Clumped isotope thermometry in earthworm carbonates

Earthworm-secreted calcium carbonate can store carbon derived from the soil-atmosphere interface on geological timescales [1]. The mechanism of calcification [2,3,4] is well understood based on multiple years of research conducted both under controlled and natural conditions. We analysed carbonate granules produced by the earthworm Lumbricus terrestris cultured in variable pH and temperature for δ18O to establish thermometry [2]. The governing equation proposed for the thermometry differed from the inorganic calcite precipitation relationship, capturing the signature of kinetic processes during carbonate growth. We have now analysed the granules for clumped isotope thermometry. This provides an opportunity to understand the role of kinetic processes in governing the relationship of clumped isotope in the carbonate system. The clumped isotopic composition of these carbonates yields the following relationship with varying temperature: The linear regression relationship obtained in this study has a similar slope as seen in case of inorganic calcite [5] and otolith carbonate [6]. However, the intercept of the governing equation varied significantly denoting carbonate growth rate. The study presented here provides the first experimental results of clumped isotope composition on carbonates precipitated under monitored disequilibrium conditions and thus, enables quantification of growth rate dependency on clumping. The intercept of the linear regression relationship differs from the line proposed for inorganic calcite precipitation and thus introduces a new parameter to quantify the kinetic process. In this study replicate experiments were performed on carbonate granules generated at controlled temperature and with a knowledge of water isotopic compositio

Biomineralisation by earthworms: an investigation into the stability and distribution of amorphous calcium carbonate

Background Many biominerals form from amorphous calcium carbonate (ACC), but this phase is highly unstable when synthesised in its pure form inorganically. Several species of earthworm secrete calcium carbonate granules which contain highly stable ACC. We analysed the milky fluid from which granules form and solid granules for amino acid (by liquid chromatography) and functional group (by Fourier transform infrared (FTIR) spectroscopy) compositions. Granule elemental composition was determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and electron microprobe analysis (EMPA). Mass of ACC present in solid granules was quantified using FTIR and compared to granule elemental and amino acid compositions. Bulk analysis of granules was of powdered bulk material. Spatially resolved analysis was of thin sections of granules using synchrotron-based μ-FTIR and EMPA electron microprobe analysis. Results The milky fluid from which granules form is amino acid-rich (≤ 136 ± 3 nmol mg−1 (n = 3; ± std dev) per individual amino acid); the CaCO3 phase present is ACC. Even four years after production, granules contain ACC. No correlation exists between mass of ACC present and granule elemental composition. Granule amino acid concentrations correlate well with ACC content (r ≥ 0.7, p ≤ 0.05) consistent with a role for amino acids (or the proteins they make up) in ACC stabilisation. Intra-granule variation in ACC (RSD = 16%) and amino acid concentration (RSD = 22–35%) was high for granules produced by the same earthworm. Maps of ACC distribution produced using synchrotron-based μ-FTIR mapping of granule thin sections and the relative intensity of the ν2: ν4 peak ratio, cluster analysis and component regression using ACC and calcite standards showed similar spatial distributions of likely ACC-rich and calcite-rich areas. We could not identify organic peaks in the μ-FTIR spectra and thus could not determine whether ACC-rich domains also had relatively high amino acid concentrations. No correlation exists between ACC distribution and elemental concentrations determined by EMPA. Conclusions ACC present in earthworm CaCO3 granules is highly stable. Our results suggest a role for amino acids (or proteins) in this stability. We see no evidence for stabilisation of ACC by incorporation of inorganic components

Clumped isotope thermometry in earthworm carbonates

Earthworm-secreted calcium carbonate can store carbon derived from the soil-atmosphere interface on geological timescales [1]. The mechanism of calcification [2,3,4] is well understood based on multiple years of research conducted both under controlled and natural conditions. We analysed carbonate granules produced by the earthworm Lumbricus terrestris cultured in variable pH and temperature for δ18O to establish thermometry [2]. The governing equation proposed for the thermometry differed from the inorganic calcite precipitation relationship, capturing the signature of kinetic processes during carbonate growth. We have now analysed the granules for clumped isotope thermometry. This provides an opportunity to understand the role of kinetic processes in governing the relationship of clumped isotope in the carbonate system. The clumped isotopic composition of these carbonates yields the following relationship with varying temperature: The linear regression relationship obtained in this study has a similar slope as seen in case of inorganic calcite [5] and otolith carbonate [6]. However, the intercept of the governing equation varied significantly denoting carbonate growth rate. The study presented here provides the first experimental results of clumped isotope composition on carbonates precipitated under monitored disequilibrium conditions and thus, enables quantification of growth rate dependency on clumping. The intercept of the linear regression relationship differs from the line proposed for inorganic calcite precipitation and thus introduces a new parameter to quantify the kinetic process. In this study replicate experiments were performed on carbonate granules generated at controlled temperature and with a knowledge of water isotopic compositio

Seasonally resolved growth of freshwater bivalves determined by oxygen and carbon isotope shell chemistry

By means of a monitoring experiment in two rivers in the Netherlands, we establish a relationship between seasonally resolved growth rates in unionid freshwater bivalves and their environment. We reconstructed these seasonally resolved growth rates by using relationships of stable isotopes in the shells and their ambient river water. The reconstructed growth rates reveal that shells grow fastest in spring-early summer, when highest food availability occurs in the rivers. In addition, the reconstructed growth rates show that onset and cessation of growth are mainly influenced by water temperature

Multiple nutritional strategies of hydrothermal vent shrimp (Rimicaris hybisae) assemblages at the Mid-Cayman Rise

Alvinocaridid shrimp occurring in dense assemblages close to vigorously venting orifices are characteristic of many vent fields on the Mid-Atlantic Ridge, Central Indian Ridge, and Mid-Cayman Rise. Episymbiotic bacteria of these shrimp are exposed to vent fluids enriched in inorganic nutrients (carbon dioxide, sulfide) that, together with dissolved oxygen in the surrounding seawater, sustain autotrophic growth and supply nourishment to the shrimp. Enigmatically, conspecific shrimp may also be found sparsely distributed in the periphery of a vent field, where there is little visual evidence of vent fluid flux. We tested the null hypothesis that nourishment sources were identical for the central (dense) and peripheral shrimp assemblages, using gut content and stable isotope analyses. Rimicaris hybisae were sampled from central and peripheral assemblages at the Von Damm Vent Field (Mid-Cayman Rise). Guts of centrally aggregated shrimp contained a white material inferred to be bacteria, while peripheral individuals contained this white material and/or pieces of crustacean exoskeletons. C, N, and S isotopic compositions of shrimp muscle tissues were significantly different between central and peripheral shrimp assemblages, and little overlap in isotopic space was found. A comparison of δ13C and δ34S values of gut contents and abdominal tissues revealed that abdominal tissue composition reflects the shrimp's source of nourishment. Slight but significantly elevated δ15N values in peripheral shrimp, together with crustacean exoskeleton fragments in the gut, suggest facultative carnivory in peripherally aggregated shrimp. The lower δ13C and δ34S values in individuals from the peripheral assemblages are also consistent with a mixotrophic diet. We conclude that central and peripheral assemblages of R. hybisae have different nourishment sources, with central assemblages relying on episymbionts, while peripheral assemblages have diverse nourishment sources comprising bacteria and Crustacea

Can shells of freshwater mussels (Unionidae) be used to estimate low summer discharge of rivers and associated droughts?

This paper examines if shell oxygen isotope ratios (d18Oar) of Unio sp. can be used as a proxy of past discharge of the river Meuse. The proxy was developed from a modern dataset for the reference time interval 1997–2007, which showed a logarithmic relationship between discharge and measured water oxygen isotope ratios(d18Ow). To test this relationship for past time intervals,d18Oar values were measured in the aragonite of the growth increments of four Unio sp. shells; two from a relatively wet period and two from a very dry time interval (1910–1918 and 1969–1977, respectively). Shell d18Oar records were converted into d18Ow values using existing water temperature records. Summer d18Ow values, reconstructed from d18Oar of 1910–1918, showed a similar range as the summer d18Ow values for the reference time interval 1997–2007, whilst summer reconstructed d18Ow values for the time interval 1969–1977 were anomalously high. These high d18Ow values suggest that the river Meuse experienced severe summer droughts during the latter time interval. d18Ow values were then applied to calculate discharge values. It was attempted to estimate discharge from the reconstructed d18Ow values using the logarithmic relationship between d18Ow and discharge. A comparison of the calculated summer discharge results with observed discharge data showed that Meuse low-discharge events below a threshold value of 6 m3/s can be detected in the reconstructed d18Ow records, but true quantification remains problematic

Periodic time series modeling of environmental proxy records with guaranteed positive growth rate estimation

Identifying a periodic time-series model from environmental records, without imposing the positivity of the growth rate, does not necessarily respect the time order of the data observations. Consequently, subsequent observations, sampled in the environmental archive, can be inversed on the time axis, resulting in a non-physical signal model. In this paper an optimization technique with linear constraints on the signal model parameters is proposed that prevents time inversions. The activation conditions for this constrained optimization are based upon the physical constraint of the growth rate, namely, that it cannot take values smaller than zero. The actual constraints are defined for polynomials and first-order splines as basis functions for the nonlinear contribution in the distance-time relationship. The method is compared with an existing method that eliminates the time inversions, and its noise sensitivity is tested by means of Monte Carlo simulations. Finally, the usefulness of the method is demonstrated on the measurements of the vessel density, in a mangrove tree, Rhizophora mucronata, and the measurement of Mg/Ca ratios, in a bivalve, Mytilus trossulus

Fewer invited talks by women in evolutionary biology symposia

Lower visibility of female scientists, compared to male scientists, is a potential reason for the under-representation of women among senior academic ranks. Visibility in the scientific community stems partly from presenting research as an invited speaker at organized meetings. We analysed the sex ratio of presenters at the European Society for Evolutionary Biology (ESEB) Congress 2011, where all abstract submissions were accepted for presentation. Women were under-represented among invited speakers at symposia (15% women) compared to all presenters (46%), regular oral presenters (41%) and plenary speakers (25%). At the ESEB congresses in 2001–2011, 9–23% of invited speakers were women. This under-representation of women is partly attributable to a larger proportion of women, than men, declining invitations: in 2011, 50% of women declined an invitation to speak compared to 26% of men. We expect invited speakers to be scientists from top ranked institutions or authors of recent papers in high-impact journals. Considering all invited speakers (including declined invitations), 23% were women. This was lower than the baseline sex ratios of early-mid career stage scientists, but was similar to senior scientists and authors that have published in high-impact journals. High-quality science by women therefore has low exposure at international meetings, which will constrain Evolutionary Biology from reaching its full potential. We wish to highlight the wider implications of turning down invitations to speak, and encourage conference organizers to implement steps to increase acceptance rates of invited talks.