Genetic and environmental influences on leaf phenology and cold hardiness of native and introduced riparian trees

To explore the roles of plasticity and genetic variation in the response to spatial and temporal climate variation, we established a common garden consisting of paired collections of native and introduced riparian trees sampled along a latitudinal gradient. The garden in Fort Collins, Colorado (latitude 40.6°N), included 681 native plains cottonwood (Populus deltoides subsp. monilifera) and introduced saltcedar (Tamarix ramosissima, T. chinensis and hybrids) collected from 15 sites at 29.2–47.6°N in the central United States. In the common garden both species showed latitudinal variation in fall, but not spring, leaf phenology, suggesting that the latitudinal gradient in fall phenology observed in the field results at least in part from inherited variation in the critical photoperiod, while the latitudinal gradient in spring phenology observed in the field is largely a plastic response to the temperature gradient. Populations from higher latitudes exhibited earlier bud set and leaf senescence. Cold hardiness varied latitudinally in both fall and spring for both species. For cottonwood, cold hardiness began earlier and ended later in northern than in southern populations. For saltcedar northern populations were hardier throughout the cold season than southern populations. Although cottonwood was hardier than saltcedar in midwinter, the reverse was true in late fall and early spring. The latitudinal variation in fall phenology and cold hardiness of saltcedar appears to have developed as a result of multiple introductions of genetically distinct populations, hybridization and natural selection in the 150 years since introduction.     

Regulation of the loss of frost hardiness in Pinus radiata by photoperiod and temperature

Abstract. In controlled environments, the interactive effects of warm (16: 8°C, day: night) and cool (12: 4°C, day: night) temperatures and long (13.5 h) and short (10 h) photoperiods on the dehardening of seedlings of Pinus radiata D. Don were investigated. In another experiment, the effect of four photoperiods from 9 to 14 h was examined. In a third, dehardening at constant temperatures from 5 to 17°C was followed. There was no evidence for an interaction between photoperiod and temperature. Dehardening was temporarily delayed by photoperiods below about 10 h, but there was no other quantitative effect of photoperiod. At constant temperatures, the rate of dehardening was initially constant but declined as the minimum summer frost hardiness was reached. In the initial phase the rate of dehardening was a linear function of temperature, increasing from 0.05°C day⁻¹ at 8°C to 0.30 °C day⁻¹ at 17°C. Temperature controlled the loss of frost hardiness by regulating the rate of dehardening.     

Abscisic acid content at defined levels of bud dormancy and frost tolerance in two contrasting populations of Picea abies grown in a phytotron

Seedlings of a southern (Romanian) and a northern (Swedish) population of Picea abies were cultivated under continuous light and 20°C for 10 weeks. To arrest growth, induce terminal bud dormancy and promote frost tolerance the seedlings were then exposed to 16 h nights for 12 weeks, with gradually lower temperature during the last 6 weeks. Samples for estimating the abscisic acid content of the needles were taken just before the onset of the night treatment, at day 3 of the treatment, and then with one, and later 2 week, intervals. From the second week onwards (third week for frost tolerance) bud dormancy and frost tolerance were assessed at the same time as abscisic acid (ABA) determinations. Phosphate-buffered saline extracts were purified on mini-columns (in some cases immunoaffinity colums) and quantified by HPLC. The degree of dormancy was estimated by transferring the seedlings to growth conditions and determining the number of days until growth was resumed. The frost tolerance of the needles exposed to –10°C and –20°C was classified in 6 classes. The frost tolerance of the terminal buds was estimated as the number of seedlings that showed some growth after 6 weeks in growth conditions. The night treatment rapidly induced terminal bud dormancy in both populations, but the release of dormancy occurred earlier in the northern population. The needles and the terminal buds became highly frost tolerant more rapidly in the northern than in the southern population and before the temperature decrease. The degree of dormancy began to decline before full frost tolerance was obtained in the southern population and this decline continued in both populations, while frost tolerance remained at a high level. The southern population showed a transient peak in ABA content at day 3. Although the ABA content of the northern population was lower than in the southern before the 16-h night treatment, it increased in the northern population during the treatment period, in particular after the temperature decrease.     

The effects of long-term elevation of air temperature and CO on the frost hardiness of Scots pine

The frost hardiness of 20 to 25-year-old Scots pine (Pinus sylvestris L.) saplings was followed for 2 years in an experiment that attempted to simulate the predicted climatic conditions of the future, i.e. increased atmospheric CO₂ concentration and/or elevated air temperature. Frost hardiness was determined by an electrolyte leakage method and visual damage scoring on needles. Elevated temperatures caused needles to harden later and deharden earlier than the controls. In the first year, elevated CO₂ enhanced hardening at elevated temperatures, but this effect disappeared the next year. Dehardening was hastened by elevating CO₂ in both springs. The frost hardiness was high (相似文献   

Predicting spring frost sensitivity by bud development and temperature sum in Norway spruce seedlings

Nurseries would benefit greatly if frost hardiness (FH) of seedlings could be predicted by some environmental variable or by bud development in spring. We investigated the FH of 1-year-old Norway spruce (Picea abies (L.) Karst.) seedlings of local origin. The seedlings were stored frozen until incubated in the growth chamber at six different temperature sums (TSs) (0, 55, 88, 142, 185 and 240 d.d., >5°C) from mid-February to mid-March. FH of the buds, stems and previous year needles was assessed on three occasions. When the TS was 88 d.d. or less, buds exhibited only microscopic signs of development, even when seedlings tolerated temperatures below −10°C. As TS increased, primordial needles and primordial stems of buds grew while FH weakened, especially in previous year needles. When the TS was at least 142 d.d., all plant parts were frost hardy to approximately −6°C. Monitoring TS and bud development can help predict FH of Norway spruce seedlings in spring. However, more studies with seedlings of different ages and from multiple locations are necessary to appreciate the generality of our results.     

The after-effects of temperature and irradiance during early growth of winter oilseed rape (Brassica napus L. var. oleifera, cv. Górczański) seedlings on the progress of their cold acclimation

Experiments performed under controlled conditions showed that level of PPFD (photosynthetic photon flux density) during early seedlings growth (preceding cold acclimation at +2 °C) was not the key factor for the development of frost resistance. It did not modify the beneficial effects of prehardening (Rapacz 1997, in this issue) at moderately low (+12 °C) day temperature. Now I have shown that the increase of PPFD may replace to some extent prehardening in the development of frost resistance. It was particularly seen in non-prehardened plants, which had been grown under warm-day (+20 °C) conditions. Prehardening performed under controlled conditions, as well as seedlings growth under natural autumn conditions in the field, allowed to maintain a high net-photosynthesis rate at chilling temperatures. A net-photosynthesis rate during cold acclimation at +2 °C corresponded well with higher frost resistance. As a result, seedlings non subjected to prehardening and grown before cold acclimation under low PPFD acclimated better, if the cold treatment was applied only at nights (+20/2 °C day/night). Only under such conditions the photosynthetic rate was sufficiently high to allow plants to reach a higher level of frost resistance. All other plants acclimated better when they were exposed to the hardening temperature continuously during days and nights (+2/2 °C day/night).     

Periodicity of cambial activity in Abies balsamea. I. Effects of temperature and photoperiod on cambial dormancy and frost hardiness

The relationship between from hardiness and growth potential, and their dependence on temperature and photoperiod, was investigated in the one-year-old cambium of balsam fir [Abies balsamea (L.) Mill.]. Six-year-old trees were exposed for 9 weeks to either the natural environment or one of 4 controlled environments in the fall (18 September-18 November), spring (12 April–14 June) and summer (19 July – 19 September). The 4 controlled environments were (1) WS, warm temperature (24/20°C in day/night) + short day (8 h). (2) WL. warm temperature (24/20°C) + long day (8 h + 1 h night break), (3) CS. cold temperature (9/5°C) + short day (8 h) and (4) CL, cold temperature (9/5°C) + long day (8 h + 1 h night break). At the beginning and end of each exposure, cambial activity was measured by recording the number of xylem, cambium and phloem cells, frost hardiness was estimated from the cambium's ability to survive freezing to –40°C, and cambial growth potential was deduced from the duration of the cell cycle and the production of xylem, cambium and phloem cells in cuttings cultured for 4 weeks with exogenous indole-3-acetic acid (IAA) under environmental conditions favourable for cambial activity. In the natural environment, frost hardening began in September and was completed in November, while dehardening occurred when the cambium reactivated. CL, CS, and to a lesser extent WS, promoted hardening in the summer and fall, but did not prevent dehardening in the spring. The cambial growth potential in the natural environment declined from a maximum in April to a low level in June, reached a minimum in September, then increased to a high level in November. This potential was promoted by CL and CS on all dates by WL in the summer and fall. The ratio of xylem to phloem induced by IAA treatment was greatest in June and least in September in cuttings from trees exposed to the natural environment, and was increased by CL and CS in the fall. The cambium in intact branches of trees protected from chilling during the fall and winter resumed cell cycling after less than 9 weeks of dormancy, but produced mostly or only phloem in the subsequent growing period. It is concluded that the frost hardiness of the cambium, the IAA-induced cycling of cambial cells, and IAA-induced xylem to phloem ratio vary independently with season, temperature and photoperiod, and that the periodicity of these processes is regulated endogenously.     

Summer frost resistance and freezing patterns measured in situ in leaves of major alpine plant growth forms in relation to their upper distribution boundary

Summer frost resistance and ice nucleation temperatures for 33 alpine plant species were measured in situ to avoid the shortcomings of laboratory tests. Species were selected to investigate the relationship between plant stature and upper distribution boundary, and frost resistance and freezing patterns. The species tested in situ were on average 1.1 K (± 0.2, SE) frost hardier than in laboratory tests. Frost resistance (LT₅₀) ranged from ?4.5 to ?14.6 °C and appeared insufficient to protect against air temperature minima, corroborating reports of natural frost damage. All species tolerated extracellular ice formation (recorded at ?1.9 ± 0.2 °C; E1). Initial frost damage occurred at average temperatures 4.9 K below E1. In 64% of the species a second exotherm (E2) and frost damage were recorded between ?3.7 and ?9.4 °C. In the highest ranging species E2 was not detectable. Frost resistance increased with increasing upper distribution boundary (0.4 K per 100 m), corresponding well with the altitudinal decrease in air temperature minima. No relationship between plant stature and frost resistance was found. Graminoids were significantly frost hardier than other growth forms. Frost survival at high altitudes will depend not only on altitudinal increase in frost resistance but also on freezing avoidance strategies, snow cover protection and a high recuperation capacity.     

Impact of climate change on cold hardiness of Douglas‐fir (Pseudotsuga menziesii): environmental and genetic considerations

The success of conifers over much of the world's terrestrial surface is largely attributable to their tolerance to cold stress (i.e., cold hardiness). Due to an increase in climate variability, climate change may reduce conifer cold hardiness, which in turn could impact ecosystem functioning and productivity in conifer‐dominated forests. The expression of cold hardiness is a product of environmental cues (E), genetic differentiation (G), and their interaction (G × E), although few studies have considered all components together. To better understand and manage for the impacts of climate change on conifer cold hardiness, we conducted a common garden experiment replicated in three test environments (cool, moderate, and warm) using 35 populations of coast Douglas‐fir (Pseudotsuga menziesii var. menziesii) to test the hypotheses: (i) cool‐temperature cues in fall are necessary to trigger cold hardening, (ii) there is large genetic variation among populations in cold hardiness that can be predicted from seed‐source climate variables, (iii) observed differences among populations in cold hardiness in situ are dependent on effective environmental cues, and (iv) movement of seed sources from warmer to cooler climates will increase risk to cold injury. During fall 2012, we visually assessed cold damage of bud, needle, and stem tissues following artificial freeze tests. Cool‐temperature cues (e.g., degree hours below 2 °C) at the test sites were associated with cold hardening, which were minimal at the moderate test site owing to mild fall temperatures. Populations differed 3‐fold in cold hardiness, with winter minimum temperatures and fall frost dates as strong seed‐source climate predictors of cold hardiness, and with summer temperatures and aridity as secondary predictors. Seed‐source movement resulted in only modest increases in cold damage. Our findings indicate that increased fall temperatures delay cold hardening, warmer/drier summers confer a degree of cold hardiness, and seed‐source movement from warmer to cooler climates may be a viable option for adapting coniferous forest to future climate.     

Cold-acclimation of Hibiscus rosa-sinensis L. and Hibiscus syriacus L. in natural and controlled environments

Abstract Seasonal cold-acclimation patterns and the effects of photoperiod and temperature on cold-hardiness of Hibiscus rosa-sinensis L. and Hibiscus syriacus L. were determined. Field-grown H. rosasinensis consistently failed to survive freezing at - 2°C. Two genotypes of field- and container-grown H. syriacus initiated cold-acclimation in mid September, in response to decreasing daylength, and continued to an ultimate midwinter hardiness level of - 27°C in early February. Controlled environment experiments using combinations of short days (SD) and cool day/night temperatures were unable to induce even minimal cold acclimation of H. rosasinensis. In controlled environments, H. syriacus attained a moderate amount of cold tolerance at warm temperatures and long days (LD). Low night temperature combined with LD, warm day produced the same degree of cold-acclimation as the SD treatments. While not essential, SD enhanced H. syriacus cold-acclimation in controlled environments. A - 5°C frost treatment of intact plants did not enhance cold-hardiness of H. syriacus.     

The Influence of Photoperiod and Temperature on the Development of Frost Hardiness in Seedlings of Pinus silvestris and Picea abies

The influence of short days and low temperature on the development of frost hardiness in seedlings of Scots pine (Pinus silvestris L.) and Norway spruce [Picea abies (L.) Karst.], grown for 6 months in glasshouses and climate chambers, was investigated. The degree of hardiness was estimated by freezing the shoots of the seedlings to predetermined temperatures. After 8 weeks in a glasshouse the viability of the seedlings was determined by establishing bud flushing. The most effective climate for the development of frost hardiness was short days (SD) and low temperature (2°C); the next most effective was SD and room temperature (20°C). However, long days (LD) and low temperature also had a marked effect on the development of hardiness. A combination of 3 weeks’treatment with SD and 20°C, and 3 weeks with SD and 2°C gave the same results as 6 weeks with SD and 2°C. The results clearly demonstrate the importance of the photoperiod prior to low temperature for the development of frost hardiness. In conclusion both short days and low temperature induce frost hardiness development. Probably this occurs by initiation of different processes in the two cases. The degree of frost hardiness development appears to depend on the sum of these different processes and on the timing between them.     

An investigation of the frost hardiness of grapevine (Vitis vinifera) during bud break

The aim of this investigation was to assess ice nucleation and frost resistance of two varieties of grapevine (Siegrebbe and Madeleine Angevine) during bud burst under radiative freezing conditions analogous to those during Spring in the UK. During bud burst, grapevines were almost entirely resistant to freezing during frosts of less than -3°C by virtue of their ability to supercool. The risk of frost damage increased significantly as bud development progressed, and once buds had passed growth stage DS3 they became more sensitive to freezing and freezing damage was more extensive. The two varieties did not differ in frost resistance but, because of its earlier developing habit, variety Siegrebbe could be more prone to frost damage in the field. Buds were more prone to damage after freezing once bud burst had commenced and the damage could not be reversed by acclimating plants for periods of 7 to 21 days at 4°C in an 8 h photoperiod. Such acclimation appeared to predispose frozen buds to more extensive damage.     

Quantitative and qualitative changes in carbohydrates associated with spring deacclimation in contrasting Hydrangea species

Cold deacclimation and associated changes in soluble carbohydrates and water status of two Hydrangea species differing in susceptibility to frost injuries was followed under natural conditions. In fully cold hardy plants of H. macrophylla stem freezing tolerance fluctuated in parallel with changes in air temperature, while in a seasonal perspective increased temperatures caused a sigmoid deacclimation pattern in both H. macrophylla and H. paniculata. Timing of deacclimation was approximately synchronized in the two species, but H. paniculata, the hardier species based on mid-winter hardiness, deacclimated faster than H. macrophylla, indicating that deacclimation kinetics were not correlated with mid-winter hardiness. In both species concentrations of soluble sugars decreased during deacclimation and were highly correlated with stem cold hardiness and air temperatures. This suggests that sugar hydrolysis may be an important temperature-driven mechanism of deacclimation in Hydrangea. Accumulation patterns of specific carbohydrates differed between the two species, suggesting that they utilize different strategies to overcome cold. In H. paniculata, deacclimation was associated with an increase in stem water content, which occurred shortly before bud burst and hence may be a prerequisite for leafing out.     

The effect of LAB 173711 and ethephon on time of flowering and cold hardiness of peach flower buds

Peach flowers are often killed during bloom by spring frosts. LAB 173711, a compound with abscisic (ABA)-like activity, and ethephon delayed flowering in peach trees. In greenhouse experiments, LAB 173711, at concentrations of 10^?3–10^?2 M, was most effective in delaying bloom when applied after a 5°C cold storage period, rather than before the dormancy breaking treatment. In contrast, ethephon delayed bloom most effectively when applied before 5°C cold storage; ethephon caused flower bud abscission when treatments were made after the chilling requirement had been satisfied. In field experiments, ethephon delayed flowering by 6–7 days, which reduced bud injury after a spring frost during bloom. No flower bud injury was found on ethephon-treated trees after temperatures of ?4.3°C; whereas without ethephon 25% of the flower buds were frost damaged. LAB 173711 delayed the time to 50% bloom by 2–3 days. However, this was not long enough to avoid low-temperature injury to the flower buds.     

Differences in frost hardiness of two Norway spruce morphotypes growing at Mt. Brocken, Germany

Norway spruce (Picea abies (L.) Karst.) exhibits strong ecotypic variation along altitudinal gradients in morphological traits, e.g. slenderness of crowns or arrangement of second-order branches. We were interested whether montane and lowland morphotypes differ in a key trait for the survival in cold environments, i.e. frost hardiness, and asked: (i) are montane morphotypes more resistant to frost damage and (ii) do they have a lower risk of frost damage by late frosts in spring than lowland morphotypes?We used the electrolyte leakage-method to measure frost hardiness on a monthly basis from October 2006 to May 2007 in stands of the montane and lowland morphotypes at Mt. Brocken in the Harz Mountains, Germany.LT₅₀ (i.e. the temperature that results in 50% of maximum electrolyte leakage) was assessed by freezing treatments in a frost chamber and was significantly influenced by morphotype, month and minimum ambient temperatures. LT₅₀ was significantly lower in the montane than in the lowland morphotype, with −107 °C and −49 °C, respectively. However, the interactions between morphotype with minimum ambient temperature or month were not significant. Thus, as frost hardiness of the two morphotypes responded to temperature in the same way, both morphotypes can be supposed to be exposed to the same risk of frost damage during hardening in autumn and dehardening in spring.     

Effects of Temperature on Cold Acclimation and Deacclimation in Flower Buds of Evergreen Azaleas

The effects of various storage temperature/duration combinations(5, 10 and 17°/4, 8, 12 and 16 weeks) on cold acclimationand deacclimation of flower buds were studied in four speciesof evergreen azaleas having different natural distribution andcold hardiness. The freezing process and the exotherm temperaturedistribution of florets in excised whole buds determined bydifferential thermal analysis were used as the diagnostics todetermine the degree of bud acclimation and deacclimation. Theacclimation in buds lasted for as long as 12 to 16 weeks at5°C storage, and from 8 to 12 weeks at 10°C, and itappeared to be maintained after the chilling requirement forbreaking bud dormancy had been satisfied. Therefore, bud acclimationseems to be maintained independently from bud dormancy. Thedehardening effect on acclimated buds occurred as a result ofshort exposures to higher temperatures or long exposures tolower temperatures, and there was no relation between the rateof deacclimation and the degree of hardiness in each species.Among three storage temperatures examined, 5°C was the mosteffective for the maintenance of cold acclimation in flowerbuds and the small difference of floret water contents at 5and 10°C storage is not significant. (Received August 28, 1982; Accepted February 4, 1983)     

Regulation of frost resistance during cold de-acclimation and re-acclimation in oilseed rape. A possible role of PSII redox state

A possible role of photosynthetic apparatus during cold de-acclimation was studied in oilseed rape ( Brassica napus var. oleifera ). Plants of spring (Star) and winter (Górczañski) cultivars were cold acclimated at + 5°C, and de-acclimated during 4 weeks at combinations of + 12 and + 20°C operating in the light or/and dark, with a 12-h photoperiod. Evidence is presented that the photosynthetic apparatus may be involved in temperature perception during de-acclimation. De-acclimation was faster under a 20/12°C (day/night) treatment than under the reverse 12/20°C (day/night). De-acclimation rate was constant when the day temperature was constant, irrespective of the night temperature both under cold day temperature regimes (12/20, 12/12°C (day/night) and warm-day treatments (20/12, 20/20°C (day/night). The fast decrease in frost resistance observed under warm-day de-acclimation was always accompanied by an acceleration of elongation growth. In the spring cultivar, elongation growth increased starting from the second week of de-acclimation, regardless of temperature conditions. Once elongation growth had commenced during de-acclimation, it continued throughout the period necessary for re-acclimation to low temperature. Re-acclimation to the initial freezing tolerance level was only possible when plant elongation was reduced. In addition re-acclimation of the photosynthetic apparatus to low temperature was impossible in fast growing plants. A possible relationship between PSII, growth rate and frost resistance during cold acclimation and de-acclimation is discussed.     

Predicting spatial and temporal patterns of bud‐burst and spring frost risk in north‐west Europe: the implications of local adaptation to climate

The timing of spring bud‐burst and leaf development in temperate, boreal and Arctic trees and shrubs fluctuates from year to year, depending on meteorological conditions. Over several generations, the sensitivity of bud‐burst to meteorological conditions is subject to selection pressure. The timing of spring bud‐burst is considered to be under opposing evolutionary pressures; earlier bud‐burst increases the available growing season (capacity adaptation) but later bud‐burst decreases the risk of frost damage to actively growing parts (survival adaptation). The optimum trade‐off between these two forms of adaptation may be considered an evolutionarily stable strategy that maximizes the long‐term ecological fitness of a phenotype under a given climate. Rapid changes in climate, as predicted for this century, are likely to exceed the rate at which trees and shrubs can adapt through evolution or migration. Therefore the response of spring phenology will depend not only on future climatic conditions but also on the limits imposed by adaptation to current and historical climate. Using a dataset of bud‐burst dates from twenty‐nine sites in Finland for downy birch (Betula pubescens Ehrh.), we parameterize a simple thermal time bud‐burst model in which the critical temperature threshold for bud‐burst is a function of recent historical climatic conditions and reflects a trade‐off between capacity and survival adaptation. We validate this approach with independent data from eight independent sites outside Finland, and use the parameterized model to predict the response of bud‐burst to future climate scenarios in north‐west Europe. Current strategies for budburst are predicted to be suboptimal for future climates, with bud‐burst generally occurring earlier than the optimal strategy. Nevertheless, exposure to frost risk is predicted to decrease slightly and the growing season is predicted to increase considerably across most of the region. However, in high‐altitude maritime regions exposure to frost risk following bud‐burst is predicted to increase.     

Vegetative growth and frost hardiness of cloudberry (Rubus chamaemorus) as affected by temperature and photoperiod

The effect of photoperiod and temperature on growth and induction and development of frost hardiness in cloudberry ( Rubus chamaemorus L.) was examined in two experiments. The photoperiods were 8, 12 or 24 h and the temperatures were 18, 15, 12, 9, 4, 3, –3 or –4°C depending on the experiment. The level of hardiness was expressed as LT₆₆ or LT₅₀ (the lethal temperature for 66 or 50% of the plant material) for percentage of bud break and for the degree of coloring by triphenyltetrazolium chloride for rhizomes. The vegetative growth was clearly affected by daylength; petiole elongation, leaf growth, shoot dry weight and number of shoots per plant were all reduced under short days compared with long days. However, the photoperiod had no significant effect on hardening of buds or rhizomes. Hardening increased with successively decreasing temperatures. To get the maximum hardiness, plants had to be exposed to freezing temperatures.     

The influence of snowfall,temperature and social relationships on sleeping clusters of Japanese monkeys during winter in Shiga Heights

We studied Japanese monkeys (Macaca fuscata) of the Shiga A₁ troop at their sleeping sites in Shiga Heights, Japan, for 41 nights during 3 winters. Monkeys chose their sleeping sites in Japanese cedars and in deciduous broad-leaved forests on non-snowing nights and in Japanese cedar forests on snowing nights. We counted 399 sleeping clusters in which 2 or more monkeys remained in physical contact through the night and 43 solitary sleeping monkeys, though monkeys did not maintain physical contact with others in the daytime. We found 397 clusters on tree branches and 2 clusters on rocks. The mean size of huddling clusters was 3.06±1.22 SD. The cluster size (3.17±1.26 SD) at lower ambient temperatures between −7 and −4°C was larger than that at higher temperatures between −2 and 4°C (cluster size 2.88±1.13 SD). Most clusters were composed of kin. Females kept close to related females in the daytime and huddled with them at night. The highest-ranking male mainly huddled with his kin and his familiar females. Other males kept farther apart from each other in the daytime, probably to avoid social conflicts. Through cold winter nights, however, such males reduced inter-individual distances and huddled with other males. Japanese monkeys appear to recognize three types of inter-individual distances: an intimate distance less than 1 m, a personal distance of 1–3 m and a social distance of 3–20 m; they change their inter-individual distances according to social and ecological circumstances.