Clasping behavior and the asymmetrically latitudinal structure of the testes in the male dwarf gourami Colisa lalia
2010
Hayakawa, Y., International Christian Univ., Mitaka, Tokyo (Japan) | Kobayashi, M.
During the course of spawning, the male dwarf gourami Colisa lalia exhibits a clasping behavior where the male bends his body around the female under the floating bubble nest. In this study, in order to investigate the role of this clasping behavior, we observed the mating behavior of C. lalia in aquaria and conducted examinations of the male's reproductive system anatomically and histologically. Forcing two males to compete for spawning with a female resulted in one male becoming dominant over the other and ultimately clasping the female. The losing male did not attempt to 'sneak' during spawning, and it was possible to confirm that the clasping behavior is indispensable for sperm emission and only performed by the dominant male. Although testes of teleosts generally longitudinally elongate (i.e., parallel to the body axis), the testes of C. lalia were latitudinally elongate (i.e., vertically with respect to the body axis) and located asymmetrically between the liver and gallbladder. The latitudinal structure of the testes was also confirmed histologically, as the main testicular duct develops vertically. The asymmetric testes did not appear to influence the way in which the body bent during the clasping maneuver because the male was observed to bend its body equally to the right and left during clasping. However, the testes were situated in the vicinity of the fulcrum formed when the male bends its body, suggesting that the latitudinal testes are structurally related to its clasping behavior (i.e., a mechanism analogous to that of a nutcracker). Following physical principles (i.e., levers and mechanical advantage), it can be proposed that male dwarf gourami squeeze semen out from their latitudinal testes by bending their bodies.
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