Spermatogenesis and sperm storage in the testes of the behaviorally distinctive male morphotypes of Macrobrachium rosenbergii (Decapoda, Palaemonidae)

Adult males of the freshwater prawn Macrobrachium rosenbergii differentiate into three morphotypes. Each morphotype develops in sequence in the adult male population from small males through orange claw males to dominant blue claw males. Small males and blue claw males are sexually active, while orange claw males represent a sexually inactive intermediate stage engaged in somatic growth.
To further examine these behavioral characteristics on a physiological level, testes from each of the morpho types were cultured in vitro. The rate of [3H]-thymidine incorporation, representing DNA synthesis, and the amount of sperm released into the culture media were recorded. In parallel, the relative wet weight of testes from the different morphotypes were recorded and histological preparations were examined.
The relative weight of the testes from small males was significantly greater than in the other morphotypes. The testes of small males were both active in spermatogenesis and contained a large amount of mature sperm. Transition to the orange claw morphotype is marked by spermatogenically active testes, characterized by a multilayered spermatogenic zone and a high rate of thymidine incorporation. The testes of the orange claw morphotype develop into organs containing mainly spermatocytes. The fully differentiated orange claw male will transform by a metamorphic molt into the sexually active blue claw male. Almost no spermatogenic activity was recorded in the testes of the blue claw males. The testes of the blue claw males contained, almost exclusively, mature sperm.
The anatomical, physiological, and histological status of the male morphotypes are closely associated with the growth pattern and behavioral attributes of the morphotypes as they differentiate through the developmental pathway from the small male through the orange claw to the blue claw male morphotype.