C. Richard Tracy

THE PHYSIOLOGICAL ECOLOGY OF REPTILIAN EGGS AND EMBRYOS. AND THE EVOLUTION OF VIVIPARITY WITHIN THE CLASS REPTILIA

1. Eggs of Crocodilia and Chelonia, like those of birds, have a pair of egg membranes separating a thick layer of albumen from the calcareous shell. In contrast, eggs of oviparous Lepidosauria have only a single shell membrane, upon which relatively small amounts of calcium carbonate are deposited; and the volume of albumen in eggs is extraordinarily small at the time of oviposition.

The effect of the thermal environment on the ability of hatchling Galapagos land iguanas to avoid predation during dispersal

SummaryDuring the month of February 1979, several hundred hatchling land iguanas (Conolophus pallidus) were observed emerging from their natal burrows in a 2 ha communal nesting area on Isla Santa Fe, Galapagos Islands. During this emergence, as many as nine Galapagos hawks were observed to patrol the nesting area and attack hatchling iguanas.The hypothesis that the ability of hatchling land iguanas to escape predation could be influenced by the interaction of the physiological state of the lizards and the thermal environment was analyzed using (1) empirical data on the effect of body temperature (Tb) on locomotory ability of iguanas and (2) biophysical modeling of the Tbs of hatchlings under natural conditions. This hypothesis was tested by assessing the success of natural hawk attacks on lizards exposed to different thermal environments.During those periods when predicted Tbs of hatchlings were always <32°C, (at which temperatures land iguanas were shown to have less than maximal ability to sprint rapidly) hawks were successful in 67% of the observed attacks. However, when Tbs of hatchlings were always ≧32° C, hawks were successful on only 19% of observed attacks. During periods when hatchling Tbs could be <32° C or 32–40° C (depending upon which microhabitat the hatchling occupied before the attack), the hawks were successful in 46% of the observed attacks.These data indicate that the physical environment, as mediated through the physiological state of the lizards and to correlated locomotary abilities, significantly affects the ability of hatchling land iguanas to escape predation.

The importance of physiological ecology in conservation biology.

Many of the threats to the persistence of populations of sensitive species have physiological or pathological mechanisms, and those mechanisms are best understood through the inherently integrative discipline of physiological ecology. The desert tortoise was listed under the Endangered Species Act largely due to a newly recognized upper respiratory disease thought to cause mortality in individuals and severe declines in populations. Numerous hypotheses about the threats to the persistence of desert tortoise populations involve acquisition of nutrients, and its connection to stress and disease. The nutritional wisdom hypothesis posits that animals should forage not for particular food items, but instead, for particular nutrients such as calcium and phosphorus used in building bones. The optimal foraging hypothesis suggests that, in circumstances of resource abundance, tortoises should forage as dietary specialists as a means of maximizing intake of resources. The optimal digestion hypothesis suggests that tortoises should process ingesta in ways that regulate assimilation rate. Finally, the cost-of-switching hypothesis suggests that herbivores, like the desert tortoise, should avoid switching food types to avoid negatively affecting the microbe community responsible for fermenting plants into energy and nutrients. Combining hypotheses into a resource acquisition theory leads to novel predictions that are generally supported by data presented here. Testing hypotheses, and synthesizing test results into a theory, provides a robust scientific alternative to the popular use of untested hypotheses and unanalyzed data to assert the needs of species. The scientific approach should focus on hypotheses concerning anthropogenic modifications of the environment that impact physiological processes ultimately important to population phenomena. We show how measurements of such impacts as nutrient starvation, can cause physiological stress, and that the endocrine mechanisms involved with stress can result in disease. Finally, our new syntheses evince a new hypothesis. Free molecules of the stress hormone corticosterone can inhibit immunity, and the abundance of free corticosterone in the blood (thought to be the active form of the hormone) is regulated when the corticosterone molecules combine with binding globulins. The sex hormone, testosterone, combines with the same binding globulin. High levels of testosterone, naturally occurring in the breeding season, may be further enhanced in populations at high densities, and the resulting excess testosterone may compete with binding globulins, thereby releasing corticosterone and reducing immunity to disease. This sequence could result in physiological and pathological phenomena leading to population cycles with a period that would be essentially impossible to observe in desert tortoise. Such cycles could obscure population fluctuations of anthropogenic origin.

Physical and biotic determinants of space utilization by the Galapagos land iguana (Conolophus pallidus)

SummaryHome ranges of the Galapagos land iguana (Conolophus pallidus) were examined with respect to food availability and the thermal environment. Activity patterns, the amount of space used per day, and time required to use the entire home range were also investigated. The effects of, and the relationships between, these factors vary seasonally, as do home range sizes and preferred body temperatures.Food supplementation experiments resulted in only temporary reductions in use of space. Home range sizes were not different between the seasons with the least (Fall) and the most (Hot) food availalble, but home ranges were significantly smaller in Garua when food supplies were low, but not as low as in Fall. Calculations of metabolic expenditures in each season suggests that food availability alone does not explain seasonal patterns of home range size in this species.The thermal environment within each home range was characterized by microclimatic measurements and measurements of the area of sun, shade, and semi-shade. An index with units of m2h was used to quantify the thermal quality of each home range. Iguanas exploited optimal (with respect to body temperature) conditions more than would be expected from random use of their home ranges. Thermal transients (due to large body size) and optimal conditions were exploited to the largest degree in Fall.During Garua, low metabolic rates and time constraints imposed by an abundance of stressful thermal environments may result in small home ranges. In Fall, increased temperatures cause higher metabolic rates and allow more time for exploitation of the cooler portions of the home range, hence, home range sizes increase. In the Hot season, there is abundant food and optimal thermal conditions, but home ranges remain large. Searching for preferred foods may cause the large home ranges in this season.

Tenebrionid beetles in the shortgrass prairie: daily and seasonal patterns of activity and temperature

ABSTRACT. 1. Patterns of daily and seasonal activity for seven species of tenebrionid beetles, genus Eleodes, were investigated in the shortgrass prairie of northeastern Colorado. The relationship between time of activity, body temperatures, and rates of water loss of the beetles was examined in the field and in laboratory experiments.

Phenotypic variation in electromorphs previously considered to be genetic markers in Microtus ochrogaster

SummaryThe allelic frequencies of the plasma enzymes transferrin (Tf) and leucine aminopeptidase (LAP) have been shown previously to correlate with population density, population growth rate and mortality in Microtus ochrogaster. Such changes in allozymic frequencies of Tf and LAP have been used by others as evidence supporting the Chitty/Krebs genetic-behavioral hypothesis of population growth. In this study, prairie voles were captured in midwinter and in midsummer, and brought to the lab where their allozymes of Tf and LAP were determined. The voles were then placed in controlled environments approximating some of the conditions of other seasons of the year, and their allozymes were redetermined in subsequent weeks. Changes in allozymes occurred in all experiments. Animals subected to opposite seasons (i.e. captured in winter and subjected to summer conditions, and captured in summer and subjected to winter environments) had the highest percentage of changes in electromorphs. A review of the literature revealed a plethora of evidence that Tf and LAP proteins could change electromorphs on starch gels in response to differences in blood chemistry and presumably to physiological state influenced by diet, reproductive state, and disease. Thus, since it appears that electromorphs of Tf and LAP proteins can change in voles subjected to different environments, and that these proteins may change in electronegativity in response to the physiological state of the animals, observed changes in allelic frequencies in populations of voles may be of limited value as evidence for the proposed genetic-behavioral hypothesis explaining population cycles.

The role of dehydration and antidiuretic hormone on water exchange in Rana pipiens

Abstract 1. 1. Experiments were performed to evaluate the effects of 8-arginine vasotocin on the effective water potential and on the hydraulic conductance of leopard frogs (Rana pipiens) during water uptake through their ventral integument. 2. 2. Vasotocin apparently decreases the effective water potential of intact frogs, thus bringing the effective water potential into close correspondence with the osmotic potential of extracellular fluids. 3. 3. Thus, well-hydrated frogs, which release little AVT, have effective water potentials considerably higher (more positive) than the osmotic potentials of their plasma, and therefore, demonstrate a diminished capacity to absorb water. 4. 4. Dehydrated frogs release AVT which causes their effective water potential to become essentially identical to the osmotic potential of their plasma. 5. 5. We hypothesize that the action of AVT is to mobilize water from the site of absorption by the frog, thereby resulting in maintenance of a high water potential gradient between the environment and the frog. and in increased rates of water uptake.