Flooding and soil composition determine beta diversity of lowland forests in Northern South America

Beta diversity may be determined by dispersal limitation, environment, and phylogeographic history. Our objective was to advance the understanding of plant species turnover in rain forests in northern South America and determine which factors are affecting species beta diversity. We evaluated the relative effect of environmental variables (i.e., soil, climate, fragmentation, and flooding frequency) and dispersal limitation (i.e., geographical distance and resistance distance due mountain barriers) on tree beta diversity in 32 1‐ha lowland forest plots. We found that tree species turnover was better explained by environmental distance than by geographical distance. Although soil conditions and flooding regime were good predictors of tree species composition, almost half of the variance remained unexplained. In our study system, the eastern Andean ridge had no significant effect on plant beta diversity, probably because of its young age in relation to the phylogeny. Our results provide support for the importance of environmental factors and suggest a more restricted role of dispersal limitation. Therefore, we advise that conservation strategies of lowland trees should consider specific forest types (e.g., seasonally flooded vs. terra firme, as well as piedmont vs. central Amazonian forests).     

Genes as Cues of Relatedness and Social Evolution in Heterogeneous Environments

There are many situations where relatives interact while at the same time there is genetic polymorphism in traits influencing survival and reproduction. Examples include cheater-cooperator polymorphism and polymorphic microbial pathogens. Environmental heterogeneity, favoring different traits in nearby habitats, with dispersal between them, is one general reason to expect polymorphism. Currently, there is no formal framework of social evolution that encompasses genetic polymorphism. We develop such a framework, thus integrating theories of social evolution into the evolutionary ecology of heterogeneous environments. We allow for adaptively maintained genetic polymorphism by applying the concept of genetic cues. We analyze a model of social evolution in a two-habitat situation with limited dispersal between habitats, in which the average relatedness at the time of helping and other benefits of helping can differ between habitats. An important result from the analysis is that alleles at a polymorphic locus play the role of genetic cues, in the sense that the presence of a cue allele contains statistical information for an organism about its current environment, including information about relatedness. We show that epistatic modifiers of the cue polymorphism can evolve to make optimal use of the information in the genetic cue, in analogy with a Bayesian decision maker. Another important result is that the genetic linkage between a cue locus and modifier loci influences the evolutionary interest of modifiers, with tighter linkage leading to greater divergence between social traits induced by different cue alleles, and this can be understood in terms of genetic conflict.     

Robust calling performance in frogs infected by a deadly fungal pathogen

Reproduction is an energetically costly behavior for many organisms, including species with mating systems in which males call to attract females. In these species, calling males can often attract more females by displaying more often, with higher intensity, or at certain frequencies. Male frogs attract females almost exclusively by calling, and we know little about how pathogens, including the globally devastating fungus, Batrachochytrium dendrobatidis, influence calling effort and call traits. A previous study demonstrated that the nightly probability of calling by male treefrogs, Litoria rheocola, is elevated when they are in good body condition and are infected by B. dendrobatidis. This suggests that infections may cause males to increase their present investment in mate attraction to compensate for potential decreases in future reproduction. However, if infection by B. dendrobatidis decreases the attractiveness of their calls, infected males might experience decreased reproductive success despite increases in calling effort. We examined whether calls emitted by L. rheocola infected by B. dendrobatidis differed from those of uninfected individuals in duration, pulse rate, dominant frequency, call rate, or intercall interval, the attributes commonly linked to mate choice. We found no effects of fungal infection status or infection intensity on any call attribute. Our results indicate that infected males produce calls similar in all the qualities we measured to those of uninfected males. It is therefore likely that the calls of infected and uninfected males should be equally attractive to females. The increased nightly probability of calling previously demonstrated for infected males in good condition may therefore lead to greater reproductive success than that of uninfected males. This could reduce the effectiveness of natural selection for resistance to infection, but could increase the effectiveness of selection for infection tolerance, the ability to limit the harm caused by infection, such as reductions in body condition.     

Purification and properties of calf liver γ-butyrobetaine hydroxylase

Calf liver γ-butyrobetaine hydroxylase has been purified some 400-fold by DEAE, gel permeation, and hydroxylapatite chromatography. The homogeneous enzyme is a dimer of 46,000-dalton subunits. The K_m values for substrates and cofactors and the apparent activation constants for ascorbate and catalase have been determined. Inhibition of the enzyme by a number of divalent metals supports the function of sulfhydryl groups in metal binding. An antibody to the enzyme has been obtained; this does not cross-react with homogeneous γ-butyrobetaine hydroxylase from a Pseudomonas strain. The antibody, coupled to Sepharose 4B, has been used to purify the calf liver hydroxylase 350-fold in one step.     

Immunogold identification of the somatotrophs of domestic fowl of different ages

Summary The somatotrophs of the pituitary gland of the male domestic fowl were identified by means of an immuno-electron-microscopic method based on gold as the electron-opaque label and an antibody to growth hormone. Gold particles indicating sites of growth hormone were restricted to cells in which virtually all of the granules were labelled. Little, if any, gold label was found outside the granules in these cells designated as somatotrophs, or at sites outside these cells. The size of these gold-labelled secretory granules presumed to contain growth hormone decreased with age, from a mean sectional diameter of 256±6.2 nm (SEM) at 4–6 weeks to 221±5.7 nm at 11–18 weeks and 205±8.6 nm at 24–30 weeks of age. On the basis of these values for mean sectional diameters the change between the first two periods represents a decrease in granule volume of about 36%. However, during the same period the growth hormone concentration of the granules increased. Accordingly, growth hormone content per granule changed little if at all. In contrast, from 11–18 weeks to 24–30 weeks of age there was a decrease of 31% in growth hormone content per granule. These data indicate that growth hormone packaging in the chicken somatotroph changes with age. The first change results in the production of smaller granules of higher growth hormone concentration. During this period growth hormone content per granule remains relatively constant. The later change results in the production of granules of lower growth hormone content than that of younger animals.This is a paper of the Journal Sciences, New Jersey Agriculture Experimental Station supported in part by the State and Hatch Act Funds and a grant from the National Science Foundation (PMC-8022727)     

Fine structure of trypsin-dissociated rat adrenal cells

Summary Electron micrographs of trypsin-dissociated rat adrenal showed predominantly intact rounded cells without internal damage. The population contained cells from the glomerular, intermediary and fascicular zones with cells from the zona fasciculata predominant. The presence or absence of cells from the reticular zone could not be determined. Cells from the medullary zone were absent. The addition of adrenocorticotropic hormone (ACTH) to the cellular suspension for 2 hours produced corticosterone. However, these stimulated cells did not display any significant ultrastructural change.Supported by research grants from the U.S.P.H.S. (No. GM15872), and the Research Council of Rutgers University, and the National Science Foundation (No. GB7427 to Dr. George Sayers). We are indebted to Mrs. Jean A. Gibney, Miss Rose-Marie Ma, and Mrs. Mary Vegh for their excellent technical assistance.Postdoctoral Trainee, U.S.P.H.S. Training Grant No. 5T01-GM00899-11.     

Lack of light colour effects when sampling fish at night in low visibility environments

We compared night deployments of Baited Remote Underwater Video Stations (BRUVS) in South Australia, illuminated by either red or blue light and found similar species compositions and abundances with both colours. We observed c. 1800 individuals from 52 species across 107 night-time deployments, with only one site out of six showing differences in assemblages between the two colours. With five out of six sites showing similarities between light colours our results differ from previous results and more generally suggest that the most suitable colour can differ among studies.     

Postembryonic establishment of megabase-scale gene silencing in nucleolar dominance

Nucleolar dominance is an epigenetic phenomenon in plant and animal genetic hybrids that describes the expression of 45S ribosomal RNA genes (rRNA genes) inherited from only one progenitor due to the silencing of the other progenitor's rRNA genes. rRNA genes are tandemly arrayed at nucleolus organizer regions (NORs) that span millions of basepairs, thus gene silencing in nucleolar dominance occurs on a scale second only to X-chromosome inactivation in female mammals. In Arabidopsis suecica, the allotetraploid hybrid of A. thaliana and A. arenosa, the A. thaliana -derived rRNA genes are subjected to nucleolar dominance and are silenced via repressive chromatin modifications. However, the developmental stage at which nucleolar dominance is established in A. suecica is currently unknown. We show that nucleolar dominance is not apparent in seedling cotyledons formed during embryogenesis but becomes progressively established during early postembryonic development in tissues derived from both the shoot and root apical meristems. The progressive silencing of A. thaliana rRNA genes correlates with the transition of A. thaliana NORs from a decondensed euchromatic state associated with histone H3 that is trimethylated on lysine 4 (H3K4me3) to a highly condensed heterochromatic state in which the NORs are associated with H3K9me2 and 5-methylcytosine-enriched chromocenters. In RNAi-lines in which the histone deacetylases HDA6 and HDT1 are knocked down, the developmentally regulated condensation and inactivation of A. thaliana NORs is disrupted. Collectively, these data demonstrate that HDA6 and HDT1 function in the postembryonic establishment of nucleolar dominance, a process which recurs in each generation.