Middens (nests and caches) of Late Pleistocene arctic ground squirrels (Urocitellus parryii) that are preserved in the permafrost of Beringia archive valuable paleoecological data. Arctic ground squirrels selectively include the plant material placed in middens. To account for this selectivity bias, we used a multi-proxy approach that includes ancient DNA (aDNA) and macro- and microfossil analyses. Here, we provide insight into Pleistocene vegetation conditions using macrofossils, pollen, phytoliths and non-pollen palynomorphs, and aDNA collected from one such midden from the Yukon Territory (Canada), which was formed between 30,740 and 30,380 cal yr BP. aDNA confirmed the midden was constructed by U. parryii. We recovered 39 vascular plant and bryophyte genera and 68 fungal genera from the midden samples. Grass and other herbaceous families dominated vegetation assemblages according to all proxies. aDNA data yielded several records of vascular plants that are outside their current biogeographic range, while some of the recovered fungi yielded additional evidence for local occurrence of Picea trees during glacial conditions. We propose that future work on fossil middens should combine the study of macro- and microfossils with aDNA analysis to get the most out of these environmental archives.

Bartonella spp. are endemic in wild rodents in many parts of the world. A study conducted in two northern California counties (Sonoma and Yolo) sampling California ground squirrels (Otospermophilus beecheyi) and four other rodent species (Peromyscus maniculatus, P. boylii, P. truei and Neotoma fuscipes) led to the isolation of small Gram-negative bacilli which were identified as Bartonella spp. based on colony morphology, polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) and partial gene sequencing. Overall, Bartonella spp. were isolated from the blood of 71% (32/45) of the ground squirrels and one third (22/66) of the other rodents. PCR–RFLP analysis of the gltA and 16S rRNA genes yielded seven unique profiles, four for the ground squirrels and three for the other rodents. Isolates from each PCR–RFLP profiles were submitted for partial sequencing. Ground squirrel isolates were most closely related to B. washoensis, whereas the other rodent isolates were closest to B. vinsonii subsp. vinsonii and B. vinsonii subsp. arupensis. Two of these three species or subspecies are known zoonotic agents.

Behavioral and electrophysiological methods were used to measure sensitivity to flickering lights in a dichromatic species, the California ground squirrel (Spermophilus beecheyi). Discrimination tests were used to determine spectral sensitivity at stimulus frequencies from 5–50 Hz and increment threshold spectral sensitivity. The contributions of retinal mechanisms to these capacities were assessed by recording the responses of optic nerve fibers to temporally modulated monochromatic lights. In the ground squirrel, as in the human, the shape of the spectral-sensitivity function depends on the temporal frequency of the stimulus. Results from single-unit recording show that all of the classes of optic nerve fibers in the ground squirrel are highly phase-locked to the stimulus for modulation rates as high as 50 Hz. Neither the responses of photoreceptors nor any class of optic nerve fiber can singly account for the behavioral results. The electrophysiological results are also counter to models which propose that temporally dependent changes in the spectral sensitivity of spectrally opponent fibers account for the behavior. The temporal resolution of the optic nerve fibers exceeds that of the behaving animal suggesting that retinal mechanisms do not limit behavioral temporal resolution.