''Gambusia quadruncus'', known as the llanos mosquitofish, is a species of

bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...

in the genus '' Gambusia'', part of the family Poeciliidae, that lives in east-central Mexico. Sometimes coexisting with at least three similar species, it differs from its closest relative, '' Gambusia affinis'', in several characteristics with plausible effects on

reproductive isolation The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring ...

"Combined analysis of mitochondrial and nuclear gene sequence data indicates reciprocal monophyly of the species and its sister species ''Gambusia affinis'', with levels of genetic divergence suggesting the two species diverged from one another over a million years ago. The origin of ''Gambusia quadruncus'' may reflect a vicariant event associated with Pliocene orogenesis in the Tamaulipas Arch and a frontal section of the Sierra Madre Oriental (Lleran Mesas)."

Inhabiting a variety of freshwater habitats across regional river drainages, the range of ''G. quadruncus'' spans at least from north to south, covering over .

References

{{Taxonbar, from=Q5519751 quadruncus Live-bearing fish Freshwater fish of Mexico Fish described in 2012