Xavier Mattei

SPERMATOZOON ULTRASTRUCTURE AND PHYLOGENETIC RELATIONSHIPS IN THE MONOGENEANS (PLATYHELMINTHES)

Abstract Justine J.-L. , Lambert A. and Mattei X. 1985. Spermatozoon ultrastructure and phylogenetic relationships in the monogeneans (Platyhelminthes). International Journal for Parasitology 15: 601–608. New observations reported in this study together with bibliographical data allow comparisons of spermatozoon ultrastructure in 28 genera of monogeneans, belonging to 19 families. The authors propose to compare and classify monogenean spermatozoa using two simple ultrastructural characteristics: (a) the number of axonemes, 1 or 2, (b) the presence or absence of cortical microtubules. These traits make it possible to group monogenean spermatozoa in four patterns. Pattern 1 (2 axonemes plus microtubules) is characteristic of the polyopisthocotyleans (9 families). The three other patterns are found in the monopisthocotyleans. Pattern 2 (2 axonemes without microtubules) is found in the Capsalidae and Dionchidae, which seem closely related, and also in the Udonellidae, Gyrodactylidae and Euzetrema . Pattern 3 (1 axoneme plus 1 altered axoneme plus microtubules) is found in the Monocotylidae and Loimoidae. Pattern 4 (1 axoneme without microtubules) is found in the Amphibdellatidae, Ancyrocephalidae, Calceostomatidae and Diplectanidae. A phylogeny of the monogeneans is drawn from the data of comparative spermatology; this scheme coincides in many points with the phylogeny of Lambert (1980) which was based on the study of chaetotaxy and ciliated cells of the oncomiracidium.

Réinvestigation de l'ultrastructure du spermatozoïde d'Haematoloechus (Trematoda: Haematoloechidae)

en The threadlike spermatozoon of the frog lung fluke, Haematoloechus, shows two patterns of external ornamentation. The first type is anterior and consists of bristles on the membrane that coincide with certain peripheral microtubules. This already exists in the zone of differentiation (ZD) of the young spermatid. The ZD is pinched off from the cytoplasmic mass at the arching-membrane level. The centriolelike body and striated roots are depolymerized. The two centrioles, made up of triplets, and the bristles are retained in the anterior part of the spermatozoon. The second type is more posterior. At this level, the transverse sections of the spermatozoon are asymmetric; only the larger side has peripheral microtubules, arranged in a semicircle around the axoneme, and a thick external crenate layer on its membrane. After several micrometers, this zone ends in an open collar (collerette) enclosing the next region of the spermatozoon. Only the part anterior to the collar is motile; on spontaneously breaking off, this region is mobile, although the unbroken spermatozoon is not. After the collar there is a region without microtubules. Then comes the very long middle region with dorsally and ventrally placed microtubules; the nucleus is at the posterior end. This new spermatozoon pattern, with retained ZD and anterior centrioles, resembles what we described earlier in a didymozoid. It probably occurs often in Digenea and perhaps other Platyhelminthes as well.

Etude ultrastructurale de la spermiogenèse et du spermatozoïde d'un Plathelminthe: Gonapodasmius (Trematoda:Didymozoidae)

The technique of serial sections has been employed to study spermiogenesis and spermatozoon of Gonapodasmius. The zone of differentiation (ZD) shows no centriole-like body and no striated root. Peripheral microtubules are of two types: laterally placed thick microtubules which are spaced and coincide with external bristles on the membrane; and dorsally and ventrally placed thin microtubules which are closely aligned. The two parallel flagella fuse with the median cytoplasmic process. The nucleus, mitochondrion, and thin microtubules migrate distally. The arching membranes, at the base of the ZD, mark the area where the mature spermatozoon is pinched off from the cytoplasmic mass. The spermatozoon consists of four regions. (a) The anterior region, made of the ZD, has peripheral microtubules with external bristles, viewed in toto as longitudinal ornamentations. Two centriolar derivatives, made up of nine singlets each, are continued as two 9+“1” flagella, classic in Platyhelminthes. (b) The intermediate region shows no peripheral microtubules. (c) The middle region shows nucleus, mitochondria, and ventral microtubules without ornamentations. (d) In the terminal region, the two flagella separate. The first two regions have never been described in previously studied Platyhelminthes spermatozoa.

Comparative ultrastructural study of spermiogenesis in monogeneans (flatworms). 2. Heterocotyle (Monopisthocotylea, Monocotylidae)

The mature spermatozoon of Heterocotyle is threadlike and uniflagellate; however, the spermiogenesis exhibits two axonemes. The early zone of differentiation of the spermatid contains two centrioles which produce two parallel axonemes, at first separated as two flagella, and later incorporated in the same cytoplasm. One of the two centrioles migrates forward. This centriole is continued as a 9 + “1” axoneme which will later become the principal axoneme of the mature spermatozoon. The other centriole produces a short 9 + “1” axoneme with an altered structure; this axoneme will later disappear. The spermatozoon consists of several regions: (a) at the anterior end, the centriolar derivative of the principal axoneme, (b) a short zone which shows cortical microtubules coinciding with external ornamentations and contains vestiges of the second centriole, (c) a long region containing the distal extremity of the principal axoneme and a mitochondrion, and (d) a posterior region containing only the nucleus with no accompanying cytoplasmic organelles. This paper is the first account of spermiogenesis of a monogenean uniflagellate spermatozoon.

Atypical spermiogenesis in a parasitic flatworm, Didymozoon (trematoda: digenea: didymozoidae)

Spermiogenesis in trematodes usually involves the formation in the spermatid of a characteristic structure, a protuberance called the zone of differentiation. This structure was not found in Didymozoon. Instead, spermiogenesis in Didymozoon consists of an elongation of the whole spermatid. Spermatozoa of trematodes usually contain peripheral microtubules and two 9 + “1” axonemes. The spermatozoon of Didymozoon is devoid of microtubules and contains two axonemes of the 9 + 0 type. Didymozoon is thus different from other trematodes. There are no simple relationships between gonochorism and sperm structure in didymozoid trematodes, nor are there simple relationships between sperm structure and phylogeny in this group.

The aflagellate spermatozoon ofDiplozoon (Platyhelminthes: Monogenea: Polyopisthocotylea): A demonstrative case of relationship between sperm ultrastructure and biology of reproduction

Diplozoon is known to display an exceptional biology of reproduction: the hermaphroditic adults are permanently fused together and their genital ducts communicate. In contrast to all other polyopisthocotylean monogeneans in which the spermatozoa show an homogeneous biflagellate structure, the spermatozoon of Diplozoon is aflagellate. It is filiform, and composed of a cytoplasmic region and a nuclear region. The cytoplasmic region exhibits mitochondria, a well-developed smooth endoplasmic reticulum, and up to 450 longitudinal singlet microtubules. The microtubules show links between them; seen in cross section, they are arranged as rows or polygons. The spermatozoon nuclear region contains the nucleus surrounded by cortical longitudinal microtubules. The spermiogenesis shows no zone of differentiation, a typical structure found in all other parasitic Platyhelminthes. Diplozoon is the first case of aflagellate spermatozoon found in the parasitic Platyhelminthes. The atypical sperm structure is not linked with phylogeny, but is well correlated with the atypical biology of reproduction.

Comparative ultrastructural study of spermiogenesis in monogeneans (flatworms): 3. Two species of Amphibdelloides (Monopisthocotylea, Amphibdellatidae)

Two species of the genus Amphibdelloides are described here. They exhibit essentially the same general sperm morphology. However, some minor differences exist. The spermatozoon is filiform and uniflagellate, and is comprised of several regions: (a) anterior extremity showing a single centriolar derivative made up of doublets and a cap-shaped centriolar adjunct; (b) a middle region containing parallel mitochondrion, nucleus, and a 9 + “1” axoneme; (c) a posterior region with only nucleus and axoneme, and (d) a posterior tip where the axoneme is simplified into singlets. In Amphibdelloides sp. 1, the axoneme is altered in the posterior region only: the nucleus is tightly pressed along the axoneme, causing the peripheral doublets to display a noncircular pattern. This spermatozoon is feebly motile. In Amphibdelloides sp. 2, the alteration extends along the whole length of the axoneme, and the spermatozoon is immotile. In Amphibdelloides sp. 1, two kinds of spermatozoa may be found, one with a straight nucleus and the other with a coiled nucleus; sperm polymorphism seems to exist within this species.

Etude ultrastructurale comparée de la spermiogenènes des monogènes: I. Megalocotyle (Monopisthocotylea Capsalidae)

Abstract In Megalocotyle the zones of differentiation (ZD) are short and incomplete; there is no median cytoplasmic process or free flagella. Some peripheral microtubules are present in early ZD, but they disappear. Each nucleus of the common cytoplasmic mass inserts one extremity into a ZD. The mitochondria fuse around this extremity and form a beadlike perforated sphere. Later this sphere slides along the nucleus away from the plasmic membrane like a bead on a string. Each mitochondrial bead (MB), as it moves, trails part of its bulk in the form of a solid streamer; two parallel centrioles follow the MB, each generating a trailing 9+“1” flagellum. The result is a four-part ensemble extending from each MB to each ZD: the two axonemes, the streamer, and the nucleus, with no membrane separating it from the surrounding cytoplasm. Subsequently a cytoplasmic canal (CC) is formed. The arching membranes, originally located at the base of the ZD, migrate along the four-part ensembles as far as the MB, leaving behind two membranes which define the CC. This formation of the CC is remarkable in that it occurs after migration of the centrioles. At the end of spermiogenesis, the cytoplasmic mass reveals 64 parallel CC each containing an immature spermatozoid whose free rear extremity lengthens out. Each spermatozoid is then detached at its anterior extremity set in the cytoplasmic mass. As in most monopisthocotylean monogeneans, the mature spermatozoid of Megalocotyle lacks peripheral microtubules, although its early ZD has microtubules which subsequently disappear. This feature distinguishes it from trematodes and polyopisthocotylean monogeneans, whose mature spermatozoid keep their ZD microtubules.

Comparative ultrastructural study of spermiogenesis in monogeneans (flatworms): 5. Caideostoma (monopisthocotylea calceostomatidae)

Abstract Spermiogenesis in Calceostoma herculanea shows organelles not described previously for a monogenean: extracellular tubules and a lateral crest. The number of spermatids in each common mass is 32 instead of 64, the usual number in the monogeneans. During spermiogenesis, the axoneme of the 9+“1” flatworm pattern displays incomplete peripheral b tubules, which are finally complete in the spermatozoon. A total of 50–70 extracellular tubules (not microtubules), about 10 nm in diameter and at least 400 nm in length, are arranged longitudinally to form a row close to the membrane of the spermatid, but are not found in the mature spermatozoon. The crest of the spermatozoon is made up progressively from an electron-dense region of the spermatid. The mature spermatozoon is filiform, 63 μm in length, with a coiled posterior nucleus and a small crest placed approximately 22 μm behind the anterior extremity. The 9+“1” axoneme of the spermatozoon is noncircular. The data of comparative spermatology are in agreement with classical phylogenetic schemes.

Comparative ultrastructural study of spermiogenesis in monogeneans (flatworms): 4. Diplectanum (Monopisthocotylea diplectanidae)

In Diplectanum sp., the common cytoplasmic mass, which contains 64 fused spermatids, is starshaped at the outset of spermiogenesis, but is globular and shows 64 parallel canals at the end. The zone of differentiation of each spermatid juts laterally into the inner enlarged part of each of these canals. The zone of differentiation contains a single centriole oriented perpendicular to its axis. After differentiation within a canal, separation of the spermatozoon occurs laterally to its anterior region. The mature spermatozoon is filiform, uniflagellate, about 20 μm long, and shows (a) an anterior pointed centriolar adjunct; (b) a single centriole made up of nine singlets; (c) a 9 — “1”-type flagellum; (d) the distal tip of the axoneme, made up of only eight long singlets aligned along the cell membrane and associated with the filiform mitochondrion; (e) the nucleus, without any accompanying element. The spermatozoon pattern, with anterior flagellum and posterior nucleus, is inverted: it shows some resemblance to that of Acanthocephala.