Simple rules for construction of a geometric nest structure by pufferfish

Ryo Mizuuchi,Shigeru Kondo,Hiroshi Kawase,Hirofumi Shin,Daisuke Iwai

doi:10.1038/s41598-018-30857-0

Abstract

A small (~10 cm) male pufferfish (Torquigener albomaculosus) builds a large (~2 m) sandy nest structure, resembling a mysterious crop circle, to attract females. The circle consists of radially arranged deep ditches in the outer ring region, and maze-like shallow ditches in the central region. The configuration is geometrical. Here, we examined the process of the outer ring construction, and extracted the ‘rules’ followed by the pufferfish. During construction, the pufferfish repeatedly excavates ditches from the outside in. Generally, excavation starts at lower positions, and occurs in straight lines. The entry position, the length, and the direction of each ditch were recorded. A simulation program based on these data successfully reproduced the circle pattern, suggesting that the complex circle structure can be created by the repetition of simple actions by the pufferfish.

Highlights

Many animals build diverse and complex forms of nests, which protect their eggs and offspring from predators, and can act as a signal to attract mates[1,2]
Kawase et al found that the large circle is a nest structure built by a small male pufferfish, Torquigener albomaculosus, approximately 10 cm in length, to attract female mates[15]
According to the video recordings shown in the previous reports[15,20], the pufferfish mainly stayed near the sea bottom during the construction, suggesting the possibility that the structural patterns would spontaneously emerge by the pufferfish repeating some simple behavior triggered by a signal, which is not directly related to the whole structure of the nest

Summary

Introduction

Many animals build diverse and complex forms of nests, which protect their eggs and offspring from predators, and can act as a signal to attract mates[1,2]. A pufferfish makes a mark by pushing its belly on the sandy bottom as the central region of a nest (Supplementary Fig. S1A)[20] It repeatedly excavates the sand with its fins and body to leave marks hundreds or thousands of times, during which the radial ditches in the outer ring region gradually appear[15,20]. (For detail, see Kawase et al, 2017.) In this study, we analyzed the excavation behavior of a male pufferfish during the early and the middle stages. We determined a simple rule governing the excavation behaviors, and a computer simulation confirmed that the repetition of simple actions generates highly ordered structural patterns, similar to the geometric ring structure of the pufferfish nest

Methods

Results

Conclusion