Genetic Population Structure of the Trinidadian Guppy (Poecilia reticulata) across Trinidad and Tobago

Abstract

The Trinidadian guppy, Poecilia reticulata, is a tropical freshwater fish with a long history as a model species for the study of evolution and adaptation to changing environments. The guppy is widespread in Trinidad, and many rivers on the island are host to multiple populations subject to varying levels of predation. Population structure in the guppy is influenced by several factors, including colonization history, presence or absence of barrier waterfalls within rivers, and both documented and accidental human-mediated introduction events. This study used genetic data from both microsatellite markers and mtDNA to investigate guppy population structure in 25 rivers and lakes across Trinidad and Tobago, with particular focus on the north shore Marianne and Paria Rivers. Most sites were located in the Northern Range Mountains of northern Trinidad, where rivers are divided into three major aquatic areas – the Caroni drainage, the Oropouche drainage, and the north shore. Results show a deep genetic divide between populations in the west-flowing Caroni drainage and those in the east-flowing Oropouche drainage, likely due to the colonization of these two drainages from two separate branches of the Orinoco, a large river located on the South American mainland. On Trinidad’s north shore, guppies collected in rivers on the western side of the island appeared to be genetically related to Caroni drainage guppies, while those in rivers on the eastern side of the north shore were predominantly related to Oropouche drainage guppies but showed evidence of admixture from the Caroni. Detailed study of Marianne and Paria River guppy populations showed downstream-biased gene flow in both rivers, with waterfalls in the Marianne limiting the movement of guppies in that river. Evidence of migration between the Marianne and Paria River watersheds was also found at two separate locations.