Combining reproductive endocrinology and ROC analysis to identify changes with sex, age, and pregnancy status in botos Inia geoffrensis

Abstract

Reproductive hormone profiles were described against physical characteristics during growth and development in male and female botos (Amazon River dolphins Inia geoffrensis) and during pregnancy. We determined hormone concentrations in 226 wild botos located in Mamirauá Reserve, Amazonas State, Brazil, as a part of the long-term population monitoring program known as Projeto Boto. Additionally, we applied receiver operator characteristic (ROC) analysis to compare diagnostic probabilities of using ultrasound, hormones, or combinations of these to detect pregnancy. Based on single-point analysis of serum testosterone (T), males with <2.5 ng ml-1 T and a mean 163 cm total body length were classified as immature, 2.5 to <4.9 ng ml-1 T and 183 cm as pubescent, and >5 ng ml-1 T and 227 cm as adult botos. For females, only progesterone (P4), T, relaxin (Rlx), and the combination of P4 × T2 were significantly different between non-pregnant and pregnant females, but androstenedione (A4) and the P4:T ratio were not. ROC analysis indicated that ultrasound and P4 × T2 were considered excellent as pregnancy diagnostic tests, and P4, T, and Rlx were classified as good predictors. Results indicated that negative and positive predictive probabilities from each diagnostic test could be used to accurately predict a pregnancy and calf loss rate of 13% for this population. Application of these methods for evaluating wild population reproductive success from a single serum sample can now be used for health evaluations of wild populations of boto and provide timely information for the development or evaluation of any conservation initiatives.