A quantitative framework for ovarian dynamics

1. Ovarian dynamics describe the highly complex interplay between egg maturation, oviposition, egg resorption and the factors affecting them. While these processes have been intensively studied, further progress has been impeded by the lack of generally applicable quantitative tools to analyse experimental data. 2. The purpose of this study is to provide a quantitative framework based on a state space describing the different levels of egg maturation and resorption states (non-mature, mature, resorbing and resorbed eggs). This quantitative framework enables both the transition rates between the observable states and the unobservable states, such as resorbed eggs, to be estimated rigorously. We applied this approach to the ovarian response of the parasitoid species Nasonia vitripennis during a period of host and food deprivation. 3. A simple system of exclusively linear differential equations with four states captures the salient properties of the data. Resorption is shown to occur concurrently with egg maturation. We highlight widespread confusion associated with the use of the generic term ‘rate of egg resorption’ that has been used to describe three fundamentally different physiological processes that have contrasting rates. 4. The approach is also applied to an older data set gathered by Edwards (The Quarterly Journal of Microscopical Science, 1954, 95, 459–468), which encompasses a wider range of manipulations on host and food availabilities, as well as data on oviposition. Our analysis shows that ovaries only function at full capacity after a first host meal and hints towards anautogeny in this species. 5. While this study primarily focuses on insects, the methodology is general and is suitable for studying the reproductive biology of a broad class of organisms, including plants.