Escapes in copepods: comparison between myelinate and amyelinate species

Abstract

Rapid conduction in myelinated nerves keeps distant parts of large organisms in timely communication. It is thus surprising to find myelination in some very small organisms. Calanoid copepods, while sharing similar body plans, are evenly divided between myelinate and amyelinate taxa. In seeking the selective advantage of myelin in these small animals, representatives from both taxa were subjected to a brief hydrodynamic stimulus that elicited an escape response. The copepods differed significantly in their ability to localize the stimulus: amyelinate copepods escaped in the general direction of their original swim orientation, often ending up closer to the stimulus. However, myelinate species turned away from the stimulus and distanced themselves from it, irrespective of their original orientation. We suggest that faster impulse conduction of myelinated axons leads to better precision in the timing and processing of sensory information, thus allowing myelinate copepods to better localize stimuli and respond appropriately.

Cognitive and white-matter compartment models revealed the contribution of microstructural variability along sensorimotor tracts to simple reaction time

“…Therefore, although the NDI does not distinguish between myelin and axonal volume fraction (Jelescu et al, 2015;Stikov et al, 2015), the negative Ter-NDI correlation in the current study supports the hypothesis that participants with faster motor speed have thicker myelin sheaths or axonal diameter in the CST, which in turn results in faster nerve conduction velocity (Waxman, 1980;Fields, 2008;Seidl, 2014;Buskey et al, 2017).…”

“…The DTI measures of several white matter pathways have been shown to correlate with RT, both in adults (Tuch et al, 2005;Turken et al, 2008;Konrad et al, 2009;Mayer and Vuong, 2014) and children (Madsen et al, 2011;Tamnes et al, 2012;Scantlebury et al, 2014), possibly owing to the difference in experiments and cohorts across studies. One hypothesis of these structural-functional correlations is that the inter-individual variability in RT is due to variations in tissue microstructure, such as axon diameter or myelination that affect the nerve conduction velocity (Waxman, 1980;Fields, 2008;Seidl, 2014;Buskey et al, 2017) and in turn affect RT (Chevalier et al, 2015;Chopra et al, 2018).…”

Predatory posture and performance in a precocious larval fish targeting evasive copepods

“…Our experimental design set three larval fish age classes of the clownfish Amphiprion ocellaris Cuvier 1830 (early: 1 to 5 dph; mid: 6 to 9 dph; and late: 11 to 14 dph) against three developmental stages of the copepod prey Bestiolina similis (Sewell 1914) (nauplii: NIII-NIV stages; copepodites: CII-CIII stages; and adults: CVI stage). The choice of developmental stages provided a range in prey size (length: ∼100 to 500 µm; McKinnon et al, 2003), mechanosensitivity and escape performance (Bradley et al, 2013;Buskey et al, 2017). We designed the experiment to quantify how strike posture changed through larval development (size: ∼4 to 8 mm total length; Jackson and Lenz, 2016), while also assessing the effect of a prey's stage on its predator's posture.…”

Contrasting species functional trait structuring of subarctic versus subtropical copepod communities

“…We classified the taxa as myelinate and amyelinate based on the phylogeny of calanoid copepods 40 . Copepods with myelin covering their nervous system are reported to have more precise escape reactions to predation 69 . Lenz 40 proposes that myelinate copepods should dominate in waters with high predation risk (e.g., subarctic) because they have better capacity to escape.…”