Some notes on the distribution and certain modifications of Mahalanobis' generalized distance (D)

Different modifications of Mahalanobis' generalized distance (D²) utilized in anthropological research are given, and it is shown that they all derive from the distribution of D² when the distances between the populations investigated are real. To investigate whether observed distances are real, testing of D² for significance is stressed. It is demonstrated that D² ought to be tested for significance according to its relation to the F-distribution, but that it may be related to the chi-squared distribution as an approximation when the numbers of individuals in the samples are very large. The great disadvantages of utilizing this approximation for smaller numbers of individuals in the samples are demonstrated, as well as the dependence of D² on sample size and the number of measurements used when testing for significance.     

Colostral Transfer in the Goat of Antibodies Against Corynebacterium Pseudotuberculosis and the Antibody Status of Kids During the First 10 Months of Life

Serum and colostrum samples from goats at parturition and serum samples from their kids at 3 days and at 4, 7, 10 and 12 weeks after birth were examined for the presence of antibodies to Corynebacterium pseudotuberculosis hemolysins. The hemolysis inhibition test (HIT) was used. High correlation was found between titre values of antihemolysins in serum and colostrum of goats at parturition (correlation coefficient r = 0.83; P < 0.01). Intermediate correlation was found between antihemolysin titre in colostrum of goats and in the sera of their kids 3 days old (r = 0.56; 0.01 < P < 0.05). Furthermore, titre values for 3 day-old kids showed high correlation with the antihemolysin titres when the kids aged 4 and 7 weeks (r = 0.76 and 0.85, respectively; P < 0.01). Antihemolysin titres decreased linearly in kids from 3 days to 10 weeks old. Calculated half life of antibodies was 12 days. Most of the kids had detectable antibodies up to the age of 5–6 weeks. None of the kids were seropositive at 2½ months of age. Serum samples collected monthly from a group of kids chosen at random, aged 7–10 months, contained antibodies to hemolysins in half of the animals at the first testing. At the age of 10 months 14 out of 15 kids were seropositive. Thus, most of the kids from this herd were exposed to G. pseudotuberculosis antigens during summer and autumn of their first year of life. Prophylactic measures against caseous lymphadenitis is briefly discussed.     

Model study of muscle spindles subjected to static fusimotor activation

An earlier proposed mechanical model of the de-efferented muscle spindle endings has been developed further in order to study whether the functional effects of activating the static fusimotor fibres may be accounted for by relatively simple mechanical events in the intrafusal muscle fibres. Particular attention has been paid to important controversial problems related to the processes involved in the fusimotor activation of the mammalian muscle spindles. In order to develop an adequate model, preliminary simulation studies of the functional effects of various reasonable modifications of the original “de-efferented” model were first carried out by means of a convenient direct electronic analogue of the mechanical system. The following results apparently reflect pertinent details about the peripheral receptor mechanisms associated with the activation of the static fusimotor fibres:

1. The γ _s-activation is most adequately accounted for by mechanical events occurring in the nuclear chain fibres.
2. Any uniform chain fibre contraction fails to account for the effects of the γ _s-activation.
3. The simulation of a local chain fibre contraction could apparently account for all significant effects of the γ _s-activation.
4. A reasonable increase of the position sensitivity and the vibration sensitivity of both the primary and the secondary endings could be accounted for by increasing the stiffness of about 1/4–1/2 of the length of the simulated nuclear chain fibre by a factor of about 2–10.
5. The powerful modulation of the background discharge of the receptor endings that is associated with the γ _s-activation could be accounted for by an independent contraction force related to the intensity of the static fusimotor activity.
6. The model predicts a decrease of the rate sensitivity of the primary endings (group Ia) and a slight increase of the (moderate) rate sensitivity of the secondary endings.
7. By an adequate selection of the parameters, the simulated γ _s-activation showed a negligible influence on the absolute level of the dynamic phase of the ramp response of the simulated primary endings, in spite of a considerable increase of the steady state (background) discharge before and after the termination of a simulated stretch.

     

Glacial survival may matter after all: nunatak signatures in the rare European populations of two west-arctic species

Biogeographers claimed for more than a century that arctic plants survived glaciations in ice-free refugia within the limits of the North European ice sheets. Molecular studies have, however, provided overwhelming support for postglacial immigration into northern Europe, even from the west across the Atlantic. For the first time we can here present molecular evidence strongly favouring in situ glacial persistence of two species, the rare arctic-alpine pioneer species Sagina caespitosa and Arenaria humifusa. Both belong to the 'west-arctic element' of amphi-Atlantic disjuncts, having their few and only European occurrences well within the limits of the last glaciation. Sequencing of non-coding regions of chloroplast DNA revealed only limited variation. However, two very distinct and partly diverse genetic groups, one East and one West Atlantic, were detected in each species based on amplified fragment length polymorphisms (AFLPs), excluding postglacial dispersal from North America as explanation for their European occurrences. Patterns of genetic diversity and distinctiveness indicate that glacial populations existed in East Greenland and/or Svalbard (A. humifusa) and in southern Scandinavia (S. caespitosa). Despite their presumed lack of long-distance dispersal adaptations, intermixed populations in several regions indicate postglacial contact zones. Both species are declining in Nordic countries, probably due to climate change-induced habitat loss. Little or no current connectivity between their highly fragmented and partly distinct populations call for conservation of several populations in each geographic region.     

Serum-Free and Xenobiotic-Free Preservation of Cultured Human Limbal Epithelial Cells

Aim/Purpose of the Study

To develop a one-week storage method, without serum and xenobiotics, that would maintain cell viability, morphology, and phenotype of cultured human limbal epithelial sheets.

Materials and Methods

Human limbal explants were cultured on intact human amniotic membranes for two weeks. The sheets were stored in a hermetically sealed container at 23°C in either a serum-free medium with selected animal serum-derived compounds (Quantum 286) or a xenobiotic-free medium (Minimal Essential Medium) for 4 and 7 days. Stored and non-stored cultures were analyzed for cell viability, amniotic membrane and epithelial sheet thickness, and a panel of immunohistochemical markers for immature cells (ΔNp63α, p63, Bmi-1, C/EBP∂, ABCG2 and K19), differentiated cells (K3 and Cx43), proliferation (PCNA), and apoptosis (Caspase-3).

Results

The cell viability of the cultures was 98 ± 1% and remained high after storage. Mean central thickness of non-stored limbal epithelial sheets was 23 ± 3 μm, and no substantial loss of cells was observed after storage. The non-stored epithelial sheets expressed a predominantly immature phenotype with ΔNp63α positivity of more than 3% in 9 of 13 cultures. After storage, the expression of ABCG2 and C/EBP∂ was reduced for the 7 day Quantum 286-storage group; (P = 0.04), and Bmi-1 was reduced after 4 day Quantum 286-storage; (P = 0.02). No other markers varied significantly. The expression of differentiation markers was unrelated to the thickness of the epithelia and amniotic membrane, apart from ABCG2, which correlated negatively with thickness of limbal epithelia (R = -0.69, P = 0.01) and ΔNp63α, which correlated negatively with amniotic membrane thickness (R = -0.59, P = 0.03).

Conclusion

Limbal epithelial cells cultured from explants on amniotic membrane can be stored at 23°C in both serum-free and xenobiotic-free media, with sustained cell viability, ultrastructure, and ΔNp63α-positivity after both 4 and 7 days.     

No difference found in ribosomal DNA sequences from physiologically diverse clones of Karenia brevis (Dinophyceae) from the Gulf of Mexico

Maximum growth rate and toxin content were significantly differentamong five strains of Karenia brevis isolated from Texas andFlorida when grown under identical culture conditions. Sequenceanalysis of the 18S rRNA gene and internal transcribed spacer(ITS) regions revealed, however, that all five strains wereidentical. Consequently, a clear genetic basis for physiologicalvariability among various geographical isolates of K. brevisfrom the Gulf of Mexico could not be assessed using these geneticmarkers. Both the ITS and 18S rRNA regions may be useful inspecies-specific probe selection. At the intra-specific level,however, an alternative marker will be needed to assess thediversity among K. brevis populations in the Gulf of Mexico.     

Encounter frequencies between GPS-collared wolves (Canis lupus) and moose (Alces alces) in a Scandinavian wolf territory

Over 6,000 GPS fixes from two wolves (Canis lupus) and 30,000 GPS fixes from five moose (Alces alces) in a wolf territory in southern Scandinavia were used to assess the static and dynamic interactions between predator and prey individuals. Our results showed that wolves were closer to some of the moose when inside their home ranges than expected if they had moved independently of each other, and we also found a higher number of close encounters (<500 m) than expected. This suggests that the wolves were actively seeking the individual moose within their territory. Furthermore, the wolves showed a preference for moving on gravel forest roads, which may be used as convenient travel routes when patrolling the territory and seeking areas where the moose are. However, due to the particularly large size of the wolf territory combined with relatively high moose densities, the wolves generally spent a very small proportion of their time inside the home range of each individual moose, and the frequency of encounters between the wolves and any particular moose was very low. We suggest that the high moose:wolf ratio in this large Scandinavian wolf territory compared to that typically occurring in North America, results in a relatively low encounter frequency and a low predation risk for individual moose, as the predation pressure is spread over a high number of prey individuals.     

Model study of muscle spindle primary endings subjected to dynamic fusimotor activation

An earlier proposed model of the de-efferented muscle spindle mechano-receptors has been developed further to simulate the effects of the dynamic fusimotor ( _D) activation of the group Ia afferents (primary endings).The rate sensitivity of the original second order receptor model might be increased simply by increasing the overall viscous damping of the simulated polar regions of the nuclear bag fibre. However, adequate simulation of the typical time course of the stretch response of the primary endings during _D-activation required a subdivision of the polar regions into an active and a passive part. A reasonable behaviour of the model was obtained by simulating a local contraction covering about 50–90% of the polar regions of the nuclear bag fibres.The ramp response of the model showed a quick rate response component that increased by increasing the rate of the simulated stretch. This component was not significantly influenced by the simulated _D-activation.A slow rate component appeared to increase approximately in the same proportion as the intensity of the simulated _D-activation.The behaviour of the model closely corresponds to that of the biological prototype. The study demonstrates that the electrophysiological effects of activating the dynamic fusimotor fibres are indeed compatible with peripheral mechanical events associated with contraction phenomena within the polar regions of the nuclear bag intrafusal muscle fibres.     

A second order mechanical model of muscle spindle primary endings

Summary With reference to experimental data and the failure of earlier proposed first order linear models of mammalian muscle spindles, a second order mechanical model of de-efferented primary endings is studied. The model takes into account the presence of two different types of intrafusal muscle fibres in a complete spindle organ. It further allows the incorporation of different gain of the mechano-electric conversion into a depolarization of the sensory terminals innervating the two types of fibres.It is shown that a closer approximation to the behaviour of the biological prototype is obtained if the transducer gain of the branch corresponding to the nuclear bag intrafusal fibres is chosen significantly higher than that corresponding to the nuclear chain branch.The marked nonlinear behaviour of muscle spindle primary endings as recently reported by Matthews and Stein (1968, 1969) is interpreted as a saturation effect of the high gain mechano-electric transducer of the nuclear bag branch. The saturation is considered to reflect a condition of complete depolarization of these sensory terminals. If a higher transducer gain actually is present, a complete depolarization of these terminals would occur at a lower degree of mechanical deformation than for the nuclear chain terminals. The mechano-electric transducer system of the nuclear chain fibres might thus behave approximately linearly within a larger range of input amplitudes. The greatly reduced gain of the primary endings at large emplitudes of imposed muscle vibrations as observed experimentally (Matthews and Stein, 1968, 1969) may thus be accounted for by the transducer gain of the nuclear chain fibres alone.List of Symbols Used C Viscous stiffness, or electrical capacitance - f Frequency of a signal - K Static gain of a system - k Elastic stiffness - R Electrical resistance - s The Laplace operator - H(s) General transfer function of a system - X (s) Laplace transform of the difference between instantanous and resting length of the complete intrafusal muscle fibre, according to the suggested model shown in Fig. 2 - (s) Laplace transform of the length of the elastic component of the proposed Maxwell branch of the sensory region of the model - (s) Laplace transform of the difference between instantanous and resting length of the lumped model of the polar (non-sensory) region of the intrafusal fibres - (s) Laplace transform of the length of the purely elastic branch of the model - The transducer gain of the output from the -branch relative to that of the -branch - v(s) Laplace transform of the total output signal (s) + (s) - Time constant defined by or =RC for the mechanical and the electrical system respectively - Angular frequency equal to 2f - Rate constant describing the relation between the lead and the lag time constant of a first order lead-lag filter network