Physiology of cold hardiness in cocoons of five earthworm taxa (Lumbricidae: Oligochaeta)

Earthworm cocoons are mostly found in the uppermost soil layers and are therefore often exposed to low temperatures during winter. In the present study, cocoons of five taxa of earthworms were investigated for their tolerance to freezing, melting points of cocoon fluids and dehydration of cocoons when exposed to a frozen environment. Embryos of the taxa investigated were freeze intolerant. The melting points of fully hydrated cocoon fluids were high (above –0.3°C) and thermal hysteresis factors were absent. Exposure to a frozen environment caused the cocoons to dehydrate drastically and dehydrated cocoons showed significantly lower super-cooling points than fully hydrated cocoons, reducing the risk of freezing for dehydrated cocoons. It is proposed therefore that the cold-hardiness strategy of the earthworm cocoons is based on dehydration upon exposure to subzero temperatures in the frozen environment. Cocoons of three surface-dwelling taxa, Dendrobaena octaedra, Dendrodrilus rubidus tenuis and Dendrodrilus rubidus norvegicus had lower supercooling points and survived frost exposure better than cocoons of two deeper-dwelling taxa, Aporrectodea caliginosa and Allolobophora chlorotica. One of the investigated taxa, D. r. norvegicus, was collected from a cold alpine habitat. However, it was not more cold hardy than the closely related D. r. tenuis collected from a lowland temperate habitat. D. octaedra was the most cold hardy taxon, its cocoons being able to withstand –8°C for 3 months and –13.5°C for 2 weeks in frozen soil.Abbreviations dw dry weight - fw fresh weight - SCP supercooling point     

Adaptations to terrestrial overwintering of hatchling northern map turtles,<Emphasis Type="Italic"> Graptemys geographica</Emphasis>

We conducted a 3-year field and laboratory study of winter biology in hatchlings of the northern map turtle (Graptemys geographica). At our study area in northern Indiana, hatchlings routinely overwintered in their natal nests, emerging after the weather warmed in spring. Winter survival was excellent despite the fact that hatchlings were exposed frequently to subfreezing temperatures (to –5.4 °C). In the laboratory, cold-acclimated hatchlings exhibited low rates of evaporative water loss (mean=2.0 mg g^–1 day^–1), which would enable them to conserve body water during winter. Laboratory-reared hatchlings were intolerant of freezing at –2.5 °C for 24 h, conditions that are readily survived by freeze-tolerant species of turtles. Winter survival of hatchling G. geographica probably depended on their extensive capacity for supercooling (to –14.8 °C) and their well-developed resistance to inoculative freezing, which may occur when hatchlings contact ice and ice-nucleating agents present in nesting soil. Supercooled hatchlings survived a brief exposure to –8 °C. Others, held at –6 °C for 5 days, maintained ATP concentrations at control levels, although they did accumulate lactate and glucose, probably in response to tissue hypoxia. Therefore, anoxia tolerance, as evidenced by the viability of hatchlings exposed to N₂ gas for 8 days, may promote survival during exposure to subfreezing temperatures.Abbreviations EWL evaporative water loss - FP_eq equilibrium freezing point - INA ice-nucleating agents - T_c temperature of crystallizationCommunicated by L.C.-H. Wang     

Temperature and water content effects on the viscoelastic behavior of<Emphasis Type="Italic"> Tilia americana</Emphasis> (Tiliaceae) sapwood

The effects of temperature and water content on the viscoelasticity of living and dehydrated Tilia americana sapwood were examined using transient creep (time- and load-dependent deformation) tests under sustained bending loads. Creep tests were performed at 21.1°C and –20.5°C to determine the magnitudes and types of strains in living and dehydrated samples. Temperature had no effect on the creep rate of living sapwood. However, the creep rate of dehydrated samples at –20.5°C was significantly faster than that at 21.1°C. Regardless of temperature, sapwood had a faster creep rate than dehydrated samples. With small bending loads, the residual strains in sapwood were larger at 21.1°C compared to –20.5°C. Temperature did not significantly affect the residual strains in dehydrated samples. For small bending loads, frozen sapwood recovered all residual creep strains when thawed. With larger loads, residual and plastic (permanent) strains increased. We speculate that ice formation in cell lumens partially dehydrates (and thus stiffens and strengthens) cell wall materials and prevents cell wall buckling and elastic restoration after unloading. However, when thawed, sapwood can elastically restore its original configuration, provided it is not excessively bent (by ice or snow accumulations) when frozen.     

Physiological adaptations to low temperature and brine exposure in the circumpolar amphipod Gammarus wilkitzkii

Summary The amphipod Gammarus wilkitzkii does not survive being frozen totally into solid sea ice. When the animals are cooled in air or freezing seawater, they will freeze and die at a temperature of about-4° C. However, during sea ice growth, the amphipods may tolerate to stay in the vicinity of the ice by conforming to the ambient brine in a salinity range of 34 ppt to about 60 ppt. A passive relationship between the concentrations of the haemolymph and seawater Na⁺ and Cl^-, lowers the melting point of the body fluids of the animals, thus preventing internal ice formation at low temperatures.     

Ammonia-nitrogen excretion in Daphnia pulex

Ammonia-nitrogen excretion rates were measured in natural summer and cultured populations of Daphnia pulex from Silver Lake, Clay County, Minnesota, USA during 1973. The mean rate of ammonia-nitrogen excretion for the summer populations was 0.20 µg N animal^–1 day^–1 or 5.11 µg N mg^–1 dry body weight day^–1 (N = 80) measured at 15°, 20°, and 25°C. These rates appear to be temperature and weight dependent, but they are probably affected by factors other than temperature and dry body weight. Ammonia-nitrogen excretion rates of Daphnia pulex cultured on Chlamydomonas reinhardi yielded the following relationship with temperature: Log₁₀E = (0.061) T 1.773, where E is µg N animal^–1 day^–1 and T is temperature °C. The ammonia-nitrogen excretion on a mg^–1 dry body weight day^–1 basis was related to temperature according to the following similar expression Log₁₀E = (0.043) T + 0.153, where E is µg N mg^–1 dry body weight day^–1, and T is temperature °C. The length-weight relationship of Daphnia pulex for the summer populations (N = 1583) was log₁₀W = (0.526) Log₁₀L + 1.357, where W is weight in µg and L is length in mm.     

Factors affecting the distribution, abundance and diversity of fishes of small, soft-substrata tidal pools within Moreton Bay, Australia

Clearance rates of Limnoperna fortunei (Bivalvia) were investigated in laboratory experiments using monocultures of the alga Chlorella vulgaris. Experimental conditions included two mollusc sizes (15 and 23 mm), and three water temperatures (15, 20 and 25 °C) covering the normal seasonal range in the lower Paraná river and Río de la Plata estuary. Filtration rates obtained were, for the larger mussels: 9.9, 13.1 and 17.7 ml mg tissue dry weight^–1 h^–1 at 15, 20 and 25 °C, respectively; and for the smaller ones: 17.7, 20.8 and 29.5 ml mg^–1 h^–1. Differences between sizes and between temperatures (except 15 vs. 20 °C) were statistically significant. In absolute terms larger animals have higher clearance rates, but as a function of body mass smaller individuals feed more actively. Within the range of experimental values used, filtration rates were positively associated with water temperature. These clearance rates (125–350 ml individual^–1 h^–1) are among the highest reported for suspension feeding bivalves, including the invasive species Dreissena polymorpha, D. bugensis and Corbicula fluminea. High filtration rates, associated with the very high densities of this mollusc in the Paraná watershed (up to over 200,000 ind m^–2) suggest that its environmental impact may be swiftly changing ecological conditions in the areas colonized.     

Dehydration of earthworm cocoons exposed to cold: a novel cold hardiness mechanism

Mechanisms involved in cold hardiness of cocoons of the lumbricid earthworm Dendrobaena octaedra were elucidated by osmometric and calorimetric studies of water relations in cocoons exposed to subzero temperatures. Fully hydrated cocoons contained ca. 3 g water · g dry weight^-1; about 15% of this water (0.5 g·g dry weight^-1) was osmotically inactive or bound. The melting point of the cocoon fluids in fully hydrated cocoons was-0.20°C. Exposure to frozen surroundings initially resulted in supercooling of the cocoons dehydrated (as a result of the vapour pressure difference at a given temperature between supercooled water and ice) to an extent where the vapour pressure of water in the body fluids was in equilibrium with the surrounding ice. This resulted in a profound dehydration of the cocoons, even at mild freezing exposures, and a concomitant slight reduction in the amount of osmotically inactive water. At temperatures around-8°C, which cocoons readily survive, almost all (>97%) osmotically active water had been withdrawn from the cocoons. It is suggested that cold injuries in D. octaedra cocoons observed at still lower temperatures may be related to the degree of dehydration, and possibly to the loss of all osmotically active water. The study indicates that ice formation in the tissues is prevented by equilibrating the body fluid melting point with the exposure temperature. This winter survival mechanism does not conform with the freeze tolerance/freeze avoidance classification generally applied to cold-hardy poikilotherms. Implications of this cold hardiness mechanism for other semi-terrestrial invertebrates are discussed.Abbreviations DSC differential scanning calorimetry - dw dry weight - MP melting point(s) - II water potential - R universal gas constant - T absolute temperature - V specific volume of water     

The role of macromolecular antifreeze in the darkling beetle,Meracantha contracta

Summary Macromolecular antifreeze solutes are present in the hemolymph of the overwintering larvae of the darkling beetle,Meracantha contracta. These antifreeze solutes produce a thermal hysteresis in the hemolymph of overwinteringMeracantha larvae whereby the freezing point of the hemolymph may be 3–4 °C below the melting point. This thermal hysteresis is very similar to that produced by proteinaceous and glycoproteinaceous antifreezes which are used by many cold water, marine teleost fishes to prevent freezing. One function of the macromolecular antifreeze inMeracantha may be to hinder inoculative freezing which might otherwise occur because of the dampness of the hibernaculae. A probably more important function is to depress the supercooling point of the frost susceptibleMeracantha larvae, thereby preventing lethal ice formation in the larvae's body fluids down to temperatures of approximately –11 °C.     

Cold resistance and metabolic responses to salinity variations in the amphipod Eusirus antarcticus and the krill Euphausia superba

Summary The krill Euphausia superba, unlike the amphipod, Eusirus antarcticus, tolerates being frozen into solid sea-ice at temperatures down to about-4°C. Cooled in air, the amphipod and the krill freeze and will die at temperatures of-11° and-9°C respectively, representing the supercooling points of the animals. The krill is an osmoconformer in the salinity range of 25 to 45 ppt, while the amphipod conforms in the salinity range of 26 to 40 ppt. The animals thereby lower the melting point of their body fluids in the vicinity of the freezing sea ice, preventing internal ice formation at low temperatures. The mean oxygen consumption rates, at raised and lowered salinities, were not significantly different from rates obtained in normal (35 ppt.) seawater, indicating that salinity has little effect on the metabolism of either species.     

Effect of soil moisture at different temperatures on Rhizoctonia root rot of wheat seedlings

The effect of soil moisture at different temperatures on root rot of wheat seedlings caused by Rhizoctonia solani AG-8 was studied in temperature controlled water tanks under glasshouse conditions. Four moisture levels (15, 30, 50 and 75% of soil water holding capacity at saturation which were equal to –10, –7, –5 and –3 kPa, respectively) were tested in tanks maintained 10, 15, 20 or 25 °C. The role of microbial activity in the effect of soil moisture and temperature on disease severity was also studied by including treatments of steam treated soil. Results showed that at soil moisture levels optimum for plant growth (50 and 75% WHC) disease was more severe at a lower temperature (10 °C), but under relatively dry conditions (15% WHC) disease levels were similar at all temperatures tested. In warm soils (20 and 25 °C) at high soil moisture levels (50 and 75% WHC), disease was more severe in steam treated soil than in non-steam treated soil, indicating that the suppression of disease in natural soil under these conditions was associated with high soil microbial activity.     

Forest soil respiration rate and δ13C is regulated by recent above ground weather conditions

Soil respiration, a key component of the global carbon cycle, is a major source of uncertainty when estimating terrestrial carbon budgets at ecosystem and higher levels. Rates of soil and root respiration are assumed to be dependent on soil temperature and soil moisture yet these factors often barely explain half the seasonal variation in soil respiration. We here found that soil moisture (range 16.5–27.6% of dry weight) and soil temperature (range 8–17.5°C) together explained 55% of the variance (cross-validated explained variance; Q²) in soil respiration rate (range 1.0–3.4 mol C m^–2 s^–1) in a Norway spruce (Picea abies) forest. We hypothesised that this was due to that the two components of soil respiration, root respiration and decomposition, are governed by different factors. We therefore applied PLS (partial least squares regression) multivariate modelling in which we, together with below ground temperature and soil moisture, used the recent above ground air temperature and air humidity (vapour pressure deficit, VPD) conditions as x-variables. We found that air temperature and VPD data collected 1–4 days before respiration measurements explained 86% of the seasonal variation in the rate of soil respiration. The addition of soil moisture and soil temperature to the PLS-models increased the Q² to 93%. ¹³C analysis of soil respiration supported the hypotheses that there was a fast flux of photosynthates to root respiration and a dependence on recent above ground weather conditions. Taken together, our results suggest that shoot activities the preceding 1–6 days influence, to a large degree, the rate of root and soil respiration. We propose this above ground influence on soil respiration to be proportionally largest in the middle of the growing season and in situations when there is large day-to-day shifts in the above ground weather conditions. During such conditions soil temperature may not exert the major control on root respiration.     

A fine-structural study of the freeze-preservation of plant tissue cultures

Summary Suspension culture cells of sycamore (Acer pseudoplatanus L.) and carrot (Daucus carota L.) were frozen to ultralow temperatures under rapid ( 100 °C s^–1) and slow, controlled (1 or 2 °C min^–1) rates, in the presence and absence of cryoprotective compounds. After storage at –196 °C, cells were recovered by thawing either slowly, in air at room temperature (ca. 20 °C min^–1) or rapidly, in a water bath at 40 °C (ca. 100 °C min^–1). The ultrastructure of the thawed cells was examined by thin-sectioning and compared with unfrozen controls and cells examined in the frozen state. Cells frozen rapidly, in the presence of cryoprotectants, or frozen slowly in their absence, suffered serious ultrastructural damage and a total loss of viability. Carrot cells frozen at a rate of 2 °C min^–1 in the presence of cryoprotectants and thawed at either rate, yielded up to 70% of viable cells. The recovered aggregates of carrot cells comprised some centrally located, seriously damaged cells and, at the periphery, groups of cells with a high electron opacity neighbouring well preserved cells, showing little ultrastructural modification compared with unfrozen controls. The highest rate of survival of sycamore cells (ca. 30%) was observed when they were frozen at a rate of 1 °C min^–1 and thawed rapidly. In all recoverd cells of sycamore some ultrastructural modifications were evident. These included: dilation of mitochondria, plastids, golgi and ER cisternae and the nuclear envelope, decrease in polysomes, increase in nuclear and cytoplasmic microfilaments and changes in nuclear and nucleolar granularity. The probable causes and timing of the ultrastructural changes and their effects on the potential for regrowth of the recovered cells are discussed.     

Microbial production of testosterone and testololactone in the culture of <Emphasis Type="Italic">Aspergillus terreus</Emphasis>

Two metabolites were obtained by microbial transformation of androstendione in the culture of Aspergillus terreus PTCC 5283, a fungus isolated from soil. Their structures were established as testosterone and testololactone on the basis of the spectral data including ¹H NMR, ¹³C NMR, FTIR, MS and physical constants such as melting point and optical rotation. Aspergillus terreusproduced both metabolites after 3 days incubation at 27 °C. The bioconversion reactions observed were 17-carbonyl reduction and biological Baeyer–Villiger oxidation.     

Oligochaeta of Lake Taimyr: a preliminary survey

Lake Taimyr in Siberia is northernmost among the world's large lakes: 73°40–75°20N, 99–106°E. The lake area is up to 4650 km² in summer, with a maximum depth of 26 m and a mean depth of only 2.8 m. The ice-free period lasts about three months. The water level sinks 5.5–6 m during winter, so that 85% of the bottom surface is frozen into ice for some time and subjected to negative temperatures, probably down to –20 °C. In artificially melted sediment samples, 75–92% of animals survived. The average summer biomass of zoobenthos is about 1 g m^–2 wet weight, a half of this being formed by Oligochaeta. Altogether 76 samples with 3742 oligochaete specimens collected by V. N. Grëze in 1943–1944 were studied. At least 14 taxa of Tubificidae, Lumbriculidae, and Enchytraeidae were found in the lake, and some more enchytraeids in an adjacent river. Many immature animals could not be identified to species. Naididae were completely lacking probably due to the absence of macrovegetation. The shallow freezing zone is inhabited mostly by Alexandrovia ringulata. The profundal fauna is dominated by Lamprodrilus isoporus, Stylodrilus sp., and Isochaetides sp.     

Metabolic and cardiovascular adaptations in the western chipmunks, genusEutamias

Summary The metabolic and cardiac responses to temperature were studied in two species (four subspecies) of western chipmunks (genusEutamias), inhabiting boreal and alpine environments. A specially designed (Fig. 1) implantable biopential radiotransmitter was used to measure heart rate in unrestrained animals. The estimated basal metabolic rates (EBMR) were 1.78 (E. minimus borealis), 1.64 (E. m. oreocetes), 1.50 (E. m. operarius), and 1.69 ml O₂ g^–1 h^–1 (E. amoenus luteiventris), or 839, 752, 698, and 628 ml O₂ kg^–0.75 h^–1, respectively, for the four subspecies (Table 1). The two alpine species (E.m.or. andE.m.op.) had significantly lower EBMR than both of their boreal counterparts. The EBMR from all animals are 120–135% of the predicted values based on body weights of the animals. The thermal neutral zone for the four subspecies ranged from 23.5 to 32°C and the minimum thermal conductances were 0.113, 0.111, 0.112 and 0.112 ml O₂ g^–1 h^–1 °C^–1, respectively, or 54.4, 54.0, 50.4 and 52.1 ml O₂ kg^–0.75 h^–1 °C^–1, respectively (Fig. 2). No interspecific diffence in conductance was observed. These values are 72 to 85% of their weight specific values. The body temperature ranged between 35.0 and 39.5°C and was usually maintained between 36 and 38°C in all subspecies between ambient temperatures of 3 and 32°C. The estimated basal heart rates were 273, 296, 273 and 264 beats/min, respectively, for the four subspecies, 49–55% of their predicted weight specific values. The resultant oxygen pulses (metabolic rate/heart rate) were 5.49, 4.50, 4.48 and 5.56×10^–3 ml O₂/beat, respectively, which are 2 to 2.4 times their weight specific values (Table 2).The observed reduction of basal heart rate without the corresponding decreases of basal metabolic rate and body temperature indicate sufficient compensatory increases in stroke volume and/or A-V oxygen difference at rest. Such cardiovascular modifications provide extra reserves when demand for aerobic metabolism rises during bursts of activity typically observed in the western chipmunk.Abbreviations A-V arterio-venous - EBMR estimated basal metabolic rate (ml O₂ g^–1 h^–1) - HR heart rate (beats/min) - MR metabolic rate (ml O₂ g^–1 h^–1) - OP oxygen pulse (ml O₂/heart beat) - T_a, T_b ambient and body temperature (°C)     

Survival of sub-zero temperatures by two South Georgian beetles (Coleoptera,Perimylopidae)

Summary The ability of adults and larvae of two species of perimylopid beetles (Hydromedion sparsutum, Perimylops antarcticus) to survive sub-zero temperatures was studied at Husvik, South Georgia in summer during October–December 1990. Experiments determined their survival at constant sub-zero temperatures, their lower lethal temperatures and individual supercooling points. The effects of cooling rates (0.015°, 0.5° and 2.0°C min^–1) and starvation on survival were also assessed. Mean supercooling points of field-collected individuals of both species were in the range -3.0° to -5.4°C with Perimylops having a deeper capacity (ca. 1.5°C) for supercooling relative to Hydromedion. The former species also survived freezing temperatures significantly better than the latter and its mean lower lethal temperature was 2.5°C lower. At a constant temperature of -8.5°C, the median survival times for Perimylops adults and larvae were 19 and 26 h respectively, whilst both stages of Hydromedion died within 3 h. The three cooling rates resulted in significantly different median survival temperatures for adult Hydromedion with 0.5°C min^–1 producing maximum survival. Prior starvation did not have a significant influence on the survival of either species at sub-zero temperatures although both adults survived less well. The results support field observations on the habitats and distribution of these insects, and suggest differing degrees of freezing tolerance.     

Bioenergetics and thermal physiology of American water shrews (<Emphasis Type="Italic">Sorex palustris</Emphasis>)

Rates of O₂ consumption and CO₂ production, telemetered body temperature (T_b) and activity level were recorded from adult and subadult water shrews (Sorex palustris) over an air temperature (T_a) range of 3–32°C. Digesta passage rate trials were conducted before metabolic testing to estimate the minimum fasting time required for water shrews to achieve a postabsorptive state. Of the 228 metabolic trials conducted on 15 water shrews, 146 (64%) were discarded because the criteria for inactivity were not met. Abdominal T_b of S. palustris was independent of T_a and averaged 38.64±0.07°C. The thermoneutral zone extended from 21.2°C to at least 32°C. Our estimate of the basal metabolic rate for resting, postabsorptive water shrews (96.88±2.93 J g^–1 h^–1 or 4.84±0.14 ml O₂ g^–1 h^–1) was three times the mass-predicted value, while their minimum thermal conductance in air (0.282±0.013 ml O₂ g^–1 h^–1) concurred with allometric predictions. The mean digesta throughput time of water shrews fed mealworms (Tenebrio molitor) or ground meat was 50–55 min. The digestibility coefficients for metabolizable energy (ME) of water shrews fed stickleback minnows (Culaea inconstans) and dragonfly nymphs (Anax spp. and Libellula spp.) were 85.4±1.3% and 82.8±1.1%, respectively. The average metabolic rate (AMR) calculated from the gas exchange of six water shrews at 19–22°C (208.0±17.0 J g^–1 h^–1) was nearly identical to the estimate of energy intake (202.9±12.9 J g^–1 h^–1) measured for these same animals during digestibility trials (20°C). Based on 24-h activity trials and our derived ME coefficients, the minimum daily energy requirement of an adult (14.4 g) water shrew at T_a = 20°C is 54.0 kJ, or the energetic equivalent of 14.7 stickleback minnows.     

Zur Ökologie vonPomatoceros triqueter (Serpulidae,Polychaeta)

Based on previous studies (Klöckner, 1976b) dealing with field investigations on breeding season, choice of substratum, growth and mortality of the sessile filter-feeding tube wormPomatoceros triqueter in Helgoland waters (southern North Sea), data from laboratory experiments on the physiological potential of the polychaete in regard to temperature are presented. Adult worms tolerated temperatures from –3° C (24 h LT 28) to 30° C (24 h LT 50) when heated or cooled in steps of 1 C° d^–1; a two-week period of acclimation within 6° to 18° C did not change their tolerance. Standard oxygen consumption and regeneration of the calcareous tube were found to be dependent on temperature, body weight and food supply; acclimation periods of two weeks had no significant influence. Highly increasing metabolic rates were noted between 6° and 18° C (Q₁₀-values up to 6) and a maximum was found between 20° and 24° C (0.32 g O₂ mg^–1h^–1 and 10.2 g CaCO₃ mg^–1d^–1); tube regeneration followed a nonlinear regression of y=ax^–b when compared to body weight and was reduced by starving animals to less than 50% within 15 days. Filtration activity ofP. triqueter, however, was found to be highly independent of temperature from 12° to 24° C; maximum activity was 1 ml mg^–1 h^–1 (all data refer to fresh weight). For comparisons with the results of previous field investigations onP. triqueter some intraspecific correlations of the different parameters employed (tube sizes, fresh and dry weight) are presented as exponential functions of y=ax^b.     

Coexistence of Tetranychus urticae (Acarina: Tetranychidae) with different capacities for diapause: comparative life-history traits

Summary Individuals of the two-spotted spider mite, Tetranychus urticae Koch (Acarina: Tetranychidae), with and without a capacity for diapause, coexist in central Japan. Diapause appears to be adaptive because females in diapause suffered less mortality than non-diapausing individuals when frozen at –24°C for more than 4 h. However non-diapausing females showed good survival up to 4 h of freezing. Active non-diapausing mites survived on rose leaves in Kyoto (35°N) throughout the winters of 1988–1989 and 1989–1990. Cultures of mites with low (LD) and high (HD) diapause capacities at 18°C and 9L-15D photoperiod were successfully selected from the rose population and from a population on chrysanthemum in Nara (34.4°N). Their life-history traits at 15, 20, 25 and 30°C were characterized. HD and LD mites from both populations were of similar ages at first reproduction at 15–30° C. However, at temperatures 20° C, HD individuals produced more eggs than LD individuals, resulting in higher fecundity and intrinsic rate of natural increase. These traits allow HD individuals, which stop breeding between October and April, to increase faster in summer than LD individuals. This provides a mechanism, together with climatic fluctuations, in maintaining the coexistence of diapausing and non-diapausing T. urticae in Kyoto where winter conditions are rarely lethal to the non-diapausing individuals.     

A radio-telemetric study of the thermoregulation of free living water monitor lizards,Varanus S. salvator

Eight water monitor lizards, Varanus s. salvator, were captured; four individuals from an oil palm estate on the Malayan peninsula, and four from fresh water-deficient Tulai island 65 km off-shore in the South China Sea. They were fitted with a radio transmitter attached to a thermistor which was inserted into the cloaca of the animals and released. The heating rate during basking was measured as 0.117 and 0.118 °C·min^-1 while the daily cloacal temperature fluctuated between 29.5–37.3 °C. Cloacal temperature was measured on other individuals caught at random times during the day, which revealed a considerable daily and individual variation. The average cloacal temperature during activity was 30.4 °C. The peak activity appeared when body temperature was 31 °C. Thermoregulation by behavioural means included cooling in water and reducing heat loss at night by sleeping in burrows. The cooling rate for two individuals when submerged in 29 °C water was 0.308 and 0.340 °C·min^-1. There appeared to be a strong correlation between ambient temperature and cloacal temperature.Abbreviations bw body weight - T _a ambient temperature - T _a body temperature - T _c cloacal temperature - TOP Timor Oil Palm Estate - TUL Tulai Island