Seasonal variation in horizontal and vertical structure of larval fish assemblages off south-western Australia, with implications for larval transport

The coastal ocean off south-western Australia is characterisedby the southward-flowing Leeuwin Current, which suppresses theupwelling typically associated with other eastern boundary currentsin the southern hemisphere. This results in a unique environmentfor the transport and survival of planktonic fish larvae. Thehorizontal and vertical structure of larval fish assemblagesoff south-western Australia was investigated during winter (August2003) and summer (January 2004), and related to these unusualregional oceanographic and biological processes. Larval fishwere sampled along a four station transect running from theinner continental shelf to offshore waters, using depth-integratedbongo net tows and depth-stratified EZ net tows. The distributionof taxa across the shelf and offshore was strongly influencedby the current regime at the time of sampling. Larval fish assemblagestructure reflected the distinctive oceanographic conditionsfound during each season, and vertical depth distributions oflarvae affected their horizontal location. Continental shelfsamples were dominated by larvae of pelagic fishes, such asclupeiform species (e.g. Sardinops sagax), whereas offshoreassemblages were characterised by larvae of oceanic families,such as Myctophidae and Phosichthyidae. The winter cruise (August2003) was completed during a time of strong, southerly LeeuwinCurrent flow, whereas the northward-flowing Capes Current, incombination with surface offshore Ekman transport, predominatedduring summer. The vertical depth preferences of larvae wereparticularly influential in affecting their horizontal position;especially so for surface-dwelling larval fishes found duringsummer. This study represents the first documentation of thevertical structure of ichthyoplankton assemblages in the oligotrophicwaters off south-western Australia.     

Developmental plasticity of mating calls enables acoustic communication in diverse environments

Male calls of the katydid Neoconocephalus triops exhibit substantial developmental plasticity in two parameters: (i) calls of winter males are continuous and lack the verse structure of summer calls and (ii) at equal temperatures, summer males produce calls with a substantially higher pulse rate than winter males. We raised female N. triops under conditions that reliably induced either summer or winter phenotype and tested their preferences for the call parameters that differ between summer and winter males.Neither generation was selective for the presence of verses, but females had strong preferences for pulse rates: only a narrow range of pulse rates was attractive. The attractive ranges did not differ between summer and winter females. Both male pulse rate and female preference for pulse rate changed with ambient temperature, but female preference changed more than the male calls.As a result, the summer call was attractive only at 25 degrees C, whereas the slower winter call was attractive only at 20 degrees C. Thus, developmental plasticity of male calls compensates for differences in temperature dependency between calls and preferences and enables the communication system to function in heterogeneous environments. The potential role of call plasticity during the invasion of new habitats is discussed.     

Effects of seasonal variation on the biology and morphology of the dusky cotton bug,Oxcarenus laetus (Kirby)

The dusky cotton bug (Oxycarenus laetus, KIRBY) a pest of several crops. The effects of winter and summer on the biology and morphology was investigated. The sampled eggs of dusky cotton bug (DCB) were kept under controlled environment for biological and morphological investigations. In winter, the mating duration of DCB was observed longer significantly (74.2 days), egg development period (3.93 days), an egg laying period (3.6 days) and hatching period (6.66 days) noted longer in winter season. Interestingly, average number of hatched egg (16.8 days) observed significantly higher in summer and the percentage of the hatching of eggs (81.95%) were also observed higher in summer as compare to winter. Whereas, the longevity of all nymph stages in winter longer days as compare to summer nymph stages. Moreover, differences were also observed between male and female development days between winter and summer. In the winter, female DCB development was suggestively higher as compare to summer (24 days). Whereas, the developmental days were noted considerably more in winter for males as compare to summer (14.93 days). On other hand, for morphological parameters, no differences were observed between winter and summer population of DCB.     

Presence of three diapauses in a subtropical cockroach: control mechanisms and adaptive significance

Abstract.  Diapause is common among insects and is regarded as an adaptive response to periodic occurrence of adverse conditions. It occurs at a particular developmental stage, typically only once in a lifetime. However, little is known about the details of the control mechanism of life cycles with multiple diapauses in insects. In this study, a complex 2-year life cycle with three types of diapause is reported in a subtropical cockroach, Symploce japonica : a winter diapause in mid-nymphal instars, a summer diapause in later nymphal instars, and a reproductive diapause is reported in the adult stage. Nymphal development was extremely slow either at short days (winter diapause) or long days (summer diapause). Nymphs in summer diapause matured rapidly when transferred from long days to short days, indicating that seasonal changes in day-length are the pivotal factor in the control of this life cycle. It is proposed that the main significance of winter diapause in this subtropical species is to enable the nymphs to survive the mild winter successfully with reduced energy demand, and that of summer diapause is to delay adult emergence until late in the autumn for successful induction of the following adult diapause. Adults do not emerge until shortly before winter, yet the presence of diapause in the adult stage does not simply appear to be a response to cope with the winter conditions but, instead, ensures that reproduction will occur early the next year, before summer, because reproduction is greatly hampered at high temperature.     

Association between weather conditions and the number of patients at the emergency room in an Argentine hospital

The aim of this paper is to study the relationships between hospital emergencies and weather conditions by analysing summer and winter cases of patients requiring attention at the emergency room of a hospital in the city of Buenos Aires, Argentina. Hospital data have been sorted into seven different diagnostic groups as follows: (1) respiratory, cardiovascular and chest-pain complaints; (2) digestive, genitourinary and abdominal complaints; (3) neurological and psychopathological disorders; (4) infections; (5) contusion and crushing, bone and muscle complaints; (6) skin and allergies and (7) miscellaneous complaints. In general, there is an increase of 16.7% in winter while, for group 2 and group 6, there are more patients in summer, 54% and 75% respectively. In summer, the total number of patients for group 6 shows a significant positive correlation with temperature and dew-point temperature, and a negative correlation with the sea-level pressure for the same day. In winter, the same relationship exists, however its correlation is not as strong. The lags observed between these three variables: maximum dew-point temperature, maximum temperature, minimum air pressure and the peaks in admissions are 1, 2 and 4 days respectively. In winter, increases in temperature and dew point and decreases in pressure are followed by a peak in admissions for group 2. In winter, there are significantly more cases in group 5 on warm, dry days and on warm, wet days in the summer.     

Seasonality of some Chihuahuan Desert soil oribatid mites (Acari: Cryptostigmata)

1. Reproductive strategies of four species of oribatid mites were investigated in the Chihuahuan Desert from 1981 to 1984.
2. Breeding activity coincided with the summer rainfall period in three of the four cases: Passalozetes neomexicanus, P. californicus and Jornadia larreae. This pattern was not changed by the application of simulated rainfall at other times of the year. The strict seasonality of reproductive behaviour is interpreted as an outcome of strong selection pressure to recruit only when food quality and quantity and microclimate are most favourable.
3. Joshuella striata showed a more flexible pattern which was essentially bimodal. Periods of egg production occurred in winter and also during the summer rainfall period. This pattern is consistent with the known distribution of this species in winter- and summer-rainfall deserts in south-western USA.     

Changes in weight of the pharyngeal gland and haemolymph titres of juvenile hormone,protein and vitellogenin in worker honey bees

Four physiological parameters (haemolymph-juvenile hormone titre, protein concentration, vitellogenin concentration, and pharyngeal gland dry weight) were examined in the following categories of queenright adult worker bees: summer bees 1–40 days old, winter bees 80–130 days old, 12–100-day old bees at the beginning of winter, 100–195-day old bees at the end of winter, and 1–100-day old bees experimentally induced to live longer in summer.In contrast to the continuously increasing titre of juvenile hormone in ageing summer bees, winter bees kept a constant low level. In bees at the beginning of winter, the hormone titre never reached high values. However, at the end of winter it rose from a low to a high level, comparable with the high titre of 24–40-day old summer bees. In experimentally induced longlived bees in summer, the juvenile hormone titre did not increase as in normal summer bees but remained low as in bees at the beginning of winter. Among the known natural juvenile hormones, only juvenile hormone III was present in the haemolymph of winter bees.The results support the hypothesis of polyphenism being regulated by the titre of juvenile hormone in the haemolymph.     

Persistence and Biodegradation of Spilled Residual Fuel on an Estuarine Beach

The enrichment of hydrocarbon-degrading bacteria and the persistence of petroleum hydrocarbons on an estuarine beach after a spill of residual fuel oil on 11 April 1973 in Upper Narragansett Bay, R.I. was investigated. A rapid enrichment occurred during days 4 to 16 after the oil spill and a significant population of hydrocarbon-degrading bacteria was maintained in the beach sand for at least a year. The concentration of petroleum hydrocarbons in the mid-tide area declined rapidly during the bacterial enrichment period, remained fairly constant throughout the summer, and then declined to a low concentration after 1 year. An increased concentration of branched and cyclic aliphatic hydrocarbons in the low-tide sediment 128 days after the spill suggested a migration of hydrocarbons during the summer. Hydrocarbon biodegradation was apparent during the winter months at a rate of less than 1 mug of hydrocarbon per g of dry sediment per day.     

The seasonal distribution and characteristics of bush fly Musca vetustissima Walker populations in south-western Australia

In the agricultural region of south-western Australia the bush fly Musca ventustissima Walker was found to occur permanently in the north-eastern half but it died out during winter in the south-west. The abundance of bush flies increased rapidly throughout the overwintering zone in early spring as a result of local breeding. Flies then dispersed south-westwards, completely repopulating the region during October. Immigrant flies were large and therefore highly fecund, and of advanced reproductive maturity. Local breeding then rapidly increased the population. Maximum abundance occurred in mid-spring in the north and east and in early summer in the south and west. Abundance was greatest in the north where large overwintering populations occurred, and in the far south where repopulation occurred early in the seasonal cycle of pasture growth so that the more favourable cattle dung produced flies that were more fecund than their immigrant parents. The abundance of bush flies declined throughout the region in summer, to negligible levels near the south-west coast but, paradoxically, higher levels occurred inland where there were fewer cattle. On average, flies were smaller and reproductively younger in summer. In areas where irrigated pastures produced more favourable dung in summer, the patterns of abundance and other characteristics of flies did not differ substantially from those in comparable non-irrigated areas. The abundance and other characteristics of a bush fly population 10 km from a cattle-grazing breeding site were similar to those at the site, indicating that constant dispersal is the basis of the bush fly's ubiquity.     

A comparison of photoperiodic control of diapause between aestivation and hibernation in the cabbage butterfly Pieris melete

In the cabbage butterfly, Pieris melete, summer and winter diapause are induced principally by long and short daylengths, respectively; the intermediate daylengths (12-13 h) permit pupae to develop without diapause. In this study, photoperiodic control of summer and winter diapause was systematically investigated in this butterfly by examining the photoperiodic response, the number of days required to induce 50% summer and winter diapause and the duration of diapausing pupae induced under different photoperiods. Photoperiodic response curves at 18 and 20 degrees C showed that all pupae entered winter diapause at short daylengths (8-11 h), the incidence of diapause dropped to 82.3-85.5% at 22 degrees C without showing a significant difference between short daylengths, whereas the incidence of summer diapause induced by different long daylengths (14-18 h) was varied and was obviously affected by temperature. By transferring from various short daylengths (LD 8:16, LD 9:15, LD 10:14 and LD 11:13) to an intermediate daylength (LD 12.5:11.5) at different times after hatching, the number of cycles required to induce 50% winter diapause (7.28 at LD 8:16, 7.16 at LD 9:15, 7.60 at LD 10:14 and 6.94 at LD 11:13) showed no significant difference, whereas by transferring from various long daylengths (LD 14:10, LD 15:9, LD 16:8 and LD 17:7) to an intermediate daylength (LD 12.5:11.5) at different times, the number of cycles required to induce 50% summer diapause (5.95 at LD 14:10, 8.02 at LD 15:9, 6.80 at LD 16:8, 7.64 at LD 17:7) were significantly different. The intensity of winter diapause induced under different short daylengths (LD 8:16, LD 9:15, LD 10:14 and LD 11:13) was not significantly different with an average diapause duration of 87 days at a constant temperature of 20 degrees C and 92 days at a mean daily temperature of 19.0 degrees C, whereas the intensity of summer diapause induced under different long daylengths (LD 14:10, LD 15:9, LD 16:8 and LD 17:7) was significantly different (the diapause duration ranged from 75 to 86 days at a constant temperature of 20 degrees C and from 76 to 88 days at a mean daily temperature of 19.0 degrees C). All results suggested that photoperiodic control of diapause induction and termination is significantly different between aestivation and hibernation.     

Late immature mortality is the major influence on reproductive success of African black beetle, Heteronychus arator (Fabricius) (Coleoptera: Scarabaeidae), in a Mediterranean-climate region of Australia

In field and laboratory studies, mortality of African black beetle, Heteronychus arator, in the winter-rainfall, Mediterranean-type climate region of south-western Australia was higher in the late immature stages during summer than in the early immature stages that occur during spring, a contrast to summer-rainfall climatic regions. Greatest mortality occurred around the pupal stage in contrasting soil types, despite drying differences in summer and supplementary watering in some plots. Sampling of natural populations confirmed experimental results that mortality in late immature stages is the major factor limiting H. arator populations under a Mediterranean-type climate. Inter-generation increase in H. arator abundance was uncommon, explaining the consistent abundance typically observed between years in south-western Australia. Random dispersal of newly emerged adults in autumn was inferred to restore uniformity in adult abundance between areas of varying favourability for immature survival.     

Examination of the meroplankton community in the south-western Ross Sea, Antarctica, using a collapsible plankton net

The meroplankton community in the coastal Antarctic has been poorly studied, in part due to the presence of extensive sea-ice cover during the summer months. In this study, a collapsible plankton net was used to examine the meroplankton community at two sites in the south-western Ross Sea: at Cape Evans on Ross Island, and at Cape Roberts on the Victoria Land coast. Three samples were taken on 5 consecutive days in the early summer at each site (26–30 November and 8–12 December 2001) and 11 operational taxonomic units (OTUs) were quantified from the phyla Annelida, Mollusca, Nemertea, Echinodermata and Sipuncula and the early developmental stages of undetermined phyla. Multivariate analysis showed that there were distinct differences in the meroplankton communities at the two locations, but because there was a 2-week difference in the time of sampling between sites, location and time are confounded variables. On average, a total of 16 larvae/eggs/embryos were collected per tow (3.92 m³) at Cape Evans and 27 larvae/eggs/embryos at Cape Roberts, with a significant difference in total larval numbers and in numbers of 4/6 larval types tested between location and time. This research has shown that a collapsible plankton net can be used for meroplankton work in remote locations in the coastal Antarctic and that a diverse meroplankton community is evident in the south-western Ross Sea in the early summer.     

Summer kill rates and predation pattern in a wolf–moose system: can we rely on winter estimates?

So far the vast majority of studies on large carnivore predation, including kill rates and consumption, have been based on winter studies. Because large carnivores relying on ungulates as prey often show a preference for juveniles, kill rates may be both higher and more variable during the summer season than during the rest of the year leading to serious underestimates of the total annual predation rate. This study is the first to present detailed empirical data on kill rates and prey selection in a wolf–moose system during summer (June–September) as obtained by applying modern Global Positioning System-collar techniques on individual wolves (Canis lupus) in Scandinavia. Moose (Alces alces) was the dominant prey species both by number (74.4%) and biomass (95.6%); 89.9% of all moose killed were juveniles, representing 76.0% of the biomass consumed by wolves. Kill rate in terms of the kilogram biomass/kilogram wolf per day averaged 0.20 (range: 0.07–0.32) among wolf territories and was above, or well above, the daily minimum food requirements in most territories. The average number of days between moose kills across wolf territories and study periods was 1.71 days, but increased with time and size of growing moose calves during summer. Over the entire summer (June–September, 122 days), a group (from two to nine) of wolves killed a total of 66 (confidence interval 95%; 56–81) moose. Incorporation of body growth functions of moose calves and yearlings and wolf pups over the summer period showed that wolves adjusted their kill rate on moose, so the amount of biomass/kilogram wolf was relatively constant or increased. The kill rate was much higher (94–116%) than estimated from the winter period. As a consequence, projecting winter kill rates to obtain annual estimates of predation in similar predator–prey systems may result in a significant underestimation of the total number of prey killed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Energetics and water flux of the marbled velvet gecko (Oedura marmorata) in tropical and temperate habitats

The gecko Oedura marmorata was studied in two different climatic zones: the arid zone of central Australia and in the wet-dry tropics of northern Australia. Doubly labelled water was used to measure field metabolic rate (FMR) and water flux rates of animals in the field during the temperate seasons of spring, summer and winter, and during the tropical wet and dry seasons. FMRs were highest in the tropical wet season and lowest in the temperate winter. The geckos in central Australia expended less energy than predicted for a similarly sized iguanid lizard, but geckos from the tropics expended about the same amount of energy as predicted for an iguanid. Water flux rates of geckos from the arid zone were extremely low in all seasons compared to other reptiles, and although water flux was higher in tropical geckos, the rates were low compared to other tropical reptiles. The standard metabolic rates (SMRs) of geckos were similar between the two regions and among the seasons. Geckos selected higher body temperatures (T _bs) in a laboratory thermal gradient in the summer (33.5°C) and wet (33.8°C) seasons compared to the winter (31.7°C) and dry (31.4°C) seasons. The mean T _bs selected in the laboratory thermal gradient by geckos from the two regions were not different at a given time of year. The energy expended during each season was partitioned into components of resting metabolism, T _b and activity. Most of the energy expended by geckos from central Australia could be attributed to the effects of temperature on resting lizards in all three seasons, but the energy expended by tropical geckos includes a substantial component due to activity during both seasons. This study revealed variability in patterns of ecological energetics between populations of closely related geckos, differences which cannot be entirely attributed to seasonal or temperature effects. Received: 14 November 1997 / Accepted: 4 May 1998     

Effect of temperature and salinity on in vitro zoosporulation of Perkinsus sp. in Manila clams Ruditapes philippinarum

The effects of temperature and salinity on in vitro development of Perkinsus sp. prezoosporangia isolated from cultured Manila clams in Korea were investigated, and the difference in resistance to low temperature between prezoosporangia collected in winter and those collected in summer was compared. Temperature and salinity had significant effects on the development of prezoosporangia, and the developmental rates increased with increasing temperature and salinity. Prezoosporangia isolated in winter sporulated and released motile zoospores at 10 degrees C, although the rates were significantly lower than those at 20 and 30 degrees C. However, no prezoosporangia collected in summer sporulated at 10 degrees C. Low salinities (< or = 10/1000) had a significant negative effect on the development of prezoosporangia. A small number of prezoosporangia sampled in summer did sporulate at 5/1000, but further developments including formation and release of zoospores were not observed. However, prezoosporangia sampled in winter and incubated at 5/1000 released motile zoospores, although the rates were significantly lower than those at higher salinities.     

Energy reserves during food deprivation and compensatory growth in juvenile roach: the importance of season and temperature

The effect of 21 days of starvation, followed by a period of compensatory growth during refeeding, was studied in juvenile roach Rutilus rutilus during winter and summer, at 4, 20 and 27° C acclimation temperature and at a constant photoperiod (12L : 12D). Although light conditions were the same during summer and winter experiments and fish were acclimated to the same temperatures, there were significant differences in a range of variables between summer and winter. Generally winter fish were better prepared to face starvation than summer fish, especially when acclimated at a realistic cold season water temperature of 4° C. In winter, the cold acclimated fish had a two to three‐fold larger relative liver size with an approximately double fractional lipid content, in comparison to summer animals at the same temperature. Their white muscle protein and glycogen concentration, but not their lipid content, were significantly higher. Season, independent of photoperiod or reproductive cycle, was therefore an important factor that determined the physiological status of the animal, and should generally be taken into account when fish are acclimated to different temperature regimes. There were no significant differences between seasons with respect to growth. Juvenile roach showed compensatory growth at all three acclimation temperatures with maximal rates of compensatory growth at 27° C. The replenishment of body energy stores, which were utilized during the starvation period, was responsible for the observed mass gain at 4° C. The contribution of the different energy resources (protein, glycogen and lipid) was dependent on acclimation temperature. In 20 and 27° C acclimated roach, the energetic needs during food deprivation were met by metabolizing white muscle energy stores. While the concentration of white muscle glycogen had decreased after the fasting period, the concentrations of white muscle lipid and protein remained more or less constant. The mobilization of protein and fat was revealed by the reduced size of the muscle after fasting, which was reflected in a decrease in condition factor. At 20° C, liver lipids and glycogen were mobilized, which caused a decrease both in the relative liver size and in the concentration of these substrates. Liver size was also decreased after fasting in the 4° C acclimated fish, but the substrate concentrations remained stable. This experimental group additionally utilized white muscle glycogen during food deprivation. Almost all measured variables were back at the control level within 7 days of refeeding.     

Fifty years of changes in UV Index and implications for skin cancer in Australia

Surface ultraviolet (UV) radiation plays an important role in human health. Increased exposure to UV radiation increases the risk of skin cancer. In Australia, public campaigns to prevent skin cancer include the promotion of daily UV forecasts. If all other atmospheric factors are equal, stratospheric ozone decreases result in UV increases. Given that Australia still has the highest skin cancer rates in the world, it is important to monitor Australia’s stratospheric ozone and UV radiation levels over time because of the effects cumulative exposure can have on humans. In this paper, two long-term ozone datasets derived from surface and satellite measurements, a radiation code and atmospheric meteorological fields are used to calculate clear-sky UV radiation over a 50-year period (1959–2009) for Australia. The deviations from 1970–1980 levels show that clear-sky UV is on the rise. After the 1990s, an overall annual increase from 2 to 6% above the 1970–1980 levels was observed at all latitudes. Examining the summer and winter deviations from 1970–1980 showed that the winter signal dominated the annual changes, with winter increases almost twice those in summer. With ozone levels not expected to recover to pre-depletion levels until the middle of this century, UV levels are expected to continue to rise. Combined with Australians favoring an outdoor life-style, when temperatures are warmer, under high levels of UV, the associated risk of skin cancer will increase.     

Seasonal patterns in water use and leaf turnover of different plant functional types in a species-rich woodland,south-western Australia

Woodlands in south-western Australia are evergreen and transpire throughout the year despite the long, hot and dry summers of the Mediterranean climate. Results from a case study in a species-rich Banksia woodland are used to discuss the ecological and physiological properties that appear to be essential features of this and similar communities. Tree, shrub and perennial herbaceous species with long-lived leaves dominate the community, whereas winter-green herbaceous species with short-lived leaves constitute a minor group. The total leaf area index is therefore reasonably constant in all seasons. Leaf area index is low and canopies are open, causing good coupling between the vegetation and the atmosphere, and making stomatal control an effective regulator of transpiration. Mean maximum (winter) stomatal conductances were high at approximately 300 mmol m^–2 s^–1. Deep-rootedness allows the dominant species to access soil moisture throughout the unsaturated zone, and down to the capillary fringe of the saturated zone. Shrubs and herbs with shallow roots experience greater drought stress during summer. Rates of community evapotranspiration are limited by leaf area index in the wet season, and further reduced by stomatal closure in the dry season. Deep-rooted plants appear to decrease their stomatal conductance before the development of severe drought stress. Such conservative behaviour, possibly related to plant hydraulic constraints, is a contributing factor to the limited seasonality in community water use.     

Cyclic dormancy,temperature and water availability control germination of Carrichtera annua,an invasive species in chenopod shrublands

Abstract We studied the germination of seeds of Carrichtera annua L. from a single cohort, stored in the field for up to 18 months, when retrieved at different times and subject to different combinations of temperature and water availability. Germination was affected by season of retrieval, and temperature and water availability in a complex interactive way. Germination rates were lowest when seeds were retrieved during summer or spring, but seeds germinated readily when retrieved during autumn and winter, if exposed to temperatures simulating autumn or winter conditions, and provided water equivalent to at least 50% field capacity. High temperatures and low water availability reduced germination substantially. The results indicate that this species has a combination of cyclic dormancy and germination requirements that minimizes the risk of germination during periods when the risk of prereproductive mortality is high. Given the short life of the seeds of this species, these mechanisms may be essential for the persistence of the species in the highly unpredictable arid lands of southern Australia.     

Dependence of photosynthesis and energy dissipation activity upon growth form and light environment during the winter

Two very distinctive responses of photosynthesis to winter conditions have been identified. Mesophytic species that continue to exhibit growth during the winter typically exhibit higher maximal rates of photosynthesis during the winter or when grown at lower temperatures compared to individuals examined during the summer or when grown at warmer temperatures. In contrast, sclerophytic evergreen species growing in sun-exposed sites typically exhibit lower maximal rates of photosynthesis in the winter compared to the summer. On the other hand, shaded individuals of those same sclerophytic evergreen species exhibit similar or higher maximal rates of photosynthesis in the winter compared to the summer. Employment of the xanthophyll cycle in photoprotective energy dissipation exhibits similar characteristics in the two groups of plants (mesophytes and shade leaves of sclerophytic evergreens) that exhibit upregulation of photosynthesis during the winter. In both, zeaxanthin + antheraxanthin (Z + A) are retained and PS II remains primed for energy dissipation only on nights with subfreezing temperatures, and this becomes rapidly reversed upon exposure to increased temperatures. In contrast, Z + A are retained and PS II remains primed for energy dissipation over prolonged periods during the winter in sun leaves of sclerophytic evergreen species, and requires days of warming to become fully reversed. The rapid disengagement of this energy dissipation process in the mesophytes and shade sclerophytes apparently permits a rapid return to efficient photosynthesis and increased activity on warmer days during the winter. This may be associated with a decreasing opportunity for photosynthesis in source leaves relative to the demand for photosynthesis in the plant's sinks. In contrast, the sun-exposed sclerophytes – with a relatively high source to sink ratio – maintain PS II in a state primed for high levels of energy dissipation activity throughout much of the winter. Independent of whether photosynthesis was up- or downregulated, all species under all conditions exhibited higher levels of soluble carbohydrates during the winter compared to the summer. Thus downregulation of photosynthesis and of Photosystem II do not appear to limit carbohydrate accumulation under winter conditions. A possible signal communicating an altered source/sink balance, or that may be influencing the engagement of Z + A in energy dissipation, is phosphorylation of thylakoid proteins such as D1.This revised version was published online in October 2005 with corrections to the Cover Date.