Geographical variation in mandible morphologies specialised for collembolan predation depend on prey size in the ant Strumigenys lewisi

1. Ants in the genus Strumigenys are predator ants that feed on tiny soil arthropods. The mandibles are modified into high‐speed traps to capture swift collembolan prey. The peculiar mandible morphologies of these ants have evolved depending on characteristics of the prey. Specifically, the evolution of mandible size and shape may be directly driven by prey size. 2. In the present study, the intraspecific variation of the morphological traits of Strumigenys lewisi populations were observed in central Japan. The relationships between the morphological variations and the prey body size were analysed. 3. In workers and queens, three morphological traits, head width, mandible length, and mandible width were significantly different among the multiple sites. Specifically, the mandible length was shorter in southwestern Japan than in other sampling locations. The ancova model revealed that the allometry of the mandible length to the head width was different among the sites. 4. As predicted, the mandible length was positively correlated with the average body size of collembolans in the Entomobryidae family. Furthermore, multiple regression analysis showed that the variation of the mandible length was affected by environmental factors represented as location information. However, the effect of collembolan body size was more effective at predicting mandible length. The study suggests that the geographical variation of mandible morphologies in S. lewisi has been selected by predator–prey interactions with collembolans.     

Changes in Intracellular Concentrations of Cyclic Nucleotides during the Initiation Process of Starfish Sperm Motility

Changes in the intracellular concentrations of cyclic nucleotides during the initiation of starfish sperm motility were examined. The intracellular concentration of cGMP decreased just after dilution of sperm with sea water, whereas that of cAMP increased concomitant with initiation of sperm motility. In acidic sea water, the intracellular concentration of cGMP decreased but no increase in that of cAMP was observed and sperm remained immotile. The presence of a phosphodiesterase inhibitor enhanced the rate of increase in the intracellular concentration of cAMP and the sperm motility.
These results indicate that cAMP is involved in the initiation of sperm motility in starfish.