Chipmunk

Abstract: The importance of circadian timing was evaluated for 18 months from late-April 1997 through October 1998 in a high-density population of free-living eastern chipmunks, Tamias striatus, at a 4-ha forest site in the Allegheny Mountains. Included in the radio-collared field group were 30 chipmunks with supra-chiasmatic nucleus-targeted lesions, 24 surgical controls, and 20 intact controls. An additional 17 chipmunks were used in a laboratory study as lesion-calibration controls to correlate degree of circadian arrhythmicity with extent of supra-chiasmatic nucleus deletion. Survival was documented in the field by daily radio tracking and by regular trapping censuses except during winter hibernation. A significantly higher proportion of supra-chiasmatic nucleus-lesioned than surgical control chipmunks or intact controls were killed by weasel predation during the first 80 days after repatriation. A 28-h continuous census found no surface activity of any chipmunks during hours of darkness. However, episodes of nocturnal movement were detected within the permanent dens by radio telemetric data logging, especially in supra-chiasmatic nucleus-lesioned animals. Excavation and mapping of six chipmunk burrow systems aided in the interpretation of the telemetric activity data. Nighttime restlessness of supra-chiasmatic nucleus-lesioned animals may have acted as a clue to the predator for locating its prey.

Abstract: The effectiveness of Jeffrey pine (Pinus jeffreyi) seed dispersal performed by seed-caching yellow pine chipmunks (Tamias amoenus) and lodgepole chipmunks (Tamias speciosus) was compared to that of wind dispersal in the Sierra Nevada of western Nevada. Wind-dispersed seeds typically fall under or near the parent tree. Chipmunks removed 90 and 97% of 1064 radioactive seeds from each of two simulated wind-dispersed seed shadows in less than 24 h. "Wind-dispersed" seeds were deployed within 12 m of the two "source" trees, but chipmunk caches were found from 2-69 m from the trees. Chipmunks carried nearly all seeds away from source trees, greatly reducing the density of seeds under and near source trees. Caches contained from 1-35 seeds and most were buried 7-21 mm deep. Chipmunks cached in open bitterbrush shrubland with mineral soils much more than expected and cached in closed-canopy Jeffrey pine and lodgepole pine forests with thick needle litter much less than expected. Many Jeffrey pine seedlings and saplings grow in the bitterbrush habitat and few grow in the pine forests. Ten and 20% of the original caches survived until April, the time of seed germination, at the two sites. The movement of wind-dispersed seeds is random relative to environmental variables important in seedling survival, and the wind in coniferous forests cannot quickly bury seeds. The quality of seed dispersal rendered by chipmunks was superior to that provided by the wind because the chipmunks quickly harvested seeds on the ground, moved them away from source trees, and buried them in the ground in habitats and microhabitats where they were more likely to establish new seedlings. The increased quality of seed dispersal provided by animals relative to the wind may help explain why over twenty species of pines have evolved seeds and cones that are adapted for dispersal by seed-caching animals.

Abstract: In mammals, hibernation is expressed by only a limited number of species, and the molecular mechanisms underlying hibernation are not well understood. Recently, we have found plasma proteins which disappear from blood specifically during hibernation in a mammalian hibernator, the chipmunk. Here, we report the cDNA cloning of these chipmunk hibernation-related proteins, HP-20, -25, and -27, and analyses of their expression. All three proteins contain a collagen-like domain near the N terminus and are highly homologous to each other. Their mRNAs were detected only in liver in nonhibernating chipmunks, and in hibernating chipmunks, the amounts were reduced to less than 1/10 of those in nonhibernating chipmunks, indicating that HP-20, -25, and -27 mRNA expression is regulated similarly in association with hibernation. Southern blot analyses of the squirrel family with each of chipmunk HP-20, -25, and -27 cDNA revealed that a nonhibernating species (tree squirrel) as well as another hibernating species (ground squirrel) retained the corresponding genes. However, their transcripts were detected only with the hibernating species, and in hibernating ground squirrels, their levels were greatly reduced compared with those in nonhibernating animals, as were the cases with the chipmunk. These observations are the first line of evidence for occurrence of hibernation-associated gene regulation. The results would indicate the commitment of HP-20, -25, and -27 to hibernation and support the idea that genetic controls are involved in mammalian hibernation.

Abstract: We studied annual cycles of three sciurids and one cricetid rodent that coexist in a strongly seasonal environment in the Cascade Mountains of Washington. Spermophilus saturatus (Cascades golden-mantled ground squirrel) hibernated for 6–8 months, whereas Eutamias townsendii (Townsend's chipmunk) and E. amoenus (yellow-pine chipmunk) hibernated for only 4–4.5 months. Peromyscus maniculatus (deer mouse) did not hibernate. The three sciurids bred only once a year, with a 1- to 2-week mating period between late March and early May; E. amoenus bred about a month before the other two sciurids. Males emerged from hibernation 1–2 weeks before females, and mating occurred within a week of female emergence. P. maniculatus began breeding in February and continued through October; adult females produced as many as three litters, and the earliest juvenile cohorts reproduced in the year of birth. None of the sciurids became reproductively active until they were yearlings, and some E. townsendii and S. saturatus did not breed until 2 years of age. Average litter size was similar in the four species: S. saturatus , 4.1; E. townsendii , 3.8; E. amoenus , 5.0; and P. maniculatus , 4.6. Because female P. maniculatus bear 2–3 litters per year and juveniles breed in the year of birth, this species has the most flexible timing and greatest annual reproductive potential. The total mass of young produced at the end of gestation and upon emergence from the natal burrow imposes an energetic burden that scales inversely with body mass among the four species. Lipid reserves do not contribute directly to energy requirements of gestation and lactation. Lipid reserves play a major sustaining role during hibernation in S. saturatus (prehibernation body fat >30%), but chipmunks fatten only slightly (body fat < 7%) and rely on food caches during hibernation. P. maniculatus does not fatten substantially. S. saturatus that emerge from hibernation ready to breed contain residual hibernatory fat used for 1–2 weeks as a supplement to ingested food.