Body temperature (Tb) of seven European hamsters maintained at constant ambient temperature (Ta = 8 degrees C) and constant photoperiod (LD 8:16) was recorded throughout the hibernating season using intraperitoneal temperature-sensitive HF transmitters. The animals spent about 30% of the hibernation season in hypothermia and 70% in inter-bout normothermy. Three types of hypothermia, namely deep hibernation bouts (DHBs), short hibernation bouts (SHBs), and short and shallow hibernation bouts (SSHBs), were distinguished by differences in bout duration and minimal body temperature (Tm). A gradual development of SSHBs from the diel minimum of Tb during normothermy could be seen in individual hamsters, suggesting a stepwise decrease of the homeostatic setpoint of Tb regulation during the early hibernation season. Entry into hibernation followed a 24-h rhythm occurring at preferred times of the day in all three types of hypothermia. DHBs and SHBs were initiated approximately 4 h before SSHBs, indicating a general difference in the physiological initiation of SSHBs on the one hand and DHBs and SHBs on the other. Arousals from SHBs and SSHBs also followed a 24-h rhythm, whereas spontaneous arousals from DHBs were widely scattered across day and night. Statistical analyses of bout length and the interval between arousals revealed evidence for a free-running circadian rhythm underlying the timing of arousals. The results clearly demonstrate that entries into hypothermia are linked to the light/dark-cycle. However, the role of the circadian system in the timing of arousals from DHBs remains unclear.

This is an author-produced, peer-reviewed version of this article. © 2016, Elsevier. Licensed under the Creative Commons AttributionNonCommercial-No Derivatives 4.0 License. Details regarding the use of this work can be found at: http://creativecommons.org/licenses/by-nc-nd/ 4.0/ . The final, definitive version of this document can be found online at Physiology & Behavior, doi: 10.1016/j.physbeh.2016 Publication Information Refinetti, Roberto. (2016) E-mail address: refinetti@circadian.org (R. Refinetti). AbstractHuman chronotypes (differences in preference for early or late rising each day) have been extensively studied in recent years, but no attempt has been made to compare human chronotypes with the chronotypes of other animal species. We evaluated behavioral chronotypes in 16 mammalian species along a body size gradient of five orders of magnitude (from mice to cattle). Individuals of all species were studied under a 12L:12D photoperiod in a thermoneutral environment with food and water available at all times. Rhythms of locomotor activity were analyzed for onset time, acrophase, and robustness. Neither of these rhythmic parameters was significantly related to body size, but onset time and acrophase varied considerably from species to species, thus characterizing diurnal and nocturnal species. Chronotype spreads ranged from less than an hour in sheep to almost 24 hours in cats, thus extending both below and above the human chronotype spread of 6 hours. The variability of chronotype (as quantified by the standard deviation of group means) was much larger between species than within species and also larger between individuals of a species than within individuals on consecutive days. These results help situate the matter of human chronotypes within the broader context of variability in the phase angle of entrainment of circadian rhythms in animals.

Only a few mostly older studies analyzed the heterotrophic succession of dung beetles in the Midwestern United States. Such studies are needed to track the impacts of the climate crisis on heterotrophic succession and the associated decomposition processes that are central to soil fertility and carbon sequestration. The current study closes this knowledge gap and provides an easy and efficient method to estimate the relative attractiveness of individual dung pads during heterotrophic succession. The dung beetle community of Carpenter Farm in Adrian, Southeast Michigan was sampled for an entire year, including the winter months, using 15 pitfall traps baited with fresh cow manure. Samples were collected after 48 h and again after 72 h exposure time from the bucket content while leaving the bait unhampered. Eighty-four percent of all beetles were caught in the early sample, but only 6 species were missing in the later sample. A cluster analysis based on Pianka’s niche overlap identified a statistically higher mean overlap than expected by chance in a null model (model RA3) and divided the species community clearly into three clusters separating most relocators from most dwellers. Despite using a different method, my results confirmed the successional position of most previously described species and added data for several species with poor or unknown successional state. The successional segregation between dwellers and relocators discovered by the cluster analysis was paralleled by a significantly larger body size of relocators across taxonomic groups as compared to dwellers.

The purpose of this study was to determine whether hibernating European hamsters Cricetus cricetus, L., 1758 stay in their burrows all winter or if they occasionally spent time above ground. If 'time (spent) above ground' (TAG) occurred regularly throughout hibernation, the second objective of this work was to categorize and quantify the patterns of TAG during winter. For this purpose, 11 European hamsters were individually housed in wire mesh cages that were buried in the ground of an outdoor enclosure. Each cage was filled with soil up to ground level allowing the animals to construct their own burrows within the cages. Antennae in the bottom and top of the cage were calibrated to receive signals only when the hamsters were in their burrows or above the ground, respectively. This method enabled continuous recordings of the animal's TAG and provided ecologically meaningful results as the animals were housed in a way that closely resembled their natural habitat. About half of the hamsters stayed continuously below ground. Of these hamsters, almost all showed a dense pattern of episodes of reduced body temperature separated by only brief periods of normothermia. In contrast, the other half of the animals moved either episodically or even regularly above ground. For all of these hamsters, TAG was significantly reduced as compared to normothermic values. One hamster did not show any hibernation but did have a significantly reduced normothermic body temperature and did not leave its burrow for periods of up to 3 weeks.

The authors investigated the general activity and nest occupation patterns of fox squirrels in a natural setting using temperature-sensitive data loggers that measure activity as changes in the microenvironment of the animal. Data were obtained from 25 distinct preparations, upon 14 unique squirrels, totaling 1385 recording days. The animals were clearly diurnal, with a predominantly unimodal activity pattern, although individual squirrels occasionally exhibited bimodal patterns, particularly in the spring and summer. Even during the short days of winter (9 hours of light), the squirrels typically left the nest after dawn and returned before dusk, spending only about 7 hours out of the nest each day. Although the duration of the daily active phase did not change with the seasons, the squirrels exited the nest earlier in the day when the days became longer in the summer and exited the nest later in the day when the days became shorter in the winter, thus tracking dawn along the seasons. During the few hours spent outside the nest each day, fox squirrels seemed to spend most of the time sitting or lying. These findings suggest that fox squirrels may have adopted a slow life history strategy that involves long periods of rest on trees and short periods of ground activity each day.

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Climate change models often assume similar responses to temperatures across the range of a species, but local adaptation or phenotypic plasticity can lead plants and animals to respond differently to temperature in different parts of their range. To date, there have been few tests of this assumption at the scale of continents, so it is unclear if this is a large‐scale problem. Here, we examined the assumption that insect taxa show similar responses to temperature at 96 sites in grassy habitats across North America. We sampled insects with Malaise traps during 2019–2021 (N = 1041 samples) and examined the biomass of insects in relation to temperature and time of season. Our samples mostly contained Diptera (33%), Lepidoptera (19%), Hymenoptera (18%), and Coleoptera (10%). We found strong regional differences in the phenology of insects and their response to temperature, even within the same taxonomic group, habitat type, and time of season. For example, the biomass of nematoceran flies increased across the season in the central part of the continent, but it only showed a small increase in the Northeast and a seasonal decline in the Southeast and West. At a smaller scale, insect biomass at different traps operating on the same days was correlated up to ~75 km apart. Large‐scale geographic and phenological variation in insect biomass and abundance has not been studied well, and it is a major source of controversy in previous analyses of insect declines that have aggregated studies from different locations and time periods. Our study illustrates that large‐scale predictions about changes in insect populations, and their causes, will need to incorporate regional and taxonomic differences in the response to temperature.