Tactic-specific locomotion for ejaculation of an externally fertilising marine fish.

Body movements for ejaculation in externally fertilising fish are typically described as a rapid quiver/vibration of the body, and are often considered invariable in this group. A field study was conducted in the small marine fish, triplefin blenny (Enneapterygius etheostoma) to examine the possible variability of quiver motion, in relation to alternative reproductive tactics (i.e., sneakers and territorial males). Spontaneous ejaculation behavior recorded was quantified and compared between tactics using high-speed cameras. Ejaculation movements were kinematically discrete between tactics, with sneakers performing faster and larger undulation motions at a greater frequency, and traveling longer in time and distance than territorial males. Amplitude data showed that sneakers moved their whole bodies more than territorial males. The highest amplitudes were observed for the tail in sneakers and the head in territorial males. Overall, it called a whole-body wriggling motion for sneakers, and head vibration motion for territorial males. Sneakers spent 1/3 of the ejaculation period at a greater distance from spawning females. This may result from avoidance behaviour by sneakers but the fact that they aimed their genital papillae towards the surface of the spawning site rather than directed at the females introduces the possibility that sneakers may be targeting not just current reproduction (of newly laid eggs) but also future reproduction (of eggs laid later) as a way of offsetting potentially reduced fertilisation success due to their more distant proximity to the spawning female. Therefore, the present study suggests that different ecological demands shape tactic-specific ejaculation motions. [ABSTRACT FROM AUTHOR]