Sex-specific differences in nitrogen intake and investment by feral and laboratory-cultured cockroaches

We compared nutrient selection in a laboratory culture of the American cock roach (Periplaneta americana: Insecta, Blattodea) and a feral population wh ich was founded by escapees from the culture approximately 14 generations p rior to the study. In a first experiment, adult male and female cockroaches were provided with two nutritionally complementary synthetic foods, and th us allowed to select the protein and carbohydrate components of their diet independently. There were no differences in the amounts of carbohydrate eat en by the two populations. However, feral males ingested more protein than cultured males. In a second experiment, the construction of nitrogen budget s showed that the additional nitrogen ingested by feral males was allocated preferentially to accessory sex glands, rather than somatic tissue or excr etion via the faeces. This suggests a possible role for sexual selection in the dietary difference between the strains. By contrast with males, there was no statistically significant difference in the amount of protein eaten by females of the two populations. However, feral females were found to hav e a higher density of bacterial endosymbionts than cultured females. Since these symbionts are involved in the synthesis of essential amino acids, thi s might account for greater reproductive output observed in a previous stud y in the feral compared with the culture females. (C) 2000 Elsevier Science Ltd. All rights reserved.