Research Article |
Corresponding author: Thiago Maia-Carneiro ( tmaiacarneiro@gmail.com ) Academic editor: Ana Lúcia da Costa Prudente
© 2018 Thiago Maia-Carneiro, Gisele R. Winck, Mariana Rodrigues Pereira, Carlos Frederico Duarte Rocha.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Maia-Carneiro T, Winck GR, Pereira MR, Rocha CFD (2018) Body orientation for thermoregulation and daily activity cycle of Mabuya macrorhyncha (Squamata: Scincidae). Zoologia 35: 1-5. https://doi.org/10.3897/zoologia.35.e24575
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We investigated the daily activity and thermoregulatory body orientation of Mabuya macrorhyncha (Hoge, 1947), a lizard species that occurs in the Brazilian Atlantic Forest. We conducted this investigation in a sandy coastal dune remnant (“restinga” ecosystem) in Grussaí, state of Rio de Janeiro, Brazil, during the summer. The daily activity cycle of the lizards started around 6:00 am and ended before 7:00 pm. This is longer than observed in other populations of M. macrorhyncha (approximately 7:00 am to 5:00 pm). The activity cycle of the lizards was bimodal, with the first peak between 6:00 and 11:00 am and the second from 2:00 to 7:00 pm. This contrasts with observations on other populations of this species, which revealed an unimodal pattern. The mean body temperature of M. macrorhyncha in Grussaí was 34.2 ± 1.5 °C, which was comparatively higher than observed in other populations of the species. The differences in the daily activity and of body temperature of these lizards between our study and previous studies on this species may reflect environmental thermal conditions. The mean air and mean substrate temperatures when individuals were active were 27.8 and 30.5 °C respectively. Lizard orientation was significantly correlated with the direction of the solar incidence, suggesting that solar radiation, and particularly behavioral adjustments that maximize exposure to the sun, are important for the thermoregulation of M. macrorhyncha. Circular structures at the site, such as bromeliads, offer microhabitats with different orientations to the sunlight, favoring lizard thermoregulatory behaviors.
Activity period, body temperature regulation, microhabitat, thermoregulatory behavior
Thermal environments affect activity patterns and body temperatures of lizards throughout their daily cycles (
Mabuya macrorhyncha (Hoge, 1947) is a diurnal lizard (
The “restingas” are sand dune coastal ecosystems in the Atlantic Forest biome of Brazil. Relatively undisturbed restinga sites typically have diverse vegetation structures and physiognomies, including herbs, shrubs, and trees growing on sandy soils. We conducted our fieldwork at Restinga of Grussaí (21°44’S, 41°02’W), municipality of São João da Barra, state of Rio de Janeiro, southeastern Brazil. The local climate at the site is Aw in the Köppen-Geiger classification (tropical with dry winter), with annual mean temperatures between 22 and 24 °C (
We gathered data through time-constrained visual encounter surveys (
We searched for active perched individuals (e.g., on bromeliads or steams) to investigate their body orientation during thermoregulation, since M. macrorhyncha lizards frequently use the vegetation as thermoregulatory sites (
We collected 29 M. macrorhyncha lizards from Grussaí. Their activity pattern was bimodal, with peaks from 06:00 to 11:00 am and then between 2:00 and 7:00 pm, decreasing the activity during midday (from 11:00 am to 2:00 pm) (Fig.
The activity cycle of the lizards in our data from Grussaí was longer than recorded in the literature for other places, starting at 6:00 am and ending at approximately 7:00 pm. The following results from other studies documented shorter activity times for lizards: Barra de Maricá (Rio de Janeiro, Brazil) from 7:00 am to 4:00 pm (
In our results, the activity cycle of M. macrorhyncha is bimodal. This avoids exposure to high environmental temperatures and is consistent with observations on other lizard species (
As expected, M. macrorhyncha individuals in Grussaí regulated the temperature of their bodies through exposure to sunlight radiation, selecting sites that allow fine temperature adjustments. Their body orientations significantly correlated with the direction of the sun, suggesting that solar radiation and behavioral adjustments are important for their thermoregulation. Some bromeliad species have a circular architecture that provides different heights, inclinations, and orientations for perching lizards, making it easier for them to pose according to changes in the direction of the sun. By selecting different positions and angles, the lizard may control the quantity of solar radiation intercepted by its body. Since we observed that all perching individuals were oriented towards the sun, apparently all the different perch types functioned as thermal microhabitats for thermoregulation. Beyond thermoregulation, basking on bromeliads may also provide M. macrorhyncha lizards with other significant advantages (e.g., improved detection of or refuge from predators and food or water availability). The basking behavior of M. macrorhyncha in Grussaí differed from that of its sympatric congener Mabuya agilis, which commonly bask on leaf-litter (
We noted significant differences in the correlation coefficients of lizards’ positions and sun direction. We encountered a relatively weak negative correlation between individuals found on bromeliads and the direction of the sun, and a strong positive correlation was found for lizards on other perches and the position of the sun. Such apparently contrasting results occurred despite the little differences of their mean angles. It is possible that these differences derived from differences among microhabitats. Other perches might be located mainly in areas comparatively more open (e.g., shrub edges and clearings), which could facilitate the perception of the sun’s position in the sky, allowing lizards to position themselves more precisely according to the incidence of sunrays. The results of this study suggest that the body orientation according to the position of the sun in the sky may be of importance for the thermoregulation of M. macrorhyncha individuals.
Illustration demonstrating how we collected the data regarding cardinal directions on bromeliads (used here for exemplification), stems, and trunks in Grussaí. We obtained the pictures of the bromeliad and of the wind rose from the World Wide Web and overlapped the second over the first for the composition of the figure.
Cardinal orientations of Mabuya macrorhyncha individuals (N = 35, in degrees) at first sight on different circular-shaped substrates (mainly bromeliads) in the Restinga of Grussaí, municipality of São João da Barra, state of Rio de Janeiro, southeastern Brazil. The arrow direction represents the mean vector (µ), and its length represents the length of the mean vector (r).
We appreciate fieldwork assistance of Felipe BS Telles. We thank the Instituto Brasileiro de Recursos Naturais e Renováveis (IBAMA) for research permit (process 15322-2). We are grateful to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), which provided grants to CFDR (processes 304791/2010-5, 424473/2016-0 and 302974/2015-6). Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) granted doctoral scholarship fund to GRW (processes E-26/100.769/2008 and E-26/100.477/2011), and support CFDR through Programa Cientistas do Nosso Estado (processes E-26/102.765.2012 and E-26/202.920.2015). GRW current receive a post-doctoral fellowship grant from CNPq (process 151984/2016-6). We also thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and the FAPERJ for doctorate scholarships for TMC.