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Lines in the ice : exploring the roof of the world
\"The 2014 discovery of the HMS Erebus--a ship lost during Sir John Franklin's 1845 expedition to find the Northwest Passage--reignited popular, economic, and political interest in the Arctic's exploration, history, anthropology, and historical geography. Lines in the Ice investigates the allure of the North through topographical views, maps, explorers' diaries, and historic photographs.\"-- Provided by publisher.
Book
Enhanced Mutation Rate, Relaxed Selection, and the “Domino Effect” are associated with Gene Loss in Blattabacterium, A Cockroach Endosymbiont
Intracellular endosymbionts have reduced genomes that progressively lose genes at a timescale of tens of million years. We previously reported that gene loss rate is linked to mutation rate in Blattabacterium, however, the mechanisms causing gene loss are not yet fully understood. Here, we carried out comparative genomic analyses on the complete genome sequences of a representative set of 67 Blattabacterium strains, with sizes ranging between 511 and 645 kb. We found that 200 of the 566 analyzed protein-coding genes were lost in at least one lineage of Blattabacterium, with the most extreme case being one gene that was lost independently in 24 lineages. We found evidence for three mechanisms influencing gene loss in Blattabacterium. First, gene loss rates were found to increase exponentially with the accumulation of substitutions. Second, genes involved in vitamin and amino acid metabolism experienced relaxed selection in Cryptocercus and Mastotermes, possibly triggered by their vertically inherited gut symbionts. Third, we found evidence of epistatic interactions among genes leading to a “domino effect” of gene loss within pathways. Our results highlight the complexity of the process of genome erosion in an endosymbiont.
Journal Article
Ancient ocean crossings : reconsidering the case for contacts with the pre-Columbian Americas
In Ancient Ocean Crossings: Reconsidering the Case for Contacts with the Pre-Columbian Americas, Stephen Jett encourages readers to reevaluate the common belief that there was no significant interchange between the chiefdoms and civilizations of Eurasia and Africa and peoples who occupied the alleged terra incognita beyond the great oceans. More than a hundred centuries separate the time that Ice Age hunters are conventionally thought to have crossed a land bridge from Asia into North America and the arrival of Columbus in the Bahamas in 1492. Traditional belief has long held that earth's two hemispheres were essentially cut off from one another as a result of the post-Pleistocene meltwater-fed rising oceans that covered that bridge. The oceans, along with arctic climates and daunting terrestrial distances, formed impermeable barriers to interhemispheric communication. This viewpoint implies that the cultures of the Old World and those of the Americas developed independently. Drawing on abundant and concrete evidence to support his theory for significant pre-Columbian contacts, Jett suggests that many ancient peoples had both the seafaring capabilities and the motives to cross the oceans and, in fact, did so repeatedly and with great impact. His deep and broad work synthesizes information and ideas from archaeology, geography, linguistics, climatology, oceanography, ethnobotany, genetics, medicine, and the history of navigation and seafaring, making an innovative and persuasive multidisciplinary case for a new understanding of human societies and their diffuse but interconnected development.
Book
Dietary Diversification and Specialization in Neotropical Bats Facilitated by Early Molecular Evolution
Dietary adaptation is a major feature of phenotypic and ecological diversification, yet the genetic basis of dietary shifts is poorly understood. Among mammals, Neotropical leaf-nosed bats (family Phyllostomidae) show unmatched diversity in diet; from a putative insectivorous ancestor, phyllostomids have radiated to specialize on diverse food sources including blood, nectar, and fruit. To assess whether dietary diversification in this group was accompanied by molecular adaptations for changing metabolic demands, we sequenced 89 transcriptomes across 58 species and combined these with published data to compare ∼13,000 protein coding genes across 66 species. We tested for positive selection on focal lineages, including those inferred to have undergone dietary shifts. Unexpectedly, we found a broad signature of positive selection in the ancestral phyllostomid branch, spanning genes implicated in the metabolism of all major macronutrients, yet few positively selected genes at the inferred switch to plantivory. Branches corresponding to blood- and nectar-based diets showed selection in loci underpinning nitrogenous waste excretion and glycolysis, respectively. Intriguingly, patterns of selection in metabolism genes were mirrored by those in loci implicated in craniofacial remodeling, a trait previously linked to phyllostomid dietary specialization. Finally, we show that the null model of the widely-used branch-site test is likely to be misspecified, with the implication that the test is too conservative and probably under-reports true cases of positive selection. Our findings point to a complex picture of adaptive radiation, in which the evolution of new dietary specializations has been facilitated by early adaptations combined with the generation of new genetic variation.
Journal Article
Ecological specialization and evolutionary reticulation in extant Hyaenidae
During the Miocene, Hyaenidae was a highly diverse family of Carnivora that has since been severely reduced to four species: the bone-cracking spotted, striped, and brown hyenas, and the specialized insectivorous aardwolf. Previous studies investigated the evolutionary histories of the spotted and brown hyenas, but little is known about the remaining two species. Moreover, the genomic underpinnings of scavenging and insectivory, defining traits of the extant species, remain elusive. Here, we generated an aardwolf genome and analyzed it together with the remaining three species to reveal their evolutionary relationships, genomic underpinnings of their scavenging and insectivorous lifestyles, and their respective genetic diversities and demographic histories. High levels of phylogenetic discordance suggest gene flow between the aardwolf lineage and the ancestral brown/striped hyena lineage. Genes related to immunity and digestion in the bone-cracking hyenas and craniofacial development in the aardwolf showed the strongest signals of selection, suggesting putative key adaptations to carrion and termite feeding, respectively. A family-wide expansion in olfactory receptor genes suggests that an acute sense of smell was a key early adaptation. Finally, we report very low levels of genetic diversity within the brown and striped hyenas despite no signs of inbreeding, putatively linked to their similarly slow decline in effective population size over the last 2 million years. High levels of genetic diversity and more stable population sizes through time are seen in the spotted hyena and aardwolf. Taken together, our findings highlight how ecological specialization can impact the evolutionary history, demographics, and adaptive genetic changes of an evolutionary lineage.
Journal Article
Navigations
Navigations re-examines the Portuguese voyages of discovery by placing them in their medieval and Renaissance settings. It shows how these voyages grew out of a crusading ethos, as well as long-distance trade with Asia and Africa and developments in map-making and ship design. The slave trade, the diaspora of the Sephardic Jews and the intercontinental spread of plants and animals gave these voyages long-term global significance. The voyages of discovery are narrated within the context of Portuguese politics, and this book describes the role of the Portuguese ruling dynasty – including its female members – in the flowering of the Portuguese Renaissance and the distinctive ideology of the Renaissance state, and in the cultural changes that took place within a wider European context.
eBook
