REPRODUCTION AND LARVAL DEVELOPMENT OF LABEO UMBRATUS (PISCES,CYPRINIDAE) IN THE TYUME RIVER,EASTERN CAPE

SUMMARY

AN account is given of some aspects of the reproductive ecology and larval development of Lubeo umbrutus which is of great importance in the Eastern Cape due to its abundance in rivers and dams.

The sex ratio was found to be approximately 1:1 and females probably have a longer life span than males. Spawning takes place from October to January. Males become sexually mature at a length of 14 cm and females at a length of 20 cm. A spawning site is described. There is a curvilinear relationship between length and fecundity with the average fecundity increasing from 11 000 in fishes with a length of 20 cm to 48 000 in fishes with a length of 32 cm. Larval development from hatching to an age of 12 days is described.     

INFLUENCE OF FRESHWATER FLOW REGIME ON FISH ASSEMBLAGES IN THE GREAT FISH RIVER AND ESTUARY

Summary

Two and a half years of data were collected from the lower Great Fish River, head region and estuary to determine the fish species composition within these areas. Gilchristella aestuaria, Liza dumerilii, Rhabdosargus holubi and Pomadasys commersonnii were the four most abundant species captured, with riverine flow rate having an important effect on both species composition and numbers of fishes in the different regions. Most marine species displayed a strong inverse relationship between catch per unit effort and elevated freshwater inputs. Euryhaline marine species dominated the catches at all sampling sites during low flows but were less common during high flow periods when catadromous species were most abundant. Based on the available evidence it is suggested that for most marine species in the river this decline in abundance is related to low conductivity levels following floods rather than avoidance of elevated flows. The impact of elevated suspensoid concentrations and lowered dissolved oxygen concentrations on freshwater and estuarine fish populations during major river flooding is also discussed.     

LIFE IN THE FAST LANE: THE LIFE HISTORY OF HARBOR PORPOISES FROM THE GULF OF MAINE

We describe the life history of harbor porpoises in the Gulf of Maine by examining 239 animals killed in gill net fisheries and comparing these findings with the results of previous studies from the Bay of Fundy. Most female porpoises matured at age three and became pregnant each year thereafter. Reproduction was strictly seasonal, with ovulation, conception, and parturition occurring in the spring and early summer. The oldest specimen in the sample was 17 yr of age, but most individuals were younger than 12. The findings are similar to those of earlier studies from the Bay of Fundy and support the hypothesis that these animals form a single population. Harbor porpoises represent one end of a continuum of odontocete life histories that spans a wide diversity of strategies. In comparison with other, large odontocetes, harbor porpoises mature at an earlier age, reproduce more frequently, and live for shorter periods.     

SPATIAL AND TEMPORAL VARIATION IN SELECTION ON CORRELATED LIFE-HISTORY TRAITS AND PLANT SIZE IN CHAMAECRISTA FASCICULATA

Intraspecific studies of selection on multiple traits of a plant's life history provide insight as to how the composite life history of an organism evolves. Current understanding of selection on plant life-history traits is deficient in three important areas: 1) the effects of selection through correlated traits, 2) the effects of selection on a trait throughout the plant's lifetime, and 3) spatial and temporal variation in selection on plant life-history traits among populations and years. This study documents spatial and temporal variation in selection on three life-history and two morphological traits for two natural populations of Chamaecrista fasciculata, a native summer annual. Life-history and morphological traits (date of seedling emergence, size at establishment, size prior to reproduction, date of initial flowering, and date of initial fruit maturation) varied significantly between sites and/or years. Selection on traits varied either spatially, between sites and among transects within one site, or temporally, between years. In addition, life-history traits were phenotypically correlated among themselves and with morphological traits; correlations were generally constant over time and space. Indirect selection caused changes in means and variances in traits not under direct selection, but which were correlated with traits under selection. Selection on date of emergence varied in direction and magnitude among different life-cycle stages, while selection on other traits varied only in magnitude among life stages of the plant. This study documents the complexity of the selective process and the importance of considering multiple life stages and traits when studying the evolution of life-history traits.     

GEOGRAPHIC VARIATION IN THE LIFE HISTORY OF MASTOCARPUS PAPILLATUS (RHODOPHYTA)1

Variation in the geographic distribution of the life histories of Mastocarpus papillatus was investigated. Carpospores were isolated from 377 female gametophytes collected from eight localities on the Pacific coast of Baja California, Mexico, and California, U.S.A., and grown in laboratory culture. All carpospores from a single female gave rise either to basal discs with gametophyte-like uprights or crustose plants formerly referred to the genus Petrocelis. Early stages in the development of each type of germling were observed, and environmental factors affecting development were suggested. Based on carpospore germlings, females from each location were scored as having either the 1) sexual life history (crustose germlings) or 2) direct-development life history (discoid germlings with uprights). All females from the two southernmost locations in Baja California exhibited the sexual life history. In the three locations from the central-southern California coast, 70-95% of the females exhibited the sexual life history and the remainder exhibited the direct-development life history. In two of the three populations from the central-northern California coast, 70-90% of the females exhibited the direct-development life history and the remainder the sexual life history. In the third location from the central-northern California coast, the northernmost location sampled in the current study, 60% of the females exhibited the sexual life history and 40% the direct-development life history. The relative ecological advantages and disadvantages of the life histories are unknown as are the environmental factors that produced the ratios of sexual to direct-development females observed at each location.     

LIFE HISTORY AND HYBRIDIZATION STUDIES ON GIGARTINA STELLATA AND PETROCELIS CRUENTA (RHODOPHYTA) IN THE NORTH ATLANTIC1

Fourteen isolates of the crustose marine red alga Petrocelis cruenta J. Agardh from various localities in the British Isles, France (including the type locality), Spain and Portugal gave rise in culture to dioecious foliose plants identifiable as Gigartina stellata (Stackhouse) Batters although two isolates formed only sterile foliose blades. A total of 145 isolates of Gigartina stellata were also grown in culture from various localities in the U.S.A. (Maine), the British Isles, Iceland, Denmark, France, Spain and Portugal using both carpospores and vegetative blade apices. Two basic types of life history were found among these isolates: a direct-type life history involving the formation of further foliose plants from carpospores, some isolates of which also form spermatangia on the same papillae as the cystocarps; and a heteromorphic-type in which only crustose plants resembling Petrocelis cruenta are formed from carpospores. Only heteromorphic-type life histories were found from Spain and Portugal. Both life history types were found in plants from the U.S.A., the British Isles and northern France. Only direct-type life histories were found in plants from Iceland and Denmark. Some Petrocelis-like crusts derived from field collected G. stellata carpospores and Petrocelis crusts of hybrid progeny formed tetrasporangia in 8:16 h LD, 10° C but not in 8:16 h LD, 15° C; 16:8 h LD 10° C or 15° C; and 10:6.5:1: 6.5 h LDLD, 10° C. The spores thus formed were viable and produced normal dioecious male and female gametophytes. Short day and low temperature conditions appear necessary for tetrasporogenesis. The results from crossing experiments with 32 male and 27 female isolates of the heteromorphic-type derived from both G. stellata and P. cruenta showed that two virtually non-interbreeding populations with a high degree of geographical separation exist in the north-eastern Atlantic. Morphological differences between plants from each population are described. On the basis of culture and crossing results, Petrocelis cruenta J. Agardh is placed in synonymy with Gigartina stellata (Stackhouse in Withering) Batters.     

THE GENETICS AND COST OF CHEMICAL DEFENSE IN THE TWO-SPOT LADYBIRD (ADALIA BIPUNCTATA L.)

Ladybirds (Coccinellidae) defend themselves against attack by vertebrate predators by exuding a fluid from the femero-tibial joints. This fluid carries a noxious or toxic alkaloid. The amount of fluid produced during a single attack can be very high (up to 20% of fresh body weight), and the weight of the self-synthesized alkaloid can amount to several percent of the weight of the fluid. A study was carried out on these two defense characters and two other fitness characters (body weight and growth rate) to demonstrate a cost to defense in the form of genetic trade-offs between characters. The two sexes were analyzed separately, and a jackknife procedure was used to attach errors to the estimates of V_a and cov_a. All four characters were associated with high levels of V_a, but the cov_a values were mixed, some being negative and others positive. Principal-component analysis indicated the operation of factors constraining the cov_a values in males, and further possible reasons for the appearance of so many positive values are explored. A matrix analysis showed that the genetic variance/covariance matrices of the two sexes were significantly different from each other. Breeding values derived from sons plotted on breeding values from daughters had correlation coefficients significantly less than +1. This finding indicated that a substantial amount of sex-dependent gene expression was occurring.     

INDIVIDUAL VARIATION OF ONTOGENIES: A LONGITUDINAL STUDY OF GROWTH AND TIMING

This study of growth and developmental time in the water strider Limnoporus canaliculatus (Heteroptera: Gerridae) is based on longitudinal data from specimens reared individually in the laboratory. I analyzed multivariate allometry using a common principal components approach. This technique identified patterns of variation that were uncorrelated both within and among instars and which remained fairly constant throughout the growth period; in contrast, the overall amount of variation increased from young to older instars. Negative correlations between size and subsequent growth increments indicated convergent growth in the first three instars, but there was a transition to positive correlations (divergent growth) in later instars. Analysis of covariation among measurements made in different instars showed strong ontogenetic autocorrelation and revealed patterns remarkably similar to those found in mammals and birds; yet corresponding analyses of growth increments showed mainly independent variation in different instars. Therefore, I conclude that the strong correlations among stage-specific measurements result from the part-whole relationships inherent to these cumulative size data, but do not reflect specific properties of the organisms studied. In contrast to size increments, instar durations of water striders were highly correlated throughout the larval period, indicating that individuals tended to develop at either relatively fast or relatively slow rates in all instars. The correlations between growth increments and instar durations were nil or negative, contrary to expectations from life-history theory. The results of these analyses of individual variation match the findings from other water striders and from interspecific comparisons in the genus Limnoporus, but information about physiological mechanisms of molting and growth in insects cannot completely explain the patterns observed.     

LATITUDINAL TRENDS IN THE GROWTH AND REPRODUCTIVE SEASONALITY OF DELESSERIA SANGUINEA,MEMBRANOPTERA ALATA,AND PHYCODRYS RUBENS (RHODOPHYTA)1

The seasonality of Delesseria sanguinea, Membranoptera alata, and Phycodrys rubens (Rhodophyta) was studied at Helgoland (North Sea, Germany) and Roscoff (Brittany, France). Plants were collected at bimonthly intervals, and growth and reproduction were monitored. Growth of blades was observed mainly in spring, although small blades were found on plants of M. alata and P. rubens all year round. In summer, plants started to degenerate and in autumn they became fertile. The reproductive season of D. sanguinea lasted from October to February/April at both locations, whereas reproductive plants of M. alata and P. rubens were found until April at Helgoland and until June and August, respectively, in Roscoff_: Lower winter temperatures at Helgoland than at Rascoff may have caused these differences in the duration of the reproductive season. Using published data, the seasonal patterns at Helgoland and Roscoff were compared to those found at other locations (e.g. Barents Sea; Maine, USA; Isle of Man, UK) and local temperature/daylength conditions. Blade growth was synchronized across all populations and occurred in spring, when temperatures were usually still suboptimal for growth. Maximum reproduction was generally found in the colder half of the year but started earlier in autumn in the Barents Sea. Adaptive strategies in the seasonal control of growth and reproduction are discussed. Adequate timing of the history events (e.g. appearance of juveniles in spring) appears more important than maximal growth and reproduction of adults during the season with the most favorable temperatures.     

HETEROMORPHIC LIFE-HISTORY STRATEGIES IN THE BROWN ALGA SCYTOSIPHON LOMENTARIA (LYNGB.) LINK1

The adaptive significance of a life-history strategy, expressed as divergent morphological forms, was examined for the heteromorphic alga Scytosiphon lomentaria. Successional studies were performed by physically clearing mature, temporally-constant intertidal communities on San Clemente I., California. At week six, after clearing, complanate thalli dominated the successional plots (mean cover = 23.5%) and began to decline as the cylindrical form became abundant. The latter attained its peak cover (82.3%) at week 13, whereupon it too began a precipitous reduction. The crustose ralfsioid form appeared surprisingly early (4–13 wks) in trace amounts but did not achieve its greatest cover (85.0%) until week 43. The ranking from high to low primary productivity (cylindrical form = 8.1 mg C · g dry. wt^-1·h^-1, complanate form = 6.5 mg, crustose form = 0.5 mg) corresponded closely with the data for photosynthetic vs. structural components (cylindrical = 92.3% pigmented, complanate = 65.3%, crustose = 32.0%). This finding indicates that selection in the crust form, which is more readily accessible to epilithic grazers, has tended to increase allocation of materials to nonpigmented structural tissue at the expense of photosynthetic tissue and reduced production rates. The results for thallus losses to urchin grazing over 48 h were complanate form = 82.7% lost, cylindrical = 81.4% and crustose = 16.2%, which correlates with the calorific contents of the three forms (i.e. complanate = 4.97 kcal · ash-free g dry wt.^-1, cylindrical = 4.46 kcal and crustose = 3.55 kcal). The crustose form had tougher thalli (26 g · mm^-2 to penetrate thallus) than either the complanate form (12 g) or the cylindrical form (15 g). It is likely that opposing selective factors have resulted in the evolutionary divergences observed in algae with heteromorphic life histories. Previous work may have overemphasized the selective role of grazing because the crustose form is also adapted to withstand physical forces (sand-scouring, burial and wave-shearing) or as an overwintering stage under physiologically stressful conditions.     

A CIRCADIAN RHYTHM IN THE LONG-DAY PHOTOPERIODIC INDUCTION OF ERECT AXIS DEVELOPMENT IN THE MARINE RED ALGA NEMALION HELMINTHOIDES1,2

Two isolates of Nemalion helminthoides from the west coast of Ireland showed a heteromorphic life history in which tetraspores formed under short-day conditions on uniaxial, prostrate tetrasporophytes gave rise to uniaxial, prostrate growths similar in morphology to the tetrasporophytes. The induction of multiaxial, erect axes on tetraspore-derived plants was a long-day photoperiodic response. At 11°C, 16:8 h LD, nitrate concentration in the enriched seawater medium had little effect on the numbers of erect exes formed. Induction of erect axes occurred only in daylengths ≥ 12 h, mainly between 7–13° C, and the critical daylength, which generally lies between 14 and 16 h, changed with temperature. Night-breaks (NB) of 1 h light in the middle of 16 h night were ineffective in the promotion of erect axis formation, and day-breaks (DB) of 1 h darkness in the middle of a 16 h day did not inhibit axis formation. Neither continuous light nor NB of 1–1.5 h given at various times during the dark period of an 8:16 h LD cycle promoted the formation of erect axes. At 9° C, equivalent photon exposures (0.69 and 0.34 mol·m^?2) at two different instantaneous photon flux densities resulted in erect axis formation only in the 14 h, 16 h and DB regimes. Photoregimes of 16 h light in combination with dark cycles of various lengths resulted in the maximal promotion of the formation of erect axes in diurnal (22–24 h) and bi-diurnal (44–48 h) cycles, a diminishing response in non-diurnal cycles greater than 24 and 48 h, and a minimal response at 32 h. These data show that the formation of erect axes is a long-day photoperiodic response and provide further evidence for a connection between endogenous circadian rhythms and long-day photoperiodic responses.     

REPRODUCTION AND LIFE HISTORY OF THE RED ALGA GALAXAURA OBLONGATA (NEMALIALES,GALAXAURACEAE)1

Culture and morphological studies showed that Galaxaura oblongata (Ellis et Solander) Lamouroux has a triphasic life history with conspicuous gametophytes and small filamentous tetrasporophytes. Development of male and female reproductive structures is very similar and both begin with the enlargement of a terminal cell of a filament branch occupying a normal vegetative position within the apical pit of a thallus branch. In male thalli this modified branch forms a conceptacle in which spermatangia are produced. In female thalli, this modified branch forms a three-celled carpogonial branch consisting of a carpogonium, hypogynous cell and basal cell. Filament branches from the basal cell form a pericarp and the gonimoblast develops directly from the carpogonium. Carposporangia are produced in conceptacles which resemble the male conceptacles. About the time the first carposporangia are produced, the carpogonium, hypogynous cell and basal cell form a large fusion cell. Released carpospores germinate in a unipolar or bipolar manner and form small filamentous thalli. Under short day conditions, cruciate tetrasporangia are produced in small clusters. Tetraspores germinate similarly to carpospores and also form small filamentous thalli. Under low nutrient conditions, small cylindrical thalli develop on the filaments and these appear similar to gametophytes collected in nature.     

ECOLOGY AND NATURAL HISTORY OF IRIDAEA CORDATA (RHODOPHYTA; GIGARTINACEAE): POPULATION STRUCTURE1

The population structure of 4 California Iridaea cordata (Turner) Bory populations was studied. Random sampling procedures were used to measure seasonal variations in standing crops, density and size-class distribution of life history stages. The results describe aspects of the in situ life history; a prerequisite to realistically considering the distribution, ecology or life history expressions of an alga. Seasonal fluctuations in density occur only in the juvenile stage, which is initiated during the winter (November to January) predominantly from the basal perennial crusts. Both the gametangial and tetrasporangial stages are present throughout the year. The tetrasporangial stage is dominant in relation to the sexual stages in both density and biomass during most of the year, except spring when the new crop in just maturing and all stages are abundant. Density in nearly constant and observable changes in the populations are due to biomass fluctuations. Seasonal lows in biomass occur during the winter with the majority of thalli in the smaller size-classes. Growth and maturation culminate in peak summer crops and dominance of the tetrasporangial stage, followed by autumnal senescence and die-back in winter. Carrageenans analyzed from immature thalli showed a predominance of lambda-type, previously determined as specific for tetrasporangial plants. This indirect evidence for the tetrasporangial nature of immature plants suggests that dominance of the diploid stage occurred prior to blade development and most likely at the spore level. Alternatively, field results indicate a major contribution and possible replacement of alternation of gametangial and tetrasporangial stage by thallus perennation and vegetative reproduction.     

内蒙东部地区绵羊中华双腔吸虫生物学和流行病学的研究

中华双腔吸虫(Dicrocoelium chinensis Tang et Tang,1978)的生活史虽经研究,但本吸虫在第二中间宿主及终末宿主体内发育的情况尚未经阐明(唐崇惕等,1980).内蒙科右前旗附近数个旗县是本吸虫的流行区,1980—1981年我们在那里进行本项工作,从     

LOCAL ADAPTATION,PHENOTYPIC DIFFERENTIATION,AND HYBRID FITNESS IN DIVERGED NATURAL POPULATIONS OF ARABIDOPSIS LYRATA

Selection for local adaptation results in genetic differentiation in ecologically important traits. In a perennial, outcrossing model plant Arabidopsis lyrata, several differentiated phenotypic traits contribute to local adaptation, as demonstrated by fitness advantage of the local population at each site in reciprocal transplant experiments. Here we compared fitness components, hierarchical total fitness and differentiation in putatively ecologically important traits of plants from two diverged parental populations from different continents in the native climate conditions of the populations in Norway and in North Carolina (NC, U.S.A.). Survival and number of fruits per inflorescence indicated local advantage at both sites and aster life‐history models provided additional evidence for local adaptation also at the level of hierarchical total fitness. Populations were also differentiated in flowering start date and floral display. We also included reciprocal experimental F₁ and F₂ hybrids to examine the genetic basis of adaptation. Surprisingly, the F₂ hybrids showed heterosis at the study site in Norway, likely because of a combination of beneficial dominance effects from different traits. At the NC site, hybrid fitness was mostly intermediate relative to the parental populations. Local cytoplasmic origin was associated with higher fitness, indicating that cytoplasmic genomes also may contribute to the evolution of local adaptation.     

LIFE HISTORY AND IN SITU GROWTH RATES OF ALEXANDRIUM TAYLORI (DINOPHYCEAE, PYRROPHYTA)

Alexandrium taylori Balech is a phototrophic marine dinoflagellate. It produced recurrent blooms during the summer months (July and August) of 1994 to 1997 in La Fosca beach (NW Mediterranean). In addition to a motile vegetative form, A. taylori had two benthic forms: temporary cysts and resting cysts. Temporary cysts were a temporally quiescent stage produced from the ecdysis of the vegetative cell in both natural populations and laboratory cultures. Temporary cysts may divide to form motile cells. Resting cysts had a thicker wall than the temporary cysts and had a red accumulation body. Gametes and planozygotes were also observed in laboratory cultures. Alexandrium taylori showed in situ diurnal vertical migration with an increase of vegetative cells in the water column in the morning through midday, with concentrations peaking in the afternoon followed by lower levels at night. Most vegetative cells lost their thecae and flagella, and with them their motility, turning into temporary cysts that settled in the early evening. The number of temporary cysts in the water column rose in the evening and at night. The temporary cysts gave rise to motile cells the following morning. Synthesis of DNA occurred in vegetative cells at night, and a preferential period of cell division occurred at sunrise. The estimated division rate in the field was 0.4–0.5 vegetative cells·day⁻¹. Temporary cysts had twice the DNA of a G₁ vegetative cell. The minimum in situ division rate of the temporary cysts was 0.14 day⁻¹. The role of the resting and temporary cyst population in the annual recurrence and maintenance of the A. taylori bloom is discussed.     

补肾益气活血方对胎儿宫内生长迟缓胎盘组织一氧化氮合酶活性的影响

为了探讨补肾益气活血方对胎儿宫内生长迟缓（ＩＵＧＲ）胎盘组织一氧化氮（ＮＯ）生成的影响,本文对正常孕妇、ＩＵＧＲ患者及补肾益气活血中药治疗后患者各１２例,采用ＮＡＤＰＨ黄递酶法研究了一氧化氮合酶（ＮＯＳ）在胎盘组织的分布,应用化学发光法测定胎盘组织ＮＯＳ活性。结果表明：正常孕妇胎盘绒毛合体滋养层细胞ＮＯＳ呈强阳性反应,绒毛干血管壁呈阳性反应,终末绒毛毛细血管壁呈阴性反应;ＩＵＧＲ患者绒毛合体滋养层细胞和绒毛干血管壁ＮＯＳ染色明显变浅,而终末绒毛毛细血管壁呈阳性反应;中药治疗后合体滋养层细胞和绒毛干血管壁ＮＯＳ染色明显加深。ＮＯＳ活性测定中药组较ＩＵＧＲ未治疗组显著增高,与正常孕妇相比其差异无显著性。结果提示：ＮＯ参与ＩＵＧＲ的病理生理过程,补肾益气活血方通过增强ＮＯＳ活性促进胎盘组织ＮＯ的产生     

THE DEVELOPMENT AND REPRODUCTIVE MORPHOLOGY OF HALOSACCION AMERICANUM I. K. LEE (RHODOPHYTA,PALMARIALES)1

Halosaccion americanum, a member of Palmariaceae, was grown in culture from spores and the life history was critically examined by the use of scanning EM and light microscopy. A mature tetrasporangium of H. americanum produces four spores that germinate to form two male and two female gametophytes. The male gametophytes grow to maturity in approximately eight months and macroscopically resemble the tetrasporophyte. Following the first division of the tetraspore, the two-celled female gametophyte consists of a vegetative cell and a carpogonium with trichogynes. Fertilization is accomplished by spermatia from male plants of the preceding generation, as male plants of the same season are immature. Spermatia are formed in a continuous layer over the surface of the mature male gametophytes and, when released, are entrained in long strands of mucous. Spermatia adhere to and fuse with trichogynes and, nuclear fusions presumably follow. The carposporophyte is absent; the new tetrasporophyte develops directly from the fertilized carpogonium. Growth of the sporophyte eventually obliterates the female gametophyte, and development into a mature tetrasporophyte proceeds over a period of approximately eight months. The development of H. americanum, with its extremely abbreviated female gametophyte stage and direct development of the tetrasporophyte from the zygote, indicates that this rhodophyte has the same life history as reported for other members of the Palmariales.     

PHOTOSYNTHETIC RESPONSES TO LIGHT AND TEMPERATURE OF THE HETEROMORPHIC MARINE ALGA MASTOCARPUS PAPILLATUS (RHODOPHYTA)1

Physiological differentiation of the heteromorphic life-history phases of the red alga Mastocarpus papillatus (C. Agardh) Kützing was assessed. Photosynthetic responses to light and temperature of the erect, foliose gametophyte were compared to those of the crustose tetrasporophyte. Plants of both phases were collected from four locations on the Pacific coast of Baja California, Mexico, and California, USA, between 32–4l° N latitude. Within each location, the chlorophyll-specific, light-saturated photosynthetic rates of gametophytes were generally five times greater than those of tetrasporophytes. Initial slopes of photosynthesis: irradiance curves were greater for gametophytes than for tetrasporophytes. The crust and the blade from each location were similar with respect to dark respiration rates. For tetrasporophytes from all locations, the photosynthetic temperature optima were between 12–15° C. The photosynthetic temperature optima for gametophytes ranged from 15–17° C for plants from Trinidad Head (41° N) to 22–25° C for plants from Punta Descanso (32° N). Both gametophytes and tetrasporophytes from the northernmost location had significantly higher photosynthetic rates than the same phase from the other three locations. The photosynthetic responses to light support models for the life history in which life history phases have different ecological roles. The gametophyte, thought to be specialized for rapid growth and competition, may allocate more resources to photosynthetic machinery, hence the higher maximum photosynthetic rates. The tetrasporophyte, thought to be specialized for resistance to herbivores, may allocate more resources to structural or chemical defenses in preference to photosynthetic machinery. Consequently, the tetrasporophyte has lower photosynthetic capacity.     

AUXOSPORE FORMATION BY THE SILICA‐SINKING,OCEANIC DIATOM FRAGILARIOPSIS KERGUELENSIS (BACILLARIOPHYCEAE)1

Size restoration by the auxospore that develops from the zygote is a crucial stage in diatom life cycles. However, information on sexual events in pelagic diatom species is very limited. We report for the first time auxospore formation by the pennate diatom Fragilariopsis kerguelensis (O'Hara) Hustedt during an iron‐induced bloom in the Southern Ocean (EIFEX, European Iron Fertilization EXperiment). Auxospores of F. kerguelensis resembled those described for Pseudo‐nitzschia species. The auxospore was characterized by an outer coating, the perizonium; two caps, one at each distal end; and four chloroplasts, one at each end and two in the central part. Different stages of auxospore elongation were recorded, with a length of 24–91 μm, but only the largest auxospores contained the initial cell, whose apical axis ranged between 76 and 90 μm. Gametangial cell walls were often attached to the auxospores and ranged from 10 to 31 μm in length. Auxospore abundances were consistently higher in the fertilized patch, where an increase in the F. kerguelensis population was observed, as compared with surrounding waters.