Effects of age, weight, hormones, and hibernation on breeding success in boreal toads (Bufo boreas boreas)

The goals of this study were to test the effects of exogenous hormones and hibernation on breeding behavior and gamete release by boreal toads (Bufo boreas boreas). Each year, a subset of 77 toads was hibernated and then paired with hibernated or nonhibernated mates and treated with luteinizing hormone releasing hormone analogue (LHRHa), human chorionic gonadotropin (hCG), or left untreated. Amplexus and egg and sperm production were recorded. At 1 yr of age, only 19% of pairs exhibited amplexus, and no sperm or eggs were produced. At 2 and 3 yr of age, most male toads treated with LHRHa exhibited amplexus (56.9% and 100%, respectively). Among 2-yr-old males, amplexus was more prevalent (P < 0.05) in those that were hibernated than in those that were nonhibernated (54.0% and 33.3%, respectively), but most males in each group (93.3% and 75%, respectively) produced sperm in response to LHRHa treatment. Only one 2-yr-old and two 3-yr-old females produced eggs. At 4 yr of age, eight females produced eggs, but two died from egg retention. More nonhibernated than hibernated females developed eggs (7 of 10 vs. 1 of 10, P < 0.05). Mean (±SD) weight of female toads producing eggs (58.9 ± 11.9 g) was greater (P < 0.05) than that of nonproducing females (43.6 ± 7.0 g). Similarly, four of seven nonhibernated females (58.8 ± 8.3 g) produced eggs at 5 yr of age. All eggs were produced by females treated once with LHRHa. Number of eggs per female varied (141 to 3307), and development to tadpoles was low (0 to 36.5%), although tadpoles did become toadlets. In conclusion, male and female boreal toads matured at 2 and 4 yr of age, respectively, and heavier females were more likely to produce eggs. To enhance breeding success, males should be hibernated and treated with LHRHa. In contrast, female productivity was enhanced by improving their body condition instead of subjecting them to hibernation prior to LHRHa treatment.     

Metabolism,thermoregulation and evaporative water loss in the Chaotung Vole (Eothenomys olitor) in Yunnan-Kweichow Plateau in summer

Proper adjustment of thermoregulatory mechanisms ensures the survival of mammals when they are subjected to seasonal changes in their natural environment. To understand the physiological and ecological adaptations of Eothenomys olitor, we measured their metabolic rate, thermal conductance, body temperature (T_b) and evaporative water loss at a temperature range of 5–30 °C in summer. The thermal neutral zone (TNZ) of E. olitor was 20–27.5 °C, and the mean body temperature was 35.81±0.15 °C. Basal metabolic rate (BMR) was 2.81±0.11 ml O₂/g h and mean minimum thermal conductance (C_m) was 0.18±0.01 ml O₂/g h °C. Evaporative water loss (EWL) in E. olitor increased when the ambient temperature increased. The maximal evaporative water loss was 6.74±0.19 mg H₂O/g h at 30 °C. These results indicated that E. olitor have relatively high BMR, low body temperature, low lower critical temperature, and normal thermal conductance. EWL plays an inportant role in temperature regulation. These characteristics are closely related to the living habitat of the species, and represent its adaptive strategy to the climate of the Yunnan-Kweichow Plateau, a low-latitude, high-altitude region where annual temperature fluctuations are small, but daily temperature fluctuations are greater.     

Thermogenic characteristics and evaporative water loss in the tree shrew (Tupaia belangeri)

Thermogenic characteristics and evaporative water loss were measured at different temperatures in Tupaia belangeri. The thermal neutral zone (TNZ) of T. belangeri was 30–35 °C. Mean body temperature was 39.76±0.27 °C and mean body mass was 100.86±9.09 g. Basal metabolic rate (BMR) was 1.38±0.03 ml O₂/g h. Average minimum thermal conductance (C_m) was 0.13±0.01 ml O₂/g h °C. Evaporative water loss in T. belangeri increased when the temperature rose; the maximal evaporative water loss was 3.88±0.41 mg H₂O/g h at 37.5 °C. The results may reflect features of small mammals in the sub-tropical plateau region: T. belangeri had high basal metabolic rate and high total thermal conductance, compared with the predicted values based on their body mass whilst their body temperatures are relatively high; T. belangeri has high levels of evaporative water loss and poor water-retention capacity. Evaporative water loss plays an important role in temperature regulation.     

Keeping warm in the cold: On the thermal benefits of aggregation behaviour in an intertidal ectotherm

Temperature is a primary determinant for species geographic ranges. In the context of global warming, most attention focuses upon the potential effects of heat stress on the future distribution of ectothermic species. Much less attention has, however, been given to cold thermal stress although it also sets species thermal window limits, hence distribution ranges. This study was conducted in winter on a South-Australian rocky shore in order to investigate the potential thermal benefits of the aggregation behavior observed in the dominant gastropod Nerita atramentosa. Thermal imaging was used to measure the body temperatures of 3681 aggregated individuals and 226 solitary individuals, and surrounding substratum temperature. N. atramentosa aggregates and solitary individuals were significantly warmer than their surrounding substratum. The temperature deviation between aggregates and substratum was, however, ca. 2 °C warmer than the one observed between solitary individuals and substratum. This result is critical since a body temperature increase of only a few degrees might enhance individual performance, hence organismal fitness, and could potentially drive changes in interspecific relationships. Besides, the potential higher thermal inertia of aggregates might increase the snail adaptive ability to abrupt environmental changes. We further investigate the potential thermal heterogeneity within an aggregate in order to identify any thermally advantageous position. Patch centers are significantly warmer than their edges, hence snails experience greater thermal advantages in the aggregate center. Finally, we examined the potential effect of aggregate size on snail temperature and thermal spatial heterogeneity. We identified an aggregate size threshold (216 individuals) beyond which all snails had equal thermal benefits, regardless of their spatial positions within an aggregate. While the determinism of this aggregate size threshold requires further investigations, the present work uniquely identified the thermal benefits of aggregation behavior for intertidal ectotherms under cold weather conditions. The implications of the present finding are discussed in the general framework of the ability of ectothermic populations to face environmental changes.     

Heat tolerance, behavioural temperature selection and temperature-dependent respiration in larval Octopus huttoni

This study reports temperature effects on paralarvae from a benthic octopus species, Octopus huttoni, found throughout New Zealand and temperate Australia. We quantified the thermal tolerance, thermal preference and temperature-dependent respiration rates in 1-5 days old paralarvae. Thermal stress (1 °C increase h⁻¹) and thermal selection (∼10-24 °C vertical gradient) experiments were conducted with paralarvae reared for 4 days at 16 °C. In addition, measurement of oxygen consumption at 10, 15, 20 and 25 °C was made for paralarvae aged 1, 4 and 5 days using microrespirometry. Onset of spasms, rigour (CT_max) and mortality (upper lethal limit) occurred for 50% of experimental animals at, respectively, 26.0±0.2 °C, 27.8±0.2 °C and 31.4±0.1 °C. The upper, 23.1±0.2 °C, and lower, 15.0±1.7 °C, temperatures actively avoided by paralarvae correspond with the temperature range over which normal behaviours were observed in the thermal stress experiments. Over the temperature range of 10 °C-25 °C, respiration rates, standardized for an individual larva, increased with age, from 54.0 to 165.2 nmol larvae⁻¹ h⁻¹ in one-day old larvae to 40.1-99.4 nmol h⁻¹ at five days. Older larvae showed a lesser response to increased temperature: the effect of increasing temperature from 20 to 25 °C (Q₁₀) on 5 days old larvae (Q₁₀=1.35) was lower when compared with the 1 day old larvae (Q₁₀=1.68). The lower Q₁₀ in older larvae may reflect age-related changes in metabolic processes or a greater scope of older larvae to respond to thermal stress such as by reducing activity. Collectively, our data indicate that temperatures >25 °C may be a critical temperature. Further studies on the population-level variation in thermal tolerance in this species are warranted to predict how continued increases in ocean temperature will limit O. huttoni at early larval stages across the range of this species.     

Fatal attraction: adaptations to prey on native frogs imperil snakes after invasion of toxic toads

Adaptations that enhance fitness in one situation can become liabilities if circumstances change. In tropical Australia, native snake species are vulnerable to the invasion of toxic cane toads. Death adders (Acanthophis praelongus) are ambush foragers that (i) attract vertebrate prey by caudal luring and (ii) handle anuran prey by killing the frog then waiting until the frog''s chemical defences degrade before ingesting it. These tactics render death adders vulnerable to toxic cane toads (Bufo marinus), because toads elicit caudal luring more effectively than do native frogs, and are more readily attracted to the lure. Moreover, the strategy of delaying ingestion of a toad after the strike does not prevent fatal poisoning, because toad toxins (unlike those of native frogs) do not degrade shortly after the prey dies. In our laboratory and field trials, half of the death adders died after ingesting a toad, showing that the specialized predatory behaviours death adders use to capture and process prey render them vulnerable to this novel prey type. The toads'' strong response to caudal luring also renders them less fit than native anurans (which largely ignored the lure): all toads bitten by adders died. Together, these results illustrate the dissonance in behavioural adaptations that can arise following the arrival of invasive species, and reveal the strong selection that occurs when mutually naive species first interact.     

Hydrothermal and thermal time models for the invasive grass, Arundo donax

Controlled laboratory and field experiments were performed to determine the developmental response to temperature and moisture of Arundo donax, a riparian invasive grass and potential bioenergy crop. A logistic function was parameterized and used to predict thermal times to sprouting and the nine-leaf stage. Consistent estimates of the base temperature (T_b) and base water potential (ψ_b) below which development ceases were obtained from various statistical and mathematical analyses. Estimates of T_b and ψ_b were 12.7 ± 1.7 °C and −1.56 ± 0.43 MPa, respectively, for the median fraction of sprouting rhizomes. Median hydrothermal time to sprouting was 124.1 MPa °Cd under laboratory conditions and median thermal times, or degree-day (°Cd), to sprouting and nine-leaf stage was estimated to be 94 and 129 °Cd under field conditions, respectively. A degree-day is defined as one day (24 h) spent one degree above T_b. Results demonstrated that thermal time alone is sufficient to accurately predict time to sprouting under field conditions. Further, there may be a fixed moisture threshold of about 6% volumetric water content above which sprouting rate was constant. This threshold corresponded very closely to the −1.5 MPa for ψ_b that was estimated under laboratory conditions for the soil typically infested by A. donax. This information is crucial for assessing risk of invasive spread for A. donax.     

Evaporative water loss and energy metabolic in two small mammals,voles (Eothenomys miletus) and mice (Apodemus chevrieri), in Hengduan mountains region

Evaporative water loss (EWL) and energy metabolism were measured at different temperatures in Eothenomys miletus and Apodemus chevrieri in dry air. The thermal neutral zone (TNZ) of E. miletus was 22.5–30 °C and that of A. chevrieri was 20–27.5 °C. Mean body temperatures of the two species were 35.75±0.5 and 36.54±0.61 °C. Basal metabolic rates (BMR) were 1.92±0.17 and 2.7±0.5 ml O₂/g h, respectively. Average minimum thermal conductance (C_m) were 0.23±0.08 and 0.25±0.06 ml O₂/g h °C. EWL in E. miletus and A. chevrieri increased with the increase in temperature; the maximal EWL at 35 °C was 4.78±0.6 mg H₂O/g h in E. miletus, and 5.92±0.43 mg H₂O/g h in A. chevrieri. Percentage of evaporative heat loss to total heat production (EHL/HP) increased with the increase in temperature; the maximal EHL/HP was 22.45% at 30 °C in E. miletus, and in A. chevrieri it was 19.96% at 27.5 °C. The results may reflect features of small rodents in the Hengduan mountains region: both E. miletus and A. chevrieri have high levels of BMR and high levels of total thermal conductance, compared with the predicted values based on their body masses, while their body temperatures are relatively low. EWL plays an important role in temperature regulation.     

Skin resistance to water gain and loss has changed in cane toads (Rhinella marina) during their Australian invasion

The water‐permeable skin of amphibians renders them highly sensitive to climatic conditions, and interspecific correlations between environmental moisture levels and rates of water exchange across the skin suggest that natural selection adapts hydroregulatory mechanisms to local challenges. How quickly can such mechanisms shift when a species encounters novel moisture regimes? Cutaneous resistance to water loss and gain in wild‐caught cane toads (Rhinella marina) from Brazil, USA (Hawai''i) and Australia exhibited strong geographic variation. Cutaneous resistance was low in native‐range (Brazilian) toads and in Hawai''ian populations (where toads were introduced in 1932) but significantly higher in toads from eastern Australia (where toads were introduced in 1935). Toads from recently invaded areas in western Australia exhibited cutaneous resistance to water loss similar to the native‐range populations, possibly because toads are restricted to moist sites within this highly arid landscape. Rates of rehydration exhibited significant but less extreme geographic variation, being higher in the native range than in invaded regions. Thus, in less than a century, cane toads invading areas that impose different climatic challenges have diverged in the capacity for hydroregulation.     

The use of small subcutaneous transponders for quantifying thermal biology and torpor in small mammals

Remote measurements of body temperature (T_b) in animals require implantation of relatively large temperature-sensitive radio-transmitters or data loggers, whereas rectal temperature (T_rec) measurements require handling and therefore may bias the results. We investigated whether ∼0.1 g temperature-sensitive subcutaneously implanted transponders can be reliably used to quantify thermal biology and torpor use in small mammals. We examined (i) the precision of transponder readings as a function of temperature and (ii) whether subcutaneous transponders can be used to remotely record subcutaneous temperature (T_sub). Five adult male dunnarts (Sminthopsis macroura, body mass 24 g) were implanted with subcutaneous transponders to determine T_sub as a function of time and ambient temperature (T_a), and in comparison to thermocouple readings of T_rec. Transponder temperature was highly correlated with water bath temperature (r²=0.96–0.99) over a range of approximately 10.0–40.0 °C. Transponders provided reliable data (±0.6 °C) over the T_sub of 21.4–36.9 °C and could be read from a distance of up to 5 cm. Below 21.4 °C, accuracy was reduced to ±2.8 °C, but individual transponder accuracy varied. Consequently, small subcutaneous transponders are useful to remotely quantify thermal physiology and torpor patterns without having to disturb the animal and disrupt torpor. Even at T_sub<21.4 °C where the accuracy of the temperature readings was reduced, transponders do provide reliable data on whether and when torpor is used.     

Differential responses of the floating-leaved aquatic plant Nymphoides peltata to gradual versus rapid increases in water levels

We compared the growth responses of the floating-leaved species Nymphoides peltata to gradual and rapid rising water levels under two nutrient concentrations (1 g and 12 g of slow released fertilizer (N-P-K: 16-8-12) per container filled with 8 kg washed sand), and predicted the population expansion after these floods. The results showed that the capacity for petiole elongation was dependent on leaf age, and only leaves that were no more than five days old had the capability to reach the water surface when the water level increased rapidly from 50 cm to 300 cm. Plants subjected to a gradual rising water level tracked the increase in water depth whose petioles elongated at 3.96 ± 1.70 cm per day and 4.80 ± 0.16 cm per day under low and high nutrient concentrations respectively throughout the experiment period. When water levels were rapidly raised, leaf petioles elongated rapidly at 25.48 ± 1.51 cm per day and 26.64 ± 2.24 cm per day under low and high nutrient concentrations respectively during the first ten days. Plants under a constant water level maintained highest mean leaf recruitment (mean 3.0 ± 0.33 leaves and 24.4 ± 5.87 leaves every ten days under low and high nutrient concentrations, respectively). Therefore, more young leaves existed in the canopy ensuring that when the water level increases, young leaves can rapidly emerge after submergence. Gradual water level rise did not significantly affect biomass and ramet production (4.75 ± 1.41 g and 5.50 ± 1.22 ramets in low nutrient; 48.49 ± 21.45 g and 35.67 ± 11.78 ramets in high nutrient), but rapid water level rise negatively affected ramet production in both nutrient concentrations (3.00 ± 1.26 ramets and 11.25 ± 4.19 ramets in low and high nutrients, respectively). The results indicated that continual leaf recruitment and rapid petiole elongation were both important ways in which N. peltata adapted to increasing water levels. Extreme flooding may be a disturbance factor that affects plant growth and the population expansion of N. peltata, while small gradual water level rise should not harm this species.     

A comparison of galvanic skin conductance and skin wettedness as indicators of thermal discomfort during moderate and high metabolic rates

The relationship between local thermal comfort, local skin wettedness (w_local) and local galvanic skin conductance (GSC) in four body segments during two different exercise intensities was compared in 10 males. In a balanced order, participants walked at 35% VO_2max for 45 min (WALK) (29.0±1.9°C, 29.8±3.6% RH, no wind) in one test and in a separate test ran at 70% VO_2max for 45 min (RUN) (26.2±2.1°C, 31.1±7.0% RH, no wind). During both tests, participants wore a loose fitting 100% polyester long sleeve top and trouser ensemble with a low resistance to heat and vapour transfer (total thermal resistance of 0.154 m² K W⁻¹ and total water vapour resistance of 35.9 m² Pa W⁻¹). w_local, change from baseline in GSC (ΔGSC) and local thermal comfort were recorded every 5 min. The results suggest that both w_local and ΔGSC are strong predictors of thermal comfort during the WALK when sweat production is low and thermal discomfort minimal (r²>0.78 and r²>0.71, respectively). Interestingly, during the RUN w_local plateaued at ~0.6 to 0.8 due to the high sweat production, whilst ΔGSC gradually increased throughout the experiment. ΔGSC had a similar relationship with thermal comfort to w_local during the RUN (r²>0.95 and r²>0.94, respectively). Despite the strength of these relationships, the ability of w_local to predict local thermal comfort accurately dramatically reduces in the exponential part of the curve. In a situation of uncompensated heat stress such as high metabolic rate in hot climate, where sweat production is high, ΔGSC shows to be a better predictor of local thermal comfort than w_local. The w_local data shows regional differences in the threshold which triggers local discomfort during the WALK than RUN; lower values are found for upper arms (0.22±0.03 and 0.28 ±0.22) and upper legs (0.22±0.11 and 0.22±0.10), higher values for upper back (0.30±0.12 and 0.36 ±0.10) and chest (0.27±0.10 and 0.39 ±0.32), respectively. However, no regional differences in the threshold of discomfort are found in the ?GSC data. Instead, the data suggests that the degree of discomfort experienced appears to be related to the amount of sweat within and around the skin (as indirectly measured by ΔGSC) at each body site.     

Host species diversity and post-blood feeding carbohydrate availability enhance survival of females and fecundity in Aedes albopictus (Diptera: Culicidae)

Aedes albopictus mosquito is an opportunistic blood feeder and has a broad host range. The feeding behavior and habits of this mosquito are liable to increase the transmission potential of arboviruses. The survival and fecundity in A. albopictus fed on different hosts and post-blood meal provision of sugar were investigated in a laboratory-reared colony. Adult survival of caged female A. albopictus that were fed on blood of two different hosts (double meal) was higher than the females fed only on one host (single meal) (mean survival: 70.2 ± 9.6 vs. 55.5 ± 5.5%, respectively) when held in the laboratory for 72 h after blood feeding. Mean survival of females provided 10% sucrose solution (in water) after a single or double blood meal was higher (90.5 ± 6.4% and 89.3 ± 6.5%, respectively) than in the respective groups receiving water only following blood feeding (double meal: 49.0 ± 9.6%; single meal: 45.3 ± 10.9%). Females receiving a double meal were more fecund on average (89.0 ± 6.6 eggs) than females provided a single meal (82.3 ± 8.2 eggs).     

Change in the thermal biology of tadpoles of Odontophrynus occidentalis from the Monte desert, Argentina: Responses to photoperiod

We determined if the photoperiod regime affects the thermal biology of the tadpoles of Odontophrynus occidentalis from the Monte desert (Argentina). Variables measured were: selected body temperature (T_sel), critical thermal maximum (CT_max) and thermal critical minimum (CT_min). The tadpoles were acclimated to 15±2 °C for 15 days, and they were divided in three experimental groups: 24 h light, 24 h dark and 12 h/12 h light/dark. Data indicate that the photoperiod had an important effect upon the thermal biology of the Odontophrynus occidentalis tadpoles. The treatment group exposed to 24 h of light showed the highest selected temperature and thermal extremes. We suggest that changes in photoperiod may allow these organisms to anticipate the future changes in their thermal environment, as longer days usually involve higher temperatures.     

Metabolic thermogenesis and evaporative water loss in the Hwamei Garrulax canorus

Basal metabolic rate (BMR) is thought to be a major hub in the network of physiological mechanisms connecting life history traits. Evaporative water loss (EWL) is a physiological indicator that is widely used to measure water relations in inter- or intraspecific studies of birds in different environments. In this study, we examined the physiological responses of summer-acclimatized Hwamei Garrulax canorus to temperature by measuring their body temperature (T_b), metabolic rate (MR) and EWL at ambient temperatures (T_a) between 5 and 40 °C. Overall, we found that mean body temperature was 42.4 °C and average minimum thermal conductance (C) was 0.15 ml O₂ g⁻¹ h⁻¹ °C⁻¹ measured between 5 and 20 °C. The thermal neutral zone (TNZ) was 31.8–35.3 °C and BMR was 181.83 ml O₂ h⁻¹. Below the lower critical temperature, MR increased linearly with decreasing T_a according to the relationship: MR (ml O₂ h⁻¹)=266.59–2.66 T_a. At T_as above the upper critical temperature, MR increased with T_a according to the relationship: MR (ml O₂ h⁻¹)=−271.26+12.85 T_a. EWL increased with T_a according to the relationship: EWL (mg H₂O h⁻¹)=−19.16+12.64 T_a and exceeded metabolic water production at T_a>14.0 °C. The high T_b and thermal conductance, low BMR, narrow TNZ, and high evaporative water production/metabolic water production (EWP/MWP) ratio in the Hwamei are consistent with the idea that this species is adapted to warm, mesic climates, where metabolic thermogenesis and water conservation are not strong selective pressures.     

Disinfection and toxicological assessments of pulsed UV and pulsed-plasma gas-discharge treated-water containing the waterborne protozoan enteroparasite Cryptosporidium parvum

We report for the first time on the comparative use of pulsed-plasma gas-discharge (PPGD) and pulsed UV light (PUV) for the novel destruction of the waterborne enteroparasite Cryptosporidium parvum. It also describes the first cyto-, geno- and ecotoxicological assays undertaken to assess the safety of water decontaminated using PPGD and PUV. During PPGD treatments, the application of high voltage pulses (16 kV, 10 pps) to gas-injected water (N₂ or O₂, flow rate 2.5 L/min) resulted in the formation of a plasma that generated free radicals, ultraviolet light, acoustic shock waves and electric fields that killed ca. 4 log C. parvum oocysts in 32 min exposure. Findings showed that PPGD-treated water produced significant cytotoxic properties (as determined by MTT and neutral red assays), genotoxic properties (as determined by comet and Ames assays), and ecotoxic properties (as determined by Microtox™, Thamnotox™ and Daphnotox™ assays) that are representative of different trophic levels in aquatic environment (p < 0.05). Depending in part on the type of injected gas used, PPGD-treated water became either alkaline (pH ≤ 8.58, using O₂) or acidic (pH ≥ 3.21, using N₂) and contained varying levels of reactive free radicals such as ozone (0.8 mg/L) and/or dissociated nitric and nitrous acid that contributed to the observed disinfection and toxicity. Chemical analysis of PPGD-treated water revealed increasing levels of electrode metals that were present at ≤ 30 times the tolerated respective values for EU drinking water. PUV-treated water did not exhibit any toxicity and was shown to be far superior to that of PPGD for killing C. parvum oocysts taking only 90 s of pulsing [UV dose of 6.29 μJ/cm²] to produce a 4-log reduction compared to a similar reduction level achieved after 32 min PPGD treatment as determined by combined in vitro CaCo-2 cell culture-qPCR.     

The timing of leaf fall affects cold acclimation by interactions with air temperature through water and carbohydrate contents

Three parameters (i.e. the water content, soluble sugar content and minimal air temperature) can be used to predict the cold acclimation process of walnut trees. In order to test this assumption, two-year-old walnuts were defoliated at two different dates, i.e. mechanical defoliation in early October (early leaf fall, EF) or natural defoliation in early November (natural leaf fall, NF) and conditioned in either outdoor freeze-deprived or cold-deprived (T_min > 13 °C) greenhouses over winter. Even if early defoliation date could have affected short day signal perception (SDSP), water balance and carbohydrate metabolism were more altered. EF treatment, by stopping transpiration, significantly increased tree's water content and at warm temperature high root activity stopped normal winter dehydration. Starch content decreased in all treatments, but there was only a significant increase in soluble sugar content when water content had sufficiently decreased. Thus, depending on date of defoliation, cold-deprived trees were or were not able to acclimate to frost (minimal frost hardiness = −21.8 °C vs. −22.1 °C in controls (freeze-deprived) for NF and −13.7 °C vs. −25.3 °C in controls for EF). Different treatments showed the relationship between minimal water content observed during winter and maximal soluble sugars synthesized. Thus, the cold acclimation process appeared dependent on these physiological parameters (water and soluble sugar contents) through the interaction between air temperature and timing of leaf fall.     

Exposure provides refuge from a rootless invasive macrophyte

Free-floating Utricularia inflata Walt. has the potential to alter native isoetid communities as it expands its range from the Atlantic coastal plain into northeastern New York lakes. This field study assessed (1) in situ growth potential for U. inflata at varying depths (1.0-3.0 m), (2) displacement of U. inflata from sites with different exposures to wind and water movement, and (3) U. inflata's relative abundance over a depth range (0.5 m, 1.0 m, 1.5 m, 2.0 m, and 2.5 m) at each of nine Adirondack Mountain lake sites varying in exposure. Plants grew well in shallow water (RGR: 0.014-0.039 day⁻¹) at depths from 1.0 m to 2.5 m, but lost mass at 3.0 m. Significantly fewer U. inflata plants remained at sites and depths with greater exposure to wave action, as well as those with greater water current. Vegetation sampling confirmed greater relative frequency of U. inflata at sheltered sites and along deeper contours. Despite its potential to grow well in shallow water, water movement can prevent the accumulation of U. inflata there, and thus provide a refuge for native species able to withstand wave exposure.     

The effect of temperature, water level and burial depth on seed germination of Myriophyllum spicatum and Potamogeton malaianus

The effects of temperature, water level and burial depth on seed germination of two submerged species, Myriophyllum spicatum and Potamogeton malaianus, were investigated under controlled laboratory conditions. There was no significant difference in final germination of M. spicatum among water level treatments, but P. malaianus germinations at 1 cm and 12 cm water levels were better than at 0 cm water level at temperatures of 20 °C and 30 °C. Little to no germination was observed for either species at the temperature of 10 °C. At 15 °C, however, germination increased significantly to 66.3-70.6% for M. spicatum and to 29.4-48.1% for P. malaianus under all three water level treatments. Increased temperature from 15 °C to 30 °C had no significant effect on the final germination of M. spicatum except at the 1 cm water level, but enhanced significantly the germination of P. malaianus. Analysis of the mean time to germination revealed that M. spicatum was a faster germinator relative to P. malaianus. The two species’ germination differed markedly in response to burial depth. Germination percentage of M. spicatum was 71.3% at 0 cm burial depth, but decreased to 5.0% and to 2.5% at depths of 1 cm and 2 cm, respectively; whereas germination percentages of P. malaianus were 40.0%, 23.8%, 12.5%, 7.5% and 1.3% at depths of 0 cm, 1 cm, 2 cm, 3 cm and 5 cm, respectively. We concluded that the two species respond differently to germination strategies. The findings provided further insight into how germination strategy contributes to the seed bank formation and species invasion.