Chromosome evolution presents an enigma in the mega-diverse Lepidoptera. Most species exhibit constrained chromosome evolution with nearly identical haploid chromosome counts and chromosome-level gene collinearity among species more than 140 million years divergent. However, a few species possess radically inflated chromosomal counts due to extensive fission and fusion events. To address this enigma of constraint in the face of an exceptional ability to change, we investigated an unprecedented reorganization of the standard lepidopteran chromosome structure in the green-veined white butterfly (Pieris napi). We find that gene content in P. napi has been extensively rearranged in large collinear blocks, which until now have been masked by a haploid chromosome number close to the lepidopteran average. We observe that ancient chromosome ends have been maintained and collinear blocks are enriched for functionally related genes suggesting both a mechanism and a possible role for selection in determining the boundaries of these genome-wide rearrangements.

<p>In the Mediterranean region climate and other environmental changes have become major threats to both ecosystems and human wellbeing. Climate change is expected to be the most important threat to biodiversity in the Mediterranean over the next 10 years, followed by habitat degradation, exploitation, pollution, eutrophication and invasion of species and the loss of biodiversity. Climate change interacts with other environmental problems in the Mediterranean Basin, resulting from land use, pollution and biodiversity loss. The nature of the semi-enclosed Mediterranean Sea implies unique physiographic and ecological features. The Mediterranean Sea is considered as one of the hotspots of global biodiversity where the impact of climate change associated with other anthropogenic pressures could be the most destructive. Although it represents only 0.8% of the world's ocean surface, it is home to between 4 and 18% of the world's marine species.</p><p>The Mediterranean region is particularly vulnerable because it cumulates environmental risks, including strong warming and drying, accelerating sea-level, rapid urbanization, increasing pollution of the air and the water, and the impacts of mass tourism. Ecosystems suffer from land degradation including the loss of half of the wetlands, overfishing (20% of fish species are at risk of extinction by 2050), non-sustainable agriculture, wildfires (burnt area may double by 2100) and the invasion of non-indigenous species (‘tropicalization’). These factors strongly impact water resources, biodiversity on land and in the ocean, human health and security.</p><p>The effects of climate change in the Mediterranean basin are asymmetric. In the northern and western part of the Mediterranean, situation is heterogeneous, but historical responsibility of greenhouse emissions since industrial revolution is objectively higher than in southern and eastern part. The EU counties are facing impacts of climate change but societies are less vulnerable.  Most countries located in the Southern and Eastern Mediterranean suffer the consequences of climate change with greater effects. Climate change can be an added challenge, when a country is already facing structural issues of poverty rate, weakness of infrastructure and social services, critical demographic changes, high unemployment, economic informality and emigration, political instability, corruption and spatial inequality with fast urbanization. All Mediterranean countries are nevertheless facing cross-cutting common issues, such as biodiversity preservation, sustainable development of tourism, commercial links related to food production and consumption, stock of fishes, blue carbon, energy production, political stability, migrations and security. Their interests are linked, because their share a common resource.</p><p>The adaptive capacity of ecosystems and humans is expected to be progressively challenged due to the effects of droughts, heat waves, sea-level rise and ocean warming and acidification. Progress towards achievement of the UN Sustainable Development Goals differs strongly between Mediterranean sub-regions, with north-western countries having stronger resilience than southern and eastern countries.</p><p>Our objective is to present the threats and vulnerabilities of the Mediterranean region. Then we will see the impacts on ecosystems, economic sectors and human well-being. Finally, we will present the different adaptation options, their limits and climate-resilient development pathways. </p><p> </p><p><strong>Disclaimer :</strong> the content of IPCC reports are pre-decisional and confidential until they are formally accepted by member governments.</p><p> </p>