Behmer, S.T. and Joern, A. (2008) Coexisting
     generalist herbivores occupy unique nutritional
     feeding niches. Proceedings of the National
     Academy of Sciences, USA 105, 1977-1982.

A mainstay of ecological theory and practice is that coexisting species use different resources, leading to the local development of biodiversity. However, a problem arises for understanding coexistence of multiple species if they share critical resources too generally. Here, we employ an experimental framework grounded in nutritional physiology to show that closely related, cooccurring and generalist-feeding herbivores (seven grasshopper species in the genus Melanoplus; Orthoptera: Acrididae) eat protein and carbohydrate in different absolute amounts and ratios even if they eat the same plant taxa. The existence of species-specific nutritional niches provides a cryptic mechanism that helps explain how generalist herbivores with broadly overlapping diets might coexist. Our empirical findings and experimental approach can be extended to generate and test predictions concerning the intensity of biotic interactions between species, the relative abundance of species, yearly fluctuations in population size, and the nature of interactions with natural enemies in tritrophic niche space.

Melanoplus differentialis, one of the generalist grasshopper species used in this sudy. (photo by S. Behmer)

Warbrick-Smith, J., Behmer, S.T., Lee, K.P.,
     Raubenheimer, D. and Simpson, S.J. (2006) 
     Evolving resistance to obesity in an insect.
     Proceedings of the National Academy of
     Sciences, USA 103, 14045-14049.

Consumption of energy-rich diets can lead to obesity and is associated with deleterious consequences not only in humans but also in many other animals, including insects. The question thus arises whether animals restricted over multiple generations to high-energy diets can evolve mechanisms to limit the deposition of adverse levels of body fat. We show that Plutella xylostella caterpillars reared for multiple generations on carbohydrate-rich foods (either a chemically defined artificial diet or a high-starch Arabidopsis mutant) progressively developed the ability to eat excess carbohydrate without laying it down as fat, providing strong evidence that excess fat storage has a fitness cost. In contrast, caterpillars reared in carbohydrate-scarce environments (a chemically defined artificial diet or a low-starch Arabidopsis mutant) had a greater propensity to store ingested carbohydrate as fat. Our results provide an experimental example of metabolic adaptation in the face of changes in the nutritional environment and suggest that changes in plant macronutrient profiles may promote host-associated population divergence.

Plutella xylostella, the diamondback moth, was the caterpillar used in this sudy. (photo by S. Behmer)

Pompilio, L., Kacelnik, A. and Behmer, S.T.
     (2006) State-dependent learned valuation drives
     choice in an invertebrate. Science 313,
     1613-1615.

Humans and other vertebrates occasionally show a preference for items remembered to be costly or experienced when the subject was in a poor condition (this is known as a sunk-costs fallacy or state-dependent valuation). Whether these mechanisms shared across vertebrates are the result of convergence toward an adaptive solution or evolutionary relicts reflecting common ancestral traits is unknown. Here we show that state-dependent valuation also occurs in an invertebrate, the desert locust Schistocerca gregaria (Orthoptera: Acrididae). Given the latter's phylogenetic and neurobiological distance from those groups in which the phenomenon was already known, we suggest that state-dependent valuation mechanisms are probably ecologically rational solutions to widespread problems of choice.

The gregarious form of Schistocerca gregaria, the desert locust, was used in this sudy. (photo by S. Behmer)

In the news:

Coping with excess
     (The Wild Side (Olivia Judson's NYTimes science blog), 14 July 2009)

Spence is interviewed about a paper in Science - "The sound of six-legged majesty"

     (ScienceNOW, 6 February 2009)

A review of "Coexisting generalist herbivores occupy unique nutritional feeding niches"

     (Faculty of 1000 (Biology), 7 April 2008)

Insect biodiversity linked to nutritional preferences

     (Texas A&M University, 4 February 2008)

Post oak grasshoppers emerging

     (Texas A&M University, 17 April 2007)

Insects hold clues for human obesity
     (Texas A&M University Systemwide Newsletter, October 2006)

Bingeing bugs avoid the bulge
     (Boston University, 10 October 2006)

Scientists explain why insects don't get fat
     (University of Oxford, 27 September 2006)

Obesity crisis in insects? Not a problem, says expert
     (Texas A&M University, 20 September 2006)

Hopping for wheaties (subscription may be required)
     (The Journal of Experimental Biology, 20 July 2006)

Locust research could tell us why Elvis preferred peanut butter sandwiches
     (University of Oxford, 17 March 2006)

Locust research suggests that physical state has much to do with learning 
     (Texas A&M University, 17 March 2006)

Leerer bauch fullt den Kopf (in German) [pdf]
     (Suddeutsche Zeitung, 21 March 2006)

Grasshoppers spurn spinach 
     (news@nature.com, 11 March 1999)