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Life-history evolution in the fish genus Poecilia (Poeciliidae: Cyprinodontiformes: subgenus Pamphorichthys): an evolutionary origin of extensive matrotrophy decoupled from superfetation

We describe the occurence of extensive post-fertilization maternal provisioning (matrotrophy) in fish species in the subgenus Pamphorichthys (genus Poecilia: family Poeciliidae) that represents one of two independent origins of this adaptation in this genus. Matrotrophy is accompanied by a reduction in yolk in eggs at fertilization, a thickened follicle throughout development, and externalization and anterior extension of the embryonic pericardial membrane. These features resemble the anatomical adaptations for placentotrophy described in other members of this family and accompany a substantial increase in dry mass of the embryo during development. Species mean values for the increase in embryo mass range from a low of less than two-fold (Pamphorichthys minor) to greater than 50-fold (Pamphorichthys hasemani). Different populations of Pamphorichthys araguaiensis show a range from less than a two-fold to greater than 16-fold increase in dry mass during development. Such substantial differences in matrotrophy among closely related species and within species make Pamphorichthys a promising group with which to study the adaptive value and the genetic basis of matrotrophy.