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At least 415 records · Page 23Linked to original sources
PubMed1999

The rainbow trout Oncorhynchus mykiss interleukin-1 beta gene has a differ organization to mammals and undergoes incomplete splicing.

The rainbow trout interleukin (IL)-1 beta gene consists of six exons/five introns, in contrast to mammals which have seven exons/six introns. The missing exon appears to be at the 5' end of the gene, probably equivalent to exon 1 or 2 of mammals. Fewer and smaller introns make the trout IL-1 beta only half the size of mammalian IL-1 beta genes. Highest homology (> 60% amino acid similarity) is seen between exon 5 of trout and exon 6 of mammals. Reverse transcription-PCR analysis revealed two additional incompletely spliced variants of the trout IL-1 beta gene, containing intron 5 or introns 4 and 5. All three transcripts are detectable in gill, kidney, liver and spleen tissue from bacterially challenged fish but only the fully spliced transcript is detectable in blood. Northern blot analysis revealed that the latter transcript is also induced following stimulation of kidney leucocytes with lipopolysaccharide for 4 h. A second inducible transcript is also detected but is larger (approximately 3 kb) than any of the above, suggesting that it could be from a second gene. Southern blot analysis also suggests at least two copies of the IL-1 beta gene or genes related to the 3' end of the IL-1 beta sequence, are present in trout.

Alternative Splicing↗
PubMed1993

Seasonal reproduction in flying foxes, reviewed in the context of other tropical mammals.

Megachiroptera inhabit the Old World tropics and most are seasonal breeders having defined times of testis growth, mating and parturition. In Pteropus scapulatus, the little red flying fox, the robust rhythm of testis cycles is resistant to modification by photoperiod. P. poliocephalus, the greyheaded flying fox, can be manipulated by photoperiod but responds slowly and incompletely. Most mammals live in the tropics, many in seasonally harsh climates, and many breed seasonally. However, few long-lived tropical mammals have been investigated for photoperiodic entrainment of annual reproductive cycles, and only animals from the edge of the tropics have responded. Thus, in long-lived tropical mammals, factors that regulate seasonal breeding have not yet been identified. Endogenous oscillators may generate circannual rhythms centrally. Downstream pathways (reproduction, metabolism, antlers, etc.) may derive their rhythm directly from the oscillator or may be modified by environmental cues. Plasticity of the circannual oscillator resolves confusion from previous contrasts between circannual rhythms and environmentally cued patterns. Plasticity may continue throughout life (species responsive to zeitgebers), but the oscillator may be 'set' in utero in some tropical species. Feedback effects from temperature, nutrition, hormones, etc. can be readily tested in this model of an oscillator generating an endogenous circannual rhythm.

Animals↗
PubMed2002

Conserved regulation of the lymphocyte-specific expression of lck in the Fugu and mammals.

The lck gene encodes a lymphocyte-specific protein-tyrosine kinase that is implicated in T cell maturation and signaling. In mammals, the transcription of the lck gene is regulated by two independent promoters, the proximal promoter, which is active in thymocytes, and the distal promoter, which dominates in mature T cells. In the human and mouse lck gene loci, the two promoter elements are separated by at least 40 kb and 10 kb, respectively. In this study, we have cloned and sequenced 60 kb from the pufferfish (Fugu rubripes) lck locus. The promoter region of the Fugu lck spans only 4.2 kb and contains a proximal and a distal promoter in the 2.3-kb region adjacent to the coding sequence. By generating transgenic mice, we have demonstrated that the compact promoter of the Fugu lck contains regulatory elements that direct expression to lymphoid organs of mice. We were able to localize the regulatory elements to a short region of 830 bp without losing specificity to cultured human T cell line. These results show that the basic mechanisms that mediate lymphocyte-specific expression are conserved between teleosts and mammals. The short promoter of the Fugu lck isolated by us offers a powerful tool for labeling T cells, targeting expression, and manipulating T cell activity in fishes as well as in mammals.

Amino Acid Sequence↗
PubMed2006

Latent extinction risk and the future battlegrounds of mammal conservation.

Global conservation prioritization usually emphasizes areas with highest species richness or where many species are thought to be at imminent risk of extinction. However, these strategies may overlook areas where many species have biological traits that make them particularly sensitive to future human impact but are not yet threatened because such impact is currently low. In this article, we identify such areas for the world's mammals using latent extinction risk, the discrepancy between a species' current extinction risk and that predicted from models on the basis of biological traits. Species with positive latent risk are currently less threatened than their biology would suggest, usually because they inhabit regions or habitats still comparatively unmodified by human activity. Using large new geographic, biological, and phylogenetic databases for nearly 4,000 mammal species, we map the global geographic distribution of latent risk to reveal areas where the mammal fauna is still relatively unthreatened but has high inherent sensitivity to disturbance. These hotspots include large areas such as the Nearctic boreal forests and tundra that are unrepresented in most current prioritization schemes, as well as high-biodiversity areas such as the island arc from Indonesia to the south Pacific. Incorporating latent extinction risk patterns into conservation planning could help guard against future biodiversity loss by anticipating and preventing species declines before they begin.

Animals↗
PubMed2002

Life history consequences of mammal sibling rivalry.

Mammal life history traits relating to growth and reproduction are extremely diverse. Sibling rivalry may contribute to selection pressures influencing this diversity, because individuals that are relatively large at birth typically have an advantage in competition for milk. However, selection for increased growth rate is likely to be constrained by kin selection and physiological costs. Here, we present and test a model examining the ESS (evolutionarily stable strategy) balance between these constraints and advantages associated with increased prenatal growth in mammal sibling rivalry. Predictions of the model are supported by results of comparative analyses for the Carnivora and Insectivora, which demonstrate an increase in prenatal growth rate with increasing intensity of postnatal scramble competition, and a decrease in postnatal growth rate relative to size at birth. Because increased prenatal growth rates are predicted to select for reduced gestation length under certain conditions, our study also indicates that sibling rivalry may contribute to selection pressures influencing variation in altriciality and precociality among mammals.

Animal Nutritional Physiological Phenomena↗
PubMed1989

Modern mammal origins: evolutionary grades in the Early Cretaceous of North America.

Major groups of modern mammals have their origins in the Mesozoic Era, yet the mammalian fossil record is generally poor for that time interval. Fundamental morphological changes that led to modern mammals are often represented by small samples of isolated teeth. Fortunately, functional wear facets on teeth allow prediction of the morphology of occluding teeth that may be unrepresented by fossils. A major step in mammalian evolution occurred in the Early Cretaceous with the evolution of tribosphenic molars, which characterize marsupials and placentals, the two most abundant and diverse extant groups of mammals. A tooth from the Early Cretaceous (110 million years before present) of Texas tests previous predictions (based on lower molars) of the morphology of upper molars in early tribosphenic dentitions. The lingual cusp (protocone) is primitively without shear facets, as expected, but the cheek side of the tooth is derived (advanced) in having distinctive cusps along the margin. The tooth, although distressingly inadequate to define many features of the organism, demonstrates unexpected morphological diversity at a strategic stage of mammalian evolution and falsifies previous claims of the earliest occurrence of true marsupials.

Animals↗
PubMed1996

Distribution of endogenous type B and type D sheep retrovirus sequences in ungulates and other mammals.

The jaagsiekte sheep retrovirus (JSRV), which appears to be a type B/D retrovirus chimera, has been incriminated as the cause of ovine pulmonary carcinoma. Recent studies suggest that the sequences related to this virus are found in the genomes of normal sheep and goats. To learn whether there are breeds of sheep that lack the endogenous viral sequences and to study their distribution among other groups of mammals, we surveyed several domestic sheep and goat breeds, other ungulates, and various mammal groups for sequences related to JSRV. Probes prepared from the envelope (SU) region of JSRV and the capsid (CA) region of a Peruvian type D virus related to JSRV were used in Southern blot hybridization with genomic DNA followed by low- and high-stringency washes. Fifteen to 20 CA and SU bands were found in all members of the 13 breeds of domestic sheep and 6 breeds of goats tested. There were similar findings in 6 wild Ovis and Capra genera. Within 22 other genera of Bovidae including domestic cattle, and 7 other families of Artiodactyla including Cervidae, there were usually a few CA or SU bands at low stringency and rare bands at high stringency. Among 16 phylogenetically distant genera, there were generally fewer bands hybridizing with either probe. These results reveal wide-spread phylogenetic distribution of endogenous type B and type D retroviral sequences related to JSRV among mammals and argue for further investigation of their potential role in disease.

Animals↗
PubMed1999

The fossil record of North American mammals: evidence for a Paleocene evolutionary radiation.

Paleontologists long have argued that the most important evolutionary radiation of mammals occurred during the early Cenozoic, if not that all eutherians originated from a single common post-Cretaceous ancestor. Nonetheless, several recent molecular analyses claim to show that because several interordinal splits occurred during the Cretaceous, a major therian radiation was then underway. This claim conflicts with statistical evidence from the well-sampled latest Cretaceous and Cenozoic North American fossil record. Paleofaunal data confirm that there were fewer mammalian species during the latest Cretaceous than during any interval of the Cenozoic, and that a massive diversification took place during the early Paleocene, immediately after a mass extinction. Measurement data show that Cretaceous mammals were on average small and occupied a narrow range of body sizes; after the Cretaceous-Tertiary mass extinction, there was a rapid and permanent shift in the mean. The fact that there was an early Cenozoic mammalian radiation is entirely compatible with the existence of a few Cretaceous splits among modern mammal lineages.

Animals↗
PubMed2004

Sperm competition in mammals.

Although Darwin identified the evolutionary significance of competition between males in the context of reproduction, it is only in the past few decades that we have begun to appreciate the importance of competition at the gametic level. Sperm competition, defined as competition between the sperm of two or more males for fertilization of the same set of ova, is now recognised as a key selective force shaping male reproductive anatomy, physiology and behaviour across diverse animal groups, including mammals. The aim of this article is to provide a brief review of the selective consequences of sperm competition in mammals, with emphasis on recent theoretical advances and empirical controversies. Evidence of female influences on sperm competition outcomes in mammals is also discussed, and it is concluded that understanding the selective pressures driving coevolution between male and female reproductive traits remains a major challenge for researchers in this field.

Animals↗
PubMedDate not supplied

The principle of laplace and scaling of ventricular wall stress and blood pressure in mammals and birds.

Maximum left ventricular wall stress is calculated at end-diastolic volume and systemic arterial diastolic blood pressure, according to a thick-walled model for the principle of Laplace. Stress is independent of body mass and averages 13.9 kPa (+/-2.3; 95% confidence interval) in 24 species of mammals weighing 0.025-4,000 kg and 15.5 kPa (+/-4.7) in 12 birds weighing 0.014-110 kg. Birds have higher arterial blood pressures and larger hearts than mammals. Systolic and diastolic arterial blood pressures increase with body mass according to M(0.05) in mammals, and heart mass increases according to M(1.06) in the same species, further supporting the principle. However, blood pressure in birds is independent of body mass, and heart mass scales isometrically. End-diastolic stress values, calculated according to Laplace, are about one-third of peak stresses recorded in isolated mammalian myocardial preparations.

Animals↗
PubMed1983

Reproductive suppression among female mammals: implications for biomedicine and sexual selection theory.

Female mammals experience a very high and often unappreciated rate of reproductive failure. Among human pregnancies alone, over 50 per cent fail between conception and parturition, and the majority of these failures are unexplained. These findings present important problems for evolutionary theory as well as for health care practices. This paper addresses these high rates of reproductive failure among mammals, by extending the work of a number of evolutionary biologists regarding the reproductive consequences of environmental adversity. The basic model upon which we elaborate, termed the Reproductive Suppression Model, argues that females can optimize their lifetime reproductive success by suppressing reproduction when future conditions for the survival of offspring are likely to be sufficiently better than present ones as to exceed the costs of the suppression itself. These costs are a function of reproductive time lost and the direct phenotypic effects of the suppression itself. To evaluate the benefits and costs of suppression, the following types of cues should be assessed: the female's physical and mental health, her stage of reproduction, the physical and genetic status of her offspring, and the external conditions at the time of birth. We also examine various issues of social suppression, whereby the conditions for survival of offspring are a function of the reproduction and support of other group members. Under such conditions, some females may be able to improve current conditions for reproduction by suppressing the reproduction of others. Field data from our own work are presented, describing socially mediated reproductive competition among continuously breeding female yellow baboons and among female hoary marmots. Social suppression in other mammals is also evaluated, including that in human beings, and we conclude with some implications of the Reproductive Suppression Model for sexual selection theory regarding female-female reproductive competition, as well as human health care.

Abortion, Spontaneous↗
PubMed2000

Independent origin of IFN-alpha and IFN-beta in birds and mammals.

Phylogenetic analysis of type I interferon (IFN) from birds and mammals strongly supported the hypothesis that the gene duplication giving rise to the alpha and beta families of mammalian IFN occurred after the divergence of birds from mammals, whereas the bird IFN that have been designated alpha and beta duplicated independently in the avian lineage. Therefore, IFN designated alpha and beta in birds are not orthologous to those similarly designated in mammals.

Animals↗
PubMed2002

Serologic survey of Toxoplasma gondii in noncarnivorous free-ranging neotropical mammals in French Guiana.

The aim of this study was to determine the frequency of Toxoplasma infection in wild mammals, particularly noncarnivorous species, and to identify possible sources of infection for humans. A serological study was conducted that included 310 animals representing 10 species of terrestrial mammals from the same region (primary tropical rain forest inhabited by humans). Toxoplasmosis was diagnosed using a direct agglutination test using formalin-treated Toxoplasma gondii. The prevalence of antibodies for toxoplasmosis differed greatly between species and ranged from 0% to 62%. The seroprevalence of toxoplasmosis was zero or very low for tree-dwelling animals, which included sloth, porcupine, and howler monkey. Conversely, the prevalence of infection was 46-62% among granivores, insectivores, and burrowing animals, such as peccary, paca, and armadillo. We conclude that wild mammals in French Guiana constitute a reservoir of T. gondii parasites. Given the absence of domestic cats from the forest, noncarnivorous species may be infected by the ingestion of oocysts that are eliminated into the soil or water in the stools of wild cats and then dispersed.

Agglutination Tests↗
PubMed1994

The marsupial mitochondrial genome and the evolution of placental mammals.

The entire nucleotide sequence of the mitochondrial genome of the American opossum, Didelphis virginiana, was determined. Two major features distinguish this genome from those of other mammals. First, five tRNA genes around the origin of light strand replication are rearranged. Second, the anticodon of tRNA(Asp) is posttranscriptionally changed by an RNA editing process such that its coding capacity is altered. When the complete protein-coding region of the mitochondrial genome is used as an outgroup for placental mammals it can be shown that rodents represent an earlier branch among placental mammals than primates and artiodactyls and that artiodactyls share a common ancestor with carnivores. The overall rates of evolution of most of the mitochondrial genome of placentals are clock-like. Furthermore, the data indicate that the lineages leading to the mouse and rat may have diverged from each other as much as 35 million years ago.

Amino Acid Sequence↗
PubMed1998

Isochore evolution in mammals: a human-like ancestral structure.

Codon usage in mammals is mainly determined by the spatial arrangement of genomic G + C-content, i.e., the isochore structure. Ancestral G + C-content at third codon positions of 27 nuclear protein-coding genes of eutherian mammals was estimated by maximum-likelihood analysis on the basis of a nonhomogeneous DNA substitution model, accounting for variable base compositions among present-day sequences. Data consistently supported a human-like ancestral pattern, i.e., highly variable G + C-content among genes. The mouse genomic structure-more narrow G + C-content distribution-would be a derived state. The circumstances of isochore evolution are discussed with respect to this result. A possible relationship between G + C-content homogenization in murid genomes and high mutation rate is proposed, consistent with the negative selection hypothesis for isochore maintenance in mammals.

Animals↗
PubMedDate not supplied

Can developmentally significant spatial patterning of the egg be discounted in mammals?

Mammals are generally held to be exceptions to the rule that organization of the egg plays a role in specifying the differentiation of cells, axes, or other aspects of patterning in the early embryo. However, there are several grounds for questioning this conclusion. Not only do certain experimental findings remain unexplained but, more importantly, nearly all have been interpreted specifically in terms of the differentiation of trophectoderm versus inner cell mass. The possibility that egg organization is instrumental in patterning of the early embryo in mammals has so far been almost entirely neglected, notwithstanding evidence that the mouse blastocyst becomes bilaterally symmetrical before it implants. Difficulties confronting attempts to tackle the issue of the significance of egg organization in mammals are discussed with respect to polarity and cytoplasmic differentiation in the oocyte and zygote. Evidence for an enduring influence of the maternal genome during early development is reviewed and weaknesses in the case against a role for egg organization are exposed. Finally, consideration is given to what needs to be done if this issue is to be resolved.

Animals↗
PubMed1994

Transmission of Borrelia burgdorferi s.l. from mammal reservoirs to the primary vector of Lyme borreliosis, Ixodes ricinus (Acari: Ixodidae), in Sweden.

Factors regulating prevalence of Borrelia burgdorferi s.l. Johnson, Schmid, Hyde, Steigerwalt & Brenner in Ixodes ricinus (L.) were examined during 1991-1992 at Bogesund, near Stockholm in south-central Sweden. Nine species of small and medium-sized mammals (Sorex araneus L., S. minutus L., Neomys fodiens Pennant, Clethrionomys glareolus [Schreber], Microtus agrestis [L.], Apodemus sylvaticus [L.], A. flavicollis [Melchior], Lepus europaeus Pallas, L. timidus L.) were found to infect feeding tick larvae with B. burgdorferi s.l., whereas two species of large mammals (Capreolus capreolus L., Alces alces L.) failed to infect feeding tick larvae with this spirochete. The most important mammalian reservoirs at the study locality were S. araneus and rodents, accounting for 91% of all I. ricinus larvae infected. In view of the great number of potentially effective reservoirs for B. burgdorferi s.l. in Sweden, control of Lyme disease by reduction of abundance of reservoir hosts will be difficult to achieve. We also found that infectivity of a rodent species is related to the number of infesting, potentially infective nymphal I. ricinus. Insectivores and rodents were the most important hosts of larval I. ricinus, whereas most nymphal ticks fed on hares and cervids. Adult I. ricinus were frequently found on all species of hares and cervids examined but never on insectivores and rodents. No single species seemed to be of paramount importance as a source of blood for female ticks. Therefore, control of Lyme disease by reduction of abundance of mammal hosts available for female tick engorgement will probably require massive reductions of numbers of both C. capreolus and L. timidus.

Animals↗
PubMed1995

Effect of deer exclusion on the abundance of immature Ixodes scapularis (Acari: Ixodidae) parasitizing small and medium-sized mammals.

Effects of deer exclusion on abundance of immature Ixodes scapularis Say parasitizing small and medium-sized mammals, and the role mammals have in introducing ticks to exclosure areas, were examined at two sites in Westchester County, New York. In total, 686 mammal captures representing nine species were obtained, with white-footed mice, Peromyscus leucopus Rafinesque, composing > 80% of all captures, followed by raccoons, Procyon lotor (L.); opossums, Didelphis virginiana (Kerr); and striped skunks, Mephitis mephitis Schreber. At the Near Archives site, 14% of 81 individual mice, 46% of raccoons, and 33% of opossums captured were found to cross the exclosure fence, as did 12% of 50 mice and 38% of raccoons at the Hudson Pines site. Skunks apparently did not cross the fence at either site. Mice captured exclusively outside the Near Archives exclosure hosted significantly more larvae than mice captured inside only, with fence crossers hosting an intermediate number of larvae. At Hudson Pines, numbers of larvae on fence-crossing mice and those captured solely inside the exclosure were equivalent, with tick loads on mice captured outside the exclosure significantly greater. The number of larvae per raccoon did not differ significantly with capture location (inside, outside, or both sides of exclosure fence) at either site. Densities of host-seeking larvae and nymphs were significantly higher outside the exclosure than inside at Near Archives, though not at Hudson Pines. Differences in tick density inside and outside exclosures declined with each successive developmental stage so that adult density inside exclosures tended to converge with that outside at both sites. Although deer exclosures can have a significant impact on nymphal I. scapularis abundance, they may not reduce the risk of encountering infected adults. Mice, raccoons, and opossums have a role in introducing potentially infective ticks to areas where deer have been excluded, though the level of immigration of ticks into the area will likely depend on the density of ticks outside the exclosure.

Animals↗