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PubMed2003

The evolution of placental mammal body sizes: evolutionary history, form, and function.

The unimodal, right-skewed distribution, most frequently identified in contemporary descriptions of placental mammal body size distributions, masks an underlying multidistribution structure; a long-term evolutionary process that has generated a concatenation of two or three frequency distributions specific to locomotory modes (plantigrade, digitigrade and unguligrade). The Afrotropical assemblages are bimodal, with a tendency towards trimodality, whereas the Nearctic assemblage is unimodal. However, mixtures of two and three normal distributions fitted the Nearctic data well, suggesting a multidistribution structure masked by disproportionate species numbers within locomotory modes. Differences in proportional species numbers within modes between assemblages may reflect the evolutionary history of form and function. However, common interassemblage predictions of such proportions in contemporary distributions may be disguised by the relative severity of the Pleistocene megafaunal extinction (patterns supported by the fossil record), geographical scale, and taxonomic composition. A species gap occurs at body sizes around 1 kg at the interface between the largest plantigrade mammals and the smallest digitigrade mammals, coincident with the minimum interspecific variance of basal metabolic rate. In terms of the evolution of the optimal body size in the trade-off between mortality and production, there may be good historical and evolutionary reasons why we should not expect optimization to produce the same results in different zoogeographical assemblages. Moreover, the evolution of diverse mammalian forms and functions, especially with respect to predator-prey interactions and diet, render a single body size optimum untenable in the search for an energetic definition of fitness.

Adaptation, Physiological↗
PubMed2004

Ancient ecology of 15-million-year-old browsing mammals within C3 plant communities from Panama.

Middle Miocene mammals are known from approximately 15 million-year-old sediments exposed along the Panama Canal of Central America, a region that otherwise has an exceedingly poor terrestrial fossil record. These land mammals, which represent a part of the ancient terrestrial herbivore community, include an oreodont Merycochoerus matthewi, small camel-like protoceratid artiodactyl Paratoceras wardi, two horses Anchitherium clarencei and Archaeohippus sp., and two rhinos Menoceras barbouri and Floridaceras whitei. Bulk and serial carbon and oxygen isotope analyses of the tooth enamel carbonate allow reconstruction of the ancient climate and ecology of these fossil mammals. Ancient Panama had an equable climate with seasonal temperature and rainfall fluctuations less than those seen today. The middle Miocene terrestrial community consisted predominantly, or exclusively, of C3 plants, i.e., there is no evidence for C4 grasses. Statistically different mean carbon isotope values for the mammalian herbivores indicate niche partitioning of the C3 plant food resources. The range of individual carbon isotope analyses, i.e., delta13C from -15.9 to -10.1 per thousand, indicates herbivores feeding on diverse plants from different habitats with extrapolated delta13C values of -29.9 to -24.2 per thousand, possibly ranging from dense forest to more open country woodland. The ecological niches of individual mammalian herbivore species were differentiated either by diet or body size.

Animals↗
PubMed2005

The effect of dietary protein quality on nitrogen isotope discrimination in mammals and birds.

We tested the competing hypotheses that (1) nitrogen discrimination in mammals and birds increases with dietary nitrogen concentration or decreasing C:N ratios and, therefore, discrimination will increase with trophic level as carnivores ingest more protein than herbivores and omnivores or (2) nitrogen discrimination increases as dietary protein quality decreases and, therefore, discrimination will decrease with trophic level as carnivores ingest higher quality protein than do herbivores. Discrimination factors were summarized for five major diet groupings and 21 different species of birds and mammals. Discrimination did not differ between mammals and birds and decreased as protein quality (expressed as biological value) increased with trophic level (i.e., herbivores to carnivores). Relationships between discrimination factors and dietary nitrogen concentration or C:N ratios were either the opposite of what was hypothesized or non-significant. Dietary protein quality accounted for 72% of the variation in discrimination factors across diet groupings. We concluded that protein quality established the baseline for discrimination between dietary groupings, while other variables, such as dietary protein intake relative to animal requirements, created within-group variation. We caution about the care needed in developing studies to understand variation in discrimination and subsequently applying those discrimination factors to estimate assimilated diets of wild animals.

Animals↗
PubMed1991

The evolution of placental mammals.

Based on morphological, virological, biochemical and molecular biological data, it is proposed that the presence of endogenous retrovirus particles in the placental cytotrophoblasts of many mammals is indicative of some beneficial action provided by the virus in relation to cell fusion, syncytiotrophoblast formation and the creation of the placenta. Further, it is hypothesised that the germ line retroviral infection of some primitive mammal-like species resulted in the evolution of the placental mammals.

Animals↗
PubMed1978

The scaling of maximal oxygen consumption and pulmonary dimensions in small mammals.

This report has reexamined the relationship between standard and maximal rates of oxygen consumption (VO2std and VO2max) and pulmonary surface area in mammals whose weights extend over the lower half of the total log weight range in mammals. For combined groups of wild and laboratory animals with body weights of 2--3700 g, the following equations pertain: VO2std (ml . min-1) = 0.0602 . W0.727; VO2std, or the factorial aerobic scope, is nearly constant over this weight range at approximately 6.6 (range 5.8--7.1). In view of this finding, earlier studies relating SA or pulmonary diffusion capacity to VO2std are still appropriate models for pulmonary constraints on metabolic rate. The data summarized here suggest that, at least for wild species of mammals, pulmonary diffusion capacity may limit VO2max.

Animals↗
PubMed1995

Scaling of hypercapnic ventilatory responsiveness in birds and mammals.

The possible relationship between CO2 responsiveness and body mass in birds was explored using newly acquired ventilatory data from the barn swallow, Hirundo rustica, and the pigeon, Columbia livia, and that from the literature on four other species. Ventilatory responsiveness (% delta V) of birds to 5% inspired CO2 is scaled to body mass to the 0.145 power (% delta V alpha Mb 0.145). A similar allometric relationship exists for data on 7 species of eutherian mammals taken from the literature (% delta V alpha Mb0.130). The The reduced responsiveness to CO2 in small birds and mammals may be related to an elevated hypoxic ventilatory sensitivity, as demonstrated in mammals (Boggs and Tenney, Respir. Physiol. 58: 245-251, 1984). These scaling relationships may reflect a mechanism for minimizing the inhibition of ventilation resulting from excessive loss of CO2 which thereby permits a higher hypoxic ventilatory response in small species. Other mechanisms, however, could include size related differences in mechanics or alveolar ventilation.

Animals↗
PubMedDate not supplied

Sylvatic American trypanosomiasis in Argentina. Trypanosoma cruzi infection in mammals from the Chaco forest in Santiago del Estero.

Trypanosoma cruzi infection in sylvatic mammals of the quebracho woods of the eastern part of Santiago del Estero province, Argentina, was studied from October 1984 to December 1987. 301 mammals of 20 different species were caught. T. cruzi, characterized biologically and biochemically, was isolated by xenodiagnosis from 23 of 72 (32%) Didelphis albiventris opposums, 2/36 (5.5%) Conepatus chinga skunks, and one ferret (Galictis cuja). 53 opossum refuges were located and triatomine bugs were found in 2 of them: one male Triatoma infestans, infected with T. cruzi, and 5 uninfected nymphs of T. sordida, had all fed on opossum blood. Electrophoretic zymogram patterns of the T. cruzi populations isolated from opossums and skunks were similar to isoenzyme profiles already described for populations isolated from infected humans in Argentina. The small number of triatomines found in the opossum refuges seems inadequate to account for the prevalence of T. cruzi infection recorded for these mammals, so other possible contaminative routes of infection should be investigated.

Animals↗
PubMed1981

The relationship of DNA excision repair of ultraviolet-induced lesions to the maximum life span of mammals.

Physical and chemical agents present in the environment can potentially damage mammalian DNA. Such damage is known in some cases to be repaired by the process of DNA excision repair. This process has been extensively studied utilizing the repair of ultraviolet irradiation damage as a model system. In this study we have used this system and the 5-bromodeoxyuridine photolysis assay to measure DNA excision repair in cells derived from 21 mammalian species. We have attempted to relate the DNA repair proficiencies and the average size of the repaired regions seen in the cell cultures with the various maximum life spans of the mammals studied. There was an approximate linear correlation between life span of the mammals and the number of DNA excision repair sites measured 20-22 hours following ultraviolet irradiation of the cell cultures. Several deviations from the linear relationships were observed which remain largely unexplained. The size of the repaired regions was shown not to be related to the maximum life spans of the mammals tested.

Animals↗
PubMed1994

Toxicokinetics of chlorobiphenyls and associated physiological responses in marine mammals, with particular reference to their potential for ecotoxicological risk assessment.

For the conservation of marine mammals and their ecosystem, it is important to know whether or not they are exposed to intolerable levels of environmental pollutants. In some case studies on marine mammals, xenobiotics can be linked to reproductive and immunological disorders. Disturbed endocrine systems seem to be a common denominator, whereby metabolization systems dealing with xenobiotic as well as endocrine compounds are involved. Two sets of indicators are distinguished to evaluate the toxicity of organochlorine residues found in marine mammal tissues. These are (1) interactions of chlorobiphenyls with the cytochrome P450 enzyme system and (2) comparative physical and chemical blood parameters directly and indirectly obtained via functional immunoassays. Apart from the constitutive enzymes, the induction of each of the other 150 isoenzymes of the P450 system exhibits substrate (= compound) specificity and moreover organisms develop species and even organ specific induction profiles. Therefore, a specific enzyme profile for each compound in a given species/organ may exist. The biotransformation capacity, constitutive and/or induced, will be reflected in the extent to which biotransformation of the chlorinated biphenyls in question has occurred. This can be expressed in the ratio of the concentration of a given individual biphenyl to the concentration of a persistent reference individual biphenyl. Both these indicators will provide information on which compounds are most likely involved and to what extent. The directly obtained blood parameters include levels of vitamin A, steroid hormones and thyroxine. The blood parameters acquired via functional immunoassays include mitogen- and antigen-induced proliferative responses of peripheral blood mononuclear cells (PBMC) and natural killer (NK) activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Venomous mammals.

It is not widely appreciated that mammals can be venomous in the manner of snakes and lizards. However, it was first demonstrated scientifically 50 years ago in the case of the American short-tailed shrew. Subsequently, similar evidence has been obtained from European shrews and the Haitian solenodon, but research in this area has been almost completely neglected for the last 20 years. In complete contrast to what has been learned about other animal venoms, the identity and mode of action of mammal venom toxins are still unknown. This review draws attention once more to the pioneering work undertaken in the 1940s and 1950s, exploring in more detail than hitherto why the implications of mammal venom are just as important as the chemistry and pharmacology of the phenomenon itself.

Animals↗
PubMed1992

Prolactin as an immunoregulatory hormone in mammals and birds.

The immunoregulatory function of prolactin (PRL) and the mechanism of its action in mammals seem to be well documented. Reciprocal interdependence between PRL secretion and immune system function is essential for normal ontogeny, development and aging. PRL receptors in lymphocytes participate in the transduction of its regulatory signal into the intracellular enzymatic machinery including that of the nucleus, leading to the expression of some genes and to the synthesis of new proteins. Activation of phosphoinositide turnover and subsequent increase in protein kinase-C activity seems to be a possible mechanism acting in the regulatory influence of PRL on mammalian immune cells. These cells in turn, under mitogen or antigen stimulation, secrete a substance with PRL-like activity. The regulatory function of PRL within the avian immune system is less well known, but it seems to have some features in common with those in mammals. Direct mitogenic action on thymocytes and splenocytes in the chicken might indicate the existence of PRL receptors in these cells and could explain the immunostimulatory effect of PRL observed in vivo, which is dependent on the time of hormone administration. As the avian PRL stimulates mitogenesis of rat Nb2 lymphoma cells, the mechanism of direct PRL action on immune cells in mammals and birds seems to be similar. PRL in chickens also modifies the level and the diurnal rhythm of corticosterone which, in turn, influences the immunoregulatory effect exerted by PRL. Thus, PRL seems to be an important factor, influencing directly or indirectly the avian immune system.

Animals↗
PubMed1988

Central and systemic antidiuretic hormone and angiotensin II in salt and fluid balance of birds as compared to mammals.

1. Tonicity dominates the release of ADH with similar sensitivities (0.2-1 pg/ml per mOsm/kg) for both birds and mammals. 2. There is an inverse relationship between the volume of the extracellular fluid compartments and the plasma level of ADH. 3. Angiotensin II formation is governed by volume factors. 4. In birds the factors reducing the delivery of Na+ to the nephron distal tubules stimulate ANGII formation. 5. Mammals have a high vascular constrictor sensitivity to ADH and ANGII; there is little or no vascular sensitivity to these in birds. 6. In birds and mammals the subfornical organ and other circumventricular organs have receptors that specifically bind ANGII. 7. Dog and duck CSF levels of ADH and AII indicate their function as specific mediators of intrinsic neuronal systems controlling salt and fluid balance.

Angiotensin II↗
PubMed1988

Comparison of serum protein inhibitors from various mammals, chicken and silkworms against four proteases.

1. Protein serum inhibitors against four proteases were compared using eight mammals, chicken and silkworms. 2. The similarity of inhibition spectra and electrophoretograms was found in related mammals. 3. In the silkworm and chicken, inhibitory activities against fungal protease and subtilisin were extremely high. 4. Electrophoretic patterns of inhibitors for chymotrypsin and trypsin were very similar in mammals, but different in the silkworm, that is, mammalian inhibitors seemed to show broader protease specificity. 5. Electrophoretic bands of the silkworm inhibitors showed more dispersed molecular species than those of other animals. 6. Column chromatographic patterns of silkworm inhibitors against four proteases showed more diverse and distinct profiles than those of other animals.

Animals↗
PubMed1993

Comparative mammal model of chronic rate overload: relationship of myocardial Ca-cycling to heart, metabolic and lipoperoxidation rates.

1. The cardiac cycle is generally believed to be timed by a sarcoplasmic Ca-cycle and powered by a sarcoplasmic ATP-cycle that uses fatty acids as fuel and generates toxic free radicals as a side-product. 2. This study used a comparative mammal approach to test this model and the hypothesis that these cycles were closely coupled and correlated with fatty acid oxidation and peroxidative injury. 3. Fatty acid oxidation and ATP-cycling rates correlated to log heart rate whereas Ca-cycling rate was directly coupled to heart rate in a one-to-one relationship. 4. Both Ca-pump and Ca-channel activities coordinately increased as heart rate increased across species. 5. Thus, Ca-cycling activity is constant across mammals, when normalized to heart rate. 6. Comparison of Ca-ATPase and Ca-flux rates indicated that sarcoplasmic volume was inversely correlated with log heart rate. Basal lipoperoxidation of myocardium and susceptibility of SR to lipoperoxidation correlated with metabolic rate. 7. We identified that the horse is a metabolic outlier amongst mammals, with abnormally high fatty acid oxidation and ATP-synthetase activity compared to its heart rate.

Animals↗
PubMed1995

Towards a molecular biology of the circadian clock and sleep of mammals.

Behavioral states of rest and activity are temporally organized. Since the beginning of life on Earth, plants and animals have been forced to adapt to the daily rhythm of the planet's rotation about its axis. In complex vertebrates (birds and mammals), rest and activity have evolved into the electrophysiologically and behaviorally distinct states of sleep and wakefulness. The evolutionary emergence of bouts of rapid eye movement (REM) sleep may be even more recent; the echidna, one of the earliest mammals, lacks this sleep stage (Siegel et al., 1994), The cycling of these behavioral states is under neural control, and much is known about their cellular basis, but the underlying events at the molecular level are virtually unknown. Here each of us highlights some of the new approaches for investigating the molecular substrate for behavioral state control of circadian rhythmicity (WJS) and sleep (PJS) in mammals.

Animals↗
PubMed2006

The linear allometric relationship between total metabolic energy per life span and body mass of mammals.

The aim of this study is to establish and calculate the exact allometric relationship between the total metabolic energy per life span and the body mass in a wide range of mammals with about six orders of magnitude variation of the body mass of animals. The study shows that it exists a linear relationship between the total metabolic energy per life span PT(ls) (kJ) and the body mass M (kg) of 95 mammals (3 monotremes, Subclass Prototheria, 16 marsupialis (Subclass Theria, Infraclass Metatheria) and 76 placentals (Subclass Theria, Infraclass Eutheria)) from type: PT(ls)=A(ls)(+)M(1.0511), where P (kJ/day) is the basal rate of metabolism and T(ls) (days) is the mean life span of animals. The linear coefficient A(ls)(+)=7.158x10(5) kJ/kg is the total metabolic energy, exhausted during the life span per 1 kg body mass of the animals. The mean values of the total metabolic energy per life span, per unit body mass (A(ls)) for orders from Subclass Prototheria and Theria (Infraclass Metatheria) and orders Xenarthra, Pholidota, Soricomorpha, Rodentia (Infraclass Eutheria) varied negligible in interval (4.656-5.80)x10(5) kJ/kg. The coefficient A(ls) grows from (7.68-8.36)x10(5) kJ/kg in Lagomorpha and Artiodactyla (Eutheria) to (10.58-12.64)x10(5) kJ/kg in orders Carnivora, Pinnipeda and Chiroptera (Eutheria). A(ls) grows maximum to 18.5x10(5) kJ/kg in Primates. Thus, the values of coefficient A(ls) differ maximum four-fold in all orders. Across the all species the values of A(ls) are changes about one order of magnitude. Consequently, our survey shows that the changes of the body mass, basal metabolic rate and the life span of animals are three mutually related parameters, so that the product A(ls)=(PT(ls))/M remains relatively constant in comparison to 1 million fold difference in body mass and total metabolic energy per life span between mammals.

Animals↗
PubMed2005

Criteria for consciousness in humans and other mammals.

The standard behavioral index for human consciousness is the ability to report events with accuracy. While this method is routinely used for scientific and medical applications in humans, it is not easy to generalize to other species. Brain evidence may lend itself more easily to comparative testing. Human consciousness involves widespread, relatively fast low-amplitude interactions in the thalamocortical core of the brain, driven by current tasks and conditions. These features have also been found in other mammals, which suggests that consciousness is a major biological adaptation in mammals. We suggest more than a dozen additional properties of human consciousness that may be used to test comparative predictions. Such homologies are necessarily more remote in non-mammals, which do not share the thalamocortical complex. However, as we learn more we may be able to make "deeper" predictions that apply to some birds, reptiles, large-brained invertebrates, and perhaps other species.

Adaptation, Physiological↗
PubMed2005

Equipping the exotic mammal practice.

Many tools used in small animal practice can be adapted for use with exotic mammals. For those veterinarians with a strong interest in exotic mammals, specific equipment and supply needs need to be taken under consideration. Initial investment need not be great to get started with special species, and as the practice develops more specialized equipment can be added. Starting with equipment that aids in patient husbandry, diagnostic sampling, and routine hospital medical and surgical care is very helpful in creating confidence and expertise with these species. As the practice case load grows more sophisticated, equipment can be added, allowing for better diagnostic workups, medical treatment, and surgical care. The right equipment for the right job makes for a more rewarding and efficient exotic mammal practice. The author describes equipment and products (Table 1) he routinely uses in his private practice, and has provided a list of available sources. Readers should keep in mind that this list is not all-inclusive, and that in many instances products discussed can be found from multiple veterinary distributors or vendors. The author does not promote or recommend one supplier or manufacturer over another.

Animal Husbandry↗