Contributions to Zoology, 86 (4) 297-302 (2017) An unexpected twist: Sperm cells coil to the right in land snails and to the left in song birds Menno Schilthuizen1,2*, Rob Langelaan1, Nicola Hemmings3, Wesley van Oostenbrugge1,4, Stefan Visser1,4 1 Naturalis Biodiversity Center, Darwinweg 2, 2333CR Leiden, the Netherlands 2 Institute Biology Leiden, Leiden University, Sylviusweg 72, 2333BE Leiden, the Netherlands 3 Department of Animal and Plant Sciences, University of Sheffield, Western Bank,Sheffield S10 2TN, UK 4 Forensic Science Dept., Amsterdam University of Applied Sciences, Weesperzijde 190, 1097 DZ Amsterdam, the Netherlands * Corresponding author:
[email protected] Keywords: Gastropoda, Passeriformes, spermatozoa, chirality, dextral, sinistral Abstract is a near-ubiquitous feature (reviewed in, for example, Ludwig, 1932; McManus, 2004). Well-known exam- In animals, cell polarity may initiate symmetry breaking ples are coiled snails, claw asymmetry in crabs, eye very early in development, ultimately leading to whole-body torsion in flatfish, and vertebrate internal visceral asymmetry. Helical sperm cells, which occur in a variety of animal clades, are one class of cells that show clearly visible organisation. However, the evolutionary developmen- bilateral asymmetry. We used scanning-electron microscopy tal biology of symmetry breaking remains poorly to study coiling direction in helical sperm cells in two understood (Palmer, 2004; Schilthuizen 2013; Davison groups of animals that have figured prominently in the sperm et al., 2016). morphology literature, namely land snails, Stylommatophora Some symmetry-breaking developmental cascades (514 spermatozoa, from 27 individuals, belonging to 8 species and 4 families) and songbirds, Passeriformes (486 spermatozoa, have been partially resolved (Grande and Patel, 2009; from 26 individuals, belonging to 18 species and 8 families).