Interactive effects of temperature and photoperiod on the daily activity and energy metabolism of pouched mice (Saccostomus campestris: Cricetidae) from southern Africa

The daily activity and energy metabolism of pouched mice (Saccostomus campestris) from two localities in southern Africa was examined following warm (25 °C) and cold (10 °C) acclimation under long (LD 14:10) and short (LD 10:14) photoperiol. There was no differential effect of photoperiod on the daily activity or metabolism of pouched mice from the two localities examined, which suggests that reported differences in photoresponsivity between these two populations were not the result of differences in daily organisation. Neverthe-less, there was a significant increase in metabolism at 10 °C, irrespective of photoperiod, even though seven cold-acclimated animals displayed bouts of spontaneous torpor and saved 16.4–36.2% of their daily energy expenditure. All but one of these bouts occurred under short photoperiod, which suggests that short photoperiod facilitated the expression of torpor and influenced the daily energy metabolism of these individuals. As expected for a noctureal species, the amount of time spent active increased following acclimation to short photoperiod at 25 °C. However, there was a reduction in mean activity levels under short photoperiod at 10 °C, possibly because the stimulation of activity by short photoperiod was masked by a reduction in activity during bouts of spontaneous torpor. Cold temperature clearly had an overriding effect on the daily activity and metabolism of this species by necessitating an increase in metabolic heat production and eliciting spontaneous torpor which overrode the effect of short photoperiod on activity at an ambient temperature of 10 °C.Abbreviations 3-ANOVA three-way analysis of variance - %ACT percentage of time spent active - ADMR average daily metabolic rate - M _b body mass - MR metabolic rate - MR_dark metabolic rate recorded during the dark phase - MR_light metabolic rate recorded during the light phase - NST non-shivering thermogenesis - RQ respiratory quotient - STPD standard temperature and pressure, dry - T _a ambient temperature - T _b body temperature - VO₂ oxygen consumption     

The relative importance of photoperiod and temperature as cues for seasonal acclimation of thermoregulation in pouched mice (Saccostomus campestris: Cricetidae) from southern Africa

Summary The effect of short photoperiod and cold on metabolism and thermoregulation was investigated in pouched mice (Saccostomus campestris: Cricetidae) from three localities in southern Africa which experience contrasting climatic conditions. Mice were initially acclimated to long photoperiod (14L: 10D) at 25°C, followed first by a decline in photoperiod (to 10L: 14D) and then by a fall in temperature (to 10°C). Minimum observed metabolic rate (basal metabolic rate) was unaffected by the decline in photoperiod but increased significantly following cold acclimation. Because minimal thermal conductance remained constant throughout the study the increase in minimum observed metabolic rate caused a decline in lower critical temperature to around 26°C. In contrast to minimum observed metabolic rate, regulatory non-shivering thermogenesis improved significantly following the decline in both photoperiod and temperature. However, pouched mice from the warmest locality were significantly less responsive to photoperiod than those from the other two localities whose survival might depend upon their ability to accurately predict seasonal changes in temperature. Neither photoperiod nor temperature had any effect on body mass, yet pouched mice from the most arid locality, where food supply might be unpredictable, were significantly smaller and had lower total energy requirements than those from areas experiencing higher annual rainfall. These results indicate that S. campestris displays considerable geographical variation in energy requirements together with differences in the use of photoperiod as an anticipatory cue for predicting the onset of winter. These differences appear to be related to the availability of energy and the relative severity of climatic conditions in each locality.Abbreviations ANOVA analysis of variance - BMR basal metabolic rate - C _m minimal thermal conductance - M _b body mass - MOMR minimum observed metabolic rate - MWU Mann-Whitney U-test - NA noradrenaline - NST non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - T _a ambient temperature - T _b body temperature - T _1c lower critical temperature - oxygen consumption - maximum - following NA injection     

Seasonal energy requirements and thermoregulation of growing pouched mice,Saccostomus campestris (Cricetidae)

Pouched mice (Saccostomus campestris) were born in captivity during January and March and subsequently maintained under long photoperiod (14 h light: 10 h dark) at 25°C. During their first winter (July) and the following summer (January) the pouched mice were exposed to natural photoperiod in an unheated laboratory for 3 weeks prior to measurement. The pouched mice continued to grow during the study, and were significantly heavier after summer exposure than after winter exposure 6 months earlier. Although this increase in body mass would result in a decline in their surface area to volume ratio there was no significant decline in minimal thermal conductance (C _m) and winter-exposed pouched mice had a relatively lowerC _m than expected. Meanwhile the smaller, winter-exposed animals displayed a significantly higher capacity for non-shivering thermogenesis, together with higher levels of basal metabolism than summer individuals. These differences were not solely attributable to the contrasting body mass of each group and it is therefore clear thatS. campestris can increase thermoregulatory heat production, and modify heat loss following exposure to short photoperiod and cold during their first winter. Despite the significant increase in metabolism, the overall energy requirements of small, winter-exposed animals were significantly lower than those for heavier pouched mice following exposure to summer conditions. These results suggest that growing pouched mice can effectively adapt to lower temperature conditions during their first winter, yet accrue considerable overall savings in total energy requirements as a result of their smaller body mass.     

Reproductive activity influences thermoregulation and torpor in pouched mice, Saccostomus campestris

The Afrotropical pouched mouse Saccostomus campestris displays sexual disparity in the use of daily torpor; males reluctantly enter torpor. We tested the hypothesis that males may compensate for a limited heterothermic capacity with lower basal and resting metabolic rates relative to females. We also investigated the association between gonadal activity (testosterone) and the propensity for daily torpor. Body temperature and oxygen consumption were measured at various ambient temperatures and were compared between sexes under ad libitum and restricted-diet treatments. Whereas no significant sex differences were observed in body temperature and oxygen consumption under ad libitum treatment, there were pronounced differences in heterothermic responses under food restriction. Females employed torpor more frequently and also had lower minimum torpor body temperatures (ca. 25 degrees C) than males (ca. 29 degrees C). Testosterone inhibited torpor in males, whereas the majority of saline-treated animals employed torpor under both ad libitum and restricted-diet treatments. This study demonstrated that the limited capacity of male S. campestris to enter torpor is a consequence of reproductive activity and that opportunistic breeding and the absence of seasonal testes regression compromises the capacity to conserve energy through daily torpor.     

Noradrenaline thermogenesis in conscious and anaesthetised pouched mice (Saccostomus campestris)

1. The metabolic response to injections of noradrenaline (NA) and saline (control) was investigated in conscious and anaesthetised (sodium pentobarbitone) pouched mice, Saccostomus campestris. 2. NA injection produced a calorigenic response which was significantly greater than that elicited by saline injection in both conscious and anaesthetised animals. 3. This calorigenic response was enhanced by motor activity in conscious pouched mice, but the exclusion of measurements recorded during visible activity eliminated the influence of movement. 4. Anaesthetised pouched mice underwent mild Hypothermia and displayed a retarded metabolic response to NA injection which suggests that anaesthesia affects the expression of NA-induced thermogenesis. 5. The validity of proposed techniques for the measurement of NA thermogenesis is further discussed.     

Pre- and post-natal development of pouched mice, Saccostomus campestris

Pre- and post-natal growth of the pouched mouse ( Saccostomus campestris ) were investigated and growth curves were calculated as described by Stevens (1951). Measured values of foetal weights put into Huggett & Widdas' equation (1951) revealed that the actual correction factor for species with a gestation period of 50 days or shorter was different from the one given by Huggett & Widdas. Therefore, the calculated value of specific growth velocity for pouched mice was lower than when using the correction factor given by Huggett & Widdas (1951).
Ninety percent of the asymptotic body weight was attained at an average age of 135.2 and 143.1 days for males and females, respectively, while 90% of the asymptotic body length was achieved when males and females were 71.9 and 69.3 days old, respectively. Post-natal growth rates of females and males were not significantly different from each other, and the average rate of weight increase for male and female pouched mice was lower than for other rodents studied (see Case, 1978).
Ages at which tooth eruption, eye-opening and eye usage occurred were also recorded.     

Fostering in an African rodent, Saccostomus campestris (Cricetidae)

Fostering was studied in females of an African rodent Saccostomus campestris , the pouched mouse, which, contrary to most other rodents, is a solitary species. Females will only tolerate their own offspring and other adults are viciously attacked at all times except during the short period of pro-oestrus, when a male will be temporarily accepted.
Alien pups (n = 857) of different age-groups (0–30 days) were introduced to lactating females (n = 191) with their own pups (n = 1053) of different age-groups (0–20 days) over a period of three years. The total number of pups per female was made up to 10 (e.g. 7 own + 3 alien or 4 own + 6 alien).
The 'foster mother' readily accepted and successfully reared alien pups provided they were less than 21 days of age when introduced. Weaned alien pups, introduced when 25 or 30 days old, were viciously attacked by the foster mother and had to be removed, althoughin the breeding colony, pups that were allowed to remain with their mother after weaning were not attacked. It appears that up to weaning-age, female Saccostomus campestris may not distinguish between may not distinguis between their own and alien offspring, but rather between suckling and weaned pups.     

Evolution of African mole-rat sociality: burrow architecture, rainfall and foraging in colonies of the cooperatively breeding Fukomys mechowii

African mole rats (Bathyergidae) offer an excellent system with which to test theories relating to the evolution and maintenance of sociality in mammals. The aridity food distribution hypothesis (AFDH) suggests that, within the bathyergids, sociality has evolved in response to patterns of rainfall, its effects on food distribution, and the subsequent costs and risks of foraging and dispersal. Here, in the first detailed study of burrow architecture in a social mole-rat species, with data from 32 burrows, we show that in the giant mole-rat Fukomys mechowii burrow fractal dimension increases with colony size and is higher during the rainy season than during the dry season. The mass of food in the burrow increases with fractal dimension and is higher during the rainy season than during the dry season. These results link for the first time colony size, burrow architecture, rainfall and foraging success and provide support for two assumptions of the AFDH, namely that (1) in arid conditions burrowing may be severely constrained by the high costs of digging; and (2) the potential risks of failing to locate food may be mitigated by increases in colony size.     

Chromosomal evolution of the brown mice,genus Scotinomys (Rodentia: Cricetidae)

Early taxonomic investigations associated the genus Scotinomys with South American akodontine rodents, but more recent morphological analyses based in large part on the glans penis have linked brown mice with North American peromyscines, specifically the genus Baiomys. Differentially stained chromosomal preparations of S. xerampelinus were compared with other cricetine taxa. Chromosomally, golden mice (Ochrotomys) were found to be most similar to Scotinomys, this association based on two apparent synapomorphic G-banded chromosomes. The majority of banded chromosomes possessed by Scotinomys were found to be either uniquely derived or to appear unaltered, and therefore presumably ancestral, when compared to the G-band patterns of other cricetids. These results fail to support the morphological hypotheses that closely unite Scotinomys with Baiomys, and instead support a hypothesis that treats Scotinomys, Ochrotomys, and perhaps Baiomys as a rather loosely associated assemblage of genera that are phylogenetically intermediate between the relatively complex pene, primarily South American cricetine rodents and the more simple pene North American neotomine-peromyscines.     

Production of inulinase by Xanthomonas campestris pv phaseoli using onion (Allium cepa) and garlic (Allium sativum) peels in solid state cultivation

AIMS: To access inulinase production by Xanthomonas campestris pv phaseoli using the submerged and solid state cultivation (SSC) methods. METHODS AND RESULTS: Various carbon sources, inulin-rich solid substrates and pure synthetic inulin were tested for their efficiency in inulinase induction. The highest inulinase production (17.42 IU ml(-1)) in submerged cultures of X. campestris was observed with inulin as a carbon source with an initial pH, temperature and agitation of 7.0, 37 degrees C and 150 rev min(-1) respectively. Among the various substrates, garlic peels (117 IU gds(-1)) and onion peels (101 IU gds(-1)) were found to be the best for inulinase production. CONCLUSION: The inulinase production level of X. campestris was 6.7-fold higher in garlic and 5.8-fold in onion, under optimized SSC conditions compared with the submerged culture. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report on inulinase production from garlic and onion peels by X. campestris using SSC. SSC is an efficient method for inulinase production by X. campestris for commercial applications.     

Group size, grooming and fission in primates: a modeling approach based on group structure

In social animals, fission is a common mode of group proliferation and dispersion and may be affected by genetic or other social factors. Sociality implies preserving relationships between group members. An increase in group size and/or in competition for food within the group can result in decrease certain social interactions between members, and the group may split irreversibly as a consequence. One individual may try to maintain bonds with a maximum of group members in order to keep group cohesion, i.e. proximity and stable relationships. However, this strategy needs time and time is often limited. In addition, previous studies have shown that whatever the group size, an individual interacts only with certain grooming partners. There, we develop a computational model to assess how dynamics of group cohesion are related to group size and to the structure of grooming relationships. Groups’ sizes after simulated fission are compared to observed sizes of 40 groups of primates. Results showed that the relationship between grooming time and group size is dependent on how each individual attributes grooming time to its social partners, i.e. grooming a few number of preferred partners or grooming equally or not all partners. The number of partners seemed to be more important for the group cohesion than the grooming time itself. This structural constraint has important consequences on group sociality, as it gives the possibility of competition for grooming partners, attraction for high-ranking individuals as found in primates’ groups. It could, however, also have implications when considering the cognitive capacities of primates.     

Ecogeographic variation in body size and shape of Cape sparrows (Passer melanurus) in southern Africa

Canonical discriminant analyses were used to assess whether four populations of Cape sparrows varied in body size and shape according to predictions from Bergmann's Rule. In accordance with Bergmann's Rule, birds from two hot, arid Namib desert sites (Namib 1 and Namib 2) were smaller than birds from two cool, mesic Transvaal sites. If heat dissipation through extremities (tarsi) is important to reduce water lost from evaporative cooling, birds under hot conditions in dry environments (Namib 2) should have longer tarsi than those in more humid hot environments (Namib 1). Contrary to this, males at Namib 2 had relatively longer wings hut shorter tarsi than at Namib 1, and female relative tarsus length did not vary between desert sites     

Genetic structure of sigmodontine rodents (Cricetidae) along an altitudinal gradient of the Atlantic Rain Forest in southern Brazil

The population genetic structure of two sympatric species of sigmodontine rodents (Oligoryzomys nigripes and Euryoryzomys russatus) was examined for mitochondrial DNA (mtDNA) sequence haplotypes of the control region. Samples were taken from three localities in the Atlantic Rain Forest in southern Brazil, along an altitudinal gradient with different types of habitat. In both species there was no genetic structure throughout their distribution, although levels of genetic variability and gene flow were high.     

Distribution,diversity and conservation of Anostraca (Crustacea: Branchiopoda) in southern Africa

Southern Africa is defined here as Africa south of the Zambezi and Kunene Rivers. Here, annual average rainfall, rainfall season, and effective temperature are climatic factors which influence anostracan distribution. The type of temporary pool also appears to have some effect on distribution. Areas of high species richness are not confined to any particular climatic region and such areas occur in arid, montane and subtropical regions of southern Africa. Forty-six anostracan species have been recorded from the subcontinent and 80% of these are endemic. IUCN Red Data assessment of species revealed that two species can be considered 'Critically Endangered', while a further four are 'Endangered', and three are 'Vulnerable'. Many parts of southern Africa have been inadequately sampled but in South Africa, where the anostracans are relatively well known, temporary pool inhabitants are threatened mainly by agriculture, urbanization, pollution and pesticides. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ozone affects gas exchange, growth and reproductive development in Brassica campestris (Wisconsin fast plants)

Exposure to ozone (O(3)) may affect vegetative and reproductive development, although the consequences for yield depend on the effectiveness of the compensatory processes induced. This study examined the impact on reproductive development of exposing Brassica campestris (Wisconsin Fast Plants) to ozone during vegetative growth. Plants were exposed to 70 ppb ozone for 2 d during late vegetative growth or 10 d spanning most of the vegetative phase. Effects on gas exchange, vegetative growth, reproductive development and seed yield were determined. Impacts on gas exchange and foliar injury were related to pre-exposure stomatal conductance. Exposure for 2 d had no effect on growth or reproductive characteristics, whereas 10-d exposure reduced vegetative growth and reproductive site number on the terminal raceme. Mature seed number and weight per pod and per plant were unaffected because seed abortion was reduced. The observation that mature seed yield per plant was unaffected by exposure during the vegetative phase, despite adverse effects on physiological, vegetative and reproductive processes, shows that indeterminate species such as B. campestris possess sufficient compensatory flexibility to avoid reductions in seed production.     

Evaluation of a mathematical model structure describing the effect of (gel) structure on the growth of Listeria innocua, Lactococcus lactis and Salmonella Typhimurium

Aims:  To evaluate a novel secondary model structure ( Int J Food Microbiol 2008; 128: 67) that describes the effect of medium structure on the maximum specific growth rate ( μ _max) of Salmonella Typhimurium on the growth of S. Typhimurium, Listeria innocua , Lactococcus lactis and Listeria monocytogenes .
Methods and Results:  In the present study, the novel secondary model is validated for S . Typhimurium in more realistic media, namely, pasteurized milk and a cheese mimicking medium. The predictions were accurate. Next, the secondary model structure was evaluated in a two step and a global regression procedure on literature data. On the one hand, the growth of two other micro-organisms, namely L. innocua and L. lactis , in monoculture for varying gelatine concentrations was tested and on the other hand the growth rate of L. monocytogenes was fitted in a broth of which the viscosity was altered with polyvinylpyrrolidone. The model was able to describe the effect of increasing gelatine concentration or viscosity accurately.
Conclusions:  The proposed secondary model structure is able to describe the effect of gelatine concentration on the μ _max of the micro-organisms tested in this study.
Significance and Impact of the Study:  In predictive microbiology, much attention has been paid to the effect of food structure on the μ _max of bacteria. However, to the authors' knowledge, a lack of secondary models still exists to describe this effect. Although the proposed model is empirical, the model parameters have clear biological meaning. The predictive power of the model to describe the effect of food structure is clearly illustrated.     

Pollen morphology of Canthium,Keetia and Psydrax (Rubiaceae: Vanguerieae) in southern Africa

Pollen of all the southern African members of Canthium, Keetia and Psydrax was studied by means of LM, SEM and TEM. Palynologically these three genera can easily be distinguished from one another, exine structure and sculpturing being the most useful characters. The sexine is essentially perforate with short columellae not usually distinguishable in SEM in the Canthium type, coarsely reticulate with long columellae in the Keetia type and more finely reticulate with short columellae in the Psydrax type. Palynologically Canthium sensu stricto (used here to refer to the Canthium complex excluding Psydrax, Keetia and Pyrostria) is clearly distinct from Keetia and Psydrax, but similar to the other members of the Vanguerieae. This supports the proposed subdivision of Canthium sensu lato in southern Africa into these three genera. Differences amongst the various Canthium sensu stricto species suggest at least three different pollen sub‐types. Bridson's placement of C. inerme and C. suberosum in the subgenus Lycioserissa is supported by the pollen morphology. It is suggested that C. ciliatum, C. kuntzeanum, C. spinosum and C. vanwykii may also belong to this subgenus. The following placements are supported by palynology: C. gilfillanii and C. mundianum in the subgenus Afrocanthium and C. setiflorum in Bullockia.

The presence of intine protruding from the apertures is shown not to be an artefact, but a phenomenon characteristic of many Rubiaceae. The term “protruding oncus”; is proposed for these structures.