An investigation of turn alternation in two species of terrestrial isopods: Porcellio spinicornis and Trachelipus rathkii

It has been documented that some species of terrestrial isopods in the genera Porcellio and Armadillidium engage in turn alternation (TA) to maintain a straight path while exploring new terrains, escaping inhospitable conditions, or avoiding predators. Within Porcellio, such studies are most often conducted with Porcellio scaber (Latreille, 1804) or Porcellio laevis (Latreille, 1804), leaving the extent of TA in other species of Porcellio unexplored. Consequently, TA behavior is often assumed in other genera of isopods, despite the lack of documentation. Therefore, the current study investigated TA in Porcellio spinicornis (Say, 1818) and Trachelipus rathkii (Brandt, 1833) using a commonly employed multiple T-maze. Both P. spinicornis and T. rathkii were found to TA at frequencies significantly above random chance. The data also showed a marginal interaction between group and sex, such that T. rathkii females, but not males, and P. spinicornis males, but not females, significantly TA. The current study provides the first documentation of TA in Porcellio spinicornis and extends this behavior to the genus Trachelipus - broadening our understanding of TA behavior across isopod taxa. Furthermore, the data suggests that TA may follow a pattern of sex-specific selection that could differ among species of terrestrial isopods. Further studies on TA across a broader range of isopod species and genera may reveal important ecological and evolutionary patterns.