An analysis of theoretical systems of differentiating nervous tissue

Theoretical systems of neuroblasts differentiating according to various postulates are studied. The analysis determines the most likely patterns of connections implied by the differentiating systems. The exact expressions for the various parameters characterizing the resulting neural networks are approximated by simple analytic expressions which hold for systems having large numbers of neurons. The study is presented as a suggested approach to the more general problem of differentiating nervous systems.     

Malaria infection negatively affects feather growth rate in the house sparrow Passer domesticus

Birds often face various stressors during feather renewing, for example, enduring infection with blood parasites. Because nutritional resources are typically limited, especially for wild animals, when an individual allocates energy to one physiological system, there is subsequently less for other processes, thereby requiring a trade‐off. Surprisingly, potential trade‐offs between malaria infection and feather growth rate have not been experimentally considered yet. Here, we conducted three studies to investigate whether a trade‐off occurs among feather growth rate, malaria infection and host health conditions. First, we explored whether naturally infected and uninfected house sparrows differed in feather growth rate in the wild. Second, we asked whether experimental inoculation of malaria parasites and/or forcing the renewal of a tail feather. Lastly, we evaluated whether individual condition was affected by experimentally‐induced feather regrowth and/or malaria experimental infection. Our findings showed that feather growth rate was negatively affected by natural malaria infection status in free‐living birds and by experimental infection in captive birds. Furthermore, birds that did not increase body mass or hematocrit during the experimental study had slower feather growth. Together our results suggest that infection with blood parasites has more negative health effects than the growth of tail feathers and that these two processes (response to blood parasite infection and renewal of feathers) are traded‐off against each other. As such, our results highlight the role of malaria parasites as a potential mechanism driving other trade‐offs in wild passerines.     

Most stomatal closure in woody species under moderate drought can be explained by stomatal responses to leaf turgor

Reduced stomatal conductance (g_s) during soil drought in angiosperms may result from effects of leaf turgor on stomata and/or factors that do not directly depend on leaf turgor, including root‐derived abscisic acid (ABA) signals. To quantify the roles of leaf turgor‐mediated and leaf turgor‐independent mechanisms in g_s decline during drought, we measured drought responses of g_s and water relations in three woody species (almond, grapevine and olive) under a range of conditions designed to generate independent variation in leaf and root turgor, including diurnal variation in evaporative demand and changes in plant hydraulic conductance and leaf osmotic pressure. We then applied these data to a process‐based g_s model and used a novel method to partition observed declines in g_s during drought into contributions from each parameter in the model. Soil drought reduced g_s by 63–84% across species, and the model reproduced these changes well (r² = 0.91, P < 0.0001, n = 44) despite having only a single fitted parameter. Our analysis concluded that responses mediated by leaf turgor could explain over 87% of the observed decline in g_s across species, adding to a growing body of evidence that challenges the root ABA‐centric model of stomatal responses to drought.     

A sixth‐level habitat cascade increases biodiversity in an intertidal estuary

Many studies have documented habitat cascades where two co‐occurring habitat‐forming species control biodiversity. However, more than two habitat‐formers could theoretically co‐occur. We here documented a sixth‐level habitat cascade from the Avon‐Heathcote Estuary, New Zealand, by correlating counts of attached inhabitants to the size and accumulated biomass of their biogenic hosts. These data revealed predictable sequences of habitat‐formation (=attachment space). First, the bivalve Austrovenus provided habitat for green seaweeds (Ulva) that provided habitat for trochid snails in a typical estuarine habitat cascade. However, the trochids also provided habitat for the nonnative bryozoan Conopeum that provided habitat for the red seaweed Gigartina that provided habitat for more trochids, thereby resetting the sequence of the habitat cascade, theoretically in perpetuity. Austrovenus is here the basal habitat‐former that controls this “long” cascade. The strength of facilitation increased with seaweed frond size, accumulated seaweed biomass, accumulated shell biomass but less with shell size. We also found that Ulva attached to all habitat‐formers, trochids attached to Ulva and Gigartina, and Conopeum and Gigartina predominately attached to trochids. These “affinities” for different habitat‐forming species probably reflect species‐specific traits of juveniles and adults. Finally, manipulative experiments confirmed that the amount of seaweed and trochids was important and consistent regulators of the habitat cascade in different estuarine environments. We also interpreted this cascade as a habitat‐formation network that describes the likelihood of an inhabitant being found attached to a specific habitat‐former. We conclude that the strength of the cascade increased with the amount of higher‐order habitat‐formers, with differences in form and function between higher and lower‐order habitat‐formers, and with the affinity of inhabitants for higher‐order habitat‐formers. We suggest that long habitat cascades are common where species traits allow for physical attachment to other species, such as in marine benthic systems and old forest.     

Exploring anaerobic environments for cyanide and cyano-derivatives microbial degradation

Applied Microbiology and Biotechnology - Cyanide is one of the most toxic chemicals for living organisms described so far. Its toxicity is mainly based on the high affinity that cyanide presents...     

Centaurea zlatiborensis (Asteraceae,Cardueae−Centaureinae), a new endemic species from Zlatibor mountain range,Serbia

A new species of Centaurea sect. Acrocentron (Cass.) DC. (Asteraceae) found growing in dry, steppe‐like habitats on the Zlatibor mountain in western Serbia is described as Centaurea zlatiborensis. This novelity is compared with all other species of C. sect. Acrocentron known from Serbia and a diagnistic key to these is provided. Centaurea zlatiborensis is morphologically close to C. calocephala Willd. but the stems are simple or sparsely branched with monocephalous branches and itis generally smaller in all plant parts. The most important difference is the appendage morphology where C. zlatiborenis has triangular, dark brown appendages with short fimbriae and appendages not completely covering the bracts.     

Quasi-periodic primary structructures of core proteins of human T-lymphotropic leukemia retroviruses

Summary Fourier analysis, previously introduced by Liquori et al. (1983, 1986), has been applied to the primary structures of two core proteins of human T-lymphotropic leukemia retroviruses HTLV-1 and HTLV-II. The resulting autocorrelation functions display striking patterns that can be interpreted in terms of an approximately fourfold quasi-periodicity of the primary structures.Self-alignments of the amino acid sequences containing a few gaps are consistent with the above finding and suggest that the tertiary structure of these two homologous core proteins contains alpha-helical and delta-helical segments, the latter being characteristic of the threefold helix present in collagen structure.Presented at the FEBS Symposium on Genome Organization and Evolution, held in Crete, Greece, September 1–5, 1986