The annual reproductive cycle of the freshwater mussel Dreissena polymorpha Pallas in lakes

Summary The annual development of the gonads of Dreissena polymorpha was studied at three sampling sites in two lakes over 3 and 1 1/2 years, respectively. A resting stage occurred after the last spawning in summer/autumn. Oogenesis (accompanied by multiplying segmentation of the oogonia and early growth processes of its oocytes) restarted in specimens at least 1 year old at low temperatures (below 10° C) during winter and early spring. At one location (Fühlinger See) the onset of the spawning season was correlated with an increase of water temperatures above 12° C. At 2 m depth, two main spawning periods in May and August were normally recognized, the first at temperatures of 12–16° C, the second at 16–21° C. It was clearly demonstrated for the first time in Dreissena polymorpha that the oocytes became mature in successive cohorts within one gonad. A female mussel may spawn several times during the reproductive season. At 9 m depth, the onset of spawning also started at about 12° C; this occurred in late summer, with two spawning periods within 1 month at a temperature range of 12–16° C. At another location (Heider Bergsee) the size of the gonads and the oocytes was reduced during April of both years studied, when food supply was low simultaneously with rapidly rising water temperatures in this shallow lake. There was no spawning period during spring. The major spawning period was delayed until July (temperatures 19–22°C). This shows (1) the synchronizing influence of low winter temperatures on the annual reproductive cycle and (2) a temperature threshold of at least 12° C for the start of the spawning processes. The results are discussed with regard to the geographical limits of further spread of Dreissena polymorpha.     

Relationships among pheromone titre,calling and age in the omnivorous leafroller moth (Platynota stultana)

Temperature modified the expression of female calling in Platynota stultana. Absolute temperature levels and not necessarily a decrease in temperature appear to modulate the timing of calling by delimiting a specific time interval for calling at each temperature. Calling began earlier in the photoperiod at lower temperatures than at higher temperatures. As females aged they initiated calling at an earlier time. Pheromone production (at 24°C) was rhythmical with maximal titre being reached near to the onset of the calling period at 14°C and about 5 hr prior to the onset of calling at 24°C. Females thus appear to be capable of emitting pheromone at an appropriate rate any time during calling intervals delimited by temperatures between 14 and 24°C. Pheromone titre appears to reflect a time-dependent readiness to respond to a decrease in temperature.     

Effect of male and female age on the mating success of the obliquebanded leafrollerChoristoneura rosaceana (Lepidoptera: Tortricidae) under different ecological conditions

The present study was undertaken to test the hypothesis that male and female age, as well as temperature, can affect the mating success ofChoristoneura rosaceana, given the role that these two factors play in the pheromone biology of this species. In the laboratory, the mating success of females generally declined linearly with age, whereas in males, it increased during the first 3 days and then decreased. The decline in female mating success was more pronounced under warm than cool thermocycles, while the changes observed in males were greater under fluctuating than constant temperature regimes. The onset time of mating was unaffected by male age, however, older females always mated earlier than younger ones, with the advance being more pronounced at cool than warm temperatures. Similar results were also obtained under field conditions. When a single 3-day-old male was provided with 0-, 3-, and 5-day-old females simultaneously, older females obtained mates significantly more often than younger individuals at all temperatures, indicating that calling earlier may afford a reproductive advantage to older females. At both constant temperatures, the time spent mating was longer in older than in younger females, but not under fluctuating thermocycles. Very young and very old males generally spent more time in copula than middle-aged individuals both at constant temperatures and under the warm thermocycle. Under the cool thermocycle, the duration of mating was considerably prolonged at all ages, which could increase the risk of predation.     

Flight initiation in the egg parasitoid Trichogramma minutum: Effects of ambient temperature, mates, food, and host eggs

Emergence, preening, and flight initiation were studied in laboratory-reared Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae). Male parasitoids emerged first and flew before females. When both sexes were present in flight cylinders, female parasitoids flew before males. Flight propensity in males was negatively related to the number of emerging females, while flight propensity in females was independent of the number of males present. Ambient temperature significantly affected the propensity and timing of flight; between 70–80% of the parasitoids flew at 25 and 30 °C while less than 4%, mostly males, flew at 20 °C. No flights were observed at 15 °C. The presence of fresh host eggs caused a reduction in the proportion of female parasitoids that flew and a delay in the time to flight for the females that did fly. The presence of food increased the flight propensity of female parasitoids, but did not affect the timing of flight. The relationship between flight behaviour and the efficiency of mass-reared Trichogramma is discussed in terms of its importance for inundative release programmes.     

Flight thresholds and seasonal variations in flight activity of the light-brown apple moth,Epiphyas postvittana (Walk.) (Tortricidae), in Victoria,Australia

Summary The flight activity of Epiphyas postvittana was studied at two sites near Melbourne with the aid of suction traps, over a period of 4 years. Maximum numbers were found to fly during the period September to March with peak activity coinciding with the emergence of winter, spring and summer generation moths. E. postivittana is predominantly a nocturnal flier with maximum activity around 20.00–24.00 h. The lower temperature threshold of flight was 8–11°C. The upper temperature threshold varied from 20–21°C, 24–25°C and 27–28°C for the winter, spring and summer generation moths respectively. Flight was highly influenced by the prevailing wind. The lower wind speed threshold was 0.5–0.8 m^-s and the upper wind speed threshold was 2.6–2.7 m^-s. The relationship between wind speed and the amount of flight was non-linear, with the frequency of flights decreasing sharply with increasing wind speed. No flights occurred at wind speeds greater than 2.8 m^-s. Variation in relative humidity had no influence on flight, but lack of rain favoured flight. The amount of flight activity and the amount of rainfall were negatively correlated; flights did not occur when the daily precipitation exceeded 32.5 mm, and with a precipitation exceeding 39 mm no flights could be expected. The value of these findings to pest control programmes is discussed.     

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     

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.     

Effects of temperature and light on calling in the tiger moth Holomelina lamae (Freeman) (Lepidoptera: Arctiidae)

ABSTRACT. In Holomelina lamae Freeman daily eclosion of adults is gated, with males emerging before females. By advancing the onset of photophase and by delaying the onset of scotophase, it was demonstrated that lights-on acts as the main phase-setting cue for calling. Few females call on the day they eclose. Calling is initiated c. 9 h after the onset of photophase in 2-day-old females, and shifts to earlier times in older females. The duration of calling also increases with age. That calling is controlled by an endogenous circadian clock is indicated by its persistence in continuous light (LL) and dark (DD). In LL calling is dampened rapidly, but a single scotophase re-entrains the rhythm. Decreases in temperature advance the onset of calling and the mean hour of calling, while increases in temperature delay both. However, the magnitudes of such phase-shifts depended upon hour of the photoperiod. Moreover, cooling and heating appears to exert both transient and long-term effects on the calling rhythm. An 8 h period at a reduced temperature in LL induces calling in females whose calling is dampened, and entrains the calling rhythm. Females maintained in DD from second instar larvae to the adult stage exhibit a circadian calling rhythm set by eclosion.     

Nocturnal behaviour of female Mythimna convecta

Nocturnal behaviour of Mythimna convecta (Walker) (Lepidoptera: Noctuidae) virgin females was studied in the laboratory under 20 °C and 16:8 LD conditions. The periodicity of activity, feeding, calling, pre-oviposition extrusion and oviposition varied with female age and hour of the scotophase. Females called for the first time between the 2nd and 11th scotophases with the peak in the 4th scotophase. Maximum calling occurred on the 7th hour of the scotophase. Young moths called more frequently with shorter bouts while old moths called less often but with longer bouts. In the presence of older females, moths spent significantly more time in pre-oviposition extrusion and resting and less in activity and feeding than they did when only females of the same age or younger were present. There were no significant differences for calling suggesting that pheromones of older calling females did not affect calling of younger females.     

The effects of photoperiod and temperature on calling behaviour and egg development of the bertha armyworm,Mamestra configurata (Lepidoptera: Noctuidae)

The effects of photoperiod and temperature on calling behaviour and the effects of temperature on the relationship between egg development and calling of virgin females of Mamestra configurata Walker were examined at 3 photoperiodic regimes and seven constant temperatures. Photoperiod affected the diel periodicity of calling and length of the daily calling period. The mean onset calling times were similar if the preceding scotophase(s) was 6–10 h long, but the onset of calling was delayed by 1–5 h if the preceding scotophase(s) was 12–18 h long. Long-term, constant temperature (from emergence until death) affected 4 aspects of calling: age at first calling, diel periodicity, length of the daily calling period, and percentage of females calling. Short-term temperature changes (during a single scotophase) affected calling in 3 ways: diel periodicity, length of the daily calling period, and percentage of females calling. The optimal temperature range for calling was, at least, 10–25°C; the upper limit and threshold were near 35 and < 5°C. The time of first calling was synchronized closely with the appearance of the first chorionated eggs in the ovaries at 10–35°C. Egg development and calling were adversely affected at 30 and 35°C. The physiological and ecological significance of the data are discussed.     

Influences of daylength and temperature on the period of diapause and its ending process in dormant larvae of burnet moths (Lepidoptera,Zygaenidae)

The onset of larval diapause in the burnet moth Zygaena trifolii is clearly characterized by the larva molting into a specialized dormant morph. In a potentially bivoltine Mediterranean population (Marseille) two types of diapause can occur within 1 year: firstly, a facultative summer diapause of 3–10 weeks, and secondly, an obligate winter diapause, which can be lengthened by a period of thermal quiescence to several months in temperatures of 5°C. For the first time, three successive physiological periods have been experimentally distinguished within an insect dormancy (between onset of diapause and molting to the next non-diapause stage), using chilling periods of 30–180 days at 5°C, and varying conditions of photoperiod and temperature. These stages are: (1) a continuous Diapause-ending process (DEP); (2) thermal quiescence (Q); and finally, (3) a period of postdiapause development (PDD) before molting to the next larval instar. The result of transferring dormant larvae from chilling at 5°C to 20°C depended on the length of the chilling period. After chilling for 120–180 days, molting to the next instar occurred after 6–10 days, independent of daylength. This period corresponds with the duration of PDD. After shorter chilling periods (90, 60, 30 days and the control, 0 days) the period to eclosion increased exponentially, and included both the latter part of the previous diapause process and the 6–10 day period of PDD. However, photoperiod also influences the time to eclosion after chilling. Short daylength (8 h light / 16 h dark: LD 8/16) lengthened the diapause in comparison to long daylength (16 h light / 8 h dark: LD 16/8). Short daylength had a similar effect during chilling at 5°C, as measured by the longer time to eclosion after transfer. The shorter time to eclosion resulting from longer chilling periods (30–90 days) demonstrates that the state of diapause is continuously shortened at 5°C, and corresponds to the neuroendocrine controlled DEP. Presumably the DEP has already started after the onset of diapause. When chilling was continued after the end of the DEP, which ranged between 90 and 120 days, thermal quiescence (Q) followed (observed maximum 395 days). Different photoperiodic conditions during the pre-diapause inductive period modified diapause intensity (measured as the duration of diapause), in that a photoperiodic signal just below the critical photoperiod for diapause induction (LD 15/9) intensified diapause. Experiments simulating the summer diapause showed that PDD occurred in the range of 10–25°C. Higher temperatures (15 and 20°C) shortened the DEP at LD 16/8, so that at 20°C many individuals had already terminated diapause after 10–40 days and had molted after the 6–10 days of PDD. A temperature of 25°C unexpectedly lengthened the DEP to 110 days in several individuals. The ecological consequences and the adaptive significance of variation in the duration of the diapause are discussed in relation to the persistence of local populations predictably variable and rare climatic extremes throughout the year.     

Diel periodicity and influence of age and mating on female sex pheromone titre in Estigmene acrea (Lep., Arctiidae)

Abstract:  Calling behaviour, diel periodicity, and effect of age and mating on female sex pheromone titre in Estigmene acrea (Drury) were studied under laboratory conditions. Forty-five per cent of females started calling during the first scotophase, but the highest number of calling females was observed during the second, third and fourth scotophases. Calling behaviour occurred from the third hour after dark until just before the end of the scotophase. However, females exhibited a bimodal pattern of calling with the first peak occurring between 4 and 6 h and a second peak at 10 h after the onset of scotophase. The mean onset of calling time differed significantly with age. Older females showed a tendency to call longer, but there was no significant difference. The amount of (Z,Z)-3,6-cis-9, 10-epoxyheneicosadiene in females was quantified from the first scotophase following emergence, until the fifth scotophase. Glands of 0-day-old females presented a higher content of pheromone compared with that found in glands of 1-, 2-, 3- and 4-day-old females. Pheromone titre was determined at 2-h intervals throughout the third scotophase and photophase. (Z,Z)-3,6-cis-9,10-epoxyheneicosadiene was found in the gland during the scotophase as well as the photophase. However, there was no consistent pattern of pheromone production throughout the scotophase or photophase. Mated females of E. acrea produced significantly less pheromone than virgin females.     

The combined effect of photoperiod and temperature on the calling behaviour of the true army worm, Pseudaletia unipuncta

ABSTRACT. Pseudaletia unipuncta (Haw.) (Lepidoptera: Noctuidae) virgin females, maintained at either 10 or 25d?C under LD 12:12 or 16:8 h, started calling at different ages. For a given photoperiod, calling was initiated 11 days later at 10d?C than at 25d?C, while for a given temperature, calling at LD 12:12 h was 3–4 days later than at LD 16:8 h. At 10d?C 50.8% of females did not call within 35 days at LD 12:12 h compared with 30.8% at LD 16:8 h. Calling started earlier in the scotophase at 10d?C than at 25d?C and at LD 16:8 h than at LD 12:12 h. Under all treatments calling generally advanced on successive nights. The time elapsed between the mean onset time of calling and the mid-scotophase was relatively constant under both photoperiod conditions at 25d?C, but at 10d?C was more variable. The mean time spent calling increased significantly with calling age but did not differ significantly between the four experimental conditions tested. Older (15 days) females transferred from 10d?C, LD 16:8 h to 25d?C at either LD 163 or 12:12 h, required less time to initiate calling than younger (5 days) ones. Those transferred from 10d?C, LD 12:12 h took the same time, regardless of their age at the time of the transfer. Females experiencing either a decrease or increase in daylength as well as a temperature increase, required respectively more or less time to initiate calling, compared with individuals that only experienced an increase in temperature. If temperature was the only parameter changed females that initiated calling soon after the transfer immediately adjusted their calling periodicity to prevailing conditions. When both temperature and photoperiod were altered, it took several days before calling periodicity adjusted to the new regime. The ecological implications of temperature and photoperiodic conditions on the possible autumn migration of P. unipuncta are discussed.     

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.     

Seasonality ofOrmia depletaand Limits to Its Spread

Ormia depleta(Wiedemann) (Diptera: Tachinidae), a South American fly that homes on the calling songs of its hosts, was brought from Piracicaba, Brazil; colonized; and released in Florida for the biological control ofScapteriscusspp. mole crickets. It became established at some release sites and rapidly spread through most of peninsular Florida. The seasonal distributions of phonotactic females in Florida differed from the single summer peak recorded at Rio Claro and Piracicaba, Brazil (23° S). Near Bradenton (27° N), spring and fall peaks with a summer hiatus were quickly established and remain evident. At two sites near Gainesville (30° N), a strong fall peak and a modest-to-none spring peak developed. Peaks of phonotactic females seem to follow times of peak host availability and sometimes coincide with minima of host availability. Limits to geographical expansion ofO. depletaare poorly understood. At Gainesville, the site of earliest introduction, establishment was rapid and soundtrap catches increased for the first 3 years, exceeding 1000 per year at one site. Catches then declined for 3 years, almost reaching zero in 1994. On the other hand, annual sound-trap catches ofO. depletaat Bradenton exceeded 1000 in <2 years and have remained above that level for 5 years. Winters in Gainesville are more severe than those in Bradenton, but minimum winter temperatures in Gainesville were substantially lower duringO. depleta's increase than during its decline. Perhaps mild winters cause the flies to become active early—only to starve for lack of adequate winter nectar sources.O. depletamay yet spread to the northern limits of itsScapteriscushosts as present populations adapt to new environments. Or farther spread may require that new strains be introduced from more southerly sites in South America.     

Reproductive bionomics of the soft tick, Ornithodoros turicata (Acari: Argasidae)

The effects of different temperatures and relative humidities (RHs) were tested on various reproductive parameters of Ornithodoros turicata, an argasid tick that inhabits gopher tortoise burrows in Florida, USA. The pre-oviposition, oviposition and incubation periods of the ticks decreased as temperature increased. These periods were also affected by the RH. The number of eggs oviposited was affected significantly by the combined effect of temperature and RH. Fewer eggs were laid by ticks in the 24°C regimes and the 27°C/95%RH regime compared to those in the other temperature/RH groups. There was an inverse relationship between the number of eggs oviposited and the percentage of hatched larvae that was correlated with the temperature and RH. Ticks reared at 27°C/90%RH and 30°C/90%RH laid more eggs than those reared in the other combinations of temperature and humidity but fewer larvae hatched from these eggs. The reproductive fitness index (RFI) values were highest in females held in the 24°C groups and the 30°C/95%RH group, although significantly more larvae hatched at the lower temperatures. The optimum reproductive conditions for O. turicata under laboratory conditions appear to be 24°C and 90–95%RH. While mating occurred at all temperatures, none of the females laid eggs at 22°C. The ticks may move preferentially to low temperatures when not feeding to remain above the critical equilibrium humidity and/or below the critical metabolic level necessary for prolonged survival. However, most female ticks oviposited after 45 days when moved to 27°C/95%RH. Ornithodoros turicata females may have a limited capability to delay oviposition until an optimal microenvironment for egg deposition can be located in the burrow.     

Calling behavior of the female german cockroach,Blattella germanica (Dictyoptera: Blattellidae)

Virgin German cockroach females, Blattella germanica(L.), were observed, for the first time, to exhibit a characteristic calling behavior during which females emit a volatile sex pheromone. Under a photoperiod of 12L12D, the percentage of 7-day-old virgin females that exhibited this behavior peaked before the end of the scotophase in a similar pattern to the diel periodicity of mating. A clear relationship was evident between calling and stages of sexual receptivity during successive gonotrophic cycles. Females initiated calling 5–6 days after the imaginal molt, when their basal oocytes were 1.6 mm long. If not mated, females continued to exhibit bouts of calling during the next 3–4 days until 24 h before ovulation. Calling was completely suppressed by mating as well as the presence of an egg case in the genital atrium in both virgin and mated gravid females. We suggest that calling and the emission of a volatile sex pheromone serve to attract males from a distance as well as to potentiate responses to contact sex pheromone in aggregations.     

Environmental Determinants of Birth Seasonality in Night Monkeys (Aotus azarai) of the Argentinean Chaco

The night monkeys (Aotus azarai) of Formosa, Argentina provide an opportunity to investigate the influences of ambient temperature and photoperiod on reproduction in a highly seasonal environment: the Chaco. Between 1997 and 2000, we collected data to evaluate the relationship between rainfall, ambient temperature, photoperiod and food availability and the annual distribution of mating behavior and births in 15 groups of monkeys in the forests of the Eastern Argentinean Chaco. Our data show that the area is highly seasonal, characterized by significant fluctuations in rainfall, temperature, photoperiod and food availability. There are two rain peaks in April and November and a dry season lasting from June to August. Monthly mean temperatures were on average 11°C lower during winter months than they were during summer months. Temperatures <10°C and >33°C were also frequent through the year. Days are 3 h longer during the summer than during the winter months. Insect abundance and the percentage of tree species producing fruits, flowers or new leaves reached a low in the coldest winter months. Mating was infrequent, and we only observed it between May and September. Half the births (n = 13) occurred during a 2-week period in October. Infant survival during the first 6 mo of life was high (96%). Our findings suggest an environmental control of reproduction. Changes in photoperiod and temperature may promote reproductive activity in females that might conceive and begin pregnancy at a time void of high temperatures that could be metabolically challenging.     

A temperature effect on nondisjunction of the X chromosomes among eggs from agedDrosophila females

The effects of temperature and aging on the frequency of nondisjunction inDrosophila melanogaster eggs were investigated. At 25°C offspring arising from 3–5 day old control females had a nondisjunction frequency (0.943/1000 offspring) very similar to that for females who were 24–26 or 27 days old when eggs were collected (1.044/1000 offspring). When females were aged for the same length of time at 10°C the frequency of nondisjunctional exceptions increased to 3.368 per 1000 offspring. These results indicate that aging the females at 25°C does not increase the nondisjunction rate over that obtained from non-aged females raised at 25°. The increase in nondisjunction frequencies when the females were aged at 10°C reflects an influence of temperature on the meiotic process inDrosophila melanogaster. At the low temperature eggs were also aged since few or no eggs were laid during the aging process. Thus in addition to a temperature effect on nondisjunction rates at 10°C there may also be an age effect.     

Temperature,light, and photoperiod responses of some Northeast American and West European endemic rhodophytes in relation to their geographic distribution

The relationship between distributional boundaries and temperature responses of some Northeast American and West European endemic and amphiatlantic rhodophytes was experimentally determined under varying regimes of temperature, light, and daylength. Potentially critical temperatures, derived from open ocean surface summer and winter isotherms, were inferred from distributional data for each of these algae. On the basis of the distributional data the algae fall within the limits of three phytogeographic groups: (1) the Northeast American tropical-to-temperate group; (2) the warm-temperate Mediterranean Atlantic group; and (3) the amphiatlantic tropical-to-warm temperate group. Experimental evidence suggests that the species belonging to the northeast American tropical-to-temperate group(Grinnellia americana, Lomentaria baileyana, andAgardhiella subulata) have their northern boundaries determined by a minimum summer temperature high enough for sufficient growth and/or reproduction. The possible restriction of 2 species (G. americana andL. baileyana) to the tropical margins may be caused by summer lethal temperatures (between 30 and 35 °C) or because the gradual disintegration of the upright thalli at high temperatures (>30 °C) promotes an ephemeral existence of these algae towards their southern boundaries. Each of the species have a rapid growth and reproductive potential between 15–30 °C with a broad optimum between 20–30 °C. The lower limit of survival of each species was at least 0 °C (tested in short days only). Growth and reproduction data imply that the restrictive distribution of these algae to the Americas may be due to the fact that for adequate growth and/or reproduction water temperatures must exceed 20 °C. At temperatures 15 °C reproduction and growth are limited, and the amphiatlantic distribution through Iceland would not be permitted. On the basis of experimental evidence, the species belonging to the warm-temperate Mediterranean Atlantic group(Halurus equisetifolius), Callophyllis laciniata, andHypoglossum woodwardii), have their northern boundaries determined by winter lethal temperatures. Growth ofH. equisetifolius proceeded from 10–25 °C, that ofC. laciniata andH. woodwardii from 5–25 °C, in each case with a narrow range for optimal growth at ca. 15 °C. Tetrasporelings ofH. woodwardii showed limited survival at 0 °C for up to 4 d. For all members of the group tetrasporangia occurred from 10–20 °C. The southern boundary ofH. equisetifolius andC. laciniata is a summer lethal temperature whereas that ofH. woodwardii possibly is a winter growth and reproduction limit. Since each member of this group has a rather narrow growth and survival potential at temperatures <5 °C and >20 °C, their occurrence in northeast America is unlikely. The (irregular) distribution ofSolieria tenera (amphiatlantic tropical-to-warm temperate) cannot be entirely explained by the experimental data (possibly as a result of taxonomic uncertainties).Paper presented at the Seaweed Biogeography Workshop of the International Working Group on Seaweed Biogeography, held from 3–7 April, 1984 at the Department of Marine Biology, University of Groningen (The Netherlands). Convenor: C. van den Hoek.