Biagi F., Piras F., Farina V., Zedda M., Mura E., Floris A., Franzoi P., Fausto A.M., Taddei A.R. and Carcupino M. 2016. Testis structure, spermatogenesis and sperm morphology in pipefishes of the genus Syngnathus. -Acta Zoologica (Stockholm) 97: 90-101.Testes, spermatogenesis and sperm morphology have been analysed in four species of the Syngnathus genus. All species show testes of unrestricted lobular type, characterized by a single germinal compartment, with central lumen, and an external tunica albuginea. The spermatogenesis occurs throughout a process of semicystic type, in which germinal spermatocysts open precociously, so germ cells complete maturation in the testis lumen. Amongst them, aflagellate and flagellate multinucleate cells are recognizable. This type of spermatogenesis may be therefore related to the reduced number of simultaneously mature sperm produced by syngnathids. Only one type of mature sperm has been identified in all examined species. It is always a monoflagellate cell, characterized by an elongated head. Elongated head has generally been correlated with the internal fertilization and/or to the production of spermatophore. As this is not the case of syngnathids, a possible function to explain the particularly elongated head of syngnathids is discussed.

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This study provides data on the genetic structuring of the pipefish Syngnathus abaster in the western Mediterranean and Adriatic Seas. A total of 109 specimens were collected in brackish-water biotopes. The control region and three other regions of the mitochondrial genome were analysed. The most relevant result was the high genetic structuring found by Bayesian inference (BI), maximum likelihood (ML) and network analyses, which were consistent in showing three well-separated clusters of S. abaster populations. Furthermore, BI and ML did not support the monophyly of the taxon S. abaster. These results suggest the occurrence of a species complex in the study area, whose differentiation may have occurred since the Pleistocene. The results also show a very high genetic variability at the inter-population level, with no shared haplotypes among sites. Evolutionary forces due to the fragmented nature of the brackish-water habitats may account for the high genetic divergence found among the groups and populations. Finally, although dispersal by rafting over long distances may occasionally occur, this study suggests linear stepping-stone model of colonization to be most likely. The complexity of the results obtained suggests that further studies are needed to elucidate the phylogeny of S. abaster.

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Syngnathus abaster is a euryhaline pipefish distributed in the Mediterranean, Black Sea, and the north-eastern Atlantic. Although its populations are characterised by high morphological plasticity, neither congruent information about the morphological differentiation of S. abaster populations from the Mediterranean lagoons is available, nor population genetic surveys have been so far performed. In this context, the aims of our study were as follow: i) to describe the variation at nine meristic characters of S. abaster from two western Mediterranean brackish-water areas: the Tunis north lagoon (Tunisia) and the Mauguio lagoon (France); ii) to analyse sequences of four mitochondrial DNA regions in order to evaluate the occurrence of genetic variation between the two areas, if any. The morphological survey revealed a subdivision into two distinct groups: the first included the Tunisian specimens, the second the French ones. Genetic analysis evidenced the occurrence of a sharp genetic structuring with high levels of genetic differentiation between Tunisian and French S. abaster populations. Results suggest that the evolutionary forces driven by the different biogeographical and ecological conditions of the two Mediterranean brackish-water areas have boosted the morphological and genetic divergence of the populations here analysed. The scarce potential of long-distance dispersal of S. abaster may have also enhanced the divergence retrieved.