Hormonal biomarkers provide insights into the reproductive biology and pollutants–associated health hazards of endangered dolphins

Abstract

Contaminants are known to contribute to the reproductive health hazards of wildlife, but pollutants–associated detrimental impacts on the endangered Indo–Pacific humpback dolphins (Sousa chinensis, IPHD) are largely unknown due to a lack of reproductive parameters. Here we validated and applied blubber progesterone and testosterone as reproductive biomarkers to assess reproductive parameters of IPHD (n = 72). The gender–specific progesterone concentrations and progesterone/testosterone (P/T) supported progesterone and testosterone as valid biomarkers in identifying the genders of IPHD. Significant month–to–month variations of two hormones indicated a seasonal reproduction, in accordance with the observation of photo–identification approach, further supporting testosterone and progesterone as ideal reproductive biomarkers. Progesterone and testosterone concentrations showed significant differences between Lingding Bay and West–four region, possibly due to chronically geographic–specific pollutants differences. The significant relationships between sex hormones and multiple contaminants suggested that contaminants contribute to the disruption of testosterone and progesterone homeostasis. The best explanatory models between pollutants and hormones suggested that dichlorodiphenyltrichloroethanes (DDTs), lead (Pb) and selenium (Se) were the major risk factors jeopardizing the reproductive health of IPHD. This is the first study on the relationship between pollutant exposure and reproductive hormones in IPHD and represents a substantial advance in understanding the detrimental reproductive impacts of pollutants on endangered cetaceans.