Page 6 - Montesanto_etal-2014
P. 6

52 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 34, NO. 1, 2014

Fig. 3. Grain-size preferences for Tylos ponticus and Tylos europaeus in the geographical area surveyed within the current study.

limit of median grain size values for each species, above                     intra-specific morphological differences were recorded for
which each species does not occur. The results of this Stu-                   the populations of T. ponticus; T. europaeus exhibited a high
dent’s t-test (one sample) are reported in Table 3.                           degree of homogeneity between the different sampled popu-
                                                                              lations. The differences reported for the T. ponticus seem to
                            DISCUSSION                                        be fall within the normal range of intra-specific variation, al-
                                                                              though future morphometric and genetic studies on the sam-
The rigorous morphological analyses conducted within this                     pled populations will better assess such a degree of intra-
study have enabled the correct identification of populations                   specific differentiation, besides qualitative characters (Rohlf
within the surveyed geographical area previously recorded                     and Marcus, 1993).
as “T. latreillei” or as T. latreillii sensu lato. According to
Taiti and Ferrara (1996), our opinion is to follow Kussakin                      This study is the first to investigate in detail the influence
(1982) viewpoint, considering two valid species in the                        on the distribution of different populations of Tylos of
present study area: T. ponticus and T. europaeus.                             varying sediment particle diameters. In view of the snapshot
                                                                              nature of the sampling conducted in the present study, the
   The populations sampled in this study, the re-examination                  distributional data for the two taxa of Tylos in question
of the material from the studied collection, and the previ-                   are not absolute. To further substantiate the distributional
ous records (Giordani Soika, 1954) allowed us to determine                    data, the conduction of a multi-seasonal, and possibly even
conclusively to which of the two species all the examined                     a multi-year, sampling should take place on the beaches
individuals belong. All the morphological characters studied                  we studied. The data emerging from our current study
in the observed specimens seem to confirm the synonyms                         contradicts previous reports on the grain-size preferences of
currently accepted, and therefore the validity of the two                     T. ponticus, which was thought to be partial to coarse and
species in the study area. In terms of inter-specific diagnos-                 very coarse-sand conditions (Giordani Soika, 1954, 1956;
tic morphological traits, the characters with the highest value               Vandel, 1960; Kussakin, 1982; Caruso et al., 1987). Our
were the shape and length of the ventral plate of pleonites 4                 data also suggests that T. europaeus shows a lower degree
and 5, and the shape of the prominent process on the ba-                      of plasticity in adapting to beaches with variable sediment
sis of pereiopod 1 on the tergal margin. The most prominent                   grain sizes, whilst T. ponticus is more euryecious in that it
                                                                              can tolerate a broader range of sediment grain sizes. In fact,
Table 3. Results of single-sample t-test for the species of Tylos considered  T. europaeus appears to be competitively excluded from very
in this study. ∗Significant P values (P < α).                                  coarse-grained beaches.

Species          Hypothetical t  df P                                            In 40 years of research on isopod taxonomy and ecology
                     mean            One-tailed Two-tailed                    conducted by the research group headed by Prof. Caruso, the
                                                                              two species of Tylos in question have never been reported in
Tylos ponticus   0.500  2.4715 11 0.0155∗  0.0310∗                            sympatry from the same beach. This can be attributed to a
                 0.550  1.9429 11 0.0390∗  0.0781                             number of factors including the urbanization of the coast-
                 0.600  1.4144 11 0.0925∗  0.1849                             line, increasingly colonized by man-made artefacts, such as
                                                                              concrete walls, e.g., on the beaches of Brucoli and Castella-
Tylos europaeus  0.300  2.5574 6 0.0215∗   0.0431∗                            mare del Golfo, which could potentially thwart the longitu-
                 0.325  2.2073 6 0.0347∗   0.0694                             dinal inter-beach dispersion of Tylos. This hypothesis will be
                 0.350  1.8571 6 0.0563    0.1127                             assessed through a forthcoming genetic study that will eval-
   1   2   3   4   5   6   7