231 SEMINAL QUALITY IN WHOOPING CRANE (GRUS AMERICANA) IS AFFECTED BY STAGE OF BREEDING SEASON BUT NOT BY AGE OF INDIVIDUAL

Abstract

The whooping crane is one of the most critically endangered species in North America. The species underwent a severe genetic bottleneck with only 16 individuals remaining in the wild as of 1942. Captive breeding began in 1966 and continues to produce chicks for release in order to establish new wild populations. However, captive birds experience poor reproduction with approximately 40% of eggs being infertile. Males have been known to reach sexual maturity at 5 years of age and continue to reproduce almost as long as the duration of their adult life (i.e. 40 years). Understanding factors affecting seminal quality may assist in identifying and correcting causes of suboptimal reproduction. Our objectives were to determine the influence of age and reproductive seasonality on seminal quality. We hypothesised that seminal quality variations among whooping cranes and ejaculates within a given individual over time were due to bird age and stage of breeding season. In 2010, twenty-nine whooping cranes of 5 age groups housed at Patuxent Wildlife Research Center (Laurel, MD, USA) were studied: ≤5 years (n = 3); 6–10 years (n = 7); 11–15 years (n = 7); 16–20 years (n = 4); >20 years old (n = 8). Semen was collected using a manual manipulation technique at 3 stages of the breeding season: early (March, n = 29) mid (April, n = 24), and late (May, n = 14). Samples were evaluated for seminal volume and sperm concentration, motility, and morphology, with data evaluated by analysis of variance. Bird age had no influence on seminal quality, whereas stage of breeding season affected seminal volume and the proportion of sperm with normal morphology (95% confidence interval). Specifically, samples collected during Mid breeding season had the highest volume (mean ± SEM; early: 42.0 ± 8.0 μL; mid: 66.0 ± 15.2 μL; late: 39.7 ± 17.8 μL), but lowest proportions of structurally normal sperm (early: 78.4 ± 3.7%: mid: 61.5 ± 3.2%; late: 69.7 ± 3.4%). There was a significant difference (P = 0.06) in sperm concentration among stages of the breeding season (early: 66.3 ± 18.8 × 106 sperm mL–1; mid: 179.2 ± 46.2 × 106 sperm mL–1; late: 91.4 ± 47.8 × 106 sperm mL–1). Sperm motility was unaffected by season (early: 36.4 ± 3.5%; mid: 45.9 ± 4.1%; late: 48.0 ± 4.9%). In summary, there is a peak in seminal quality that corresponds with higher volume and more sperm during the mid stage of the season, although with higher instances of structural abnormalities. Despite the small founder base for this species, males in this population produce sperm with no variation in seminal quality across a wide variation in age.