Electric signalling and reproductive behaviour in a mormyrid fish, the bulldog Marcusenius macrolepidotus (South African form)

Abstract

Bulldog fish (Marcusenius macrolepidotus) generate short (<1 ms) electric-organ discharges (EODs), separated by much longer and highly variable interdischarge intervals (IDIs). We observed overt behaviour and electrical activity during reproductive behaviour in a male and in a female bulldog, and identified IDI patterns with putative signal functions. In contrast to Pollimyrus adspersus and Pollimyrus isidori, in which an elaborate and extended courtship precedes spawning proper, our fish started spawning almost immediately when we allowed the female to enter the male's territory. The male did not construct a nest, and neither parent provided parental care. The male showed very little aggression towards the intruding female. Fish spawned in bouts near the male's hiding place, and eggs were scattered by the female's vigorous tail flips as she left the spawning site, only to return shortly thereafter. During spawning bouts, both fish generated highly stereotyped IDI patterns: the male generated a series of IDIs gradually decreasing from about 200 ms to about 55 ms that was abruptly terminated by a long IDI. The female generated a series of relatively regular IDIs (about 54 ms) that was followed by a marked increase in IDI duration (the probable time of spawning). Finally, a sharp decrease in IDIs to about 20 ms accompanied the female's sudden escape from the spawning site. In between spawning bouts, both fish generated series of very short IDIs (high discharge rate, HD) that alternated abruptly with very low-rate inter-HD activity (especially in the male). IDIs as short as 9 ms (male) or 11 ms (female) occurred during HD displays. No visible aggression, in fact very little overt behaviour, occurred during these HD displays in both fish. Agonistic interactions between male and female, outside a reproductive context, were similar to those previously described in male pairs, including overt behavioural patterns such as parallel swimming, antiparallel display and attack, as well as HD displays. When not interacting, fish did not generate HD displays. We suggest the HD display is a communication signal in both reproductive and agonistic contexts.

Female choice by electric pulse duration: attractiveness of the males'communication signal assessed by female bulldog fish,Marcusenius pongolensis(Mormyridae, Teleostei)

“…All these behaviours, associating with a male in his territory, headbutting him, circling with or without additional head butts, occur during courtship and spawning behaviour which in M. pongolensis is rather aggressive and dominant on the female side, whereas the male appears surprisingly passive and inactive (Werneyer and Kramer, 2005). Because of the females' clear preference for long male EODs we conclude that intersexual selection must have played a significant role in the evolution of the male EOD pulse, in addition to intrasexual selection that was demonstrated previously (Hanika and Kramer, 2005).…”

“…Therefore, visiting a male and unprovoked female aggression is a good indicator of readiness, especially when the male does not or only weakly counter-attack (Werneyer and Kramer, 2005).…”

“…pongolensis appeared to be a suitable study species because aggression, territorial and reproductive behaviour have been successfully studied in this species (Werneyer and Kramer, 2002;Werneyer and Kramer, 2005), and because it responds well to electric playback stimuli (Hanika and Kramer, 2005).…”

Electrical and behavioral courtship displays in the mormyrid fish Brienomyrus brachyistius

“…Although our laboratory in the past has successfully bred B. brachyistius in captivity, courtship behavior was not documented. Recently, Werneyer and Kramer (Werneyer and Kramer, 2005) described electric signaling and behavior during courtship in one pair of Marcusenius macrolepidotus. M. macrolepidotus showed no courtship behavior and produced only one putative courtship specific SPI (Werneyer and Kramer, 2005).…”

“…However, with available technology, custom-written computer programs allowed for EOD discrimination by sex in freely behaving mormyrids. A similar method has recently been used (Werneyer and Kramer, 2005).…”