Resource-defense Polygyny and Male Territory Quality in the New Zealand Fur Seal

The polygynous New Zealand fur seal, Arctocephalus forsteri, breeds in densely-packed colonies with males defending exclusive territories. The distribution of individuals within a colony of these seals was monitored over three consecutive breeding seasons and behavioural thermoregulation was found to be an important factor influencing the site selection of both males and females. Shaded areas and pools of water were used by both sexes for cooling and use of these cooling substrates increased as rock surface temperature increased, resulting in a clumped distribution on hot days. Substrate preferences were tested experimentally by manipulating the availability of cooling substrates during two seasons. The number of females using an area increased significantly after shade or pools of water were added to that area. For males, pool additions resulted in increased use of those areas, while adding shade had no effect. Cooling substrates had a patchy distribution and could therefore be monopolised by territorial males. Using the number of females on a territory as a measure of male mating success, it was found that female numbers were most strongly positively correlated with the area of shaded substrate on a territory. Total territory area was also positively correlated with number of females. It is argued that thermoregulatory constraints are a major factor affecting female site choice, and that this in turn affects male mating success.     

THE ULTRASTRUCTURE OF SAHNIA POLLEN (PENTOXYLALES)

The micromorphology and fine structure of in situ pentoxylalean pollen are described from the holotype of Sahnia laxiphora Drinnan and Chambers 1985 collected from the Lower Cretaceous (Valanginian-Aptian) of Victoria, southeastern Australia. Pollen grains are ovoid, monosulcate, and relatively small, averaging 26 μm in length. Exine ornamentation is psilate. The sporoderm is two-parted with the sexine staining lightly throughout and approximately six times the thickness of the more darkly staining nexine. The exine over the sulcus is typically strongly invaginated, and may or may not include an extremely thin sexine layer. The outer part of the sexine is homogeneous, while the inner part is composed of relatively large granules separated by irregular lacunae of various sizes; lacunae are most pronounced at the sexinenexine interface. Faint lamellae characterize the nexine in both apertural and nonapertural regions. Granular orbicules are often associated with the exine surfaces and also occur appressed to pollen sac walls along with lamellated tapetal membranes. Sporoderm ultrastructure is compared to that of nonsaccate pollen of other groups, and particularly to pollen of Bennettitales, Gnetales, angiosperms, and similar plants, to which the Pentoxylales have been thought to be closely related. Although Sahnia laxiphora pollen is not identical to that of any of these taxa, the strongest similarity is with pollen of Bennettitales.     

VARIABILITY IN NITRATE UPTAKE KINETICS IN THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1

Short-term (1–9 min) nitrate uptake kinetics were measured in Thalassiosira pseudonana (Hust.) Hasle & Heimdal grown in nitrate-limited, ammonium-limited, and nitrate-sufficient continuous cultures. For all cultures, maximal nitrate uptake rates did not develop until approximately 3 min after nitrate addition; thereafter, nitrate uptake rates remained constant or declined slightly. The K_s and V_max for the nitrate-limited cultures were higher at any growth rate than those for the ammonium-limited or nitrate-sufficient cultures. Thus, much higher nitrate concentrations would be required to saturate nitrate uptake in nitrate-limited Thalassiosira pseudonana than is usually considered necessary. The lack of data for other species grown under a range of environmental conditions makes it difficult to generalize about the effect of preconditioning on nitrate uptake kinetics.     

EVOLUTIONARY RELATIONSHIPS BETWEEN FOUR SPECIES OF CLADOPHORA (CLADOPHORALES,CHLOROPHYTA) BASED ON DNA–DNA HYBRIDIZATION1

Analysis of the reassociation kinetics of the DNA from Cladophora pellucida (Huds.) Kütz. indicates that the genome of this benthic alga is comprised of approximately 75% repetitive sequences. Single-copy sequences reassociated with a rate constant of 1.8 × 10^?3 M^?1· s^?1, which corresponds to a haploid genome size of 4.7 × 10⁸ bp. Genotypic relationships between members of the form section Longiarticulatae were determined by the method of DNA–DNA hybridization. No significant divergence was observed between the single-copy sequences of C. pellucida isolates from the East Atlantic coast and Mediterranean Sea. Cladophora feredayi Harv. and C. att. ad pellucida from Australia and C. pellucidoidea van den Hoek from the West Atlantic coast were highly and about equally divergent from C. pellucida. The data support the hypothesis that the West Atlantic–West Pacific divergence reflects the middle Miocene closure of the Mediterranean–Indo-Pacific seaways, and the hypothesis that the Northwest Atlantic–Northeast Atlantic divergence reflects the middle Miocene thermal separation of these coasts.     

FISCHERELLIN,A NEW ALLELOCHEMICAL FROM THE FRESHWATER CYANOBACTERIUM FISCHERELLA MUSCICOLA1

The benthic cyanobacterium Fischerella muscicola (Thur.) Gom. UTEX 1829 produces a secondary metabolite, fischerellin, that strongly inhibits other cyanobacteria and to a lesser extent members of the Chlorophyceae. Eubacteria are not affected. The major active compound is lipophilic and exhibits a molecular ion at m/z 408. It is heat- and acid-stable but decomposes in 1 M sodium hydroxide (80° C. 1 h). Fischerellin inhibits the photosynthetic but not the respiratory electron transport of cyanobacteria and chlorophytes. Its site of action is located in PS II. Two other species of Fischerella also produce fischerellin, indicating that the synthesis of such allelochemicals might be characteristic of the genus.     

SECRETION AND DEPLOYMENT OF BRISTLES IN MALLOMONAS SPLENDENS (SYNUROPHYCEAE)1

Mallomonas splendens (G. S. West) Playfair has a cell covering of siliceous scales and bristles. Interphase cells bear four anterior and four posterior bristles that each articulate, at their flexed basal ends via a complex of labile fibers (the fibrillar complex), on a specialized body scale (a base-plate scale). Body scales, base-plate scales and bristles are formed independently of each other and at different times in silica deposition vesicles (SDVs) that are associated with one of the two chloroplasts. The fine structure of scale and bristle morphogenesis in M. splendens agrees with that previously described for Synura and Mallomonas. Four new posterior bristles are formed at late interphase with their basal ends towards the cell posterior. The fibrillar complex is formed in situ on the bristle in the SDV. Mature bristles are secreted one by one onto the surface of the protoplast, beneath the layer of body scales, where the basal ends of the bristles adhere to the plasma membrane via the fibrillar complex. The extrusion of posterior bristles and their deployment onto the cell surface was monitored with video. A fine cellular protuberance accompanies the bristles as they are extruded from beneath the scale layer with their basal ends leading. When distant from the cell, the basal ends of the bristles appear attached to the protuberance, possibly by way of their fibrillar complexes. Once bristles are fully extruded, and their tips free in the surrounding environment, the bristle bases are drawn back to the posterior apex of the cell, apparently by the now shortening protuberance. Thus a 180° reorientation of the posterior bristles has been effected outside the cell. Thin-sections of cells that are extruding bristles show a threadlike, cytoplasmic extension of the cell posterior which may be analogous to the protuberance seen in live cells. Four new posterior base-plate scales are secreted after the bristles have reoriented. Scanning electron microscopy indicates that the fibrillar complex is involved in positioning the bristles onto their respective base-plate scales. Anterior bristles are formed in new daughter cells in the same orientation as the posterior bristles; thus they are extruded tip first and no reorientation is required.     

Migratory Orientation of Blackcaps (Sylvia atricapilla): Population-specific Shifts of Direction during the Autumn

The population-specific orientation of two groups of blackcaps (Sylvia atricapilla), one from southwest Germany, the other from easternmost Austria, was studied outdoors in Emlen funnels. We investigated whether a seasonal shift in the migratory direction — as expected for the Austrian birds from ringing recoveries — occurs under experimental conditions and in a seasonally constant magnetic field. The West German birds, for which no shift was expected, oriented southwest during the entire season. The Austrian birds oriented southeast in October and southsouthwest in November. The clockwise shift by about 60° occurred within a 10-day period. The results indicate that in this species seasonal changes of migratory direction are probably based on an endogenous program, occur without the birds actually migrating and are independent of changes in the magnetic field. Our results provide further evidence that directional shifts in Sylvia warblers may be controlled by a different mechanism than in pied flycatchers (Ficedula hypoleuca).     

INBREEDING IN DARWIN'S MEDIUM GROUND FINCHES (GEOSPIZA FORTIS)

We studied the frequency and causes of inbreeding and its effect on reproductive success in a population of Darwin's Medium Ground Finches (Geospiza fortis) on Isla Daphne Major, Galápagos, during four breeding seasons (1981, 1983, 1984, and 1987). Pedigree analysis showed that levels of inbreeding were low but comparable with those observed in other passerine birds. For pairs with at least half of their grandparents known, approximately 20% of all pairings were between detectably related birds. The frequency of pairings between closely related birds (coefficient of kinship [φ] ≥ 0.250) among all pairs was 0.6%. We detected no effect of inbreeding on reproductive success, although sample sizes were small. The observed reproductive output of related pairs was not significantly different from the output of unrelated pairs, and there was no correlation between a pair's kinship coefficient and an estimate of the potential magnitude of inbreeding depression. Comparisons with a study of Great Tits (Parus major) by van Noordwijk and Scharloo (1981) suggest that, even if present, the fitness costs of inbreeding in this population of G. fortis would be low. Observed levels of inbreeding in each breeding episode were accurately predicted by simulations of random mating in which relatedness had no influence on pairing between individuals. This result suggests that levels of inbreeding in this population are determined more by demographic factors than by behavioral avoidance of mating with kin.