The critical thermal limits for the stone loach, Noemacheilus barbatulus, from three populations in north-west England

1. The chief objective was to determine the upper and lower thermal limits for feeding and survival in the stone loach, Noemacheilus barbatulus, using juveniles (total length 30–45 mm, live weight 0.25–0.80 g) from one population and adults (total length 77–100 mm, live weight 3.6–7.9 g) from three populations. 2. Fish were acclimatized to constant temperatures of 3, 7, 10, 15, 20, 25 and 27°C; then the temperature was changed at a rate of 1°C/30min to determine the critical limits for feeding, survival over 7 days (incipient lethal temperature), or survival for 10 min or less (ultimate lethal temperature). The rate of 1°C/30min was the optimum value from preliminary experiments, using nine rates from 0.5°C/48h to 18°Ch^?1. As values for adults were not significantly different between populations, they were pooled to provide arithmetic means (with 95% CL) for the thermal limits at each acclimation temperature. 3. Feeding limits increased with acclimation temperature to upper and lower mean values of 28.0 ± 0.15°C and 5.1 ± 0.55°C for adults, 25.0 ± 0.54°C and 6.1 ± 0.92°C for juveniles. Incipient lethal levels defined a tolerance zone within which stone loach survive for a considerable time; upper limits increased with acclimation temperature to reach a maximum plateau of 29.1 ± 0.18°C for adults and 29.0 ± 0.40°C for juveniles; lower limits also increased from near 0°C to 3.0 ± 0.40°C for adults and juveniles. Upper limits for the ultimate lethal level increased with acclimation temperature to a maximum plateau of 33.5°C for adults (95% CL ± 0.19) and juveniles (95% CL ± 0.40), whilst the lower limits increased from near 0°C to 2.5 ± 0.30°C. At acclimation temperatures below 20°C, upper incipient and ultimate lethal values were significantly lower for juveniles than those for adults. 4. The thermal tolerance of stone loach was higher than that of juvenile Atlantic salmon or brown trout, one or both of these species often being dominant in streams with stone loach.     

The critical thermal limits for the bullhead, Cottus gobio, from three populations in north-west England

1. The objective was to determine the thermal limits for feeding and survival in the bullhead, Cottus gobio, using juveniles (total length 20–30 mm, live weight 0.5–1.5 g) from one population and adults (50–70 mm, 3.5–5.5 g) from three populations. 2. Fish were acclimated to constant temperatures (3, 7, 10, 15, 20, 25 or 27 °C) and the temperature was then changed at a rate of 1 °C /30 min to determine the critical limits for feeding, survival over 7 days (incipient lethal temperature), or survival for 10 min or less (ultimate lethal temperature). The rate of 1 °C/30 min was the optimum value from preliminary experiments, using nine rates from 0.5 °C/48 h to 18 °C h^?1. As values for adults were not significantly different between populations, they were pooled to provide arithmetic means (with 95% CL) for the thermal limits at each acclimation temperature. 3. Feeding limits increased with acclimation temperature to upper and lower mean values (± 95% CL) of 26.5 ± 0.16 °C and 4.2 ± 0.20 °C for adults, 26.6 ± 0.59 °C and 5.0 ± 0.55 °C for juveniles. Incipient lethal levels defined a tolerance zone within which fish survive indefinitely; upper limits increased with acclimation temperature to a plateau of 27.6 ± 0.22 °C for adults and 27.5 ± 0.47 °C for juveniles, lower limits increased from near 0 °C to 2.5 ± 0.31 °C for adults and 2.7 ± 0.47 °C for juveniles. Ultimate lethal levels increased with acclimation temperature to a plateau of 32.5 ± 0.24 °C for adults and 32.6 ± 0.46 °C for juveniles, whilst the lower limits increased from near 0 to 0.9 ± 0.29 °C. Upper feeding, incipient and ultimate lethal values were significantly lower for juveniles than those for adults at acclimation temperatures < 20, < 20 and < 15 °C, respectively. 4. The thermal tolerance of bullheads was slightly lower than that of stone loach, similar to that of juvenile Atlantic salmon and higher than that of brown trout; the thermal limits for feeding were much wider than those for salmon or trout.     

Growth and temperature relationships for juvenile fish species in seagrass beds: implications of climate change

The effect of water temperature on growth responses of three common seagrass fish species that co‐occur as juveniles in the estuaries in Sydney (34° S) but have differing latitudinal ranges was measured: Pelates sexlineatus (subtropical to warm temperate: 27–35° S), Centropogon australis (primarily subtropical to warm temperate: 24–37° S) and Acanthaluteres spilomelanurus (warm to cool temperate: below 32° S). Replicate individuals of each species were acclimated over a 7 day period in one of three temperature treatments (control: 22° C, low: 18° C and high: 26° C) and their somatic growth was assessed within treatments over 10 days. Growth of all three species was affected by water temperature, with the highest growth of both northern species (P. sexlineatus and C. australis) at 22 and 26° C, whereas growth of the southern ranging species (A. spilomelanurus) was reduced at temperatures higher than 18° C, suggesting that predicted increase in estuarine water temperatures through climate change may change relative performance of seagrass fish assemblages.     

Variation in scope for growth: a test of food limitation among intertidal mussels

Wellington Harbour supports large populations of the mussels Aulacomya maoriana, Mytilus galloprovincialis and Perna canaliculus that are almost entirely absent from nearby coastal locations in Cook Strait. We calculated scope for growth (SFG) using ambient Cook Strait water over a broad temporal scale and a broad range of seston conditions to determine if negative SFG explains this phenomenon. Although all three mussel species had positive mean SFG values, variation in SFG was high and negative values often occurred: A. maoriana 19.1 J g⁻¹ h⁻¹, 43% of mussels showed negative SFG; M. galloprovincialis 1.26, 52% negative SFG; P. canaliculus 45.6, 27% negative SFG. Negative SFG was most often due to negative absorption efficiency caused by metabolic faecal loss that is characteristic of mussels feeding in environments with low seston quality. From our ecophysiology data we constructed a model to estimate SFG based on physiological responses to the narrow range of seston conditions typical of Cook Strait (Model One), and a model to estimate SFG based on physiological responses of mussels to the broad range of seston conditions typical of Wellington Harbour and Cook Strait (Model Two). We used seston data collected over an 18-month period from sites in Wellington Harbour and Cook Strait to derive 159 estimates of species-specific mussel SFG from both models. Both models produced higher estimates of SFG for mussels in the Harbour compared with those at Cook Strait sites. This was consistent with elevated particulate concentrations in the Harbour than at Cook Strait sites, and in agreement with previous studies. For Cook Strait mussels, both models produced negative estimates of net energy balance for long periods of time (several months), whereas for Harbour mussels negative SFG estimates were generally short in duration. We conclude that our short-term laboratory-based determinations of SFG and our long-term bioenergetics modelling estimates do not conclusively support the hypothesis of food limitation for three coexisting taxa of mussels in the intertidal region of Cook Strait, New Zealand. Handling editor: P. Viaroli     

White-Tailed Deer,Weather and Predation: a New Understanding of Winter Severity for Predicting Deer Mortality

Variation in white-tailed deer (Odocoileus virginianus) mortality during winter affects population growth in cold climates. Across the northern extent of their range, mortality increases with colder temperatures and snow. Few studies have examined the relationships between winter conditions and deer mortality, and no studies have concurrently studied this relationship for different ages of deer across multiple years and landscapes. We used recently developed cause-specific mortality models to evaluate temporal and age-class variation in deer mortality in farmland areas and compared to published results from forest areas in Wisconsin, USA, from 2011–2014. We then used temporally varying snow and temperature covariates to predict mortality trends using telemetry information from 860 deer. Cause-specific mortality in the farmland varied by age and year, similar to results from previous research in the forest. Human-related mortality was the leading cause of mortality in the farmland during most years and ranged from 4.3% to 10.3% for juveniles and 3.6% to 9.1% for adults from 2011–2014. Very little predation occurred in the farmland, and this differed from previous research in the forest where predation was the leading cause of mortality. During more severe winters (2013 and 2014), other mortality, usually associated with starvation, was the leading cause of mortality for juveniles in the farmland but not adults. In the forest, we found support for saturating effects of accumulated snow depth days >30.5 cm and accumulated temperature days >0°C on mortality. We also found support for the relationship of mortality with accumulated temperature days >0°C in the farmland but no relationship with snow depth. Deer tolerate sustained cold temperatures, but the timing of winter to spring transition is more important for deer survival in both forested and agricultural areas. In the absence of empirical survival information, managers can use our model to predict annual winter effects on deer survival, which can provide improved inference compared to traditional winter severity indices. Our results suggest changes in predator abundance may have minor influence on overwinter survival compared to winter weather. Based on mortality estimates from previous research, the highest predation rates on juvenile deer in the forest occurred when wolf (Canis lupus) counts were lowest and when wolf abundance was highest, juvenile deer predation rates were lowest. © 2021 The Wildlife Society.     

Density regulation in toad populations (Epidalea calamita,Bufotes viridis) by differential winter survival of juveniles

The size of amphibian populations varies considerably between years, so that systematic trends in dynamics are difficult to detect. Informed conservation management of presumably declining populations requires the identification of the most sensitive life stage. In temperate-zone anurans there is growing evidence that juveniles hibernating for the first time suffer from substantial winter losses. In two syntopic toads (Epidalea calamita, Bufotes viridis) we monitored survival of such juveniles during four consecutive winters in the natural habitat and in four temperature treatments (3°, 5 °C, 10°/15 °C or 20 °C, natural light-dark cycle) in temperature-controlled chambers during winter. Specifically, we tested the hypotheses that (1) winter mortality of juvenile toads which hibernate for the first time in their life is an important component of population dynamics, and that (2) mortality rates differed between the two species. Parameters quantified were size-dependent winter mortality and body condition of pre- and post-hibernating juveniles. Field data provided evidence for the important role of winter mortality of first-hibernators in population dynamics. Choice of hibernacula differed in E. calamita between small and medium-sized individuals and also between the two species suggesting distinct mortality risks. The inability of small E. calamita to reach frost-proof hibernacula by burrowing, and the exposure of small B. viridis to predators are the most probable causes of size-assortative winter mortality. In conclusion, E. calamita juveniles may benefit from rising average winter temperatures in the future by decreased risk of freezing to death, whereas predator-caused winter mortality of B. viridis juveniles will also depend on the effects of climate warming on predator phenology.     

Too cold is better than too hot: Preferred temperatures and basking behaviour in a tropical freshwater turtle

Thermoregulation is critical to the survival of animals. Tropical environments can be particularly thermally challenging as they reach very high, even lethal, temperatures. The thermoregulatory responses of tropical freshwater turtles to these challenges are poorly known. One common thermoregulatory behaviour is diurnal basking, which, for many species, facilitates heat gain. Recently, however, a north-eastern Australian population of Krefft's river turtles (Emydura macquarii krefftii) has been observed basking nocturnally, possibly to allow cooling. To test this, we determined the thermal preference (central 50% of temperatures selected) of E. m. krefftii in an aquatic thermal gradient in the laboratory. We then conducted a manipulative experiment to test the effects of water temperatures, both lower and higher than preferred temperature, on diurnal and nocturnal basking. The preferred temperature range fell between 25.3°C (±SD: 1.5) and 27.6°C (±1.4) during the day, and 25.3°C (±2.4) and 26.8°C (±2.5) at night. Based on this, we exposed turtles to three 24 h water temperature treatments (‘cool’ [23°C], ‘preferred’ [26°C] and ‘warm’ [29°C]) while air temperature remained constant at 26°C. Turtles basked more frequently and for longer periods during both the day and night when water temperatures were above their preferred range (the ‘warm’ treatment). This population frequently encounters aquatic temperatures above the preferred thermal range, and our results support the hypothesis that nocturnal basking is a mechanism for escaping unfavourably warm water. Targeted field studies would be a valuable next step in understanding the seasonal scope of this behaviour in a natural environment.     

BROAD THERMAL TOLERANCE OF THE SYMBIOTIC DINOFLAGELLATE SYMBIODINIUM MUSCATINEI (DINOPHYTA) IN THE SEA ANEMONE ANTHOPLEURA ELEGANTISSIMA (CNIDARIA) FROM NORTHERN LATITUDES1

The sea anemone Anthopleura elegantissima (Brandt) hosts two species of symbiotic dinoflagellates, known as zooxanthellae, which coexist within the host at southern latitudes only. One of these species, Symbiodinium muscatinei LaJeunesse et Trench, has a broad latitudinal distribution, occurring in intertidal anemones from Washington state to Southern California. To investigate whether high thermal tolerance contributes to the ability of S. muscatinei to inhabit anemones from northern and southern regions, the upper thermal tolerance limit for photosynthesis of symbionts in northern (48°24′ N) populations of A. elegantissima was determined by subjecting anemones to a gradual increase in temperature from 12°C to 30°C over a 10‐week period. Light‐saturated photosynthetic rates of isolated zooxanthellae were the same over the range of 12°C–24°C and declined significantly at 26°C, which is 14°C and 5°C above average summertime seawater temperatures in northern Puget Sound and Southern California, respectively. At 28°C, zooxanthellae isolated from the anemones, and those expelled by their hosts, exhibited extremely low rates of photosynthesis and highly reduced chl content. The photosynthetic rates and chl content of expelled zooxanthellae were lower than those of retained zooxanthellae. The high thermal tolerance of S. muscatinei isolated from northern populations of anemones supports the broad latitudinal distribution of this symbiont, allowing it to coexist with S. californium (#383, Banaszak et al. 1993 ) in southern populations of anemones.     

Growth and thermal tolerance of a Tibet fish Schizopygopsis younghusbandi juveniles acclimated to three temperature levels

Schizopygopsis younghusbandi is an endemic fish of Tibet characterized by slow growth. Artificial stock enhancement was applied to rebuild the natural population of S. younghusbandi in recent years. However, the optimal growth temperature and thermal tolerance of S. younghusbandi has not been studied, which restricts the production of S. younghusbandi fingerling for stock enhancement. The purpose of this paper is to determine the growth, critical thermal maximum (CTMax), lethal thermal maximum (LTMax) and acclimation response ratio (ARR) of S. younghusbandi juveniles (body weight 5.7 ± 1.2 g) at three acclimation temperature levels (10, 15, 20°C). The results showed that acclimation temperature significantly affected the growth, CTMax, LTMax and ARR of the experimental fish. Largest final weight (7.5 ± 2.3 g) was recorded in 15°C group. At a heating rate of 1°C/30 min, CTMax ranged from 30.98 to 32.01°C and LTMax ranged from 31.76 to 32.31°C in the three acclimation temperatures. Schizopygopsis younghusbandi had lower ARR value (0.097) than most other fish species. Low ARR value indicates that S. younghusbandi may have narrower thermal tolerance range and weaker acclimation ability to global warming. For successful aquaculture of S. younghusbandi juveniles, temperature should be maintained around 15°C.     

Effect of temperature and salinity on the gastric evacuation of juvenile sole Solea solea and Solea senegalensis

The juveniles of Senegal sole, Solea senegalensis, Kaup 1858, and common sole, Solea solea (Linnaeus 1758) concentrate in estuarine and coastal nurseries of widely differing temperatures and salinities. Yet, little is known about the effect of these physiologically important variables on the gastric evacuation rates of these species. Gastric evacuation experiments were performed on juveniles of S. senegalensis and S. solea. Three temperatures were tested, 26, 20 and 14°C at a salinity of 35‰. A low salinity experiment was also carried out at 15‰, at 26°C. Experimental conditions intended to reflect conditions in estuarine and coastal nurseries where juveniles of these species spend their first years of life. The relation between stomach contents and time was best described by exponential regression models for both species. An analysis of covariance (ancova ) was performed in order to test differences in evacuation rate due to temperature and salinity (slope of evacuation time against stomach contents) for each species. While increasing temperature increased evacuation rates in both species (although not at 26°C in S. solea), the effect of low salinity differed among species, leading to a decrease in gastric evacuation rate in that of S. senegalensis and an increase in S. solea. Differences in gastric evacuation rate between species were related to its metabolic optimums and to its distribution in the nursery area where fish were captured. Implications for the habitat use of estuarine and coastal nurseries are discussed.     

Analysis of the hatching site and migratory behaviour of the swordtip squid (Uroteuthis edulis) caught in the Japan Sea and Tsushima Strait in autumn estimated by statolith analysis

In contrast to the swordtip squid (Uroteuthis edulis) caught in the spring and summer, those caught in the autumn in the Japan Sea and the Tsushima Strait are characterized by thick bodies with large clubs, long tentacles and large suckers. In addition, most females and many males are immature. However, the reasons for these characteristics, as well as the hatching site and migratory behaviour, are not well known. The empirical water temperature of juveniles was estimated at ～17°C through strontium:calcium (Sr:Ca) ratios in statoliths and information on seawater temperature distribution. The ontogenetic variation in Sr:Ca ratios decreased from hatching to 60 days after hatching and then remained stable. The estimated water temperature was ～21°C after 60 days. Thus, individuals of the autumn-migrating group most likely hatch in the southern East China Sea in the winter and early spring and then move north-eastwards with currents and pass through the Tsushima Strait into the southern Japan Sea during or after July. However, the squid could be present in these waters without strong currents northeast of Tsushima Island, where thermoclines occur during summer, and become confined in limited layers until vertical mixing occurs in the autumn. The distribution of the squid would thereafter extend to fishing grounds in the southern and south-eastern Japan Sea and then to the Tsushima Strait. This migratory behaviour could be the cause of the observed characteristics because bottom seawater temperatures are much lower in the Japan Sea than in the East China Sea.     

Observations and comments on the body temperatures of some New Zealand reptiles

Abstract

Rectal body temperatures (BTs) of tuataras (Sphenodon punctatus) and of endemic, ovoviviparous gekkonid lizards—mainly Hoplodactylus maculatus (=H. pacificus) and Heteropholis manukanus—were taken together with ambient temperatures during early summer 1970 in areas of central New Zealand. The results, combined with earlier data, enable a number of conclusions to be drawn. (a) The preferred body temperature of heliotherm reptiles is best deduced from the mode of rectal BTS taken in the field, but that of non-heliotherms, when unimodal, from the median or mean. (b) Among Gekkonoidea, specific thermal relations are highly variable in several ways. (c) Sphenodon foraged on cool nights at BTs of 10.5–12.5°c, yet basked in the forest by day at BTs up to 24°c; in pasture it apparently basks within the burrow entrance. (d) Similarly, H. maculatus foraged at night at BTs of 10–13°c, but by day thermoregulated at BTs up to 33°c by ‘indirect basking’ (under thin cover) or ‘protected basking’ (in crevices penetrated by solar radiation). The average BT of females was 2°c higher than that of males, presumably because many females were gravid. (e) H. manukanus is (tertiarily) diurnal, and thermoregulated by basking up to a BT of 31 °c. Towards evening it apparently cooled down voluntarily. (f) Whereas a high daytime BT probably assists digestion in nocturnal foragers, a voluntary low night-time BT in diurnal reptiles may help to conserve energy.     

Observations on the activity and thermoregulation of the tuatara,Sphenodon punctatus (Reptilia: Rhynchocephalia), on Stephens Island

Abstract

Observations on Stephens Island, Cook Strait, in December 1978 show that although the tuatara is generally most active at night, many animals spend much of the day at or beyond burrow entrances, apparently to increase their body temperature. During the day, tuataras tend to move further from burrows which are under shaded forest than from those in open pasture. By day, mean body temperatures (±SE) ranged from 17.2±0.5°C in forest shade to 24.6±1.1°C in full sunlight; the maximum body temperature recorded was 26.3°C. The significance of these observations is discussed.     

Short-term success of a translocation of Otago skinks (Oligosoma otagense) to Orokonui Ecosanctuary

Natural habitat is not always available for translocations due to habitat modification or pressure from introduced predators. We followed the release of 30 captive-bred Otago skinks (Oligosoma otagense) into a 109?m² outdoor enclosure of artificial habitat at Orokonui Ecosanctuary in southeastern New Zealand. We evaluated the short-term success of the translocation by assessing visibility and survival of the skinks over the 3 summer months following release in spring 2013, plus survival the following spring. Skinks were visible most days, especially in warm, dry conditions. Survival was high over the first summer; 80% of skinks were seen at least once during February 2014. The following spring 63% of skinks were resighted during three surveys and breeding has since been reported. Thus, it is feasible to maintain captive-bred adults of this Nationally Endangered skink in artificially constructed, outdoor habitat in a coastal location. However, to avoid predation of juveniles by adult skinks, future translocations should avoid releasing juveniles close to adults.     

Increasing ocean temperatures allow tropical fishes to survive overwinter in temperate waters

The southeast coast of Australia is a global hotspot for increasing ocean temperatures due to climate change. The temperate incursion of the East Australian Current (EAC) is increasing, affording increased connectivity with the Great Barrier Reef. The survival of tropically sourced juveniles over the winter is a significant stumbling block to poleward range shifts of marine organisms in this region. Here we examine the dependence of overwintering on winter severity and prewinter recruitment for eight species of juvenile coral reef fishes which are carried into temperate SE Australia (30–37 °S) by the EAC during the austral summer. The probability of persistence was most strongly influenced by average winter temperature and there was no effect of recruitment strength. Long‐term (138 years) data indicate that winter water temperatures throughout this region are increasing at a rate above the global average and predictions indicate a further warming of >2 °C by the end of the century. Rising ocean temperatures are resulting in a higher frequency of winter temperatures above survival thresholds. Current warming trajectories predict 100% of winters will be survivable by at least five of the study species as far south as Sydney (34 °S) by 2080. The implications for range expansions of these and other species of coral reef fish are discussed.     

Seasonal,environmental and anthropogenic influences on nocturnal basking in turtles and crocodiles from North-Eastern Australia

Many ectotherms bask in the sun as a behavioural mechanism to increase body temperature and facilitate metabolism, digestion or gamete production, among other functions. Such behaviours are common during the day, but some nocturnal species are also known to thermoregulate at night, in the absence of solar radiation, through shifts in body posture or microhabitat selection. Additionally, recent work has documented nocturnal basking in freshwater turtles in tropical Australia, though the purpose of the behaviour remains unknown. Here, we have built upon that work to test: 1. seasonal differences, 2. the influence of environmental factors and 3. the influence of anthropogenic development (e.g. river-front houses) on nocturnal basking behaviour. We visually surveyed transects repeatedly at night on the Ross River, Townsville, QLD, Australia from March to November 2020 and documented nocturnal basking in both freshwater turtles (Emydura macquarii krefftii) and freshwater crocodiles (Crocodylus johnstoni). For both taxa, we found significantly more nocturnal basking activity during the hotter months. Likewise, water surface temperature significantly influenced nocturnal basking in both taxa, especially when water temperatures were both high and warmer than air temperatures. We propose that nocturnal basking provides a mechanism for thermoregulatory cooling when water temperatures are high (e.g. 30°C) and above-preferred temperatures. After accounting for availability in basking habitat, both turtles and crocodiles basked more frequently on the undeveloped side of the river, suggesting avoidance of human activity or disturbance. This study is the first to document nocturnal basking activity temporally throughout the year as well as the first to identify the influences of environmental factors. Nocturnal thermoregulation has been documented in many reptiles, however, thermoregulatory cooling in tropical systems is less well-known.     

Soil respiration does not acclimatize to warmer temperatures when modeled over seasonal timescales

Soil warming studies have generally demonstrated an ephemeral response of soil respiration to warming suggesting acclimatization to increased temperatures. Many of these studies depict acclimatization as an empirical temperature-respiration model with data collected from late spring through early autumn. We examined the apparent temperature sensitivity of soil respiration in chronically warmed soils over three different timescales: annually, during the growing season, and seasonally during winter, spring, summer, and fall. Temperature sensitivity was evaluated by fitting exponential and flexible temperature functions as mixed effects models. From model coefficients, we estimated annual, growing season, and season-specific Q ₁₀ values, and assessed the ability of model coefficients to predict daily soil respiration rates over a two-year period. We found that respiration in warmed soils can exhibit characteristics of acclimatized temperature sensitivity depending on the timeframe and the function (exponential or flexible) used. Models using growing season data suggested acclimatization while models using data collected in winter or spring indicated enhanced temperature sensitivity with 5 °C of warming. Differences in temperature sensitivity affected predicted daily soil respiration rates, particularly in winter and spring. Models constructed over longer timescales overestimated daily respiration rates by as much 10–40 % whereas season-specific predictions were generally within 2 % of actual values. Failure to use season-specific models to depict changes in temperature dependence may over- or under-estimate carbon losses due to climate warming, especially during the colder months of the year.     

Factors affecting cold hardiness in the small striped flea beetle, Phyllotreta undulata

The striped flea beetle, Phyllotreta undulata Kutschera (Coleoptera: Chrysomelidae), is a pest of cruciferous crops. It overwinters as an adult. During winter in northern European countries, such as Estonia, it is subject to sometimes severe temperatures that may fluctuate daily, over the season, and between seasons. The objective of this study was to investigate factors that affect its cold hardiness. In a series of five experiments, the effects of food plant, starvation, and acclimatization on the beetles’ ability to supercool and survive exposure to sub‐zero temperatures was investigated. The supercooling points (SCP) of overwintered beetles field‐collected from white mustard and Indian mustard differed from those caught from white cabbage and oilseed rape, but these differences disappeared after a 4‐day period of starvation at room temperature, indicating that gut content probably influences the potential to supercool. The duration and temperature of acclimation affected SCP in overwintered beetles. The decrease in SCP was more rapid at 22 °C than at 0 °C, probably because of faster dehydration and gut evacuation at the higher temperature. Acclimation at 0 °C for a week increased the ability of overwintered beetles to survive sub‐zero temperatures, lowering both SCP and lower lethal temperature (LLT₅₀). Some pre‐freeze mortality occurred; SCP and LLT₅₀ were correlated but the latter was a constant 3 °C higher than the former. The SCP of field‐collected pre‐winter beetles decreased gradually during the autumn. It also decreased when field‐collected pre‐winter beetles were acclimated at 0 °C in the laboratory, attaining its lowest level after 18 days. Phyllotreta undulata is well‐adapted to unstable and sometimes severe winter conditions; its high potential to supercool enhances its cold hardiness and ability to survive short periods at sub‐zero temperatures although it cannot survive freezing of its body fluids.     

The energetics of basking behaviour and torpor in a small marsupial exposed to simulated natural conditions

Limited information is available on basking behaviour in torpid mammals and its energetic consequences. We investigated the effects of physiological and behavioural strategies on the energetics of the fat-tailed dunnart (Sminthopsis crassicaudata). Metabolic rate and body temperature during torpor, basking and rest were measured over 24 h in response to simulated environmental conditions: (a) constant ambient temperature (T _a) of 15°C, (b) constant T _a of 15°C with access to a radiant heat lamp, (c) a T _a cycle (range 15–31°C), and (d) a T _a cycle with access to a radiant heat lamp. When a radiant heat source was provided, all dunnarts (n = 16) basked during all measurements, which resulted in energy savings of up to 74% during rest. Overall, torpor was used on 59% of measurements with a maximum duration of 16.2 h and reductions in metabolic rate of 90% compared to normothermic values. Torpid dunnarts actively moved from a shaded area to position themselves under the heat lamp with body temperatures as low as 17.5°C and thereby reduced rewarming costs by 66%. We demonstrated, for the first time in the laboratory, that torpid animals actively move to a heat source to bask, and that this behaviour results in considerable energy savings. Our finding supports the view that basking during normothermia and rewarming from torpor substantially reduces energetic requirements, which may be important for the survival of small dasyurids living on limited resources in the Australian arid zone.     

Field and laboratory investigations of factors controlling schizogamous reproduction in the polychaete,Autolytus

Schizogamous reproduction by stolon formation in a presumably hybrid population of Autolytus prolifer × A. brachycephalus from the Oosterschelde (The Netherlands) was investigated. Field observations proved that this population does not reproduce all year. During winter, about 50% of the worms were at early stages of stolonization, but no mature stolons at all were developed. Individuals with mature stolons, and also juveniles with less than 20 setigers, were collected in May. Nurses with long stolon chains and numerous reproductive stolons appeared during summer. Nurses collected in winter had higher numbers of stock setigers than those captured in summer; this reduction of the number of setigers mainly results from repeated incorporation of stock setigers into stolons. The influence on stolonization of nutrition, photoperiod and temperature was investigated in the laboratory. Ample food supply is an indispensable prerequisite for stolonization; starved individuals produced small regenerates, but never formed stolons. In well-fed specimens of both juvenile worms and nurses deprived of their stolons, simulated winter conditions (short-day photoperiod at 10°C) prevented stolonization, whereas approximation of summer conditions (long-day photoperiod at 15°C) induced or reinitiated stolon formation.

The results and observations on stolonization at other combinations of different photoperiods and temperatures show that the diurnal photoperiod is a dominant factor in the control of stolonization in these Autolytus spp.. This is the first experimental proof of photoperiodism within the polychaete family, Syllidae.