Urine metabolomics reveals the effects of confined environment on mating choice in adult male giant pandas.

Mate choice was an important factor affecting the success rate of natural mating of captive giant pandas. The influencing factors and mechanisms of the mate preference of captive giant pandas were still unclear, and it was speculated that they might be related to the psychological stress caused by the long-term confined environment restricting their free choice of physiological needs. In order to test this hypothesis, this work explored the urinary metabolites of 6 adult captive male giant pandas during breeding period. Differences in metabolite levels in giant panda urine samples were analyzed via Ultra High Performance LC-MS (UHPLC/-MS) comparing preservation to loss of natural reproductive capacity and success to failure of mating choice, trying to understand the psychological feelings of captive giant pandas in the process of mate choice from the perspective of all metabolites and related biochemical pathways, and fully revealed the mechanism of decline of their natural reproductive ability. The analysis results indicated that the loss of natural mating behavior of adult captive male giant pandas might be related to the disorder of tryptophan metabolism pathway and inhibition of arginine synthesis; the reason for the failure of mating choice caused by decreased libido might be related to the temporary decrease of androgen contents caused by the down-regulated of TCA cycle function and galactose metabolic pathway. These findings not only provide that adult male giant pandas in captivity do have psychological frustration caused by the inability to freely choose their favorite mate or failure of mating preference, but also showed that the changes in stress-related metabolic pathways caused by psychological frustration were an important reason for the decline of natural mating behavior of adult captive male giant pandas.