Application of geometric morphometrics for intraspecific variability analysis in mesopelagic fishes of Sternoptychidae and Myctophidae families

We present the results of application of geometric morphometrics for studies of variability in populations of the members of two families of South Atlantic mesopelagic fishes, Sternoptyx diaphana (Sternoptychidae) and Ceratoscopelus warmingii (Myctophidae), in which an almost complete genetic isolation was previously discovered within the borders of hydrographic regions. A system of landmark points is developed, describing both anatomical features and configuration of luminescent organs, photophores, which allows to consider not only the influence of external physical and ecological conditions but also the existence of population-specific signaling system as a potential cause of genetic isolation. Morphological similarities are demonstrated for S. diaphana throughout the whole studied portion of the distribution area, while certain differences affecting the head shape and position of individual photophores on the body are discovered between C. warmingii populations.