title: Preservation Methods Alter Carbon and Nitrogen Stable Isotope Values in Crickets (Orthoptera: Grylloidea).
abstract: 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, Phoremia sp. and Mellopsis doucasae, 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 δ15N, δ13C values, N(%), C(%) and C/N atomic values using continuous flow isotope ratio mass spectrometry. All preservation methods tested, significantly impacted δ13C and δ15N and C/N atomic values. Chemical preservatives caused δ13C enrichment as great as 1.5‰, and δ15N enrichment as great as 0.9‰; the one exception was M. doucasae stored in ethanol for 15 days, which had δ15N depletion up to 1.8‰. Freezing depleted δ13C and δ15N 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.
authors.affiliation: Programa de Pós-graduação em Ecologia, Departamento de Biologia Geral, Universidade Federal de Viçosa, Viçosa, MG, Brazil.
authors.forename: Fabiene Maria
authors.initials: FM
authors.lastname: Jesus
authors.affiliation: Universidade Federal do Espírito Santo, Centro de Ciências Agrárias, Departamento de Biologia, Alegre, ES, Brazil.
authors.forename: Marcelo Ribeiro
authors.initials: MR
authors.lastname: Pereira
authors.affiliation: Universidade Federal do Triângulo Mineiro, Campus Iturama, Curso de Ciências Biológicas, Iturama, MG, Brazil.
authors.forename: Cassiano Sousa
authors.initials: CS
authors.lastname: Rosa
authors.affiliation: Laboratório de Ecologia Isotópica, Centro de Energia Nuclear na Agricultura-CENA/USP, Piracicaba, SP, Brazil.
authors.forename: Marcelo Zacharias
authors.initials: MZ
authors.lastname: Moreira
authors.affiliation: Programa de Pós-graduação em Ecologia, Departamento de Biologia Geral, Universidade Federal de Viçosa, Viçosa, MG, Brazil.
authors.forename: Carlos Frankl
authors.initials: CF
authors.lastname: Sperber
mesh_terms: D000818:Animals; D002247:Carbon Isotopes / Q000032:analysis*; D006135:Gryllidae / Q000737:chemistry*; D009587:Nitrogen Isotopes / Q000032:analysis*; D011309:Preservation, Biological / Q000379:methods*
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes