DEVELOPMENTAL MUTANTS OF VOLVOX: DOES MUTATION RECREATE THE PATTERNS OF PHYLOGENETIC DIVERSITY?

The nature of the variation which is created by mutation can show how the direction of evolution is constrained by internal biases arising from development and pre-existing design. We have attempted to quantify these biases by measuring eight life history characters in developmental mutants of Volvox carteri. Most of the mutants in our sample were inferior to the wild type, but deviated by less than tenfold from the wild-type mean. Characters differed in mutability, suggesting different levels of canalisation. Most correlations between life history characters among strains were positive, but there was a significant negative correlation between the size and the number of reproductive cells, suggesting an upper limit to the total quantity of germ produced by individuals. The most extreme phenotypes in our sample were very vigorous, showing that not all mutations of large effect are unconditionally deleterious. We investigated the effect of developmental constraints on the course of evolution by comparing the variance and covariance patterns among mutant strains with those among species in the family Volvocaceae. A close correspondence between patterns at these two levels would suggest that pre-existing design has a strong influence on evolution, while little or no correspondence shows the action of selection. The variance generated by mutation was equal to that generated by speciation in the family Volvocaceae, the genus Volvox, or the section Merillosphaera, depending on the character considered. We found that mutation changes the volume of somatic tissue independently of the quantity of germ tissue, so that the interspecific correlation between soma and germ can be attributed to selection. The negative correlation between size and number of germ cells among mutants of V. carteri is also seen among the larger members of the family (Volvox spp.), but not among the smaller members, suggesting a powerful design constraint that may be responsible for the absence of larger forms in the entire group.     

CHANGES IN CELL CHEMICAL COMPOSITION DURING THE LIFE CYCLE OF SCRIPPSIELLA TROCHOIDEA (DINOPHYCEAE)1

The cellular content of carbon, nitrogen, amino acids, polysaccharides, phosphorus and adenosine trtphosphate (ATP) was determined at several stages during the life cycle of the dinoflagellate Scrippsiella trochoidea (Stein) Loeblich. Carbon per cell decreased slightly between exponential and stationary phase growth in vegetative cells whereas nitrogen per cell did not change. Both of these cellular components increased markedly on encystment and then decreased to vegetative cell levels during dormancy and germination. C/N ratios increased gradually during cyst dormancy and activation, reflecting a more rapid decrease in N than in C pools, even though both decreased through time. Amino acid composition was relatively constant during the vegetative cell stages; glutamic acid was the dominant component. Arginine was notably higher in cysts than in vegetative cells but decreased significantly during germination, suggesting a role in nitrogen storage. The ratio of neutral ammo acids to total ammo acids (NAA/TAA) decreased as cysts were formed and then gradually increased during storage and germination. The ratio of basic ammo acids to total ammo acids (BAA/TAA) changed in the opposite direction of NAA/TAA, whereas the ratio of acidic acids to total amino adds (AAA/TAA) was generally invariant. Ammo acid pools were not static during the resting slate in the cysts: there was degradation or biosynthesis of certain, but not all, classes of these compounds. The monosacchande composition of cold and hot water extracted polysaccharides was quite different between cells and cysts. A high percentage of glucose in cysts suggests that the storage carbohydrate is probably in the form of glucan. Total cellular phosphorus was higher in all cyst stages than in vegetative cells. However, ATP-cell^?1 decreased as vegetative cells entered stationary phase and encysted, and continued to decrease in cysts during dark cold storage. ATP increased only as the cysts were activated at warm temperatures in the light and began to germinate. The above data demonstrate that dormancy and quiescence are not periods of inactive metabolism but instead are times when numerous biochemical transformations are occurring that permit prolonged survival in a resting state.     

LIFE HISTORY AND SYSTEMATIC POSITION OF PSEUDOCHORDA GRACILIS SP. NOV. (LAMINARIALES,PHAEOPHYCEAE)1

Pseudochorda gracilis sp. Nov. (Pseudochordacease, Laminariales) is described from the Japan Sea coast of Hokkaido/ the species is subtidal, epilithic and annual, appearing in spring and maturing in winter. Erect thalli grow solitary or in tufts on a small discoid holdfast. They are simple, cord-shaped and hollow, with inner hyphal filaments, cylindrical medullary cells and paraphyses consisting of 3–6 cells. Hair tufts are observed only in young thalli. Unilocular sporangia are sessile and narrowly ovate. In culture, P. gracilis shows a heteromorphic life history with oogamy, characteristic of the order Laminariales. Gametophytes are dioecious and dimorphic. Gametophytes mature under lower temperature conditions (usually below 10°C), and sporophytes mature under low temperature and short-day conditions (5°C, SD). The seasonal growth pattern of the species results from the photoperiod-temperature conditions controlling saprophyte maturation.     

Pomphorhynchus laevis (Müller) in the flounder, Platichthys flesus L., in the tidal River Thames: population structure, microhabitat utilization and reproductive status in the field and under conditions of controlled salinity

The infection of R. Thames flounders, Platichthys flesus L., at Fulham by the acanthocephalan parasite Pomphorhynchus laevix (Müller) is described in terms of parasite population structure, life-cycle organization, reproductive biology and host microhabitat utilization. The parasites demonstrated 100% prevalence in this tidal but essentially freshwater locality (intestinal intensity 34.47) and were overdispersed in the flounder population (variance/mean ratio = 10.39, k= 1.04). Overall about 11% of the worms occurred in peritoneal cavity sites, the remainder being firmly attached to the gut wall in the posterior region of the intestine and rectum. The P. laevis populations were reproductively active, demonstrating that the flounder acts as a significant final host in this locality. Viable larval stages were identified in Gammarus zaddachi Sexton, a predominantly estuarine amphipod, indicating that P. laevis is likely to be able to complete its life cycle at Fulham. Over half the female parasites examined were gravid and many of the non-gravid worms were inseminated but had not yet started egg production. The proportion of females gravid, the number of ovarian balls and the number of eggs in gravid females was seen to increase with worm size. Both the identity of the intermediate host and the reproductive status of P. laevis in the Thames flounders differ from the Pomphorhynchus/flounder system studied by Kennedy (1984) in the R. Avon, suggesting that the two P. laevis populations may belong at least to discrete subspecies or strains. Parasites in flounders maintained under laboratory conditions in fresh water, 50% sea water and 100% sea water showed similar population, microhabitat and reproductive characteristics to those observed in the field. This suggests that increased salinity has a negligible effect on established parasites in the short term, and therefore that salinity may not form a barrier to the survival and dispersal of the R. Thames parasite when the flounders return to sea.     

Mediterranean juvenile bluefin tuna: life history patterns

As there is a lack of information on the growth and migrations of bluefin tuna, information about them was gathered using the structural and chemical characteristics of their otoliths and mercury levels in body tissues as indicators of physiological and habitat characteristics. The otoliths of juvenile tuna caught in the Spanish Mediterranean littoral were studied. Otolith increments, assumed to be formed daily, were enumerated. Measurements by wavelength dispersive electron microprobe confirmed the presence of strontium in otolith tissue, and an inverse relationship between strontium/calcium (Sr/Ca) concentration ratio and temperature is suggested. Electron microprobe analyses combined with daily increment analyses of otoliths provided life history profiles for individual fish. Additional Sr/Ca concentration ratio data on fish supported the idea that Sr/Ca ratios can provide information on the environmental history of individual fish. Body concentrations of mercury were related to otolith analyses to suggest age structure, critical life history periods, growth environment, stock structure, food web position, and migration history. The techniques applied present an innovative approach to management-related problems, and the combination of chemical analyses with structural analyses promises to expand our knowledge of the life history of migratory fishes.     

ULTRASTRUCTURAL ASPECTS OF SEXUAL REPRODUCTION IN THE RED TIDE DINOFLAGELLATE GONYAULAX TAMARENSIS1

The marine dinoflagellate Gonyaulax tamarensis Lebour is best known for its propensity to form blooms known as red tides in coastal waters worldwide. This paper examines the sexual cycle of this organism using light and electron microscopy. Sexual reproduction begins with contact between thecate gametes which subsequently shed their thecae to fuse along their pellicular layers. Nuclear fusion occurs well after cytoplasmic fusion and is characterized by several distinctive features: a highly vesiculate nucleoplasm without microtubules; nucleoli and V-shaped chromosomes abut the nuclear envelope distal to the region of nuclear contact; and each chromosome possesses a longitudinal line, the central chromosomal axis. Fusion results in a planozygote with numerous cytoplasmic storage products and a slightly thickened layer beneath the pellicle. Subsequent loss of thecal plates and a thickening of the sub-pellicular layer results in a non-motile hypnozygote. A newly-formed hypnozygote possesses numerous minute papillae along its outer surface, formed by the up-folding of the accumulating wall layer. Maturation of the hypnozygote wall results in a smooth three-layered wall, the outermost layer of which is the pellicular layer. Hypnozygote germination produces a large quadriflagellate plan-omeiocyte with a single nucleus and thecal plates identical to vegetative cells. Two subsequent divisions, presumably meiotic, result in Jour cells morphologically identical to vegetative cells.     

The role of meiofauna in the marine ecosystem: evolutionary considerations*

The meiobenthos are regarded as the first metazoans to appear on earth This paper considers some aspects of their role in the marine ecosystem over evolutionary time. It is speculatively suggested that they have had a profound influence on many structural and functional attributes of the marine ecosystem as we see it today, both in the benthic and pelagic realms. Certain features such as size spectra, the life-history characteristics of the macrobenthos, and the energetic balance between ecological compartments of the marine ecosystem are considered to result from evolution away from negative interactions with the meiobenthos.     

The Early Silurian brachiopod Eocoelia from the Hudson Bay Basin, Canada

Eocoelia akimiskii sp. nov. from the Lower Silurian (upper Telychian) Attawapiskat Formation of Akimiski Island, James Bay, Nunavut, is the first and oldest Eocoelia to be described from the Hudson Bay Basin, one of three largest inland basins of North America. The new species lacks dental plates, dental cavities, and marginal deflection or lip, which indicates a post-Aeronian form of the well-known Eocoelia lineage. In rib numbers, Eocoelia akimiskii falls between E. curtisi and E. sulcata , being closer to E. sulcata . In rib strength, however, the new species is more closely allied to E. curtisi . Although Eocoelia is currently assigned to the Rhynchonellida because of its lack of spiralia, several features (particularly the lack of a septalium, the presence of a unique notothyrial platform and cardinal process, and dense, free-hanging fibrous growth frills) of the genus and other leptocoeliids are distinctly atypical of the rhynchonellides. The new species occurs in an inter-reef, shelly packstone facies within the Attawapiskat Formation, which is characterized by coral-stromatoporoid reefs with abundant, diverse, reef-dwelling brachiopods and other shelly organisms. The close association of Eocoelia akimiskii with the Attawapiskat reefs supports a shallow subtidal (BA2) setting generally assigned to the Eocoelia Community. The reefs themselves, however, host an extremely abundant brachiopod fauna dominated by Pentameroides , Trimerella , Septatrypa , and Gypidula . Four species of Clorinda are also common elements of the reef-dwelling brachiopods. This demonstrates that the concept of the classic Early Silurian level-bottom brachiopod communities cannot be directly applied to reef-dwelling brachiopod communities.     

Image and statistical analyses of early sorghum remains (8000 B.P.) from the Nabta Playa archaeological site in the Western Desert, southern Egypt

Carbonized grains of sorghum, with consistent radiocarbon dates of ca. 8000 B.P., have been excavated at an early Holocene archaeological site (E-75-6) in Nabta Playa near the Egyptian-Sudanese border. The objective of the investigations reported here was to classify these early sorghum grains within the known wild or domesticated races or working groups of sorghum through the use of image-analysis procedures. Image-analysis is a non-destructive analytical method that can provide rapid, repeatable, and accurate measurements of ancient cereal grains. Measurements were taken on samples representing the five major domesticated sorghum races, eight wild relatives, and samples from the Nabta Playa and Jebel et Tomat excavation sites. Statistical and clustering techniques indicated significant differences existed among the sorghums with respect to the various measurements made. Sorghum from Nabta Playa was significantly smaller, with respect to most measurements, than either the wild relatives or the five cultivated sorghums. Smaller grain size and the lack of any spikelets containing attached branchlets of the inflorescence or rachis fragments suggest that the material harvested and eaten at the Nabta Playa site were of a wild type.     

Evidence for plant exploitation and vegetation history from three Early Neolithic pre-pottery sites on the Euphrates (Syria)

Archaeobotanical results based on a limited number of samples from three aceramic sites dating from 9800 to 7800 B.P., which are under excavation in the valley of the Middle Euphrates, are discussed. The finds are presented simply by presence, and are compared to the contemporary vegetation and finds from similar sites. Carbonised plant remains recovered by flotation from levels dated to between 9800 and 9200 B.P. (Dja'de and Jerf al Ahmar) indicate that wild cereals (einkorn wheat, rye and barley) and pulses (lentils, pea and bitter vetch) were exploited. Other plants such as wild grasses, Pistacia, wild almond and oak, suggest that the local vegetation provided a rich diversity of resources. A study of possible weed taxa is being carried out in order to see whether this assemblage could be used to identify the cultivation of morphologically wild cereals for this period. Ninth millennium B.P. levels at Halula see the appearance of domestic crops such as emmer, naked wheat and barley, but wild-type cereals persist. The cultivars appear to have been introduced from elsewhere and later ninth millennium B.P. species include olive and flax. Ash, vine, maple, plane, alder and elm from the gallery forest, wild rye, wild einkorn, deciduous oak, wild almond, Pistacia, and Pyrus, from the hinterland, indicate cooler conditions.