Body size and fin length as determinants in the geographic distribution of Loliginid squids

Abstract

Macroecological studies have mainly focused on exploring the relationships between body size and geographic distribution on large scales, whether regional, continental or even global, and most of them have been conducted on terrestrial species. Few studies have been conducted on aquatic species, and even fewer have considered the importance of phylogeny in the observed patterns. Cephalopod molluscs are a good model to tackle these problems given that they have large geographic and bathymetric ranges, a wide range of body sizes, as well as diverse fin sizes and shapes. Here, we evaluate the relationships between body and fin size with the geographic distribution of 30 squid species of the family Loliginidae distributed worldwide. To test a macroecological hypothesis, we evaluated the phylogenetic signal and correlated evolution of the three traits to assess the role of phylogenetic relationships in squid distribution using a molecular phylogeny based on two mitochondrial and one nuclear gene. The analyses showed the existence of a relationship between body size and geographic distribution. Similarly, relative fin size showed a positive relationship with distribution. Phylogenetic signals were high for morphological traits (body and fin size), while it was low for distribution. The geographic distribution of loliginid squids evolved in relation to body size, where larger squids with large fins (e.g. genus Sepioteuthis) have wide distributions, while small-finned species (e.g. genus Pickfordioteuthis) have narrow distributions. This study opens the gates to explore such relationships in other squid families or other marine swimming animals.