Ultrastructural investigations of sperm and genital systems in Gamasida (Acari: Anactinotrichida) current state and perspectives for future research
2001 - Volume: 42 Issue: 2 pages: 107-126
Keywordsphylogeny reproduction spermatozoa systematics ultrastructure
An overview on the current knowledge on gamasid reproductive systems, referring to behaviour, anatomy and ultrastructure including sperm morphology is given. Frequently, the terms tocospermy and podospermy are used to describe gamasid reproductive modes. Tocospermy is an insemination process in which the male uses the primary genital opening of the female for sperm transfer. However, tocospermy occurs in taxa with very different genital systems and behaviour, and hence the term puts together systems with fundamental differences, which are thus obscured. Podospermy refers to sperm transfer in which the male manipulates its sperm via secondary insemination pores into the female. The terms archispermy and neospermy were suggested to emphasize the fundamental differences between two groups of tocospermous taxa (i.e. Parasitina vs. the other tocospermous taxa). Archispermy refers to taxa with vacuolated sperm and a female genital system regarded to be plesiomorphic. Neospermy represents a derivative character set (ribbon-sperm, derivative female genital system) that is found in the tocospermous Parasitina and podospermous taxa. Podospermy is regarded to be a subtype of neospermy. To make these character states more precise and to clarify the problem, the following refined terminology is suggested: architocospermy should describe anactinotrichid taxa that have vacuolated sperm and a plesiomorphic genital system, e.g. paired oviducts, tubular ovary without nutritive tissue. Those taxa which possess ribbon sperm, unpaired oviducts, an ovary with nutritive tissue and males with chelicerae modified for sperm transfer represent neospermy with two subtypes: neotocospermy (Parasitina: no insemination pores, no peculiar sperm access system) and neopodospermy (Dermanyssina: with insemination pores and peculiar sperm access system). Parasitina and Dermanyssina are considered to represent sister groups. Though knowledge on genital systems of Anactinotrichida and Gamasida in particular has increased considerably during the last decades, many important problems await future investigation to improve these ideas. Some open questions are listed.
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