Establishing Endocrine and Behavioral Parameters of Reproduction in Pacific Walrus (Odobenus rosmarus divergens)

Abstract

Reproduction of walrus (Odobenus rosmarus) in zoos and aquaria has met with limited success. While basic information on reproductive characteristics is available, there is limited knowledge of reproductive physiology and endocrinology for walrus. The overall goal of the research was to monitor reproductive events and seasonal changes that occur in ex situ walrus of North America by utilizing a variety of methods. To track changes in males, longitudinal hormonal analysis of saliva samples, changes in testicular size, presence or absence of spermatozoa and seasonal fluctuations in behavior were examined. Saliva samples were collected from six male walrus for periods of 12 to 36 months. Measurements of testicular length and width were collected on a weekly basis. Baseline testosterone values for each animal were established using an iterative process that eliminated elevated values. Elevations were defined as values ≥ 2 times the individual’s baseline (range 0.838-4.228 ng/ml). The mean combined baseline testicular measurement for individuals (R linear length + R linear width + L linear length + L linear width) was 54.81±2.13 cm while the mean combined increased testicular measurement (an increase of 15% or more over minimum values) was 65.38±1.71. Three of six animals displayed the typical rise and fall of testosterone concentrations observed in seasonal breeders in the wild and elevations were coincident with reproductive behaviors. Behaviors included visual and vocal courtship displays, pursuit of females, clasping and penetration. Sperm presence in a single walrus during two years coincided with increased testicular measurements and mean duration of spermatozoal presence was 131±3 days. Endocrine profiles varied extensively among animals, demonstrating within-animal decline in testosterone levels over time, a lack of testosterone elevations coincident with the wild walrus breeding season and a blind male with a unique derivation in his endocrine profile, hormone elevations directly opposite the wild walrus breeding season. To track female reproductive cycles, longitudinal hormonal analysis of saliva samples and seasonal fluctuations in behavior were examined. Saliva samples were collected from six female walrus at least three times a week for periods of 12 to 55 months. Salivary estradiol-17β was deemed an unreliable indicator of the follicular phase because hormone concentrations did not display a rise in estrogen concentrations prior to a rise in progesterone concentrations nor increased estrogen concentrations coincident with estrus behaviors. The most commonly reported signs of behavioral estrus were soliciting male attention, clasping and penetration. In general, behavioral observation also was not a consistently reliable method for detecting impending estrus. Salivary progesterone was found to be unsuitable for monitoring the functional capacity of the corpus luteum because profiles were difficult to interpret biologically or physiologically. Progesterone profiles did not appear to coincide with behavioral or seasonal changes. However, periods of elevated progesterone concentrations were demonstrated in two of six females and were most likely representative of consecutive pseudopregnancies (mean 204.27 days). An inconsistency elucidated in this study involved a blind female with a unique derivation in her endocrine profile, inconsistent with the wild walrus breeding season and varying in time frame each year. Issues with walrus reproduction elucidated by this study included: within-animal decline in testosterone levels over time, unsynchronized cycles between animals residing together and the inconsistent timing of reproductive events in blind animals. To increase breeding success of the ex situ walrus population the following changes are proposed: a) increase the number of walrus in the population or consolidate existing walrus into larger social groups; and b) separate the genders during the non-breeding season or move animals to different facilities. Facility collaboration and continued monitoring of reproductive functioning via endocrine, anatomical and behavioral parameters would allow evaluation of the efficacy of the proposed changes.