Sexual Selection on male cuticular hydrocarbons via male-male competition and female choice.

Traditional views of sexual selection assumed that male-male competition and female mate choice work in harmony, selecting upon the same traits in the same direction. However, we now know that this is not always the case and that these two mechanisms often impose conflicting selection on male sexual traits. Cuticular hydrocarbons (CHCs) have been shown to be linked to both social dominance and male attractiveness in several insect species. However, although several studies have estimated the strength and form of sexual selection imposed on male CHCs by female mate choice, none have established whether these chemical traits are also subject to sexual selection via male-male competition. Using a multivariate selection analysis, we estimate and compare sexual selection exerted by male-male competition and female mate choice on male CHC composition in the broad-horned flour beetle Gnatocerus cornutus. We show that male-male competition exerts strong linear selection on both overall CHC abundance and body size in males, while female mate choice exerts a mixture of linear and nonlinear selection, targeting not just the overall amount of CHCs expressed but the relative abundance of specific hydrocarbons as well. We discuss the potential implications of this antagonistic selection with regard to male reproductive success.

Heavy metal pollution and co-selection for antibiotic resistance: A microbial palaeontology approach.

Frequent and persistent heavy metal pollution has profound effects on the composition and activity of microbial communities. Heavy metals select for metal resistance but can also co-select for resistance to antibiotics, which is a global health concern. We here document metal concentration, metal resistance and antibiotic resistance along a sediment archive from a pond in the North West of the United Kingdom covering over a century of anthropogenic pollution. We specifically focus on zinc, as it is a ubiquitous and toxic metal contaminant known to co-select for antibiotic resistance, to assess the impact of temporal variation in heavy metal pollution on microbial community diversity and to quantify the selection effects of differential heavy metal exposure on antibiotic resistance. Zinc concentration and bioavailability was found to vary over the core, likely reflecting increased industrialisation around the middle of the 20th century. Zinc concentration had a significant effect on bacterial community composition, as revealed by a positive correlation between the level of zinc tolerance in culturable bacteria and zinc concentration. The proportion of zinc resistant isolates was also positively correlated with resistance to three clinically relevant antibiotics (oxacillin, cefotaxime and trimethoprim). The abundance of the class 1 integron-integrase gene, intI1, marker for anthropogenic pollutants correlated with the prevalence of zinc- and cefotaxime resistance but not with oxacillin and trimethoprim resistance. Our microbial palaeontology approach reveals that metal-contaminated sediments from depths that pre-date the use of antibiotics were enriched in antibiotic resistant bacteria, demonstrating the pervasive effects of metal-antibiotic co-selection in the environment.

An empirical study of the power of the Terpstra-Jonckheere test using binary data.

A Monte-Carlo simulation is performed to evaluate the power of the Terpstra-Jonckheere test for monotonic trend as applied to binary data. The effects of the magnitude and shape of the underlying response and of varying the number of treatment levels for in vitro experiments in cytogenetics are examined. It is shown that choice of the number and spacing of the treatment levels can be critical factors in determining the power of the test. These findings indicate that selection of the proper experimental design is a very important step in the process of conducting a viable study.

Tissue mineral levels in victims of sudden infant death syndrome I. Toxic metals--lead and cadmium.

Lung, liver, kidney, and rib specimens were obtained at autopsy from 66 sudden infant death syndrome (SIDS) infants and 23 infants who died suddenly from other causes between the ages of 4-26 wk. Tissue levels of lead and cadmium were measured by atomic absorption spectroscopy and are expressed as microgram/g dry weight. Because these metals are cumulative with age in storage tissues, the levels were corrected for age (adjusted to age 13 wk). The SIDS liver and rib specimens contained significantly more lead than non-SIDS tissues (liver, 1.095 microgram/g versus 0.761 microgram/g, P less than 0.05; rib, 1.754 microgram/g versus 1.041 microgram/g, P less than 0.01, respectively). There were no significant differences in cadmium concentration between the SIDS and non-SIDS tissues. All four tissues showed significant increases with age in both lead and cadmium concentrations in SIDS. The increase in lung lead concentration with age was significantly greater in SIDS than in non-SIDS cases, P less than 0.05. In non-SIDS only kidney cadmium showed an increase with age (P less than 0.0001). These data collectively suggest an increased exposure of the SIDS infant to lead either prenatally and/or postnatally. Any physiologic effects of the increased tissue lead levels are unknown. They may be only a marker of the known epidemiology of SIDS.

Tissue mineral levels in victims of sudden infant death syndrome II. Essential minerals: copper, zinc, calcium, and magnesium.

Deficiencies of various vitamin and minerals per se have been suggested as possible causes of sudden infant death syndrome (SIDS). Further, a deficiency of essential minerals may lead to enhanced toxicity of toxic elements, in particular, lead and cadmium to explore the possibility of mineral deficiencies or interactions with the toxic metals, lead and cadmium, lung, liver, kidney, and rib specimens were obtained at autopsy from 66 SIDS infants and 23 infants who died suddenly from other cases. Tissue copper, zinc, calcium, and magnesium were measured by atomic absorption spectroscopy. No differences were found between SIDS and non-SIDS for any element in any tissue except for more magnesium in the liver (P less than 0.0001) and less copper in the lungs (P less than 0.02) in the SIDS group. Only sporadic interactions between toxic and essential elements could be found. We found no evidence of any essential mineral deficiencies per se or significant interactions of essential and toxic minerals that might potentiate the effects of toxic metals. The physiologic significance, if any, of the higher liver magnesium and lower lung copper found in SIDS is unclear.