William I. Lutterschmidt

Alarm response by a plethodontid salamander (Desmognathus ochrophaeus): Conspecific and heterospecific “Schreckstoff”

The detection of chemical alarm cues plays an important role for predator avoidance in many taxonomic groups, but little is known about the presence of such chemical cues in adult or caudate amphibians. We investigated the response (i.e., aversion or nonaversion) to chemical cues from damaged salamander skin and mealworms (Tenebrio molitor) in the plethodontid salamander,Desmognathus ochrophaeus. Avoidance responses were demonstrated to skin extracts of both conspecific and heterospecific salamanders. However, salamanders (D. ochrophaeus) did not avoid heated conspecific skin, fresh conspecific viscera, fresh mealworm, or freshPlethodon richmondi skin extracts. These results indicate that chemical alarm cues are: (1) present in the skin ofDesmognathus salamanders, (2) not present in mealworm or the viscera ofDesmognathus salamanders, and (3) denatured or deactivated by heating. These results also suggest that an avoidance response to chemical cues from damaged conspecifics has adaptive value in predator avoidance in terrestrial as well as aquatic vertebrates.

Comparative thermal physiology of two sympatric sunfishes (Centrarchidae: Perciformes) with a discussion of microhabitat utilization

We investigated temperature-dependent responses of metabolism and thermal tolerance in bluegill (Lepomis macrochirus) and longear sunfish (L. megalotis). Each species showed significant differences in standard metabolic rate (SMR) and thermal tolerance among the three acclimation temperatures (10°C, 20°C, and 30°C). These sympatric centrarchids colonize microhabitats with different hydrodynamic and thermal regimes, which may be related to species differences in physiological responses to temperature. We found no interspecific differences in SMR and thermal tolerance. However, because there are differences in microhabitat utilization which may promote an adaptive suite of physiological tolerances unique to each species, we provide evidence suggesting that L. megalotis has greater physiological plasticity for SMR than L. macrochirus and that L. macrochirus has greater plasticity in thermal tolerance than L. megalotis. Trends in physiological plasticity with correlates of microhabitat utilization are discussed.

Relative Medial and Dorsal Cortex Volume in Relation to Sex Differences in Spatial Ecology of a Snake Population

In non-avian reptiles the medial and dorsal cortices are putative homologues of the hippocampal formation in mammals and birds. Studies on mammals and birds commonly report neuro-ecological correlations between hippocampal volume and aspects of spatial ecology. We examined the relationship between putative homologous cortical volumes and spatial use in a population of the squamate reptile, Agkistrodon piscivorus, that exhibits sex differences in spatial use. Do male A. piscivorus that inhabit larger home ranges than females also have larger putative hippocampal volumes? Male and female brains were sectioned and digitized to quantify regional cortical volumes. Although sex differences in dorsal cortex volume were not observed, males had a significantly larger medial cortex relative to telencephalon volume. Similar to studies on mammals and birds, relative hippocampal or medial cortex volume was positively correlated with patterns of spatial use. We demonstrate volumetric sex differences within a reptilian putative hippocampal homologue.

PHYSIOLOGICAL PERFORMANCE AND STREAM MICROHABITAT USE BY THE CENTRARCHIDS LEPOMIS MEGALOTIS AND LEPOMIS MACROCHIRUS

Two centrarchids, Lepomis megalotis and L. macrochirus, were compared in laboratory studies of prey capture success, swimming endurance, morphology, hydrodynamic drag, and thermal tolerance, as well as field observations of focal point velocity and depth. For both species, capture of planktonic prey declined as current velocity increased, but L. megalotis was more efficient than L. macrochirus at higher current velocities. Capture of floating prey was not influenced by current velocity, but L. megalotis was more efficient overall at all velocities. Of the two species, L. megalotis was significantly more streamlined, had relatively lower hydrodynamic drag, and had higher swimming endurance in current. Both species had significantly higher critical thermal maxima (CTMax) in summer than in winter, but variance in CTMax was greater for L. megalotis than for L. macrochirus in both summer and winter. Differences between L. megalotis and L. macrochirus in performance and morphology may have direct influence on their relative abundances in small streams. Field observations showed L. megalotis was more common than L. macrochirus in faster, shallower microhabitats.

Locomotor Performance in Juvenile and Adult Box Turtles (Terrapene carolina): A Reanalysis for Effects of Body Size and Extrinsic Load Using a Terrestrial Species

vestigated the relationship between body size and locomotor performance. Sprint or burst speed in some iguanid and helodermatid species is mass independent (e.g., Garland, 1984; Beck et al., 1995), whereas sprint speed in some agamid and lacertid species increases with body mass (e.g., Garland, 1985; Avery et al., 1987). Within families of lizards, sprint speed is generally independent of body mass (Garland, 1982). Lizards and snakes with an increased natural load re-

The Comparative Method Revisited

C studies in biology use an investigative philosophy that many scientists identify as the “comparative method.” In one sense, for those concerned with evolutionary history, the comparative method provides insights into adaptation by correlating differences among species with ecological factors (Futuyma 1986). In another sense, biologists often study the particular features of one species to learn about some aspect of a second species. C. Barker Jørgensen (2001) reviewed the historical development of a fundamental tenet of the comparative method known as the “August Krogh principle” (AKP) and discussed the influences that both Claude Bernard and August Krogh had on the basic investigative principles of comparative physiology. Many have recognized Bernard as the father of modern physiology (e.g., Fox 2002). His articulation of rigorous research methods and the concept of an “internal environment” ushered in the modern area of experimental physiology. Krogh was a brilliant researcher who specialized in comparative physiology, particularly areas relating to respiration. He was awarded the Nobel Prize in Physiology or Medicine in 1920 for his discovery of the mechanism regulating capillaries in skeletal muscle. Krogh’s (1929a, p. 247, 1929b, p. 202) statement,“For a large number of problems, there will be some animal of choice on which it can be most conveniently studied,” eloquently captured a longstanding postulate of comparative biology. Specifically, Krogh encapsulated the idea, present long before Darwin, that parts or processes that are difficult or impossible to study in one species may be much more accessible in an alternate species. Hans Krebs (1975) formulated the August Krogh principle as “for many problems there is an animal on which it can be most conveniently studied.” As Jørgensen in his review (2001) pointed out, Krogh did not formulate his principle from scratch, but rather offered an explicit statement of a principle that was already generally accepted within comparative biology. Jørgensen presents an excellent argument for the historical role of Claude Bernard in the formulation of this principle: There are also experiments in which it is proper to choose certain animals which offer favorable arrangements or special susceptibility to certain influences. This is so important that the solution of a physiological problem often depends solely on the appropriate choice of the animal for the experiment so as to make the result clear and searching (Bernard [1865] 1957, p. 123).

Behavioral Thermoregulation and the Role of Melatonin in a Nocturnal Snake

Daily and seasonal variations in hormone levels influence the complex interactions between behavior and physiology. Ectothermic animals possess the unique ability behaviorally to adjust body temperature (T(b)) to control physiological rate processes. Thus, a hormone may indirectly influence a physiological rate by directly influencing the behaviors that adjust or control that rate process. Although many hormonal influences on behavioral regulation of T(b) remain uninvestigated, melatonin (MEL) generally is considered a hormone that decreases mean preferred T(b). Many ectotherms demonstrate the selection of lower T(b)s in response to increased MEL concentrations. Here, we examined the influence of MEL on the behavioral regulation of T(b) in the nocturnal African house snake Lamprophis fuliginosus. A series of experiments with two injection regimes of MEL had no significant effect on the mean preferred T(b) of L. fuliginosus. In addition, mean preferred T(b)s during the photophase did not differ significantly from those during scotophase. Our findings suggest that L. fuliginosus does not respond to elevated concentrations of either endogenous or exogenous MEL. To verify that the African house snake is nocturnal, we investigated activity patterns of L. fuliginosus throughout the photoperiod. The activity period of L. fuliginosus occurs in the scotophase of the photoperiod, a pattern consistent with that of nocturnal species. This suggests that nocturnal organisms such as L. fuliginosus may not respond to MEL in the same manner as many diurnal species. Our results support the hypothesis that some animals, particularly nocturnal species, may have developed alternative responses to increased plasma concentrations of MEL.

The Ecological Significance of Helminth Endoparasites on the Physiological Performance of two Sympatric Fishes

Abstract We investigated the effects of helminth endoparasite load on the physiological performance of 2 sympatric fishes, Lepomis macrochirus and Lepomis megalotis (Centrarchidae). Species-specific swimming endurance and thermal tolerance were used as measures of physiological performance. A discriminant function analysis for endurance indicated that only kidney parasite load significantly correlated with the first discriminant function. However, overall increases in parasite load within the mesentery, heart, liver, and small intestine were each associated with observed decreases in endurance for both species. A discriminant function analysis also indicated that increases in mesentery and liver parasite load were significantly correlated with decreases in thermal tolerance. An overall increase in parasite load within the mesentery, heart, liver, small intestine, and spleen was also correlated with decreased thermal tolerance. Thus, our results suggest that helminth endoparasite load may play an important role in the physiological performance of these sympatric fishes. Differences in microhabitat utilization and partitioning of L. macrochirus and L. megalotis correlate with species-specific physiological performance. For example, microhabitats with greater current velocities are used by L. megalotis because of the greater capacity of this species for endurance. However, parasite loads that significantly reduce endurance would force changes in habitat utilization causing direct competition among species normally partitioned. We offer a theoretical discussion of how parasite load may create opportunities for interaction and competition among individuals and species usually partitioned by physiologically based preferences in microhabitat utilization.

Melatonin and Chlorpromazine: Thermal Selection and Metabolic Rate in the Bullsnake, Pituophis melanoleucus

Abstract We investigated the effects of melatonin (MEL) and chlorpromazine (CPZ) on the thermal selection and metabolic rate of the bullsnake, Pituophis melanoleucus. Adult snakes were acclimatized for 5 weeks to a constant temperature of 25 ± 1°C (range) and an L12:D12 photoperiod; photophase was centered on 1200 hr CST and began at 0600 hr. Temperatures selected by snakes in response to intraperitoneal (IP) injections of saline (control), MEL (5 mg kg−1 body mass), and CPZ (25 mg kg−1 body mass), a melatonin antimetabolite, were measured in a linear thermal gradient over a 36-hr experimental period. Using a repeated measures design, we showed that mean preferred body temperature (Tb) of snakes when receiving either MEL (19.6°C, SE = 1.86, n = 11) or CPZ (15.7°C, SE = 1.12, n = 11) differed significantly from the preferred Tb of animals receiving control injections of saline solution (24.1°C, SE = 1.90, n = 11). Changes in metabolic rate were determined with closed system respirometry to measure oxygen consumption before and 3 hr after treatments of: 1) non-injected control, 2) injected-saline control, 3) MEL (5 mg kg−1 body mass), and 4) CPZ (25 mg kg−1 body mass). Static samples of oxygen consumption before and after treatments showed that MEL and CPZ had no significant effect upon the resting metabolic rate (RMR) 3 hr after injection. A multiple comparisons test of the among-treatment differences indicated that there were no statistically significant changes in RMR (F = 0.975; df = 3,27; P = 0.419). However, the difference between before and after mean RMR for the CPZ experiment was almost significant (W = 35; df = 9; P = 0.084), and may be biologically meaningful. Both exogenous and endogenous MEL may play a role in behavioral and physiological thermoregulation of vertebrates and also may influence metabolic rate.

SEASONAL ACTIVITY, RELATIVE ABUNDANCE, AND SIZE-CLASS STRUCTURE OF THE AMERICAN ALLIGATOR (ALLIGATOR MISSISSIPPIENSIS) IN A HIGHLY DISTURBED INLAND LAKE

Abstract We monitored an inland population of American alligator (Alligator mississipiensis) in Lake Raven, Huntsville State Park, Walker County, Texas from September 2000 to August 2001. We found alligators exhibited year-round activity in Lake Raven, with the lowest occurrence of alligators in December and January. The greatest numbers of alligators were surveyed in June and September. However, in September, 47% of the observed individuals were hatchlings. Water temperature was a significant predictor of alligator activity over air temperature and explained 37% of the observed variation in seasonal activity. A population index estimated that Lake Raven supported 0.19 alligators per hectare, with most of these alligators being juveniles and in the size class of 0.6 to 0.9 m. We also found alligators used all regions of the perimeter of the lake and were observed mostly 5 m from the shoreline. Because there is limited information on inland alligator populations in Texas, this study offers information on the seasonal activity, relative abundance, and size-class structure of alligators inhabiting a relatively small (85 ha) and highly disturbed inland lake. This information might be useful for future studies and comparisons with coastal alligator populations.