Prenatal steroid hormones increase natal dispersal in Sceloporus jarrovii

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Sarah E. Manka-Worthington and Diana K. Hews, Biology, Indiana State University, Terre Haute, IN

Background/Question/Methods
Maternal steroid hormones can affect offspring dispersal, as has been found in Lacerta vivipara, a live-bearing species. We examined this in Sceloporus jarrovii, a distantly-related ovoviviparous lizard. Further, this species exhibits female-female aggression peaks during the months when birth occurs. Predators, including conspecifics, regularly eat offspring Sceloporus jarrovii. This led us to the question: Will elevated levels of stress hormones in the late-gestational stage affect offspring dispersal patterns in this live-bearing lizard? To understand associations of maternal corticosterone (a hormone released in stress responses, abbreviated hereafter as CORT) with offspring dispersal behavior, we measured maternal CORT at time points prior to and after parturition. We also recorded newborn movements in large outdoor natal arenas. We collected daily offspring dispersal data until final measurement and release on Day 14 after birth.
Results/Conclusions
Maternal steroid hormones were elevated in the last weeks of gravidity. The female CORT decreased immediately after parturition and decreased in the late post-parturition stage for the natural experiment. In the CORT-implanted females, CORT increased immediately after parturition and then decreased. Blank-implanted females maintained their CORT levels through both parturition stages.
Maternal plasma CORT levels decreased after parturition. Offspring associated with dams and with each other after birth, then exhibited potential dispersal behavior starting on Day 6 after birth. Pups maintained associations with littermates until at least Day 14 after birth. Offspring of females with highest prenatal CORT dispersed soonest, around Day 4 after birth. In a second field season, we manipulated late-gestation maternal CORT levels using implants. Control females received blank implants. Again, we found that apparent offspring dispersal was earlier in offspring of CORT-implanted dams, relative to offspring from control-implanted females.
Higher maternal CORT levels may reflect stressful environments. This supports the hypothesis that earlier offspring dispersal from stressful environments may be mediated by higher prenatal maternal CORT levels. Highly stressed adult females may consume offspring – kin or not – to restore some lost energy resources after parturition.