Histology and morphometrics of testes of the white-sided dolphin (Lagenorhynchus acutus) in bycatch samples from the northeastern Atlantic

Abstract

The testes of 31 Atlantic white-sided dolphins, Lagenorhynchus acutus bycaught in the northeastern Atlantic were studied by histological and morphometric techniques. Twenty specimens were classified as mature, nine as immature and two as pubescent. Between immature and mature specimens there were overlappings in body length and body weight, but clear differences in the diameter of seminiferous tubules (o80 and 480 mm) and the proportion of seminiferous tubules to interstitial tissue (ST:INT-ratio). Also relative testes weight differed clearly. The pubescent specimens showed intermediate characteristics. Spermatogenetic activity of mature dolphins ranged from quiescent to different degrees of activity and varied even in animals from the same site and capture date. The fact that we found mature males with quiescent testes suggests a seasonal rather than a continuous spermatogenesis. We assume that sexual activity in L. acutus begins at an age of 7-8 GLGs and that the reproductive season of this species in the northeastern Atlantic starts in February. Further, the ultrastructure of the spermatozoon is similar to that of the related Lagenorhynchus obliquidens.

Morphology and Ultrastructure of the Amazon River Dolphin (Inia geoffrensis) Spermatozoa

“…The postacrosomal region of I. geoffrensis spermatozoa has a smooth surface like that of all cetacean sperm previously examined, with the exception of the Delphinidae family (Fleming et al, ; Mogoe et al, ; Kita et al, ; Miller et al, ; Meisner et al, ; Plön and Bernard, ; Miller et al, ; Neuenhagen et al, ; Li et al, ). The spermatozoa from all delphinids already examined, excluding killer whale ( Orcinus orca ), show several parallel longitudinal ridges in the postacrosomal region.…”

“…Among cetaceans already evaluated, the spermatozoa morphology varies between whales and dolphins, as well as among dolphin families (Fleming et al, ; Miller et al, ; Meisner et al, ; Plön and Bernard, ; Miller et al, ; Neuenhagen et al, ; Li et al, ). Those variations are related to differences in phylogenetics and mating strategies, as reported in other mammals.…”

Variation in sexual behaviors in a group of captive male Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis): motivated by physiological changes?

“…Seasonal reproduction has also been described in aquatic mammals, including sea lions (Eumetopias jubatus) [6], manatees (Trichechus manatus manatus) [7], and seals (Phoca vitulian) [8]. Male cetaceans are reported to enter a resting phase in the nonbreeding season, during which testis size decreases and sex hormones decline, as demonstrated in common dolphin (Delphinus delphis) [9], white-sided dolphin (Lagenorhynchus acutus) [10], and blue white dolphin (Stenella caeruleoalba) [11].…”

Biological matrices for sampling free‐ranging cetaceans and the implications of their use for reproductive endocrine monitoring

“…) or on histological examination of gonads and reproductive tracts from by‐caught, harvested, or stranded animals (Neuenhagen et al. ). Though very valuable, these sample sets are frequently biased, because certain demographic groups are either over‐represented or under‐represented (Thayer et al.…”

“…Most of the existing information on marine mammal reproductive physiology is based on the observation of captive individuals (Robeck et al 2001) or on histological examination of gonads and reproductive tracts from by-caught, harvested, or stranded animals (Neuenhagen et al 2007). Though very valuable, these sample sets are frequently biased, because certain demographic groups are either over-represented or under-represented (Thayer et al 2003, Ferreira et al 2014.…”