Litter Overlap in Gambusia hubbsi: Superfetation Revisited

The frequency of litter overlap, the simultaneous presence of two litters at different stages of development within a single female, varies among populations of Gambusia hubbsi in different habitats on Andros, Bahamas. In freshwater bluehole and shallow water populations, less than 2% of the females carried two litters, independent of the difference in developmental stage between the litters. In well field populations, 2% of the females carried two litters composed of immature and mature oocytes, whereas 10% carried developing oocytes and late stage embryos, and 16% carried mature oocytes (or older) and late stage embryos. Among females from populations that we introduced into unoccupied well fields 2% carried two litters composed of immature and mature oocytes, about 14% carried developing oocytes and late stage embryos, and less than 6% carried mature oocytes (or older) and late stage embryos. When two litters composed developing oocytes and late stage embryos were present, the two litters were of equal size, and the total number of offspring was 1.5 times larger than expected on the basis of female body length. When two litters composed mature oocytes (or older stages) and late stage embryos were present, the two litters were also of equal size, and the total number of offspring was as expected on the basis of female body length. Litter overlap was independent of female size. A comparison of the consequences of litter overlap for strictly lecithotrophic and strictly matrotrophic modes of reproduction with the patterns of litter overlap observed in G. hubbsi, suggests that litter overlap in G. hubbsi reduces the cost of reproduction, but does not increase the rate of offspring production.     

A new species and two new combinations of Ecuadorian Bromeliaceae (Tillandsioideae)

A new species of Guzmania, G. henniae , from southeastern Ecuador is described and illustrated. Two new combinations in the newly erected, segregate genus Racinaea (formerly Tillandsia subgenus Pseudocatopsis), R. dielsii and R. undulifolia are presented and discussed.     

Nuclear magnetic resonance studies of amphiphile hydration: Effects of cholesterol on phosphatidyl choline hydration

Water which remains unfrozen at ?25 °C in the presence of phosphatidyl choline (PC) gives rise to a proton magnetic resonance signal which can be used to measure the hydration of single-walled vesicles and multilamellar liposomes of PC. The proton magnetic resonance signal of the unfrozen water in these systems is strongly dependent upon the nature of the molecular domain in which the water is situated. For example, at cholesterol to PC molar ratios below 35 mol%, the vesicle hydration signal consists of a relatively narrow symmetric peak (line width, ~150 Hz). At higher molar ratios, however, rather broad asymmetric signals appear (line widths, ~300–1000 Hz) which indicate that when significant quantities of cholesterol are packed in the bilayer there must be regions in which there is a preferred direction for motion of the unfrozen water. It is possible to solubilize significant quantities of cholesterol by sonicating it in concentrated solutions of sodium dodecyl sulfate. Addition of cholesterol to PC vesicles via these sodium dodecyl sulfate-cholesterol complexes caused hydration changes in the PC, which, at high cholesterol to PC molar ratios, paralleled the effects of cholesterol on PC hydration in homogeneous vesicles in which the cholesterol and PC were simply cosonicated.     

Seepocken der deutschen Küstengewässer

Barnacles of German coastal waters. An attempt is made to provide a guide for the identification of seven barnacle species occurring in German coastal waters of the western Baltic and the North Sea. Variations in morphological characters observed in sessile adults are described, and figures drawn to differentiate the larvae of the nauplius and cypris stage. The information available on the distribution and ecology of the barnacles considered is reviewed.      

Association of acetylcholine receptors with peripheral membrane proteins: evidence from antibody-induced coaggregation

Acetylcholine receptors (AChR) are associated with several peripheral membrane proteins that are concentrated on the cytoplasmic face of the plasma membrane at the neuromuscular junction, and at aggregates of AChR that form in vitro. We tested the linkage among these proteins by inducing microaggregation of AChR, then determining if a given peripheral membrane protein accumulated with the receptors in microaggregates. In most experiments, we used isolated membrane fragments that are rich in AChR and accessible to antibodies against intracellular antigens. We showed that the 43 kD receptor-associated protein always aggregated with AChR, whether microaggregation was driven by antibodies to the 43 kD protein, or to the receptor itself. Antibodies to the 58 kD receptor-associated protein also always aggregated the 58 kD protein with the receptor. Our results are consistent with a model for AChR-rich membrane in which the 43 kD and 58 kD proteins are both closely associated with the AChR.When we induced microaggregation in intact muscle cells with anti-AChR antibodies, our results were less definitive. The 43 kD receptor-associated protein microaggregated with AChR, but the 58 kD protein was not especially enriched at AChR microaggregates. We discuss the advantages of using isolated AChR-rich membrane fragments to study the association of AChR with peripheral membrane proteins.We thank J. Strong for his expertise in obtaining the data for Figs. 6–8, and W. Resneck, A. O'Neill, and K. Douville for their assistance throughout this work. Our research has been supported by grants from the Muscular Dystrophy Association (to R.J.B., R.S., D.W.P. and S.C.F.) and from the National Institutes of Health (NS17282 to R.J.B.; NS27171 to P.W.L.; NS15513 to D.W.P.; NS15293 to R.S.; NS14871 to S.C.F.).     

Mate preferences of female mottled sculpins, Cottus bairdi

Experimental manipulation of breeding site quality did not alter the mate preference of female mottled sculpins (Cottus bairdi). Females of this species appear to choose mates on the basis of male size. By choosing a larger male, a female increases the probability that some of her eggs will hatch because large males are unlikely to abandon their nest sites.