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PubMed2006

Bycatch of marine mammals in U.S. and global fisheries.

Fisheries bycatch poses a significant threat to many populations of marine mammals, but there are few published estimates of the magnitude of these catches. We estimated marine mammal bycatch in U.S. fisheries from 1990 to 1999 with data taken from the stock assessment reports required by the U.S. Marine Mammal Protection Act. The mean annual bycatch of marine mammals during this period was 6215 +/- 448 (SE). Bycatch of cetaceans and pinnipeds occurred in similar numbers. Most cetacean (84%) and pinniped (98%) bycatch occurred in gill-net fisheries. Marine mammal bycatch declined significantly over the decade, primarily because of a reduction in the bycatch of cetaceans. Total marine mammal bycatch was significantly lower after the implementation of take reduction measures in the latter half of the decade. We derived a crude first estimate of marine mammal bycatch in the world's fisheries by expanding U.S. bycatch with data on fleet composition from the Food and Agriculture Organization. The global bycatch of marine mammals is in the hundreds of thousands. Bycatch is likely to have significant demographic effects on many populations of marine mammals. Better data are urgently needed to fully understand the impact of these interactions.

Animals↗
PubMed2005

Seasonal thermoregulatory responses in mammals.

This study examined the proportional seasonal winter adjustments of total and mass-specific basal power (watts and watts g-1, respectively), thermal conductance (watts g-1 degrees C-1), non-shivering thermogenesis capacity (ratio of NST/basal power), body temperature ( degrees C), and body mass (g) of mammals. The responses are best summarized for three different body size classes; small mammals (<100 g), intermediate-sized mammals (0.1-10 kg), and large mammals (>10 kg). The principal adjustments of the small mammals center on energy conservation, especially the Dehnel Effect, the winter reduction in body size of as much as 50%, accompanied by reductions in mass-specific basal power. On average, these reductions reduce the total basal power approximately in direct proportion to the mass reductions. Reductions in mass-specific basal power are matched by concomitant reductions in conductance to maintain the setpoint body temperature during winter. The overall thermoregulatory adjustments in small mammals serve to (a) lower overall winter power consumption, (b) maintain the setpoint body temperature, and (c) lower the lower critical limit of thermoneutrality and hence thermoregulatory costs. In intermediate-size mammals, the seasonal response is centered more on increasing thermogenic capacity by increasing basal power and NST capacity, accompanied by predictable and large reductions in conductance. The Dehnel effect is negligible. Very large mammals undergo the largest reductions in total and mass-specific basal power and conductance. However, there are too few data to resolve whether the reductions in total basal power can be attributed to the Dehnel effect, because the moderate decreases in body mass may also be caused by nutritional stress. Apart from the seasonal changes in basal power, these observations are consistent with the predictions of Heldmaier's seasonal acclimatization model.

Acclimatization↗
PubMed2006

Differences in the umbrella effects of African amphibians and mammals based on two estimators of the area of occupancy.

Conservation organizations are collecting large-scale data regarding distribution and threats to vertebrate taxa. These data sets will enable planners to systematically identify large-scale conservation priorities; however, they will cover only a tiny proportion of living organisms. Therefore, it is essential to investigate to what extent the areas selected for conservation actions can provide protection for other species. We analyzed the umbrella effect between amphibians and mammals across mainland Africa. We built habitat suitability models within the geographic ranges of 1654 species, based on data collected in the framework of the World Conservation Union (IUCN) Global Amphibian Assessment and IUCN Global Mammal Assessment. We applied systematic reserve selection algorithms to two sets of estimators of the area of occupancy of amphibians and mammals (geographic ranges and estimated suitable areas) and thus selected four reserve systems. We then quantified the protection that each of the four systems provided for amphibians and mammals. Reserves selected for amphibians and mammals were comparable in area, with the former concentrated in the Afrotropical region and the latter more evenly dispersed. Mammal reserves left fewer gaps in species coverage among amphibians than the reverse, but amphibian reserves included a larger proportion of each mammal's area of occupancy than the reverse. For both taxa, setting reserves to include estimated suitable areas instead of ranges resulted in the clustering of reserves in the tropics. Furthermore, it efficiently protected hidden gaps (species with unsuitable portions of their range inside protected areas) in the other taxon and included a higher proportion of the area of occupancy of the other taxon. Overall, amphibians and mammals in Africa acted as an umbrella for a high proportion of species in the other taxon. Focusing on estimated suitable areas instead of ranges improved the umbrella effect of both taxa.

Africa↗
PubMed1999

Energetics of free-ranging mammals, reptiles, and birds.

We summarize the recent information on field metabolic rates (FMR) of wild terrestrial vertebrates as determined by the doubly labeled water technique. Allometric (scaling) relationships are calculated for mammals (79 species), reptiles (55 species), and birds (95 species) and for various taxonomic, dietary, and habitat groups within these categories. Exponential equations based on body mass are offered for predicting rates of daily energy expenditure and daily food requirements of free-ranging mammals, reptiles, and birds. Significant scaling differences between various taxa, dietary, and habitat groups (detected by analysis of covariance with P < or = 0.05) include the following: (a) The allometric slope for reptiles (0.889) is greater than that for mammals (0.734), which is greater than that for birds (0.681); (b) the slope for eutherian mammals (0.772) is greater than that for marsupial mammals (0.590); (c) among families of birds, slopes do not differ but elevations (intercepts) do, with passerine and procellariid birds having relatively high FMRs and gallinaceous birds having low FMRs; (d) Scleroglossan lizards have a higher slope (0.949) than do Iguanian lizards (0.793); (e) desert mammals have a higher slope (0.785) than do nondesert mammals; (f) marine birds have relatively high FMRs and desert birds have low FMRs; and (g) carnivorous mammals have a relatively high slope and carnivorous, insectivorous, and nectarivorous birds have relatively higher FMRs than do omnivores and granivores. The difference detected between passerine and nonpasserine birds reported in earlier reviews is not evident in the larger data set analyzed here. When the results are adjusted for phylogenetic effects using independent contrasts analysis, the difference between allometric slopes for marsupials and eutherians is no longer significant and the slope difference between Scleroglossan and Iguanian lizards disappears as well, but other taxonomic differences remain significant. Possible causes of the unexplained variations in FMR that could improve our currently inaccurate FMR prediction capabilities should be evaluated, including many important groups of terrestrial vertebrates that remain under- or unstudied and such factors as reproductive, thermoregulatory, social, and predator-avoidance behavior.

Animals↗
PubMed2006

Small mammals and forest fuel reduction: national-scale responses to fire and fire surrogates.

Forest fuel reduction treatments are increasingly used by managers to reduce the risk of high-severity wildfire and to manage changes in the ecological function of forests. However, comparative ecological effects of the various types of treatments are poorly understood. We examined short-term patterns in small-mammal responses to mechanical thinning, prescribed-fire, and mechanical thinning/prescribed-fire combination treatments at eight different study areas across the United States as a part of the National Fire and Fire Surrogate (FFS) Project. Research questions included: (1) do treatments differ in their effect on small mammal densities and biomass? and (2) are effects of treatments consistent across study areas? We modeled taxa-specific densities and total small-mammal biomass as functions of treatment types and study area effects and ranked models based on an information-theoretic model selection criterion. Small-mammal taxa examined, including deer mice (Peromyscus maniculatus), yellow-pine chipmunks (Tamias amoenus), and golden-mantled ground squirrels (Spermophilus lateralis), as well as all Peromyscus and Tamias species, had top-ranked models with responses varying both by treatment type and study area. In each of these cases, the top-ranked model carried between 69% and 99% of the total weight in the model set, indicating strong support for the top-ranked models. However, the top-ranked model of total small-mammal biomass was a model with biomass varying only with treatment (i.e., treated vs. untreated), not by treatment type or study area; again, this model had strong support, with 75% of the total model weight. Individual species and taxa appear to have variable responses to fuel reduction treatment types in different areas; however, total small-mammal biomass appears generally to increase after any type of fuel reduction. These results suggest that there is substantial variability in taxa-specific responses to treatments and indicate that adaptive management policies may be necessary when applying fuel reduction treatments in areas where management of small-mammal populations is of interest. Adaptive management can be used by managers who are conducting fuel reduction treatments to reduce uncertainty as to which treatments are locally optimal for meeting objectives for the management of small-mammal populations.

Animals↗
PubMed2006

Future directions in training of veterinarians for small exotic mammal medicine: expectations, potential, opportunities, and mandates.

Small exotic mammals have been companions to people for almost as long as dogs and cats have been. The challenge for veterinary medicine today is to decipher the tea leaves and determine whether small mammals are fad or transient pets or whether they will still be popular in 20 years. This article focuses on pet small-mammal medicine, as the concerns of the laboratory animal are better known and may differ profoundly from those of a pet. Dozens of species of small exotic mammals are kept as pets. These pet small-mammal species have historically served human purposes other than companionship: for hunting, for their pelts, or for meat. Now, they are common pets. At present, most veterinary schools lack courses in the medical care of these animals. Veterinary students need at least one required class to introduce them to these pets. Currently, there are no small-mammal-only residency programs. This does not correspond with current needs. The only way to judge current needs is by assessing what employers are looking for. In a recent JAVMA classified section, almost 30% of small-animal practices in suburban/urban areas were hiring veterinarians with knowledge of exotic pets. All veterinarians must recognize that pet exotic small mammals have changed the landscape of small-animal medicine. It is a reality that, today, many small-animal practices see pet exotic small mammals on a daily basis.

Animal Husbandry↗
PubMed2005

[Jaws of primitive mammals].

Some of main osteological differences between mammals and reptiles are seen in the number of bones that constitute lower jaw and in jaw articulation. A lower jaw of mammals consists of only one bone, while in reptiles it consists of several bones (e.g., four to six in lizards and five in crocodiles). The jaw articulation in mammals is performed by squamosal of the skull and the mandible ( = dentary), while in reptiles it is done by quadrate of the skull and articular of the lower jaw. When mammals first appeared about 200 million years ago in the Mesozoic Era, the jaws of primitive mammals were morphologically intermediate between those of reptiles and typical mammals. Here, I briefly introduce the evolution of lower jaw morphology from the reptilian one to the mammalian one, showing lower jaw features of some mammal-like reptiles and primitive mammals.

Animals↗
PubMed2000

Cloning and expression, pharmacological characterization, and internalization kinetics of the pituitary GnRH receptor in a metatherian species of mammal.

Gonadotropin-releasing hormone receptors (GnRH-Rs) expressed in the pituitary of eutherian species of mammal are unique in lacking the cytoplasmic C-terminal tail characteristic of GnRH-Rs of nonmammalian vertebrates and other G protein-coupled receptors. To further investigate evolutionary relationships among vertebrate GnRH-Rs, a full-coding region cDNA of the pituitary GnRH-R was cloned from a metatherian marsupial mammal, the Australian brushtail possum (Trichosurus vulpecula). We have determined the pharmacological characteristics and internalization kinetics of this GnRH-R from an early evolved, metatherian species of mammal and compared it with the corresponding receptors in eutherian species of mammal and nonmammalian vertebrates. The predicted GnRH-R protein from the possum pituitary has high homology with the other mammalian GnRH-Rs (80% identity) and, in common with other mammals, lacks an intracellular C-terminal tail. The ligand selectivity of the possum GnRH-R transfected into COS-1 cells, assessed using inositol phosphate assays and radioreceptor binding assays, was similar to that of the other mammalian GnRH-Rs, and distinct from those of the nonmammalian GnRH-Rs. The pharmacological characteristics of the possum GnRH-R were similar to those of other mammalian GnRH-Rs, for a selection of agonists (including naturally occurring GnRH ligands and superagonists) and antagonists. Receptor-mediated internalization of GnRH agonist by the possum GnRH-R was slightly more rapid than that of the human GnRH-R, while the internalization kinetics of the chicken GnRH-R, in which a cytoplasmic C-terminal tail is present, was considerably more rapid. In terms of the evolution of the GnRH-R in vertebrates, the possum (a metatherian mammal) GnRH-R has a striking resemblance, in both structure and pharmacological characteristics, to GnRH-Rs in eutherian mammals, which are quite distinct from the nonmammalian vertebrate GnRH-Rs, and are unique among G protein-coupled receptors in lacking an intracellular C-terminal tail. The distinct structure of the pituitary GnRH-R in mammalian vertebrates is likely to have important functional consequences in the reproductive physiology of mammals.

Amino Acid Sequence↗
PubMed1995

Membrane fatty acid composition of tissues is related to body mass of mammals.

Phospholipids were extracted from tissues (heart, skeletal muscle, kidney cortex, liver and brain) of mammals representing a 9,000-fold range in body mass (mouse, rat, rabbit, sheep and cattle) and their fatty acid composition was determined. In heart, skeletal muscle and kidney cortex, there were significant allometric decreases in the Unsaturation Index (UI; average number of double bonds per 100 fatty acid molecules) with increasing body mass. There were significant inverse allometric relationships between body mass and the proportion of docosahexaenoic acid (22:6 omega 3) in heart and skeletal muscle. In heart, skeletal muscle and kidney cortex, larger mammals also had shorter fatty acid chains in their phospholipids and a higher proportion of monounsaturates. In liver, smaller mammals had a higher UI than larger mammals (except the rabbit, which had the lowest UI and very low proportions of omega 3 fatty acids). The brain of all mammals maintained a high UI with similar levels of polyunsaturated fatty acids, especially 22:6 omega 3. Our results suggest that in heart, skeletal muscle and kidney cortex the activity of the elongases and desaturases are reduced in large mammals compared to small mammals. The allometric trends in membrane composition may be involved in modifying membrane permeability. It is proposed that the elevated degree of polyunsaturation in the membranes of several tissues from small mammals is related to their higher metabolic activity.

Animals↗
PubMed2002

Biochemical aspects of pressure tolerance in marine mammals.

Some marine mammals can dive to depths approaching 2000 m. At these hydrostatic pressures (200 atm), some fish species show alterations in enzyme structure and function that make them pressure-tolerant. Do marine mammals also possess biochemical adaptations to withstand such pressures? In theory, biochemical alterations might occur at the control of enzymatic pathways, by impacting cell membrane fluidity changes or at a higher level, such as cellular metabolism. Studies of marine mammal tissues show evidence of all of these changes, but the results are not consistent across species or diving depth. This review discusses whether the elevated body temperature of marine mammals imparts pressure tolerance at the biochemical level, whether there are cell membrane structural differences in marine mammals and whether whole, living cells from marine mammals alter their metabolism when pressure stressed. We conclude that temperature alone is probably not protective against pressure and that cell membrane composition data are not conclusive. Whole cell studies suggest that marine mammals either respond positively to pressure or are not impacted by pressure. However, the range of tissue types and enzyme systems that have been studied is extremely limited and needs to be expanded before more general conclusions about how these mammals tolerate elevated pressures on a biochemical level can be drawn.

Adaptation, Physiological↗
PubMed1989

Basic functional properties of the cardiac muscle of the common shrew (Sorex araneus) and some other small mammals.

The resting heartbeat frequency of all the studied wild small mammals (body mass 3-20 g) was lower than that predicted by the allometric equation for a typical mammal. The heart rate of the laboratory mouse was a little higher than the expected value. The ventricular mass of the small wild mammals was higher than predicted for their size, but that of the laboratory mouse was below the expected value. Thus, adequate cardiac output in the wild small mammals is achieved by compensating the low heartbeat frequency with greater stroke volume. The shrew species are notable exceptions, which, despite having a metabolic rate 2-3 times higher than the mammalian average, neither have exceptionally high heart rates nor larger hearts than other wild small mammals. The adaptation of the shrew heart to high metabolic rate may reside in the shape of heart. The ventricular myocardium of shrews is characteristically long and narrow with a tapered apex, whereas other small mammals have rounder hearts. The duration of the ventricular action potential was short and inversely proportional to the resting heart rate of the mammalian species. Caffeine (5 mmol l-1) strongly decreased the isometric contractile force of right ventricular strips in all the studied mammals. These findings suggest that in the small mammals intracellular stores are the main source of activating Ca2+, whereas transsarcolemmal Ca2+ movement may only serve the triggering function.

Action Potentials↗
PubMed1986

How do food passage rate and assimilation differ between herbivorous lizards and nonruminant mammals?

What digestive adaptations permit herbivorous nonruminant mammals to sustain much higher metabolic rates than herbivorous lizards, despite gross similarity in digestive anatomy and physiology? We approached this question by comparing four herbivorous species eating the same diet of alfalfa pellets: two lizards (chuckwalla and desert iugana) and two mammals (desert woodrat and laboratory mouse). The mammals had longer small and large intestines, greater intestinal surface area, much higher (by an order of magnitude) food intake normalized to metabolic live mass, and much faster food passage times (a few hours instead of a few days). Among both reptiles and mammals, passage times increase with body size and are longer for herbivores than for carnivores. The herbivorous lizards, despite these much slower passage times, had slightly lower apparent digestive efficiencies than the mammals. At least for chuckwallas, this difference from mammals was not due to differences in body temperature regime. Comparisons of chuckwallas and woodrats in their assimilation of various dietary components showed that the woodrat's main advantage lay in greater assimilation of the dietary fiber fraction. Woodrats achieved greater fiber digestion despite shorter residence time, but possibly because of a larger fermentation chamber, coprophagy, and/or different conditions for microbial fermentation. We conclude with a comparative overview of digestive function in herbivorous lizards and mammals, and with a list of four major unsolved questions.

Adaptation, Biological↗
PubMed1984

Organ scaling in mammals: the kidneys.

Values of kidney weight in adult male and female mammals, both terrestrial and aquatic, as well as values for renal blood flow and glomerular number and diameter, were submitted to linear (log-log) regression analysis. The slope of the regression line for kidney weight in 63 species of adult terrestrial mammals was 0.85 %/- 0.01. No statistically significant difference was found between the slopes of the regression lines for male and female terrestrial mammals. The slope of regression line for kidney weight in eight species of adult aquatic mammals was 0.92 +/- 0.01. Again, no statistically significant difference was found between the slopes for males and females. However, the slope (0.92) of the regression line for aquatic mammals was significantly different from the slope (0.85) for terrestrial mammals (P much less than 0.001). The slope of the regression of renal blood flow on body weight was 0.82 +/- 0.01. This value is consistent with the hypothesis that renal blood flow represents a constant fraction of cardiac output (over about 3.4 orders of magnitude in body weight). The slopes of the regression lines for glomerular number (per kidney) and mean glomerular diameter were 0.59 +/- 0.02 and 0.11 +/- 0.01, respectively. A schematic model representing the scaling of energy-partitioning in mammals is introduced.

Animals↗
PubMed1988

Biochemical and toxigenic characteristics of Aeromonas spp. isolated from diseased mammals, moribund and healthy fish.

In this study we describe biochemical, toxigenic and surface characteristics of 33 motile Aeromonas isolated from diseased mammals, 3 from moribund marine mammals, 24 from healthy fish and 4 from moribund fish. Aeromonas hydrophila, A. caviae and A. sobria were isolated from both mammals and fish but at a different incidence. Aeromonas hydrophila was the predominant species isolated from clinical specimens; it was isolated from pneumonia, wound infections, septicemia and abortion in horses, cattle and pigs. Aeromonas sobria was isolated from one mammal and 11 healthy fish. Aeromonas caviae was isolated in 2 cases from healthy fish and in 9 cases from diseased mammals. Variations in some biochemical tests including sorbitol, amylase and citrate, were observed between isolates from different sources. However, these differences did not allow the differentiation of isolates from diseased mammals and healthy fish. The majority of A. hydrophila isolates produced different extracellular products; A. sobria isolates produced less exotoxin. With A. caviae isolates no hemolysin, protease, enterotoxin or elastase were detected. There was no quantitative difference in hemolysin, protease, enterotoxin or elastase production between isolates from mammals and fish. It is suggested that A. hydrophila could be a potential pathogen for domestic animals, and fish may represent a potential reservoir of infection.

Aeromonas↗
PubMed2006

Resting breathing frequency in aquatic mammals: a comparative analysis with terrestrial species.

Several species of aquatic mammals, while resting at the water surface, breathe with a low frequency (f). We asked if this was a general characteristic of mammals adapted to life in water. Measurements of f were obtained in 42 aquatic mammals of 19 species, during resting conditions. Data of additional 10 species were available from the literature. The allometric function for aquatic mammals was f=33W(-0.42) (f, breaths/min; W, kg; N=29, one data point per species, from six mammalian orders). This exponent was significantly different from that of the allometric curve of terrestrial mammals (W(-0.25)). The difference between aquatic and terrestrial species was small up to about 10kg, and widened with the increase in W. Out of several possibilities, it seems that the breath-holding response to favour buoyancy at the water surface could have contributed to the evolution of the low-f breathing, but a satisfactory explanation for the allometric pattern of f is still unavailable. In semi-aquatic mammals the low-f pattern observed at the water surface was maintained ashore, with no difference in the allometric function. As in the adult, also in the newborn of aquatic species f was low, compared to same-size neonates of terrestrial species. Hence, the low f has evolved to be part of the genetic makeup of aquatic mammals, retained when the animal is ashore, and already expressed at birth.

Adaptation, Physiological↗
PubMed2006

The evolution of a physiological system: the pulmonary surfactant system in diving mammals.

Pulmonary surfactant lines the alveolar air-water interface, varying surface tension with lung volume to increase compliance and prevent adhesion of respiratory surfaces. We examined whether the surfactant system of diving mammals exhibits adaptations for more efficient lung function during diving, to complement other respiratory adaptations. Here we review adaptations at the molecular, compositional, functional and cellular levels and during development for animals beginning life on land and progressing to an aquatic environment. Molecular adaptations to diving were examined in surfactant protein C (SP-C) from terrestrial, semi-aquatic and diving mammals using phylogenetic analyses. Diving species exhibited sites under positive selection in the polar N-terminal domain. These amino acid substitutions may lead to stronger binding of SP-C to the phospholipid film and increased adsorption to the air-liquid interface. The concentration of shorter chain phospholipid molecular species was greater and SP-B levels were lower in diving than terrestrial mammals. This may lead to a greater fluidity and explain the relatively poor surface activity of diving mammal surfactant. There were no consistent differences in cholesterol between diving and terrestrial mammals. Surfactant from newborn California sea lions was similar to that of terrestrial mammals. Secretory activity of alveolar type II epithelial cells of sea lions demonstrated an insensitivity to pressure relative to sheep cells. The poor surface activity of diving mammal surfactant is consistent with the hypothesis that it has an anti-adhesive function that develops after the first entry into the water, with a surfactant film that is better suited to repeated collapse and respreading.

Adaptation, Physiological↗
PubMed1997

A new symmetrodont mammal from China and its implications for mammalian evolution.

A new symmetrodont mammal has been discovered in the Mesozoic era (Late Jurassic or Early Cretaceous period) of Liaoning Province, China. Archaic therian mammals, including symmetrodonts, are extinct relatives of the living marsupial and placental therians. However, these archaic therians have been mostly documented by fragmentary fossils. This newfossil taxon, represented by a nearly complete postcranial skeleton and a partial skull with dentition, is the best-preserved symmetrodont mammal yet discovered. It provides a new insight into the relationships of the major lineages of mammals and the evolution of the mammalian skeleton. Our analysis suggests that this new taxon represents a part of the early therian radiation before the divergence of living marsupials and placentals; that therians and multituberculates are more closely related to each other than either group is to other mammalian lineages; that archaic therians lacked the more parasagittal posture of the forelimb of most living therian mammals; and that archaic therians, such as symmetrodonts, retained the primitive feature of a finger-like promontorium (possibly with a straight cochlea) of the non-therian mammals. The fully coiled cochlea evolved later in more derived therian mammals, and is therefore convergent to the partially coiled cochlea of monotremes.

Animals↗
PubMed2002

Common mammals drive the evolutionary increase of hypsodonty in the Neogene.

During the past 20 million years, herbivorous mammals of numerous lineages have evolved hypsodont, or high-crowned, cheek teeth. Hypsodonty is informative ecologically because it is well developed in mammals eating fibrous and abrasive foods that are most abundant in open and generally or seasonally dry environments. Here we report that in the Neogene of Europe mammals with the greatest locality coverages showed an increase in hypsodonty. We used a data set of 209 localities to measure whether large mammals occurring in many fossil localities show a similar increase in hypsodonty to mammals occurring in single or few localities. Taxonomic and morphological groupings show a low average hypsodonty in the early Miocene epoch. From the middle Miocene onwards, only the hypsodonty of commonly found mammals shows a marked increase. Therefore, in the drying Europe of the late Miocene, only increasingly hypsodont mammals may have been able to expand their share of habitats and food resources. These results suggest that the relatively small number of species known from multiple localities are palaeoecologically informative by themselves, irrespective of the rest of the known species.

Animals↗