Direct and short-term culture preparation of chorionic villi. Is any one method best?

Chorionic villi from 20 diagnostic cases were prepared for cytogenetic analysis by a direct and two short-term culture methods. No significant differences were found between the methods in the quality and quantity of metaphases obtained. A further study using villi from 20 pre-termination patients indicated an inherent variation in the quality of villi resulting in inconsistent processing and variation in the response of a sample to the methods. This suggests that it would be advantageous to process the villi by more than one method.     

Minute theropod eggs and embryo from the Lower Cretaceous of Thailand and the dinosaur-bird transition

We report on very small fossil eggs from the Lower Cretaceous of Thailand, one of them containing a theropod embryo, which display a remarkable mosaic of characters. While the surficial ornamentation is typical of non-avian saurischian dinosaurs, the three-layered prismatic structure of the eggshell is currently known only in extant and fossil eggs associated with birds. These eggs, about the size of a goldfinch's, mirror at the reproductive level the retention of small body size that was paramount in the transition from non-avian theropods to birds. The egg-layer may have been a small feathered theropod similar to those recently found in China.     

Carbon-isotope ratio gradients in western arctic zooplankton

Zooplankton from 87 stations in the Bering, Chukchi and Beaufort Seas sampled in 1985, 1986 and 1987 showed a geographic gradient in stable carbon-isotope ratios (¹³C). The zooplankton most depleted in ¹³C were found in the central and eastern Beaufort Sea and those most enriched were from the Bering and Chukchi Seas. Average ¹³C values ranged from-20.9 to-26.7 for copepods and from-19.4 to-25.1 for euphausiids. Euphausiids show a minimum of 1.0 enrichment relative to copepods throughout the study area. Relative biomasses of the major zooplankton taxa varied significantly across the Alaskan Beaufort Sea in October 1986, with euphausiids dominating in the west and copepods in the east. These differences in taxonomic composition affected the weighted ¹³C values for total zooplankton and may produce an even more pronounced geographic gradient in zooplankton ¹³C than that found within a single taxon. The bowhead whale Balaena mysticetus migrates between wintering areas in the Bering Sea and summering areas in the Beaufort Sea and feeds over this geographic range. The zooplankton ¹³C gradient is the probable source of ¹³C oscillations found along the baleen plates of this planktivore.     

Biotic control of stream fluxes: spawning salmon drive nutrient and matter export

Organisms can control movements of nutrients and matter by physically modifying habitat. We examined how an ecosystem engineer, sockeye salmon (Oncorhynchus nerka), influences seasonal fluxes of sediments, nitrogen (N), and phosphorus (P) in streams of southwestern Alaska. The purpose of this study was to investigate whether salmon act as net importers or net exporters of matter and nutrients from streams and how these roles change as a function of salmon population density. We measured discharge and concentrations of suspended sediments and total N and P every 7-14 days for up to four summers in 10 streams spanning a gradient in salmon densities. We statistically allocated whole-season fluxes to salmon activities, such as excretion and bioturbation, and to export by hydrologic discharge. In addition, we used counts of spawning salmon to estimate nutrient and matter imports by salmon to streams. Large seasonal pulses of suspended sediments, P, and N were associated with salmon spawning activities, often increasing export an order of magnitude higher than during pre-salmon levels. Years and streams with more salmon had significantly higher levels of export of sediments and nutrients. In addition, years with higher precipitation had higher background export of P and N. Salmon exported an average of the equivalent of 189%, 60%, and 55% of total matter, P, and N that salmon imported in their bodies. The relative magnitude of export varied; salmon exported more than their bodies imported in 80%, 20%, and 16% across all streams and years for sediments, P, and N, respectively. A bioassay experiment indicated that the P exported by salmon is directly available for use by primary producers in the downstream lake. These results demonstrate that salmon not only move nutrients upstream on large spatial scales via their migration from the ocean and subsequent death, but also redistribute matter and nutrients on finer spatial scales through their spawning activities.     

Is sex-specific mass gain in Cory’s shearwaters <Emphasis Type="Italic">Calonectris diomedea</Emphasis> related to begging and steroid hormone expression?

Mass differences between the sexes of dimorphic bird species often appear early in the nestling development. But how do adults know how much to feed a chick in a sexually dimorphic species? Do chicks of the heavier sex beg more? We studied begging in Cory’s shearwaters Calonectris diomedea, a species with heavier adult and juvenile males than females. We found that begging rates and call numbers were not different between male and female chicks, but parameters of begging intensity differed between the sexes in their relationship to chick body condition. For the same body condition, males had significantly higher begging call numbers and rates. Acoustical parameters, which were analysed semi-automatically, included the lengths of call and silence intervals, the minimum, mean and maximum frequency in a call and the number of frequency peaks within a call. We found no consistent differences of acoustic begging call elements between the sexes. Male and female chicks did not differ in the levels of the steroid hormones testosterone or corticosterone in the second quarter of the nestling period, and the mechanism leading to sex-related differences in begging rates for a given body condition remains unknown.