Ovarian apoptosis is regulated by carbohydrate intake but not by protein intake in speckled cockroaches

When the likelihood of reproducing successfully is low, any prior investment in developing oocytes may be wasted. One means of recouping this investment is oosorption - where ova are absorbed and resources salvaged so they can be re-allocated to other traits. Food-limited female speckled cockroaches (Nauphoeta cinerea) appear to use this strategy. However, it is unclear if total food intake or the availability of specific nutrients induces this process. Here, we used the geometric framework of nutrition to determine how protein, carbohydrate and energy intake affect levels of ovarian apoptosis and necrosis (controlled versus uncontrolled cell death) in the terminal oocytes of female N. cinerea. We then compare the effects of nutrient intake on apoptosis (a key step towards oosorption) and offspring production to better understand the relationship between diet, apoptosis and female fitness. We found that even when food was abundant, females experienced high levels of apoptosis if their diet lacked carbohydrate. Necrosis was reduced when energy intake was high, but largely irrespective of nutrient ratio. Offspring production peaked on a low protein, high carbohydrate nutrient ratio (1_P:7.96_C), similar to that which minimized apoptosis (1_P:7.34_C) but not in the region of nutrient space that minimized necrosis. Thus, females consuming an ideal nutrient blend for reproduction can invest heavily in their current brood without needing to salvage nutrients from developing ova. However, offspring production was more dependent on carbohydrate consumption than apoptosis was, suggesting that the importance of carbohydrate in reproduction goes beyond regulating oosorption. This reliance on carbohydrate for female reproduction may reflect the unusual reproductive and nutritional physiology of speckled cockroaches; attributes that make this species an exciting model for understanding how diet regulates reproduction.