ABSTRACTS OF POSTERS –ECOLOGY


E 02 comparative aspects of reproductive seasonality in male common dolphins (Delphinus delphis) and harbour porpoises (Phocoena phocoena)


Sinéad Murphy (1,2,3), Rob Deaville (1), Paul D Jepson (1), Robert J Reid (4)


(1) Institute of Zoology, Regents Park, London, NW1 4RY, UK (2) Coastal-Marine Research Group, Institute of Natural Sciences, Massey University, Private Bag 102 904, Auckland, New Zealand (3) Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, St Andrews, KY16 8LB, UK (4) Wildlife Unit, SAC Veterinary Services, Inverness, IV2 4JZ, UK


s.n.murphy@massey.ac.nz


At both the species and population level males adapt different reproductive cycles and mating strategies, reflected in physiological and morphogical adaptations, due to reproductive isolation and availability of receptive females. Reproductive seasonality synchronises energetically demanding biological periods, such as lactation in females, to the most favourable time of the year. Consequently, male seasonal breeders may exhibit spermatogenesis regulation with individuals being subject to cycles of testis involution and reactivation. Testicular activity is controlled both genetically and hormonally, though environmental and other factors can inhibit reproduction. Within the current study, a full assessment of seasonal changes in testicular function and structure in mature males was undertaken on two cetacean species exhibiting reproductive seasonality and inhabiting temperate environments. Histological evaluations of spermatogenesis were carried out on stranded and by-caught mature males from North-east Atlantic populations of the common dolphin (Delphinus delphis) (n=92) and harbour porpoise (Phocoena phocoena) (n=78). Models were used to describe seasonal variations in testicular size and proportion of germinal cells present in the seminiferous tubules, and included covariates such as age, health and nutritional status. Both species partake in sperm competition, identified by their relative testes size. Considering the cost of such testicular maintenance, it would be expected that males undergo a period of involution or complete arrestment of spermatogenesis outside the breeding period. For both species, males exhibited seasonal testicular regression, though not a complete cessation of spermatogenesis. Meiosis was ongoing and spermatozoa were observed in seminiferous tubules collected outside the defined breeding period. This is in contrast to a contiguous P. phocoena population in the western North Atlantic, where complete involution and recrudescence was observed. Comparative aspects between both species in testicular form and function, effects of nutritional condition on sperm production and the presence of old sterile individuals are explored further within the study.


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