Female gestation and lactation as zeitgebers for circannual rhythmicity in the hibernating ground squirrel, Citellus lateralis

Effect of age and parity on weight gain and entry into hibernation in Richardson's ground squirrels

“…Thus there was an interrelationship between parity, weight cycles, and timing of fall immergence. Pengelley and Asmundson (1975) have suggested that gestation and lactation act as zeitgebers that are necessary to ensure appropriate timing of the annual cycle with the seasons but this study supports a previous conclusion of mine (Michener 1977a) that all adult females emerge within a few days of each other in spring, regardless of the previous year's breeding success and the range of times of entry into hibernation. Early immergence into hibernation, as a consequence of failure to breed successfully, does not consign a female to an inappropriately early emergence the following spring but instead results in prolonged hibernation.…”

“…Although weight cycles have been followed over several years in captive squirrels (e.g., Pengelley and Fisher 1963;Blake 1972;Morrison and Galster 1975), these studies have not included the effect of annual reproduction, in part because of the difficulty of breeding ground squirrels in captivity. The only study that attempted to assess the effects of reproduction on annual cycles (Pengelley and Asmundson 1975) by capturing pregnant females discussed time of entry into hibernation but not weight-gain patterns. Since virtually all sexually mature female Richardson's ground squirrels breed (Michener 1974), weightgain cycles in the field can be expected to differ from those in captivity.…”

Annual cycles of body weight in the Namie's frosted bat, Vespertilio superans superans

“…For instance, experiments on the influences of environmental factors such as temperature, light and food upon both of the circannual rhythms have been conducted (Pengelley & Fisher, 1963;Pengelley, 1967;Heller & Poulson, 1970;Mrosovsky & Fisher, 1970;Mrosovsky & Lang, 1971;Pengelley, Asmundson, et a/., 1976;Phillips, 1979;Mrosovsky, 1977Mrosovsky, , 1980a. Furthermore, the possibility that pregnancy and lactation may act as Zeitgebers has been pointed out by Pengelley & Asmundson (1975). Problems on the mechanisms of generating the circannual rhythm (Mrosovsky, 1968;Pengelley & Asmundson, 1972;Mrosovsky, 1976Mrosovsky, , 1978 including their endogenous aspects (Pengelley & Asmundson, 1969;Armitage & Schulenberger, 1972;Mrosovsky, Boshes et al, 1976;Pengelley, Aloia et af., 1978) also have been discussed.…”