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opencc-by-4.0Apr 2023View details →

TABLE 3 in Beavers and flying squirrels (Rodentia: Castoridae, Pteromyini) from the Late Pliocene of Hambach 11 C, Germany

TABLE 3. — Measurements (in mm) of Pliopetaurista pliocaenica (Depéret, 1897) and Blackia miocaenica Mein, 1970 teeth from Hambach 11C.<table><tbody><tr><th></th><th></th><th></th><th></th><th>Maximum</th><th>Maximum</th><th>Minimum</th><th>Minimum</th><th>Mean</th><th>Mean</th><th>Number</th></tr></tbody><tbody><tr><th>Museum</th><td></td><td></td><td></td><td>length</td><td>width</td><td>length</td><td>width</td><td>length</td><td>width</td><td>of</td></tr><tr><th>number</th><td>Locality</td><td>Species</td><td>Position</td><td>(mm)</td><td>(mm)</td><td>(mm)</td><td>(mm)</td><td>(mm)</td><td>(mm) specimens</td></tr><tr><th>HaR-5614,</th><td>Hambach 11/2</td><td>Pliopetaurista</td><td>m1/2</td><td>3.08</td><td>3.23</td><td>2.95</td><td>2.86</td><td>3</td><td>3</td><td>3</td></tr><tr><th>5625, 5627</th><td></td><td>pliocaenica</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><th>HaR-5628</th><td>Hambach 11/2</td><td>Pliopetaurista</td><td>m3</td><td>2.62</td><td>2.28</td><td>–</td><td>–</td><td>–</td><td>–</td><td>1</td></tr><tr><th></th><td></td><td>pliocaenica</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><th>HaR-5629,</th><td>Hambach 11/2</td><td>Pliopetaurista</td><td>P4</td><td>3.38</td><td>3.08</td><td>3.02</td><td>2.89</td><td>3.2</td><td>2.99</td><td>2</td></tr><tr><th>5631</th><td></td><td>pliocaenica</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><th>HaR-5632, 5633, Hambach 11/2</th><td>Pliopetaurista</td><td>M1/2</td><td>2.83</td><td>3.14</td><td>2.55</td><td>2.8</td><td>2.7</td><td>2.97</td><td>4</td></tr><tr><th>5634, 5635</th><td></td><td>pliocaenica</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><th>HaR-5636</th><td>Hambach 11/2</td><td>Blackia</td><td>M3</td><td>1.6</td><td>1.51</td><td>–</td><td>–</td><td>–</td><td>–</td><td>1</td></tr><tr><th></th><td></td><td>miocaenica</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

opennotspecifiedJan 2024View details →

Figure 2 in New dietary records for the rare Thomas's Flying Squirrel (Aeromys thomasi, Sciuridae: Pteromyini) from Sabah, Malaysian Borneo

Figure 2: Female Thomas's Flying Squirrel (Aeromys thomasi) feeding on young,furled leaf shoots of a White Seraya tree (Parashorea malaanonan). Rainforest Discovery Centre, Sepilok, Sabah, Malaysia.

opennotspecifiedJan 2024View details →

Figure 1 in New dietary records for the rare Thomas's Flying Squirrel (Aeromys thomasi, Sciuridae: Pteromyini) from Sabah, Malaysian Borneo

Figure 1: Female Thomas's Flying Squirrel (Aeromys thomasi) feeding on the bark of a White Seraya tree (Parashorea malaanonan). Rainforest Discovery Centre, Sepilok, Sabah, Malaysia.

opencc-zeroDec 2015View details →

Data from: Evolutionary history of endemic Sulawesi squirrels constructed from UCEs and mitogenomes sequenced from museum specimens

Background: The Indonesian island of Sulawesi has a complex geological history. It is composed of several landmasses that have arrived at a near modern configuration only in the past few million years. It is the largest island in the biodiversity hotspot of Wallacea—an area demarcated by the biogeographic breaks between Wallace's and Lydekker's lines. The mammal fauna of Sulawesi is transitional between Asian and Australian faunas. Sulawesi's three genera of squirrels, all endemic (subfamily Nannosciurinae: Hyosciurus, Rubrisciurus and Prosciurillus), are of Asian origin and have evolved a variety of phenotypes that allow a range of ecological niche specializations. Here we present a molecular phylogeny of this radiation using data from museum specimens. High throughput sequencing technology was used to generate whole mitochondrial genomes and a panel of nuclear ultraconserved elements providing a large genome-wide dataset for inferring phylogenetic relationships. Results: Our analysis confirmed monophyly of the Sulawesi taxa with deep divergences between the three endemic genera, which predate the amalgamation of the current island of Sulawesi. This suggests lineages may have evolved in allopatry after crossing Wallace's line. Nuclear and mitochondrial analyses were largely congruent and well supported, except for the placement of Prosciurillus murinus. Mitochondrial analysis revealed paraphyly for Prosciurillus, with P. murinus between or outside of Hyosciurus and Rubrisciurus, separate from other species of Prosciurillus. A deep but monophyletic history for the four included species of Prosciurillus was recovered with the nuclear data. Conclusions: The divergence of the Sulawesi squirrels from their closest relatives dated to ~9.7–12.5 million years ago (MYA), pushing back the age estimate of this ancient adaptive radiation prior to the formation of the current conformation of Sulawesi. Generic level diversification took place around 9.7 MYA, opening the possibility that the genera represent allopatric lineages that evolved in isolation in an ancient proto-Sulawesian archipelago. We propose that incongruence between phylogenies based on nuclear and mitochondrial sequences may have resulted from biogeographic discordance, when two allopatric lineages come into secondary contact, with complete replacement of the mitochondria in one species.

opencc-zeroDec 2017View details →

Data from: Genome-wide markers reveal a complex evolutionary history involving divergence and introgression in the Abert's squirrel (Sciurus aberti) species group

Background: Genetic introgression between divergent lineages is now considered more common than previously appreciated, with potentially important consequences for adaptation and speciation. Introgression is often asymmetric between populations and patterns can vary for different types of loci (nuclear vs. organellar), complicating phylogeographic reconstruction. The taxonomy of the ecologically specialized Abert's squirrel species group has been controversial, and previous studies based on mitochondrial data have not fully resolved the evolutionary relationships among populations. Moreover, while these studies identified potential areas of secondary contact between divergent lineages, the possibility for introgression has not been tested. Results: We used RAD-seq to unravel the complex evolutionary history of the Abert's squirrel species group. Although some of our findings reinforce inferences based on mitochondrial data, we also find significant areas of discordance. Discordant signals generally arise from previously undetected introgression between divergent populations that differentially affected variation at mitochondrial and nuclear loci. Most notably, our results support earlier claims (disputed by mitochondrial data) that S. aberti kaibabensis, found only on the north rim of the Grand Canyon, is highly divergent from other populations. However, we also detected introgression of S. aberti kaibabensis DNA into other S. aberti populations, which likely accounts for the previously inferred close genetic relationship between this population and those south of the Grand Canyon. Conclusions: Overall, the evolutionary history of Abert's squirrels appears to be shaped largely by divergence during periods of habitat isolation. However, we also found evidence for interbreeding during periods of secondary contact resulting in introgression, with variable effects on mitochondrial and nuclear markers. Our results support the emerging view that populations often diversify under scenarios involving both divergence in isolation and gene flow during secondary contact, and highlight the value of genome-wide datasets for resolving such complex evolutionary histories.

opennotspecifiedFeb 2014View details →

Figure 2 in Endoparasites of the European ground squirrel (Spermophilus citellus) (Rodentia: Sciuridae) in central Macedonia, Greece

Figure 2. The sampling sites of Spermophilus citellus in central Macedonia, Greece (1: University Agriculture Farm, 2: C Army Veterinary Hospital, 3: Axios – eastern coast, 4: Axios – western mound, 5: Anatoliko, 6: Aggelochori salt pits).

FIGURE 2 in Genetic evaluation of the Baja California rock squirrel Otospermophilus atricapillus (Rodentia: Sciuridae)

FIGURE 2. Topology of phylogenetic relationships among specimens of O. atricapillus and O. beecheyi from California and the Baja California Peninsula based on the complete Cyt b gene Callospermophilus madrensis, C. lateralis, and C. saturatus was used as outgroup. The main topology recovered from all the analyses shows that O. atricapillus (haplotypes 29 to 32) and O. beecheyi (haplotypes 1-28) are monophyletic. All the phylogenetic analyses revealed three major clades. The first clade groups all specimens from lowlands across California and Baja California Peninsula (Clade A, Southern Clade); the second one contains specimens from the California highlands in El Dorado Natural Forest (Clade B, Northern Clade); and the third contains specimens from the California highlands in Yosemite (Clade C, Central Clade). The nodal support values in each of the main nodes are in order: NJ bootstrap, maximum-likelihood bootstrap, Bayesian posterior probabilities (x100), and maximumparsimony bootstrap. At the tip of each branch is the number of the haplotype.

FIGURE 1 in Genetic evaluation of the Baja California rock squirrel Otospermophilus atricapillus (Rodentia: Sciuridae)

FIGURE 1. Map of California and the Baja California Peninsula showing 20 geographic groups (A to T) from which specimens for the genetic analysis were collected. Localities are listed in Table 1. Localities are clustered into geographical groups. The light gray area represents the distribution of O. beecheyi and dark gray that of O. atricapillus. Solid circles are specimens from Clade A; solid squares from Clade B; and solid rhomboids from Clade C.

FIGURE 4 in Genetic evaluation of the Baja California rock squirrel Otospermophilus atricapillus (Rodentia: Sciuridae)

FIGURE 4. Observed (wide line) and expected (thin line) mismatch distributions for 800 cyt b gene, including Otospermophilus atricapillus and O. beecheyi. A) All the sample specimens from the seven subspecies of O. beecheyi and O. atricapillus. B) Specimens from Northern Clade. C) The specimens from Central Clade. D) Specimens from O. atricapillus, and E) All specimens Southern Clade.

FIGURE 3. Haplotype network for the 800 in Genetic evaluation of the Baja California rock squirrel Otospermophilus atricapillus (Rodentia: Sciuridae)

FIGURE 3. Haplotype network for the 800-bp Cyt b data set includes populations from California and the Baja California Peninsula. Each perpendicular hash mark across the line between adjacent haplotypes in the network represents a single-base substitution. The circle size is directly proportional to the number of specimens per haplotype; the key to the haplotype (Table 1) is adjacent to each circle; some haplotypes are present in more than one population. The clades are in boxes; Clade A (Southern Clade, lowlands across California and Baja California Peninsula); Clade B (Northern Clade, El Dorado Natural Forest); and Clade C (Central Clade, California highlands in Yosemite). Color for the haplotype circles are based on subspecies designation (see material and methods from subspecies allocation. Solid circle = O. b. atricapillus, dark gray circle O. b. beecheyi, light gray circle O. b. douglasii, open circle = O. b. fisheri, solid ellipse = O. b. nudipes, dark gray ellipse = O. b. parvulus, light gray ellipse = O. b. rupinarum, and open ellipse = O. b. sierrae.

opencc-zeroAug 2021View details →

Richardson's Ground Squirrel occurrence in Saskatchewan

Richardson's ground squirrel (Urocitellus richardsonii, Sabine 1822) is a widespread burrowing mammal on the Northern Great Plains. This species is a key prey item for a variety of predators, and its burrows provide important habitat for other wildlife; however, Richardson's ground squirrel is also considered an economically damaging agricultural pest. Despite the ecological importance of Richardson's ground squirrels and their status as pests, there are gaps in our knowledge about large-scale habitat associations for this species. In 2011 and 2012, we conducted 1840 road-side surveys in a 130,000-km2 area of southern Saskatchewan, Canada to understand which habitat features are associated with Richardson's Ground Squirrel occurrence. Ground squirrels were observed during only 8% of the surveys. Probability of ground squirrel occurrence was highest in areas with moderate amounts of grassland (approximately 30%), areas that were developed by humans (>30%), and had a high proportion of clay loam soils, presumably for burrowing. Our study highlights the importance of heterogeneous landscapes and that areas disturbed by humans may provide suitable vegetation structure for ground squirrels. This information can help to identify important habitat for species that rely on Richardson's ground squirrels and identify areas where they could come into conflict with agriculture.

opencc-zeroOct 2021View details →

Social effects on annual fitness in red squirrels

When resources are limited, mean fitness is constrained and competition can cause genes and phenotypes to enhance an individual's own fitness while reducing the fitness of their competitors. Negative social effects on fitness have the potential to constrain adaptation, but the interplay between ecological opportunity and social constraints on adaptation remains poorly studied in nature. Here, we tested for evidence of phenotypic social effects on annual fitness (survival and reproductive success) in a long-term study of wild North American red squirrels (Tamiasciurus hudsonicus) under conditions of both resource limitation and super-abundant food resources. When resources were limited, populations remained stable or declined, and there were strong negative social effects on annual survival and reproductive success. That is, mean fitness was constrained and individuals had lower fitness when other nearby individuals had higher fitness. In contrast, when food resources were super-abundant, populations grew and social constraints on reproductive success were greatly reduced or eliminated. Unlike reproductive success, social constraints on survival were not significantly reduced when food resources were super-abundant. These findings suggest resource-dependent social constraints on a component of fitness, which have important potential implications for evolution and adaptation.

opencc-zeroJan 2023View details →

Dataset: Evolution of gliding in squirrel-related rodents (Mammalia: Sciuromorpha) did not induce a new optimum on the cortical thickness of the scapular glenoid fossa

Many of the squirrel-related rodents (i.e., Sciuromorpha) are tree-dwelling species known to be very agile climbers. This taxon also includes the most diverse clade of gliding (aerial) mammals that likely descended from a non-gliding arboreal ancestor and evolved a patagium (i.e., a gliding membrane) to increase gliding performance. Glides can cover distances of up to 150 m and landing is typically accomplished by stalling the patagium to reduce impact velocity. It remains unclear if this behavior suffices to keep stresses on the locomotor apparatus similar to those experienced by their arboreal relatives or whether gliding behavior increases landing forces and stresses. The sparsely available support reaction force data are ambiguous, but bone microstructure is highly adaptable to changes in loading regime and likely provides insights into this question. Using µCT scans, we compared the cortical thickness of the glenoid fossa of the shoulder joint between arboreal and aerial Sciuromorpha using evolutionary model comparison, while also accounting for regional differences of the glenoid fossa. We did not find any differences between these locomotor behaviors, irrespective of the region. These findings agree with previous analyses of the microstructure of the femur in Sciuromorpha. We discuss different aspects that could explain the similarity in cortical thickness. According to our analysis of glenoid cortical thickness the loading regime appears not to have changed after the evolution of gliding locomotion, likely due to adjustments in landing performance.

opencc-zeroMar 2023View details →

Craniodental divergence associated with bite force between hybridizing pine squirrels (Tamiasciurus)

Bite force can be a limiting factor in foraging and can significantly affect the competitive ability and lifetime fitness of mammals. Tamiasciurus squirrels feed primarily on conifer seeds and have a strong bite force to mechanically extract seeds from conifer cones with their mouths. In the North Cascades region, Douglas squirrels (Tamiasciurus douglasii) and red squirrels (T. hudsonicus) occupy ecologically different forests with different hardnesses in conifer cones. The ranges of these species overlap in a narrow hybrid zone where these forests meet near the crest of the North Cascades. We examined interspecific divergence in dietary ecomorphology in allopatry, in sympatry within the hybrid zone, and between hybrids and each parental species. We focused on three craniodental traits, including the incisor-strength index as a proxy measure for maximal bite force, cranial-suture complexity, and mandible shape. We find that these sister squirrel species differ in bite force and suture complexity in allopatry and sympatry and that mandible shape changes with the expected hardness of accessed food items, but is not significantly different between species. Furthermore, we find that hybrids display morphologies that overlap with hybrid zone red squirrels but not with hybrid zone Douglas squirrels. This work shows how important ecological processes at shallow evolutionary timescales can impact the divergence of morphological traits in taxa with extreme conservation of craniomandibular shape.

Fig. 4 in Big Cypress fox squirrel (Sciurus niger avicennia) ecology and habitat use in a cypress dome swamp-pine forest mosaic

Fig. 4.—Mean (± SD) length (km) of linear features (roads, random lines) and area (ha) of rectangular features (oilpads, random rectangles) overlapped by Big Cypress fox squirrel male and female 95% home range kernels from 2007 to 2011, within the Raccoon Point area of Big Cypress National Preserve, Florida.

Fig. 2 in Big Cypress fox squirrel (Sciurus niger avicennia) ecology and habitat use in a cypress dome swamp-pine forest mosaic

Fig. 2.—Mean (± SD) percent overlap of individual Big Cypress fox squirrel 95% home range kernels by dyad (MF = males overlapping females, MM = males overlapping males, FF = females overlapping females) within the Raccoon Point area of Big Cypress National Preserve, Florida. Overlaps are summarized for animals that actually overlapped in time and space from 2007 to 2011 (i.e., telemetry data were collected contemporaneously) and animals that potentially overlapped spatially (i.e., home ranges were calculated across years and seasons and overlaps calculated among all home ranges independent of year and season). Means were calculated from overlapping kernels only.

Fig. 1 in Big Cypress fox squirrel (Sciurus niger avicennia) ecology and habitat use in a cypress dome swamp-pine forest mosaic

Fig. 1.—Color phases of Big Cypress fox squirrels captured from 2007 to 2011 within the Raccoon Point area of Big Cypress National Preserve, Florida. A) Orange phase BCFS (n = 17); B) Black phase BCFS (n = 6); C) Tan phase BCFS (n = 1). Photos copyright Ralph Arwood. BCFS = Big Cypress fox squirrels.

Fig. 3 in Big Cypress fox squirrel (Sciurus niger avicennia) ecology and habitat use in a cypress dome swamp-pine forest mosaic

Fig. 3.—Comparison of use versus availability for 7 vegetation types used by Big Cypress fox squirrels from 2007 to 2011, in the Raccoon Point area of Big Cypress National Preserve, Florida. Bars represent the mean percentage of each vegetation community type used minus the mean percentage of vegetation community type available at 3 orders of selection.

Fig. 5 in Big Cypress fox squirrel (Sciurus niger avicennia) ecology and habitat use in a cypress dome swamp-pine forest mosaic

Fig. 5.—Total male (n = 10) and female (n = 10) Big Cypress fox squirrel food item use (n = 702) percentage per month within the Raccoon Point area of Big Cypress National Preserve, Florida, from 2007 to 2011.