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The acanthocephalan Acanthocephalus dirus is a trophically transmitted parasite that infects freshwater isopods as intermediate hosts and fish as definitive hosts. Using a laboratory-based experiment, we examined if parasite infection was associated with changes in mating behaviour, refuge use and neurochemical levels of infected isopods (Caecidotea intermedius). Infected isopods were less likely to engage in mating behaviour and more likely to be located in the open than uninfected isopods. Infected isopods also contained lower levels of serotonin (5-HT) and dopamine (DA) and had a greater mass of neural tissue (CNS) than uninfected isopods. We propose that the parasite-related changes in mating behaviour and refuge use may be modulated by the serotonergic and dopaminergic systems. We also suggest that the parasites could potentially be modulating these behavioural changes by exploiting the neural-immune system of the hosts through their neuroinflammatory responses.

Predator avoidance behaviours occur when prey detect a predator but the predator has not yet detected and identified prey. These defences are critical because they prevent predation at the earliest possible stages when prey have the best chance of escape. We tested for predator avoidance behaviours in an aquatic macroinvertebrate (Caecidotea intermedius; order Isopoda) in a series of three experiments. The first experiment attempted to determine if isopods possess alarm cues by exposing them to stimuli from macerated conspecifics. We then exposed isopods to kairomones from non-predatory tadpoles (Rana catesbiana) and predatory fish (Lepomis macrochirus) that had been fed a benign diet. Finally, we exposed isopods to kairomones of predatory fish that had been fed a diet exclusively of isopods. We found that isopods did not respond to any kairomone cues or dietary cues from any potential predator, but did reduce activity in response to alarm cues. These results suggest that isopods exhibit predator avoidance responses toward chemical cues in a limited setting (they do not respond unless the information suggests an attack has occurred in the immediate past) or that bluegill have the ability to modify or mask the alarm cues from their prey.

Caecidotea xochimilca n. sp. is described from specimens found in the roots of the water hyacinth in Lake Xochimilco, Mexico City. There are two other epigean Mexican species: Caecidotea xochimilca n. sp. differs from C. williamsi Escobar-Briones & Alcocer, 2002 by the shape of the palmar processes on male pereopod 1, and the aesthetasc formula and number of flagellar articles in antenna 2. Caecidotea puebla Cole & Minkley, 1968 differs from the new species by the body proportions, the number of flagellar articles in antenna 1 and antenna 2, the flagellum of antenna 1 reaching to the distal border of the peduncle of antenna 2 when reflected, a lateral sinuosity in the exopod of pleopod 2 of the female, the number of setae in pleopods 4 and 5, and uropodal characters. A key for the Mexican species of the genus is given. Caecidotea xochimilca n. sp. es descrita de especimenes encontrados en la raiz de lirio acuatico del Lago de Xochimilco, Ciudad de Mexico. Hay otras dos especies Mexicanas epigeas. Caecidotea xochimilca n. sp. difiere de C. williamsi Escobar-Briones & Alcocer, 2002 por tener diferente la forma del proceso palmar del pereopodo 1 del macho, la formula de aestetascos y el numero de artejos flagelares en la antena 2. Caecidotea puebla Cole & Minkley, 1968 difiere de la especie nueva por la proporcion del cuerpo, el numero de artejos flagelares en la antena 1 y antena 2, el flagelo de la antena 1 cuando esta extendido alcanza el borde distal del pedunculo de la antena 2, la sinuosidad lateral en el exopodo del pleopodo 2 de la hembra, numero de setas en los pleopodos 4 y 5 y las caracteristicas del uropodo. Se proporciona una clave para especies mexicanas del genero.