Larval and post-larval morphogenesis in the gutless protobranch bivalve Solemya reidi (Cryptodonta: Solemyidae)

Structural changes occurring in the alimentary tract, perivisceral cavity, foot, hypobranchial gland, and gills of larval and post-larval Solemya reidi, a gutless protobranch bivalve, were examined using both light and electron microscopy at 1, 3, 5, 18, 34 and 42 d after fertilization. A fully developed mouth, esophagus, and anus, together with the rudiments of a stomach and rectum are present before metamorphosis. At metamorphosis, the cells making up the dorsal and lateral walls of the stomach dissociate, and by 18 d the mouth and anus are the only remaining portions of the alimentary tract. The larval test is ingested into the perivisceral cavity at metamorphosis and its autolysis continues through at least the 42nd day after fertilization. The foot, gills, and hypobranchial gland, poorly developed at metamorphosis, develop slowly and are still undergoing extensive morphogenesis at 42 d.Harbor Branch Oceanographic Institution Contribution No. 601.     

The importance of investigating for uniparental disomy in prenatally identified balanced acrocentric rearrangements

We report the finding of paternal isodisomy for chromosome 14 in a fetus found to have a der(14;14)(q10;q10) by amniocentesis. The pregnancy was complicated by severe polyhydramnios and elevated amniotic fluid alpha-fetoprotein (AFP). The infant showed features consistent with paternal uniparental disomy (UPD) including postnatal growth retardation, poor respiratory function, feeding difficulties, and evidence of hypertrophic cardiomyopathy. The present case, in addition to other reported cases of UPD involving balanced acrocentric rearrangements, supports testing for UPD in prenatally detected Robertsonian translocations and isochromosomes. Copyright © 2002 John Wiley & Sons, Ltd.     

Zooplankton feeding ecology: contents of fecal pellets of the copepods Temora turbinata and T. stylifera from continental shelf and slope waters near the mouth of the Mississippi River

In-situ feeding habits of the copepods Temora turbinata and T. stylifera were investigated by scanning electron microscope examination of fecal pellets, the contents of which reflected copepod gut contents upon capture. Pellet contents were compared with assemblages of available phytoplankton in the water column at the times of zooplankton sampling. Samples were collected in continental shelf and slope waters of the Gulf of Mexico near the mouth of the Mississippi River. Both species ingested a wide size range and taxonomic array of phytoplankters, and to a lesser extent, other crustaceans. Fecal pellets contained primarily the remains of the phytoplankters that were most abundant in the water at times of collection. There was considerable overlap in the food items ingested by adult females of both copepod species, or two stages of T. turbinata copepodites. Thus, T. turbinata and T. stylifera are omnivores, but primarily opportunistic herbivores.     

Mass encystment of a planktonic oligotrich ciliate

Sediment traps were deployed in a 60 m water column near the Eddystone Lighthouse on the south west coast of England for one year from March 1984. In April, the traps collected the cysts of a planktonic ciliate with a flux of almost 35 000 m^-2 d^-1. The cysts were attributed to a planktonic oligotrich [provisionally identified as Strombidium crassulum (Leegard) Kahl], which was common in the water at the time. Identification was achieved through the discovery of the incipient formation of the cysts in preserved water samples and by the similarity of the morphology of the cysts with that of other oligotrichid ciliates. Attempts to prove the relationship by incubation have so far failed. The production of the cysts followed the main spring bloom of diatoms and coincided with a small bloom of autotrophic oligotrichs. In the traps, the total number and percentage of cysts with contents decreased rapidly after the encystment event. However, potentially viable cysts were still recorded in the plankton eleven months later, with minimum fluxes of 200 cysts m^-2 d^-1. Resuspension of bottom sediments by tides and storms ensured that a large population of cysts was always present in the water column during the winter, awaiting the right conditions to stimulate excystment and the initiation of a new motile population.     

Residency and depth movements of a coastal group of Atlantic cod (Gadus morhua L.)

Atlantic cod stocks are subdivided into geographically and biologically discrete populations; some being locally resident, others migratory. The reasons for the variation in migration pattern and the consequences it may have for population structuring is poorly understood. We studied a group of cod from the coastal waters of the Shetland Isles in the northern North Sea. During the spawning season, electronic tags that record depth and temperature over time were implanted into 133 individuals and the fish released within a few kilometres of where they were captured. Thirty-nine cod have been recaptured up to 608 days later, throughout the year and, in all but two cases, within 15 km of their release site. Geolocation methods based on temperature and bathymetry also suggested that the cod had a limited home range, remaining resident year-round in coastal waters. The cod were deeper during the winter and moved to shallower water in late spring and summer. They showed diel, fortnightly and monthly cycles in depth movement that varied much within and between individuals over the season. Residency and the individual variability in vertical movement may reflect a combination of locally complex depth strata, variable seabed substrate and the wide range of seasonally available prey resources.     

Effects of Land-Use and Tsetse Fly Control on Bird Species Richness in Southwestern Ethiopia

Successful control of tsetse (Glossina spp.)-transmitted trypanosomiasis in the Ghibe Valley, Ethiopia, appears to have accelerated conversion of wooded grassland into cropland. Land conversion, in turn, may have fragmented wildlife habitat. Our objective was to assess the influence of the expansion of agricultural land-use, brought about by tsetse control, on ecological properties by using bird species richness and composition as indicators of environmental impacts. We sampled bird species richness and composition (using Timed-Species counts) and habitat structure (using field sampling and remote sensing) in four land cover/land-use types in areas subjected to tsetse fly control and adjacent areas without control. At the height of the growing season bird species numbers and vegetative complexity were greater in the small-holder, oxen-plowed fields and riparian woodlands than in wooded grasslands or in large-holder, tractor-plowed fields. Species composition was highly dissimilar (40–70% dissimilarity) comparing among land-use types, with many species found only in a single type. This implies that trypanosomiasis control that results in land conversion from wooded grasslands to small-holder farming in this region may have no adverse impacts on bird species numbers but will alter composition. These results also suggest that moderate land-use by humans (e.g., small-holder field mosaics) increases habitat heterogeneity and bird species richness relative to high levels of use (e.g., tractor-plowed fields). Tsetse control may be indirectly maintaining species richness in the valley by encouraging the differential spread of these small-scale, heterogeneous farms in place of large-scale, homogeneous farms. Nevertheless, if the extent of small-holder farms significantly exceeds that of present levels, negative impacts on bird species richness and large shifts in species composition may occur.