Economical load carrying in immature cockroaches

The energetic costs of carrying loads can significantly impact animal fitness but appear to vary dramatically among animals. For some, they equal the cost of carrying an equivalent amount of extra body mass, while others carry loads more economically. Locomotor systems can plastically respond to acute and chronic loading, but how such responses impact the energetics of locomotion is unclear. We asked how loading affects the energetics of an immature hemimetabolous insect, the cockroach Blaberus discoidalis, at rest and during locomotion at various speeds, and whether energetics change as animals adjust to chronic loading. Cockroaches carried loads economically as early as 2 h after load addition, with no change in energetic costs during a 10 day period. We discuss the implications of these findings and potential mechanisms underlying economical load carrying in arthropods.