Polymorphisme intraspecifique chez le Syngnathe aiguille Syngnathus acus (Osteichthyes,syngnathidae) des eaux tunisiennes (Méditerranée centrale)

Abstract

Two hundreds and sixty seven greater pipefishes, Syngnathus acus Linnaeus, 1758, were collected in Tunisian waters: 204 in the Bahiret EL Biban (southern Tunisia), 24 in Tunis Southern Lagoon and 39 off Halq EL Wadi (northern Tunisia). Three categories of studies were carried out: the first study was based on analysis of both variances and means of some morphological characters using Fisher's F test and Student's t test; the second and the third study were submitted to multivariate and multidimensional analysis, respectively. Both first and second study revealed significant differences in variances and means for several examined characters, in the three areas compared two by two. In the third study, the Principle Component Analysis (PCA), the morphological variables did not allow to discriminate the three populations, for the Factorial Correspondance Analysis (FCA), these variables made it possible to distinguish the individuals within the same sample but not from the samples of various sources. However, the Discriminant Canonical Analysis (CAND) showed that these same biometric variables have a capacity of discrimination between the individuals of the three sources. The quantification of differences between the three areas using the distance of Mahalanobis (D²) confirms the occurrence of three populations significantly different. Additionally, specimens from Tunis Southern Lagoon and those of Bahiret El Biban were relatively similar probably because they inhabit brackish areas