# Comparative Study of Sun Compass Orientation in Migrating Anadromous versus Resident Freshwater Threespine Sticklebacks (Gasterosteus aculeatus)

## TL;DR

This study compares how migrating and non-migrating threespine sticklebacks use the sun to navigate, finding that only the migratory type shows consistent orientation.

## Contribution

The study provides the first evidence of sun compass orientation in anadromous threespine sticklebacks.

## Key findings

- Anadromous sticklebacks consistently use sun compass orientation.
- Freshwater sticklebacks show no directional preference in orientation.
- Ecotype-specific differences in orientation behavior were confirmed through behavioral experiments.

## Abstract

In the northern coastal hemisphere, different ecotypes of the threespine stickleback (Gasterosteus aculeatus) can be distinguished phenotypically by a different number of lateral bone plates and by their body shape and size. We focused on (1) anadromous sticklebacks, which migrate from the sea to rivers to spawn and (2) freshwater sticklebacks, which live in rivers all year round. Migration behavior is a key feature in the evolution of ecotypes, but the underlying mechanisms of migration are poorly understood. To learn more about possible orientation mechanisms that could lead to goal-directed migration, we tested anadromous sticklebacks for their sun compass orientation and compared their orientation behavior with that of the freshwater ecotype. Behavioral experiments revealed ecotype-dependent differences, whereby the ability to orient is consistently present in the anadromous ecotype, whereas the orientation in the freshwater ecotype corresponds to a random directional distribution.