C. M. Gienger

Dry season habitat use by lizards in a tropical deciduous forest of Western Mexico

Tropical deciduous or dry forests are characterized by strong seasonality in precipitation, typically having a prolonged dry season lasting at least four months (Bullock, 1986; Murphy and Lugo, 1986). As the dry season progresses, the forest canopy changes from a relatively homogeneous dense cover of the wet season to a more variable and open canopy (Lott et al., 1987; Bullock and Solis-Magallanes, 1990). As deciduous trees lose their leaves, more sunlight penetrates the canopy and creates a variety of forest gaps and thermal microenvironments on or near the ground. In contrast, forest habitat near seasonally dry watercourses (arroyos), remains green throughout the dry season, providing shaded habitats with dense canopy cover (Lott et al., 1987; Bullock and Solis-Magallanes, 1990). The dry season in a tropical deciduous forest represents a challenging time of year for most ground dwelling vertebrates. Water and energy resources are at the yearly low (Janzen and Schoener, 1968; Lister and Garcia, 1992), and thermal options may also be reduced, especially in the more shaded habitats of arroyos. Many vertebrates show reduced activity or seasonal changes in habitat use during the dry season (Beck and Lowe, 1991; Ceballos, 1995). Other species may move away from upland habitats and into arroyos or watercourses, which are used as dry season refuges (Ceballos, 1990). Those that remain active tend to be juveniles or adults of smaller species (Fleming and Hooker, 1975; Lister and Garcia, 1992; Casas-Andreu and Gurrola-Hidalgo, 1993; Fitzgerald et al., 1999). We know little about how dry forest lizards respond to seasonal changes in habitat structure or of the patterns of activity exhibited by lizards that remain active during the dry season. Our study examines how lizard habitat use and activity (i.e., species found to be active, timing, and amount of activity) are influenced by the variability in forest structure during the dry season in a tropical deciduous forest in southwest Mexico. We address the following questions: (1) During the dry season, does lizard activity differ between arroyo and upland habitats? (2) Is lizard activity related to forest canopy cover during the dry season?

Removing the rubbish: frogs eliminate foreign objects from the body cavity through the bladder

During the course of a telemetry study on three species of Australian frogs (Litoria caerulea, Litoria dahlii and Cyclorana australis), we found that many of the surgically implanted transmitters had migrated into the bladder. We subsequently implanted small beads into L. caerulea and they were expelled from the body in 10–23 days. Beads implanted into cane toads (Rhinella marina) to document the process were either expelled or were enveloped into the bladder. This appears to be a unique pathway for expulsion of foreign objects from the body, and suggests that caution should be employed in telemetry studies when interpreting the separation of some animals from their transmitters as a mortality event.

Ecological Interactions Between Gila Monsters (Heloderma suspectum) and Desert Tortoises (Gopherus agassizii)

Abstract We report on ecological interactions between the Gila monster (Heloderma suspectum) and the desert tortoise (Gopherus agassizii) in the Mojave Desert of southern Nevada. Eggs of desert tortoises are an important source of food for Gila monsters, and although tortoises are not always successful, they vigorously defend their nests from predation by Gila monsters. Shelters were co-occupied by these two species only during the nesting season for desert tortoises, and Gila monsters occupied shelters almost exclusively with female tortoises, probably because these shelters were nesting sites.

COMPARISON OF CURRENT METHODS FOR THE DETECTION OF CHRONIC MYCOPLASMAL URTD IN WILD POPULATIONS OF THE MOJAVE DESERT TORTOISE (GOPHERUS AGASSIZII)

Abstract Pathogens that cause subclinical diseases or exhibit low infection intensities are difficult to quantify in wild populations. Mojave desert tortoises (Gopherus agassizii) have been the focus of much research aimed at measuring the presence of upper respiratory disease (URTD) and URTD-associated pathogens, and techniques used to quantify disease in Gopherus species have also been used for disease surveillance in other species of turtles and tortoises of conservation concern. Published surveys of G. agassizii populations have found a relatively low prevalence of URTD, with most URTD-positive animals exhibiting moderate, intermittent signs of morbidity. Therefore, multiple tests have been developed to quantify URTD including genetic detection of the pathogens Mycoplasma agassizii and Mycoplasma testudineum, detection of M. agassizii-specific antibodies, and standardized quantification of clinical signs of URTD and body condition. These diagnostic tests have only been compared in diseased or moribund, semicaptive animals. We compared diagnostic techniques (TaqMan® and SYBR™ Green qPCR, serology, and visible examination) to detect M. agassizii-associated URTD in 126 wild desert tortoises sampled in Nevada and California, US in 2010. All had healthy body condition indices and none exhibited more than mild-to-moderate visual signs of URTD. Pairwise comparisons of diagnostic techniques indicated poor performance in diagnosing disease in individual animals. We found stronger, but inconsistent, statistical associations among diagnostic techniques at the population level. Our findings have implications for quantifying subclinical respiratory disease in tortoises.

Born to win? Maybe, but perhaps only against inferior competition

• We tested the ‘fighting hypothesis’ using data from the Ultimate Fighting Championship (UFC).

Energetic costs of digestion in Australian crocodiles

We measured standard metabolic rate (SMR) and the metabolic response to feeding in the Australian crocodiles, Crocodylus porosus and C. johnsoni. Both species exhibit a response that is characterised by rapidly increasing metabolism that peaks within 24 h of feeding, a postfeeding metabolic peak (peak O2) of 1.4–2.0 times SMR, and a return to baseline metabolism within 3–4 days after feeding. Postfeeding metabolism does not significantly differ between species, and crocodiles fed intact meals have higher total digestive costs (specific dynamic action; SDA) than those fed homogenised meals. Across a more than 100-fold range of body size (0.190 to 25.96 kg body mass), SMR, peak O2, and SDA all scale with body mass to an exponent of 0.85. Hatchling (≤1 year old) C. porosus have unexpectedly high rates of resting metabolism, and this likely reflects the substantial energetic demands that accompany the rapid growth of young crocodilians.

Alligators and Crocodiles Have High Paracellular Absorption of Nutrients, But Differ in Digestive Morphology and Physiology

Much of what is known about crocodilian nutrition and growth has come from animals propagated in captivity, but captive animals from the families Crocodilidae and Alligatoridae respond differently to similar diets. Since there are few comparative studies of crocodilian digestive physiology to help explain these differences, we investigated young Alligator mississippiensis and Crocodylus porosus in terms of (1) gross and microscopic morphology of the intestine, (2) activity of the membrane-bound digestive enzymes aminopeptidase-N, maltase, and sucrase, and (3) nutrient absorption by carrier-mediated and paracellular pathways. We also measured gut morphology of animals over a larger range of body sizes. The two species showed different allometry of length and mass of the gut, with A. mississippiensis having a steeper increase in intestinal mass with body size, and C. porosus having a steeper increase in intestinal length with body size. Both species showed similar patterns of magnification of the intestinal surface area, with decreasing magnification from the proximal to distal ends of the intestine. Although A. mississippiensis had significantly greater surface-area magnification overall, a compensating significant difference in gut length between species meant that total surface area of the intestine was not significantly different from that of C. porosus. The species differed in enzyme activities, with A. mississippiensis having significantly greater ability to digest carbohydrates relative to protein than did C. porosus. These differences in enzyme activity may help explain the differences in performance between the crocodilian families when on artificial diets. Both A. mississippiensis and C. porosus showed high absorption of 3-O methyl d-glucose (absorbed via both carrier-mediated and paracellular transport), as expected. Both species also showed surprisingly high levels of l-glucose-uptake (absorbed paracellularly), with fractional absorptions as high as those previously seen only in small birds and bats. Analyses of absorption rates suggested a relatively high proportional contribution of paracellular (i.e., non-mediated) uptake to total uptake of nutrients in both species. Because we measured juveniles, and most paracellular studies to date have been on adults, it is unclear whether high paracellular absorption is generally high within crocodilians or whether these high values are specific to juveniles.

Life in the Lizard Slow Lane: Gila Monsters Have Low Rates of Energy Use and Water Flux

Field metabolic rates (FMR) and water influx rates (WIR) were measured in Gila Monsters (Heloderma suspectum) in the Mojave Desert of southern Nevada. Gila Monsters had rates of energy use that were less than half of those expected for lizards of their size, including species that live in arid habitats. Free-living Gila Monsters also had comparatively low water flux rates. The annual energy requirements of adult Gila Monsters averaged approximately 3,766 kJ, with two-thirds of the total (2,533 kJ) allocated to activity while above ground, and one-third to resting metabolism (1,233 kJ; mostly while below ground). Unusually low rates of resting metabolism caused relative costs of activity to be high: compared to other lizards, Gila Monsters have among the highest proportional use of energy for activity, relative to total energy use. The average annual water expenditure of adults was approximately 775 mL, and lizards achieved positive mass balance by drinking rain water during the late summer monsoon season. Drinking may be critical in meeting annual water requirements. FMR and WIR differed between seasons but were both highest in early summer (mid-May through June), coinciding with the peak of foraging and breeding activities. Levels of above-ground activity significantly influenced both FMR and WIR, whereas body temperature while burrowed influenced only WIR, and body mass (over the range of 270 to 420 g) did not significantly influence either whole-animal FMR or WIR.

Ontogenetic comparisons of standard metabolism in three species of crocodilians

Due in part to their large size, aggressive temperament, and difficulty in handling, there are few physiological studies of adult crocodilians in the literature. As a result, studies comparing individuals across an ontogenetic series and comparisons among species are also lacking. We addressed this gap in knowledge by measuring standard metabolic rates (SMR) of three species of crocodilians (Crocodylus porosus, C. johnsoni, and Alligator mississippiensis), and included individuals that ranged from 0.22 to 114 kg. Allometric scaling of SMR with body mass was similar among the species, but C. porosus had significantly higher SMR than did C. johnsoni or A. mississippiensis. Differences in SMR among species are potentially related to behavioural differences in levels of aggression; C. porosus are the most aggressive of the crocodilians measured, and have rates of standard metabolism that are approximately 36% higher at the grand mean body size than those measured for C. johnsoni or A. mississippiensis, which are among the least aggressive crocodilians.

Small mammals of Pyramid Lake and Anaho Island (Nevada)

Abstract We report on a survey of the small mammal communities of Anaho Island and the mainland surrounding Pyramid Lake in the Great Basin of western Nevada. Ten rodent species were detected on the mainland, but only the deer mouse (Peromyscus maniculatus) was detected on Anaho Island. Although the mean abundance of deer mice on the Pyramid Lake mainland was more than double that of Anaho Island (12.5 ± 10.1 individuals per trap grid compared with 5.0 ± 3.4 individuals per trap grid), we did not detect a significant difference between locations. Deer mice on Anaho Island were significantly larger in body size (mean body length = 86 ± 4 mm) than mainland mice (mean = 75 ± 7 mm), but it is unclear what mechanisms might have produced the observed divergence in body size.