Exploring diet shifts and ecology in modern sharks using calcium isotopes and trace metal records of their teeth.

Sharks occupy all living environments of the marine realm as well as some freshwater systems. They display varied and flexible feeding behaviours, but understanding their diet remains challenging due to their elusive ecology and the invasiveness of stomach content analyses in regard of their threatened status. As a potential alternative, we discuss the variability in δ44/42 Ca values recorded in the tooth enamel of size-graded individuals belonging to three species of large sharks with distinct diets (Isurus oxyrinchus, Hexanchus griseus and Carcharodon carcharias). The preliminary results highlight shifts in diet linked to ontogeny (I. oxyrinchus and H. griseus) and spatial distribution (C. carcharias) characterizing feeding behaviour in these species at individual and population level. These outcomes agree with the results of traditional stomach analyses supporting that nontraditional stable isotopes thus represent new perspectives for the study of modern and extinct shark ecology. In addition, for the first time, the Sr/Ca elemental ratios measured in H. griseus reflect sexual differences that could be interpreted in terms of spatial segregation or physiological heterogeneities.

Calcium isotopic patterns in enamel reflect different nursing behaviors among South African early hominins.

Nursing is pivotal in the social and biological evolution of hominins, but to date, early-life behavior among hominin lineages is a matter of debate. The calcium isotopic compositions (δ44/42Ca) of tooth enamel can provide dietary information on this period. Here, we measure the δ44/42Ca values in spatially located microsized regions in tooth enamel of 37 South African hominins to reconstruct early-life dietary-specific variability in Australopithecus africanus, Paranthropus robustus, and early Homo. Very low δ44/42Ca values (<-1.4‰), indicative of milk consumption, are measured in early Homo but not in A. africanus and P. robustus. In these latter taxa, transitional or adult nonmilk foods must have been provided in substantial quantities relative to breast milk rapidly after birth. The results suggest that early Homo have continued a predominantly breast milk-based nursing period for longer than A. africanus and P. robustus and have consequently more prolonged interbirth interval.

Extreme Arsenic Bioaccumulation Factor Variability in Lake Titicaca, Bolivia.

Latin America, like other areas in the world, is faced with the problem of high arsenic (As) background in surface and groundwater, with impacts on human health. We studied As biogeochemical cycling by periphyton in Lake Titicaca and the mine-impacted Lake Uru Uru. As concentration was measured in water, sediment, totora plants (Schoenoplectus californicus) and periphyton growing on stems, and As speciation was determined by X-ray absorption spectroscopy in bulk and EDTA-extracted periphyton. Dissolved arsenic was between 5.0 and 15 µg L-1 in Lake Titicaca and reached 78.5 µg L-1 in Lake Uru Uru. As accumulation in periphyton was highly variable. We report the highest As bioaccumulation factors ever measured (BAFsperiphyton up to 245,000) in one zone of Lake Titicaca, with As present as As(V) and monomethyl-As (MMA(V)). Non-accumulating periphyton found in the other sites presented BAFsperiphyton between 1281 and 11,962, with As present as As(III), As(V) and arsenosugars. DNA analysis evidenced several taxa possibly related to this phenomenon. Further screening of bacterial and algal isolates would be necessary to identify the organism(s) responsible for As hyperaccumulation. Impacts on the ecosystem and human health appear limited, but such organisms or consortia would be of great interest for the treatment of As contaminated water.

Euryhaline ecology of early tetrapods revealed by stable isotopes.

The fish-to-tetrapod transition-followed later by terrestrialization-represented a major step in vertebrate evolution that gave rise to a successful clade that today contains more than 30,000 tetrapod species. The early tetrapod Ichthyostega was discovered in 1929 in the Devonian Old Red Sandstone sediments of East Greenland (dated to approximately 365 million years ago). Since then, our understanding of the fish-to-tetrapod transition has increased considerably, owing to the discovery of additional Devonian taxa that represent early tetrapods or groups evolutionarily close to them. However, the aquatic environment of early tetrapods and the vertebrate fauna associated with them has remained elusive and highly debated. Here we use a multi-stable isotope approach (δ13C, δ18O and δ34S) to show that some Devonian vertebrates, including early tetrapods, were euryhaline and inhabited transitional aquatic environments subject to high-magnitude, rapid changes in salinity, such as estuaries or deltas. Euryhalinity may have predisposed the early tetrapod clade to be able to survive Late Devonian biotic crises and then successfully colonize terrestrial environments.

Rome's urban history inferred from Pb-contaminated waters trapped in its ancient harbor basins.

Heavy metals from urban runoff preserved in sedimentary deposits record long-term economic and industrial development via the expansion and contraction of a city's infrastructure. Lead concentrations and isotopic compositions measured in the sediments of the harbor of Ostia-Rome's first harbor-show that lead pipes used in the water supply networks of Rome and Ostia were the only source of radiogenic Pb, which, in geologically young central Italy, is the hallmark of urban pollution. High-resolution geochemical, isotopic, and 14C analyses of a sedimentary core from Ostia harbor have allowed us to date the commissioning of Rome's lead pipe water distribution system to around the second century BC, considerably later than Rome's first aqueduct built in the late fourth century BC. Even more significantly, the isotopic record of Pb pollution proves to be an unparalleled proxy for tracking the urban development of ancient Rome over more than a millennium, providing a semiquantitative record of the water system's initial expansion, its later neglect, probably during the civil wars of the first century BC, and its peaking in extent during the relative stability of the early high Imperial period. This core record fills the gap in the system's history before the appearance of more detailed literary and inscriptional evidence from the late first century BC onward. It also preserves evidence of the changes in the dynamics of the Tiber River that accompanied the construction of Rome's artificial port, Portus, during the first and second centuries AD.

A lead isotope perspective on urban development in ancient Naples.

The influence of a sophisticated water distribution system on urban development in Roman times is tested against the impact of Vesuvius volcanic activity, in particular the great eruption of AD 79, on all of the ancient cities of the Bay of Naples (Neapolis). Written accounts on urbanization outside of Rome are scarce and the archaeological record sketchy, especially during the tumultuous fifth and sixth centuries AD when Neapolis became the dominant city in the region. Here we show that isotopic ratios of lead measured on a well-dated sedimentary sequence from Neapolis' harbor covering the first six centuries CE have recorded how the AD 79 eruption was followed by a complete overhaul of Neapolis' water supply network. The Pb isotopic signatures of the sediments further reveal that the previously steady growth of Neapolis' water distribution system ceased during the collapse of the fifth century AD, although vital repairs to this critical infrastructure were still carried out in the aftermath of invasions and volcanic eruptions.