Perspectives on the clonal persistence of presumed ‘ghost’ genomes in unisexual or allopolyploid taxa arising via hybridization

Although hybridization between non-sibling species rarely results in viable or fertile offspring, it occasionally produces self-perpetuating or sexually-parasitic lineages in which ancestral genomes are inherited clonally and thus may persist as 'ghost species' after ancestor extinction. Ghost species have been detected in animals and plants, for polyploid and diploid organisms, and across clonal, semi-clonal, and even sexual reproductive modes. Here we use a detailed investigation of the evolutionary and taxonomic status of a newly-discovered, putative ghost lineage (HX) in the fish genus Hypseleotris to provide perspectives on several important issues not previously explored by other studies on ghost species, but relevant to ongoing discussions about their detection, conservation, and artificial re-creation. Our comprehensive genetic (allozymes, mtDNA) and genomic (SNPs) datasets successfully identified a threatened sexual population of HX in one tiny portion of the extensive distribution displayed by two hemi-clonal HX-containing lineages. We also discuss what confidence should be placed on any assertion that an ancestral species is actually extinct, and how to assess whether any putative sexual ancestor represents a pure remnant, as shown here, or a naturally-occurring resurrection via the crossing of compatible clones or hemi-clones.P. J. Unmack, M. Adams, J. Bylemans, C. M. Hardy, M. P . Hammer, A. George

Phylogeny and biogeography of the eleotrid genus Hypseleotris (Teleostei: Gobioidei: Eleotridae), with redescription of H. cyprinoides

Thacker, Christine, Unmack, Peter J. (2005): Phylogeny and Biogeography of the Eleotrid Genus Hypseleotris (Teleostei: Gobioidei: Eleotridae), With Redescription of H. cyprinoides. Records of the Australian Museum 57 (1): 1-13, DOI: 10.3853/j.0067-1975.57.2005.1436, URL: https://journals.australian.museum/thacker-and-unmack-2005-rec-aust-mus-571-113

Marine-freshwater transitions are associated with the evolution of dietary diversification in terapontid grunters (Teleostei: Terapontidae)

The ecological opportunities associated with transitions across the marine–freshwater interface are regarded as an important catalyst of diversification in a range of aquatic taxa. Here, we examined the role of these major habitat transitions and trophic diversification in a radiation of Australasian fishes using a new molecular phylogeny incorporating 37 Terapontidae species. A combined mitochondrial and nuclear gene analysis yielded a well-supported tree with most nodes resolved. Ancestral terapontids appear to have been euryhaline in habitat affiliation, with a single transition to freshwater environments producing all Australasian freshwater species. Mapping of terapontid feeding modes onto the molecular phylogeny–predicted carnivorous dietary habits was displayed by ancestral terapontids, which subsequently diversified into a range of additional carnivorous, omnivorous, herbivorous and detritivorous dietary modes upon transition to freshwater habitats. Comparative analyses suggested that following the freshwater invasion, the single freshwater clade has exhibited an increased rate of diversification at almost three times the background rate evident across the rest of the family. The marine–freshwater transition within Terapontidae appears to have resulted in substantial dietary radiation in freshwater environments, as well as increased lineage diversification rates relative to euryhaline–marine habitats