DOI: 10.5061/dryad.dncjsxm9d
title: Will I stay or will I go? Eye morphology predicts individual migratory propensity in a partial migrant

description: Billions of animals undertake migratory journeys every year, with powerful
 consequences for ecosystem dynamics. Key behaviours that enable successful
 migration are often guided by the visual system. The amount and quality of
 information that animals can extract from visual scenes are directly
 related to structural eye size — larger eyes can house larger pupils,
 enhancing light-gathering capacity and vision by improving visual acuity
 and contrast sensitivity. Migration should exert strong demands on
 individual visual performance, for example via foraging, anti-predator
 benefits or navigational requirements. Yet, it remains elusive whether
 variations in eye morphology and corresponding visual capabilities are
 associated with migratory propensity. Here, we capitalize upon
 intra-population variation in migratory propensity (a.k.a. partial
 migration) in roach, a common freshwater fish, to directly test for
 migration-associated variation in image-forming eyes within a species. In
 a multi-year field study tracking the migration decisions of over 2000
 individuals in two different lake systems, we found that relative pupil
 size was positively associated with individual migration propensity.
 Computational simulations of the visual ecology associated with the
 observed differences in pupil size show that migrants have an extended
 visual detection range, and that the performance gain is most pronounced
 for viewing small targets (e.g. planktonic prey) under low-light
 conditions. These results suggest that the larger pupils of migrants
 represent an adaptation for increased foraging efficiency to aid in the
 accumulation of critical pre-migratory energy reserves. Together, our
 anatomical and functional findings provide new perspectives on visual
 system design in relation to individual-level migratory
 decision-making. 
description: Data for this study consists of measurements of relative eye and
 pupil size extracted from digital photographs, as well as migration
 propensities of individual roach (Rutilus rutilus) migrating between lakes
 and connected streams. Data was collected for multiple years and from two
 different lakes (Loldrup and Søgård Sø) using passive biotelemetry with
 stationary and continuously operating antenna arrays.
description: # Will I stay or will I go? Eye morphology predicts individual migratory
 propensity in a partial migrant
 [https://doi.org/10.5061/dryad.dncjsxm9d](https://doi.org/10.5061/dryad.dncjsxm9d) ## Description of the data and file structure Data Collection Methods: Data for this study consists of measurements of relative eye and pupil size extracted from digital photographs, as well as migration propensities of individual roach (Rutilus rutilus) migrating between lakes and connected streams. Data was collected for multiple years and from two different lakes (Loldrup and Søgård Sø) using passive biotelemetry with stationary and continuously operating antenna arrays. See text for further details. ### Files and variables #### File: Dryad\_Eyes\_JAE.xlsx **Description:** Data used to test for associations between eye morphology and individual migration propensity as well as to perform computational simulations of the visual ecology associated with observed differences in pupil size. ##### Variables Information on Data Column Labels: PIT_ID: Passive integrated transponder ID of tagged fish. Lake_ID: Population of origin of fish. Sog=Søgård Sø: (55°29′ N, 9°19′E). Lol= Loldrup Sø:(56°29′N, 9°26′E),respectively. Year: The specific year a fish individual was PIT-tagged and monitored for migration propensity. SL_mm: The standard body length (mm) of fish individuals at tagging. Eye diameter_mm: The widest part of the eye (mm) at tagging. Pupil diameter_mm: The widest part of the pupil (mm) at tagging. Migr_in_period(yes/no): Fish that undertook a migration (1) or remained as residents in the lake (0) during the study period. ## Code/software Raw data is provided as an Excel file