How reliable are the Powell–Wetherall plot method and the maximum-length approach? Implications for length-based studies of growth and mortality

Length-based methods are the cornerstone of many population studies and stock assessments. This study tested two widely used methods: the Powell–Wetherall (P–W) plot and the L_max approach (i.e., estimating L_∞ directly from L_max). In most simulations, P–W estimates of the ratio total mortality/growth (Z/K ratio) were biased beyond acceptable limits (bias?>?30%). Bias in Z/K showed a complex behavior, without possible corrections. Estimates of asymptotic length (L_∞) were less biased than Z/K, but were very sensitive to intra-cohort variability in growth and to changes in the occurrence of large individuals in the sample. Exclusion of the largest size classes during the regression procedure or weighing by abundance does not solve these issues. Perfect linearization of the data and extremely narrow confidence intervals for Z/K will lead users to erroneous overconfidence in outputs. Clearly, the P–W method is not suitable for the assessment of Z/K ratios of natural populations. Estimation of L_∞ may be tentatively possible under very specific conditions, with necessary external verifications. Also, this study demonstrates that there is no way to estimate L_∞ directly from L_max, since there is no particular relationship to expect a priori between L_∞ and L_max. Errors in estimating L_∞ directly affect the estimate of the growth constant K and all other subsequent calculations in population studies, stock assessments and ecosystem models. New approaches are urgently needed for length-based studies of body growth (e.g., unconstrained curve fit with subsequent bootstrapping), that consider the inherent uncertainty regarding the underlying data and processes.     

Central nervous control of hindleg coordination in stridulating grasshoppers

 Stridulation in many gomphocerine grasshoppers is characterized by specific phase shifts between the two hindlegs as well as different movement patterns produced by the left and the right leg. The underlying neuronal excitation patterns are generated by networks on either side of the metathoracic ganglion. The role of the intraganglionic commissures in right-left coordination and the production of differing movement patterns was investigated by transecting the metathoracic ganglion mediosagittally in Omocestus viridulus, Chorthippus biguttulus and Chorthippus mollis. In all three species, after this operation both hindlegs produced the same pattern and no longer different movements. The effects of transection on coordination differed: rapid movement rhythms, like those typical of Ch. biguttulus and the vibratory parts of the song of Ch. mollis, on the two sides drifted with respect to one another. In contrast, the slow rhythms characteristic of O. viridulus and the song subunits of Ch. mollis were completely synchronized. It is inferred that in intact animals the pathways for coordination of the rapid stridulatory rhythms are exclusively intraganglionic, whereas the phase relations of the slow rhythms are additionally influenced by way of anterior right-left connections, perhaps within the suboesophageal ganglion. Accepted: 15 October 1996     

Aminergic neuron systems of lobsters: morphology and electrophysiology of octopamine-containing neurosecretory cells

In the American lobster (Homarus americanus) the biogenic amines serotonin and octopamine appear to play important and opposite roles in the regulation of aggressive behavior, in the establishment and/or maintenance of dominant and subordinate behavioral states and in the modulation of the associated postural stances and escape responses. The octopamine-containing neurosecretory neurons in the thoracic regions of the lobster ventral nerve cord fall into two morphological subgroups, the root octopamine cells, a classical neurohemal group with release regions along second thoracic roots, and the claw octopamine cells, a group that selectively innervates the claws. Cells of both subgroups have additional sets of endings within neuropil regions of ganglia of the ventral nerve cord. Octopamine neurosecretory neurons generally are silent, but when spontaneously active or when activated, they show large overshooting action potentials with prominent after-hyperpolarizations. Autoinhibition after high-frequency firing, which is also seen in other crustacean neurosecretory cells, is readily apparent in these cells. The cells show no spontaneous synaptic activity, but appear to be excited by a unitary source. Stimulation of lateral or medial giant axons, which excite serotonergic cells yielded no response in octopaminergic neurosecretory cells and no evidence for direct interactions between pairs of octopamine neurons, or between the octopaminergic and the serotonergic sets of neurosecretory neurons was found.     

A familial mutation in the testis-determining gene SRY shared by both sexes

A familial mutation in SRY, the gene coding for the testis-determining factor TDF, was identified in an XY female with gonadal dysgenesis, her father, her two brothers and her uncle. The mutation consists of a T to C transition in the region of the SRY gene coding for a protein motif known as the high mobility group (HMG) box, a protein domain known to confer DNA-binding specificity on the SRY protein. This point mutation results in the substitution, at amino acid position 109, of a serine residue for phenylalanine, a conserved aromatic residue in almost all HMG box motifs known. This F109S mutation was not found in 176 male controls. When recombinant wildtype SRY and SRY^F109S mutant protein were tested in vitro for binding to the target site AAC AAAG, no differences in DNA-binding activity were observed. These results imply that the F109S mutation either is a rare neutral sequence variant, or produces an SRY protein with slightly altered in vivo activity, the resulting sex phenotype depending on the genetic back-ground or environmental factors.This paper is dedicated by G. S. to Professor Ulrich Wolf on the occasion of his 60th birthday     

Signatures of seaway closures and founder dispersal in the phylogeny of a circumglobally distributed seahorse lineage

Background  

The importance of vicariance events on the establishment of phylogeographic patterns in the marine environment is well documented, and generally accepted as an important cause of cladogenesis. Founder dispersal (i.e. long-distance dispersal followed by founder effect speciation) is also frequently invoked as a cause of genetic divergence among lineages, but its role has long been challenged by vicariance biogeographers. Founder dispersal is likely to be common in species that colonize remote habitats by means of rafting (e.g. seahorses), as long-distance dispersal events are likely to be rare and subsequent additional recruitment from the source habitat is unlikely. In the present study, the relative importance of vicariance and founder dispersal as causes of cladogenesis in a circumglobally distributed seahorse lineage was investigated using molecular dating. A phylogeny was reconstructed using sequence data from mitochondrial and nuclear markers, and the well-documented closure of the Central American seaway was used as a primary calibration point to test whether other bifurcations in the phylogeny could also have been the result of vicariance events. The feasibility of three other vicariance events was explored: a) the closure of the Indonesian Seaway, resulting in sister lineages associated with the Indian Ocean and West Pacific, respectively; b) the closure of the Tethyan Seaway, resulting in sister lineages associated with the Indo-Pacific and Atlantic Ocean, respectively, and c) continental break-up during the Mesozoic followed by spreading of the Atlantic Ocean, resulting in pairs of lineages with amphi-Atlantic distribution patterns.     

Kinetics of Oxygen Release from ORC

Oxygen release compounds (ORC) are one possibility to enhance aerobic degradation in contaminated aquifers. However, some applications have been reported where oxygen concentrations did not meet expectations, this was attributed to ground water composition, e.g., high pH. Column experiments have been performed and the measurements were interpreted using a numerical model to investigate oxygen release kinetics from ORC in more detail. Because the zero-order rate law recommended by the manufacturer did not reflect the measurements, a more complex kinetic scheme was developed. The simulations show a minor influence of inorganic ground water constituents on oxygen release from ORC in the columns due to buffering by mineral precipitation, but an enhanced oxygen release if aerobic degradation takes place. If ORC is applied as socks, the impact of inorganic ground water composition increases compared to the application in column experiments. A simple quadratic equation is provided to estimate oxygen release rate from the buffer capacity of the ground water versus increasing pH—a parameter easily determinable in the laboratory. For slightly mineralized waters with high pH, this equation forecasts decreased oxygen release, but no total inhibition of oxygen release.     

Cell adhesion molecule in the hexactinellid Aphrocallistes vastus

Abstract. The Hexactinellida sponge Aphrocallistes vastus contains a soluble aggregation factor (AF) whose purification has been described in this communication. It is characterized by a S°_20.w value of 37 and a buoyant density of 1.45 g/cm³. The AF is a glycoporteinaceous particle composed of three major protein species; no core structure could be visualized. In the presence of Ca²⁺, the AF causes secondary aggregation of single cells. The aggregation process is temperature, pH, and ionic strength independent within a broad range. Evidence is presented indicating that two (or more) AF molecules are required for the establishment of a stable cell: cell interaction. In contrast to the AFs from demosponges, the hexactinellid AF functions species-unspecifically.     

Maximum Likelihood Estimation of Genetic Parameters in Cell Populations

In this paper we consider a cell population such as bacteria consisting of two types of cells, mutant and nonmutant. Under the mutation and homogeneous pure birth processes, this paper derives a maximum likelihood estimation procedure for estimating mutation rate and birth rate. The method is applied to Newcombe's data; further some Monte Carlo studies are generated. The numerical results indicate that the method is quite efficient for estimating genetic parameters in cell populations.     

LATERAL CYSTS AND FISTULAS OF THE NECK

The embryonic origin of lateral cysts and fistulas remains controversial. They are, however, located in the general anatomic pattern of the embryonic thymic duct, which starts in the lateral pharyngeal wall and passes under the sternomastoid muscle to enter the mediastinum. The cyst is a unilocular, semiattached, non-translucent mass which has a tendency to become infected in 30 per cent of cases.The preauricular sinus occurs in front of the ear and is due either to a branchial cleft or an inclusion of one of the six primitive buds which form the external ear.Cystic hygroma is due to sequestrated lymphatic channels. These are always multilocular and rather invasive and may extend into mediastinum and arms.Diagnosis and treatment are considered in this presentation.