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PubMed1998

Cope's rule and the dynamics of body mass evolution in North American fossil mammals.

Body mass estimates for 1534 North American fossil mammal species show that new species are on average 9.1% larger than older species in the same genera. This within-lineage effect is not a sampling bias. It persists throughout the Cenozoic, accounting for the gradual overall increase in average mass (Cope's rule). The effect is stronger for larger mammals, being near zero for small mammals. This variation partially explains the unwavering lower size limit and the gradually expanding mid-sized gap, but not the sudden large increase in the upper size limit, at the Cretaceous-Tertiary boundary.

Animals↗
PubMed2006

Tick-borne rickettsial pathogens in ticks and small mammals in Korea.

In order to investigate the prevalence of tick-borne infectious agents among ticks, ticks comprising five species from two genera (Hemaphysalis spp. and Ixodes spp.) were screened using molecular techniques. Ticks (3,135) were collected from small wild-caught mammals or by dragging/flagging in the Republic of Korea (ROK) and were pooled into a total of 1,638 samples (1 to 27 ticks per pool). From the 1,638 tick samples, species-specific fragments of Anaplasma phagocytophilum (1 sample), Anaplasma platys (52 samples), Ehrlichia chaffeensis (29 samples), Ehrlichia ewingii (2 samples), Ehrlichia canis (18 samples), and Rickettsia rickettsii (28 samples) were amplified by PCR assay. Twenty-one pooled and individual tick samples had mixed infections of two (15 samples) or three (6 samples) pathogens. In addition, 424 spleen samples from small captured mammals (389 rodents, 33 insectivores, and 2 weasels) were screened for selected zoonotic pathogens. Species-specific DNA fragments of A. phagocytophilum (110 samples), A. platys (68 samples), E. chaffeensis (8 samples), E. ewingii (26 samples), E. canis (51 samples), and Rickettsia sp. (22 samples) were amplified by PCR assay. One hundred thirty small mammals had single infections, while 4, 14, and 21 striped field mice (Apodemus agrarius) had mixed infections of four, three, and two pathogens, respectively. Phylogenetic analysis based on nucleotide sequence comparison also revealed that Korean strains of E. chaffeensis clustered closely with those from China and the United States, while the Rickettsia (rOmpA) sequences clustered within a clade together with a Chinese strain. These results suggest that these agents should be considered in differential diagnosis while examining cases of acute febrile illnesses in humans as well as animals in the ROK.

Anaplasma↗
PubMed1983

Isolation and characterization of Campylobacter jejuni and Campylobacter coli from domestic and wild mammals in Norway.

A total of 1,262 domestic and wild mammals from Norway were surveyed for fecal carriage of Campylobacter jejuni and Campylobacter coli. Of the five species of domestic mammals examined, the highest isolation rate was recorded among swine (100.0%), followed by sheep (8.1%) and cows (0.8%). No strains were recovered from horses or goats. Among wild mammals, C. jejuni was isolated from 1 of 23 hares, and no isolated were obtained from three species of cervids and three species of rodents. Of the 133 Campylobacter strains isolated, 114 were classified as C. coli, 18 were C. jejuni biotype 1, and 1 belonged to C. jejuni biotype 2. All 114 strains from swine were C. coli. Milk samples from 113 domestic animals with clinically diagnosed mastitis (106 cows, 5 sheep, 1 horse, and 1 pig) were negative for campylobacters.

Animals↗
PubMed1991

Intestinal carriage of Yersinia pseudotuberculosis by wild birds and mammals in Japan.

Fecal specimens were obtained from wild birds and mammals in the eastern part of Shimane Prefecture, Japan, an area where serotype 1b, 2b, 3, and 4b strains of Yersinia pseudotuberculosis were found to be prevalent in humans. Each of 869 animals, including 259 wild birds and 610 wild mammals, was screened for yersiniae. A total of 37 strains of Y. pseudotuberculosis were isolated from 34 (5.6%) mammals, including 23 raccoon dogs (Nyctereutes procyonoides), eight deer (Cervus nippon), two hares (Lepus brachyurus), and one marten (Martes melampus), and from two (0.8%) birds, including one eastern spot-billed duck (Anas poecilorhyncha) and one wigeon (Anas penelope). The Y. pseudotuberculosis isolates collected belonged to virulence plasmid-positive (serotypes 1b, 2b, 3, 4b, and 6) and virulence plasmid-negative (serotype 5a) strains, the most predominant serotype being 4b. The close relationship between the regional distributions of Y. pseudotuberculosis in wild animals and humans suggests that wild animals are an important source of infection.

Animals↗
PubMed2005

Isolation of Mycobacterium avium subsp. paratuberculosis from free-ranging birds and mammals on livestock premises.

Surveys for Mycobacterium avium subsp. paratuberculosis infection in free-ranging mammals and birds were conducted on nine dairy and beef cattle farms in Wisconsin and Georgia. Specimens were collected from 774 animals representing 25 mammalian and 22 avian species. Specimens of ileum, liver, intestinal lymph nodes, and feces were harvested from the larger mammals; a liver specimen and the gastrointestinal tract were harvested from birds and small mammals. Cultures were performed by using radiometric culture and acid-fast isolates were identified by 16S/IS900/IS1311 PCR and mycobactin dependency characteristics. M. avium subsp. paratuberculosis was cultured from tissues and feces from 39 samples from 30 animals representing nine mammalian and three avian species. The prevalence of infected wild animals by premises ranged from 2.7 to 8.3% in Wisconsin and from 0 to 6.0% in Georgia. Shedding was documented in seven (0.9%) animals: three raccoons, two armadillos, one opossum, and one feral cat. The use of two highly polymorphic short sequence repeat loci for analysis of 29 of the 39 strains identified 10 alleles. One allelic pattern broadly shared in domestic ruminants ("7,5") appeared in approximately one-third of the wildlife M. avium subsp. paratuberculosis isolates studied. Given the few cases of shedding by free-ranging animals compared to the volume of contaminated manure produced by infected domestic ruminant livestock, contamination of the farm environment by infected wildlife was negligible. Wildlife may, however, have epidemiological significance for farms where M. avium subsp. paratuberculosis recently has been eliminated or on farms free of M. avium subsp. paratuberculosis but located in the geographic vicinity of farms with infected livestock.

Animal Husbandry↗
PubMed2000

Nucleotypic effects without nuclei: genome size and erythrocyte size in mammals.

Previously reported haploid genome sizes (C-values) and erythrocyte sizes (measured as mean dry diameters) were compared for 67 species of mammals representing 31 families and 16 orders. Measurements on erythrocytes of four species of bats were also included in the study. Erythrocyte size was significantly positively correlated with genome size at each of the specific, generic, familial, and ordinal levels, with the relationship becoming much stronger following the exclusion of the order Artiodactyla, a group unique among mammals in terms of red blood cell morphology. Physiologically, these results are relevant in light of the known relationship between C-value and mass-corrected metabolic rate in homeotherms. In evolutionary terms, they provide insights into the constraints on genome expansion among mammals and are therefore of interest in attempts to solve the long-standing C-value enigma (also known as the C-value paradox).

Animals↗
PubMed1985

Circadian neural rhythms in mammals.

A number of different experimental findings indicate that endogenous circadian neural rhythms are generated within the SCN region of mammals. Rhythmic neural signals from the SCN directly, or indirectly, appear to regulate many, if not all, biochemical, physiological, and behavioral circadian rhythms. The circadian system in mammals is referred to as being "multioscillatory" in nature, although this term is often used to mean different things. The SCN itself may contain many circadian neural oscillators and the coordinated output of these multioscillators may regulate circadian rhythms. The term multioscillatory is also used to indicate the presence of anatomically distinct oscillators. However, the location and properties of circadian pacemakers that may lie outside of the SCN region remain unknown. Indeed, there is no conclusive evidence that circadian rhythms can be generated over a prolonged period of time in the absence of the SCN in mammals maintained under constant environmental conditions. Whereas the SCN appears capable of generating circadian neural signals indefinitely in the absence of any 24-hr fluctuations in the external environment, other components of the circadian system may function as damped oscillators (i.e. persist for only a few cycles in the absence of a periodic input) and/or only emit diurnal rhythms in the presence of rhythmic input from either the external (e.g. light-dark cycle) and/or internal (e.g. SCN) environment. On a conceptual as well as a physiological level, our understanding of the organization of the mammalian circadian system remains limited at the present time. Unfortunately, the limitations on our understanding of the circadian system are not always fully appreciated, and quite often a hypothesis based on limited experimental data is treated as fact. The study of the circadian system is still in the early stages of development, and further progress in elucidating the physiological mechanisms underlying the generation and expression of circadian rhythms may require new ways of looking at old problems as well as new experimental approaches. One final comment should be made concerning the importance of an increased understanding of circadian rhythms for human health. Because the study of the physiology of the circadian system is still in its early stages of development, little is known about the importance of the normal functioning of the circadian system for the health and well-being of the organism. Recent studies in humans suggest that disorders within the circadian system itself may be involved in the etiology of at least some forms of mental illness.

Acetylcholine↗
PubMed1975

Blood oxygen affinity and alveolar ventilation in relation in body weight in mammals.

The validity of the concept relating blood oxygen affinity and alveolar ventilation to body weight in homeothermic mammals was reexamined with blood pH used as the fixed variable. Blood Po2 at 50% saturation at pH 7.4 (P50(7.4)) and PCO2 of oxygenated blood at pH 7.4 (PCO2(7.4)) from a variety of homeothermic mammals were determined at 37 degrees C by in vitro equilibration techniques. In some species, arterial PCO2, PO2, and pH were also measured. PCO2(7.4), which was similar to arterial PCO2, showed a correlation coefficient of +0.33 with body weight over the range of 28-100,000 g and +0.90 among the species under 200 g. P50(7.4) values, which ranged from 26.0 to 38.7 mmHg for all the species, were not well correlated (r = -0.43) with body weight. For the small mammals (less than 200 g) the correlation coefficient was -0.91. In vivo P50 at the body temperature and arterial pH, although different from P50(7.4), showed a similar correlation with body weight. The lack of valid generalization suggests that body weight is only one of the composite factors that influence O2 transport systems.

Animals↗
PubMed2007

Hypothalamic expression of thyroid hormone-activating and -inactivating enzyme genes in relation to photorefractoriness in birds and mammals.

Photorefractoriness is the insensitivity of gonadal development to the stimulatory effects of long photoperiods in birds and to the inhibitory effects of short photoperiods in small mammals. Its molecular mechanism remains unknown. Recently, it has been shown that reciprocal expression of thyroid hormone-activating enzyme [type 2 deiodinase (Dio2)] and -inactivating enzyme [type 3 deiodinase (Dio3)] genes in the mediobasal hypothalamus is critical for photoperiodically induced gonadal growth. Since thyroid hormones are required not only for photoinduction, but also for the induction of photorefractoriness, we examined the expression of these genes in relation to photorefractoriness in birds and mammals. Transfer of birds to long photoperiods induced strong expression of Dio2. This was maintained in tree sparrow when they later became photorefractory, but decreased somewhat in quail. In hamsters, transfer to long photoperiods also induced strong expression of Dio2. High values were not maintained under long photoperiods, and, indeed, expression decreased at the same rate as in animals transferred to short photoperiods. There was no renewed expression of Dio2 associated with testicular growth as animals became refractory to short photoperiods. Expression of Dio3 was high under short photoperiods and low under long photoperiods in all the animals examined, except for the short photoperiod-refractory hamsters. Our present study revealed complex regulation of deiodinase genes in the photoinduction and photorefractory processes in birds and mammals. These gene changes may be involved in the regulation of photorefractoriness, as well as photoinduction.

Animals↗
PubMed1980

Comparative nephron function in reptiles, birds, and mammals.

Volume and osmolarity of urine produced by kidneys of reptiles, birds, and mammals depend on anatomic relationships among nephrons, epithelial permeability to water controlled by antidiuretic hormone, and, for reptiles and birds, probably on volume flow rate through collecting ducts and excretion of uric acid. Urine volume and volume flow rate through collecting ducts in reptiles and birds depend on number of filtering nephrons controlled by antidiuretic hormone. Mammalian nephrons do not filter intermittently but control of nephron filtration rates in all three vertebrate classes may have important similarities and differences. Uric acid excretion by birds and many reptiles permits excretion of inorganic cations in excess of amounts permitted by osmolarity of urine. This process may require tubular absorption of water without sodium. Such absorption, which has been found in reptilian proximal tubules, may be very important for osmoregulation in all birds and uricotelic reptiles and may provide insight into the mechanism of fluid absorption in mammals. Urea excretion in mammals may be important for enhancing concentrating ability. Much more must be learned about these processes, but similarities and differences among them in the three vertebrate classes may help illuminate details of each.

Animals↗
PubMed1984

Pulmonary transit time and diffusing capacity in mammals.

Allometry is used as a tool to explain the apparent mismatch of oxygen consumption and diffusing capacity in the mammalian lung. By combining equations for pulmonary capillary volume and cardiac output, it is apparent that erythrocyte transit time through the lung must scale disproportionately to body mass. This inequality is a consequence of physical and mechanical properties setting optimal cardiac and respiratory frequencies. Because of much shorter transit times, the mean alveolar-capillary oxygen pressure difference increases as body size decreases. The time course of oxygen binding to hemoglobin may limit maximum oxygen consumption in the smallest mammals. To assure carbon dioxide diffusion equilibrium, levels of carbonic anhydrase are much higher in small than in large mammals. Because of the differences in transit time, the pulmonary diffusing capacity must scale linearly to body mass to assure adequate oxygen delivery in all mammals.

Animals↗
PubMed1994

Allometry of muscle, tendon, and elastic energy storage capacity in mammals.

This paper considers the structural properties of muscle-tendon units in the hindlimbs of mammals as a function of body mass. Morphometric analysis of the ankle extensors, digital flexors, and digital extensors from 35 quadrupedal species, ranging in body mass from 0.04 to 545 kg, was carried out. Tendon dimensions scale nearly isometrically, as does muscle mass. The negative allometry of muscle fiber length results in positive allometric scaling of muscle cross-sectional areas in all but digital extensors. Maximum muscle forces are predicted to increase allometrically, with mass exponents as high as 0.91 in the plantaris, but nearly isometrically (0.69) in the digital extensors. Thus the maximum amount of stress a tendon may experience in vivo, as indicated by the ratio of muscle and tendon cross-sectional areas, increases with body mass in digital flexors and ankle extensors. Consequently, the capacity for elastic energy storage scales with positive allometry in these tendons but is isometric in the digital extensors, which probably do not function as springs in normal locomotion. These results suggest that the springlike tendons of large mammals can potentially store more elastic strain energy than those of smaller mammals because their disproportionately stronger muscles can impose higher tendon stresses.

Animals↗
PubMed1998

Role of the archistriatal nucleus taeniae in the sexual behavior of male Japanese quail (Coturnix japonica): a comparison of function with the medial nucleus of the amygdala in mammals.

Nucleus taeniae (Tn) is a prominent cell group within the medial archistriatum of birds. Based upon similarities in sex-steroid binding sites, this nucleus has been hypothesized to be homologous to the medial nucleus of the amygdala (Me) in mammals, which is known to modulate the expression of sexual behavior in rodents. We therefore tested whether or not Tn likewise plays a role in the expression of sexual behavior in male Japanese quail. We found that bilateral damage to Tn produced deficits in several components of male responses toward female stimuli that were indicative of decreased sexual arousal, including goal-oriented responses, vocalizations associated with courtship, and motor reflexes that precede copulation. Our results suggest that Tn influences a wide range of behavioral functions in response to sexual stimuli, and they indicate a function for this nucleus similar to that subserved by the Me in mammals. These results strengthen the argument that these sex-steroid accumulating cell groups are homologous and suggest a conservation of function for them despite the vastly divergent evolutionary histories separating birds and mammals.

Amygdala↗
PubMed2000

Mammal-like striatal functions in Anolis. I. Distribution of serotonin receptor subtypes, and absence of striosome and matrix organization.

Serotonin (5-HT) 5-HT(2A) and 5-HT(2C) receptors are thought to play important roles in the mammalian striatum. As basal ganglia functions in general are thought highly conserved among amniotes, we decided to use in situ autoradiographic methods to determine the occurrence and distribution of pharmacologically mammal-like 5-HT(2A) and 5-HT(2C) receptors in the lizard, Anolis carolinensis, with particular attention to the striatum. We also determined the distributions of 5-HT(1A), 5-HT(1B/D), 5 HT(3), and 5-HT(uptake) receptors for comparison. All 5-HT receptors examined showed pharmacological binding specificity, and forebrain binding density distributions that resembled those reported for mammals. Anolis 5 HT(2A/C) and 5-HT(1A) site distributions were similar in both in vivo and ex vivo binding experiments. 5-HT(2A & C) receptors occur in both high and low affinity states, the former having preferential affinity for (125)I-(+/-)-2,5-dimethoxy-4-iodo-amphetamine hydrochloride ((125)I-DOI). In mammals (125)I-DOI binding shows a patchy density distribution in the striatum, being more dense in striosomes than in surrounding matrix. There was no evidence of any such patchy density of (125)I-DOI binding in the anole striatum, however. As a further indication that anoles do not possess a striosome and matrix striatal organization, neither (3)H-naloxone binding nor histochemical staining for acetylcholinesterase activity (AChE) were patchy. AChE did show a band-like striatal distribution, however, similar to that seen in birds.

Animals↗
PubMed2003

Solitary chemosensory cells in mammals?

In fish, solitary chemosensory cells (SCCs) occur in the oropharynx, gills and skin and have often been found in association with taste buds. Among amphibia, a diffuse chemosensory system has been described on the ventral skin of toads, and a structural resemblance of SCCs to taste bud cells has been reported in frogs. Putative solitary chemoreceptors have been described in mammals too, at specific sites in the digestive or respiratory apparatus. In newborn rodents, a specific set of SCCs (composed of elements positive for alpha-gustducin, a marker of chemosensory cells) is associated with the gustatory epithelium. In conclusion, the available data suggest that a SCC system is not restricted to fish but is present in amphibia and mammals as well. At our present level of knowledge, establishing a precise homology between different species is difficult. However, the data from mammals and amphibia fully confirm previous findings in fish, and the use of chemical markers to study the diffuse chemosensory systems of vertebrates seems promising.

Amphibians↗
PubMed2004

Brain size scaling and body composition in mammals.

Brain size scales with body size across large groups of animals, but exactly why this should be the case has not been resolved. It is generally assumed that body size is a general proxy for some more important or specific underlying variable, such as metabolic resources available, surface area of the body, or total muscle mass (which is more extensively innervated than is, e.g., adipose tissue). The present study tests whether brain size in mammals scales more closely with muscle mass (and other components of lean body mass) than with total fat. Felsenstein's independent comparisons method was used to control for phylogenetic effects on body composition in organ weight data taken from a previously published comparative sample of 39 species in 8 different orders of mammals, all collected and processed by the same researchers. The analysis shows that the size of the central nervous system (CNS) is more closely associated with components of fat-free weight than it is to fat weight. These results suggest a possible explanation for why metabolic resources and brain size both share the same general relationship with body size across mammals. They also suggest that some measure of lean body mass is a more appropriate scaling parameter for comparing brain size across species than is overall body weight.

Animals↗
PubMed2004

On the evolutionary significance of encephalization in some eutherian mammals: effects of adaptive radiation, domestication, and feralization.

Allometries of the brain to body size relationship in eutherian mammals are examined in this study as they can be used for comparative analyses concerning encephalization. In contrast with some modern presentations of this issue, an older concept is revived and expanded through this author's current study. Three allometries with clearly different slopes are valid and lead to reliable results: interspecific, intraspecific, and ontogenetic allometries. Interspecific allometries follow lines with slope values of 0.56 or 0.63 for larger and smaller species, respectively, and characterize different average encephalization plateaus with rodents and lagomorphs generally more strongly encephalized compared to basal insectivores. Artiodactyls, perissodactyls and carnivores as a whole are again on a higher but rather similar plateau. Several species of carnivores have reached different encephalization levels with respect to their average plateau indicating diverse radiations. A phylogenetic brain size increase from fossil to recent radiations is also evident. Intraspecific allometries have slope values of about 0.25. These are of help in comparing brain sizes of ancestral species with their domesticated relatives. Domestication has generally led to a brain size decrease, but species on higher encephalization plateaus show this trend more strongly than species on a lower level of encephalization. Several brain parts and the sense organs also decrease in size during the domestication process, but vary arbitrarily and to different degrees. Ontogenetic growth allometries are species-specific, but are especially different between altricial and precocial mammals. A very steep 1st phase slope of highly encephalized species is particularly useful for understanding evolutionary and adaptive phenomena. Domesticated mammals that have become feral do not show an increase in brain size despite living many generations in wild habitats.

Adaptation, Physiological↗
PubMed2006

The evolution of cathemerality in primates and other mammals: a comparative and chronoecological approach.

Non-primate mammalian activity cycles are highly variable across and within taxonomic groups. In contrast, the order Primates has historically been recognized as displaying a diurnal-nocturnal dichotomy that mapped, for the most part, onto the taxonomic division between haplorhines and strepsirhines. However, it has become clear over the past two decades that activity cycles in primates are not quite so clear cut. Some primate species--like many large herbivorous mammals, mustelids, microtine rodents, and shrews--exhibit activity both at night and during the day. This activity pattern is often polyphasic or ultradian (several short activity bouts per 24-hour period), in contrast to the generally monophasic pattern (one long bout of activity per 24-hour period) observed in diurnal and nocturnal mammals. Alternatively, it can vary on a seasonal basis, with nocturnal activity exhibited during one season, and diurnal activity during the other season. The term now generally employed to describe the exploitation of both diurnal and nocturnal phases in primates is 'cathemeral'. Cathemerality has been documented in one haplorhine, the owl monkey, Aotus azarai, in the Paraguayan and Argentinian Chaco and in several Malagasy strepsirhines, including Eulemur spp., Hapalemur sp. and Lemur catta. In this paper, we review patterns of day-night activity in primates and other mammals and investigate the potential ecological and physiological bases underlying such 24-hour activity. Secondly, we will consider the role of cathemerality in primate evolution.

Animals↗