Food choice of Antarctic soil arthropods clarified by stable isotope signatures

Antarctic soil ecosystems are amongst the most simplified on Earth and include only few soil arthropod species, generally believed to be opportunistic omnivorous feeders. Using stable isotopic analyses, we investigated the food choice of two common and widely distributed Antarctic soil arthropod species using natural abundances of 13C and 15N and an isotope labelling study. In the laboratory we fed the isotomid springtail Cryptopygus antarcticus six potential food sources (one algal species, two lichens and three mosses). Our results showed a clear preference for algae and lichens rather than mosses. These results were corroborated by field data comparing stable isotope signatures from the most dominant cryptogams and soil arthropods (C. antarcticus and the oribatid mite Alaskozetes antarcticus). Thus, for the first time in an Antarctic study, we present clear evidence that these soil arthropods show selectivity in their choice of food and have a preference for algae and lichens above mosses

Preservation Methods Alter Carbon and Nitrogen Stable Isotope Values in Crickets (Orthoptera: Grylloidea)

<div><p>Stable isotope analysis (SIA) is an important tool for investigation of animal dietary habits for determination of feeding niche. Ideally, fresh samples should be used for isotopic analysis, but logistics frequently demands preservation of organisms for analysis at a later time. The goal of this study was to establish the best methodology for preserving forest litter-dwelling crickets for later SIA analysis without altering results. We collected two cricket species, <i>Phoremia</i> sp. and <i>Mellopsis doucasae</i>, from which we prepared 70 samples per species, divided among seven treatments: (i) freshly processed (control); preserved in fuel ethanol for (ii) 15 and (iii) 60 days; preserved in commercial ethanol for (iv) 15 and (v) 60 days; fresh material frozen for (vi) 15 and (vii) 60 days. After oven drying, samples were analyzed for <i>δ</i>¹⁵N, <i>δ</i>¹³C values, N(%), C(%) and C/N atomic values using continuous flow isotope ratio mass spectrometry. All preservation methods tested, significantly impacted <i>δ</i>¹³C and <i>δ</i>¹⁵N and C/N atomic values. Chemical preservatives caused <i>δ</i>¹³C enrichment as great as 1.5‰, and <i>δ</i>¹⁵N enrichment as great as 0.9‰; the one exception was <i>M. doucasae</i> stored in ethanol for 15 days, which had <i>δ</i>¹⁵N depletion up to 1.8‰. Freezing depleted <i>δ</i>¹³C and <i>δ</i>¹⁵N by up to 0.7 and 2.2‰, respectively. C/N atomic values decreased when stored in ethanol, and increased when frozen for 60 days for both cricket species. Our results indicate that all preservation methods tested in this study altered at least one of the tested isotope values when compared to fresh material (controls). We conclude that only freshly processed material provides adequate SIA results for litter-dwelling crickets.</p></div