Behavioral rules and tail-up display in extra- and intra-pair interactions of the butterflyfish,Chaetodon lunulatus

Abstract

The butterflyfish,Chaetodon lunulatus, forms monogamous pair bonds. Each pair defends a feeding territory against conspecifics. The tail-up or lateral display of the butterflyfish is performed not only towards non-partners in territorial disputes (extra-pair interaction), but also towards partners (intra-pair interaction). In order to explain this phenomenon, I investigated the two interaction types, and found that a simple model explains both interactions very well. The model consists of four behavioral rules and two provisos for applying the rules. Rule 1: Perform the tail-up display when approached by another individual. Rule 2: Perform the tail-up display when another individual performs the tail-up display. Rule 3: Attack another individual that neither approaches nor performs the tail-up display. Rule 4: Swim with your partner. Proviso 1: Apply Rules 1 and 2 when you do not intend to run away. Proviso 2: Apply Rules 1, 2, and 3 when you do not recognize another individual as your partner. When Rules 1–4 and Provisos 1–2 are applied, the display can prevent improper attacks between partners caused by imperfect partner recognition.