Trophic niche of forest litter-dwelling crickets: an analysis using stable isotopes of carbon and nitrogen

Vários mecanismos propostos por ecólogos teóricos buscam elucidar os processos envolvidos na coexistência de espécies em comunidades biológicas. Dentre esses mecanismos destacam-se aqueles que preveem a coexistência de espécies sendo facilitada por uma partição de recursos, associando processos competitivos à teoria de nicho. Assim, a coexistência e as interações entre as espécies têm sido investigadas por meio dos conceitos de nicho postulados e revisados por diversos estudiosos. Alguns autores têm proposto uma abordagem metodológica e tecnológica relativamente nova baseada em análise de isótopos estáveis (AIE), que pode ser utilizada para medir algumas das muitas dimensões dos nichos ecológicos. Neste contexto, a utilização da AIE em tecidos animais está permitindo descrever nichos isotópicos, cujos eixos em um espaço multidimensional seriam diferentes assinaturas isotópicas (por exemplo, δ 15 N e δ 13 C). A utilidade da AIE reside no fato de que os tecidos em expansão apresentam grandes variações temporais de δ 15 N e δ 13 C que refletem diretamente a gama de recursos alimentares consumidos e isotopicamente contrastantes ao longo do tempo. No entanto, estudos que utilizam AIE para estimar nicho trófico exigem o conhecimento de alguns fatores que podem alterar os valores isotópicos de δ 15 N e δ 13 C em tecidos animais, tais como: (i) os tipos de preservação que as amostras são submetidas antes da análise; (ii) o fracionamento isotópico que ocorre em tecidos de consumidores com relação a sua dieta. Neste contexto, esta tese apresenta três capítulos. No primeiro capítulo, nosso objetivo foi estabelecer uma metodologia que preservasse amostras de grilos para posterior AIE sem que houvesse alterações nos valores de δ 15 N e δ 13 C. Para isso, nós comparamos amostras de grilos recém processadas (controle) com amostras submetidas a dois métodos de preservação: físico (congelamento) e químico (etanol comercial e combustível) por 15 e 60 dias. Nossos resultados indicam que todos os métodos de preservação testados alteram pelo menos um dos valores isotópicos dos grilos quando comparado com o controle. Assim, recomendamos o uso de material recém-processado para AIE em grilos. No segundo capítulo, nosso principal objetivo foi avaliar como se dá o fracionamento dos valores isotópicos de δ 13 C e δ 15 N encontrados em corpos de grilos alimentados com dieta artificial e com isso fornecer informações de base para interpretar resultados de nicho trófico baseados na AIE de grilos em comunidades biológicas. Para isso, estimamos os valores isotópicos de δ 13 C e δ 15 N de indivíduos de três espécies de grilos alimentados com dieta artificial, e comparamos com os valores isotópicos da dieta artificial. Estimamos também os valores isotópicos de δ 13 C e δ 15 N encontrados em corpos de grilos alimentados em campo (dieta natural desconhecida). Nós demonstramos que a AIE é uma ferramenta promissora para investigar a posição trófica dos grilos de serrapilheira, uma vez que temos estimativas do quanto o 15 N varia nos grilos com relação à sua dieta. E por último, no terceiro capítulo descrevemos o nicho trófico da comunidade de grilos, avaliando a partição de nicho entre espécies coocorrentes de grilos. Encontramos evidências de que a coexistência de espécies de grilos em comunidades naturais envolve partição de recursos alimentares. O local de forrageamento influenciou diretamente no uso da dieta e conseqüentemente na posição trófica dos grilos, os quais apresentaram até três níveis tróficos quando avaliados em um contexto global da dieta. Essa partição é evidenciada pelos diferentes valores de δ 15 N encontrados nos corpos dos grilos. Os valores de δ 13 C evidenciam que os grilos utilizam recursos alimentares com origem em plantas C 3 . Finalmente, encontramos evidências de estreitamento do nicho trófico à medida que aumenta o número de espécies coocorrentes.Several mechanisms proposed by theoretical ecologists try to determine the processes involved in the coexistence of species in biological communities. Among these mechanisms include those which predict the species coexistence is facilitated by a partition of resources, associating competitive processes to niche theory. Thus, the coexistence and interactions among species have been investigated by niche concepts postulated and reviewed by many scientists. Some authors have proposed a relatively new methodological and technological approaches based stable isotope analysis (hereafter, SIA), that can be used for measure a few of the many dimensions of ecological niches. In this context, the use of SIA on animal tissues is allowing describing isotopic niches, whose axes in a multidimensional space would be different isotopic signatures (e.g. δ 13 C and δ 15 N). The usefulness of SIAs lies in the fact that the continuously growing tissues record temporal variations in δ 13 C and δ 15 N that directly reflect the range of isotopically contrasting food resources consumed over time. However, studies using SIA to estimate trophic niche requires knowledge of some factors that can change the isotopic values of δ 13 C and δ 15 N in animal tissues such as: (i) the types of preservation that the samples are subjected before analysis; (ii) the isotopic fractionation that occur in consumer tissues with regard to your diet. In this context, this thesis has three chapters. In the first chapter, our goal was to establish the best methodology for preserving forest litter- dwelling crickets for later SIA analysis without altering in the values of δ 13 C and δ 15 N. In this regard, we compare crickets freshly processed (control) and samples subjected to two preservation methods: physical (freezing) and chemical (commercial and fuel ethanol) for 15 and 60 days. Our results indicate that all tested preservation methods alter at least one of the isotopic values of the crickets when compared with the control. We therefore recommend the use of freshly processed material for SIA in crickets. In the second chapter, our main objective was to evaluate the isotopic fractionation of 13 C and 15 N associated with converting artificial diet into consumer cricket bodies and thus basic information has to be given in order to interpret the trophic niche crickets, based on SIA. In this regard, we estimate the isotopic values of δ 13 C and δ 15 N individuals of three species of crickets fed on artificial diet and compared with the isotopic values of the artificial diet. Also estimated the isotopic values of δ 13 C and δ 15 N found in bodies of crickets fed the field (unknown natural diet). We demonstrate that the SIA is a promising tool to investigate the trophic position of crickets, since estimate the isotopic fractionation of 13 C and 15 N in cricket bodies. Finally, in the third chapter we describe the trophic niches of crickets communities, evaluating the niche partition among coocorrentes species. We found evidence that the coexistence of species of crickets in natural communities involves partitioning of food resources. The foraging site directly influenced the use of diet and consequently on the trophic position of crickets, which submitted up to three trophic levels when evaluated in a global context of the diet. This partition is evidenced by the different δ15N values found in the bodies of crickets. The δ 13 C values show that crickets uses food resources originating from C 3 plants. Finally, we find evidence of narrowing of trophic niche as you increase the number of coocorrentes species.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

FIGURE 4. Pepoapua cariacica Jesus & Pereira n in A new genus and species of Neotropical Nemobiinae (Insecta: Orthoptera: Grylloidea: Trigonidiidae: Nemobiinae)

FIGURE 4. Pepoapua cariacica Jesus & Pereira n. sp., genitalia of male paratype. A—Photograph in ventral view; B— Photograph in dorsal view; C—Photograph in lateral view; D—Illustration in ventral view; E—Illustration in dorsal view; F— Illustration in lateral view. Abbreviations: ps.a.l—pseudepiphallic apical lobe; ps.m.l—pseudepiphallic median lobe; ps.ppseudepiphallic parameres; ps.sc—pseudepiphallic sclerite; ec.f—ectophallic fold; v.v—ventral valve; end.sc—endophallic sclerite; a.g—accessory gland

Carbon and nitrogen stable isotope values, and C/N atomic values for <i>Mellopsis doucasae</i>.

<p>Mean ± standard deviation of (a) <i>δ</i>¹⁵N, (b) <i>δ</i>¹³C, and (c) C/N atomic values from the following treatments: Fuel Et. 15—preserved in fuel ethanol for 15 days; Fuel Et. 60—preserved in fuel ethanol for 60 days; Com.Et. 15—preserved in 92.8% commercial ethanol for 15 days; Com.Et. 60—preserved in 92.8% commercial ethanol for 60 days; Frozen 15—frozen for 15 days; Frozen 60—frozen for 60 days; Control—freshly processed material (highlighted in gray). Different letters indicate significant differences between treatment groups (P < 0.05). All preservation methods resulted in significant ¹⁵N depletion compared to controls.</p

Carbon and nitrogen stable isotope values, and C/N atomic values for <i>Phoremia</i> sp.

<p>Mean ± standard deviation of (a) <i>δ</i>¹⁵N, (b) <i>δ</i>¹³C, and (c) C/N atomic values from the following treatments: Fuel Et. 15—preserved in fuel ethanol for 15 days; Fuel Et. 60—preserved in fuel ethanol for 60 days; Com. Et. 15—preserved in 92.8% commercial ethanol for 15 days; Com. Et. 60—preserved in 92.8% commercial ethanol for 60 days; Frozen 15—frozen for 15 days; Frozen 60—frozen for 60 days; Control—freshly processed material (highlighted in gray). Different letters indicate significant differences between treatment groups (P < 0.05).</p

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