Bottlenose dolphin (Tursiops truncatus) sperm revisited: Motility, morphology and ultrastructure of fresh sperm of consecutive ejaculates

Gerhard van der Horst, Katarina Medger, Daniela Steckler, Ilse Luther, Paul Bartels

University of the Western Cape, Private Bag X17, Bellville 7535, South Africa; National Zoological Garden, South African National Biodiversity Institute, PO Box 754, Pretoria 0001, South Africa; Department of Zoology and Entomology, University of Pretoria, Hatfield/Pretoria 0028, South Africa; Section of Reproduction, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, Pretoria 0110, South Africa; GEOsperm, Brits 0250, South Africa; Department of Nature Conservation, Tshwane University of Technology, Pretoria-West 0001, South Africa.

Abstract: Computer aided sperm analysis systems allow detailed examination of sperm motility and morphology variables, which are important for the understanding of the spermatology of a species and the development of assisted reproductive techniques. Cetacean biology is too complex to study in the wild and data from captive individuals provide an important alternative for the conservation of these charismatic animals. The present study evaluates ejaculate and sperm characteristics, including sperm motility, kinematic variables and quantitative sperm morphology and ultrastructure, of consecutive ejaculates from Atlantic bottlenose dolphins (Tursiops truncatus). Sperm concentrations and total and progressive motilities were greater in the second than the first ejaculate, with all ejaculates being of very high quality (6.9–1127 × 106/ml sperm concentration, 75% to 91% total motility and 89% to 96% normal sperm). Most sperm in an ejaculate (≥84%) were highly (VCL>150 μm/s) and progressively motile with very few abnormal sperm. The sperm have small heads, a short but very bulky midpiece and a long tail. Detailed sperm morphometrics using CASA indicated there were similarities from one ejaculate to the next. The large mitochondria with extensive cristae mitochondriales are tightly packed in the midpiece resulting in a large midpiece volume. All the semen and sperm characteristics indicate high quality sperm and support the assumption that a multimale mating system is present in T. truncatus.

https://doi.org/10.1016/j.anireprosci.2018.06.009