Reproductive trade-offs in the colorado checkered whiptail lizard (Aspidoscelis neotesselatus): an examination of the relationship between clutch and follicle size

Abstract

Life history theory predicts that there should be an inverse relationship between offspring size and number, because individuals cannot simultaneously maximize both when resources are limited. Although extensively studied in avian species, the occurrence and determinants of reproductive tradeoffs in oviparous reptiles are far less understood, particularly in parthenogenetic species. We studied this trade-off in the Colorado Checkered Whiptail, Aspidoscelis neotesselatus, a female-only parthenogenetic lizard. Using data previously collected in 2018 and 2019, we tested for clutch and egg size trade-offs and determined whether this relationship could be influenced by female size and aspects of physiological condition. Physiological condition included energy-mobilizing hormone (i.e. corticosterone ‘CORT’), oxidative stress (i.e. reactive oxygen metabolites ‘ROMs’), and innate immune function (bacterial killing ability ‘BKA’). We found the effect of clutch size on follicle size was significant, but not linear. Specifically, follicle size was on average larger in females with clutches of two follicles when compared to clutches of one follicle, but smaller in females with clutches of three when compared to clutches of two. In addition, females that were larger produced larger follicles regardless of clutch size. Neither CORT nor BKA affected the relationship between follicle size and clutch size. However, ROMs did explain variability in this relationship: oxidative stress was more elevated in females that produced larger clutches and larger follicles. We conclude that clutch size and body size are key life history traits that shape follicle size, and that investments into larger clutches and follicle size come at the cost of oxidative damage.