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The predominant definition of extinction risk in conservation biology involves evaluating the cumulative distribution function (CDF) of extinction time at a particular point (the "time horizon"). Using the principles of decision theory, this article develops an alternative definition of extinction risk as the expected loss (EL) to society resulting from eventual extinction of a species. Distinct roles are identified for time preference and risk aversion. Ranges of tentative values for the parameters of the two approaches are proposed, and the performances of the two approaches are compared and contrasted for a small set of real-world species with published extinction time distributions and a large set of hypothetical extinction time distributions. Potential issues with each approach are evaluated, and the EL approach is recommended as the better of the two. The CDF approach suffers from the fact that extinctions that occur at any time before the specified time horizon are weighted equally, while extinctions that occur beyond the specified time horizon receive no weight at all. It also suffers from the fact that the time horizon does not correspond to any natural phenomenon, and so is impossible to specify nonarbitrarily; yet the results can depend critically on the specified value. In contrast, the EL approach has the advantage of weighting extinction time continuously, with no artificial time horizon, and the parameters of the approach (the rates of time preference and risk aversion) do correspond to natural phenomena, and so can be specified nonarbitrarily.

Congenital urachal anomalies are usually asymptomatic. However, infection or obstruction of urachal remnant may result in serious complications. The giant umbilical cords with suspected internal communications could contain remnants and require surgical exploration. With timely recognition and surgical intervention, the outcome is generally good.

Aluminum toxicity is associated with anemia, impaired bone metabolism, neurologic defects, and parenteral nutrition (PN)-associated liver disease. This element is a ubiquitous contaminant of PN components, especially in infant formulations. We assessed the current levels of aluminum contamination in infant PN at a level III neonatal intensive care unit.Thirty samples of PN prepared in the same hospital for infants aged30 days (mean [SD] weight, 1.54 [0.71] kg) were collected from discarded solution. Each sample was analyzed for aluminum content via inductively coupled plasma mass spectrometry. The components of PN (from label) and measured aluminum content were then compared using linear regression and 1-way analysis of variance.The mean (SD) aluminum contamination of infant PN was 14.02 (6.51) mcg/kg/d. Only 3 samples were5 mcg/kg/d. Aluminum levels and infant weight were not associated. Linear regression revealed a significant correlation between aluminum and both calcium gluconate ( P.0001) and phosphate ( P = .05), with a trend between aluminum and potassium ( P = .07).Aluminum contamination in infant PN remains almost 3 times higher than the advised maximum exposure (5 mcg/kg/d, Food and Drug Administration 2004). Unexpectedly, an association between infant weight and aluminum exposure was not apparent, likely due to the homogeneity of our population. Isolating the source of aluminum contamination is difficult, as multiple components appear to be involved. Calcium gluconate is likely still a major contributor, but further investigations into individual components are warranted to promote the reduction of aluminum in infant PN.

Lack of guidance for interpreting the definitions of endangered and threatened in the U.S. Endangered Species Act (ESA) has resulted in case-by-case decision making leaving the process vulnerable to being considered arbitrary or capricious. Adopting quantitative decision rules would remedy this but requires the agency to specify the relative urgency concerning extinction events over time, cutoff risk values corresponding to different levels of protection, and the importance given to different types of listing errors. We tested the performance of 3 sets of decision rules that use alternative functions for weighting the relative urgency of future extinction events: a threshold rule set, which uses a decision rule of x% probability of extinction over y years; a concave rule set, where the relative importance of future extinction events declines exponentially over time; and a shoulder rule set that uses a sigmoid shape function, where relative importance declines slowly at first and then more rapidly. We obtained decision cutoffs by interviewing several biologists and then emulated the listing process with simulations that covered a range of extinction risks typical of ESA listing decisions. We evaluated performance of the decision rules under different data quantities and qualities on the basis of the relative importance of misclassification errors. Although there was little difference between the performance of alternative decision rules for correct listings, the distribution of misclassifications differed depending on the function used. Misclassifications for the threshold and concave listing criteria resulted in more overprotection errors, particularly as uncertainty increased, whereas errors for the shoulder listing criteria were more symmetrical. We developed and tested the framework for quantitative decision rules for listing species under the U.S. ESA. If policy values can be agreed on, use of this framework would improve the implementation of the ESA by increasing transparency and consistency.

Halosaccion americanum, a member of Palmariaceae, was grown in culture from spores and the life history was critically examined by the use of scanning EM and light microscopy. A mature tetrasporangium of H. americanum produces four spores that germinate to form two male and two female gametophytes. The male gametophytes grow to maturity in approximately eight months and macroscopically resemble the tetrasporophyte. Following the first division of the tetraspore, the two-celled female gametophyte consists of a vegetative cell and a carpogonium with trichogynes. Fertilization is accomplished by spermatia from male plants of the preceding generation, as male plants of the same season are immature. Spermatia are formed in a continuous layer over the surface of the mature male gametophytes and, when released, are entrained in long strands of mucous. Spermatia adhere to and fuse with trichogynes and, nuclear fusions presumably follow. The carposporophyte is absent; the new tetrasporophyte develops directly from the fertilized carpogonium. Growth of the sporophyte eventually obliterates the female gametophyte, and development into a mature tetrasporophyte proceeds over a period of approximately eight months. The development of H. americanum, with its extremely abbreviated female gametophyte stage and direct development of the tetrasporophyte from the zygote, indicates that this rhodophyte has the same life history as reported for other members of the Palmariales.

Three classes of mammalian phosphoinositide-specific phospholipase C (PLC) have been characterized, PLCβ, PLCγ and PLCδ, that are differentially regulated by heterotrimeric G-proteins, tyrosine kinases and calcium. Here we describe a fourth class, PLCe, that in addition to conserved PLC domains, contains a GTP exchange factor (GRF CDC25) domain and two C-terminal Ras-binding (RA) domains, RA1 and RA2. The RA2 domain binds H-Ras in a GTP-dependent manner, comparable with the Ras-binding domain of Raf-1; however, the RA1 domain binds H-Ras with a low affinity in a GTP-independent manner. While Gαq, Gβγ or, surprisingly, H-Ras do not activate recombinant purified protein in vitro, constitutively active Q61L H-Ras stimulates PLCe co-expressed in COS-7 cells in parallel with Ras binding. Deletion of either the RA1 or RA2 domain inhibits this activation. Site-directed mutagenesis of the RA2 domain or Ras demonstrates a conserved Ras–effector interaction and a unique profile of activation by Ras effector domain mutants. These studies identify a novel fourth class of mammalian PLC that is directly regulated by Ras and links two critical signaling pathways.

The heavy metal cadmium causes nephrotoxicity and alters the transport function of epithelial cells. In the shark rectal gland, chloride secretion is regulated by secretagogues and inhibitors acting through receptors coupled to G proteins and the cyclic AMP-protein kinase A pathway. We examined the effects of cadmium on the response to the inhibitory peptide somatostatin (SRIF), and to the stimulatory secretagogues forskolin and vasoactive intestinal peptide (VIP). In control experiments, SRIF (100 nM) entirely inhibited the chloride secretory response to 10 μM forskolin (maximum chloride secretion with forskolin 1984 ± 176 μEq/h/g; with forskolin + SRIF 466 ± 93 μEq/h/g, P < 0.001). Cadmium (25 μM) entirely reversed the inhibitory response to SRIF (chloride secretion 2143 ± 222 μEq/h/g) and caused an overshoot (2917 ± 293 μEq/h/g) that exceeded the response to forskolin (P < 0.01). Cadmium also enhanced forskolin-stimulated chloride secretion (2628 ± 418 vs. 1673 ± 340 μEq/h/g, P < 0.02) and reversed the declining phase of the forskolin response. Cadmium had a concentration-dependent, biphasic effect on the response to VIP. Cd (10–100 μM) increased both chloride secretion and tissue cyclic AMP content, whereas higher concentrations (1 mM) inhibited chloride secretion and cyclic AMP accumulation. Our findings provide evidence that Cd disrupts the signal transduction pathways of both inhibitory receptors and secretagogues regulating cAMP mediated transport in an intact epithelia. The results are consistent with direct effects of cadmium on adenylate cyclase and/or phosphodiesterase activity in this marine epithelial model. J. Exp. Zool. 279:530–536, 1997. © 1997 Wiley-Liss, Inc.

The discovery in the early 1980s that meiosis occurs during germination of conchospores of Porphyra yezoensis Ueda suggested that the sexually divided fronds of Porphyra purpurea (Roth) C. Agardh might similarly originate from meiotic segregation of a pair of sex-determining alleles during early sporeling development. After establishing conditions suitable for propagating P. purpurea in culture, observations on developing sporelings demonstrated that meiosis takes place during the first two divisions of the germinating conchospores. In the first division, the spore is split into an upper and lower cell. In the second, an anticlinal division in the upper cell yields two daughter cells situated one beside the other, and a periclinal division in the bottom cell gives two cells arranged one above the other. Thus, during normal development, the first four cells of the sporeling constitute a meiotic tetrad whose cells are arranged in a characteristic fashion. Stable color mutants of P. purpurea were isolated, genetically characterized, and used as genetic markers to follow the fate of individual cells of the tetrad during subsequent frond development. Nearly the entire blade of the mature thallus is derived from the two upper cells of the tetrad, with the two lower cells mostly giving rise to the rhizoidal holdfast region. Cell lineage boundaries laid down by the segregation of color alleles at meiosis corresponded perfectly with those later defined by sexual differentiation on the same fronds, strongly supporting the hypothesis that sex determination in P. purpurea is controlled by alleles at a segregating chromosomal locus.

A congenital syndrome of long, thin limbs, severe joint and tendon laxity, microspherophakia, ectopia lentis, heart murmurs and aortic dilatation was identified in 7 calves. All affected calves were sired by a single phenotypically normal bull suspected of germline mosaicism for a new mutation resulting in this disease. One of the calves subsequently died with ruptured aorta at age 16 months. Histopathologic and electron microscopic studies of the aortic media of affected calves demonstrated disorganized elastin and narrowed elastic lamina separated by widened spaces. This bovine disease provides a unique animal model of the human Marfan syndrome. A herd of cattle with this disease is being developed for further studies.