Poeciliidae are a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of freshwater

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

es of the order

Cyprinodontiformes Cyprinodontiformes is an order (biology), order of Actinopterygii, ray-finned fish, comprising mostly small, freshwater fish. Many popular aquarium fish, such as killifish and Poeciliidae, live-bearers, are included. They are closely related t ...

, the tooth-carps, and include well-known live-bearing aquarium fish, such as the

guppy The Greater Underwater Propulsion Power Program (GUPPY) was initiated by the United States Navy after World War II to improve the submerged speed, maneuverability, and endurance of its submarines. (The "Y" in the acronym was added for pronouncea ...

, molly, platy, and swordtail. The original distribution of the family was the

Southeastern United States The Southeastern United States, also known as the American Southeast or simply the Southeast, is a geographical List of regions in the United States, region of the United States located in the eastern portion of the Southern United States and t ...

to north of

Río de la Plata The Río de la Plata (; ), also called the River Plate or La Plata River in English, is the estuary formed by the confluence of the Uruguay River and the Paraná River at Punta Gorda, Colonia, Punta Gorda. It empties into the Atlantic Ocean and ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. Due to release of aquarium specimens and the widespread use of species of the genera '' Poecilia'' and '' Gambusia'' for mosquito control, though, introduced poeciliids can today be found in all tropical and subtropical areas of the world. In addition, ''Poecilia'' and ''Gambusia'' specimens have been identified in hot springs pools as far north as

Banff, Alberta Banff is a resort town in Banff National Park, Alberta, Canada, in Alberta's Rockies along the Trans-Canada Highway, west of Calgary, east of Lake Louise, Alberta, Lake Louise, and above Banff was the first municipality to incorporate within ...

Live-bearing

All species in the Poecilidae are live-bearers. Differences are seen in the mode and degree of support the female gives the developing larvae. Many members of the family Poeciliidae are considered to be lecithotrophic (the mother provisions the

oocyte An oocyte (, oöcyte, or ovocyte) is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ger ...

with all the resources it needs prior to fertilization, so the egg is independent of the mother), but others are matrotrophic (literally "mother feeding": the mother provides the majority of resources to the developing offspring after fertilization). Lecithotrophy and matrotrophy are not discrete traits. Most scientific studies quantify matrotrophy using a matrotrophy index (MI), which is the dry mass of fully developed offspring divided by the dry mass of a fertilized egg. Members of the genus ''

Poeciliopsis ''Poeciliopsis'' is a genus of poeciliid fishes that primarily are native to Mexico and Central America. The only exceptions are ''P. turrubarensis'' where the range extends into Colombia, and ''P. occidentalis'' where the range extends into Ari ...

'', for example, show variable reproductive life history adaptations. '' Poeciliopsis monacha'', '' P. lucida'', and '' P. prolifica'' form part of the same

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

within that genus. However, their modes of maternal provisioning vary greatly. ''P. monacha'' can be considered to be lecithotrophic because it does not really provide any resources for its offspring after fertilization - the pregnant female is basically a swimming egg sac. ''P. lucida'' shows an intermediate level of matrotrophy, meaning that to a certain extent the offspring's metabolism can actually affect the mother's metabolism, allowing for increased nutrient exchange. ''P. prolifica'' is considered to be highly matrotrophic, and almost all of the nutrients and materials needed for fetal development are supplied to the oocyte after it has been fertilized. This level of matrotrophy allows ''Poeciliopsis'' to carry several broods at different stages of development, a phenomenon known as superfetation. Because the space for developing embryos is limited, viviparity reduces brood size. Superfetation can compensate for this loss by keeping embryos at various stages and sizes during development. ''P. elongata'', ''P. turneri'', and ''P. presidionis'' form another clade that could be considered an outgroup to the ''P. monacha'', ''P.lucida'', and ''P. prolifica'' clade. These three species are very highly matrotrophic - so much so that in 1947, C. L. Turner described the follicular cells of ''P. turneri'' as "pseudo-placenta, pseudo-chorion, and pseudo-allantois". The greater degree of matrotrophy in a species is linked with a higher degree of placentation, including "a thicker maternal follicle, higher degree of vascularization, and greater number of villi in the placenta". The reason for placental evolution in Poeciliids is controversial, and involves two major groups of hypotheses, adaptive and conflict hypotheses. Adaptive hypotheses, including the locomotor hypothesis, Trexler-DeAngelis Model (reproductive allotment), and life-history facilitation, broadly suggest that the placenta evolved to facilitate the evolution of another advantageous trait in the fish's environment. The conflict hypothesis suggests the placenta is a nonadaptive byproduct of genetic "tug-o-war" between the mother and the offspring for resources.

Taxonomy

Until recently, the egg-laying African killifish (genera now placed in Procatopodidae and Pantanodontidae) were also placed in the Poecilidae. This treatment led to hypotheses that the Poecilidae are an ancient clade that antedate the breakup of

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

(the split between Africa and South America) 100 million years ago, and that live-bearing subsequently evolved in South America.Hrbek, T., J. Seekinger, and A. Meyer. 2007. A phylogenetic and biogeographic perspective on the evolution of poeciliid fishes. ''Molecular Phylogenetics and Evolution'' 43:986-998. However, more recent studies have found this taxonomic treatment to be paraphyletic, and have placed these families outside the Poecilidae. These new taxonomic treatments support that the Poecilidae are much younger than previously thought, are entirely a live-bearing group, and are only native to the Americas. Poeciliids colonized North America through the

Antilles The Antilles is an archipelago bordered by the Caribbean Sea to the south and west, the Gulf of Mexico to the northwest, and the Atlantic Ocean to the north and east. The Antillean islands are divided into two smaller groupings: the Greater An ...

, while they were connected 44 million years ago. Poeciliids then moved to Central America by the Aves land bridge on the Caribbean Plate. When South America connected to Central America three million years ago, some further dispersal southward occurred, but South American species did not move into Central America.

Genera

The family is divided into subfamilies and

tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...

s as follows: * Subfamily Poeciliinae ** Tribe Alfarini Hubbs, 1924 ***Genus '' Alfaro'' ** Tribe Gambusini ***Genus '' Belonesox'' ***Genus '' Brachyrhaphis''Regan, 1913 ***Genus '' Gambusia'' Poey, 1854 ***Genus '' Heterophallus'' ** Tribe Heterandriini ***Genus '' Heterandria'' ***Genus ''

Neoheterandria ''Neoheterandria'' is a genus of poeciliids native to Panama and Colombia. Species There are currently three recognized species in this genus: * '' Neoheterandria cana'' ( Meek & Hildebrand, 1913) * '' Neoheterandria elegans'' Henn Henn is a ...

Henn Henn is a both a surname and an Estonian masculine given name. Notable people with the name include: As a given name * Henn-Ants Kurg (1898–1943), Estonian military colonel and diplomat * Henn Pärn (born 1941), Estonian politician * Hen ...

, 1916 ***Genus ''

'' ***Genus '' Priapichthys'' ***Genus '' Pseudopoecilia'' ***Genus '' Xenophallus'' ** Tribe Poeciliini *** Genus '' Limia'' *** Genus '' Micropoecilia'' *** Genus '' Pamphorichthys'' *** Genus '' Phallichthys'' *** Genus '' Poecilia'' *** Genus '' Xiphophorus'' ** Tribe Cnesterodontini *** Genus '' Cnesterodon'' *** Genus '' Phalloceros'' Eigenmann, 1907 *** Genus '' Phalloptychus'' *** Genus '' Phallotorynus'' ** Tribe Scolichthyini Rosen, 1967 *** Genus ''

Scolichthys ''Scolichthys'' is a genus of poeciliid fishes endemism, endemic to river basins in Guatemala. Species There are currently two recognized species in this genus: * ''Scolichthys greenwayi'' Rosen, 1967 * ''Scolichthys iota'' Rosen, 1967 Referenc ...

'' *Subfamily Tomeurinae **Genus '' Tomeurus''Eigenmann, 1909 *Subfamily Xenodexiinae **Genus '' Xenodexia''Hubbs, 1950

References

* * {{Authority control Percomorpha families Fishkeeping Freshwater fish of Central America Freshwater fish of South America Freshwater fish of Mexico Freshwater fish of the United States Live-bearing fish Ovoviviparous fish Viviparous fish Taxa named by Charles Lucien Bonaparte