Fine-scale differences in diel activity among nocturnal freshwater planarias (Platyhelminthes: Tricladida)

Abstract

BackgroundAlthough most freshwater planarias are well known photonegative organisms, their diel rhythms have never been quantified. Differences in daily activity rhythms may be particularly important for temperate-climate, freshwater planarias, which tend to overlap considerably in spatial distribution and trophic requirements.MethodsActivity of stress-free, individually tested young adults of three common planarian species was recorded at 3-h intervals in a 10-d experiment under natural sunlight and photoperiod during autumnal equinox (D:L ~12:12). Individual activity status was averaged over the 10-d experiment, each tested individual thus serving as a true replicate. Twelve individuals per species were tested. Food was provided every 36 h, resulting in alternating day- and nighttime feeding events. Activity during the first post-feeding h was recorded and analyzed separately. Statistical procedures included ANOVAs, correlations, and second-order analyses of angles.ResultsDugesia (= Girardia) tigrina Girard 1850 exhibited clear nocturnal behavior, Dugesia (= Schmidtea) polychroa Schmidt 1861 was predominantly but not exclusively nocturnal, and Polycelis tenuis Ijima 1884 was relatively more active from midnight through noon. Species-specific activity peaks were statistically similar, with peaks at dawn for P. tenuis and just before midnight for the two dugesiids; however, D. tigrina was comparatively more active in the early night hours, while D. polychroa was more active than D. tigrina during daytime. D. tigrina also responded less readily to daytime food addition. P. tenuis remained poorly active and unresponsive throughout the experiment. Individual variability in diel behavior was highest for D. polychroa and lowest for D. tigrina. P. tenuis's general low degree of activity and late activity peak in the experiment may be related to a strong reliance on external stimuli.ConclusionsThe tested species are mainly nocturnal, consistent with their photonegative characteristics. The fine-scale differences in diel behavior among these three triclad species may not be sufficient to allow coexistence in the wild, with the nonnative D. tigrina eventually displacing D. polychroa and P. tenuis in many European waters. The link between planarian diel rhythms and ecological characteristics are worth of further, detailed investigation.

Microplate tectonics and environmental factors as distribution drivers in Western Mediterranean freshwater planarians

“…Therefore, the distribution dynamics of the Dugesia lineages arriving from Africa to Western Europe at around 30 Mya were likely influenced by the freshwater planarian species that were already found on the European continent, such as the genus Polycelis or Schmidtea (Lázaro et al, 2011; Leria et al, 2018). In the case of D. subtentaculata and P. felina , both species may be currently competing, or past interspecific competition may have resulted in niche differentiation associated with certain environmental characteristics that have not been evaluated in the present study, such as trophic, circadian or microhabitat differentiation (Afonso & Eterovick, 2007; Boddington & Mettrick, 1974; Lombardo et al, 2011), and these allowed the two species to coexist in several localities.…”

Girardia dorotocephala transcriptome sequence, assembly, and validation through characterization of piwi homologs and stem cell progeny markers

“…Planarians have also been the subject of recent work in toxicology, as well as behavioral, ecological, and evolutionary biology research (Alvarez-Presas et al, 2008; Hagstrom et al, 2016, 2015; Hicks et al, 2006; Inoue et al, 2015; Levin et al, 2016; Lombardo et al, 2011; Majdi et al, 2014; Shomrat and Levin, 2013), broadening their use as a model beyond fields related to developmental biology. In the classroom, these charismatic organisms have been an important component in K-12 science education and tools are being developed to modernize their use in college level courses (Accorsi et al, 2017; Eberhardt et al, 2015; Pagan et al, 2009; Valverde, 2015).…”

Ammonia excretion in the freshwater planarianSchmidtea mediterranea

“…0.25molg -1 FM) (Sashaw et al, 2010). Tolerance to high body ammonia and the capability for an active or secondary active ammonia excretion mode might be attributable to the benthic lifestyle of many freshwater planarians (Lombardo et al, 2011). Long-term exposure even to low environmental ammonia concentrations (100moll -1 NH 4 Cl) caused an increase in body ammonia levels, suggesting that normal ammonia concentrations in the interstitial fluids are fairly low.…”