Foraging strategies of the acellular slime moulds Didymium iridis and Didymium bahiense

Reactivity to pseudorandom environmental patterns in woodlice: Effects of hydric deprivation and light exposure

Exploratory activity is an essential component of animal behavior, including among invertebrate species. This study examined the effects of hydric deprivation and their possible modulation by light exposure on locomotion and rearing-up behavior in two woodlice species, Porcellio scaber (Latreille 1804) and Armadillidium vulgare (Latreille 1804). It was also an attempt to replicate previous findings on the stimulation of these behaviors in P. scaber, exposed to (pseudo)random vs. regular visual and tactile patterns in a small enclosure. In Experiment 1, two groups of P. scaber and two groups of A. vulgare were exposed to randomly vs. regularly distributed visual (black and white) and tactile (grained and smooth) patterns for approximately 20min. No rewards were present in the environment and the woodlice were tested without preliminary hydric deprivation. In Experiment 2, the same procedure was used but the woodlice were tested following a 20-min hydric deprivation under a bottle cap (darkness). Experiment 3 replicated this procedure with the 20-min hydric deprivation spent in a plastic cup (light exposure). The results of Experiments 1 and 3 provide partial replication with A. vulgare, but not P. scaber, of the previous findings: Random patterns stimulate rearing-up behavior on the apparatus' vertical walls more than regular patterns. Also, a more aversive stimulation in Experiment 3 compared to Experiment 2, increased locomotion, especially in the random environment. The role of hydric deprivation and light exposure in the process of escaping from a hostile environment is discussed, as well as the effects of the treatments used in these experiments.

The Response of Litter-Associated Myxomycetes to Long-Term Nutrient Addition in a Lowland Tropical Forest

Myxomycetes (plasmodial slime molds) are abundant protist predators that feed on bacteria and other microorganisms, thereby playing important roles in terrestrial nutrient cycling. Despite their significance, little is known about myxomycete communities and the extent to which they are affected by nutrient availability. We studied the influence of long-term addition of N, P, and K on the myxomycete community in a lowland forest in the Republic of Panama. In a previous study, microbial biomass increased with P but not N or K addition at this site. We hypothesized that myxomycetes would increase in abundance in response to P but that they would not respond to the sole addition of N or K. Moist chamber cultures of leaf litter and small woody debris were used to quantify myxomycete abundance. We generated the largest myxomycete dataset (3,381 records) for any single locality in the tropics comprised by 91 morphospecies. In line with our hypothesis, myxomycete abundance increased in response to P addition but did not respond to N or K. Community composition was unaffected by nutrient treatments. This work represents one of very few large-scale and long-term field studies to include a heterotrophic protist highlighting the feasibility and value in doing so.

Slime moulds use heuristics based on within-patch experience to decide when to leave

Animals foraging in patchy, non- or slowly-renewing environments must make decisions about how long to remain within a patch. Organisms can use heuristics (‘rules of thumb’) based on available information to decide when to leave the patch. Here we investigate proximate patch departure heuristics in two species of giant, brainless amoeba: the slime moulds Didymium bahiense and Physarum polycephalum. We explicitly tested the importance of information obtained through experience by eliminating chemosensory cues of patch quality. In Physarum polycephalum, patch departure was influenced by the consumption of high, and to a much lesser extent low, quality food items such that engulfing a food item increased patch residency time. Physarum polycephalum also tended to forage for longer in darkened, ‘safe’ patches. In Didymium bahiense, engulfment of either a high or low quality food item increased patch residency irrespective of that food item's quality. Exposure to light had no effect on the patch residency time of D. bahiense. Given that our organisms lack a brain, our results illustrate how the use of simple heuristics can give the impression that individuals make sophisticated foraging decisions.