Data from: Natural hybridization between divergent lineages in a selfing hermaphroditic fish

By definition, mating between individuals is infrequent in highly selfing
organisms, and so too, therefore, hybridization should be rare between
genetically divergent lineages in predominantly self-fertilizing species.
Notwithstanding these expectations, here we report a remarkable case of
natural hybridization between highly diverged phylogeographic lineages of
the mangrove rivulus, a small killifish that reproduces predominantly by
self-fertilization and typically is found as highly homozygous lines in
most parts of its extensive geographic range. Two distinctive genetic
lineages (Kryptolebias marmoratus and a “Central clade” closely related to
K. hermaphroditus) previously were not known in sympatry, but were found
by us to co-occur on San Salvador, Bahamas. Genetic analyses of a
mitochondrial and multiple nuclear markers determined the direction of a
cross producing a hybrid fish. Furthermore, we show that this hybrid
individual was viable, as it successfully reproduced by self-fertilization
for two generations. Additional sampling of this population will be
necessary to determine if backcrossing of hybrids to the parental lineages
occurs in nature and to analyze whether such backcross progeny are viable.
Application of the biological species concept (BSC) is traditionally
difficult in clonally reproducing organisms. Our results show that
although mangrove rivulus fish are mostly highly selfing in nature
(resulting in isogenic, effectively clonal and homozygous progeny),
classification within this taxonomic complex need not be incompatible with
the BSC.