As social insect workers mature, outside-nest tasks associated with foraging and defense are typically performed at higher frequencies. Foraging in ants is often a pheromonally mediated collective action performed by mature workers; age-dependent differences in olfactory response thresholds may therefore proximately regulate task repertoire development. In the ant Pheidole dentata, foraging activity increases with chronological age in minor workers, and is chemically controlled. The onset of foraging in minor workers is accompanied by marked neuroanatomical and neurochemical changes, including synaptic remodeling in olfactory regions of the brain, proliferation of serotonergic neurons, and increased brain titers of monoamines, notably serotonin. We examined the linkage of serotonin and olfactory responsiveness by assaying trail-following performance in mature P. dentata minor workers with normal serotonin levels, or serotonin levels experimentally lowered by oral administration of the serotonin synthesis inhibitor α-methyltryptophan (AMTP). By assessing responsiveness to standardized pheromone trails, we demonstrate that trail-following behaviors are significantly reduced in serotonin-depleted workers. AMTP-treated individuals were less likely to initiate trail following, and oriented along pheromone trails for significantly shorter distances than untreated, similar-age workers. These results demonstrate for the first time that serotonin modulates olfactory processes and/or motor functions associated with cooperative foraging in ants.

The growth, reproduction, and senescence patterns of the epiphytic marine alga Phaeosaccion collinsii were tracked over two consecutive seasons at its type locality of Little Nahant, Nahant, MA (USA). We investigated the potential and/or combined effects of temperature and ambient nutrient supply (NO 3 -and PO 4 3-) on the phenology of this ephemeral species in its natural environment by collecting microscopic and macroscopic P. collinsii specimens from blades of eelgrass (Zostera marina) in a shallow coastal subtidal zone. Our results suggest that temperature is a strong driver of the alga's in situ cycle and that the optimal temperature for P. collinsii growth and reproduction may be between 5 and 8°C, a narrower temperature threshold than previous laboratory studies on this subject have suggested. Several large winter storms also allowed us to observe the effect of physical disturbance on the integrity of the eelgrass beds and the population of microscopic and macroscopic P. collinsii. This study contributes the first in situ information on the abiotic conditions necessary for the successful growth and development of P. collinsii and a greater understanding of the life cycle of this unique golden brown alga.

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