Evol Ecol Res 13: 461-477 (2011)     Full PDF if your library subscribes.

Dietary differences among colour morphs of pygmy grasshoppers revealed by behavioural experiments and stable isotopes

Einat Karpestam and Anders Forsman

School of Natural Sciences, Linnaeus University, Kalmar, Sweden

Correspondence: A. Forsman, School of Natural Sciences, Linnaeus University, 391 82 Kalmar, Sweden.
e-mail: anders.forsman@lnu.se


Question: Do alternative colour morphs differ in food preferences and realized dietary niches?

Hypothesis: Colour morphs represent alternative phenotypes that exploit different dietary niches due to combined effects of differences in food preferences and physiological demands, availability and spatial distribution of alternative food types, and morph-specific microhabitat utilization.

Organisms: Adult female Tetrix subulata pygmy grasshoppers belonging to one of three colour morphs: dark, pale or striped. Colour pattern in these grasshoppers is genetically influenced and barely, if at all, affected by developmental plasticity in response to environmental cues. Tetrix subulata inhabits damp places, primarily on the soil surface, and feeds on algae, short grass, moss, and humus. We collected and studied individuals of seven populations in southeast Sweden: three from pastures, two from alkaline fens, and two from burnt clear cuts.

Methods: First, we performed two multiple-choice feeding experiments: (1) between individuals from five different source populations, and (2) between individuals of different colour morphs from the same population. Second, we measured natural abundances of carbon and nitrogen stable isotope ratios (δ13C and δ15N) in free-ranging individuals from two populations to test for differences in long-term diets among populations and colour morphs.

Results: In the multiple-choice feeding experiments, utilization of food types differed both among populations and among colour morphs within a population. The comparisons of stable isotope ratios indicated long-term differences in diet both among populations and among colour morphs.

Conclusions: Food preferences and dietary niches differ among pygmy grasshopper populations and colour morphs.

Keywords: colour polymorphism, insect, niche, resource partitioning, Tetrix subulata.

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