Trophic Niche Dynamics and Diet Partitioning of King Crab Lithodes santolla in Chile’s Sub-Antarctic Water

The southern king crab Lithodes santolla is one of the most economically important fishery species in the southern waters of the Atlantic and Pacific Oceans. A combination of stomach content and stable isotope analyses was used to reveal the potential dietary characteristics, isotopic niche, overlap among maturity stages and sexes, and trophic relationships of an L. santolla population in the Nassau Bay, Cape Horn region. Stable isotope analyses indicated that L. santolla assimilated energy from a basal carbon source, the giant kelp Macrocystis pyrifera, forming the trophic baseline of the benthic food web. Moreover, the trophic position of L. santolla varied among late juveniles and adults, suggesting that the southern king crab does undergo an ontogenetic diet shift. L. santolla exhibited intraspecific isotopic niche variation, reflecting niche differentiation which allows the species to partition resources. The trophic relationships of L. santolla with the associated fauna suggested some potential interactions for food resources/habitat use when they are limited. This study is the first attempt to characterize the trophic dynamics of the southern king crab in the Cape Horn area and, by generating more data, contributes to the conservation of the king crab population and the long-term management of local fisheries that rely on this resource.

Exploring New Ways to Reconstruct the Forma Urbis Romae: An Archaeometric Approach (CL Color and Stable Isotope Analyses)

The Forma Urbis Romae (F.U.) was a 3rd-century-AD monumental map of ancient Rome consisting of 151 rectangular marble slabs. Several efforts have been made to reconstruct it from its current incomplete and fragmentary condition. In this paper, we explore the potential of an archaeometric approach to serve this purpose. Almost a hundred F.U. fragments have been characterized, particularly focusing on cathodoluminescence (CL) microscopy and stable isotopes (δ18O and δ13C). Different statistical methods have been used to quantify the similarity between samples. The central assumption is that samples from a given slab share similar CL colors and isotopic ratios. The assumption has been verified for samples from single fragments and then it has been used to check ten debated reconstruction hypotheses. The measured isotopic ratios confirm the Proconnesian nature of the F.U. marble, except for a fragment. Beyond provenance, the results cast doubts on four out of the ten checked reconstruction hypotheses and support the other six. The reconstruction of the F.U. remains a fascinating challenge, and both isotopic and CL analyses have demonstrated their potential to tackle it. Further research could extend the presented methodology to a higher number of samples. The innovative use of CL to reconstruct a fragmented artwork could be applied to other projects.

Do It Yourself! – Experiences with Self-Synthesized CsTFA for RNA-SIP Analyses

Cesiumtrifluoroacetate (CsTFA) is a key chemical for RNA-based stable isotope analyses to link the structure and function of microbial communities. We report a protocol to easily synthesize CsTFA from Cesiumcarbonate (Cs2CO3) and Trifluoroacetate (TFA) and show that self-synthesized CsTFA behaves similar to commercial CsTFA in the separation of isotopically labelled and unlabelled E. coli RNA.

Trophic specialization on unique resources in one of the most celebrated examples of sympatric speciation, Barombi Mbo crater lake cichlids

Divergent ecological selection often results in trophic niche partitioning and is one of the central processes underlying sympatric speciation. However, there are still few studies of niche partitioning in putative examples of sympatric speciation in the wild. Here we conducted the first quantitative study of dietary niche partitioning in one of the most celebrated examples of sympatric speciation, Barombi Mbo cichlids, using stomach contents and stable isotope analyses. We found little evidence for trophic niche partitioning among any Barombi Mbo cichlids, even among the nine species coexisting in sympatry in the littoral zone. Stable isotope analyses supported these conclusions of minimal dietary overlap. However, we did find extraordinary dietary specialization in some species, including spongivory and feeding on terrestrial ants, both unique feeding strategies among freshwater fishes. Stomach contents of the spongivore (Pungu maclareni) were 20% freshwater sponge, notable considering that only 0.04% of all fishes consume sponges. Overall, we conclude that while there is less trophic niche partitioning than expected among Barombi Mbo cichlids, there is evidence for dietary specialization on rare resources in support of Liem's paradox.