Ultrastructure of the unusual spermatozoon of the Eurasian bullfinch (Pyrrhula pyrrhula)

Publication Type:Journal Article
Year of Publication:2007
Authors:Birkhead, TR, Giusti, F, Immler, S, JAMIESON, BGM
Journal:Acta Zoologica
Date Published:2007
ISBN Number:1463-6395
Keywords:bullfinch Pyrrhula, Fringillidae, neoteny, Pyrrhula, Pyrrhula pyrrhula, sperm ultrastructure
Abstract:Abstract The Eurasian bullfinch spermatozoon differs from typical passeridan spermatozoa in several major respects. The mature acrosome consists of a concavo-convex vesicle differing from the typical passeridan acrosome, which is a helical structure, is usually longer than the nucleus and has a prominent helical keel. The nucleus differs from that of other oscines in not showing a twisted cylindrical form, in being shorter, and in tending to be an elongate ellipsoid in shape. The chromatin often appears in an uncondensed form reminiscent of a spermatid and consists of discrete fascicles. A small proportion of the mature sperm population however, is characterized by marked chromatin condensation. The midpiece comprises a small group of mitochondria clustered around the nuclear–axonemal junction in contrast to the single, long mitochondrion wound helically around the axoneme that is found in typical Passerida. The presence of a proximal centriole (in addition to the distal one) is a notable difference from all other oscine passerines. We suggest that the unusual morphology of the Eurasian bullfinch spermatozoon, resembling that of a spermatid, is the result of the progressive suppression of the final stages of spermiogenesis and is associated with the likelihood that sperm competition is infrequent in this species.
Short Title:Acta Zoologica
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