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388 results for “Squirrels”
Data from: The enemy of my enemy is my friend: native pine marten recovery reverses the decline of the red squirrel by suppressing grey squirrel populations
Shared enemies may instigate or modify competitive interactions between species. The dis-equilibrium caused by non-native species introductions has revealed that the outcome of such indirect interactions can often be dramatic. However, studies of enemy mediated competition mostly consider the impact of a single enemy, despite species being embedded in complex networks of interactions. Here we demonstrate that native red and invasive grey squirrels in Britain, two terrestrial species linked by resource and disease-mediated apparent competition, are also now linked by a second enemy-mediated relationship involving a shared native predator recovering from historical persecution, the European pine marten. Through combining spatial capture recapture techniques to estimate pine marten density, and squirrel site occupancy data, we find that the impact of exposure to predation is highly asymmetrical, with non-native grey squirrel occupancy strongly negatively affected by exposure to pine martens. In contrast, exposure to pine marten predation has an indirect positive effect on red squirrel populations. Pine marten predation thus reverses the well-documented outcome of resource and apparent competition between red and grey squirrels.
Up-regulation of sarcoplasmic reticulum function protects skeletal muscle against cytoplasmic calcium overload during hibernation in ground squirrels
<p>We investigated the potential mechanism of the SR in maintenance of calcium (Ca<sup>2+</sup>) homeostasis of slow-twitch muscle (soleus, SOL), fast-twitch muscle (extensor digitorum longus, EDL) and mixed muscle (gastrocnemius, GAS) in hibernating ground squirrels (<i>Spermophilus dauricus</i>). Results showed that cytosolic and SR Ca<sup>2+</sup> concentrations in distinct skeletal muscle fibers increased and decreased during late torpor, respectively, but both returned to summer-active levels during early torpor. Ryanodine receptor1 (RyR1) and sarco/endoplasmic reticulum Ca<sup>2+</sup> ATPase isoform 1 (SERCA1) protein expression increased during hibernation. Up-regulation factors of SERCA activity: Phospholamban phosphorylation increased in the SOL and GAS, β-adrenergic receptor-2 protein expression increased in the GAS, and calmodulin kinase-2 phosphorylation increased in the SOL during hibernation. Down-regulation factors of SERCA activity: Sarcolipin and SERCA1 co-localization decreased in the EDL and GAS. These data suggest that SERCA activity in skeletal muscle fibers increases likely during hibernation. FKBP12/calsequestrin1 (negative regulatory factors of RyR1) and RyR1 co-localization decreased in the GAS, indicating that the RyR1 channel opening probability increased during hibernation. Dihydropyridine receptors protein expression and its co-localization with RYR1 decreased during hibernation prompts that the contractility of skeletal muscle was weakened. Protein expression of Ca<sup>2+</sup>-binding proteins calsequestrin1 and calmodulin increased indicating that the ability of intracellular free calcium binding increased during whole hibernation period. These findings confirm that the release, uptake, and binding of free Ca<sup>2+</sup> in the SR were enhanced in different skeletal muscles during hibernation. Up-regulation of muscular sarcoplasmic reticulum function protects skeletal muscle fibers against cytoplasmic calcium overload during hibernation in ground squirrels.We investigated the potential mechanism of the SR in maintenance of calcium (Ca<sup>2+</sup>) homeostasis of slow-twitch muscle (soleus, SOL), fast-twitch muscle (extensor digitorum longus, EDL) and mixed muscle (gastrocnemius, GAS) in hibernating ground squirrels (<i>Spermophilus dauricus</i>). Results showed that cytosolic and SR Ca<sup>2+</sup> concentrations in distinct skeletal muscle fibers increased and decreased during late torpor, respectively, but both returned to summer-active levels during early torpor. Ryanodine receptor1 (RyR1) and sarco/endoplasmic reticulum Ca<sup>2+</sup> ATPase isoform 1 (SERCA1) protein expression increased during hibernation. Up-regulation factors of SERCA activity: Phospholamban phosphorylation increased in the SOL and GAS, β-adrenergic receptor-2 protein expression increased in the GAS, and calmodulin kinase-2 phosphorylation increased in the SOL during hibernation. Down-regulation factors of SERCA activity: Sarcolipin and SERCA1 co-localization decreased in the EDL and GAS. These data suggest that SERCA activity in skeletal muscle fibers increases likely during hibernation. FKBP12/calsequestrin1 (negative regulatory factors of RyR1) and RyR1 co-localization decreased in the GAS, indicating that the RyR1 channel opening probability increased during hibernation. Dihydropyridine receptors protein expression and its co-localization with RYR1 decreased during hibernation prompts that the contractility of skeletal muscle was weakened. Protein expression of Ca<sup>2+</sup>-binding proteins calsequestrin1 and calmodulin increased indicating that the ability of intracellular free calcium binding increased during whole hibernation period. These findings confirm that the release, uptake, and binding of free Ca<sup>2+</sup> in the SR were enhanced in different skeletal muscles during hibernation. Up-regulation of muscular sarcoplasmic reticulum function protects skeletal muscle fibers against cytoplasmic calcium overload during hibernation in ground squirrels.</p>
Data from: Kin effects on energy allocation in group-living ground squirrels
The social environment has potent effects on individual phenotype and fitness in group-living species. We asked whether the presence of kin might act on energy allocation, a central aspect of life-history variation. Using a 22-year data set on reproductive and somatic allocations in Columbian ground squirrels (Urocitellus columbianus), we tested the effects of co-breeding and non-breeding kin on the fitness and energy allocation balance between reproduction and personal body condition of individual females. Greater numbers of co-breeding kin had a positive effect on the number of offspring weaned, through the mechanism of altering energy allocation patterns. On average, females with higher numbers of co-breeding kin did not increase energy income but biased energy allocation towards reproduction. Co-breeding female kin ground squirrels maintain close nest burrows, likely providing a social buffer against territorial invasions from non-kin ground squirrels. Lower aggressiveness, lower risks of infanticide from female kin and greater protection of territorial boundaries may allow individual females to derive net fitness benefits via their energy allocation strategies. We demonstrated the importance of kin effects on a fundamental life-history trade-off.
Data from: The effect of landscape structure on dispersal distances of the Eurasian red squirrel
Landscape structure can affect dispersal and gene flow in a species. In urban areas, buildings, roads and small habitat patches make the landscape highly fragmented and can inhibit movement and affect dispersal behavior. Similarly, in rural forested areas, large open areas, such as fields, may act as barriers to movement. We studied how landscape structure affects natal dispersal distances of Eurasian red squirrels (Sciurus vulgaris) in an urban area and a rural area in Finland, by monitoring juvenile red squirrels with radio telemetry. We observed extremely long dispersal distances—up to 16 km—in the rural study area, but shorter distances—on average only half a kilometer—in the urban study area. The landscape structure affected the eventual dispersal paths; in the rural landscape, dispersers favored spruce dominated areas and avoided fields along their dispersal route, although they occasionally even crossed wide fields. In the urban landscape, squirrels preferred areas with deciduous or coniferous trees. The movement steps made by dispersers were longer in the more hostile landscape compared to forested areas. Despite these effects on movement path, the landscape structure only had a minor effect on straight-line dispersal distances moved from the natal nest. In other words, individuals moved longer distances and were likely to circumvent barriers in their path, but this did not affect how far they settled from their natal home. This result indicates that, although landscape structure has obvious effects on movement, it still may have only a small effect on other aspects of the population, for example, gene flow.
Data from: Behavioral flexibility versus rules of thumb: how do grey squirrels deal with conflicting risks?
In order to test how flexibly animals are able to behave when making trade-offs that involve assessing constantly changing risks, we examined whether wild Eastern grey squirrels showed flexibility of behavioral responses in the face of variation in 2 conflicting risks, cache pilferage, and predation. We established that cache pilferage risk decreased with distance from cover and was thus negatively correlated with long-term predation risk. We then measured changes in foraging and food-caching behavior in the face of changes in the risk of predation and food theft over a short time-scale. We found that, overall, squirrels move further away from the safety of cover when they cache, compared to when they forage, as predicted by pilferage risk. However, there was no effect of immediate pilferage or predation risk (i.e., the presence of potential predators or pilferers) on the distance from cover at which they cached, and only a slight increase in forage distance when predation risk increased. These results suggest that "rules of thumb" based on static cues may be more cost-effective for assessing risk than closely tracking changes over time in the way suggested by a number of models of risk assessment.
Data from: Predators, energetics and fitness drive neonatal reproductive failure in red squirrels
Neonatal reproductive failure should occur when energetic costs of parental investment outweigh fitness benefits. However, little is known about the drivers of neonatal reproductive failure in free ranging species experiencing continuous natural variation in predator abundance and in the energetic and fitness costs and benefits associated with parental investment. Long-term comprehensive studies are required to better understand how biotic, abiotic, and life history conditions interact to drive occurrences of reproductive failure in the wild. Using 24 years (1987-2011) of reproductive data from a northern boreal population of North American red squirrels in southwestern Yukon, we examined the effects of predator abundance, energetics (resource availability, ambient temperature and litter size), and fitness benefits (probability of overwinter juvenile survival and maternal age) on occurrences of neonatal reproductive failure (494/2670 reproductive attempts; 18.5%). Neonatal reproductive failure was driven by a combination of predator abundance, and the energetic and fitness costs and benefits of parental investment. The abundance of mustelids and maternal age were positively related to the occurrence of neonatal reproductive failure. High energy costs associated with a combination of low resource availability and cold ambient temperatures or large litters, corresponded to increased occurrences of neonatal reproductive failure. However, the strength of these relationships was influenced by variation in juvenile overwinter survival (i.e. fitness benefits). We provide evidence that predation pressure is an important driver of neonatal reproductive failure. In addition, we found a trade-off occurs between resource-dependent energetic and fitness costs and benefits of raising the current litter to independence
Data from: Stress in biological invasions: introduced invasive grey squirrels increase physiological stress in native Eurasian red squirrels
1. Invasive alien species can cause extinction of native species through processes including predation, interspecific competition for resources, or disease-mediated competition. Increases in stress hormones in vertebrates may be associated with these processes and contribute to the decline in survival or reproduction of the native species. 2. Eurasian red squirrels (Sciurus vulgaris) have gone extinct across much of the British Isles and parts of Northern Italy following the introduction of North American invasive grey squirrels (Sciurus carolinensis). We extracted glucocorticoid metabolites from faecal samples to measure whether the presence of the invasive species causes an increase in physiological stress in individuals of the native species. 3. We show that native red squirrels in seven sites where they co-occurred with invasive grey squirrels had glucocorticoid concentrations that were three times higher than those in five sites without the invasive species. Moreover, in a longitudinal study, stress hormones in native red squirrels increased after colonisation by grey squirrels. When we experimentally reduced the abundance of the invasive grey squirrels, the concentration of faecal glucocorticoid metabolites in co-occurring red squirrels decreased significantly between pre- and post-removal periods. 4. Hence, we found that the invasive species acts as a stressor which significantly increases the concentrations of glucocorticoids in the native species. 5. Given that sustained elevations in glucocorticoids could reduce body growth and reproductive rate, our results are consistent with previous studies where the co-occurrence of the invasive grey squirrel was associated with smaller size and lower reproductive output in red squirrels.
Data from: 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.
Data from: Independent reversals to terrestriality in squirrels (Rodentia: Sciuridae) support ecologically mediated modes of adaptation
The family Sciuridae is one of the most widespread and ecologically diverse lineage of rodents and represents an ideal model for investigating the evolution of locomotion modes and the historical biogeography of terrestrial mammals. We used a comprehensive database on locomotion modes, an updated phylogeny and novel biogeographic comparative methods to re-assess the evolution of locomotion of squirrels and to investigate if these locomotion modes evolved convergently in different continents. We found that locomotion changes occurred in different independent lineages of the family, including four reversals to terrestriality and one evolution of gliding. We also found evidence for Eurasia as the center of origin of Sciuridae, challenging the classification of the oldest squirrel fossil records from the early Oligocene in North America. Additionally, Eurasia is also the possible center of origin for most of squirrel sub-families and tribes, and where locomotion changes have occurred. Parallel locomotion shifts could be explained by the adaptation towards different ecological niches followed by colonization of new continents.
Data from: Phylogeographic diversification of antelope squirrels (Ammospermophilus) across North American deserts
We investigated the biogeographic history of antelope squirrels, genus Ammospermophilus, which are widely distributed across the deserts and other arid lands of western North America. We combined range-wide sampling of all currently recognized species of Ammospermophilus with a multilocus data set to infer phylogenetic relationships. We then estimated divergence times within identified clades of Ammospermophilus using fossil-calibrated and rate-calibrated molecular clocks. Lastly, we explored generalized distributional changes of Ammospermophilus since the last glacial maximum using species distribution models, and assessed responses to Quaternary climate change by generating demographic parameter estimates for the three wide-ranging clades of A. leucurus. From our phylogenetic estimates we inferred strong phylogeographic structure within Ammospermophilus and the presence of three well-supported major clades. Initial patterns of historical divergence were coincident with dynamic alterations in the landscape of western North America, and the formation of regional deserts during the Late Miocene and Pliocene. Species distribution models and demographic parameter estimates revealed patterns of recent population expansion in response to glacial retreat. When combined with evidence from co-distributed taxa, the historical biogeography of Ammospermophilus provides additional insight into the mechanisms that impacted diversification of arid-adapted taxa across the arid lands of western North America. We propose species recognition of populations of the southern Baja California peninsula to best represent our current understanding of evolutionary relationships among genetic units of Ammospermophilus.
Data from: Ultrasonic vocalizations emitted by flying squirrels
Anecdotal reports of ultrasound use by flying squirrels have existed for decades, yet there has been little detailed analysis of their vocalizations. Here we demonstrate that two species of flying squirrel emit ultrasonic vocalizations. We recorded vocalizations from northern (Glaucomys sabrinus) and southern (G. volans) flying squirrels calling in both the laboratory and at a field site in central Ontario, Canada. We demonstrate that flying squirrels produce ultrasonic emissions through recorded bursts of broadband noise and time-frequency structured frequency modulated (FM) vocalizations, some of which were purely ultrasonic. Squirrels emitted three types of ultrasonic calls in laboratory recordings and one type in the field. The variety of signals that were recorded suggest that flying squirrels may use ultrasonic vocalizations to transfer information. Thus, vocalizations may be an important, although still poorly understood, aspect of flying squirrel social biology.
FIGURE 6. A in A taxonomic revision of the Paranoplocephala primordialis (Douthitt) complex (Cestoda: Anoplocephalidae) in voles and squirrels
FIGURE 6. A. Scolex of Paranoplocephala nearctica n. sp. (ex. Microtus longicaudus, Alaska). B. Scolex of Paranoplocephala sp. (ex. Microtus oeconomus, Alaska). C. Mature proglottid of Paranoplocephala sp. (ex. Mi. oeconomus, Alaska). D. Mature proglottid of P. nearctica n. sp. (ex. Mi. longicaudus, Alaska). E. Gravid proglottids of Paranoplocephala sp. (ex. Mi. oeconomus, Alaska). Scale-bars in mm.
FIGURE 5. Paranoplocephala alaskensis n in A taxonomic revision of the Paranoplocephala primordialis (Douthitt) complex (Cestoda: Anoplocephalidae) in voles and squirrels
FIGURE 5. Paranoplocephala alaskensis n. sp. from Microtus miurus, Alaska. A. Scolex. B, C. Mature proglottids. D. Early uterus. E. Pregravid uterus. F. Gravid proglottids. Scale-bars in mm.
FIGURE 4. Paranoplocephala nearctica n in A taxonomic revision of the Paranoplocephala primordialis (Douthitt) complex (Cestoda: Anoplocephalidae) in voles and squirrels
FIGURE 4. Paranoplocephala nearctica n. sp. A. early uterus (ex. Myodes rutilus, Alaska). B. pregravid uterus (ex. My. rutilus, Alaska). C. Gravid proglottids (ex. My. rutilus, Alaska). D. Gravid proglottids (ex. Myodes gapperi, British Columbia). Scale-bars in mm.
FIGURE 3. Paranoplocephala nearctica n in A taxonomic revision of the Paranoplocephala primordialis (Douthitt) complex (Cestoda: Anoplocephalidae) in voles and squirrels
FIGURE 3. Paranoplocephala nearctica n. sp. A. scolex (ex. Myodes rutilus, Alaska). B. Scolex (ex. Myodes gapperi, British Columbia). C. Mature proglottid (ex. My. rutilus, Alaska). D. Mature proglottid (ex. My. rutilus, Alaska). E. Mature proglottid (ex. My. gapperi, Quebec). Scale-bars in mm.
Geographic patterns in scatterhoarding behavior of eastern gray squirrels (Sciurus carolinensis)
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Figure 2 in The systematics of the dusky striped squirrel, Funambulus sublineatus (Waterhouse, 1838) (Rodentia: Sciuridae) and its relationships to Layard's squirrel, Funambulus layardi Blyth, 1849
Figure 2. Primers used and approximate lengths (base pairs) of DNA targeted (parenthesis). Primer annealing position indicated by base number of primary target along its length.
Figure 5 in The systematics of the dusky striped squirrel, Funambulus sublineatus (Waterhouse, 1838) (Rodentia: Sciuridae) and its relationships to Layard's squirrel, Funambulus layardi Blyth, 1849
Figure 5. Discrepancy between means of linear characters including information from skins (excluding tail length), subtracting the same character values of Funambulus sublineatus sublineatus from F. s. obscurus, given that the latter is typically larger. Data from all suitable specimens (Table 2).
Figure 1 in The systematics of the dusky striped squirrel, Funambulus sublineatus (Waterhouse, 1838) (Rodentia: Sciuridae) and its relationships to Layard's squirrel, Funambulus layardi Blyth, 1849
Figure 1. Twenty-five measurements and their definitions used in this study, figure is based on a Funambulus tristriatus skull.
Figure 8. Rooted Bayesian trees from molecular analyses, Table 3 in The systematics of the dusky striped squirrel, Funambulus sublineatus (Waterhouse, 1838) (Rodentia: Sciuridae) and its relationships to Layard's squirrel, Funambulus layardi Blyth, 1849
Figure 8. Rooted Bayesian trees from molecular analyses, Table 3 identifies the specimens. Nodal support values in each phylogenetic tree (BI/ML/MP/NJ) are given on branches.
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