Multiple benefits of juvenile play: A ground squirrel's perspective.

Adaptive functions of play can vary across species, and also within species, reflecting behavioral ecology and evolutionary history. We evaluated juvenile play in Belding's ground squirrels (Urocitellus beldingi), a species for which field studies have assessed play behavior in the context of the squirrels' ecology and life history. Social play behavior in U. beldingi appears not to have the range of adaptive benefits related to social behavior apparent in species with more complex social organization. Play in juvenile U. beldingi improves general motor skill, which may translate to more proficient performance of behaviors during and beyond the juvenile period. Social play in juvenile squirrels is associated with refinement of temperament and behavior, promoting behavioral shifts toward less docile responses as well as more cautious behavior. Social play also influences behavior of juvenile squirrels in novel situations, fostering greater exploration and adaptability of responses. Important life events in U. beldingi such as the timing of natal dispersal and defense of maternal territories can be influenced by juvenile play.

Spillover of an alien parasite reduces expression of costly behaviour in native host species.

Understanding the effects of invasive alien species (IAS) on native host-parasite relationships is of importance for enhancing ecological theory and IAS management. When IAS and their parasite(s) invade a guild, the effects of interspecific resource competition and/or parasite-mediated competition can alter existing native host-parasite relationships and the dependent biological traits such as native species' behaviour. We used a natural experiment of populations of native red squirrels Sciurus vulgaris that were colonized by the alien grey squirrel Sciurus carolinensis, comparing repeated measurements of red squirrel parasite infection and personality with those taken in sites where only the native species occurred. We explored two alternative hypotheses: (a) individual differences in personality traits (activity and/or sociability) of native red squirrel positively affect the probability of macroparasite spillover and thus the likelihood to acquire the alien's parasitic helminth Strongyloides robustus; (b) the combined effects of grey squirrel presence and parasite infection result in a reduction of costly personality traits (activity and/or exploration). Using data from 323 arena tests across three experimental (native species and IAS) and three control sites (only native species), we found negative correlations between native species' activity and infection with S. robustus in the sites invaded by the alien species. Activity was also negatively correlated with infection by its native helminth Trypanoxyuris sciuri but only when grey squirrels were present, while in the red-only sites there was no relationship of T. sciuri infection with any of the personality traits. Moreover, individuals that acquired S. robustus during the study reduced their activity after infection, while this was not the case for animals that remained uninfected. Our results show that parasite-mediated competition is costly, reducing activity in individuals of the native species, and altering the native host-native parasite relationships.

Subtle short-term physiological costs of an experimental augmentation of fleas in wild Columbian ground squirrels.

Parasites affect many aspects of host physiology and behavior, and thus are generally thought to negatively impact host fitness. However, changes in form of short-term parasite effects on host physiological markers have generally been overlooked in favor of fitness measures. Here, we studied flea (Oropsylla idahoensis and Oropsylla opisocroistis tuberculata) parasitism on a natural population of Columbian ground squirrels (Urocitellus columbianus) in Sheep River Provincial Park, AB, Canada. Fleas were experimentally added to adult female U. columbianus at physiologically demanding times, including birth, lactation and weaning of their young. The body mass of adult females, as well as their oxidative stress and immunity were recorded multiple times over the active season under flea-augmented and control conditions. We also measured the prevalence of an internal parasite (Trypanosoma otospermophili). Doubly labeled water (DLW) was intra-peritoneally injected at peak lactation to examine energy expenditure. Effects of parasites on oxidative stress were only observed after offspring were weaned. There was no direct effect of experimentally heightened flea prevalence on energy use. A short-term 24 h mass loss (-17 g) was detected briefly after parasite addition, likely due to U. columbianus preferentially allocating time for grooming. Our parasite augmentation did not strongly affect hosts and suggested that short-term physiological effects were unlikely to culminate in long-term fitness consequences. Columbian ground squirrels appear to rapidly manage parasite costs, probably through grooming.

Bats are not squirrels: Revisiting the cost of cooling in hibernating mammals.

Many species use stored energy to hibernate through periods of resource limitation. Hibernation, a physiological state characterized by depressed metabolism and body temperature, is critical to winter survival and reproduction, and therefore has been extensively quantified and modeled. Hibernation consists of alternating phases of extended periods of torpor (low body temperature, low metabolic rate), and energetically costly periodic arousals to normal body temperature. Arousals consist of multiple phases: warming, euthermia, and cooling. Warming and euthermic costs are regularly included in energetic models, but although cooling to torpid body temperature is an important phase of the torpor-arousal cycle, it is often overlooked in energetic models. When included, cooling cost is assumed to be 67% of warming cost, an assumption originally derived from a single study that measured cooling cost in ground squirrels. Since this study, the same proportional value has been assumed across a variety of hibernating species. However, no additional values have been derived. We derived a model of cooling cost from first principles and validated the model with empirical energetic measurements. We compared the assumed 67% proportional cooling cost with our model-predicted cooling cost for 53 hibernating mammals. Our results indicate that using 67% of warming cost only adequately represents cooling cost in ground squirrel-sized mammals. In smaller species, this value overestimates cooling cost and in larger species, the value underestimates cooling cost. Our model allows for the generalization of energetic costs for multiple species using species-specific physiological and morphometric parameters, and for predictions over variable environmental conditions.

Within- and between-year variations of reproductive strategy and cost in a population of Siberian chipmunks.

Reproduction costs depend on the general life-history strategies employed by organisms for resource acquisition, the decision rules on resource allocation, and the resource availability. Although the predictability of resource availability is expected to influence the breeding strategy, the relationship between predictability and strategy has rarely been investigated at the population level. One reason is that, while the resource availability is commonly variable in space and time, their predictability is generally assumed constant. Here, we addressed the temporal variation of the breeding strategy and its associated survival cost in a hibernating population of Tamias sibiricus, in which food resources vary in their availability between years and in their predictability within years. Based on 11 years of mark-recapture data, we used multi-event modelling to investigate seasonal variations in reproduction costs of female chipmunks that breed twice a year (spring and summer). In summer, during which a large variety and quantity of resources is available (income breeding strategy), the proportion of breeding females was consistent across years and reproduction yielded no mortality cost. In contrast, in spring, the proportion of breeding females was positively correlated with the amount of resources available for hibernation (partial capital breeding strategy). Spring reproduction yielded no immediate cost, but induced a delayed mortality cost over the next winter if future unknown conditions were unfavorable. Our findings highlight complex temporal reproductive patterns in a short-lived species: not only does the modality of resource acquisition vary among seasons, but also the decision rule to breed and its associated cost.

Assessment of Outer Retinal Remodeling in the Hibernating 13-Lined Ground Squirrel.

Purpose: We examined outer retinal remodeling of the euthermic and torpid cone-dominant 13-lined ground squirrel (13-LGS) retina using optical coherence tomography (OCT) imaging and histology. Methods: Retinas and corneas of living 13-LGSs were imaged during euthermic and torpid physiological states using OCT. Retinal layer thickness was measured at the visual streak from registered and averaged vertical B-scans. Following OCT, some retinas were collected immediately for postmortem histologic comparison using light microscopy, immunofluorescence, or transmission electron microscopy. Results: Compared to OCT images from euthermic retinae, OCT images of torpid retinae revealed significantly thicker inner and outer nuclear layers, as well as increases in the distances between outer retinal reflectivity bands 1 and 2, and bands 3 and 4. A significant decrease in the distance between bands 2 and 3 also was seen, alongside significant thinning of the choriocapillaris and choroid. OCT image quality was reduced in torpid eyes, partly due to significant thickening of the corneal stroma during this state. Conclusions: The torpid retina of the hibernating 13-LGS undergoes structural changes that can be detected by OCT imaging. Comparisons between in vivo OCT and ex vivo histomorphometry may offer insight to the origin of hyperreflective OCT bands within the outer retina of the cone-dominant 13-LGS.

Assessment of Detection Methods and Vegetation Associations for Introduced Finlayson's Squirrels (Callosciurus finlaysonii) in Italy.

Managing biological invasions requires rapid, cost-effective assessments of introduced species' occurrence, and a good understanding of the species' vegetation associations. This is particularly true for species that are elusive or may spread rapidly. Finlayson's squirrel (Callosciurus finlaysonii) is native to Thailand and southeastern Asia, and two introduced populations occur in peninsular Italy. One of the two introduced populations is rapidly expanding, but neither effective monitoring protocols nor reliable information on vegetation associations are available. To fill this gap, we conducted visual surveys and hair tube sampling in a periurban landscape of southern Italy to compare the effectiveness of these two methods in assessing presence of Finlayson's squirrel. We also determined the species' association with vegetation types at detection locations and nesting sites. Both visual and hair tube sampling effectively assessed the species' presence, but hair tubes resulted in fewer false absences. Moreover, when we controlled for the costs of labor and equipment, hair tubes were 33.1% less expensive than visual sampling. Presence of squirrels and their nests was positively correlated with shrub species richness, indicating that the occurrence of forests with well-developed understory may inhibit the spread of the species.

Improving the assessment of predator functional responses by considering alternate prey and predator interactions.

To improve understanding of the complex and variable patterns of predator foraging behavior in natural systems, it is critical to determine how density-dependent predation and predator hunting success are mediated by alternate prey or predator interference. Despite considerable theory and debate seeking to place predator-prey interactions in a more realistic context, few empirical studies have quantified the role of alternate prey or intraspecific interactions on predator-prey dynamics. We assessed functional responses of two similarly sized, sympatric carnivores, lynx (Lynx canadensis) and coyotes (Canis latrans), foraging on common primary (snowshoe hares; Lepus americanus) and alternate (red squirrels; Tamiasciurus hudsonicus) prey in a natural system. Lynx exhibited a hyperbolic prey-dependent response to changes in hare density, which is characteristic of predators relying primarily on a single prey species. In contrast, the lynx-squirrel response was found to be linear ratio dependent, or inversely dependent on hare density. The coyote-hare and coyote-squirrel interactions also were linear and influenced by predator density. We explain these novel results by apparent use of spatial and temporal refuges by prey, and the likelihood that predators commonly experience interference and lack of satiation when foraging. Our study provides empirical support from a natural predator-prey system that (1) predation rate may not be limited at high prey densities when prey are small or rarely captured; (2) interference competition may influence the predator functional response; and (3) predator interference has a variable role across different prey types. Ultimately, distinct functional responses of predators to different prey types illustrates the complexity associated with predator-prey interactions in natural systems and highlights the need to investigate predator behavior and predation rate in relation to the broader ecological community.

Comparative Phylogenomic Assessment of Mitochondrial Introgression among Several Species of Chipmunks (Tamias).

Many species are not completely reproductively isolated, resulting in hybridization and genetic introgression. Organellar genomes, such as those derived from mitochondria (mtDNA) and chloroplasts, introgress frequently in natural systems; however, the forces shaping patterns of introgression are not always clear. Here, we investigate extensive mtDNA introgression in western chipmunks, focusing on species in the Tamias quadrivittatus group from the central and southern Rocky Mountains. Specifically, we investigate the role of selection in driving patterns of introgression. We sequenced 51 mtDNA genomes from six species and combine these sequences with other published genomic data to yield annotated mitochondrial reference genomes for nine species of chipmunks. Genomic characterization was performed using a series of molecular evolutionary and phylogenetic analyses to test protein-coding genes for positive selection. We fit a series of maximum likelihood models using a model-averaging approach, assessed deviations from neutral expectations, and performed additional tests to search for codons under the influence of selection. We found no evidence for positive selection among these genomes, suggesting that selection has not been the driving force of introgression in these species. Thus, extensive mtDNA introgression among several species of chipmunks likely reflects genetic drift of introgressed alleles in historically fluctuating populations.

Stereological assessment of normal Persian squirrels (Sciurus anomalus) kidney.

The functions of the mammalian kidney are closely related to its structure. This suggests that renal function can be completely characterized by accurate knowledge of its quantitative morphological features. The aim of this study was to investigate the histomorphometric features of the kidney using design-based and unbiased stereological methods in the Persian squirrel (Sciurus anomalus), which is the only representative of the Sciuridae family in the Middle East. The left kidneys of five animals were examined. Total volume of the kidney, cortex, and medulla were determined to be 960.75 ± 87.4, 754.31 ± 77.09 and 206.1 ± 16.89 mm3, respectively. The glomerular number was 32844.03 ± 1069.19, and the total glomerular volume was estimated to be 36.7 ± 1.45 mm3. The volume and length of the proximal convoluted tubule were estimated at 585.67 ± 60.7 mm3 and 328.8 ± 14.8 m, respectively, with both values being greater than those reported in the rat kidney. The volume and length of the distal convoluted tubule were calculated at 122.34 ± 7.38 mm3 and 234.4 ± 17.45 m, respectively, which are also greater than those reported in the rat kidney. Despite the comparable body weight, the total number and mean individual volume of glomeruli in the Persian squirrel kidney were greater than those in the rat kidney. Overall, the stereological variables of the kidneys elucidated in this study are exclusive to the Persian squirrel. Our findings, together with future renal physiological data, will contribute to a better understanding of the renal structure-function relationship in the Persian squirrel.

Low-cost functional plasticity of TRPV1 supports heat tolerance in squirrels and camels.

The ability to sense heat is crucial for survival. Increased heat tolerance may prove beneficial by conferring the ability to inhabit otherwise prohibitive ecological niches. This phenomenon is widespread and is found in both large and small animals. For example, ground squirrels and camels can tolerate temperatures more than 40 °C better than many other mammalian species, yet a molecular mechanism subserving this ability is unclear. Transient receptor potential vanilloid 1 (TRPV1) is a polymodal ion channel involved in the detection of noxious thermal and chemical stimuli by primary afferents of the somatosensory system. Here, we show that thirteen-lined ground squirrels (Ictidomys tridecemlineatus) and Bactrian camels (Camelus ferus) express TRPV1 orthologs with dramatically reduced temperature sensitivity. The loss of sensitivity is restricted to temperature and does not affect capsaicin or acid responses, thereby maintaining a role for TRPV1 as a detector of noxious chemical cues. We show that heat sensitivity can be reengineered in both TRPV1 orthologs by a single amino acid substitution in the N-terminal ankyrin-repeat domain. Conversely, reciprocal mutations suppress heat sensitivity of rat TRPV1, supporting functional conservation of the residues. Our studies suggest that squirrels and camels co-opt a common molecular strategy to adapt to hot environments by suppressing the efficiency of TRPV1-mediated heat detection at the level of somatosensory neurons. Such adaptation is possible because of the remarkable functional flexibility of the TRPV1 molecule, which can undergo profound tuning at the minimal cost of a single amino acid change.

Using accelerometers to remotely and automatically characterize behavior in small animals.

Activity budgets in wild animals are challenging to measure via direct observation because data collection is time consuming and observer effects are potentially confounding. Although tri-axial accelerometers are increasingly employed for this purpose, their application in small-bodied animals has been limited by weight restrictions. Additionally, accelerometers engender novel complications, as a system is needed to reliably map acceleration to behaviors. In this study, we describe newly developed, tiny acceleration-logging devices (1.5-2.5 g) and use them to characterize behavior in two chipmunk species. We collected paired accelerometer readings and behavioral observations from captive individuals. We then employed techniques from machine learning to develop an automatic system for coding accelerometer readings into behavioral categories. Finally, we deployed and recovered accelerometers from free-living, wild chipmunks. This is the first time to our knowledge that accelerometers have been used to generate behavioral data for small-bodied (<100 g), free-living mammals.

CARDIAC ASSESSMENT OF ZOO-KEPT, BLACK-TAILED PRAIRIE DOGS (CYNOMYS LUDOVICIANUS) ANESTHETIZED WITH ISOFLURANE.

Cardiomyopathy is suggested to be a relatively common disease condition in prairie dogs; however, there are no reports of normal cardiac echosonography and radiology in the prairie dog ( Cynomys spp.). The objective of this study was to report the ultrasonographic and radiographic measurements of the heart, and plasma troponin concentration in captive healthy anesthetized black-tailed prairie dogs ( Cynomys ludovicianus ). Zoo-kept prairie dogs with no signs of cardiac disease (n = 17) were evaluated. Each animal was anesthetized with isoflurane via face mask and a complete clinical assessment was performed, including complete blood cell count and plasma biochemistry, urinalysis, blood gasses, plasma troponin concentration, three-view whole body radiography, and echocardiogram. Standard measurements were taken. Few trivial findings were identified on echocardiographic evaluation. Further research with a larger sample size is needed to determine if these variations are normal, or represent early or mild cardiac disease. The data presented here can aid, with the necessary caution, in evaluating prairie dogs with possible cardiac disease, potentially resulting in earlier diagnosis and more successful treatment.

Managing anabolic steroids in pre-hibernating Arctic ground squirrels: obtaining their benefits and avoiding their costs.

Androgens have benefits, such as promoting muscle growth, but also significant costs, including suppression of immune function. In many species, these trade-offs in androgen action are reflected in regulated androgen production, which is typically highest only in reproductive males. However, all non-reproductive Arctic ground squirrels, irrespective of age and sex, have high levels of androgens prior to hibernating at sub-zero temperatures. Androgens appear to be required to make muscle in summer, which, together with lipid, is then catabolized during overwinter. By contrast, most hibernating mammals catabolize only lipid. We tested the hypothesis that androgen action is selectively enhanced in Arctic ground squirrel muscle because of an upregulation of androgen receptors (ARs). Using Western blot analysis, we found that Arctic ground squirrels have AR in skeletal muscle more than four times that of Columbian ground squirrels, a related southern species that overwinters at approximately 0°C and has low pre-hibernation androgen levels. By contrast, AR in lymph nodes was equivalent in both species. Brain AR was also modestly but significantly increased in Arctic ground squirrel relative to Columbian ground squirrel. These results are consistent with the hypothesis that tissue-specific AR regulation prior to hibernation provides a mechanism whereby Arctic ground squirrels obtain the life-history benefits and mitigate the costs associated with high androgen production.

Defining landscape resistance values in least-cost connectivity models for the invasive grey squirrel: a comparison of approaches using expert-opinion and habitat suitability modelling.

Least-cost models are widely used to study the functional connectivity of habitat within a varied landscape matrix. A critical step in the process is identifying resistance values for each land cover based upon the facilitating or impeding impact on species movement. Ideally resistance values would be parameterised with empirical data, but due to a shortage of such information, expert-opinion is often used. However, the use of expert-opinion is seen as subjective, human-centric and unreliable. This study derived resistance values from grey squirrel habitat suitability models (HSM) in order to compare the utility and validity of this approach with more traditional, expert-led methods. Models were built and tested with MaxEnt, using squirrel presence records and a categorical land cover map for Cumbria, UK. Predictions on the likelihood of squirrel occurrence within each land cover type were inverted, providing resistance values which were used to parameterise a least-cost model. The resulting habitat networks were measured and compared to those derived from a least-cost model built with previously collated information from experts. The expert-derived and HSM-inferred least-cost networks differ in precision. The HSM-informed networks were smaller and more fragmented because of the higher resistance values attributed to most habitats. These results are discussed in relation to the applicability of both approaches for conservation and management objectives, providing guidance to researchers and practitioners attempting to apply and interpret a least-cost approach to mapping ecological networks.

Fox squirrels match food assessment and cache effort to value and scarcity.

Scatter hoarders must allocate time to assess items for caching, and to carry and bury each cache. Such decisions should be driven by economic variables, such as the value of the individual food items, the scarcity of these items, competition for food items and risk of pilferage by conspecifics. The fox squirrel, an obligate scatter-hoarder, assesses cacheable food items using two overt movements, head flicks and paw manipulations. These behaviors allow an examination of squirrel decision processes when storing food for winter survival. We measured wild squirrels' time allocations and frequencies of assessment and investment behaviors during periods of food scarcity (summer) and abundance (fall), giving the squirrels a series of 15 items (alternating five hazelnuts and five peanuts). Assessment and investment per cache increased when resource value was higher (hazelnuts) or resources were scarcer (summer), but decreased as scarcity declined (end of sessions). This is the first study to show that assessment behaviors change in response to factors that indicate daily and seasonal resource abundance, and that these factors may interact in complex ways to affect food storing decisions. Food-storing tree squirrels may be a useful and important model species to understand the complex economic decisions made under natural conditions.

Two-step source tracing strategy of Yersinia pestis and its historical epidemiology in a specific region.

Source tracing of pathogens is critical for the control and prevention of infectious diseases. Genome sequencing by high throughput technologies is currently feasible and popular, leading to the burst of deciphered bacterial genome sequences. Utilizing the flooding genomic data for source tracing of pathogens in outbreaks is promising, and challenging as well. Here, we employed Yersinia pestis genomes from a plague outbreak at Xinghai county of China in 2009 as an example, to develop a simple two-step strategy for rapid source tracing of the outbreak. The first step was to define the phylogenetic position of the outbreak strains in a whole species tree, and the next step was to provide a detailed relationship across the outbreak strains and their suspected relatives. Through this strategy, we observed that the Xinghai plague outbreak was caused by Y. pestis that circulated in the local plague focus, where the majority of historical plague epidemics in the Qinghai-Tibet Plateau may originate from. The analytical strategy developed here will be of great help in fighting against the outbreaks of emerging infectious diseases, by pinpointing the source of pathogens rapidly with genomic epidemiological data and microbial forensics information.

Oxidative damage increases with reproductive energy expenditure and is reduced by food-supplementation.

A central principle in life-history theory is that reproductive effort negatively affects survival. Costs of reproduction are thought to be physiologically based, but the underlying mechanisms remain poorly understood. Using female North American red squirrels (Tamiasciurus hudsonicus), we test the hypothesis that energetic investment in reproduction overwhelms investment in antioxidant protection, leading to oxidative damage. In support of this hypothesis we found that the highest levels of plasma protein oxidative damage in squirrels occurred during the energetically demanding period of lactation. Moreover, plasma protein oxidative damage was also elevated in squirrels that expended the most energy and had the lowest antioxidant protection. Finally, we found that squirrels that were food-supplemented during lactation and winter had increased antioxidant protection and reduced plasma protein oxidative damage providing the first experimental evidence in the wild that access to abundant resources can reduce this physiological cost.

Seasonal and sex differences in the hippocampus of a wild rodent.

Studies across and within species suggest that hippocampus size is sexually dimorphic in polygamous species, but not in monogamous species. Although hippocampal volume varies with sex, season and mating system, few studies have simultaneously tested for sex and seasonal differences. Here, we test for sex and seasonal differences in the hippocampal volume of wild Richardson's ground squirrels (Urocitellus richardsonii), a polygamous species that lives in matrilineal, kin-based social groups and has profound sex differences in behavior. Based on the behavior and ecology of this species, we predicted that males would have a significantly larger hippocampus than females and that the hippocampus would be largest in males during the breeding season. Analyses of both absolute and relative volumes of the hippocampus yielded a significant difference between the sexes and seasons as well as an interaction between the two such that non-breeding males have significantly larger hippocampal volumes than breeding males or females from either season. Dentate gyrus, CA1 and CA3 subfield volumes were generally larger in the non-breeding season and in males, but no significant interaction effects were detected. This sex and seasonal variation in hippocampal volume is likely the result of their social organization and male-only food caching behavior during the non-breeding season. The demonstration of a sex and seasonal variation in hippocampal volume suggests that Richardson's ground squirrel may be a useful model for understanding hippocampal plasticity within a natural context.

The energetic and survival costs of growth in free-ranging chipmunks.

The growth/survival trade-off is a fundamental aspect of life-history evolution that is often explained by the direct energetic requirement for growth that cannot be allocated into maintenance. However, there is currently no empirical consensus on whether fast-growing individuals have higher resting metabolic rates at thermoneutrality (RMRt) than slow growers. Moreover, the link between growth rate and daily energy expenditure (DEE) has never been tested in a wild endotherm. We assessed the energetic and survival costs of growth in juvenile eastern chipmunks (Tamias striatus) during a year of low food abundance by quantifying post-emergent growth rate (n = 88), RMRt (n = 66), DEE (n = 20), and overwinter survival. Both RMRt and DEE were significantly and positively related to growth rate. The effect size was stronger for DEE than RMRt, suggesting that the energy cost of growth in wild animals is more likely to be related to the maintenance of a higher foraging rate (included in DEE) than to tissue accretion (included in RMRt). Fast growers were significantly less likely to survive the following winter compared to slow growers. Juveniles with high or low RMRt were less likely to survive winter than juveniles with intermediate RMRt. In contrast, DEE was unrelated to survival. In addition, botfly parasitism simultaneously decreased growth rate and survival, suggesting that the energetic budget of juveniles was restricted by the simultaneous costs of growth and parasitism. Although the biology of the species (seed-storing hibernator) and the context of our study (constraining environmental conditions) were ideally combined to reveal a direct relationship between current use of energy and future availability, it remains unclear whether the energetic cost of growth was directly responsible for reduced survival.