Sperm development and structure in Bursaphelenchus luxuriosae (Nematoda: Aphelenchoidea: Aphelenchoididae)

Abstract

Sperm development and structure in the wood-inhabiting fungal and plant-feeding nematode, Bursaphelenchus luxuriosae, were studied using transmission electron microscopy to evaluate interspecific similarities and differences of spermatozoa in nematodes. In general, spermatogenesis in B. luxuriosae fits the ‘rhabditid’ pattern supported by morphological and phylogenetic analysis of the order Rhabditida. Spermatocyte development includes formation of complexes of fibrous bodies (FBs) with membranous organelles (MOs), the complexes dissociate in the spermatids into separate components, and the immature sperm contain MOs but lack FBs, which transform into a dense matrix of sperm cytoplasm. The female spermatheca contains mature spermatozoa as bipolar cells subdivided into a pseudopod devoid of organelles and a main cell body containing a nucleus without a nuclear envelope, numerous mitochondria, and peripheral MOs as pouches opening to the exterior via pores. Data on B. luxuriosae are used for analysis of variable quantitative and morphological characteristics of spermatozoa in Aphelenchoidea. General size of spermatozoa and their MOs have little value for comparative analysis. The MO knobbles look uniform in immature spermatozoa of each aphelenchoidid species studied and may be considered as a taxonomically specific ultrastructural feature. The presence or absence of FBs in immature spermatozoa demonstrates the diagnostic value of the aphelenchoidid sperm structure at the species level. Analysis also shows close similarity of spermatozoa in Bursaphelenchus spp. and Caenorhabditis elegans, the model species with comprehensive data on sperm biology. This may be used to identify new ways for the control and suppression of harmful nematode species such as B. xylophilus.