Diverging patterns of introgression from Schistosoma bovis across S. haematobium African lineages

Hybridization is a fascinating evolutionary phenomenon that raises the question of how species maintain their integrity. Inter-species hybridization occurs between certain Schistosoma species that can cause important public health and veterinary issues. In particular hybrids between Schistosoma haematobium and S. bovis associated with humans and animals respectively are frequently identified in Africa. Recent genomic evidence indicates that some S. haematobium populations show signatures of genomic introgression from S. bovis. Here, we conducted a genomic comparative study and investigated the genomic relationships between S. haematobium, S. bovis and their hybrids using 19 isolates originating from a wide geographical range over Africa, including samples initially classified as S. haematobium (n = 11), S. bovis (n = 6) and S. haematobium x S. bovis hybrids (n = 2). Based on a whole genomic sequencing approach, we developed 56,181 SNPs that allowed a clear differentiation of S. bovis isolates from a genomic cluster including all S. haematobium isolates and a natural S. haematobium-bovis hybrid. All the isolates from the S. haematobium cluster except the isolate from Madagascar harbored signatures of genomic introgression from S. bovis. Isolates from Corsica, Mali and Egypt harbored the S. bovis-like Invadolysin gene, an introgressed tract that has been previously detected in some introgressed S. haematobium populations from Niger. Together our results highlight the fact that introgression from S. bovis is widespread across S. haematobium and that the observed introgression is unidirectional.