Adaptive Melanin Response of the Soil Fungus Aspergillus niger to UV Radiation Stress at “Evolution Canyon”, Mount Carmel, Israel

BACKGROUND:Adaptation is an evolutionary process in which traits in a population are tailored by natural selection to better meet the challenges presented by the local environment. The major discussion relating to natural selection concerns the portraying of the cause and effect relationship between a presumably adaptive trait and selection agents generating it. Therefore, it is necessary to identify trait(s) that evolve in direct response to selection, enhancing the organism's fitness. "Evolution Canyon" (EC) in Israel mirrors a microcosmic evolutionary system across life and is ideal to study natural selection and local adaptation under sharply, microclimatically divergent environments. The south-facing, tropical, sunny and xeric "African" slope (AS) receives 200%-800% higher solar radiation than the north-facing, temperate, shady and mesic "European" slope (ES), 200 meters apart. Thus, solar ultraviolet radiation (UVR) is a major selection agent in EC influencing the organism-environment interaction. Melanin is a trait postulated to have evolved for UV-screening in microorganisms. Here we investigate the cause and effect relationship between differential UVR on the opposing slopes of EC and the conidial melanin concentration of the filamentous soil fungus Aspergillus niger. We test the working hypothesis that the AS strains exhibit higher melanin content than strains from the ES resulting in higher UV resistance. METHODOLOGY/PRINCIPAL FINDINGS:We measured conidial melanin concentration of 80 strains from the EC using a spectrophotometer. The results indicated that mean conidial melanin concentration of AS strains were threefold higher than ES strains and the former resisted UVA irradiation better than the latter. Comparisons of melanin in the conidia of A. niger strains from sunny and shady microniches on the predominantly sunny AS and predominantly shady ES indicated that shady conditions on the AS have no influence on the selection on melanin; in contrast, the sunny strains from the ES displayed higher melanin concentrations. CONCLUSIONS/SIGNIFICANCE:We conclude that melanin in A. niger is an adaptive trait against UVR generated by natural selection

Ribosomal DNA polymorphism and its association with geographical and climatic variables in 27 wild barley populations from Jordan

Ribosomal DNA (rDNA) repeat unit length polymorphism was examined in 285 accessions of wild barley, Hordeum spontaneum C. Koch, which were collected from 27 locations across Jordan. As many as 19 spacer length variants (slvs) or rDNA alleles were available, which formed 70 slv phenotypes. The two missing alleles (098, 099) of the series (097, 100-118) and one additional allele 119 were also discovered in the present study thus raising the number of ribosomal slvs in barley to 24. Relatively more frequent rDNA alleles were analyzed in detail, and it was shown that they occurred non-randomly at locations with different environmental factors (annual rainfall, highest and lowest temperatures, altitude, longitude, latitude) and exhibited association with specific environments. Ecogeographical factors, rather than geographical factors per se, seem to affect the distribution of rDNA alleles. The present study thus demonstrates that rDNA repeat unit length polymorphism in some cases can be adaptive in nature

Spiny mice modulate eumelanin to pheomelanin ratio to achieve cryptic coloration in "evolution canyon," Israel.

Coat coloration in mammals is an explicit adaptation through natural selection. Camouflaging with the environment is the foremost evolutionary drive in explaining overall coloration. Decades of enquiries on this topic have been limited to repetitive coat color measurements to correlate the morphs with background/habitat blending. This led to an overwhelming endorsement of concealing coloration as a local phenotypic adaptation in animals, primarily rodents to evade predators. However, most such studies overlooked how rodents actually achieve such cryptic coloration. Cryptic coloration could be attained only through optimization between the yellow- to brown-colored "pheomelanin" and gray to black-colored "eumelanin" in the hairs. However, no study has explored this conjecture yet. "Evolution Canyon" (EC) in Israel is a natural microscale laboratory where the relationship between organism and environment can be explored. EC is comprised of an "African" slope (AS), which exhibits a yellow-brownish background habitat, and a "European" slope (ES), exhibiting a dark grayish habitat; both slopes harbor spiny mice (Acomys cahirinus). Here, we examine how hair melanin content of spiny mice living in the opposing slopes of EC evolves toward blending with their respective background habitat.We measured hair-melanin (both eumelanin and pheomelanin) contents of 30 spiny mice from the EC using high-performance liquid chromatography (HPLC) that detects specific degradation products of eumelanin and pheomelanin. The melanin pattern of A. cahirinus approximates the background color of the slope on which they dwell. Pheomelanin is slightly (insignificantly) higher in individuals found on the AS to match the brownish background, whereas individuals of the ES had significantly greater eumelanin content to mimic the dark grayish background. This is further substantiated by a significantly higher eumelanin and pheomelanin ratio on the ES than on the AS.It appears that rodents adaptively modulate eumelanin and pheomelanin contents to achieve cryptic coloration in contrasting habitats even at a microscale

Retrotransposon BARE-1 and its role in genome evolution in the genus Hordeum

The replicative retrotransposon life cycle offers the potential for explosive increases in copy number and consequent inflation of genome size. The BARE-1 retrotransposon family of barley is conserved, disperse, and transcriptionally active. To assess the role of BARE-1 in genome evolution, we determined the copy number of its integrase, its reverse transcriptase, and its long terminal repeat (LTR) domains throughout the genus Hordeum. On average, BARE-1 contributes 13.7 × 103 full-length copies, amounting to 2.9% of the genome. The number increases with genome size. Two LTRs are associated with each internal domain in intact retrotransposons, but surprisingly, BARE-1 LTRs were considerably more prevalent than would be expected from the numbers of intact elements. The excess in LTRs increases as both genome size and BARE-1 genomic fraction decrease. Intrachromosomal homologous recombination between LTRs could explain the excess, removing BARE-1 elements and leaving behind solo LTRs, thereby reducing the complement of functional retrotransposons in the genome and providing at least a partial “return ticket from genomic obesity.”The research reported here was supported by grants from the Academy of Finland Genome Research Program and the European Union Directorate for Biotechnology research program on Molecular Tools for Biodiversity. E.N. thanks the Israel Discount Bank Chair of Evolutionary Biology and the Ancell-Teicher Research Foundation for Genetics and Molecular Evolution for financial support.Peer reviewe

Eumelanin/Pheomelanin ratio of <i>A. cahirinus</i> from “Evolution Canyon” I, Israel.

<p>(A) in the opposite slopes, (B) across stations. Means with the same letter are not significantly different according to Waller-Duncan k-ratio t-test.</p

Contents of eumelanin and pheomelanin in hairs of spiny mice (<i>Acomys cahirinus</i>) from “Evolution Canyon” I, Israel.

<p>(A) in the opposite slopes, (B) across stations. Means with the same letter are not significantly different according to Waller-Duncan k-ratio t-test.</p