Biological traits as determinants in the macroecological patterns of distribution in loliginid squids

Macroecological studies have primarily focused on investigating the relationships between body size and geographic distribution on large scales, including regional, continental, and even global levels. While the majority of these studies have been conducted on terrestrial species, a limited number of studies have been carried out on aquatic species, and even fewer have considered the importance of phylogeny in the observed patterns. Cephalopods provide a good model for examining these macroecological patterns due to their large geographic and bathymetric ranges, wide range of body sizes, as well as diverse fin sizes and shapes. In this study, we assess the relationships between mantle length, fin size, and hatchling size with the geographic and bathymetric distribution of 30 squid species from the worldwide distributed family Loliginidae. To test a macroecological hypothesis, we evaluated the phylogenetic signal and correlated evolution to assess the role of biological traits in squid distribution, using a molecular phylogeny based on two mitochondrial and one nuclear genes. Biological traits (mantle length and fin size) exhibit high phylogenetic signals, while distribution demonstrates low signal. The correlation analyses revealed the existence of a relationship between adult mantle length and fin size with geographic and bathymetric distribution, but not with hatchling size. The geographic distribution of loliginid squids evolved in relation to mantle length, where larger squids with large fins (e.g. Sepioteuthis) have wide distributions, while small-finned species (e.g. Pickfordiateuthis) have narrow distributions. This study paves the way for exploring similar relationships in other squid families or other marine swimming animals.