ABSTRACT
Marine mammals1 have streamlined body shapes, hypertrophied axial musculoskeletal systems, and thick fatty layers that are morphological features, which reduce the energetic costs of both swimming and whole body thermoregulation (reviewed in Pabst et al. 1998). Interestingly, some of these morphological features would appear to threaten the temperature-sensitive reproductive tissues of these marine mammals. For example, male dolphins possess ascrotal testes – a condition identified as an adaptation for body streamlining (e.g., Howell 1930; Slijper 1936, 1979). As a consequence of streamlining and axial swimming style, the testes and epididymides are literally juxtaposed against or between thermogenic axial and abdominal locomotor muscles (Boice et al. 1964; Arkowitz and Rommel 1985; Pabst et al. 1998) and their reproductive tissues could potentially be exposed to core or above-core body temperatures. Cetaceans have core temperatures between 35 and 38 ºC, which are within the range of most other mammals (Costa and Williams 1999; Williams et al. 2001). These temperatures can effectively block spermatogenesis (Cowles 1958; Van Demark and Free 1970) and abdominal
temperatures can detrimentally affect long-term storage of spermatozoa in the epididymis (Bedford 1977). In many mammals, viable sperm production and epididymal storage require temperatures 2-6 °C below core temperatures (Moore 1926; Cowles 1965; Bedford 1977).
