Life history responses of the cladoceran Ceriodaphnia cf. dubia to variation in food concentration

The effect of five different food concentrations on the life history of Ceriodaphnia cf. dubia was examined by following cohorts of 25 individuals from <24 hours until the death of all individuals. The food concentrations used in the study were chosen to reflect densities found in lentic freshwater systems and those commonly used in toxicity testing, and ranged from 1 × 10⁴ cells mL^-1 to 15 × 10⁴ cells mL^-1. Food concentration was found to have a significant effect (p<0.05) on several life history parameters, with a decrease in food concentration leading to a decrease in brood sizes and population growth rate, and an increase in longevity. Population growth rates varied from approximately 0.39 neonates d^-1 to 0.54 neonates d^-1, while mean lifespan ranged from 16.7 days to 42.9 days. A decrease in food concentration also led to an increase in the mean generation time.     

Life history and production of Caenis luctuosa (Burmeister) (Ephemeroptera, Caenidae) in two nearby reaches along a small stream

Population dynamics and production of C. luctuosa were compared in two reaches of the Agüera stream (northern Spain). This species showed univoltine winter life history in both sites. However, the start of the recruitment period, and the cohort production interval differed in 1 month between reaches. Secondary production of C. luctuosa ranged from 76 mg m^–2 year^–1 (upper site) to 93 mg m^–2 year^–1 (lower site). Although annual production seemed to be mainly influenced by the biomass found at each site, changes in life history may have also been important. The need to have accurate information about life history of the analysed species at the study sites when assessing secondary production is highlighted.     

FLOW CYTOMETRY AND MICROSCOPY OF GAMETOGENESIS IN NITZSCHIA PUNGENS,A TOXIC,BLOOM-FORMING,MARINE DIATOM1

The domoic acid-producing diatom Nitzschia pungens Grunow f. multiseries Hasle, which is responsible for amnesic shellfish poisonings in Prince Edward Island, Canada, underwent gametogenesis when senescent cells (i.e. in stationary growth phase for more than 290 days) were subcultured into fresh FE medium and light intensity was increased from 33 to 530 μE · m^?2· s^?1. The number of gametes produced varied with the salinity of the medium, with a maximum at 23.5‰. Cells in the exponential growth phase (0.8 div · d^?1) did not produce gametes, nor did senescent cells when transferred without change in light intensity. Anisogamous gametes, probably haploid, were isolated by combining conventional microscopy with flow cytometry. Zygotes resulting from syngamy yielded cigar-shaped naviculoid cells, morphologically different from parent cells (heteromorphism). These cells, with a division rate of 1.9 div · d^?1, could serve as a seed population and explain the origin and rapid progression of the toxic blooms of red-water proportions that have been a public health problem in Eastern Canada. Production of domoic acid by postexponential and moribund cells but not by gametes, zygotes, or immediately resulting cells, provides an insight into the dependence of toxicity on the developmental history of this diatom.     

Sequential Involvement of NK Cells and CD8+ T Cells in Granuloma Formation of Rhodococcus aurantiacus-Infected Mice

We investigated the effect of in vivo administration of antibodies against T-cell subsets and natural killer (NK) cells on endogenous gamma interferon (IFN-γ) production and granuloma formation in Rhodococcus aurantiacus-infected mice. High titers of endogenous IFN-γ were detected in the extracts of the livers and spleens during 24 hr of the infection, reaching the peak at 8 hr, and the IFN-γ production was reduced by in vivo administration of anti-NK 1.1 monoclonal antibody (MAb) or antibody against asialo GM1⁺ cells. Endogenous IFN-γ declined until 2 days of the infection, then reappeared from 1 week and peaked at 3 weeks. Endogenous IFN-γ at 1 and 3 weeks was reduced by in vivo administration of anti-CD8 MAb, but not by anti-CD4 MAb or anti-NK 1.1 MAb. Granulomatous lesions in the livers and spleens began to appear from 1 week of the infection and developed in 3 weeks. In vivo administration of rat anti-IFN-γ MAb reduced the development of granulomas. In addition, granuloma formation was reduced by depletion of NK cells prior to the infection or depletion of CD8⁺ T cells at 1 week of the infection. Based on these findings, it is presumed that the biphasic production of IFN-γ is attributable to NK cells in the early phase of the infection and CD8⁺ T cells in the phase of granuloma formation, and that granuloma formation is regulated by NK cells and CD8⁺ T cells through the secretion of endogenous IFN-γ.     

THE LIFE HISTORY OF CALLITHAMNION BYSSOIDES IN CULTURE

The life history of Callithamnion byssoides Arnott ex Harv. in Hook. has been shown to comprise a regular sequence of gametophytic, carposporophytic, and tetrasporophytic phases in unialgal culture using supplemented seawater media. Tetraspore germlings gave rise to gametophytes bearing either antheridia or carpogonia in 13 days. Fertilization, carposporophyte development, and carpospore release took place within 5 days. Carpospore germlings produced mature tetrasporophytes in 13 days. The life history thus required approximately 1 month for completion. No deviations from this pattern were observed.     

Clonal erosion and genetic drift in cyclical parthenogens – the interplay between neutral and selective processes

The occurrence of alternating phases of clonal and sexual reproduction may strongly impact the interplay between neutral and selective genetic variation in populations. Using a physiologically structured model of the life history of Daphnia, we investigated to what extent clonal erosion associated with selection during the clonal phase affects the genetic structure as observed by neutral markers. Incorporating conservative levels of quantitative genetic variation at 11 physiological and life history traits induces strong clonal erosion, reducing clonal diversity (CD) near the end of the simulations (1000 days) to a level between 1 and 5, even in habitats with high initial CD (10⁸ clones). This strong clonal erosion caused by selection can result in reduced genetic diversity, significant excess of heterozygotes and significant genetic differentiation between populations as observed by neutral markers. Our results indicate that, especially in relatively small habitats, clonal selection may strongly impact the genetic structure and may contribute to the often observed high level of neutral genetic differentiation among natural populations of cyclical parthenogens.     

Life table demography and population growth of Brachionus variabilis Hempel, 1896 in relation to Chlorella vulgaris densities

We studied the life history variables and population growth characteristics of Brachionus variabilis, which was recorded for the first time from Mexico. The animals were fed Chlorella, using five concentrations (0.25, 0.5, 1, 2 and 4 × 10⁶ cells ml^–1) at 25 °C. Food density was observed to have significant effect on life expectancy, average lifespan, gross reproductive rate, net reproductive rate, generation time and population growth rate. The average lifespan ranged from 3 to 6 days depending on the food density. The net reproductive rate ranged from 2 to 7 neonates female^–1 d^–1. The rate of population increase per day varied from 0.14 to 0.35. The highest net reproductive rate and average lifespan and life expectancy were recorded at Chlorella concentrations of 1 × 10⁶ and 2 × 10⁶ cells ml^–1.     

INDUCED DIMORPHIC LIFE CYCLE OF A COCCOLITHOPHORID,CALYPTROSPHAERA SPHAEROIDEA (PRYMNESIOPHYCEAE,HAPTOPHYTA)1

The holococcolith Calyptrosphaera sphaeroidea Schiller was collected at Miyake‐jima Island, Japan and unialgal cultures established. Alternation of the holococcolith and heterococcolith phases was induced using new culture media (MNK, TR, and LO). Cells synchronized in the holococcolith phase were transferred into TR medium to induce a life cycle change. The heterococcolith phase, which has never been reported before, appeared after more than 40 days. The heterococcoliths were very small elliptical discs, about 0.5 μm wide and 1 μm long. Typical diploid‐type organic scales on the cell surface were observed. This phase was very stable in culture and was tolerant of unfavorable conditions. To reverse the life phase, cells in the heterococcolith phase were transferred into cold LO medium and exposed to low temperature (4°C) and low light (2 μmol photons·m^?2·s^?1) for 30 min before culturing at normal conditions (22.5°C and 20 μmol photons· m^?2·s^?1). The swimming behavior of the holococcolith cells seemed to be an indicator of the life cycle phase transition. This article reports for the first time a set of conditions that could control the transition of a coccolithophorid from one life phase to the other. Selected vitamins and trace metals induced the heterococcolith phase, whereas a slightly higher concentration of components in the basic medium along with concomitant stresses of light and temperature induced the holococcolith phase. Based on the results, we propose a hypothesis that the alternation of coccolithophorid life phases is regulated by changes between pelagic and coastal environments coupled with changes in seasonal conditions.     

The life history of Porphyra endiviifolium from the South Shetland Islands, Antarctica

This paper describes the reproduction and life history of an intertidal species, Porphyra endiviifolium, from Antarctica. Field specimens were examined microscopically, prepared for electron microscopy and used to establish cultures. Wild populations comprised two kinds of leafy thalli, morphologically similar but distinguished by their mode of reproduction, either sexual or asexual. Carpospores from monoecious leafy gametophytes developed into conchocelis filaments in culture, and under “winter-spring” conditions these formed conchospores that germinated to produce leafy thalli. Monospores from asexual leafy thalli developed directly into two different forms of leafy thalli. Only one of the cultured morphotypes became fertile, reproducing asexually by monospores. We conclude that the phases of the life history of P. endiviifolium show different ecological strategies, the conchocelis phase reproducing in response to short days unlike the leafy thalli in which growth and reproduction respond primarily to irradiance. Received: 2 May 1997 / Accepted: 11 October 1997     

Rapid growth and short life spans characterize pipefish populations in vulnerable seagrass beds

The life‐history traits of two species of pipefish (Syngnathidae) from seagrass meadows in New South Wales, Australia, were examined to understand whether they enhance resilience to habitat degradation. The spotted pipefish Stigmatopora argus and wide‐bodied pipefish Stigmatopora nigra exhibit some of the shortest life spans known for vertebrates (longevity up to 150 days) and rapid maturity (male S. argus 35 days after hatching (DAH) and male S. nigra at 16–19 DAH), key characteristics of opportunistic species. Growth rates of both species were extremely rapid (up to 2 mm day^?1), with seasonal and sex differences in growth rate. It is argued that short life spans and high growth rates may be advantageous for these species, which inhabit one of the most threatened marine ecosystems on earth.     

Discontinuous gas exchange patterns of beet armyworm pupae, Spodoptera exigua (Lepidoptera: Noctuidae): effects of Bacillus thuringiensis Cry1C toxin, pupal age and temperature

Abstract. Changes in the discontinuous gas exchange cycle of pupal beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), exposed or not to Cry1C Bacillus thuringiensis toxin, are examined against developmental age (1–7 days) and at different temperatures (10–25 °C) using flow through respirometry. Both exposed and nonexposed pupae exhibit discontinuous gas exchange, but only at 10 °C; the frequency of cyclic release of CO₂ increases with increasing temperatures. The three phases of the discontinuous gas exchange cycle are distinct for both treatment groups. However, the duration of each phase is significantly greater for pupae exposed previously to toxin. The closed phase is 40 ± 14% longer, the flutter phase 23 ± 19% longer, and the open phase is 28 ± 12% longer when pupae were exposed to toxin. Respiratory water loss is 4.5 ± 1.3% for toxin exposed pupae and 2.1 ± 2.4% for unexposed pupae. Furthermore, the exposed pupae have significantly greater cuticular permeability (26.01 ± 1.9 µg cm⁻² h⁻¹ mmHg⁻¹) than the nonexposed pupae (9.64 ± 0.9 µg cm⁻² h⁻¹ mmHg⁻¹). However, in both strains, cuticular transpiration (>93%) far exceeds respiratory transpiration. Overall, total water loss is significantly greater in pupae whose larvae are exposed to toxin compared with pupae from nontreated larvae. Toxin exposed pupae have a mean cycle duration of 60 ± 2.5 min whereas that of nonexposed pupae is 42 ± 1.8 min.(ml g⁻¹ h⁻¹) of the open phase is greater earlier in pupal life followed by a minimum at mid-pupal stage and an increase at late-pupal development in both treatment groups. Combining all 7 days, closed, flutter and open phase (ml g⁻¹ h⁻¹), pupae exposed to toxin produce significantly more CO₂ during each phase. On average, toxin exposed pupae produce 52 ± 12, 43 ± 10 and 15 ± 37% more CO₂ than the untreated pupae during the closed, flutter and open phases, respectively. Therefore, the present study reinforces the need to use insects of similar developmental age in studies of insect respiration patterns and energy metabolism.     

First report on the life history of the marine amphipod Ceradocus mizani and its implication for aquaculture

The search for alternative live feed for aquaculture stocks has inspired research into marine amphipods. In this study, the life history of Ceradocus mizani was evaluated to better understand how this amphipod might be used in aquaculture as an alternative feed. The amphipods did not display copulatory behavior during the study period. The females were multivoltine and attained sexual maturity on average in 23.6 days at a mean length of 4.64 mm. The incubation period lasted 8.8 days, and the mean number of juveniles produced per brood during that incubation period was relatively low (7.58). Females produced a mean of 5.2 consecutive broods and 39.4 total juveniles over the life span. (i.e., 0.33 juveniles/day). Sex ratio was female skewed (1.55:1). Female size and the number of juveniles produced per brood were positively correlated (R² = 0.63). The mean life span for females and males was 119.4 and 91.2 days, respectively. Mean maximum length was 9.26 mm for males and 8.18 mm for females. This is the first account of the life history of C. mizani and forms the basis for future studies of this marine amphipod.     

Heritability of resistance to oxidative stress in early life

Oxidative stress has recently been suggested to play an important role in life‐history evolution, but little is known about natural variation and heritability of this physiological trait. Here, we explore phenotypic variation in resistance to oxidative stress of cross‐fostered yellow‐legged gull (Larus cachinnans) chicks. Resistance to oxidative stress was not related to plasma antioxidants at hatching, which are mostly derived from maternal investment into eggs. Common environmental effects on phenotypic variation in resistance to oxidative stress were not significant. Heritability was relatively low and nonsignificant in hatchlings, but interestingly, the chicks of age 8 days showed high and significant heritability (h² = 0.59). Our results suggest that resistance to oxidative stress is determined mainly by the genotype as chicks grow. Further work is required to explore the genetic role of oxidative stress in life‐history evolution.     

Critical periods for developmental acclimation to cold in the Queensland fruit fly, Dacus tryoni

Rapid acclimation to cold can occur in Dacus tryoni during two short stages of its life history: the stage immediately prior to the “hopping larva” phase and the “pharate adult” stage within the puparium. Transfer from 25 to 15°C at either of these stages can produce full acclimation to cold within a few days. Acclimation is not detectable at other times in puparial life: during adult life it takes over 100 days.     

Biological studies upon Enchytraeus variatus Bouguenec & Giani 1987 in breeding cultures

The life history of an enchytraeid worm, Enchytraeus variatus, was studied under laboratory conditions at 18–22 °C. This species can reproduce simultaneously by asexual (architomy) or sexual reproduction. The number of ova per cocoon varies from 5 to 20 (x = 10.9). The generation period (from cocoon to next cocoon) varies from 14 to 39 days (x = 26.1) according to the period of the year. The number of generations per year is between 7.3 and 26.1 (x = 14). A mature worm can lay between 23.7 and 25.8 cocoons during its life (254 days as maximum observed) at a mean rate of 0.12 cocoon worm^–1 day^–1. Experimental cultures were carried out to determine the structure, density and biomass of the populations. A maximal density of 1 396 314 worms was recorded after 85 days of culture. Net production reached 21.48 g m^–2 day^–1 after 26 days in a culture initiated from cocoons.     

Environment-phenotype interactions: Influences of brackish-water rearing on lake trout (<Emphasis Type="Italic">Salvelinus namaycush</Emphasis>) physiology

Fertilization and development in salmonids occurs almost exclusively within freshwater environments (< 1 ppt). A less common life history strategy in this group of fishes is the brackish-water resident life history, where entire life cycles occur in brackish water (> 1 ppt). In the present study, we tested the hypothesis that differences in rearing environment (fresh or brackish water) results in significant differences in the ability of lake trout to ionoregulate when faced with a salinity challenge later in life. To test this, genetically similar lake trout were fertilized and raised at either 0 or 5 ppt saltwater. At approximately 240 days post hatch, lake trout from both rearing environments were acutely transferred to 20 ppt salt water or their respective rearing environments as a control. Individuals were sampled at time 0, 1, 7, and 14 days post transfer. Fish raised in 5 ppt transferred to 20 ppt saltwater had significantly higher gill Na⁺ K⁺-ATPase activity, gill Na⁺ K⁺-ATPase α1b expression, and lower plasma osmolality when compared to freshwater reared lake trout transferred to 20 ppt across various time points. Additionally, the 5 ppt control treatment had greater overall aerobic scope than 0 ppt control fish and those transferred from 0 ppt to 20 ppt. These data imply that populations exhibiting a brackish-water resident life history, as has been observed in Arctic Canada, may have an advantage over freshwater reared conspecifics when foraging in marine influenced environments and colonizing new locations in coastal regions.     

The mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis

1. Quantitative aspects of the mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis, including duration and frequency of mating, duration of various phases of the oviducal cycle, egg production rate and adult longevity were studied under laboratory conditions. One set of copepods was fed the alga Chlamydomonas reinhardtii whose density was adjusted to 2 × 10⁵ cells mL^?1 (about 10 mg C L^?1), another set was fed a mixed diet consisting of natural plankton (copepod nauplii, small rotifers and large algae) in the size range of 50–150 μm (dry mass approximately 90 mg L^?1). 2. The entire mating process, from the grasping of the female by the male’s right geniculate antennule to the separation of the pair, lasted about 2 min. Spermatophore placement started at about 30 s to 1 min after mating began and took approximately 1 min. Immediately after the spermatophore had been fixed in the female’s genital segment, the pair separated. 3. The total oviducal cycle, including the gravid phase where the female carried ripe oocytes and the non‐gravid phase where the female did not carry ripe oocytes, lasted about 5–6 days. The non‐gravid phase was particularly long; it was longer than the gravid phase and constituted 62–72% of the total cycle. 4. Mating and spermatophore placement usually occurred with gravid females although occasionally (in 30 of 200 observations) spermatophores were attached in the genital segment of non‐gravid females. Generally two to four, but up to seven, spermatophores were observed at a female’s genital segment at the same time. 5. Clutch size, rate of egg production and adult longevity depended on food. When fed on C. reinhardtii, females carried 7–8 eggs clutch^?1, produced a mean of 1.3 clutches and lived 14 days on average. When fed natural mixed food, females carried 10 eggs clutch^?1, produced 5.6 clutches and lived 37 days on average. 6. Removal of males after the first clutch resulted in no further egg production. Re‐mating is necessary in E. gracilis for continuous clutch production and the production of fertile eggs. 7. Mating duration is comparatively short and the non‐gravid phase comparatively long in E. gracilis. This could be an adaption to the life in the pelagic zone of the lake, where fish predators are present. Fish select ovigerous females, pairs in copula and, probably, females with ripe oocytes which make them conspicuous. Thus, a short mating duration and a prolonged period without conspicuous oocytes, can be advantageous.     

A bioenergetic study of a benthic nematode,plectus palustris de man 1880, throughout its life cycle

Summary Growth and reproduction of the parthenogenetic freshwater nematode,Plectus palustris, were studied at different controlled levels of food densities at 20° C. A bacteria-sloppy agar mixture was used as substrate and food medium. No growth or reproduction occurred at the lowest food density (8.10⁷ bacterial cells ml^-1). At 8.10⁸ cells ml^-1, the larval duration was 18.5 days, the instantaneous growth rate (g) of young larvae 0.2 d^-1 and the daily fecundity rate during a prolonged period of constant egg production 12.6 eggs·d^-1. At a food density of 8.10⁹ cells ml^-1, the corresponding values are 12.5 days, 0.4 d^-1 and 37.7 eggs d^-1.By including the data on respiration from a previous paper (Klekowski et al., 1979), the energetics of the species at different food densities can be discussed: production processes are apparently more dependent on food supply than respiration. However, prolongation of the larval phase in lower food densities greatly increases the cumulated respiratory costs per unit production. A second point is the ability to produce smaller-sized primiparous females in sub-optimal food which shortens the immature life period and serves to reduce the burden of cumulated metabolic costs for attaining sexual maturity.A comparison of the range of food densities used in the experiments with bacterial densities known from lake sediments of different trophic type suggests that food is likely to be the main factor governing the population dynamics of bacterivorous species under field situations.     

Life history and ecological role of the xylophagous aquatic beetle, Lara avara LeConte (Dryopoidea: Elmidae)

SUMMARY.

• 1 This study documents the life history of the xylophagous elmid beetle, Lara avara, and estimates its contribution to wood degradation in Oregon streams. The life cycle was found to be 4 to 6 or more years long, with all but 2–3 months of that spent in the larval stage.
• 2 Larvae grow through seven instars, taking about 1 year for instars 1–3, and from 3 to 5 or more years for instars 4–7.
• 3 Last-instar larvae leave the water to pupate. Adults live approximately 3 weeks and occur from May to August. The eggs are deposited on submerged wood.
• 4 Larvae probably obtain their nutrition by absorbing substances liberated into decaying wood by microbial activity. They do not produce their own cellulase, nor do they have a symbiotic gut flora similar to that of xylophagous cranefly (Tipulidae) larvae.
• 5 Faecal production by L. avara larvae averaged 13% dry body wt d^-1. This yields an estimate of faecal production of 1.6 g m^-2 y^-1 in Oregon Coast Range streams (about 0.3% y^-1 of wood standing crop).

     

Influence of <Emphasis Type="Italic">Lecanicillium attenuatum</Emphasis> on the development and reproduction of the cotton aphid, <Emphasis Type="Italic">Aphis gossypii</Emphasis>

The activity of entomopathogens on insect pests has been investigated for many species but the influence of entomopathogenic fungi on factors other than mortality relating to population increase has not been frequently studied. The influence of Lecanicillium attenuatum CS625 (=Verticillium lecanii CS625) on development and reproduction of cotton aphid (Aphis gossypii) was investigated. A conidia suspension of the isolate was applied onto first instar nymphs. Increased spore concentration did not significantly affect each nymphal stage, total nymphal period, pre-reproductive period and the age of first larviposition. A significant dose effect on reduction of life span, reproductive period and fecundity was observed in 1st and 3rd instars after spore application. When conidia were applied to 1st instars, life span was significantly reduced to 10.8 and 8.4 days at 1 × 10⁴ and 1 × 10⁸ conidia/ml, respectively from 12.2 days in the control. During the life span, total fecundity was 41 ± 7.3, 26 ± 0.8 and 22 ± 5.7 nymphs per female at 1 × 10⁴, 1 × 10⁶ and 1 × 10⁸ conidia/ml, respectively compared with 51 ± 2.0 nymphs per untreated female. Reproduction period was also significantly shortened with increasing spore concentration. Application of spores to 3rd instars showed a similar trend. However, daily fecundity of individual aphids was not affected by spore dose. It was concluded that the isolate of L. attenuatum is able to affect populations of cotton aphid by reducing life span and total fecundity as well as by killing the aphids directly.