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PubMed2005

Large Mesozoic mammals fed on young dinosaurs.

Mesozoic mammals are commonly portrayed as shrew- or rat-sized animals that were mainly insectivorous, probably nocturnal and lived in the shadow of dinosaurs. The largest known Mesozoic mammal represented by substantially complete remains is Repenomamus robustus, a triconodont mammal from the Lower Cretaceous of Liaoning, China. An adult individual of R. robustus was the size of a Virginia opossum. Here we report a new species of the genus, represented by a skeleton with most of the skull and postcranium preserved in articulation. The new species is 50% larger than R. robustus in skull length. In addition, stomach contents associated with a skeleton of R. robustus reveal remains of a juvenile Psittacosaurus, a ceratopsian dinosaur. Our discoveries constitute the first direct evidence that some triconodont mammals were carnivorous and fed on small vertebrates, including young dinosaurs, and also show that Mesozoic mammals had a much greater range of body sizes than previously known. We suggest that Mesozoic mammals occupied diverse niches and that some large mammals probably competed with dinosaurs for food and territory.

Animals↗
PubMedDate not supplied

The influence of foraging mode and arid adaptation on the basal metabolic rates of burrowing mammals.

Two competing but nonexclusive hypotheses to explain the reduced basal metabolic rate (BMR) of mammals that live and forage underground (fossorial species) are examined by comparing this group with burrowing mammals that forage on the surface (semifossorial species). These hypotheses suggest that the low BMR of fossorial species either compensates for the enormous energetic demands of subterranean foraging (the cost-of-burrowing hypothesis) or prevents overheating in closed burrow systems (the thermal-stress hypothesis). Because phylogentically informed allometric analysis showed that arid burrowing mammals have a significantly lower BMR than mesic ones, fossorial and semifossorial species were compared within these groups. The BMRs of mesic fossorial and semifossorial mammals could not be reliably distinguished, nor could the BMRs of large (>77 g) arid fossorial and semifossorial mammals. This finding favours the thermal-stress hypothesis, because the groups appear to have similar BMRs despite differences in foraging costs. However, in support of the cost-of-burrowing hypothesis, small (<77 g) arid fossorial mammals were found to have a significantly lower BMR than semifossorial mammals of the similar size. Given the high mass-specific metabolic rates of small animals, they are expected to be under severe energy and water stress in arid environments. Under such conditions, the greatly reduced BMR of small fossorial species may compensate for the enormous energetic demands of subterranean foraging.

Acclimatization↗
PubMed1993

Ticks (Acari: Ixodidae) infesting medium-sized wild mammals in southwestern Tennessee.

Seven species of ixodid ticks (n = 2,661) were found on medium-sized wild mammals (n = 295) during a 13-mo study in Shelby County, Tennessee. The seven tick species collected were Dermacentor variabilis (Say), Amblyomma americanum (L.), Rhipicephalus sanguineus (Latreille), Ixodes texanus (Banks), I. cookei (Packard), I. scapularis (Say), and Haemaphysalis leporispalustris (Packard). The raccoon had the greatest tick species diversity in all of the aforementioned ticks except H. leporispalustris and R. sanguineus. The raccoon and opossum accounted for 96.9% of the ticks collected and were the most commonly captured medium-sized mammals. The only tick collected in high enough numbers for statistical analysis was D. variabilis. Mammal species and habitat type were the most important factors affecting the mean number of adult D. variabilis per mammal. The mean number of D. variabilis adults carried by raccoons was significantly higher than opossums. Whether a habitat occurred within Memphis city limits or outside city limits also affected the number of adult D. variabilis on mammals. The interaction between habitat, mammal, and whether inside or outside the city limits was near statistical significance. It is suggested that there is biological significance; within city limits, medium-sized wild mammals are forced into wooded areas where there is a subsequent increase in tick populations in these habitat patches.

Animals↗
PubMed1984

A neural theory of circadian rhythms: Aschoff's rule in diurnal and nocturnal mammals.

A neural model of the suprachiasmatic nuclei suggests how behavioral activity, rest, and circadian period depend on light intensity in diurnal and nocturnal mammals. These properties are traced to the action of light input (external zeitgeber) and an activity-mediated fatigue signal (internal zeitgeber) on the circadian pacemaker. Light enhances activity of the diurnal model and suppresses activity of the nocturnal model. Fatigue suppresses activity in both diurnal and nocturnal models. The asymmetrical action of light and fatigue in diurnal vs. nocturnal models explains the more consistent adherence of nocturnal mammals to Aschoff's rule, the consistent adherence of both diurnal and nocturnal mammals to the circadian rule, and the tendency of nocturnal mammals to lose circadian rhythmicity at lower light levels than diurnal mammals. The fatigue signal is related to the sleep process S of Borbély (Hum. Neurobiol. 1: 195-204, 1982.) and contributes to the stability of circadian period. Two predictions follow: diurnal mammals obey Aschoff's rule less consistently during a self-selected light-dark cycle than in constant light, and if light level is increased enough during sleep in diurnal mammals to compensate for eye closure, then Aschoff's rule will hold more consistently. The results are compared with those of Enright's model.

Animals↗
PubMed2006

Eye morphology in cathemeral lemurids and other mammals.

The visual systems of cathemeral mammals are subject to selection pressures that are not encountered by strictly diurnal or nocturnal species. In particular, the cathemeral eye and retina must be able to function effectively across a broad range of ambient light intensities. This paper provides a review of the current state of knowledge regarding the visual anatomy of cathemeral primates, and presents an analysis of the influence of cathemerality on eye morphology in the genus Eulemur. Due to the mutual antagonism between most adaptations for increased visual acuity and sensitivity, cathemeral lemurs are expected to resemble other cathemeral mammals in having eye morphologies that are intermediate between those of diurnal and nocturnal close relatives. However, if lemurs only recently adopted cathemeral activity patterns, then cathemeral lemurids would be expected to demonstrate eye morphologies more comparable to those of nocturnal strepsirrhines. Both predictions were tested through a comparative study of relative cornea size in mammals. Intact eyes were collected from 147 specimens of 55 primate species, and relative corneal dimensions were compared to measurements taken from a large sample of non-primate mammals. These data reveal that the five extant species of the cathemeral genus Eulemur have relative cornea sizes intermediate between those of diurnal and nocturnal strepsirrhines. Moreover, all Eulemur species have relative cornea sizes that are comparable to those of cathemeral non-primate mammals and significantly smaller than those of nocturnal mammals. These results suggest that Eulemur species resemble other cathemeral mammals in having eyes that are adapted to function under variable environmental light levels. These results also suggest that cathemerality is a relatively ancient adaptation in Eulemur that was present in the last common ancestor of the genus (ca. 8-12 MYA).

Adaptation, Biological↗
PubMed1985

[Ontogeny and morphology of the round window and aqueduct of cochlea in Tupaia and other mammals].

Studied the morphogenesis of the Fenestra rotunda and of the Aquaeductus cochleae in a series of 23 dated embryos and postnatal stages of Tupaia belangeri. The ontogeny of the Fenestra rotunda is the result of the caudal growth of the Processus recessus (DE BEER 1937). The Processus arises from the caudal ridge of the floor of the cochlear part of the otic capsule. On the 28th d of ontogeny (the gestation period of Tupaia belangeri is 43 d), it is fused with the lateral edge of the parachordal plate. On the 40th d, the Processus recessus joins the ventral surface of the canalicular part of the otic capsule, which develops a small cartilaginous process to meet it. In Tupaia, the Processus recessus is a large cartilaginous plate in a nearly horizontal position. It does not reach the plane of the Foramen perilymphaticum. The Processus recessus can be regarded as a part of the parachordal plate that was shifted laterally together with the Recessus scalae tympani by the enlargement of the cochlear part of the otic capsule in the ancestors of living mammals. The Processus forms the floor of the Aquaeductus cochleae, by which the laterally shifted Recessus scalae tympani of mammals remains connected with the cranial cavity. The Aquaeductus cochleae contains the Ductus perilymphaticus connecting the Cavum perilymphaticum of the inner ear with the Cavum leptomeningeum. The Fenestra rotunda of mammals is homologous with the lateral aperture of the Recessus scalae tympani of reptiles. In some mammals (e.g. Micropotamogale), the Membrana tympani secundaria spans the lateral aperture of the Recessus scalae tympani, as in many reptiles. Both the Membrana tympani secundaria of reptiles and that of mammals are homologous. Secondarily, in a large number of therian mammals (e.g. Myotis [Frick 1952]), the tympanic cavity extends into the Recessus scalae tympani displacing the Membrana tympani secundaria medially from the lateral aperture of the Recessus scalae tympani (= Fenestra rotunda of mammals) and even into the plane of the Foramen perilymphaticum. Thereby the Fossula fenestrae rotundae is formed, which in bounded medially by the Membrana tympani secundaria.

Animals↗
PubMed2001

A killer appetite: metabolic consequences of carnivory in marine mammals.

Among terrestrial mammals, the morphology of the gastrointestinal tract reflects the metabolic demands of the animal and individual requirements for processing, distributing, and absorbing nutrients. To determine if gastrointestinal tract morphology is similarly correlated with metabolic requirements in marine mammals, we examined the relationship between basal metabolic rate (BMR) and small intestinal length in pinnipeds and cetaceans. Oxygen consumption was measured for resting bottlenose dolphins and Weddell seals, and the results combined with data for four additional species of carnivorous marine mammal. Data for small intestinal length were obtained from previously published reports. Similar analyses were conducted for five species of carnivorous terrestrial mammal, for which BMR and intestinal length were known. The results indicate that the BMRs of Weddell seals and dolphins resting on the water surface are 1.6 and 2.3 times the predicted levels for similarly sized domestic terrestrial mammals, respectively. Small intestinal lengths for carnivorous marine mammals depend on body size and are comparatively longer than those of terrestrial carnivores. The relationship between basal metabolic rate (kcal day(-1)) and small intestinal length (m) for both marine and terrestrial carnivores was, BMR=142.5 intestinal length(1.20) (r(2)=0.83). We suggest that elevated metabolic rates among marine mammal carnivores are associated with comparatively large alimentary tracts that are presumably required for supporting the energetic demands of an aquatic lifestyle and for feeding on vertebrate and invertebrate prey.

Animals↗
PubMed2003

Global distribution of radionuclides (137Cs and 40K) in marine mammals.

Concentrations of anthropogenic radionuclides were measured in the muscle of marine mammals collected from various locations all over the world, and the global distribution of 137Cs in marine mammals was investigated. 40K was detected in all the specimens of marine mammals with no apparent difference between regions. An anthropogenic radionuclide, 137Cs, was detected in most of the species of marine mammals. With regard to the worldwide distribution of 137Cs, the highest concentration was noticed in the U.K. coast, followed by Lake Baikal, and decreases toward the southern sampling points. A strong positive correlation was observed between 137Cs levels in the muscle of marine mammals and the ambient seawater. Marine mammals feeding on fishes showed a higher concentration factor (CF) for 137Cs than those feeding on cephalopods. To our knowledge, this is the first report on the global distribution of 137Cs and the effect of feeding habits on the CF values of 137Cs in marine mammals.

Animals↗
PubMed1991

Genetic analysis of the Rous sarcoma virus subgroup D env gene: mammal tropism correlates with temperature sensitivity of gp85.

Subgroup D avian sarcoma and leukosis viruses can penetrate a variety of mammalian cells in addition to cells from their natural host, chickens. Sequences derived from the gp85-coding domain within the env gene of a mammal-tropic subgroup D virus (Schmidt-Ruppin D strain of Rous sarcoma virus [SR-D RSV]) and a non-mammal-tropic subgroup B virus (Rous-associated virus type 2) were recombined to map genetic determinants that allow penetration of mammalian cells. The following conclusions were based on host range analysis of the recombinant viruses. (i) The determinants of gp85 that result in the mammal tropism phenotype of SR-D RSV are encoded within the 160 codons that lie 3' of codon 121 from the corresponding amino terminus of the gp85 protein. (ii) Small linear domains of the SR-D RSV gp85-coding domain placed in the subgroup B background did not yield viruses with titers equal to that of the subgroup D virus in a human cell line. (iii) Recombinant viruses that contained subgroup D sequences within the hr1 variable domain of gp85 showed modest-to-significant increases in infectivity on human cells relative to chicken cells. A recombinant virus that contained three fortuitous amino acid substitutions in the gp85-coding domain was found to penetrate the human cell line and give a titer similar to that of the subgroup D virus. In addition, we found that the subgroup D virus, the mutant virus, and recombinant viruses with an increased mammal tropism phenotype were unstable at 42 degrees C. These results suggest that the mammal tropism of the SR-D strain is not related to altered receptor specificity but rather to an unstable and fusogenic viral glycoprotein. A temperature sensitivity phenotype for infectivity of mammalian cells was also observed for another mammal-tropic avian retrovirus, the Bratislava 77 strain of RSV, a subgroup C virus, but was not seen for any other avian retrovirus tested, strengthening the correlation between mammal tropism and temperature sensitivity.

Animals↗
PubMed1981

Comparison of the "mammal machine" and the "reptile machine": energy use and thyroid activity.

Oxygen consumption of tissue slices of liver, kidney, and brain were measured at 37 degrees C to assess in vitro metabolism of tissues of Amphibolurus nuchalis and Mus musculus (a reptile and mammal with same weight and body temperature). "Sodium transport" metabolism was also assessed (with use of ouabain) in these tissues. The mammal had an in vitro tissue metabolism that was two to five times that of the reptile and its sodium transport metabolism was four- to ninefold greater. Growth of reptile young and mammal young at the same body temperature was measured and the mammal showed a growth rate that was an order of magnitude greater than the reptile. Thyroid activity was assessed in the reptile and mammal by measurement of thyroidal uptake and release of 125I and serum thyroxine concentration. All parameters indicated a greater thyroid activity in the mammal. These findings are discussed in relation to the action of the thyroid hormones, the paleoecology of mammals and reptiles and the evolution of endothermy.

Aging↗
PubMed2003

Whole-body mechanics and gaits in the gray short-tailed opossum Monodelphis domestica: integrating patterns of locomotion in a semi-erect mammal.

Gaits (footfall patterns) and external mechanical energy patterns of the center of mass were quantified in a generalized, semi-erect mammal in order to address three general questions. First, do semi-erect mammals exhibit the walk/run gait transitions that have been proposed as the primitive condition for tetrapods? Second, do small, semi-erect mammals employ the energy-saving pendular and spring-based mechanics used by erect mammals? Third, how well do mechanical locomotor patterns of the center of mass correlate with gaits? Monodelphis domestica utilizes only fast walking and running trot gaits over a fivefold increase in speed, over which we could illicit constant velocity steps, although running trots were their preferred gait. In sustained level locomotion the opossums did not use other walking gaits presumed to be primitive for tetrapods. Across the full range of speeds their trotting gaits exhibited force patterns and in-phase mechanical energy fluctuations that are characteristic of spring-mass mechanics. Thus, opossums appear to prefer trotting gaits with bouncing mechanics for sustained locomotion. Integration of center-of-mass versus footfall perspectives reveals that spring-mass mechanics is associated with both walking trot and running trot gaits. Furthermore, the onset of an aerial phase was not clearly associated with either the walk/run gait transition (50% duty factor) or a change in center-of-mass mechanics. The assumption that energy-saving mechanisms are ubiquitous among mammals is tenuous because small non-cursorial mammals do not appear to use pendular-based mechanics for sustained locomotion and, although they prefer spring-based mechanics, they probably lack clear musculoskeletal spring elements that could store energy during running. Thus, it appears that simply paying for locomotion with muscular work may be the primitive condition for mammals.

Animals↗
PubMed2024

High prevalence of PRDM9-independent recombination hotspots in placental mammals.

In many mammals, recombination events are concentrated in hotspots directed by a sequence-specific DNA-binding protein named PRDM9. Intriguingly, PRDM9 has been lost several times in vertebrates, and notably among mammals, it has been pseudogenized in the ancestor of canids. In the absence of PRDM9, recombination hotspots tend to occur in promoter-like features such as CpG islands. It has thus been proposed that one role of PRDM9 could be to direct recombination away from PRDM9-independent hotspots. However, the ability of PRDM9 to direct recombination hotspots has been assessed in only a handful of species, and a clear picture of how much recombination occurs outside of PRDM9-directed hotspots in mammals is still lacking. In this study, we derived an estimator of past recombination activity based on signatures of GC-biased gene conversion in substitution patterns. We quantified recombination activity in PRDM9-independent hotspots in 52 species of boreoeutherian mammals. We observe a wide range of recombination rates at these loci: several species (such as mice, humans, some felids, or cetaceans) show a deficit of recombination, while a majority of mammals display a clear peak of recombination. Our results demonstrate that PRDM9-directed and PRDM9-independent hotspots can coexist in mammals and that their coexistence appears to be the rule rather than the exception. Additionally, we show that the location of PRDM9-independent hotspots is relatively more stable than that of PRDM9-directed hotspots, but that PRDM9-independent hotspots nevertheless evolve slowly in concert with DNA hypomethylation.

Animals↗
PubMed1994

Predicting ecotoxicological impacts of environmental contaminants on terrestrial small mammals.

This review examines whether the effects of environmental contaminants on wild small mammals can be predicted from the results of single-species, laboratory toxicity studies. Heavy metals, organochlorines, chlorinated aromatic hydrocarbons, and OP/carbamate pesticides were identified as the groups of xenobiotics for which there are toxicity data for terrestrial small mammals and that, on the basis of persistence, acute toxicity, and bio-accumulation potential, present the greatest hazard to wild mammals. Laboratory-generated toxicity data, which used lethality and reproduction as measurable endpoints, were reviewed and intake and residue LOAELs estimated for representative chemicals (lead, endrin, PCBs) from the heavy metal, organochlorine, and chlorinated aromatic hydrocarbon substance groups; the OPs and carbamates were reviewed as a whole. Intakes and residues of these compounds in wild small mammals were compared with laboratory-defined LOAELs and the likelihood of effects predicted. The accuracy of these predictions was examined and the efficacy of extrapolating toxicity data from laboratory to wild species assessed. Qualitative extrapolation from laboratory to wild species was good for all the chemicals considered, laboratory tests correctly identifying the types of effects chemicals had on a wide range of wild mammals. In contrast, the quantitative extrapolation of dose-response data was either poor or largely unvalidated. This is because interspecies variation in sensitivity to xenobiotics and the effects on toxicity of differences in exposure pattern between laboratory and wild species are largely unquantified. Based upon the limited evidence available, errors in the direct extrapolation of dose-response data from laboratory to field may be as large as three orders of magnitude. Direct extrapolation of residue-response data from laboratory to wild mammals is good both for the effects of heavy metals on specific organs and for residues and acetylcholinesterase inhibition associated with pesticide-induced mortality. The use of organ residues or biomarkers to predict the severity of sublethal effects on reproductive output may be possible, although large residues or biomarker responses are not necessarily indicative of the severity of wider physiological effect. Appropriate residues/biomarkers may differ for various xenobiotics and even between species for the same xenobiotic. Further research is required to identify suitable markers that can be correlated with the occurrence and magnitude of ecologically important effects. Xenobiotics likely to have a direct effect on population dynamics are those that are persistent and adversely affect survival and reproduction. At present, this weak correlation is the only one that can be made between single-species laboratory tests and population effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2000

Fast evolution of interleukin-2 in mammals and positive selection in ruminants.

Interleukin-2 (IL-2) is a cytokine involved in induction and regulation of the immune response in mammals. There have been numerous reports about the search for IL-2 in species other than mammals, and recently an IL-2-like gene has been isolated in chicken. Using PCR, we searched for IL-2 gene sequences in a wide variety of mammals, including marsupials and monotremes, as well as in birds. Although we can readily amplify IL-2 gene fragments in placental mammals, no amplification was obtained in other species. This is best explained by very high substitution rates. This suggest that strategies to isolate IL-2 homologous genes outside mammals should involve functional assays, as for the chicken gene, and not hybridization-based techniques. Nonsynonymous substitution rates are especially high in ruminants, due to positive selection acting on regions important in term of structure-function. We suggest that, although globally similar, the immune response of various mammals is not identical, mainly at the level of cytokine-mediated regulations.

Amino Acid Sequence↗
PubMed1983

Respiratory adaptations in diving mammals.

This report examines the evidence for the presence of oxygen stores in the lungs, blood and systemic musculature of diving mammals, the modifications in the respiratory functions of blood that may be important in utilizing the lung and blood oxygen stores, and the potential importance of the oxygen stores and the respiratory functions of blood in supporting short-duration, aerobic dives. Increasing oxygen stores by increasing lung volume does not occur in diving mammals. The long-duration diving whales have small lung volumes which results in lung collapse during dives and the seals dive following partial expiration which produces the same effect. The short-duration diving dolphins, porpoises and rodents have lung volumes comparable to terrestrial mammals, dive following inspiration and appear to use the lungs as an oxygen store. Adaptations in the oxygen affinity of the blood parallel the modifications in lung volume. Where the lungs do not represent a potential oxygen store the oxygen affinity is low, maximizing the unloading of oxygen while maintaining a high tissue oxygen tension. Where the lungs do represent an oxygen store, the affinity is high, maximizing the uptake of oxygen from the alveolar space. Increases in the concentration of respiratory pigment in the blood and in muscle are important adaptations in diving mammals. The blood oxygen stores in diving mammals vary from near normal to over three times normal for terrestrial mammals while the muscle oxygen stores vary from near normal to nearly ten times normal. The degree to which the blood and muscle oxygen stores are increased can be equated to the duration of the dive and demands for oxygen; longer duration divers and those with higher metabolic demands have greater oxygen stores than divers that remain submersed for shorter periods or have lower rates of oxygen utilization.

Animals↗
PubMed1994

The evolution of the dorsal thalamus of jawed vertebrates, including mammals: cladistic analysis and a new hypothesis.

The evolution of the dorsal thalamus in various vertebrate lineages of jawed vertebrates has been an enigma, partly due to two prevalent misconceptions: the belief that the multitude of nuclei in the dorsal thalamus of mammals could be meaningfully compared neither with the relatively few nuclei in the dorsal thalamus of anamniotes nor with the intermediate number of dorsal thalamic nuclei of other amniotes and a definition of the dorsal thalamus that too narrowly focused on the features of the dorsal thalamus of mammals. The cladistic analysis carried out here allows us to recognize which features are plesiomorphic and which apomorphic for the dorsal thalamus of jawed vertebrates and to then reconstruct the major changes that have occurred in the dorsal thalamus over evolution. Embryological data examined in the context of Von Baerian theory (embryos of later-descendant species resemble the embryos of earlier-descendant species to the point of their divergence) supports a new 'Dual Elaboration Hypothesis' of dorsal thalamic evolution generated from this cladistic analysis. From the morphotype for an early stage in the embryological development of the dorsal thalamus of jawed vertebrates, the divergent, sequential stages of the development of the dorsal thalamus are derived for each major radiation and compared. The new hypothesis holds that the dorsal thalamus comprises two basic divisions--the collothalamus and the lemnothalamus--that receive their predominant input from the midbrain roof and (plesiomorphically) from lemniscal pathways, including the optic tract, respectively. Where present, the collothalamic, midbrain-sensory relay nuclei are homologous to each other in all vertebrate radiations as discrete nuclei. Within the lemnothalamus, the dorsal lateral geniculate nucleus of mammals and the dorsal lateral optic nucleus of non-synapsid amniotes (diapsid reptiles, birds and turtles) are homologous as discrete nuclei; most or all of the ventral nuclear group of mammals is homologous as a field to the lemniscal somatosensory relay and motor feedback nuclei of non-synapsid amniotes; the anterior, intralaminar and medial nuclear groups of mammals are collectively homologous as a field to both the dorsomedial and dorsolateral (including perirotundal) nuclei of non-synapsid amniotes; the anterior, intralaminar, medial and ventral nuclear groups and the dorsal lateral geniculate nucleus of mammals are collectively homologous as a field to the nucleus anterior of anamniotes, as are their homologues in non-synapsid amniotes. In the captorhinomorph ancestors of extant land vertebrates, both divisions of the dorsal thalamus were elaborated to some extent due to an increase in proliferation and lateral migration of neurons during development.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2006

Longevity and the evolution of the mitochondrial DNA-coded proteins in mammals.

The amino acids sequences of the mitochondrial DNA-coded peptides of placental mammals evolved at different rates in different branches of the mammalian phylogenetic tree. Adaptive selection was suggested to account for the faster evolution of some mitochondrial DNA-coded proteins in several branches of the mammalian tree, but the driving force(s) for the accelerated evolution has not been elucidated. Mitochondria generate reactive oxygen species (ROS) that appear to constrain the life span of many species. Therefore, I tested the hypothesis that the evolution of mammalian longevity drives the accelerated evolution of mitochondrial DNA-coded peptides. Using rodents as an outgroup for a clad that included most placental mammals (excluding rodents and hedgehogs) the computed rates of amino acid substitution per site were positively correlated with genus longevity (maximal observed averaged life span) for most of the mitochondrial DNA-coded peptides. The substitution per site of ATP6, the proton conducting subunit of ATPsynthase, CYTB, the core subunit of ubiquinone oxidoreductase that participate in both electron and proton transport, and ND3, a subunit of NADH dehydrogenase, showed the strongest correlations with longevity. Additional confirmation for the hypothesis was obtained by the observation that the genetic distances between placental mammals species that belong to different orders are positively correlated with the sum of longevities of the species pairs. The substitutions per site for the entire amino acid sequence coded by the heavy strand mtDNA were also positively correlated with the average longevities of the placental mammals orders. These results support the hypothesis that the evolution of longevity in mammals drove the accelerated evolution of mtDNA-coded peptide. It is suggested that, in mammals, adaptive selection of mutations that decrease the rate of production of reactive oxygen species, directly or indirectly (e.g. by increasing proton leak), increases longevity.

Animals↗
PubMed2002

Relative importance of lizards and mammals as hosts for ixodid ticks in northern California.

Abstract Lizards and mammals were trapped and examined for ticks from August 1992 to June 1993 in two habitat types, chaparral and woodland-grass, in northern California. Five tick species were collected from mammals (Dermacentor occidentalis, Haemaphysalis leporispalustris, Ixodes pacificus, I. spinipalpis, I. woodi), but only I. pacificus was found on lizards. Dermacentor occidentalis, I. pacificus, and I. woodi occurred in both habitats, whereas H. leporispalustris and I. spinipalpis were found only on animals trapped in chaparral. The tick species most commonly encountered on mammals was D. occidentalis in chaparral and I. pacificus in woodland-grass. Peak infestation of mammals occurred in spring for I. pacificus immatures and H. leporispalustris, summer for D. occidentalis immatures, fall through spring for I. woodi immatures, and fall through winter for I. spinipalpis. The primary aim of the study was to quantify the relative importance of the western fence lizard (Sceloporus occidentalis), which is reservoir-incompetent for Borrelia burgdorferi sensu lato (s.l.), and mammalian B. burgdorferi s.l.-reservoirs as hosts for the immature stages of I. pacificus in spring. The estimated relative utilization by I. pacificus of the western fence lizard versus mammals was 88% for larvae and 99% for nymphs in chaparral in May. When tick infestation data were corrected for a two-fold lower efficiency of field examinations for rodents than for lizards, the western fence lizard still accounted for 78% of larval and 98% of nymphal feedings. In woodland-grass, 46% of 100 I. pacificus larvae and 100% of 52 nymphs recovered from mammals or western fence lizards during May-June were collected from the lizards. However, this may represent an underestimate of the importance of the western fence lizard as a larval host in this habitat because inclement weather during the late May sampling period doubtless resulted in significantly decreased lizard activity. In conclusion, the western fence lizard was more heavily utilized by I. pacificus immatures, especially nymphs, than were rodents.

Animals↗