Otolith shape differences between Micropogonias manni and M. altipinnis (Sciaenidae)
Sagitta morphology is much used in sciaenid systematics, as well as in archaeological, paleontological and ecological studies. Although morphometric characteristics of sagitta (length, height, thickness, weight,…) are useful to discriminate some marine and freshwater species, they are not fully conclusive in the case of Micropogonias altipinnis and M. manni. In order to give new elements for characterizing and discriminating these species we propose here to apply the geometric morphometry technique to sagittae of these species by combining landmarks and sliding semi-landmarks. We measured 40 sagittae of Micropogonias altipinnis and 46 sagittae of M. manni, and quantified their differences in shape and centroid size. We also tested for an effect of the length and weight of Micropogonias specimens on the shape of the sagitta. Our results show that it is possible to discriminate the two species. Moreover, sagitta shape differs significantly between species, while centroid size does not. These results validate the application of our protocol for characterizing and discriminating the shape of the sagitta, and show that the combined use of landmarks and sliding semi-landmarks is a very powerful option to capture the elusive morphological changes present in Micropogonias sagittae.