Implications of the Bacteroid Urate System

The bacteroid-assisted ability of cockroaches to store, mobilize, and in some cases, transfer urates uniquely allows them to utilize nitrogen that is typically lost via excretion in the vast majority of insects (Cochran, 1985). These symbionts thus have a great deal of power in structuring the nutritional ecology and life history strategies of their hosts. Bacteroids damp out natural fluctuations in food availability, allowing cockroaches a degree of independence from the current food supply. An individual can engorge prodigiously at a single nitrogenous bonanza, like a bird dropping or a dead conspecific, then later, when these materials are required for reproduction, development, or maintenance, slowly mobilize the stored reserves from the fat body like a time-release vitamin. The legendary ability of cockroaches to withstand periods of starvation is at least in part based on this storage-mobilization physiology. The beauty of the system, however, is that stored urates are not only recycled internally by an individual, but, depending on the species, may be transferred to conspecifics, and used as currency in mating and parental investment strategies. Any individual in an ag

Fig. 5.8 "Salt and pepper" feces of Paratemnopteryx (= Shawella) couloniana; male, right; female and ootheca, left. The pile of feces to the left of the ootheca shows the variation in color of the pellets. Some of these have been separated into piles of the dark-colored fecal waste pellets (above the female) and the white, urate-filled pellets (arrow). Photo courtesy of Donald G. Cochran.

Fig. 5.8 "Salt and pepper" feces of Paratemnopteryx (= Shawella) couloniana; male, right; female and ootheca, left. The pile of feces to the left of the ootheca shows the variation in color of the pellets. Some of these have been separated into piles of the dark-colored fecal waste pellets (above the female) and the white, urate-filled pellets (arrow). Photo courtesy of Donald G. Cochran.

Fig. 5.9 Urate pellet excretion by adult female Parcoblatta fulvescens in relation to the reproductive cycle and level of dietary nitrogen. Filled triangles, 4.0% nitrogen diet; filled circles, 5.4% nitrogen diet; filled squares, 6.7% nitrogen diet. EC, egg case formation; ECD, egg case deposition. From Cochran (1986b), courtesy of Donald G. Cochran, with permission from Elsevier Press.

Days of the Reproductive Cycle of Female Parcoblatta fulvescens

Fig. 5.9 Urate pellet excretion by adult female Parcoblatta fulvescens in relation to the reproductive cycle and level of dietary nitrogen. Filled triangles, 4.0% nitrogen diet; filled circles, 5.4% nitrogen diet; filled squares, 6.7% nitrogen diet. EC, egg case formation; ECD, egg case deposition. From Cochran (1986b), courtesy of Donald G. Cochran, with permission from Elsevier Press.

gregation of the cockroaches that excrete urate pellets (like Parcoblatta) potentially benefits when just one of them exceeds its nitrogen threshold (Lembke and Cochran, 1990). In cockroach species in which the male transfers urates to the female during or after mating (Mullins and Keil, 1980; Schal and Bell, 1982), it would not be surprising to discover that female mate or sperm choice decisions are based on the size or quality of the nuptial gift (Chapter 6). The diversity of modes of post-ovulation provisioning of offspring observed in cockroaches (brood milk, gut fluids, exudates) is likely to be rooted in the ability of a parent to mobilize and transfer stored reserves of nitrogen (Nalepa and Bell, 1997). Finally, cockroaches are able to use the uric acid scavenged from the feces of birds, reptiles, and non-blattarian insects, adding to the list of advantages of a generalized coprophagous lifestyle (Schal and Bell, 1982).

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