@article{HilgersHartmannHofreiteretal.2018,
  author    = {Hilgers, Leon and Hartmann, Stefanie and Hofreiter, Michael and von Rintelen, Thomas},
  title     = {Novel Genes, Ancient Genes, and Gene Co-Option Contributed o the Genetic Basis of the Radula, a Molluscan Innovation},
  series = {Molecular biology and evolution},
  volume    = {35},
  journal   = {Molecular biology and evolution},
  number    = {7},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0737-4038},
  doi       = {10.1093/molbev/msy052},
  pages     = {1638 -- 1652},
  year      = {2018},
  abstract  = {The radula is the central foraging organ and apomorphy of the Mollusca. However, in contrast to other innovations, including the mollusk shell, genetic underpinnings of radula formation remain virtually unknown. Here, we present the first radula formative tissue transcriptome using the viviparous freshwater snail Tylomelania sarasinorum and compare it to foot tissue and the shell-building mantle of the same species. We combine differential expression, functional enrichment, and phylostratigraphic analyses to identify both specific and shared genetic underpinnings of the three tissues as well as their dominant functions and evolutionary origins. Gene expression of radula formative tissue is very distinct, but nevertheless more similar to mantle than to foot. Generally, the genetic bases of both radula and shell formation were shaped by novel orchestration of preexisting genes and continuous evolution of novel genes. A significantly increased proportion of radula-specific genes originated since the origin of stem-mollusks, indicating that novel genes were especially important for radula evolution. Genes with radula-specific expression in our study are frequently also expressed during the formation of other lophotrochozoan hard structures, like chaetae (hes1, arx), spicules (gbx), and shells of mollusks (gbx, heph) and brachiopods (heph), suggesting gene co-option for hard structure formation. Finally, a Lophotrochozoa-specific chitin synthase with a myosin motor domain (CS-MD), which is expressed during mollusk and brachiopod shell formation, had radula-specific expression in our study. CS-MD potentially facilitated the construction of complex chitinous structures and points at the potential of molecular novelties to promote the evolution of different morphological innovations.},
  language  = {en}
}
@article{HilgersHartmannPfaenderetal.2022,
  author    = {Hilgers, Leon and Hartmann, Stefanie and Pfaender, Jobst and Lentge-Maass, Nora and Marwoto, Ristiyanti M. and von Rintelen, Thomas and Hofreiter, Michael},
  title     = {Evolutionary divergence and radula diversification in two ecomorphs from an adaptive radiation of freshwater snails},
  series = {Genes},
  volume    = {13},
  journal   = {Genes},
  number    = {6},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2073-4425},
  doi       = {10.3390/genes13061029},
  pages     = {16},
  year      = {2022},
  abstract  = {(1) Background: Adaptive diversification of complex traits plays a pivotal role in the evolution of organismal diversity. In the freshwater snail genus Tylomelania, adaptive radiations were likely promoted by trophic specialization via diversification of their key foraging organ, the radula. (2) Methods: To investigate the molecular basis of radula diversification and its contribution to lineage divergence, we used tissue-specific transcriptomes of two sympatric Tylomelania sarasinorum ecomorphs. (3) Results: We show that ecomorphs are genetically divergent lineages with habitat-correlated abundances. Sequence divergence and the proportion of highly differentially expressed genes are significantly higher between radula transcriptomes compared to the mantle and foot. However, the same is not true when all differentially expressed genes or only non-synonymous SNPs are considered. Finally, putative homologs of some candidate genes for radula diversification (hh, arx, gbb) were also found to contribute to trophic specialization in cichlids and Darwin's finches. (4) Conclusions: Our results are in line with diversifying selection on the radula driving Tylomelania ecomorph divergence and indicate that some molecular pathways may be especially prone to adaptive diversification, even across phylogenetically distant animal groups.},
  language  = {en}
}