Statistical convenience vs biological insight: consequences of data transformation for the analysis of fitness variation in heterogeneous environments

In plants, more favourable environmental conditions can lead to dramatic increases in both mean fitness and variance in fitness. This results in data that violate the equality-of-variance assumption of anova, a problem that most empiricists would address by log-transforming fitness values. Using heuristic data sets and simple simulations, we show that anova on log-transformed fitness consistently fails to match the outcome of selection in a heterogeneous environment or its sensitivity to environmental frequency. Only anova based on relative fitness within environments accurately predicts the sensitivity of genotype selection to the frequency of alternative environments. Parallel analyses of variance based on absolute fitness and relative fitness can bracket the expected success of alternative genotypes under hard and soft selection, respectively. For example, for Sinapis arvensis growing in full sun and partial shade treatments, families achieving high fitness in the best environment are favoured under hard selection, whereas soft selection favours different families that achieve consistently good performance across environments. Based on these findings, we recommend that log-transformation of fitness should no longer be standard practice in ecological genetics studies. Weighted anova is a preferable method for dealing with unequal variances, and investigators should also make greater use of techniques such as quantile regression or resampling to describe and evaluate fitness variation across heterogeneous environments.     

Coccidian assemblages in the Wyoming ground squirrel, Spermophilus elegans elegans.

One thousand nineteen Wyoming ground squirrels (Spermophilus elegans elegans) from 4 populations in southern Wyoming were examined for intestinal parasites. The most prevalent parasites were 6 species of coccidia: Eimeria beecheyi, Eimeria bilamellata, Eimeria callospermophili, Eimeria larimerensis, Eimeria morainensis, and Eimeria spermophili. Most ground squirrels harbored 2 or more species. This eimerian assemblage was present across populations and over years. Differences in the prevalence of infection were not found among host age classes or between sexes. The presence or absence of helminths was independent of the presence and absence of Eimeria. A log-linear model to test the independence of the distribution of Eimeria spp. among hosts revealed 3 significant positive associations, for E. bilamellata and E. beecheyi, E. morainesis and E. callospermophili, and E. larimerensis and E. bilamellata.     

Influence of the thromboxane-mimetic U-46619 and the prostacyclin metabolite 6-keto prostaglandin E1 on vasoconstriction induced by noradrenaline and 5-HT in rat mesenteric vasculature

The aim of this study was to investigate the effects of U-46619, a thromboxane A2-mimetic, and 6-keto prostaglandin E1 (6-keto PGE1) a biologically active metabolite of prostacyclin, on vasoconstrictor responses to noradrenaline and 5-hydroxytryptamine (5-HT). In vitro, U-46619 (3-100 nmol/l) amplified responses to both noradrenaline and 5-HT in a concentration-dependent manner. This effect was not caused by an increase in the affinity of the alpha-adrenoceptor for noradrenaline because U-46619 (100 nmol/l) did not alter the pA2 of phentolamine. In vivo, U-46619 (100 nmol/l) induced vasoconstriction and consequently significantly shifted the log-concentration-effect curves to noradrenaline and 5-HT upward in an additive manner. 6-Keto PGE1 (1 mumol/l) did not affect either perfusion pressure or vasoconstriction in response to noradrenaline in vivo. The study highlights some differences in responses between in vitro- and in vivo-perfused mesentery.     

pEOC01: a plasmid from Pediococcus acidilactici which encodes an identical streptomycin resistance (aadE) gene to that found in Campylobacter jejuni

The complete nucleotide sequence of pEOC01, a plasmid (11,661 bp) from Pediococcus acidilactici NCIMB 6990 encoding resistance to clindamycin, erythromycin, and streptomycin was determined. The plasmid, which also replicates in Lactococcus and Lactobacillus species contains 16 putative open reading frames (ORFs), including regions annotated to encode replication, plasmid maintenance and multidrug resistance functions. Based on an analysis the plasmid replicates via a theta replicating mechanism closely related to those of many larger Streptococcus and Enterococcus plasmids. Interestingly, genes homologous to a toxin/antitoxin plasmid maintenance system are present and are highly similar to the omega-epsilon-zeta operon of Streptococcus plasmids. The plasmid contains two putative antibiotic resistance homologs, an ermB gene encoding erythromycin and clindamycin resistance, and a streptomycin resistance gene, aadE. Of particular note is the aadE gene which holds 100% identity to an aadE gene found in Campylobacter jejuni plasmid but which probably originated from a Gram-positive source. This observation is significant in that it provides evidence for recent horizontal transfer of streptomycin resistance from a lactic acid bacterium to a Gram-negative intestinal pathogen and as such infers a role for such plasmids for dissemination of antibiotic resistance genes possibly in the human gut.     

Testosterone is positively associated with risk taking in the Iowa Gambling Task

The association between testosterone and economic risk is not well-understood and is understudied. The present study aimed to further characterize what if any relationship testosterone has with risky economic decisions. To do so, 154 participants (78 men) completed the Iowa Gambling Task (IGT) (Bechara et al., 1994) and also provided saliva samples, which were assayed for endogenous testosterone levels using radioimmunoassay. High-levels of endogenous testosterone were associated with choosing less frequently from advantageous IGT decks of cards, indicating greater risk taking. The data showed that the effects of testosterone on IGT performance were similar for men and women. High-testosterone women and high-testosterone men made riskier choices than their low-testosterone counterparts of the same sex, and this effect was pronounced in women. Thus, high levels of testosterone are associated with willingness to incur greater risk in both sexes.     

Use of immunohistochemistry to diagnose chytridiomycosis in dyeing poison dart frogs (Dendrobates tinctorius)

Chytridiomycosis, caused by Batrachochytrium dendrobatidis, is an emerging disease of both wild and captive amphibians, posing a threat to their survival in many parts of the world. As the disease can be difficult to diagnose on routine pathologic sections, the purpose of this study was to develop an additional method for visualization. To accomplish this, immunohistochemical staining was applied to histologic skin sections from four experimentally infected Dyeing poison dart frogs (Dendrobates tinctorius). Staining of the positive tissue sections was distinct and readily visualized, making this technique a valuable ancillary diagnostic test for this important disease.     

Chlortetracycline-resistant intestinal bacteria in organically raised and feral Swine

Organically raised swine had high fecal populations of chlortetracycline (CTC)-resistant (growing at 64 μg CTC/ml) Escherichia coli, Megasphaera elsdenii, and anaerobic bacteria. By comparison, CTC-resistant bacteria in feral swine feces were over 1,000-fold fewer and exhibited lower taxonomic diversity.