Egg diapause and clonal structure in parthenogenetic populations of Heterocypris incongruens (Ostracoda)

A study of the clonal structure of parthenogenetic populations of Heterocypris incongruens from rice-fields in Northern Italy carried out over two-year period is summarized. Significantly different levels of genetic polymorphism were found among populations. The coexistence of different electrophoretic clones and similar patterns of clonal seasonal succession have been observed in at least two different rice fields. The clone or group of clones present in fall, winter and early spring is substituted by other multilocus genotypes in late spring and summer. Different egg diapause induction mechanisms drive the clonal substitution in different clones. Here we report a new laboratory experiment designed to test the effect of temperature and photoperiod found in winter (12 °C 8:16 L:D), spring (24°C 12:12 L:D) and summer (28°C 16:8 L:D) conditions on the deposition and hatching of diapausal eggs in different multilocus genotypes. Clones respond in a way compatible with their sustained presence in the field in different seasons.     

Sexual reproduction of Daphnia pulex in a temporary habitat

Species of Daphnia (Crustacea: Cladocera) typically reproduce by cyclical parthenogenesis, in which a period of all-female parthenogenetic reproduction is followed by sexual reproduction. Sex in Daphnia is determined by the environment, with factors such as temperature, photoperiod and crowding stimulating the production of males and sexual females. Previous studies on Daphnia pulex from temporary pond habitats demonstrated the coexistence of male-producing and non-male-producing (NMP) females, as determined under crowding in the laboratory. A strong genetic component to this sex allocation variation suggested that sex expression in D. pulex is better described as a result of genotype-environment interaction. The present study examined the switch from parthenogenetic to sexual reproduction in two temporary-pond populations of D. pulex. Both populations showed a very early investment in sexual reproduction, independent of population density, by producing males very soon after the populations were reestablished from resting eggs in the early spring. Approximately 40% of the initial broods were male. Additional evidence for gender specialization was obtained by observing the sex of two or three successive broods for 85 individual females. Fifty-eight females produced successive broods of females, 13 females produced successive broods of males and 14 females produced successive broods which included both male and female broods. Females that produced successive female broods under natural conditions included a higher frequency of NMP females compared to a random sample of females, confirming the existence of NMP females. Sexual females were observed in both populations after the first appearence of males, suggesting that the presence of males may stimulate the production of sexual females. For D. pulex populations in a temporary environment, there appears to be an increased emphasis on sexual reproduction and a decreased influence of the environment on sex determination, compared to Daphnia populations in more permanent habitats. Received: 19 February 1996 / Accepted: 20 January 1997     

Age related changes in the calling behaviour and the attractiveness of obliquebanded leafroller virgin females, Choristoneura rosaceana, under different constant and fluctuating temperature conditions

C. rosaceana (Lepidoptera: Tortricidae) virgin females initiated calling in the first scotophase following emergence at both 15° and 20°C constant temperature under a 16L:8D photoperiod. As females aged, the onset of calling occurred much earlier, and the time spent calling increased significantly at both temperature conditions. For a given age, the onset of calling occurred significantly earlier at 15°C than at 20°C, but the duration of calling did not vary with temperature. Similar results were obtained under warm and cold thermocycles that simulated natural conditions prevailing during the summer and fall flight periods. A comparison of the degree of attractancy of different-aged females (0, 3, and 5 days old) in the field showed that the attractiveness of 0-day-old females relative to that of 3-day old females did not vary between flights. However, compared to day-5 females, the relative attractiveness of 0- and 3-day-old females was greater in the summer than in the fall flights. The potential adaptative value of these changes for seasonal mating success are discussed.     

Fitness comparison between clones differing in their ability to produce sexuals in the aphid Thopalosiphum padi

This study aimed at evaluating the intrinsic rate of increase (r _m ) of clones of the cereal aphid Rhopalosiphum padi (L.) that differ in their ability to produce sexuals. The value of r _m was measured for wingless parthenogenetic females in experiments conducted at two temperatures (15 °C and 20 °C). We studied six holocyclic clones, five androcyclic clones and five anholocyclic clones and showed that life-cycle has no significant effect on the age at first reproduction, on fecundity nor on longevity. As a result there is no influence on (summer) fitness: on the one hand, holocyclic clones do not compensate their lower fitness in mild winters by a higher fitness during the summer. On the other hand, anholocyclic and androcyclic clones do not seem to obtain any advantage from living on a more restricted range of hosts: there appears to be no cost of polyphenism for holocyclic clones.     

Base temperature and heat units for leaf flushing emission and growth ofHevea brasiliensis Muell. Arg.

In this study we determined the base temperature and Heat units for leaf flushing initiation and growth of RRIM-600 and GT1Hevea clones. The minimum base temperature was found to be approximately 16° C for leaf flushing emission and 19° C for shoot growth in terms of height. Approximately 420 degree days at 16° C as base temperature is required for successive leaf flushing initiation. Linear equations with correlation coefficients above 0.95 allow an estimation of the height increase from the accumulated degree days, corrected or otherwise for photoperiod. The highest correlation coefficients demonstrated a positive effect of the photoperiod among the factors influencing the shoot growth.     

The formation and degradation of cyanobacterium Aphanizomenon flos-aquae blooms: the importance of pH, water temperature, and day length

Investigation of annual changes in phytoplankton community structure in a small artificial eutrophic pond was carried out from May 2002 to April 2003. A heavy bloom of Aphanizomenon flos-aquae var. klebahnii Elenk. (Cyanobacteria) persisted in most of the water column from June to the end of October. In November, the A. flos-aquae bloom suddenly crashed and green algae were predominant until the end of spring. Weekly monitoring suggested strong involvement of the changes in abiotic factors in the cyanobacterial bloom degradation. To clarify the effects of pH, water temperature, and day length on the growth of A. flos-aquae, laboratory batch experiments were conducted. The results showed that A. flos-aquae could not grow below pH 7.1 and 11°C, and the growth tended to be suppressed under a 10L:14D photoperiod. pH, water temperature, and day length are vital factors in the growth of A. flos-aquae and, additionally, grazing by cyclopoid copepods also seemed important in bloom collapse.     

Life history variation among low-arctic clones of obligately parthenogenetic Daphnia pulex: a diploid-polyploid complex

Summary Laboratory life table experiments were conducted using nine clones of obligately parthenogenetic Daphnia pulex that were collected from a site in the Canadian low-arctic. Two of the nine clones were diploids, while the other seven clones were polyploids. Significant clonal differences in age at first reproduction, size at first reproduction, number of offspring in each of the first three broods, offsrring sizes for the first two broods, and intrinsic rates of natural increase were detected. Differences in life histories were evident between polyploids and diploids. Generally, polyploid clones reached maturity at later ages, matured at larger sizes, produced smaller broods, and larger offspring than the diploid clones. The data are discussed in reference to potential biotic (i.e. invertebrate predation) and abiotic factors (i.e. physicochemical gradients) that may influence life history variation in this clonal assemblage.     

Action of photoperiod at cold in diapausing Chrysopa carnea females (Chrysopidae,Neuroptera)

Summary To reveal the effect of photoperiod on insects under low temperatures, dormant females of Chrysopa carnea were exposed for 3 months (November–January) to cold (7°±2.5°C) and to long- or short-day conditions (18L:6D or 12L:12D). They were thereafter activated under short-day conditions at 25°C.The samples differed considerably in the incidence of ovipositing females, duration of pre- and post-oviposition period, and fecundity. All parameters evidenced a considerably higher reproductive activity of insects chilled under short-day conditions. It was thus confirmed that adults of C. carnea perceive photoperiod at cold. The action of short photoperiod at cold does not impair the subsequent oviposition; by contrast it promotes future reproduction, apparently also due to photoperiod changes. Although short-day photoperiod inhibits the activation at warm temperatures, it enables diapause development under cold temperatures.Dedicated to Prof. Dr. Hans Joachim Müller, Jena, on the occasion of his 65th birthday     

Effects of photoperiod and raised winter temperatures on egg development and timing of oviposition in the willow psyllid Cacopsylla moscovita

Nymphal development of Cacopsylla moscovita (And.) (Homoptera: Psylloidea) takes place only on female catkins of Salix repens L. and close phenological synchrony is crucial because development times of catkins and nymphs are similar. Eggs are laid on catkins as soon as they develop and close synchrony between oviposition and budburst maximizes time available for nymphal development. Sampling adult C. moscovita in the field revealed little synchrony between egg development and budburst, with over 60% of females containing mature eggs four weeks before catkins first appeared. In the laboratory, egg development was influenced by both temperature and photoperiod. At 10°C, egg development occurred approximately one month earlier than at 5°C and two weeks earlier than in the field. Adult survival in the laboratory was substantially reduced at increased temperature, with only 20% of adults surviving longer than two weeks at 10°C, compared with over 95% at 5°C. Body condition (weight corrected for size) of males and females decreased significantly in the field over winter. However, body condition of females levelled off before budburst, coincident with egg development implying that females had resumed feeding. We discuss our results in relation to regulation of phenological synchrony between oviposition and catkin appearance.     

Interactive effects of temperature and photoperiod on the daily activity and energy metabolism of pouched mice (Saccostomus campestris: Cricetidae) from southern Africa

The daily activity and energy metabolism of pouched mice (Saccostomus campestris) from two localities in southern Africa was examined following warm (25 °C) and cold (10 °C) acclimation under long (LD 14:10) and short (LD 10:14) photoperiol. There was no differential effect of photoperiod on the daily activity or metabolism of pouched mice from the two localities examined, which suggests that reported differences in photoresponsivity between these two populations were not the result of differences in daily organisation. Neverthe-less, there was a significant increase in metabolism at 10 °C, irrespective of photoperiod, even though seven cold-acclimated animals displayed bouts of spontaneous torpor and saved 16.4–36.2% of their daily energy expenditure. All but one of these bouts occurred under short photoperiod, which suggests that short photoperiod facilitated the expression of torpor and influenced the daily energy metabolism of these individuals. As expected for a noctureal species, the amount of time spent active increased following acclimation to short photoperiod at 25 °C. However, there was a reduction in mean activity levels under short photoperiod at 10 °C, possibly because the stimulation of activity by short photoperiod was masked by a reduction in activity during bouts of spontaneous torpor. Cold temperature clearly had an overriding effect on the daily activity and metabolism of this species by necessitating an increase in metabolic heat production and eliciting spontaneous torpor which overrode the effect of short photoperiod on activity at an ambient temperature of 10 °C.Abbreviations 3-ANOVA three-way analysis of variance - %ACT percentage of time spent active - ADMR average daily metabolic rate - M _b body mass - MR metabolic rate - MR_dark metabolic rate recorded during the dark phase - MR_light metabolic rate recorded during the light phase - NST non-shivering thermogenesis - RQ respiratory quotient - STPD standard temperature and pressure, dry - T _a ambient temperature - T _b body temperature - VO₂ oxygen consumption     

Adaptive significance of egg size plasticity in response to temperature in the migrant skipper, Parnara guttata guttata (Lepidoptera: Hesperiidae)

Females of the migrant skipper, Parnara guttata guttata, that are reared under lower temperatures lay smaller eggs. The adaptive significance of egg size plasticity in response to temperature is unknown in this species. We suggest, based on the following experimental results, that P. g. guttata uses temperature as an indirect cue to predict the host condition (leaf toughness) of the next generation. First, larvae were reared under the typical conditions of temperature and photoperiod experienced during the immature stages in the first, second, and overwintering (third) generations (LD 16:8 at 25°C, LD 14:10 at 25°C and LD 14:10 at 20°C). Females reared under LD14:10 at 20°C produced more, smaller eggs than those reared under LD14:10 and LD16:8 at 25°C. Secondly, survival rates of first instar larvae derived from females reared under the three photoperiod/temperature treatments were measured on young soft rice leaves (soft), or tough, old rice leaves (tough). Survival rates of hatchlings reared on soft and tough leaves did not differ when females were reared under LD16:8 and LD14:10 at 25°C. However, hatchling survival was significantly higher on soft than on tough leaves when females were reared under LD14:10 at 20°C. Thirdly, we found that egg size plasticity in response to temperature in P. g. guttata may be a threshold response. Temperatures below 20°C experienced during the immature stages may be effective for production of smaller and more eggs in the overwintering generation of P. g. guttata.     

Life history,resting egg formation,and hatching may explain the temporal-geographical distribution ofArtemia strains in the Mediterranean basin

Life history traits are presented for the sexual species (Artemia tunisiana) and for parthenogenetic diploid and tetraploid strainsA. parthenogenetica reared at 15 °, 24 ° and 29.5 °C.In laboratory cultures, we present evidence that the seasonal appearance of the sexualArtemia tunisiana (the dominant winter-spring population), and of two parthenogenetic populations ofArtemia (the dominant spring-summer populations) in certain Spanish saltworks is controlled by temperature through its effect on reproductive and survival traits. Minimum and maximum reproductive output and survival for the sexual and parthenogenetic populations, respectively, occurred at a typical temperature (24 °C) of the late-spring season when the sexual population is replaced by parthenogenetic forms. Furthermore, the high production and hatchability of cysts from the sexual population at low temperatures (15 °C), and of the parthenogenetic populations at middle temperature (24 °C), indicate the role of dormancy as an adaptation regulating seasonal occurrence.     

Diapause induction and termination in the predatory mite Euseius finlandicus in peach orchards in northern Greece

The course of diapause induction as well as of diapause termination infemales of the predatory mite Euseius (Amblyseius)finlandicus Oudemans (Acari: Phytoseiidae) in Northern Greece wasdetermined by transferring females during winter and early spring from peachtrees to a short day (LD 8:16) or a long day (LD 16:8) photoperiod both at 20°C. The first diapause females were found in mid September andby the first week of October all the females were in diapause. The mean numberof days required for diapause termination under the short day photoperiod LD8:16 was gradually reduced from 93.7 days in the beginning of October to lessthan 20 days in mid February and early March. Under the long day photoperiod ofLD 16:8 diapause was terminated in less than 20 days irrespective of the dateof collection. These results indicate that by mid February photoperiodicsensitivity of females was lost and diapause was terminated. However, femaleswere found in their overwintering sites until the second half of March,probablybecause of the prevailing relatively low temperatures and lack of adequatefood.     

Survivorship,growth and reproduction of the non-native <Emphasis Type="Italic">Caprella mutica</Emphasis> Schurin, 1935 (Crustacea: Amphipoda)

Caprella mutica Schurin is an epifaunal amphipod crustacean which originates in north-east Asia and has spread throughout the world, yet very little is known about fundamental aspects of this species biology. This paper examined the survivorship of C. mutica reared under laboratory conditions at 13–14 °C, 14 h light: 10 h dark photoperiod and fed commercial salmon feed, the diatom Cylindrotheca fusiformis Reumann and Lewin, the macroalgae, Fucus vesiculosus L. and given no additional feed. In addition, growth, maturation and reproduction of C. mutica fed C. fusiformis were assessed. No significant difference in survivorship of C. mutica was observed for the diet types over the experimental period. C. mutica was able to survive for upto 20 days without additional food. Average survival time of males and females fed the diatom, C. fusiformis was 68.8 d (range = 62–73 d) and 82.0 d (range = 76–92 d). Juvenile C. mutica emerged from the brood pouch at a body length of 1.33 mm and moulted at 5.0–11.0 day intervals. Males exhibited faster growth rates than females after Instar VII. Females produced their first brood at Instar VII, 24–26 days post-hatching and with an average body length of 8.5 mm. Each female had an average of two broods sequentially and these were released at 20.2 day intervals. Brood size for a single female increased from 11.3 (±9.9) hatchlings at Instar VII to 25.5 (±11.5) at Instar IX and the maximum number of hatchlings produced by a single female was 82. The results suggest that C. mutica exhibits a number of life-history traits that would potentially enable it to withstand global transportation and to rapidly become established in an introduced region, if environmental conditions are suitable.     

Maternal and direct effects of natural-like changes of photoperiod and food condition manipulation on life history parameters in <Emphasis Type="Italic">Daphnia</Emphasis>

This study analyzed changes of life history parameters of a Daphnia pulicaria clone in response to increasing (spring conditions) versus decreasing (fall conditions) photoperiod and low and high food concentrations in maternal and offspring environments. One treatment increased the photoperiod from 12 to 16 h at a rate of 3 min per day, while the other treatment decreased the photoperiod from 16 to 12 h at the same rate. We also used two food concentrations: low (0.2 mg C/l) and high (0.5 mg C/l). Maturation time, first clutch size, survivorship, and somatic growth in offspring depended on the direction of photoperiodic changes for Daphnia grown under high food concentration. Natural-like changes of photoperiod on life history parameters and abrupt changes resulted in similar effects on life history parameters of Daphnia (see Alekseev and Lampert 2004 Hydrobilogia 526:225–230).     

Life history of Euseius scutalis feeding on citrus red mite Panonychus citri at various temperatures

The aim of this study was todetermine the biology and reproductivepotential of Euseius scutalis(Athias-Henriot) (Acari: Phytoseiidae) atvarious temperatures. These data are of valuein relation to mass rearing and the developmentof population dynamics models. The developmenttime, survival and fecundity of E.scutalis were determined at 20, 25 and30 ± 1 °C, 65 ± 10% RH and 16:8photoperiod. Total development times of E.scutalis were 6.7, 4.9 and 4.2 days at 20, 25and 30 ± 1 °C, respectively, using adiet of all life stages of the spider mite Panonychus citri (McGregor) (Acari:Tetranychidae). In general, preoviposition andpostoviposition periods of E. scutaliswere shortened as temperature increased, butthe oviposition period was longer at 25 °C than at 20 and 30 °C. Theshortest survival time of E. scutalis, at30 °C, was 10.1 days, followed by 23.7days and 28.6 days at 20 and 25 °C,respectively. Mated females laid on average1.1, 1.4 and 1.7 eggs per female per day and21.5, 39.7 and 17.1 eggs over their entire lifetime at 20, 25 and 30 °C, respectively.The sex ratios of E. scutalis were2.11/1, 2.24/1 and 2.11/1 female/male at 20, 25and 30 °C, respectively. The intrinsicrate of natural increase (r _m) increasedwith rising temperatures from 0.166 at 20 °C to 0.295 females/female/day at 30 °C. The net reproductive rate (R ₀)was highest at 25 °C (26.03females/female) and lowest at 30 °C(12.95 females/female). Mean generation time(T ₀) was longest at 25 °C (17.50days) and shortest (9.53 days) at 30 °C.     

Effects of photoperiod and temperature on testicular development in male ayu,Plecoglossus altivelis

Synopsis Growth, gonadosomatic index and plasma steroid profiles in male ayu,Plecoglossus altivelis, cultured under short/long photoperiods and cool/warm temperatures were determined. Juvenile males were assigned to each of four different photoperiod/temperature regimes (16 L/18°C, 16 L/24°C, 8 L/18°C and 8 L/24°C) at random. Fish were killed and examined bi-weekly over the following 16 weeks. Mean body weight in the 16 L/18°C treated fish was the highest among four treated groups. No significant differences between body weights of the 16 L/24°C, 8 L/18°C and 8 L/24°C treated groups were observed. Ayu in the 8 L/18°C treated group had the highest values of gonadosomatic index, plasma testosterone (T) and 17-hydroxyprogesterone (17-OH P). No significant differences of plasma E₂ were observed among the treated groups. In the 8L/18°C and 8L/24°C groups, peak levels of 17-OH P occurred after 12 and 14 weeks of treatment, respectively. No peak levels of plasma T and 17-OH P were observed in 16 L/18°C or 16 L/24°C treated ayu. Spermiation occurred only in ayu with 8 L/18°C treatment. The data suggest that testicular development in ayu is temperature and photoperiod dependent: short photoperiod and cool temperature favour gonadal development.     

Seasonal variations in the immune system of the tench,Tinca tinca (Cyprinidae): proliferative response of lymphocytes induced by mitogens

The proliferation of tench lymphocytes induced by mitogens was studied during the four seasons of the year. Fish were maintained under natural conditions of photoperiod and temperature (mean ± SD: 12±2°C in winter, 22±3°C in spring, 30±3°C in summer and 21±3°C in autumn). Cultures were performed in vitro at 22°C in all seasons and the results were compared. Subsequently, in seasons with extreme water temperatures, cultures in vitro were performed at the same temperature as that of the water (12°C in winter and 30°C in summer) and the results were compared seasonally at the seasonal temperature, i.e. at 22°C in spring, 30°C in summer, 22°C in autumn and 12°C in winter. Phytohemagglutinin, concanavalin A, lipolisaccharide from E. coli and pokeweed mitogen were used as mitogens. Studies performed at 22°C as assay temperature in all seasons showed profound seasonal changes: while in spring, summer and autumn the mitogenic response of lymphocytes to phytohemagglutinin, concanavalin A, lipolisaccharide from E. coli and pokeweed mitogen was very low, during winter the results obtained were significantly higher. However, when the assays were performed at the corresponding seasonal temperature the differences were not as pronounced between the different seasons, and the mitogenic responses of lymphocytes were found to be the lowest during the winter and the highest during the summer with all mitogens used. This fact suggests that immunosuppression occurs in winter and an immunostimulation occurs in summer. However, the higher response found in winter when assaying at 22°C suggests that this property of lymphocytes needs an assay temperature higher than the in vivo temperature in order to observe accurate mitogenic responses.Abbreviations Con A concanavalin A - cpm counts per minute - LPS E. coli lipolisaccharide - MS222 tricainemethane sulphonate - PBS phosphate-buffered saline - PHA phytohemagglutinin - PWM pokeweed mitogen - SI stimulation index     

Location,reproduction and movement of Neoseiulus californicus (Acari: Phytoseiidae) during the autumn,winter and spring in orchards in the south of France

Field samples and experiments conducted in apple orchards in the south of France showed that Neoseiulus californicus (McGregor) searched for prey on the trees and in the ground cover as late as mid-November 1993, and at least as early in the spring as the end of February 1994. Overwintering females fed, expanded and produced viable eggs within 7.9±0.3 (SE) days given the natural light regime, adequate food and temperatures of 17.0±20.6°C. The first generation of N. californicus developed in the field during March and April 1994. N. californicus nymphs, females and males readily moved over bare ground and through a grass ground cover to trap plants located on stakes 1 m above the ground. In the laboratory, the rate of movement of adult females on 0.5 mm copper wire was a linear function of temperature above a threshold of 11.9±0.9°C. At 25°C they travelled 10 m per h. The migration rate of N. californicus to trap plants on stakes placed in an orchard 13 Apr. increased in 2 weeks from 0.07 to 0.57 predators/trap plant/degree-day, while the migration rate to plants placed directly in the ground cover was 1.45 predators/trap plant/degree-day. The largest population of N. californicus in April occurred on Barley, Hordeum murinum L. This plant produces pollen in April and May, and may be useful in biocontrol programs.     

Egg production in response to combined alternative foods by the predator Coccinella transversalis

The peformance of the parasitoid Anagyrus kamali Moursi [Hymenoptera: Encyrtidae], as a function of host density, temperature, and photoperiod was investigated with the objective to optimize a mass-rearing system in the context of a biological control program. The number of hosts parasitized at densities varying from 2–100 hibiscus mealybug (HMB), Maconellicoccus hirsutus Green [Homoptera: Pseudococcidae], corresponded to a type II-III functional response in fixed-time conditions and a type III in variable-time conditions. Twenty-six percent of the oviposited eggs led to progeny emergence with a sex ratio of 0.49±0.102 (M/F), regardless of host density. Fecundity and oviposition period under six abiotic combinations (i.e., two temperatures (26±2 °C and 32±2 °C) and three photoperiods (L0:D24, L12:D12, L24:D0)) were measured. Lifetime fecundity and reproductive life were significantly affected by temperature and photoperiod conditions. Optimum female parasitoid lifetime fecundity was attained at 26±2 °C, L0:D24 with an average of 116.1±17.43 eggs. At 32±2 °C, L24:D0 and L12:D12, an average of 79.4±34.57 and 85.8±35.81 eggs were laid, respectively. Reproductive longevity was maximal at 26±2 °C, L0:D24 with 12±4.85 days of oviposition. Because the parasite A. kamali can be reared optimally without light, this may save tremendous energy costs.