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PubMed1986

A review of metal accumulation and toxicity in wild mammals. I. Mercury.

Release of Hg compounds into the environment from point sources has largely been curtailed due to the known impacts of Hg on biological systems. Mercury continues to be released into the environment, however, from nonpoint sources such as combustion of fossil fuels and smelting operations. While the accumulation and toxicity of Hg in aquatic biota, domestic animals, and humans is well documented, relatively little is understood about these processes in wild terrestrial mammals. The purpose of this paper is to review the available literature on Hg levels and toxicity in wild mammals (excluding marine mammals). It is clear that Hg levels are biomagnified within terrestrial food chains, where carnivores greater than omnivores greater than herbivores. Among carnivorous species, Hg levels are generally highest in fish-eating animals. There is usually a high degree of correlation of Hg levels between different animal tissues. The age and sex of an animal appear to influence observed Hg levels, but field data are conflicting for both factors. Tissue Hg levels are affected by location, with significant differences attributable to both local contamination and natural background variability. Experimental studies have shown many mammal species to sensitive to Hg intoxication, but documented incidents of Hg poisoning in wild mammals are rare. Such rarity may be more a function of our inability to observe and demonstrate Hg poisoning in wild populations, rather than an absence of the disease.

Absorption↗
PubMed2001

Adaptations to pressure in the RBC metabolism of diving mammals.

Marine mammals are known to dive up to 2000 m and, therefore, tolerate as much as 200 atm. of hydrostatic pressure. To examine possible metabolic adaptations to these elevated pressures, fresh blood samples from marine and terrestrial mammals were incubated for 2 h at 37 degrees C under 136 atm (2000 psi) of hydrostatic pressure. The consumption of plasma glucose and the production of lactate over the 2-h period were used to assess glycolytic flux in the red cells. The results indicate that glycolytic flux as measured by lactate production under pressure can be significantly depressed in most terrestrial mammals and either not altered or accelerated in marine mammals. The data also suggest that there is a significant shift in the ratio of lactate produced to glucose consumed under pressure. Interestingly, human and dolphin blood do not react to pressure. These combined data imply a metabolic adaptation to pressure in marine mammal RBC that may not be necessary in human or dolphin cells due to their unique patterns of glucose metabolism.

Animals↗
PubMed2004

Failure of anti-tumor immunity in mammals--evolution of the hypothesis.

Observations on the morphological and functional similarity between embryonic or trophoblast tissues and tumors are very old. Over a period of time many investigators have created different hypotheses on the origin of cancerogenesis or tumor efficiency in relation to the host immune system. Some of these ideas have been rejected but many of them are still current. A presumption of the inefficiency of anti-tumor immunity in mammals due to the high similarity between trophoblast and embryonic cells to tumor cells is very real. The mechanisms for the escape of tumors from the immune response are very similar to the mechanisms for the escape of a fetoplacental unit from the maternal immune response. The similarity between these two mechanisms is so great that any randomness must be banished. At the same time, an incidence of malignant tumors and the types of more frequent tumors in non-mammalian vertebrates is significantly different to that in mammals. Lastly, the mechanisms of anti-tumor immunity in mammals are substantially different from the mechanisms of anti-tumor immunity in other classes of vertebrates. These facts indicate that the immune system of mammals during anti-tumor immune response is tricked by the similarity between tumor cells and trophoblast or other placental cells. From this aspect, our conclusion is that anti-tumor immunity failure in mammals can be defined as an immunoreproductive phenomenon, which is developed under the evolutionary pressure of autoimmunity and reproductive effectiveness.

Animals↗
PubMedDate not supplied

Regeneration of skeletal and cardiac muscle in mammals: do nonprimate models resemble human pathology?

Most of the available information regarding the regenerative potential and compensatory remodeling of mammalian tissues has been obtained from nonprimate animals, mainly rodent experimental models. The increasing use of transgenic mice for studies of the mechanisms controlling organogenesis and regeneration also requires a clear understanding of their applicability as experimental models for studies of similar processes in humans and other mammals. Application of modern cell biology methods to studies of regenerative processes has provided new insights into similarity and differences in cellular responses to injury in the tissues of different mammalian species. During more than 200-million years of progressive divergent evolution of mammals, cellular mechanisms of tissue regeneration and compensatory remodeling evolved together with increasingly adaptive functional specialization and structural complexity of mammalian tissues and organs. Rodents represent a phylogenetically ancient order of mammals that has conservatively retained a number of morphofunctional characteristics of early representatives of this class, which include enhanced regenerative capacity of tissues. A comparative analysis of regenerative processes in skeletal and cardiac muscle, as well as in several other mammalian tissues, shows that time courses and intensities of regeneration in response to the same type of injury vary even within taxonomically related species (e.g., rat, mouse, and hamster). The warm bloodedness of mammals facilitated the development of more complex mechanisms of metabolic, immune, and neurohumoral regulation, which resulted in a stronger dependence of regenerative processes on vascularization and innervation. For this reason, interspecies modifications of regenerative responses are limited by the capacity of the animal to resorb rapidly the foci of necrosis and to revascularize and reinnervate the volume of the regenerating tissue. These differences, among other factors, result in significantly lower rates of reparative regeneration in mammals possessing larger body sizes than rodents. A review of these data strongly indicates that the phylogenetic age and biological differences between different species should be taken into account before extrapolation of regenerative properties of nonprimate tissues on the regenerative responses in the primates.

Animals↗
PubMed2006

Miocene mammal reveals a Mesozoic ghost lineage on insular New Zealand, southwest Pacific.

New Zealand (NZ) has long been upheld as the archetypical example of a land where the biota evolved without nonvolant terrestrial mammals. Their absence before human arrival is mysterious, because NZ was still attached to East Antarctica in the Early Cretaceous when a variety of terrestrial mammals occupied the adjacent Australian portion of Gondwana. Here we report discovery of a nonvolant mammal from Miocene (19-16 Ma) sediments of the Manuherikia Group near St Bathans (SB) in Central Otago, South Island, NZ. A partial relatively plesiomorphic femur and two autapomorphically specialized partial mandibles represent at least one mouse-sized mammal of unknown relationships. The material implies the existence of one or more ghost lineages, at least one of which (based on the relatively plesiomorphic partial femur) spanned the Middle Miocene to at least the Early Cretaceous, probably before the time of divergence of marsupials and placentals > 125 Ma. Its presence in NZ in the Middle Miocene and apparent absence from Australia and other adjacent landmasses at this time appear to reflect a Gondwanan vicariant event and imply persistence of emergent land during the Oligocene marine transgression of NZ. Nonvolant terrestrial mammals disappeared from NZ some time since the Middle Miocene, possibly because of late Neogene climatic cooling.

Animals↗
PubMed1984

Pharmacokinetic aspects of penicillins, aminoglycosides and chloramphenicol in birds compared to mammals. A review.

Based on a review of the literature, a comparison is made of the pharmacokinetics of penicillins, aminoglycosides, and chloramphenicol in birds and mammals. Penicillins in birds are likely to be more dependent for their elimination on biotransformation than in mammals. Amoxycillin had a relatively low availability (0.34) after p.o. administration. Higher doses (2 to 8 times) were needed to achieve the same peak levels in birds and mammals. Aminoglycosides, which for their elimination largely depend on renal excretion by glomerular filtration, show only minor differences in pharmacokinetics between birds and mammals. Chloramphenicol is mainly excreted after biotransformation and large differences in pharmacokinetic parameters are to be found, not only between birds and mammals, but also between avian species.

Aminoglycosides↗
PubMedDate not supplied

Molecular dating and biogeography of the early placental mammal radiation.

The timing and phylogenetic hierarchy of early placental mammal divergences was determined based on combined DNA sequence analysis of 18 gene segments (9779 bp) from 64 species. Using rooted and unrooted phylogenies derived from distinct theoretical approaches, strong support for the divergence of four principal clades of eutherian mammals was achieved. Minimum divergence dates of the earliest nodes in the placental mammal phylogeny were estimated with a quartet-based maximum-likelihood method that accommodates rate variation among lineages using conservative fossil calibrations from nine different nodes in the eutherian tree. These minimum estimates resolve the earliest placental mammal divergence nodes at periods between 64 and 104 million years ago, in essentially every case predating the Cretaceous-Tertiary (K-T) boundary. The pattern and timing of these divergences allow a geographic interpretation of the primary branching events in eutherian history, likely originating in the southern supercontinent Gondwanaland coincident with its breakup into Africa and South America 95-105 million years ago. We propose an integrated genomic, paleontological, and biogeographic hypothesis to account for these earliest splits on the placental mammal family tree and address current discrepancies between fossil and molecular evidence.

Animals↗
PubMed2004

Modeling the impact of DNA methylation on the evolution of BRCA1 in mammals.

The modified base 5-methylcytosine ((m)C) plays an important functional role in the biology of mammals as an epigenetic modification and appears to exert a striking impact on the molecular evolution of mammal genomes. The collective epigenetic functions of (m)C revolve around its effect on gene transcription, while the influence of this modified base on the evolution of mammal genomes derives from the greatly elevated spontaneous mutation rate of (m)C to T. In mammals, (m)C occurs at the dinucleotides CpG, CpA, and CpT. As a step toward a comprehensive statistical examination of the role of (m)C in mammal molecular evolution, we have developed novel Markov models of codon substitution that incorporate dinucleotide-level terms relevant to (m)C mutation. We apply these models to two data sets of aligned BRCA1 exon 11 sequences from bats and primates. In all cases, terms specific to mutations that affect the dinucleotides CpG, CpA, and CpT significantly improved model fit. For the CpG-specific terms, both transition and transversion substitution rates were elevated. These rates differed between the data sets. Bats exhibited a lower relative rate of substitutions at CpG-containing codons. Transition substitutions were significantly less than 1 at CpA-containing codons but greater than 1 at CpT-containing codons. The inclusion of interaction terms in the codon models to represent possible confounding with the effect of natural selection were supported for codons that contained CpG and CpT, but not CpA. From the results, we infer that mutation of (m)C is a probable factor that affects BRCA1 codons containing the dinucleotide CpG, a possible factor for CpA-containing codons, and an unlikely factor that affects CpT-containing codons. The confounding of estimated terms with the effect of natural selection indicate this confounding must be addressed for comparisons between different coding and noncoding regions.

Animals↗
PubMed1995

The expressed class II alpha-chain genes of the marsupial major histocompatibility complex belong to eutherian mammal gene families.

The major histocompatibility complex (Mhc) is a multigene family found in vertebrates. Mhc genes code for heterodimeric cell-surface molecules involved in presentation of peptides to T-lymphocytes. There are two classes of Mhc, and in eutherian mammals four main families of class II genes have been recognized; DR, DQ, DP, and DN/DO. Each class II family contains genes that code for one or more alpha and beta chains. Do the class II genes of marsupial mammals belong to any of these eutherian mammal class II families? The results to date are conflicting. The expressed class II beta-chain genes could not be satisfactorily assigned to any eutherian class II gene family and were designated as new gene families, while, conversely, a partial sequence of an expressed alpha-chain gene was clearly very similar to the DNA gene of eutherian mammals. The aim of this study was to conduct a more thorough analysis of the alpha-chain genes in a marsupial by obtaining full-length sequences of all the expressed alpha-chain genes in the red-necked wallaby, Macropus rufogriseus. Two class II alpha-chain genes were isolated from a spleen-derived cDNA library, and both have the potential to code for fully functional MHC molecules. Phylogenetic analysis indicated they belonged to previously identified eutherian class II families and are designated as Maru-DRA and Maru-DNA. Northern blot data indicated processed transcript sizes of approximately 1.6 kb for Maru-DRA and approximately 2.5 kb for Maru-DNA and that the latter was expressed at a lower level than the former. The phylogeny shows that the DR, DQ, DP, and DN/DO gene families diverged prior to the divergence of the marsupial and eutherian mammal lineages.

Animals↗
PubMed2005

Scaling of elastic energy storage in mammalian limb tendons: do small mammals really lose out?

It is widely believed that elastic energy storage is more important in the locomotion of larger mammals. This is based on: (a) comparison of kangaroos with the smaller kangaroo rat; and (b) calculations that predict that the capacity for elastic energy storage relative to body mass increases with size. Here we argue that: (i) data from kangaroos and kangaroo rats cannot be generalized to other mammals; (ii) the elastic energy storage capacity relative to body mass is not indicative of the importance of elastic energy to an animal; and (iii) the contribution of elastic energy to the mechanical work of locomotion will not increase as rapidly with size as the mass-specific energy storage capacity, because larger mammals must do relatively more mechanical work per stride. We predict how the ratio of elastic energy storage to mechanical work will change with size in quadrupedal mammals by combining empirical scaling relationships from the literature. The results suggest that the percentage contribution of elastic energy to the mechanical work of locomotion decreases with size, so that elastic energy is more important in the locomotion of smaller mammals. This now needs to be tested experimentally.

Animals↗
PubMed2005

Predator-induced synchrony in population oscillations of coexisting small mammal species.

Comprehensive analyses of long-term (1977-2003) small-mammal abundance data from western Finland showed that populations of Microtus voles (field voles M. agrestis and sibling voles M. rossiaemeridionalis) voles, bank (Clethrionomys glareolus) and common shrews (Sorex araneus) fluctuated synchronously in 3 year population cycles. Time-series analyses indicated that interspecific synchrony is influenced strongly by density-dependent processes. Synchrony among Microtus and bank voles appeared additionally to be influenced by density-independent processes. To test whether interspecific synchronization through density-dependent processes is caused by predation, we experimentally reduced the densities of the main predators of small mammals in four large agricultural areas, and compared small mammal abundances in these to those in four control areas (2.5-3 km(2)) through a 3 year small-mammal population cycle. Predator reduction increased densities of the main prey species, Microtus voles, in all phases of the population cycle, while bank voles, the most important alternative prey of predators, responded positively only in the low and the increase phase. Manipulation also increased the autumn densities of water voles (Arvicola terrestris) in the increase phase of the cycle. No treatment effects were detected for common shrews or mice. Our results are in accordance with the alternative prey hypothesis, by which predators successively reduce the densities of both main and alternative prey species after the peak phase of small-mammal population cycles, thus inducing a synchronous low phase.

Animals↗
PubMed2003

Mammal population regulation, keystone processes and ecosystem dynamics.

The theory of regulation in animal populations is fundamental to understanding the dynamics of populations, the causes of mortality and how natural selection shapes the life history of species. In mammals, the great range in body size allows us to see how allometric relationships affect the mode of regulation. Resource limitation is the fundamental cause of regulation. Top-down limitation through predators is determined by four factors: (i). body size; (ii). the diversity of predators and prey in the system; (iii). whether prey are resident or migratory; and (iv). the presence of alternative prey for predators. Body size in mammals has two important consequences. First, mammals, particularly large species, can act as keystones that determine the diversity of an ecosystem. I show how keystone processes can, in principle, be measured using the example of the wildebeest in the Serengeti ecosystem. Second, mammals act as ecological landscapers by altering vegetation succession. Mammals alter physical structure, ecological function and species diversity in most terrestrial biomes. In general, there is a close interaction between allometry, population regulation, life history and ecosystem dynamics. These relationships are relevant to applied aspects of conservation and pest management.

Animals↗
PubMed1975

Comparative study of the innervation of the facila disc of selected mammals.

The greatest concentration of sensory nerves in the muzzle and facial disc of mammals is in the nose. In most nocturnal mammals, these nerves penetrate the epidermis of the naked nose either or in bundles which resemble the corpuscles of Eimer. The hair follicles around the nose, lips, and eyes, as well as the heaviply innervated vibrissae follicles found in all hairy mammals except man, are well innervated; those elsewhaere are not. Everywhere on the human body both large and small follicles abound in sensory nerves. These morphologic observations suggest that in most mammals the most sensitivie areas of the skin are at the anterior and posterior ends (not reported here), and that human skin is better equipped for cutaneous sensibility than that of any other mammal.

Animals↗
PubMed2004

Rates of evolution of hybrid inviability in birds and mammals.

Almost 30 years ago, A. C. Wilson and colleagues presented results indicating that hybrid inviability between species evolves 10 times faster in mammals than in birds and frogs. Here I revisit this question for birds and mammals using modern molecular data (mitochondrial cytochrome b DNA) and a more phylogenetically appropriate statistical approach. My analyses confirm that diverging mammals lose the ability to form viable hybrids faster than birds. To explain the difference in rates of evolutionary loss of hybridization potential, Wilson and coworkers proposed that mammals have higher rates of regulatory evolution, causing higher probabilities of developmental incompatibilities between mammal species. I briefly discuss this and other potential explanations.

Animals↗
PubMed1998

Evolution of daily torpor and hibernation in birds and mammals: importance of body size.

1. The evolution of hibernation and daily torpor in mammals and birds remains a controversial subject. The original view was that use of torpor reflects a primitive thermoregulation, as it occurs in ancestral groups of mammals. 2. This view is no longer widely supported. However, the interpretation of a polyphyletic derivation of torpor also has been challenged because of the astonishing similarity of torpor patterns among various orders and even the two classes. 3. A recent argument is that mutations required for torpor and hibernation are unlikely to occur simultaneously and that torpor must be plesiomorphic (ancestral), although it is not functionally primitive. Homeothermy is interpreted as a loss of the ability to enter torpor in those groups that could survive without the requirement of heterothermic periods for energy conservation. 4. Interestingly, while torpor in mammals occurs in the phylogenetically old groups, lending support to the hypothesis of an ancestral derivation of torpor, the opposite is the case for birds. Modern bird groups and ancestral mammal groups contain mainly small species that often rely on fluctuating food supply, whereas modern mammalian orders and ancient bird orders contain the largest species with low energy requirements for maintenance and thermoregulation. 5. It is, therefore, possible that not phylogenetic position but size and diet determine the occurrence of heterothermy. Moreover, because endothermy and torpor in birds has apparently evolved separately from that in mammals and because it is possible that daily torpor and hibernation represent two distinct torpor patterns that evolved separately, a convergent evolution of torpor in endotherms cannot be excluded.

Animals↗
PubMed1993

The distribution and nature of colour vision among the mammals.

1. An oft-cited view, derived principally from the writings of Gordon L. Walls, is that relatively few mammalian species have a capacity for colour vision. This review has evaluated that proposition in the light of recent research on colour vision and its mechanisms in mammals. 2. To yield colour vision a retina must contain two or more spectrally discrete types of photopigment. While this is a necessary condition, it is not a sufficient one. This means, in particular, that inferences about the presence of colour vision drawn from studies of photopigments, the precursors of photopigments, or from nervous system signals must be accepted with due caution. 3. Conjoint signals from rods and cones may be exploited by mammalian nervous systems to yield behavioural discriminations consistent with the formal definition of colour vision. Many mammalian retinas are relatively cone-poor, and thus there are abundant opportunities for such rod/cone interactions. Several instances were cited in which animals having (apparently) only one type of cone photopigment succeed at colour discriminations using such a mechanism. it is suggested that the exploitation of such a mechanism may not be uncommon among mammals. 4. Based on ideas drawn from natural history, Walls (1942) proposed that the receptors and photopigments necessary to support colour vision were lost during the nocturnal phase of mammalian history and then re-acquired during the subsequent mammalian radiations. Contemporary examination of photopigment genes along with the utilization of better techniques for identifying rods and cones suggest a different view, that the earliest mammals had retinas containing some cones and two types of cone photopigment. Thus the baseline mammalian colour vision is argued to be dichromacy. 5. A consideration of the broad range of mammalian niches and activity cycles suggests that many mammals are active during photic periods that would make a colour vision capacity potentially useful. 6. A systematic survey was presented that summarized the evidence for colour vision in mammals. Indications of the presence and nature of colour vision were drawn both from direct studies of colour vision and from studies of those retinal mechanisms that are most closely associated with the possession of colour vision. Information about colour vision can be adduced for species drawn from nine mammalian orders.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2001

An ossified Meckel's cartilage in two Cretaceous mammals and origin of the mammalian middle ear.

An ossified Meckel's cartilage has been recovered from two early Cretaceous mammals from China. This element is similar to Meckel's cartilage in prenatal and some postnatal extant mammals and indicates the relationship of Meckel's cartilage with the middle ear in early mammals. The evidence shows that brain expansion may not be the initial factor that caused the separation of postdentary bones from the dentary as middle ear ossicles during mammalian evolution. The failure of the dentary to seize reduced postdentary elements during ontogeny of early mammals is postulated as an alternative mechanism for the separation. Modifications of both feeding and hearing apparatuses in early mammals may have led to the development of the definitive mammalian middle ear.

Animals↗
PubMed2005

Identification of a new Borrelia species among small mammals in areas of northern Spain where Lyme disease is endemic.

The role of small mammals as reservoir hosts for Borrelia burgdorferi was investigated in several areas where Lyme disease is endemic in northern Spain. A low rate of infestation by Ixodes ricinus nymphs was found in the small mammal populations studied that correlated with the near-absence of B. burgdorferi sensu lato in 184 animals tested and with the lack of transmission of B. burgdorferi sensu lato to I. ricinus larvae that fed on them. In contrast, questing ticks collected at the same time and in the same areas were found to carry a highly variable B. burgdorferi sensu lato repertoire (B. burgdorferi sensu stricto, Borrelia garinii, Borrelia valaisiana, and Borrelia afzelii). Interestingly, the only isolate obtained from small mammals (R57, isolated from a bank vole) grouped by phylogenetic analyses with other Borrelia species but in a separate clade from the Lyme disease and relapsing fever organisms, suggesting that it is a new species. This new agent was widely distributed among small mammals, with infection rates of 8.5 to 12% by PCR. Moreover, a high seroprevalence to B. burgdorferi sensu lato was found in the animal sera, suggesting cross-reactivity between B. burgdorferi sensu lato and R57. Although small mammals do not seem to play an important role as reservoirs for B. burgdorferi sensu lato in the study area, they seem to be implicated in the maintenance of spirochetes similar to R57.

Animals↗