Food manipulation and selection in the omnivorous grapsoid crab <em>Neohelice granulata</em> (Decapoda: Varunidae)

Abstract

Summary:Neohelice granulata is an omnivorous, semi-terrestrial burrowing crab endemic to southwestern Atlantic saltmarshes that behaves as a herbivore when it inhabits vegetated saltmarsh areas or a deposit feeder on bare mudflats. In order to gain insights into how non-specialized crabs manage to rely on low quality diets, we studied in laboratory i) how they use feeding appendages to manipulate the food items commonly eaten (halophytic plant leaves and sediment), and ii) their ability to sort particles when they act as deposit feeders by analysing the food particle content of sediment and stomach. According to the source of food consumed, different behaviours and mouthparts involved in food processing were observed. Sex differences were found in handling halophytic plant leaves in the herbivore feeding mode. In deposit feeding, a concentration of potentially N-rich items of animal origin was detected in stomach contents. Indirect evidence of food item concentration from sediment was revealed by analysis of the C and N content of sediment and feces. N. granulata seems to be an effective deposit feeder even though it lacks the characteristic mouthparts commonly associated with this type of food source. Keywords: crabs; deposit feeding; Neohelice granulata; feeding appendages; feeding mechanisms; food selection; omnivory.Manipulación y selección del alimento en el cangrejo grapsoideo omnívoro Neohelice granulata (Decapoda: Varunidae)Resumen: Neohelice granulata es un cangrejo semiterrestre cavador y omnívoro, endémico de las marismas del Atlántico sudoccidental. Se comporta como herbívoro cuando habita en áreas con vegetación halófila y como sedimentívoro cuando habita en llanuras fangosas. Se estudiaron en el laboratorio dos aspectos del comportamiento alimentario de este cangrejo para comprender cómo logra mantenerse en base a dietas de baja calidad: i) la manera en que usa los apéndices bucales para manipular los diferentes tipos de alimento comúnmente consumidos en cada hábitat (hojas de plantas halófitas y sedimento), y ii) su habilidad para seleccionar partículas cuando se alimenta de fango, comparando la composición de las partículas alimenticias presentes en el estómago y en el sedimento. Los cangrejos utilizaron diferentes piezas bucales y tuvieron distintos comportamientos de acuerdo al tipo de alimento consumido. Además, la manipulación de las hojas de plantas halófitas difirió entre sexos. El contenido estomacal de los cangrejos alimentados con fango mostró una mayor concentración de partículas ricas en N que el sedimento. El análisis del contenido de C y N del sedimento y las heces evidenció además la capacidad de selección de partículas nutritivas. N. granulata puede ser un sedimentívoro eficiente aunque sus piezas bucales no posean las características comúnmente asociadas al consumo de este tipo de alimento.Palabras clave: Cangrejos; alimentación de depósitos; Neohelice granulata; apéndices bucales; mecanismos de alimentación; selección del alimento; omnivoría.Citation/Como citar este artículo: Lan...

Effect of different protein supply on growth of three populations of a crab adapted to low energy diets

“…They eat mainly fresh leaves of halophytic plants (being able to degrade cellulose; [14]) and sediments (and the small organisms contained in it as crustaceans and foraminiferans) [3,14,15]. Both types of food are of low quality, being most of the organic components carbohydrates, with a very small proportion of protein (about 5 % in fresh plants and even lower in sediments, [15]). Therefore, the diet of N. granulata matches well with those described for more strictly herbivorous land crabs reviewed by Linton and Greenaway [17], which adapt their digestive apparatus, metabolism and life cycle to a low nitrogen intake.…”

“…SAO population has been previously studied [2] and compared to Mar Chiquita lagoon (MC, Fig. 1), a northern, genetically separated and extensively studied population ( [3,7,14,15,19,20] and references thereof ). Individuals from SAO were smaller and presented a shorter reproductive period and these differences were attributed, at least in part, to food availability.…”

Inter‐population differences in feeding ecology under nitrogen‐limited diets: Field growth and the role of cannibalism in limiting/improving reserve accumulation

“…obs. ) indicate that the proportion of sediment ingested during feeding in mudflats is significantly lower than the proportion observed in adults by Lancia, Bas, and Spivak (2014), and therefore, the information on adult feeding should not be extrapolated to juveniles. If diet varies during ontogeny, available energy could vary markedly depending on the size of individuals, and growth rate or energy storage could vary widely with age (Lucifora, Garcia, Menni, Escalante, & Hozbor, 2009).…”