Read Ebook: Metabolic Adaptation to Climate and Distribution of the Raccoon Procyon Lotor and Other Procyonidae by Mahlke Johnson Kathleen P Mugaas John N Seidensticker John

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Materials and Methods 6 Live-trapping 6 Metabolic Studies 6 Basal and Thermoregulatory Metabolism 6 Evaporative Water Loss 7 Body Temperature 7 Calibrations 7 Calorimeter 7 Body Temperature Transmitters 8 Statistical Methods 8 Estimating Intrinsic Rate of Natural Increase 8 Comparison of Adaptive Units 8

Results 8 Body Mass 8 Basal Metabolic Rate 9 Minimum Thermal Conductance 9 Evaporative Water Loss 11 Thermoregulation at Low Temperatures 12 Body Temperature 12 Summer 14 Winter 14 Thermoregulation at High Temperatures 16 Body Temperature 16 Summer 16 Winter 16 Daily Cycle of Body Temperature 16

Appendix: List of Symbols 29

Literature Cited 30

$Introduction$

DEFINING THE PROBLEM

In the early Tertiary, mid-latitudes of North America were much warmer than they are now, but not fully tropical, and temperate deciduous forests, associated with strongly seasonal climates, occurred only in the far north . Major climatic deteriorations, with their attendant cooling of northern continents, occurred during the Eo-Oligocene transition, in the middle Miocene, at the end of the Miocene, and at about 3 MYBP . This last deterioration corresponds with closure of the Panamanian isthmus . Climatic deterioration went on at an accelerating rate during the late Tertiary, with glacial conditions developing at the poles by the mid-Pliocene . Therefore, throughout the Tertiary, as continents cooled, northern climate zones moved toward the tropics .

These are considered conspecific in some current taxonomies ; however, the scheme followed here maintains them as separate species .

During the late Miocene, late Pliocene, and Pleistocene, the Bering land bridge between North America and Asia formed periodically, offering an avenue for dispersal between northern continents . However, by the late Tertiary, northern continents had cooled to the extent that climate, with its attendant sharply defined vegetative zones, became the major factor limiting dispersal by this route . Those Holarctic mammals that did cross the Bering land bridge in the late Tertiary were "cold-adapted" species associated with relatively cool, but not alpine, climates . Among carnivores this included some canids, ursids, mustelids, and felids . Procyonids, however, did not cross the Bering land bridge into Asia, and Ewer ascribes this to their being an "essentially tropical group." Miocene radiation of procyonids occurred at a time when two of the four major climatic deteriorations were taking place . These deteriorations had the effect of cooling the middle latitudes to the extent that temperate forest forms began to appear in mid-latitude floras, along with a rapid influx of herbaceous plants . The procyonid radiation did not penetrate beyond these climatically changing middle latitudes, which implies that these animals were "warm-adapted," and were, therefore, physiologically excluded from reaching the Bering land bridge. Today, three of the six genera and over half of the 18 species that comprise Procyonidae remain confined to tropical regions of North and South America .

ADAPTIVE SIGNIFICANCE OF THE VARIABLES

EXPERIMENTAL DESIGN AND SUMMARY

ACKNOWLEDGMENTS

The authors would like to thank John Eisenberg and Devra Kleiman for their support and encouragement throughout the study. This investigation was supported by research grants from the West Virginia School of Osteopathic Medicine , and Friends of the National Zoo . Logistic support was provided by the National Zoological Park's Conservation and Research Center , and the departments of Mammalogy and Zoological Research. Our ability to conduct physiological research at CRC was made possible by the thoughtful support and encouragement provided by Chris Wemmer. His excellent staff at CRC, especially Jack Williams, Junior Allison, and Red McDaniel, were very helpful in providing hospitality and logistical support to the senior author and his family during their various visits to the Center. The assistance of several people at the National Zoo also is gratefully acknowledged: Mitch Bush and Lyndsay Phillips not only provided veterinary support throughout the investigation, but also performed surgical procedures required to implant temperature-sensitive radio transmitters in several raccoons; Olav Oftedal made his laboratory available to us at various times and loaned us equipment to use at CRC; Miles Roberts and his staff provided care for our captive raccoons in the Department of Zoological Research during various parts of the investigation. Greg Sanders and Ken Halama, supported by FONZ assistantships, cared for our captive raccoons at CRC, provided assistance in the laboratory whenever needed, and were an invaluable source of aid. Their friendship and help is gratefully acknowledged. Ellen Broudy and Andy Meyer, supported by WVSOM and a student work study grant, respectively, provided assistance in the laboratory. David Brown, John Eisenberg, Mary Etta Hight, Brian McNab, Steve Thompson, and W. Chris Wozencraft critically reviewed various phases of the manuscript and provided many helpful suggestions. We deeply appreciate the work of Jean B. McConville, whose beneficial editorial suggestions helped us improve several early versions of the manuscript. We also gratefully acknowledge Diane M. Tyler, our editor at the Smithsonian Institution Press, whose expertise helped us mold the manuscript into its final form. Jill Mellon and Sriyanie Miththalapa, supported by FONZ traineeships, assisted in measuring the daily cycle of body temperature in raccoons. The Virginia Commission of Game and Inland Fisheries gave us permission to use wild-caught raccoons in this project.

$Materials and Methods$

LIVE-TRAPPING

Raccoons were caught from May 1980 through December 1984 on a trapping grid of 30 to 35 stations that covered about one-third of the National Zoological Park's Conservation and Research Center near Front Royal, Virginia . Animals were trapped during 10 consecutive days each month, and in this five-year interval 407 raccoons were captured and marked with tattoos and ear tags. All captured animals were individualized with respect to age, reproductive status, physical condition, parasite load, and mass and body dimensions. These data characterized the structure and dynamics of the raccoon population at CRC and provided information on the annual cycle of fattening for raccoons in north central Virginia.

Animals used for metabolic measurements were captured at CRC about 1.5 km south of the trapping grid and thus were genetically representative of the area. Six males were captured and measured during the summer of 1983. These animals were kept isolated for a week before being measured and were released later that summer at the site of their capture. The other seven animals used in our study were from the collection of the National Zoological Park and all of them had their origins at CRC.

METABOLIC STUDIES

Metabolic measurements, conducted at CRC, were carried out on eight males during July and August 1983, on four females and three males from November 1983 through March 1984, and on four females during June and July 1984.

Raccoons were housed throughout the study such that they were constantly exposed to a natural cycle of temperature and photoperiod. Weather records for the Front Royal area indicate that average temperatures are around -0.5?C in January and 23.3?C in July . Light:dark periods for the latitude of CRC , calculated from duration of daylight tables , were 14.9:9.1 and 9.4:14.6 hours L:D for summer and winter solstices, respectively, and 12.2:11.8 hours L:D for vernal and autumnal equinoxes.

Our animals were fed a measured amount of food daily, and they usually ate most of what was provided. Occasionally these animals would eat very little or none of their ration, and on some days they would eat all that was given to them. We fed them either feline diet or canned mackerel ) along with high-protein dog chow ). When available, fresh fruit also was added to their diet. Water was always provided ad libitum.

Measurements were conducted during the raccoons' daily inactive period in both summer and winter. Oxygen consumption was measured in a flow-through metabolism chamber at 5?C intervals from -10?C to 35?C. Animals were held at each temperature until the lowest rate of oxygen consumption had been obtained and maintained for at least 15 minutes. During each determination, oxygen consumption was monitored for 30 minutes to one hour beyond a suspected minimum value to see if an even lower reading could be obtained. Raccoons attained minimum levels of oxygen consumption more quickly at warm than at cold temperatures. Depending on the temperature, therefore, each measurement took from two to five hours to complete. On days when two measurements could be completed, the second trial was always at a temperature 10?C warmer than the first.

The metabolism chamber was constructed from galvanized sheet metal and was painted black inside. Within the chamber, the animal was held in a cage constructed from turkey wire that also was painted black. This cage prevented the raccoons from coming into contact with the walls of the chamber, yet it was large enough to allow them to stand and freely move about. The bottom of the cage was 11 cm above the chamber floor, which was covered to a depth of one cm with mineral oil to trap urine and feces.

Columns of Drierite and Ascarite removed water vapor and carbon dioxide, respectively, from air entering and leaving the chamber. Dry carbon-dioxide-free room air was pumped into the chamber at a rate of 3.0 L/min . Downstream from the chemical absorbents, an aliquot of dry carbon-dioxide-free air was drawn off the chamber exhaust line and analyzed for oxygen content . All gas values were corrected to standard temperature and pressure for dry gas. Oxygen consumption was calculated from the difference in oxygen content between inlet and outlet air using Eq. 8 of Depocas and Hart .

Each raccoon was fasted for at least 12 hours before oxygen consumption measurements began. At the start and end of each metabolic trial the animal was weighed to the nearest 10 g . The body mass used in calculating minimum oxygen consumption and evaporative water loss was estimated from timed extrapolations of the difference between starting and ending weights, and the time at which these variables were measured.

During metabolic measurements at temperatures above freezing, evaporative water loss was determined gravimetrically. Upstream from the chemical columns, an aliquot of air was drawn off the exhaust line and diverted for a timed interval through a series of preweighed U-tubes containing Drierite. The aliquot then passed through a second series of U-tubes containing Ascarite before entering the oxygen analysis system. Evaporative water loss was calculated using Eq. 1

Veterinarians at the National Zoological Park surgically implanted calibrated temperature-sensitive radio transmitters into abdominal cavities of two female and two male raccoons. Transmitter pulse periods were monitored with a digital processor coupled to a receiver . During some metabolic measurements, body temperatures of these animals were recorded to the nearest 0.1?C at 30-minute intervals. The daily cycle of body temperature of these raccoons also was measured once a month.

CALIBRATIONS

Our earlier tests of the efficiency of our system indicated that although we underestimated actual oxygen consumption of the ethanol lamp, we did so with a fair degree of precision; probably because flow rates were closely controlled. During our metabolic measurements, chamber flow rates also were closely controlled at 3.0 L/min, and we believe, therefore, that these measurements also were carried out with a high degree of precision. Consequently, all measured values of oxygen consumption and water production were considered to be 84% of their actual value and were adjusted to 100% before being included in this report.

The calibration of all temperature-sensitive radio transmitters drifted over time. Transmitters were calibrated before they were surgically implanted and again after they were removed from the animals. Although the drift of each transmitter was unique, it was also linear . All body temperature measurements were corrected from timed extrapolations of the difference between starting and ending calibrations.

STATISTICAL METHODS

ESTIMATING INTRINSIC RATE OF NATURAL INCREASE

COMPARISON OF ADAPTIVE UNITS

The correlation between number of climates these species occupy and their composite scores was tested by linear regression.

$Results$

BODY MASS

According to monthly live-trapping records, the body mass of free-ranging female raccoons increased from 3.6 ?0.6 kg during summer to 5.6 ?0.8 kg in early winter, and the mass of free-ranging males increased from 4.0 ?0.5 to 6.7 ?0.9 kg during the same interval. These seasonal changes in body mass were due to fluctuations in the amount of body fat and represent a mechanism for storing energy during fall for use in winter. In summer, captive and trapped male and captive female raccoons had the same body mass . Mass of captive females did not change between seasons, whereas captive males were heavier in winter than summer . This seasonal change in mass of our captive males was of a much smaller magnitude than that observed for wild males . During winter, captive males were heavier than captive females . Thus, our captive animals maintained a body mass throughout the year that was intermediate to the range of values found for wild raccoons in the same area.

BASAL METABOLIC RATE

MINIMUM THERMAL CONDUCTANCE

Minimum wet and dry thermal conductances were calculated using Eqs. 4 and 5

EVAPORATIVE WATER LOSS

In winter, males and females had similar rates of evaporative water loss across the full range of temperatures tested . Therefore, data for both sexes were combined. The intercept and coefficients of this equation did not differ from those for summer females, but they did differ from those in the regression for trapped males in the X? and X? terms. As was the case for females in summer, rates of water loss for winter animals increased most rapidly at temperatures above 25?C .

THERMOREGULATION AT LOW TEMPERATURES

THERMOREGULATION AT HIGH TEMPERATURES

DAILY CYCLE OF BODY TEMPERATURE

$Discussion$

BASAL METABOLIC RATE

TABLE 7.--Metabolic characteristics of several procyonid species.

Conductance calculated as the slope of the line describing oxygen consumption at temperatures below the lower critical temperature.

Inactive-phase thermal conductance: estimated from Scholander et al. , assuming that active-phase thermal conductance is 52% higher than values determined during the inactive phase .

+ <20% by volume when found. | 1%-19% frequency of occurrence. ++ >20% by volume when found. || 20%-50% frequency of occurrence. ||| >50% frequency of occurrence.

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