Loss of RXFP2 and INSL3 genes in Afrotheria shows that testicular descent is the ancestral condition in placental mammals

• DOI: 10.1371/journal.pbio.2005293
• Publication Date: 2018-06-28T17:29:30Z
• Authors: Virag Sharma; Thomas Lehmann; Heiko Stuckas; Liane Funke; Michael Hiller
• Keywords: Gubernaculum

Descent of testes from a position near the kidneys into lower abdomen or scrotum is an important developmental process that occurs in all placental mammals, with exception five afrotherian lineages. Since soft-tissue structures like are not preserved fossil record and since key parts mammal phylogeny remain controversial, it has been debated whether testicular descent ancestral derived condition mammals. To resolve this debate, we used genomic data 71 mammalian species analyzed evolution two genes (relaxin/insulin-like family peptide receptor 2 [RXFP2] insulin-like 3 [INSL3]) induce development gubernaculum, ligament crucial for descent. We show both RXFP2 INSL3 lost nonfunctional exclusively four afrotherians (tenrec, cape elephant shrew, golden mole, manatee) completely lack The presence remnants once functional orthologs these shows gene losses happened after split ancestor. These "molecular vestiges" provide strong evidence condition, irrespective persisting phylogenetic discrepancies. Furthermore, absence shared gene-inactivating mutations our estimates loss at different time points strongly suggest was independently Afrotheria. Our results molecular mechanism explains and, more generally, highlight how vestiges can insights characters.