James R. Spotila

Pacific Leatherback Turtles Face Extinction

The dwindling numbers of leatherback turtles are signalling a threat to biodiversity in the oceans. A mathematical model based on our assessment of a once-large leatherback population predicts that unsustainable adult mortality, apparently due to human fishing activity, will soon drive this population to extinction.

A Mathematical Model for Body Temperatures of Large Reptiles: Implications for Dinosaur Ecology

A mathematical model for heat conduction through large reptiles is developed. The animal is approximated by a large cylinder with a central core of tissue kept at a uniform temperature by blood flow, surrounded by six layers of fat. An iterative mathematical procedure is used to solve equations for heat flowing into, heat flowing out of, and heat stored in each layer and the core during a specified time period. This yields the temperatures of the core and insulating layers at the end of the time period. Physiological and environmental parameters are incremented and calculations repeated for a new time period. These calculations show that a large reptile (D = 100 cm) would have a relatively constant high body temperature when exposed to warm, diurnally fluctuating environmental conditions, even with a low metabolic rate, as long as the average values of the physical parameters result in a body temperature within tolerable limits. Changes in fat thickness are of minor importance in determining the constancy of body temperature. If exposed to excessively hot or cold climates, large reptiles would have a constant excessively high or low body temperature. A time-constant equation is developed to describe the effect of size on the response of body temperature to environmental heat loads in small and large reptiles. Gigantism would be a very useful strategy for reptiles, providing a constant, equable internal temperature in a stable, warm climate. This strategy may have been selected for in dinosaurs, giving them a high stable body temperature without a high metabolic rate. Our calculations support the hypothesis that thermal stress resulting from decreased equability of climate may have been a primary factor in the extinction of dinosaurs during the late Cretaceous.

Determination of skin resistance and the role of the skin in controlling water loss in amphibians and reptiles.

Abstract 1. 1. Evaporative water loss rates are presented for the box turtle, Terrapene carolina , the American chameleon, Anolis carolinensis , the frog Rana pipiens and the salamander Desmognathus ochrophaeus acclimated to 20°C, LD 12:12. 2. 2. A theoretical framework is developed to describe the process of evaporative water loss from the surface of an animal. 3. 3. Agar replicas of each experimental animal are used to determine boundary layer resistance and facilitate the computation of skin resistance. 4. 4. Skin resistance (sec cm −1 ) was in the following order: A. carolinensis (196.4), T. carolina (77.6), D. ochrophaeus (0.09) and R. pipiens (0.05).

Sequence and expression analysis of WT1 and Sox9 in the red-eared slider turtle, Trachemys scripta.

Temperature-dependent sex-determination (TSD) is a phenomenon that has been characterized at the ecological, morphological, and endocrinological levels in some reptilian species. We have begun to investigate TSD at the level of molecular development by cloning, sequencing, and analyzing the expression of two genes, WT1 and Sox9, in the red-eared slider turtle Trachemys scripta. We obtained almost full-length cDNA clones for WT1 and Sox9 that were greater than 73% identical to the human homologues at the nucleotide level. WT1 was expressed in urogenital tissue at all developmental stages examined (Yntema stages 12-20) at incubation temperatures that produce males (26 degrees C) or females (32 degrees C). Sox9 was also expressed throughout these same stages, but some differences were observed. At both 26 degrees C and 32 degrees C Sox9 was expressed in the mesonephroi and the undifferentiated gonads until Yntema stage 20, when only the gonad from the 26 degrees C embryos expressed a high level. In addition, there were two transcripts of Sox9 at all stages, but the relative proportion of the two transcripts differed at the two temperatures. Although the similarities in gene expression between a TSD species and other species with genotypically determined sex probably reflect the common features of organogenesis, differences may illustrate unique mechanisms for TSD.

Nesting Ecology of the Leatherback Turtle, Dermochelys coriacea, at Parque Nacional Marino Las Baulas, Costa Rica: 1988–1989 to 1999–2000

Abstract We collected data on nesting ecology and identified individual turtles that nested at Parque Nacional Las Baulas, Costa Rica, one of the few remaining nesting sites for Pacific leatherbacks, from 1988–1989 to 1999–2000. We tagged individual female turtles with flipper tags and later with Passive Integrated Transponder (PIT) tags that permitted permanent identification. During the full calendars years of 1990 and 1995, over 93% of nests were laid between the beginning of October and the end of February. We found that 92.4 ± 1% of nesting attempts resulted in successful oviposition, with a mean clutch size of 64.7 ± 1.4 yolked and 38.5 ± 1.0 yolkless eggs (n = 1389). Mean standard curved carapace length and curved carapace width during the surveyed years ranged from 144.4 ± 0.6 cm to 147.6 ± 0.3 cm and from 103.9 ± 0.3 cm to 105.5 ± 0.6 cm, respectively. Reproductive output as determined by estimated clutch frequency (ECF) ranged from 4.3 ± 0.2 to 7.9 ± 0.3 clutches per female per nesting season. The mean period between nesting seasons for an individual turtle was 3.7 ± 0.2 years; only 15% of turtles tagged in 1993/1994 returned to nest again within six years. The nesting population declined from 1367 adult females in 1988/1989 to 231 in 1999/2000. The decline in the nesting population was apparently because of the low incidence of turtles returning to nest in more than one season.

Physiological constraints on organismal response to global warming: Mechanistic insights from clinally varying populations and implications for assessing endangerment.

Recent syntheses indicate that global warming affects diverse biological processes, but also highlight the potential for some species to adapt behaviourally or evolutionarily to rapid climate change. Far less attention has addressed the alternative, that organisms lacking this ability may face extinction, a fate projected to befall one-quarter of global biodiversity. This conclusion is controversial, in part because there exist few mechanistic studies that show how climate change could precipitate extinction. We provide a concrete, mechanistic example of warming as a stressor of organisms that are closely adapted to cool climates from a comparative analysis of organismal tolerance among clinally varying populations along a natural thermal gradient. We found that two montane salamanders exhibit significant metabolic depression at temperatures within the natural thermal range experienced by low and middle elevation populations. Moreover, the magnitude of depression was inversely related to native elevation, suggesting that low elevation populations are already living near the limit of their physiological tolerances. If this finding generally applies to other montane specialists, the prognosis for biodiversity loss in typically diverse montane systems is sobering. We propose that indices of warming-induced stress tolerance may provide a critical new tool for quantitative assessments of endangerment due to anthropogenic climate change across diverse species.

THERMAL ECOLOGY OF DESERT TORTOISES IN THE EASTERN MOJAVE DESERT: SEASONAL PATTERNS OF OPERATIVE AND BODY TEMPERATURES, AND MICROHABITAT UTILIZATION

We monitored meteorological variables, daily and seasonal patterns of body tem- perature, corresponding operative temperatures, and microhabitat utilization by desert tortoises (Gopherus agassizii) during the 1991 and 1992 activity seasons of tortoises in the eastern Mojave desert. We studied tortoises in enclosures of natural habitat at the Desert Tortoise Conservation Center (DTCC) near Las Vegas, Nevada and a population of free-ranging tortoises in a field site adjacent to the DTCC. Air, ground and operative temperatures coincided with daily and monthly patterns of incident solar radiation. Variation in body temperature was primarily a consequence of microhabitat selection, principally use of burrows. During July-October, in the morning, body temperatures of tortoises in burrows were cooler than those of individuals on the surface. During midday, tortoises remained in burrows where body temperatures were cooler than extreme surface operative temperatures. While tortoises remained in burrows during much of the day, tortoises typically did not sleep in burrows at night. Microhabitat utilization was dictated by avoidance of extreme temperatures during midday, and microhabitat selection corresponded qualitatively to maintenance of energy and water balances. Effective conservation efforts to preserve habitat of desert tortoises will focus upon managing variables associated with integrity of burrows. ulation

Operative environmental temperatures and basking behavior of the turtle Pseudemys scripta

Operative environmental temperatures (T/sub e/, an index of the thermal environment) were measured for basking Pseudemys scripta in South Carolina. Operative environmental temperatures were good predictors of the basking behavior of P. scripta. Turtles in this study generally did not bask unless T/sub e/ was 28/sup 0/C (preferred body temperature) or higher. This demonstrated that basking was not a random behavior in respect to T/sub e/, and implicated thermoregulation as a major factor eliciting basking behavior. Operative environmental temperature was positively related to short-wave and total solar radiation as well as to air and substrate temperature. Substrate temperature was the best single predictor of T/sub e/. A multiple regression equation (T/sub e/ = 0.005R + 0.103T/sub a/ - 1.16 log V + 0.932T/sub s/ - 2.54, r/sup 2/ = .90, where R = total radiation in watts per square metre, T/sub a/ = air temperature in degrees Celsius, V = wind speed in metres per second, and T/sub s/ = substrate temperature in degrees Celsius) defines the relationship of T/sub e/ to microclimate variables. Movement of the sun through the day results in spatial variation in T/sub e/s available to turtles and influences their location and basking behavior.

Low reproductive success of leatherback turtles, Dermochelys coriacea, is due to high embryonic mortality

We examined the mechanism responsible for low reproductive success in leatherback turtles (Dermochelys coriacea) at Playa Grande, Costa Rica: low egg fertilization versus high rates of embryonic death. Leatherbacks at this beach had a high rate of fertility (X=93.3%� 2.5%, n=819). We incubated 10 eggs from every clutch encountered of 19 females during 3 months of the 1998– 1999 nesting season. Fertility rate of some females decreased during the nesting season, but overall was high. Detection of fertility was difficult using standard methods because fertility rates cannot be determined accurately from nests excavated after hatching because of egg decomposition. Removal and incubation of eggs from nests provided a better estimate. Embryonic death, particularly in the beginning of incubation before embryos are visible to the unaided eye, was the cause of low hatching success in this population. Hatching success increased with increasing fertility and differed between females, with some mothers having 71–81% success and others 23–32%. Embryonic death and not low egg fertility drives poor recruitment at Playa Grande. Improved conservation of this species at Playa Grande will require a better understanding of the mechanism behind embryonic death. # 2003 Elsevier Ltd. All rights reserved.

Seasonal variation in heat shock proteins (hsp 70) in stream fish under natural conditions

1. 1.|Fish (Pimephales promelas, Salmo trutta, Ictalurus natalis and Ambloplites rupestris) respond to seasonal changes in their environment by synthesizing heat shock proteins with a molecular weight of approximately 70 Kd (hsc/hsp-70). 2. 2.|Lowest levels of hsc/hsp-70 measured with ELISA occurred in winter, followed by a high level in spring, a significant decrease in summer and another in fall. 3. 3.|Caution must be applied in developing heat shock proteins as biomarkers so that their presence in organisms under “normal” conditions is not misinterpreted as an indication that the organisms are stressed.