Fig. 2

Detail on sperm morphology and phylogenetic trees. a Macrostomum sperm schematic with key structures and measured traits. b Phylogeny (H-IQ-TREE) of 96 Macrostomum species from [13], based on the alignment of 94,625 amino acids across 385 genes. Concentric circles: 0.1 substitutions/site. Branch colors: collection locations (red: Lake Tanganyika, blue: Zambia, black: other). Note the short branches at the base of the Tanganyika, indicating rapid speciation. c Phylogeny (C-IQ-TREE) of the outlined clades from (b), based on the alignment from (b) supplemented with sequences from a 28 S rRNA fragment to include species without transcriptome data, namely M. acus, M. obtusa, M. gracilistylum, M. sp. 10, M. sp. 16, M. sp. 17, and M. sp. 18. Note that because only one gene is present for these species their branch-lengths are not as suitable for the assessment of the diversification rate. White circled nodes: maximum support. First column circles: mating syndrome from [19] (black: reciprocal, white: hypodermic, grey: not assigned). Second column circles: habitat type (see legend). Dual-color circles: species from multiple habitats. Branch colors, as in (b)