Familiarity and sex modulate size-dependent following behaviour in the Mediterranean killifish
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Living in a group offers the chance to follow the choices and the behaviours of other individuals. Following a group mate might confer fitness advantages if the group mate knows about resources such as food or shelters. Shoaling fish often follow larger group mates which, in most species, are generally older and therefore more experienced. Yet, the effect of individuals’ characteristics other than size on following behaviour remains to be understood. For example, familiar fish and female shoals have been reported as more cohesive, which might be due to a differential tendency to follow in relation to familiarity and sex. Here, we investigated whether size, familiarity, sex, and the interaction between these factors affect fish following behaviour. We observed pairs of differently sized Mediterranean killifish, Aphanius fasciatus, exploring a new environment, and we recorded whether the rear fish followed the front fish when the latter changed swimming direction. In female and male pairs, and in unfamiliar pairs, smaller fish were more likely to follow the directional change of the larger fish than vice versa. In mixed-sex pairs and in familiar pairs, however, size did not affect following behaviour and larger fish followed as much as smaller fish did. Our results revealed that killifish’s following decisions are determined by the size of the individuals, their level of familiarity, and their sex. These characteristics may have a notable impact on the behaviour of fish groups in nature.
KeywordsAphanius fasciatus Familiarity Following decision Sex differences Social behaviour
We would like to thank the 2014 ‘Biodiversity and Behaviour’ class (Marine Biology course, Università di Padova) for help during the experiments, and Angelo Bisazza and Federica Poli for logistical support. We are indebted with Avelie Stuart and four anonymous reviewers for their constructive comments on the manuscript.
This work was supported by the Università di Padova under Grant ‘Progetto di Ricerca di Ateneo 2015’ to MG (grant no. PRAT 2015 CPDA153859).
Compliance with ethical standards
The experiments complied with the laws of Italy, the country in which they were performed (Decreto Legislativo 4 marzo 2014, n. 26), and they have been approved by Università di Padova’s Ethical Committee (protocol no. 10985). Fish sampling was conducted with permission from Veneto Region (protocol no. 207154, Decreto N. 20 del 14 maggio 2015, Legge Regionale 28 aprile 1998). No physically invasive manipulation was performed on fish that were released into their natural environment after the experiments.
Conflict of interest
The authors declare that they have no conflict of interest.
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