Population differences in gonad and pyloric caeca cycles of the New Zealand seastarSclerasterias mollis (Echinodermata: Asteroidea)

Inshore and offshore populations ofSclerasterias mollis (Hutton, 1872) were sampled on the outer continental shelf off the Otago Peninsula, New Zealand, and their nutritional and reproductive cycles are described from 1985–1986. Histological changes in the gonads are generally typical of other asteroids. The gametogenic cycle takes 12 mo. The gonad and pyloric caeca indices in both females and males had an inverse relationship.S. mollis accumulates nutrients in the pyloric caeca during summer and early autumn. The gonads develop in the autumn and winter. Offshore seastars were much larger and had significantly higher gonad and pyloric caeca indices than inshore individuals. These differences in body sizes and organ indices arise from differences in food availability and/or population density.     

Thermal behaviour of a small spider (Araneae : Araneidae : Araneinae) on horizontal webs in semi-arid Western Australia

Summary The solar orientation response of a small spider (gen. nov.: Araneae: Araneidae: Araneinae) is examined at a semi-arid location in tropical Western Australia. The spiders rest beneath horizontal dome-shaped webs close to the ground surface on spinifex (Triodia sp.). The spiders are small (c. 5 mm long) and robust, being only twice as long as wide. Spider orientation, elevation, wind velocity, radiation and wet and dry bulb temperatures together with spider and egg-sac temperatures were measured throughout the day. The spiders orientated their long axis to the solar azimuth through much of the day and postured to the solar elevation; in so doing they tracked the apparent movement of the sun throughout the day with considerable precision, far exceeding that of other spiders studied. Stepwise regression indicated that the solar position was the most important environmental factor associated with the posturing and orientation. The variance in the orientation of the population was associated with a suite of environmental variables related to wind velocity and temperature. Spider (abdominal) temperature had a curvilinear relationship with ambient temperature, with a plateau at c. 35° C, whereas egg-sac temperature had a strictly linear relationship with ambient temperature. Stepwise regression indicates that both the spider and egg-sac temperatures are related mainly to net radiation and ambient temperature. The spiders can alter the incident radiation to which they are exposed by c. 2.2 times which represent the limits of the exposed silhouette area between full dorsal sunlight and the posterior (or anterior) aspect. Under hot conditions the spiders posture and orientate such that the long axis of the body is orientated abdomen towards the sun.     

Ecological Correlates of Extinction Proneness in Australian Tropical Rain Forest Mammals

Abstract. There is a dire need to predict the vulnerability of tropical forest biotas to habitat fragmentation I tested the efficacy of seven ecological traits (body size Iongeuity, fecundity, trophic level, dietary specialization, natural abundance in rain forest and abundance in the surrounding habitat matrix) for predicting responses of 16 nonflying mammal species to rain forest fragmentation in tropical QueenslaM Australia An ordination analysis revealed that most (84%) of the variation in traits was described by two axes, the first separating rand K-selected species, and the second discriminating rare species with specialized diets from common species with generalized diets.
Using multiple regression analysis, the two ordination axes explained 51.7% of variation in mammal extinction proneness (F = 9.96 P = 0.009). Howem, univariate tests revealed tbat a single trait abundance in the mawas a betterpredictor of vulnerability (r²= 63.8%, F = 24.69, P < 0.001). Partial correlations demonstrated that once the effects of matrix abundance tuete remove4 no other traits or ordination axes were significant predictors of extinction proneness.
These results highlight the importance of tolerance of modijied habitats in determining survival of nonpying mammals in tropical forest fragments. Species tbat traverse or exploit modaxied habitats tend to remain stable or inmase in fragments whereas those tbat avoid these habitats often disappem The implications of these findings for hopical forest conservation are discussed.     

Reproductive performance in lesser snow geese: are two parents essential?

Summary The roles of male and female lesser snow geese (Anser caerulescens) in offspring care are well documented, but we know little about flexibility in these roles and how essential they are for offspring survival. We asked whether uni-parental care was adequate, which sex was required at various stages of the reproductive cycle, and what the costs and consequences were of variable amounts of parental care. We found that two parents were important in acquiring nest sites and producing clutches. Widows losing mates during the latter part of laying or in early incubation experienced similar rates of success in hatching clutches to paired females, but males losing mates during incubation experienced total nest failure. Partial clutch loss, hatch loss, intraspecific nest parasitism, duration of incubation periods and gosling weights at hatch did not differ for pairs or widows. In 1983 at La Pérouse Bay, Manitoba, Canada, widows and pairs had similar incubation behaviour, but widows were harassed more and spent more time in full alert posture while on their nests. In 1952 and 1953 at Southhampton Island, Northwest Territories, widows were significantly lighter in body weight prior to hatch than paired females. Thus while widows can bring clutches to hatch successfully, the loss of mates may result in additional physiological costs. Although all possibilities have not been tested experimentally, it appears that costs to uni-parental care up to hatch are not significant. Data collected so far on consequences of uni-parental care provided during the post-hatch period are equivocal, as in one year survival of goslings from single parent broods seemed poor and in another it did not appeart to differ from pairs. The minimum amount of parental care required to raise snow goslings from hatch to recruitment has yet to be determined.     

Hebella parasitica (Cnidaria,Hydroida): A thecate polyp producing an anthomedusa

The thecate hydroid Hebella parasitica (Ciamician), reared under controlled conditions, produced an ephemerous medusa with gonads on the manubrium. This feature does not agree with the current classification of hydroids, according to which a thecate polyp is expected to produce a medusa with gonads on its radial canals. As no data on the reproduction of other species of Hebella are available, the systematic position of H. parasitica should be considered uncertain.Work done within the Finalized Project Oceanografia e i fondi marini, sub-project Risorse biologiche of the C.N.R.     

Influence of predation on infaunal abundance in Upper Chesapeake Bay,USA

The importance of predators in controlling the densities of infaunal (>0.5 mm) organisms was investigated in the mesohaline region of the Upper Chesapeake Bay (USA) using field experiments. The role of predators in controlling infaunal density and community characteristics varied with habitat type, season (i.e., predator abundance) and developmental or successional stage of the community. Few infaunal species were adversely affected by predator exclusion. Species that increased greatly in abundance in the absence of predators (e.g. Eteone heteropoda, Streblospio benedicti, Nereis succinea, and juvenile Macoma balthica and Mya arenaria) lived near the sediment-water interface and had major population pulses from fall through spring. Species whose abundances increased moderately or were not affected by predator exclusion were deeper burrowing organisms (e.g. Heteromastus filiformis and adult Mya arenaria), or were relatively small organisms (e.g. Paraprionospio pinnata, Scolecolepides viridis and Peloscolex gabriellae) whose principal predators could be other members of the infauna. Competition did not appear to be an important factor controlling infaunal density in these experiments.This work is Contribution No. 973 of the Center for Environmental and Estuarine Studies of the University of Maryland     

Aggregation and foraging behavior of whirligig beetles (Gyrinidae)

Summary Whirligig beetles aggregate in the daytime into dense single-and multispecies groups (rafts) of hundreds or thousands of individuals. On the 22km shoreline of Lake Itasca in northern Minnesota, these aggregations were on the average 0.8 km apart, and they were usually found day after day in the same ocations.Most beetles apparently do not home to the aggregation of their origin after dispersing at night because (a) the species composition of some aggregations changed greatly, and (b) paint-marked beetles (Dineutus horni) moved overnight from one aggregation as far as 4km, joining 11 of the 14 large (>300 beetles) D. horni groups on the lake.Throughout the night, the largest concentrations of beetles remained within 100m of the diurnal aggregation sites. Beetles reconvened into the compact rafts before daybreak, in part by following each other in sometimes long single files or trains. Their forward motion stopped after they joined large number of other beetles. We infer that following behavior enables those individuals that have dispersed from their original aggregations (during their nocturnal foraging) to find and join other aggregations before daylight.Naive fish ate the beetles despite their noxious secretions. However, fish living near rafting sites and feeding on insects on the water surface in daylight should soon learn to avoid the beetles. The rafting sites would then become safe places. We observed fish attacking only those beetles that had been either dispersed from their rafts or released into open water away from raft sites in the daytime. We speculate that the evolutionary significance of the aggregation behavior is related to predator (fish) avoidance.     

Photosynthesis and ion loss in the brown algae Dictyopteris membranacea and Fucus virsoides

The sublittoral brown alga Dictyopteris membranacea (Stackhouse) Batters is very sensitive to low salinities. A one minute exposure to distilled water causes total breakdown of photosynthesis and respiration. The breakdown phenomena were studied as after-effects following re-exposure to sea water. Since rate of ion loss is highest during the first minute of osmotic stress, the irreversible metabolic depression appears to be due to fast ion loss. Photosynthesis of Fucus virsoides J.Ag is not affected by distilled water, even over very long periods of time.     

Metabolic diversity in oceanic animals

Relatively little overlap exists in faunal assemblages in the oceanic waters found north of, and over the reef-like structure south of, Cape Hatteras, North Carolina, USA. To better understand the mechanisms influencing the zoogeography of these animals, metabolic-temperature patterns have been characterized for both larvae and adults of animals collected in waters north and south of Cape Hatteras and from the Caribbean Sea. Southern affinity species from north of Cape Hatteras are the most metabolically labile of the groups, based on seasonal and laboratory-acclimated studies. Adults having a northern affinity found north of Cape Hatteras are metabolically depressed at high temperatures, whereas species from the reef area and the Caribbean are metabolically depressed at low temperatures. Metabolic rates of first stage zoea of crabs from the reef area are depressed at lower temperatures than larvae of the same stage of other species of crabs from the Cape Hatteras region or the Caribbean Sea.Supported by Grant NSF GB 7435 from the National Science Foundation. The authors thank Duke University Marine Laboratory and the Cooperative Program of Biological Oceanography for the use of the R.V. Eastward. The Co-operative Program is supported through the National Science Foundation Grant GB-8189.     

A ciliate red tide at Barrow,Alaska

In September 1968 the first occurrence of extensive red water in the Arctic Ocean in the vicinity of Point Barrow, Alaska, was recorded. The organism causing this water discoloration was a fairly large (100 to 150 ) ciliated protozoan, with chlorophyll-containing endosymbionts. This ciliate, which is not identical to the commonly reported Mesodinium or Cyclotrichium species, is described in this paper, but cannot be identified with any organism described in the literature. Concentrations of dissolved inorganic nutrients and trace metals were determined on water samples obtained from the red water and also in the clear water adjacent to it. These data are discussed relative to the hydrographic conditions in the Chuckchi Sea around Point Barrow. A direct species' analysis by microscopic methods indicated that the plankton were quite similar in all the water samples except for the aforementioned red ciliate, which accounted for over 90% of the total cellular organic carbon in the samples from the red water. Chemical analyses indicated that the red tide ciliate contained approximately 51% protein, 33% lipid, 8% carbohydrate, 0.2% chlorophyll a, and 1.2% DNA.