Abstract

Feeding of two amphibian species (Anura: Hylidae) during the low temperatures season and its relationship with energy storage in Santa Fe, Argentina. In environments with thermal and pluvial seasonality such as those of the Middle Paraná River floodplain (Province of Santa Fe, Argentina), most amphibian species reproduce during the warm season and drastically diminish their activity during winter. Even though, a few species remain active during the cold season, such as Hypsiboas pulchellus that has its reproductive peak during the autumn-winter period (and the consequent energy demand). The objective of this study was to analyze and compare the feeding and development of fat bodies during the low temperature season for H. pulchellus and Dendropsophus nanus. We analyzed entire gastrointestinal tract contents of both species (H. pulchellus = 110 specimens; D. nanus = 114 specimens) and applied an index (IRI%) that combines prey abundance, volume and frequency to describe frogs diets; we used fat bodies weights as indicators of stored energy reserves. We compared diet between species with a niche overlap index (Ojk: 0-1) and used null models to ascribe statistical significance to evaluate overlap; and we analyzed variation in empty guts proportions through months and between species. Also, using ANCOVAs we explored differences in fat bodies, number and volume of prey consumed along months, between species and sexes. The most important preys in H. pulchellus diet during the cold season were Araneae (IRI% = 34.96), Chironomidae (IRI% = 33.08), Tipulidae (IRI% = 11.44) and Gryllidae (IR1% = 7.31); while for D. nanus, Chironomidae (IR1% = 48.14), Tipulidae (IRI% = 18.41), Psychodidae (IRI% = 7.44) and Araneae (IRI% = 7.34). Diet overlap between species was elevated (Ojk=0.78) and higher than expected by chance (mean simulated indices: Ojk = 0.04; p[observed > or = expected]<0.01; p[observed < or = expected] = 1). In H. pulchellus there was a monthly variation in number of prey per gut, while in D. nanus there was a difference in fat bodies development between sexes. Fat bodies development, number of prey per gut and preys volume also varied between species. Despite diet similarity between H. pulchellus and D. nanus, each species showed a different strategy to accumulate energy and support their activity during the cold season. The low rate of gastrointestinal emptiness in H. pulchellus (< 10% in any analyzed month) together with the poor development of their fat bodies, allows us to point out that, to sustain the breeding elevated energy demands, this species continues with a high feeding rate even at the low temperatures of cold season. On the other hand, the rate of gastrointestinal emptiness of D. nanus was higher than that of H. pulchellus (May = 17.24%, July = 22.22% and August = 35.71%), while their fat bodies were well developed. Thus, D. nanus would depend more on their stored reserves to sustain the energy demands of being active during the low temperatures season and hence would reach the reproductive season in spring-summer in good body condition.

Highlights

  • En las regiones de climas con estacionalidad térmica y pluviométrica, la mayoría de las especies de los ensambles locales de anfibios se alimentan y reproducen en la estación cálida y lluviosa (Sánchez et al 2007, López et al 2011)

  • En los meses más fríos, la mayoría de las especies entran en hibernación, disminuyendo drásticamente la actividad de sus poblaciones (López et al 2011)

  • Los especímenes capturados fueron inmediatamente sacrificados mediante la aplicación de un anestésico de uso humano sobre la piel de la cabeza y vientre, y fijados in situ con una solución al 10% de formalina amortiguada en el transcurso de no más de una hora posterior a la eutanasia (McDiarmid 1994, Angulo et al 2006)

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Summary

Introduction

En las regiones de climas con estacionalidad térmica y pluviométrica, la mayoría de las especies de los ensambles locales de anfibios se alimentan y reproducen en la estación cálida y lluviosa (Sánchez et al 2007, López et al 2011). CUADRO 1 Análisis (ANCOVAs) de los cuerpos grasos y de la cantidad y volumen de las presas consumidas entre sexos, entre meses y entre especies (en H. pulchellus no se compararon los sexos debido al reducido número de hembras)

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