Perspectives on Proterozoic surface ocean redox from iodine contents in ancient and recent carbonate

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 463 (2017): 159-170, doi:10.1016/j.epsl.2017.01.032.The Proterozoic Eon hosted the emergence and initial recorded diversification of eukaryotes. Oxygen levels in the shallow marine settings critical to these events were lower than today’s, although how much lower is debated. Here, we use concentrations of iodate (the oxidized iodine species) in shallow-marine limestones and dolostones to generate the first comprehensive record of Proterozoic near-surface marine redox conditions. The iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters. To assess the validity of our approach, Neogene-Quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate-iodine contents. Despite the potential for diagenetic loss, maximum Proterozoic carbonate iodine levels are elevated relative to those of the Archean, particularly during the Lomagundi and Shuram carbon isotope excursions of the Paleo- and Neoproterozoic, respectively. For the Shuram anomaly, comparisons to Neogene-Quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends. The baseline low iodine levels in Proterozoic carbonates, relative to the Phanerozoic, are linked to a shallow oxic-anoxic interface. Oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes. However, the diagnostically low iodine data from mid-Proterozoic shallow-water carbonates, relative to those of the bracketing time intervals, are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans. This redox instability may have challenged early eukaryotic diversification and expansion, creating an evolutionary landscape unfavorable for the emergence of animals.TL, ZL, and DH thank NSF EAR-1349252. ZL further thanks OCE-1232620. DH, ZL, and TL acknowledge further funding from a NASA Early Career Collaboration Award. TL, AB, NP, DH, and AK thank the NASA Astrobiology Institute. TL and NP received support from the Earth-Life Transitions Program of the NSF. AB acknowledges support from NSF grant EAR-05-45484 and an NSERC Discovery and Accelerator Grants. CW acknowledges support from NSFC grant 40972021

Holoprosencephaly–polydactyly/pseudotrisomy 13: a presentation of two new cases and a review of the literature

Patients with a combination of holoprosencephaly and polydactyly, but with apparently normal chromosomes, may be clinically diagnosed with holoprosencephaly–polydactyly syndrome (HPS), also termed pseudotrisomy 13. However, the criteria for HPS have been controversial since the advent of the diagnostic term, and a clear understanding of the condition lacks definitive delineation. We review the historical and current perspectives on the condition and analyze findings in 40 patients with apparent HPS, including cases from the literature and two previously unreported patients. Overall, our analysis suggests previously unrecognized trends in patients diagnosed with HPS. Specifically, there appears to be a higher prevalence of visceral anomalies, most significantly cardiac and genitourinary, but also with increased gastrointestinal, pulmonary, adrenal, skeletal, and renal abnormalities, in patients with HPS. Although these visceral anomalies may not be essential for the identification of HPS, clinicians should be aware of the presence of such characteristics in these patients to optimize management and help establish etiologies

Trace elements at the intersection of marine biological and geochemical evolution

Life requires a wide variety of bioessential trace elements to act as structural components and reactive centers in metalloenzymes. These requirements differ between organisms and have evolved over geological time, likely guided in some part by environmental conditions. Until recently, most of what was understood regarding trace element concentrations in the Precambrian oceans was inferred by extrapolation, geochemical modeling, and/or genomic studies. However, in the past decade, the increasing availability of trace element and isotopic data for sedimentary rocks of all ages has yielded new, and potentially more direct, insights into secular changes in seawater composition – and ultimately the evolution of the marine biosphere. Compiled records of many bioessential trace elements (including Ni, Mo, P, Zn, Co, Cr, Se, and I) provide new insight into how trace element abundance in Earth's ancient oceans may have been linked to biological evolution. Several of these trace elements display redox-sensitive behavior, while others are redox-sensitive but not bioessential (e.g., Cr, U). Their temporal trends in sedimentary archives provide useful constraints on changes in atmosphere-ocean redox conditions that are linked to biological evolution, for example, the activity of oxygen-producing, photosynthetic cyanobacteria. In this review, we summarize available Precambrian trace element proxy data, and discuss how temporal trends in the seawater concentrations of specific trace elements may be linked to the evolution of both simple and complex life. We also examine several biologically relevant and/or redox-sensitive trace elements that have yet to be fully examined in the sedimentary rock record (e.g., Cu, Cd, W) and suggest several directions for future studies

The Evolution of the Family

Biological levels of complexity usually begin with the cell and extend forward to tissues, organs, organ systems, organisms, populations, community, and end with ecosystems. The family is a unit of biological complexity is missing. As a result, the evolution of altruism and cooperation from a natural selection perspective has not been produced. In the following chapters, I argue that the family is a unit of biological complexity will illuminate such mysteries as the evolution of eusociality, theories of lifetime fitness—sometimes referred to as Lifetime Reproductive Success (LRS)— cultural learning and its importance as a parallel mechanism of inheritance, finally, the resolution of evolutionary arms races. The key insight offered here is that the formation of family groups may offer an alternative to past models of group formation in organisms as diverse as snakes and humans, cultural evolution in humans and other primates and arms races in marine organisms. Each of the attempts to model the evolution of altruism and cooperation has been unsuccessful because they have ignored the fundamental reality that an extended period of parental investment combined with cooperative brood care has led to some of the most ecologically dominant organisms on earth: humans, social insects and birds

A 4D natural selection model illuminates the enigma of altruism in the Shedao pit viper.

Endemic to a small island off the coast of China, the Shedao pit viper, Gloydius shedaoensis, is known for its ‘accidental altruism.’ Juvenile pit vipers often kill passerine birds too large to swallow. Large prey carcasses are scavenged by neighboring adults. In turn, adult pit vipers kill hawks that prey on juvenile pit-vipers, but are not a threat to the adults themselves. Using agent-based computer simulations, we quantified the lifetime fitness of pit viper breeders with one of three genotypes: selfish, altruistic or both selfish and altruistic. Our simulation was based on a four-dimensional (4D) model of social behavior which included interactions of pit viper offspring with predators and prey as well as conspecifics. Results showed that, over ten breeding seasons, pit viper breeders with flexible altruistic and selfish genotypes averaged seven times the number of surviving offspring relative to breeders with pure-selfish genotypes, and 23 times the number of surviving offspring as breeders with pure-altruistic genotypes. In summary, viewing animal behavior through the lens of the 4D model will extend our understanding of the evolutionary pathway to social behaviors through natural selection processes

Diagenetic effects on uranium isotope fractionation in carbonate sediments from the Bahamas

© 2018 Elsevier Ltd Uranium isotope variations (δ238U) recorded in sedimentary carbonate rocks are a promising new proxy for the extent of oceanic anoxia through geological time. However, the effects of diagenetic alteration on the U isotopic composition in carbonate sediments, which are crucial to understand the accurate reconstruction of marine δ238U, are currently poorly constrained. Here we examine the effects of the aragonite-to-calcite transition in the Pleistocene Key Largo Limestone of South Florida, and assess the effects of vadose meteoric, phreatic meteoric, and phreatic marine diagenesis on U isotope fractionation in carbonate sediments from the Bahamas Transect, including the well-studied Clino, Unda, and ODP Site 1006 drill cores. Our results suggest that early diagenetic processes in Bahamas carbonate sediments fractionate U isotopes by an average of 0.27 ± 0.14‰ (1 SD) heavier than contemporaneous seawater. Downcore variations of δ238U in slope and basin sediments display little, if any, correlation with U concentration and common geochemical indicators of diagenesis (δ13C, δ18O, Mn/Sr, Mg/Ca, Sr/Ca), enrichments of redox-sensitive elements, or rare earth elements anomalies. We propose two possible mechanisms to interpret the positive change in the δ238U during carbonate diagenesis: authigenic enrichment of isotopically positive U(IV) in carbonates and preferential incorporation of isotopically positive aqueous U(VI) species into carbonates. These processes likely operate during early (syndepositional) diagenesis on the banktop. Further diagenesis during deeper burial is limited by the low solubility of U(IV) under reducing pore water conditions. The early diagenetic behavior of U isotopes in Bahamas carbonate sediments is likely broadly representative of carbonate diagenesis in the geological past. We suggest that the mean diagenetic offset determined in this study be applied when reconstructing seawater δ238U from ancient carbonates. Furthermore, early diagenesis induces significant statistical variability in sediment δ238U values, pointing to the need for large, high resolution data sets in order to average out stochastic variations in individual bulk sediment samples