Identifying chemical signals and examining their role in reproduction in the maned wolf (Chrysocyon brachyurus)

Abstract

The maned wolf (Chrysocyon brachyurus) is a Neotropical canid species that exhibits a rare reproductive mechanism, induced ovulation. Unlike most other canids, the maned wolf is solitary, so induced ovulation is an important adaptation to ensure successful reproduction. Though the mechanism of ovulation induction remains unknown, it is suspected to be a urinary chemical signal. This dissertation has three main objectives: (1) Identify volatile organic compounds (VOCs) that are consistently found in maned wolf urine; (2) Examine differences in VOCs according to sex and reproductive status to distinguish putative semiochemicals; and (3) Investigate the behavioral and hormonal responses of female maned wolves to male urine stimuli. Monthly urine samples were collected from 11 maned wolves (five males, six females) in 2013 and weekly samples were collected from 13 maned wolves (six males, one castrated male, six females) in 2014. Urinary VOCs were extracted using headspace solid-phase microextraction and gas chromatography-mass spectrometry. The VOCs found in highest abundance and ubiquitously across samples were pyrazines, likely responsible for the pungent smell of maned wolf urine, and hemiterpenoid alcohols. The VOCs that contributed the most to classification as a male or female were 3-iodo-E-2-octenoic acid, 10-methyl-2-oxecanone, an unidentified compound, 1,1'-thiobis-cyclopentane, and 2-nonen-4-one. Fifty VOCs differed between intact males and a castrated male. The behavioral study assessed whether presenting male urine to females could prompt ovarian activity and behavioral interest without the physical presence of a male. Secondarily, this study investigated the effect of group housing females on reproductive hormones and behaviors. Three co-housed females were exposed to male urine for thirty days while four females housed as two sister pairs were controls and were not exposed. Daily behavioral observations were conducted on the treatment females pre-, during, and post-exposure. Fecal samples from all seven individuals were collected to assess metabolites of gonadal hormones. While none of the seven females ovulated, treatment females showed significantly higher estrogen metabolite concentrations than controls and behavioral interest was highest when urine was present. In two of the three groups, one female had higher reproductive hormone concentrations than conspecifics. Co-housed females engaged in agonistic encounters on average 8.5 times per hour. The female with the highest reproductive hormone levels was the dam, and she was the only individual to scent mark. This dissertation provided the most comprehensive analysis of maned wolf urinary VOCs to date and identifies several putative semiochemicals. The behavioral evidence supports the presence of urinary semiochemicals, and offered the first evidence that reproductive suppression may occur when co-housing females. Future studies to bioassay the putative semiochemicals and to systematically study reproductive suppression are recommended to further elucidate reproductive mechanisms in the maned wolf.