Joshua R. Ennen

Nest-Guarding by Female Agassiz's Desert Tortoise (Gopherus agassizii) at a Wind-Energy Facility Near Palm Springs, California

Abstract We observed behavior consistent with nest-guarding in Agassizs desert tortoise (Gopherus agassizii) at two nests in a large wind-energy-generation facility near Palm Springs, California, locally known as the Mesa Wind Farm. As researchers approached the nests, female desert tortoises moved to the entrance of their burrows and positioned themselves sideways, directly over their nests. One female stretched her limbs outward and wedged herself into the burrow (her plastron directly above the nest). Guarding of nests is rarely observed in Agassizs desert tortoise but can occur as a result of attempted predation on eggs by Gila monsters (Heloderma suspectum) or in direct response to the perceived threat posed by researchers. This is the first report of nest-guarding for G. agassizii in the Sonoran Desert ecosystem of California. Resumen Observamos el comportamiento de las tortugas del desierto (Gopherus agasiizii) que parece vigilar a sus nidos. Observamos este comportamiento en dos nidos que estuvieron ubicados en las instalaciones para la generación de energía eólica, cerca de Palm Springs, California, conocida localmente como Mesa Wind Farm. Cuando los investigadores se acercaron a los nidos, las tortugas hembras se desplazaron hacia la entrada de su madriguera y se posicionaron a los lados directamente sobre sus nidos. Una hembra estiró sus extremidades hacia fuera asegurándose ella misma dentro de la madriguera (dejando el plastrón directamente encima del nido). Es muy raro observar la vigilancia de nidos en las tortugas del desierto, pero puede ocurrir como resultado de intentos de depredación de huevos por el monstruo de Gila (Heloderma suspectum) o como respuesta directa al percibir a los investigadores como una amenaza. Este es el primer reporte del comportamiento de vigilancia de nidos de la tortuga G. agassizzi en California en el ecosistema del desierto de Sonora.

Morphological and Molecular Reassessment of Graptemys oculifera and Graptemys flavimaculata (Testudines: Emydidae)

Abstract The turtle genus Graptemys consists of 15 recognized taxa, distinguished largely on the basis of pigmentation pattern (i.e., soft tissue and shell), head size, and shell morphology. However, phylogenetic studies have shown limited sequence divergence within the genus and between Graptemys oculifera and Graptemys flavimaculata relative to most other members of the Emydidae. Graptemys oculifera of the Pearl River drainage and G. flavimaculata of the Pascagoula River drainage have been recognized as species since 1890 and 1954, respectively. However, the description of G. flavimaculata was based on a limited number of morphological characters. Several of these characters overlap between G. flavimaculata and G. oculifera, and no attempt was made to test for significant morphological differentiation. In this study, we reevaluated the morphological and genetic distinctiveness of G. flavimaculata and G. oculifera with (1) multivariate statistical analyses of 44 morphological characters and (2) 1,560 bp of sequence data from two mitochondrial genes (control region and ND4). The morphological and molecular analyses produced incongruent results. The principal components analysis ordinations separated the two species along a pigmentation gradient with G. flavimaculata having more yellow pigmentation than G. oculifera. Likewise, clustering analyses separated the specimens into two distinct groups with little overlap between the species. Our mitochondrial data supported previous findings of limited genetic differentiation between the two species. However, the results of our morphological analyses, in conjunction with recently published nuclear gene sequence data, support the continued recognition of the two species.

Using motion-sensor camera technology to infer seasonal activity and thermal niche of the desert tortoise (Gopherus agassizii)

Understanding the relationships between environmental variables and wildlife activity is an important part of effective management. The desert tortoise (Gopherus agassizii), an imperiled species of arid environments in the southwest US, may have increasingly restricted windows for activity due to current warming trends. In summer 2013, we deployed 48 motion sensor cameras at the entrances of tortoise burrows to investigate the effects of temperature, sex, and day of the year on the activity of desert tortoises. Using generalized estimating equations, we found that the relative probability of activity was associated with temperature (linear and quadratic), sex, and day of the year. Sex effects showed that male tortoises are generally more active than female tortoises. Temperature had a quadratic effect, indicating that tortoise activity was heightened at a range of temperatures. In addition, we found significant support for interactions between sex and day of the year, and sex and temperature as predictors of the probability of activity. Using our models, we were able to estimate air temperatures and times (days and hours) that were associated with maximum activity during the study. Because tortoise activity is constrained by environmental conditions such as temperature, it is increasingly vital to conduct studies on how tortoises vary their activity throughout the Sonoran Desert to better understand the effects of a changing climate.

Turbines and Terrestrial Vertebrates: Variation in Tortoise Survivorship Between a Wind Energy Facility and an Adjacent Undisturbed Wildland Area in the Desert Southwest (USA)

With the recent increase in utility-scale wind energy development, researchers have become increasingly concerned how this activity will affect wildlife and their habitat. To understand the potential impacts of wind energy facilities (WEF) post-construction (i.e., operation and maintenance) on wildlife, we compared differences in activity centers and survivorship of Agassiz’s desert tortoises (Gopherus agassizii) inside or near a WEF to neighboring tortoises living near a wilderness area (NWA) and farther from the WEF. We found that the size of tortoise activity centers varied, but not significantly so, between the WEF (6.25xa0±xa02.13xa0ha) and adjacent NWA (4.13xa0±xa01.23xa0ha). However, apparent survival did differ significantly between the habitat types: over the 18-year study period apparent annual survival estimates were 0.96xa0±xa00.01 for WEF tortoises and 0.92xa0±xa00.02 for tortoises in the NWA. High annual survival suggests that operation and maintenance of the WEF has not caused considerable declines in the adult population over the past two decades. Low traffic volume, enhanced resource availability, and decreased predator populations may influence annual survivorship at this WEF. Further research on these proximate mechanisms and population recruitment would be useful for mitigating and managing post-development impacts of utility-scale wind energy on long-lived terrestrial vertebrates.

Distribution and habitat utilization of the gopher tortoise tick (Amblyomma tuberculatum) in Southern Mississippi.

Abstract The distribution of the gopher tortoise tick (Amblyomma tuberculatum) has been considered intrinsically linked to the distribution of its primary host, gopher tortoises (Gopherus polyphemus). However, the presence of G. polyphemus does not always equate to the presence of A. tuberculatum. There is a paucity of data on the ecology, habitat preferences, and distribution of A. tuberculatum. The goals of this study were to assess the distribution of A. tuberculatum in southern Mississippi and to determine which, if any, habitat parameters explain the distribution pattern of A. tuberculatum. During 2006–2007, we examined 13 G. polyphemus populations in southern Mississippi for the presence of A. tuberculatum, and we measured a suite of habitat parameters at each site. Only 23% of the G. polyphemus populations supported A. tuberculatum, suggesting a more restricted distribution than its host. The results of our multivariate analyses identified several habitat variables, e.g., depth of sand and percentage of sand in the topsoil and burrow apron, as being important in discriminating between sites with, and without, A. tuberculatum. Amblyomma tuberculatum was only found at sites with a mean sand depth of >100 cm and a mean percentage of topsoil and burrow apron sand composition >94.0 and 92.4, respectively. Thus, environmental factors, and not just its hosts range, seem to influence the distribution of A. tuberculatum.

Macroecological patterns of sexual size dimorphism in turtles of the world

Sexual size dimorphism (SSD) is a well‐documented phenomenon in both plants and animals; however, the ecological and evolutionary mechanisms that drive and maintain SSD patterns across geographic space at regional and global scales are understudied, especially for reptiles. Our goal was to examine geographic variation of turtle SSD and to explore ecological and environmental correlates using phylogenetic comparative methods. We use published body size data on 135 species from nine turtle families to examine how geographic patterns and the evolution of SSD are influenced by habitat specialization, climate (annual mean temperature and annual precipitation) and climate variability, latitude, or a combination of these predictor variables. We found that geographic variation, magnitude and direction of turtle SSD are best explained by habitat association, annual temperature variance and annual precipitation. Use of semi‐aquatic and terrestrial habitats was associated with male‐biased SSD, whereas use of aquatic habitat was associated with female‐biased SSD. Our results also suggest that greater temperature variability is associated with female‐biased SSD. In contrast, wetter climates are associated with male‐biased SSD compared with arid climates that are associated with female‐biased SSD. We also show support for a global latitudinal trend in SSD, with females being larger than males towards the poles, especially in the families Emydidae and Geoemydidae. Estimates of phylogenetic signal for both SSD and habitat type indicate that closely related species occupy similar habitats and exhibit similar direction and magnitude of SSD. These global patterns of SSD may arise from sex‐specific reproductive behaviour, fecundity and sex‐specific responses to environmental factors that differ among habitats and vary systematically across latitude. Thus, this study adds to our current understanding that while SSD can vary dramatically across and within turtle species under phylogenetic constraints, it may be driven, maintained and exaggerated by habitat type, climate and geographic location.