5. Reproductive frequency and embryonic development
Because mothers must rebuild energy reserves following reproduction (Sperry & Weatherhead 2009), we calculated the maximum reproductive frequency of oviparous species by dividing the yearly energy budget of non-reproductive females of an adult female by the energy needed to produce a clutch (energy content of a clutch of eggs; Table S1). We assumed a female began her first clutch after accumulating sufficient energy to produce a clutch (energy content of a clutch of eggs; Table S1). Thereafter, she would deposit that clutch after embryos had completed 1/3 of development (embryo temperature assumed to match the mother’s temperature (Andrews & Mathies 2000)). We then calculated the incubation time as the time needed for remaining 2/3 of development (in soil – 6cm depth and 50% shade (Angilletta et al. 2009)). We assumed females would not produce a new clutch of eggs when the projected incubation time would be over 100 days (Tinkle & Gibbons 1977) or the number of clutches in a year reached the maximum reproductive frequency.
Because most viviparous squamates ovulate large yolked eggs and have placentae with little complexity (type I placentae) (Blackburn 1993), we assumed that viviparous embryos have no ‘placental’ connections with maternal bodies (embryos use energy only from yolks to fuel development (Ma et al. 2018)). Similarly, we assumed a clutch of viviparous embryos started to develop inside the mother’s body after the female accumulated sufficient energy to produce a clutch (energy content of a clutch of eggs; Table S1), and calculated the time needed to complete development. We assumed viviparous females would not have a litter of embryos if the required developmental time (1 of development) would be over 150 days referring to the “100 day” limits for incubation time of oviparous species (2/3 of development). We calculated developmental times (Function S4) by accumulating hourly developmental rates (D), which were a function of developmental temperatures. We calculated developmental success (percentage of survived embryos) with a function of mean daily minimum and maximum developmental temperatures (Function S5).