The circadian rhythm of locomotor activity in the spiny mouse Acomys spinosissimus from South Africa was investigated under controlled laboratory conditions. Nine individuals were subjected to six successive light cycles of approximately 2 weeks each as follows: (1) a standard light/dark (12:12LD) cycle; (2) a period of constant darkness (DD); (3) a second standard light/dark (12 L:12D) cycle; (4) an inverse of the LD (12:12DL) cycle; (5) a short day cycle (8:16LD); and (6) a long day cycle (16:8LD). All the animals exhibited entrainment of their activity to the LD and DL lighting regimes. Locomotor activity of A. spinosissimus occurred predominantly during the dark phases of the LD, DL, long day and short day cycles. Under LD, the mean percentage of activity was 88.7 ± 0.07% during the dark phase. When subjected to constant darkness, all animals expressed free‐running rhythms of locomotor activity (mean ± 1 standard deviation = 23.81 ± 0.33 h; range = 23.2–24.1 h). On the reverse LD cycle, the mean percentage of activity was 81.4 ± 0.09% during the dark phase of the cycle. Mice exhibited significantly more daytime activity during the long day cycle (20.3 ± 5.8%) and no significant change in dark phase activity during the short day cycle (90.1 ± 4.01). The spiny mouse possesses a circadian rhythm of locomotor activity that entrains strongly to light. Locomotory activity occurs predominantly during the dark phase and can therefore be considered a nocturnal mammal.
Small mammals, and particularly shrews and mice, have relatively high mass-specific metabolic rates and may be constrained to habitats where they can avoid extreme temperatures. Although their phylogeny differs, shrews and rodents often inhabit the same environments and compete for resources due to their similar body masses and dietary overlap. Our aim was to elucidate the variation in thermal parameters of sympatric species. We examined Myosorex varius, Crocidura flavescens and Mus minutoides, by measuring metabolic rate, evaporative water loss (EWL), body temperature (T b ) and thermal conductance over a range of ambient temperatures (T a ). Body temperatures of all three species remained above 32°C across the range of T a . For all species, there was no relation between T a <35°C and EWL, although EWL in C. flavescens was considerably lower compared to the other two species. Dry thermal conductance was much higher in Mu. minutoides than in either of the shrews. Resting metabolic rate of all three species declined with T a <35°C. The thermoneutral zone of My. varius was between T a = 35°C and T a = 40°C, whereas that of C. flavescens was between T a = 30°C and T a = 33°C. No discernible thermoneutral zone was evident for Mu minutoides. Our data reveal considerable variation in thermal physiology among three sympatric species of small mammal at a single site and generally conform to the plesiomorphic-apomorphic endothermy model. Differences in body size, life-history traits and evolutionary history may all play a role in the thermoregulatory patterns of these sympatric species.
Photoperiodism involves the use of both absolute measures of day length and the direction in which day length is changing as a cue for regulating seasonal changes in physiology and behaviour so that birth and lactation coincide with optimal resource availability, increasing offspring survival. Induced ovulation and opportunistic breeding is often found in species that are predominantly solitary and territorial. In this study, the photoperiodic reproductive responses of male greater red musk shrews (Crocidura flavescens (I. Geoffroy Saint-Hilaire, 1827)) were investigated in the laboratory. The presence of spermatozoa regardless of the light cycle, suggest that although the shrews are photoresponsive, they may be capable of breeding throughout the year. Significantly greater testicular volume and seminiferous tubule diameter following exposure to a short day-light cycle suggests that these animals may have breeding peaks that correspond to short days. The presence of epidermal spines on the penis indicates that the shrew is likely also an induced ovulator.Flexible breeding patterns combined with induced ovulation affords this solitary species the greatest chance of reproductive success. ___________________________________________________________________
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.