7). This may provide support for the hypothesis that females prefer larger males to smaller males, because unlike small male lizards, larger males would have no need to approach the female if she approached them first.
Supported by the literature, this study found that greater full length was significantly related to aggressive behaviors, however, Pinky, the longest male, was the only individual to exhibit aggressive behaviors (Fig. 5).
Overall activity was greatly increased in the small aquarium compared to the large cage, likely due to stress from being held in such a small container (Fig 8). A single male and up to eight females usually require a
110-L glass aquarium (Lovern et al., 2004). However, the lizards did not turn brown significantly more in the small aquarium than in the large cage (Fig. 9). The length of time the lizards stayed brown was not measured, therefore, it is possible that the lizards spent more time brown in the small aquarium than in the large cage.
Measuring the amount of time spent performing a behavior along with the frequency of the behavior would improve upon the study. An increased sample size with a greater ratio of females, and lizards without tails would also help. Another change to the study would be to measure the lizards in millimeters instead of inches. Lastly, containers with perches and better resources would better mimic nature and enhance the behaviors would be a better representation of what occurs in nature.
The lizards frequently jumped on each other, climbed each other, used each other's tails as climbing ropes, and pulled each other from the wall to the ground in the small aquarium. It is likely that these behaviors occurred because the aquarium was too small for all six lizards, because these behaviors were absent in the large cage, but no information on these behaviors could be located. Future research could focus on the identifying these unidentified behaviors.
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