Hormonal Regulation of Testicular Development in the Finless Porpoise Neophocaena asiaeorientalis sunameri: Preliminary Evidence from Testicular Histology and Immunohistochemistry

Circulating concentrations of thyroid hormones and cortisol in wild and semi-natural Yangtze finless porpoise (Neophocaena asiaeorientalis)

Our understanding about how environmental and biological variables may influence circulating thyroid and adrenal hormones in free-ranging cetaceans is limited. As such, we used liquid chromatography-mass spectrometry to determine concentrations of circulating cortisol and thyroid hormones (THs; tT3, tT4) in 132 Yangtze finless porpoises (YFPs) located in Poyang Lake, (PL, n = 92) and Tian-E-Zhou Oxbow reserve (TZO, n = 40). For overall hormone comparisons, animals were partitioned by age [juvenile and adult (male and non-pregnant, non-lactating female)], sex, season (winter or spring) and geographical location. Geographically, during winter, circulating THs were significantly higher in the PL versus TZO population. Seasonally, within PL, THs were significantly higher in the winter versus spring season. Animals were further binned into groups as follows: juvenile male (JM) and juvenile female (JF), adult male (AM), non-pregnant adult female, pregnant female and non-pregnant lactating female. Intra-group comparisons between locations showed a significant increase in JM THs at PL. Significant increases in THs during winter compared to spring were detected between JM and JF groups. Mean comparisons of cortisol within and between locations for each group identified a significant increase for TZO AM versus TZO pregnant female and JM and JF. Seasonally, in PL, only JF has significantly higher cortisol in winter versus spring. Finally, we established reference values of THs and cortisol for YFPs in different geographical locations. These references are important baselines from which the effects of environmental and biological variables on THs and cortisol may be evaluated.

Histological Variation in Blubber Morphology of the Endangered East Asian Finless Porpoise (Neophocaena asiaeorientalis sunameri) with Ontogeny and Reproductive States

The highly lipid-rich blubber in the hypodermis is a specialized structure that functions in thermoregulation, energy storage, buoyancy control, locomotion, and streamlining the body shape in marine mammals. The key objective of this study was to investigate blubber development in the East Asian Finless Porpoise (Neophocaena asiaeorientalis sunameri) across the ontogenetic (fetuses, calves, and adults) and reproductive states (adults, pregnant, and lactating). Blubber samples were collected from East Asian Finless Porpoises (EAFP) that were accidentally caught in the fishing nets in the Bohai/Yellow Sea from late April to mid May of 2015. The mean blubber depth was significantly thinner in fetuses across the ontogenetic groups and significantly thicker in pregnant and lactating vs. adult females across the reproductive states. Across the four regions in each group, we did not find significant variations in blubber depth. However, the correlations between body length and weight vs. blubber depth was significant. Histological observation identified three layers of stratified blubber with a significantly smaller adipocyte cell size in fetuses and a significantly higher area ratio of structural fiber in the middle and inner layers across the ontogenetic groups. Across the reproductive states, we did not observe a statistically significant difference in the adipocyte cell size or area ratio of the structural fiber. Our results suggest that prenatal blubber growth is characterized by an increase in the adipocyte cell count, while postnatal growth is the result of an increase in cell size. They also indicate that ontogeny can affect blubber depths and cellular measurements in the EAFP.