Rostral Geometric Morphometrics in a Hippolytid Shrimp: Are There Elements That Reflect the Homozygous/Heterozygous State of Its Morphotypes?

Abstract

Geometric morphometry has been widely used in decapods’ studies for taxonomic needs, and for eco-morphological adaptation and intraspecific variations recordings. Among the 40 species of the genus Hippolyte, the Mediterranean endemic Hippolyte sapphica is the only one with two distinct conspecific morphotypes, without intermediate forms: morph-A with a long, dentate and morph-B with a very short, toothless rostrum. Previous studies have shown that the “rostral loss” in morph-B seems to be controlled by a single pair of alleles, with a complete dominance of allele b, expressed in morph-B. We aim to elucidate morphotypes’ rostral pattern in relation to size, sex, and season. Shrimps were collected during two different (dry/wet) seasons from two sites: s.1 with a mixed (morph-A and B) and s.2 with a pure, unmixed (morph-A) species populations. After morph and sex identification, individuals were photographed and geometric morphometric analysis of rostrum was carried out on a set of landmarks. The data suggest that only morph-A rostral shape seems to be influenced by shrimp’s size, sex, and time of the year. Interestingly, two distinct morph-B clusters appear, which probably correspond to the homozygous and heterozygous state (BB and BA) of the gene site that controls the species morphotypes’ phenology.