Changes among wild House mice (Mus musculus) bred for ten generations in a cold environment, and their evolutionary implications

Wild House mice, Mus musculus , bred at 23°C (controls) changed little in reproductive performance over ten generations. Similar mice bred at 3°C (Eskimo) became more fertile and heavier. Eskimo body fat also rose. Control adrenal weights declined; Eskimo adrenal weights were heavier than those of controls, but only during the first four generations. The Eskimo phenotype after ten generations was a combined result of a direct response to cold, parental effects and genetical changes in the Eskimo population. Maternal effects were probably especially important. In such conditions, the minimum unit of selection that it is useful to consider is the female and her litter.     

Interaction of genotype and parental environment in the adaptation of wild House mice Mus musculus to cold

Wild House mice, Mus musculus, were bred in two laboratory environments, one warm (controls) and one cold (Eskimo). At the seventh generation, mice of both stocks were cross-fostered at birth in both environments. In the warm environment, differences in both genotype and nest environment influenced growth: (1) Eskimo reared by Eskimo females were the heaviest of the four classes of fostered young; and (2) control foster parentage retarded growth. There was, however, no good evidence of differences in the reproductive performance of the four classes of fostered mice. In the cold environment, the effects of both genetical differences and of fostering were greater. Both the superior growth of Eskimo reared by Eskimo and the retarding effect of control foster parentage were more marked. Moreover, adult males with control foster parents had less fat than had those with Eskimo foster parents. Reproductive performance was also affected: (1) the young of the pairs with Eskimo genotype were heavier than the young of control pairs; (2) the litters of mice with Eskimo foster parents were larger than those of mice with control foster parents, and their young were heavier. Differences among the young of fostered mice represent a grandmother effect. Evidently, selection in a cold environment had led, not only to adaptive genetical changes in the ability to respond directly to cold, but also to changes in parental performance; and the latter enhanced the fitness, in the cold environment, of their offspring and grandoffspring.     

MATERNAL PROCESSES IN THE COLD-ADAPTATION OF MICE

• 1 Both laboratory and wild house mice, Mus musculus, given bedding, can breed in captivity in an environment kept at – 3°C. The nest temperature when a young litter is present then fluctuates widely. In a typical laboratory (at 21°C) the temperature of the nest is both higher and more constant.
• 2 The ovaries of pregnant mice breeding at – 3°C have more corpora lute a than controls at 21°C. This is not an index of a higher ovulation rate, but is evidently due to the presence of corpora lutea from a pievious ovulation.
• 3 In the absence of concurrent lactation, weights and numbers of foetuses at the sixteenth day of gestation are little affected by cold; but in both environments foetal weight diminishes with increasing size of litter. This is a systemic effect: foetal weight is hardly if at all influenced by the number of other foetuses in the same uterine horn.
• 4 Cold delays the onset of breeding and lengthens the interval between litters. Mean litter sizes are usually lower than in the warm environment, mainly through absence of large litters.
• 5 The body weights of laboratory mice are usually lower at – 3°C than 21°C at all ages from 3 weeks. This does not, however, apply to strain C57BL, which never stores much fat in adipose tissue. Wild mice bred at – 3°C are heavier than controls at 21°C, possibly because only the heavier individuals survive in early life.
• 6 F ₁ hybrids produced by crossing two inbred strains breed better and more consistently than the parent strains at both temperatures; but the effect of heterozygosis is much greater in the cold environment.
• 7 Food intake changes little during pregnancy, but rises greatly during the first 10 days of lactation at both temperatures.
• 8 At 21°C, body weight, excluding the weight of the litter, increases only slightly during pregnancy; but the weights of the heart and liver are greatly increased. The weight of the stomach also rises; the small intestine lengthens, but becomes lighter. During lactation the liver becomes still heavier, and the small intestine more than restores its loss of weight. The kidneys also become heavier. At – 3°C similar changes occur, but the heart is heavier at all stages of the reproductive cycle than it is at 21°C. The kidneys, too, are consistently heavier in the cold, and so is the small intestine. By contrast, the liver of pregnant or lactating females at – 3°C is no heavier than in the warm environment.
• 9 Pregnancy entails an increase in the absolute amount of nitrogen in the body, in both environments; but females at – 3°C have less nitrogen and collagen than controls. Pregnancy does not alter body fat at either temperature, but lactation is accompanied by some loss. At birth, mice born in the cold environment have more than twice as much body fat as controls.
• 10 When mice are bred for their full reproductive span, the effect of a cold environment depends markedly on genotype. Mice of strain A2G/Tb eventually produce as many young in the cold environment as in the warm, but take longer to do so; C57BL/Tb produce fewer young, Wild mice produce fewer litters at – 3°C, and have a much higher nestling mortality. Most of the mortality is due to loss of whole litters.
• 11 The preceding statements apply to mice of the first two or three generations in a cold environment, There are further effects of breeding for many generations in the cold. Wild mice bred for ten generations lose fewer litters in later than in earlier generations. After ten generations, some wild mice were moved from –3 to 21°C. Their reproductive performance was then much superior to that of controls which had been kept at 21°C throughout. The transferred mice were also quicker than the controls to make a nest of paper.
• 12 Genetically heterogeneous laboratory mice, after twelve generations in the cold, were similarly returned to the warm environment. Their offspring were heavier than controls; but there was no superiority in reproductive performance.
• 13 A2G/Tb mice kept at –3°C, though highly inbred, also improved in reproductive performance over a number of generations: in particular, their infant mortality declined. This was probably not due to a genetical change, but to a cumulative maternal effect.
• 14 Maternal performance was studied by cross-fostering young at birth between these ‘Eskimo’ mice, ‘immigrant’ mice of the first or second generation reared in the cold, and controls at 21°C. There was some evidence of an effect of true parentage, regardless of foster parentage, on body weight: the young of the Eskimo mice tended to be heavier than the others. There was also evidence that this influence persisted into a second generation. Mortality among the fostered young was influenced only by true parentage, not by foster parentage or environmental temperature. Some of the fostered mice were mated. Again, among their young, mortality in the nest was not affected by environmental temperature; but those whose true ancestry was Eskimo displayed a lower mortality than the others.
• 15 If a young mammal is given special treatment (such as exposure outside the nest), the treatment may influence, not only the individual treated, but also the behaviour of the parents; and the altered parental behaviour may in turn affect the development of the young. Enhanced parental attention in the nest has been directly observed after young have been exposed to cold or other treatment. It can probably accelerate maturation, and improve reproductive performance by lowering mortality among the young of the treated mice. Hence the direct effects of treatment in infancy can never be distinguished with certainty from indirect effects through changed parental behaviour, unless the experimental animals are reared artificially.
• 16 A comprehensive theory of ‘stress’, that is, of the response of a species to an environmental change for the worse, requires that attention should be paid to the following: (i) the effects of physiological (ontogenetic) adaptation to one ‘stressor’, such as cold, on response to another, such as infection; (ii) the ways in which conditions of rearing, especially early exposure to mildly adverse conditions such as lower temperature, influence later physiological, reproductive and behaviour al performance; (iii) the relationships of the above with the adaptive changes of pregnancy and lactation.

     

WILD MICE IN THE COLD: SOME FINDINGS ON ADAPTATION

The house mouse, Mus domesticus, can thrive in natural environments much below its optimum temperature. Thermogenesis is then above that at more usual temperatures. In addition, body weight, and the weights of brown adipose tissue and the kidneys, may be higher than usual. In free populations of house mice cold lowers fertility and may prevent breeding. Other possible limiting factors on breeding are food supply, shelter for nesting and social interactions. In captivity, wild-type house mice exposed to severe cold (around 0 degrees C) at first adapt ontogenetically by shivering and reduced activity. But raised thermogenesis is soon achieved without shivering; nest-building improves; and readiness to explore may be enhanced. Endocrine changes probably include, at least initially, a rise in adrenal cortical activity and in catecholamine secretion. Some females become barren, but many remain fertile. The maturity of fertile females is, however, delayed and intervals between births are lengthened; nestling mortality rises. A limiting factor during lactation may be the capacity of the gut. Similar adaptive changes are observed during winter in some species of small mammals that do not hibernate. But neither the house mouse nor other species present a single, universal pattern of cold-adaptation. Wild-type mice bred for about 10 generations in a warm laboratory environment (20-23 degrees C) change little over generations. In cold they become progressively heavier and fatter at all ages; they mature earlier, and nestling mortality declines. The milk of such 'Eskimo' females is more concentrated than that of controls. If 'Eskimo' mice are returned to a warm environment, they are more fertile, and rear heavier young, than controls that remained in the warm. Despite the heavier young, litter size is not reduced: it may be increased, probably as a result of a higher ovulation rate. Parental effects have been analyzed by cross-fostering and hybridizing. Survival, growth and fertility are all favourably influenced by the intra-uterine and nest environments provided by 'Eskimo' females. 'Eskimo' males are also better fathers. Hence after ten generations the phenotype of cold-adapted house mice shows the combined effects of (a) an ontogenetic response to cold, (b) a superior parental environment and (c) a change genotype. The secular changes in the cold that lead to this phenotype give the appearance of evolution in miniature; but it is equally possible that they represent a genetical versatility that allows rapid, reversible shifts in response to environmental demands.(ABSTRACT TRUNCATED AT 400 WORDS)     

Intergenerational acclimation in aphid overwintering

Abstract.  1. When first instar nymphs and adults of the grain aphid Sitobion avenae (Fabricius) (Hemiptera: Aphidiae) were maintained in long-term cultures (>6 months) at 20 °C and 10 °C, the LT₅₀ decreased from −8 and −8.8 °C to −16.0 and −13.5 °C, respectively.
2. When aphids from the 20 °C culture were transferred to 10 °C, there was a progressive increase in cold tolerance through three successive generations. Transfer of newly moulted pre-reproductive adults reared at 10 °C for three generations back to 20 °C resulted in a rapid loss of cold hardiness in their nymphal offspring.
3. In all generations reared at 10 °C, first born nymphs were more cold hardy than those born later in the birth sequence. The LT₅₀ of nymphs produced on the first day of reproduction in the first, second and third generations maintained at 10 °C were −14.8, −17.0 and −16.6 °C, respectively. Thereafter, nymphal cold hardiness decreased over the subsequent 14 days of reproduction in each generation at 10 °C with mean LT₅₀ values of −10.3, −12.6 and −14.8 °C, respectively. By contrast, the cold tolerance of first born nymphs of aphids reared continuously at 20 °C did not differ in comparison with later born siblings. The LT₅₀ of adult aphids was also unaffected by ageing.
4. The ecological relevance of these findings is discussed in relation to the overwintering survival of aphids such as S. avenae .     

Temperature and daylength control of flower initiation in winter oilseed rape (Brassica napus L.)

The influence of low temperature and daylength on pre-floral growth and flower initiation in winter oilseed rape cv. Mikado was examined under controlled environment conditions at the University of Newcastle upon Tyne during 1985 and 1986.
The vernalisation requirement of Mikado was most effectively fulfilled by temperatures of 6 °C and 9 °C. Plants maintained at both higher and lower temperatures had an extended pre-floral growth phase. The transition from vegetative to reproductive growth in plants maintained at 12 °C was delayed by slow accumulation of the cold requirement, whereas flower initiation appeared to be delayed by limited leaf production, dry matter accumulation and/or assimilate availability in plants grown at 3 °C. The mechanism of floral induction remained unresolved but it was clear that flower initiation was not controlled by low temperature per se . Short days partially substituted for the cold requirement at 12 °C but photoperiodic induction of flower initiation was less important than the influence of low temperature.     

Effect of long-term and rapid cold hardening on the cold torpor temperature of an aphid

Abstract.  The effect of long-term (seasonal) acclimation and rapid cold hardening is investigated on the cold torpor temperature ( CT _min) of adult grain aphids, Sitobion avenae, reared at 20 or 10 °C for more than 6 months before experimentation. Rapid cold hardening is induced by exposing aphids reared at 20 to 0 °C for 3 h and aphids reared at 10 to 0 °C for 30 min (acclimation regimes previously found to induce maximum rapid cold hardening). The effect of cooling aphids from the same rearing regimes from 10 to −10 °C at 1, 0.5 and 0.1 °C min⁻¹ is also investigated. In the 20 °C acclimated population, rapid cold hardening and cooling at 0.1 °C min⁻¹ both produce a significant decrease in CT _min from 1.5 ± 0.3 to –0.9 ± 0.3 and –1.3 ± 0.3 °C, respectively. Rapid cold hardening also results in a significant reduction in CT _min of the population reared at 10 °C from 0.8 ± 0.1 to –0.9 ± 0.2 °C. However, none of the cooling regimes tested reduces the CT _min of the winter-acclimated (10 °C) population. The present study demonstrates that rapid cold-hardening induced during the cooling phase of natural diurnal temperature cycles could lower the movement threshold of S. avenae , allowing insects to move and continue feeding at lower temperatures than would otherwise be possible.     

Differential cold hardiness in adults and nymphs of the peach-potato aphid Myzus persicae

The LT₅₀ (lethal temperature) of first instar and adult stages of the peach-potato aphid Myzus persicae was lowered following long term acclimation at low temperatures.
First instars consistently showed greater cold hardiness than adult stages at each acclimation temperature, with the differential increasing as the temperature was lowered. When maintained at 5°C (the lowest acclimation regime) nymphs and adults had dLT₅₀8.3°C and 4.7°C respectively lower than those for non-acclimated individuals.
When 10°C acclimated adults were returned to 20°C, the acclimation effect was retained in full for 6 days but complete deacclimation occurred by day 10. In contrast the LT₅₀ of their progeny increased gradually from the first day of adult deacclimation towards the level of the unacclimated control over a period of 10 days.
A change in cold hardiness was observed in first instars according to their position in the birth sequence. The LT₅₀ of first-born nymphs (day 1 of reproduction) from 20°C parents was - 15.9°C rising to - 8.3°C by day 4 and remaining at this level until the end of the reproductive period.
The differential mortality between nymphs and adults observed in the laboratory was supported by the results of a field experiment. Adult aphids kept in clip-cages on a crop of oilseed rape showed greater mortality compared with those introduced as nymphs when the minimum temperature fell below -4°C for the first time in winter. At - 10°C mortality of aphids introduced as adults approached 100% whereas more than 50% of those introduced as nymphs were still alive at this temperature.     

Effects of cold on nest-building by wild and domestic mice, Mus musculus L.

Nest-building by male and virgin female wild and laboratory mice kept at a temperature of 2^o C was compared with that of controls kept at 23^o C. The amount of cotton wool pulled into the cage was recorded over 24 hours. Nest quality was also assessed. The tests of nest-building were conducted in both cold and warm environments. Cotton pulling was usually at a lower rate in the cold environment, but there was no corresponding decrement in final nest quality. Previous experience in the cold, compared with absence of such experience, resulted in higher scores by wild mice tested in either environment, and by laboratory mice tested in the cold environment. Wild mice that built high quality nests used less cotton wool in the cold than in the warm environment. The tendency for wild mice to pull more cotton wool and build better nests than laboratory mice was more pronounced among cold-treated animals. Differences in body weight did not account for the differences between wild and laboratory mice.
In further experiments nest-building was observed over 16 days. In the cold environment there was an initial depression of nest-building by both wild and laboratory mice, followed by a steady improvement over 6 days.
Both males and virgin females sometimes made well constructed nests even in the warm environment. In the cold environment the effect of previous cold-exposure on wild mice was the rapid construction of a good nest.     

Interactive effects of diet and thermal regime on growth of the midge Pseudochironomus richardsoni Malloch

1. Larvae of Pseudochironomus richardsoni were reared to pupation in individual enclosures, in one of three thermal habitats in a northern California stream. The average temperature range in cold seeps was 15–21 °C, while the main channel ranged from 20 to 27 °C, and side pools ranged from 18 to 33 °C. Diet consisted of either diatoms or algal detritus.
2. Specific growth rate ranged from 0.057 to 0.267 day^–1. Specific growth and developmental rates were highest on a diatom diet, and increased with temperature. Regressions of growth rate on mean microsite temperature were also significantly altered by diet. Differences in specific growth rate due to diet are magnified at higher temperatures.
3. Pupae reared on diatoms were larger than those reared on detritus. The mass of pupae reared on detritus decreased with increasing temperature. However, there was no significant relationship between pupal mass and temperature for larvae reared on diatoms.
4. The combined effects of food quality and thermal environment on growth of the midge P. richardsoni are significantly different from the independent effects of diet and temperature. Interactive effects of food quality and temperature may influence the contribution of certain aquatic habitats (algal mats) to invertebrate secondary production.     

Sex ratio of offsprings of rats bred at 5°C

The sex ratio at birth was examined in offsprings of rats reared in 5°C for successive generations. The sex ratio of their offsprings significantly skewed toward females and the litter size markedly reduced, as compared with those of controls reared in 22°C. Continuous administration of norepinephrine for 12 weeks which purports to simulate a cold stress resulted in a reduction of litter size with a tendency of skewness in sex ratio toward females.     

布氏田鼠哺乳期低温经历抑制成年期神经再生

哺乳动物在出生前后所经历的环境条件对其成年后的行为和生理等具有重要影响。环境温度是影响动物后代表型的重要因素之一。本研究将分娩当天的布氏田鼠母体和幼仔在常温（23℃±1℃）或低温（4℃±1℃）饲养,断乳（21日龄）时转至常温环境,至第63日龄时再随机将两组动物各分为常温组和低温暴露组,期间检测体重、摄食量、静止代谢率、认知能力和神经细胞增殖和存活等,以验证哺乳期的低温经历可影响成年动物的代谢生理、行为表型和相关脑区神经再生的假说。结果发现：哺乳期低温经历导致成年布氏田鼠摄食量显著降低,与代谢有关的下丘脑以及学习记忆有关的海马区细胞增殖和存活数量减少。当动物在成年期面临冷暴露时,与哺乳期常温经历的动物相比,哺乳期低温经历的动物摄食量较低,在Y迷宫新异臂中的穿梭次数和停留时间显著降低,但海马和下丘脑部分核团的细 胞增殖以及海马CA的细胞存活明显升高。这表明哺乳期低温经历对布氏田鼠的能量代谢、行为和相关脑区的成体神经再生产生了持久的抑制效应,但成年后再次面对低温时,动物的代谢能力和代谢及学习记忆相关脑区的神经细胞可塑性优于哺乳期未曾经历低温的动物。     

Influence of food quality and temperature on life history characteristics of the parthenogenetic mayfly, Cloeon triangulifer

SUMMARY. 1. Laboratory and field data indicate that Cloeon triangulifer McDunnough has at least three generations per year in White Clay Creek (Pennsylvania, U.S.A.).
2. The duration of the egg stage ranged from 5 days at 30°C to about 90 days at 10°C.
3. Larvae completed development (i.e. first instar to adult) in 27 days at 25°C, 45 days at 20°C, and 179 days at 10°C on an algal diet dominated by diatoms.
4. Larvae reared on hickory leaves completed development in 30 days at 25°C but died prior to metamorphosis at 10, 15 and 20°C.
5. Adult size (i.e. body length, wing length and dry mass) and fecundity were inversely related to rearing temperature for all laboratory and field experiments.
6. The significant interaction of food quality and temperature suggest that these factors may be important in understanding geographic variation in the life history of C. triangulifer.     

Diapause in a Glasgow strain of the flour moth, Ephestia kuehniella

ABSTRACT. The incidence of diapause in Ephestia kuehniella Zeller from an unhealed granary in Scotland was influenced by both photoperiod and temperature. At 25°C, nearly 50% of larvae entered diapause when reared in continuous darkness (DD) and up to 30% did so in short photoperiods. Little diapause was detected around LD 14:10 but a second, smaller peak of about 20% occurred at LD 16:8 and LD 18:6, falling away again to nearly zero in continuous light. More larvae entered diapause when reared continuously at 15 or 20°C than at 25 and 30°C. However, when larvae reared from hatch at 25°C in LD 16:8 were transferred after 1 week to 15°C in LD 9:15, almost twice as many entered diapause as did those reared at 15°C throughout. The sensitive phase for diapause induction occurred near the start of the final instar. The mean duration of diapause was between 2 and 3 months in most photoperiods at 20 and 25°C, and was shorter at 15°C. However, in DD at 25°C, it lasted about 7 months. Termination of diapause was hastened in larvae reared at 25°C in DD by transferring them to LD 14:10, and also by chilling them at 7.5°C for 6 weeks before returning to 25°C in DD. In an unhealed store in southern England, viable adults emerged from May to July and originated from larvae which terminated diapause relatively late. It would appear from the results of transferring larvae back to the laboratory at various times during the winter that some phases of diapause development were completed quite early after exposure to low temperatures, although no further development took place in the store until temperatures rose again in April.     

Divergent nutrition-related adaptations in two cockroach populations inhabiting different environments

Developmental, reproductive and size‐related variables were compared between two ecologically different strains of Periplaneta americana (L.). One strain was a laboratory‐reared culture, and the other a feral strain inhabiting an urban environment. The feral population was originally founded by escapees from the culture, but may also include immigrants from other urban populations. Both final‐instar nymphs and adults of the feral insects were heavier than their equivalents from the cultured population, this weight difference being due to a higher capacity for the storage of water and heavier fat‐free carcasses. Feral cockroaches also had heavier oothecae, which contained heavier offspring than those from cultured females. Feral animals had one or two more larval stadia and higher growth rates. Size‐related differences persisted in first and second filial generations reared under laboratory conditions on a nutritionally balanced diet, but were not apparent in first filial insects reared on a vegetable diet. Greater resistance to starvation was found in feral animals, and this was attributed primarily to their larger water stores. Feral animals were found to harbour a higher density of endosymbiotic bacteria in the fat body, which are known to enhance the efficiency of protein utilization. The data suggest that the characteristics of feral animals have been selected in the nutritionally harsh feral environment compared with the more benign culture conditions, with water availability playing a role.     

Growth and development of Hymenolepis nana in mice maintained at different environmental temperatures

Growth and development of Hymenolepis nana in mice maintained at different environmental temperatures. International Journal for Parasitology16: 13–17. On days 3 and 4 post infection (p.i.) the number of Hymenolepis nana cysticercoids in the villi of male mice kept at 5°C did not differ from those in controls (21°C), but fewer larvae were observed in hosts at 35°C. However, on day 10 and 14 p.i. in cysticercoid and egg-induced infections respectively, the incidence of infection was higher and significantly more worms per host were found in mice at 5°C than in those kept at 21 or 35°C. Also, worms from mice maintained at 5°C were significantly heavier and became patent 1 day earlier than those from 21°C, which, in turn, were significantly heavier than those grown in hosts at 35°C.     

Early development of the skull of Sander lucioperca (L.) (Teleostei: Percidae) relating to growth and mortality

The early osteological development of the skull (chondrocranium and osteocranium) of the pikeperch Sander lucioperca was studied. Specimens were reared at two temperatures, 15·5 and 18·0° C, from hatching until 47 and 43 days after fertilization (DAF), respectively. The skeletal elements characteristic for the different developmental stages were the same at both rearing temperatures, but pikeperch reared at 15·5° C reached the developmental stages later. The formation of the functional complexes, the neurocranium, jaws and suspensorium, branchial basket and hyoid arch, was evaluated chronologically. The focus was on skull development during several functional changes: at hatching, at the shift from endogenous to mixed feeding, the shift to exclusively exogenous feeding and upon reaching the final prey-capture mechanism. Growth in total length differed between fishes reared at the two temperatures, except during a phase of very slow growth from the end of the embryonic stage until the second larval stage. The latter phase, in which most of the bony elements of the viscerocranium started to form, was marked by high mortality. When exogenous feeding began, the growth rates at both temperatures increased distinctly and the first bony elements were formed in the neurocranium. Specimens reared at 18·0° C grew continuously, but those at 15·5° C showed a second period of slow growth and high mortality. Fish reared at 18·0° C reached the successive larval stages distinctly earlier than fish reared at 15·5° C.     

Effects of temperature on developmental performance, survival and growth of sea lamprey embryos

This study assesses the influence of thermal regime on the development, survival rates and early growth of embryos of sea lamprey Petromyzon marinus incubated at five constant temperatures (7, 11, 15, 19 and 23° C). The time from fertilization to 50% hatching and from hatching to 50% burrowing were inversely related to incubation temperature. All the embryos incubated at 7° C died at very early stages, while those maintained at 11° C did not attain the burrowing stage. Survival from fertilization to hatching was 61, 89, 91 and 89% at 11, 15, 19 and 23° C, decreasing to 58, 70 and 70% from hatching to burrowing at 15, 19 and 23° C, respectively. Larvae reared during the first 3 months of exogenous feeding in a common environment at constant 21° C, revealed maximum survival for an incubation temperature of 15° C (43% of burrowed larvae) decreasing strongly at 19° C (16%) and 23° C (one suvivor among 240 larvae). Body length at the burrowing stage was maximum for embryos incubated at 19° C, but body mass increased in the interval 15–23° C. Mean incubation temperatures experienced by 117 broods during the embryonic development in the source river were estimated in 15·3±2·30° C and 16·7±1·76° C (mean±1 s.d .) for the periods fertilization-to-hatching and hatching-to burrowing, respectively.     

The effects of temperature acclimation on organ/tissue mass and cytochrome c oxidase activity in juvenile cod (Gadus morhua)

Cod were acclimated to 5 and 15° C (cold and warm acclimation, respectively) for at least 43 days after which tissue-somatic indices, tissue protein, DNA content, and cytochrome c oxidase (CCO) activity were measured. Liver, stomach, intestine, total heart and ventricle-somatic indices were all increased significantly in the cold acclimated animals compared with their warm acclimated counterparts. There were no differences in gill or white muscle-somatic indices between the acclimation temperatures. Tissue protein concentration (mg protein g tissue⁻¹) was generally unaffected by temperature acclimation. Cold acclimation resulted in higher white muscle and lower ventricle CCO specific activities(μmol cytochrome c oxidized min⁻¹· g tissue⁻¹) compared with the respective warm acclimated tissues. No significant differences in CCO specific activity were observed in the remaining tissues (when measured at an intermediate temperature of 10° C). Total tissue CCO activity (measured at an intermediate temperature of 10° C) did not differ significantly between the cold and warm acclimated fish.     

Salmonella DNA persistence in natural seawaters using PCR analysis

The risks of false-positive responses were examined when using the polymerase chain reaction (PCR) method for the detection of Salmonella in the marine environment (water and shellfish). The degradation rates of DNA, both free and from dead Salmonella , were evaluated in natural seawaters maintained at 10° and 20°C, using PCR with Vir and invA primers. The DNA of dead Salmonella was detected up to 55 d in seawater collected in winter and stored at 10°C. But in summer, the persistence was shorter: 10 d or even 2 d for a smaller inoculum (3 × 10³ Salmonella ml⁻¹). The role of the planktonic organisms present in spring and summer was pinpointed. For free DNA, the persistence times were shorter: from 2 to 4 d at 20°C, and from 3 to 8 d at 10°C showing that the nuclease activity of marine organisms is higher at warm temperatures. These data led us to recommend careful interpretations of direct PCR results, especially during cold periods and for samples collected close to terrestrial discharges of high concentrations of live, dead or lysed Salmonella . PCR is a rapid, specific and sensitive method, but should be applied with care to marine samples, in order to avoid false-positive responses.