The existence of males and females, which are often strikingly different in morphology, reproductive strategies and behavior, is one of the most widespread phenomena in biology. However, the genetic mechanisms that generate this ubiquitous pattern are surprisingly diverse and do not follow a phylogenetic pattern. Sex-determination mechanisms can differ between even closely related species and arise frequently and independently. Fish provide a paradigmatic example, as their sex-determination mechanisms range from environmental to different modes of genetic determination. The evolutionary meaning of this remarkable plasticity is unknown. For genetic sex determination, where the trigger for female or male development comes from the genetic constitution of the individual, the evolution of sex-determination mechanisms is connected to a very peculiar genomic process, namely the formation of sex chromosomes [1][2][3][4] .To improve understanding of the function and evolution of sex chromosomes, their genetic organization must be deciphered.However, owing to their degenerate nature and high repetitive DNA content, sex chromosomes pose almost insurmountable problems in deciphering their gene content and organization. So far, only the human 5 , chimpanzee 6 and rhesus macaque Y chromosomes 7 and the male-specific region on the Y chromosome of one fish, the medaka 8 , have been sequenced. These analyses have nevertheless provided important insights into the evolution of Y chromosomes, their genomic organization and their degeneration processes, as well as predictions as to their likely evolutionary fate 9-12 .Much less genomic information exists on W chromosomes because, as with Y chromosomes, they are predominantly highly repetitive in nature. The prevailing theory of the evolution of sex chromosomes predicts that degeneration of the heterogametic sex chromosome is a stepwise process that occurs over an extended period of time. We therefore reasoned that an evolutionarily young W chromosome Whole-genome sequence of a flatfish provides insights into ZW sex chromosome evolution and adaptation to a benthic lifestyle Genetic sex determination by W and Z chromosomes has developed independently in different groups of organisms. To better understand the evolution of sex chromosomes and the plasticity of sex-determination mechanisms, we sequenced the whole genomes of a male (ZZ) and a female (ZW) half-smooth tongue sole (Cynoglossus semilaevis). In addition to insights into adaptation to a benthic lifestyle, we find that the sex chromosomes of these fish are derived from the same ancestral vertebrate protochromosome as the avian W and Z chromosomes. Notably, the same gene on the Z chromosome, dmrt1, which is the male-determining gene in birds, showed convergent evolution of features that are compatible with a similar function in tongue sole. Comparison of the relatively young tongue sole sex chromosomes with those of mammals and birds identified events that occurred during the early phase of sex-chromosome evolution. Pertinent to...

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As the lowest point in the surrounding landscape, lakes act as sensors in the landscape to provide insights into the response of both terrestrial and aquatic ecosystems to climate change. Here a novel suite of climate forcing optical indices (CFOI) from lakes across North America is found to respond to changes in air temperature, precipitation, and solar radiation at timescales ranging from a single storm event to seasonal changes to longerterm interdecadal trends with regression r 2 values ranging from 0.73 to 0.89. These indices are based on two optical metrics of dissolved organic carbon (DOC) quality: DOC specific absorbance (a* 320 ) and spectral slope (S 275-295 ), where the ratio a* 320 to S 275-295 gives a composite climate forcing index. These indices of DOC quality are more responsive to climate forcing than is DOC concentration. A similar relationship between the component indices a* 320 and S 275-295 is observed across a wide range of lake types. A conceptual model is used to examine the similarities and differences in DOC-related mechanisms and ecological consequences due to increased temperature vs. precipitation. While both warmer and wetter conditions increase thermal stratification, these two types of climate forcing will have opposite effects on water transparency as well as many ecological consequences, including oxygen depletion, the balance between autotrophy and heterotrophy, and depth distributions of phytoplankton and zooplankton.

Integrated multi-trophic aquaculture (IMTA) involves the farming of species from different trophic positions or nutritional levels in the same system. In China, IMTA has been practiced for many decades, with dozens of species farmed in close proximity to each other at the scale of whole coastal bays. Articles in this Theme Section present results from the MoST-China Project on 'Sustainability of Marine Ecosystem Production under Multi-stressors and Adaptive Management ' (2011−2015). This project sought to understand the interactions between biogeochemical cycles and ecosystem function in the IMTA system of Sanggou Bay, China, which produces a total of > 240 000 t of seafood each year from > 30 species in approximately 100 km 2 of production space. Results include measurements of carbon, nitrogen flow and trophic relationships among cultured species; impacts of IMTA on benthic nutrient fluxes, reduced inorganic sulfur in sediments, distribution of dissolved inorganic selenium, and nutrient cycling; distribution and seasonal variation of picoplankton; and a model for kelp growth. Combined, the articles enable a complex understanding of the dynamics between IMTA and the environment in one of the most important coastal aquaculture production systems in the world.

We obtained and analyzed whole genome data for more than 160 representatives of skipper butterflies (family Hesperiidae) from all known subfamilies, tribes and most distinctive genera. We found that two genera, Katreus Watson, 1893 and Ortholexis Karsch, 1895, which are sisters, are well-separated from all other major phylogenetic lineages and originate near the base of the Hesperiidae tree, prior to the origin of some subfamilies. Due to this ancient origin compared to other subfamilies, this group is described as Katreinae Grishin, subfam. n. DNA sequencing of primary type specimens reveals that Ortholexismelichroptera Karsch, 1895 is not a female of Ortholexisholocausta Mabille, 1891, but instead a female of Ortholexisdimidia Holland, 1896. This finding establishes O.dimidia as a junior subjective synonym of O.melichroptera. Furthermore, we see that Chamunda Evans, 1949 does not originate within Pyrginae Burmeister, 1878, but, unexpectedly, forms an ancient lineage of its own at the subfamily rank: Chamundinae Grishin, subfam. n. Finally, a group of two sister genera, Barca de Nicéville, 1902 and Apostictopterus Leech, [1893], originates around the time Hesperiinae Latreille, 1809 have split from their sister clade. A new subfamily Barcinae Grishin, subfam. n. sets them apart from all other Hesperiidae.