Poeciliidae

The **Poeciliidae** are a family of fish of the order Cyprinodontiformes, the tooth-carps.  They live in fresh water.  Many live-bearing aquarium fish, such as the guppy, molly, platy, and swordtail are in Poeciliidae. These fish are from the United States to north of Río de la Plata, Argentina, and Africa, including Madagascar. Human beings took these fish to many other parts of the world and set them free there, so they have become invasive species.  Today, poeciliid fish live in all tropical and subtropical parts of planet Earth. People have seen fish in the genuses _Poecilia_ and _Gambusia_ in hot spring pools as far north as Banff, Alberta in Canada.

## Live-bearing

Although all fish in Poeciliidae are called "live bearers" (viviparous), some species do lay eggs with external fertilization.  All African fish in Poeciliidae lay eggs.  Almost all the American Poeciliidae bear live young (except for fish in the genus _Tomeurus_).

Poeciliidae has three subfamilies. The fish in subfamily Aplocheilichthyinae live only in Africa. Most Poeciliinae live in the Americas (except for _Rhexipanchax_, which lives in Africa). Most fish in Procatopodinae live in Africa (_Fluviphylax_ and _Pseudopoecilia_ live in South America). Scientists say this means the ancestors of Poeciliidae fish the split between Africa and South America 100 million years ago, and that fish that went to South America evolved to bear live young after they got there. Poeciliids came to North America through the Antilles.  They were able to do this because the Antilles and North America 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 of the fish moved further south, but South American species did not move north into Central America.

The live-bearing species fish can be different from each other depending on how much the mother fish does for the developing larvae. Many fish in the family Poeciliidae are lecithotrophic (the mother provisions the oocyte with all the resources it needs prior to fertilization, so the egg is independent of the mother), but others are matrotrophic ("mother feeding": the mother provides the majority of resources to the developing offspring after fertilization). Lecithotrophy and matrotrophy are not always completely separate. Most scientific studies use a matrotrophy index (MI) to say how matrotrophic an animal is. This uses the dry mass of fully developed offspring (how much they weigh when they are not wet) divided by the dry mass of a fertilized egg.

Fish in the genus _Poeciliopsis_, for example, have many different adaptations. _Poeciliopsis monacha_, _P. lucida_, and _P. prolifica_ are part of the same group in that genus. However, they have three different ways of helping baby fish: _P. monacha_ is lecithotrophic because it does not give its babies any resources after fertilization.  The mother fish swims around with her eggs in a sac but that is all. _P. lucida_ shows a middle level of matrotrophy. This means that the eggs's metabolism can change the mother's metabolism, so some food chemicals go back and forth. _P. prolifica_ is very matrotrophic.  The mother fish gives the eggs almost all of the food chemicals they need after fertilization. This level of matrotrophy allows _Poeciliopsis_ to carry several groups of eggs that were start at different times.  This is called superfetation.

Because the mother fish only has so much space in her body for developing embryos, 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 an outgroup to the _P. monacha_, _P.lucida_, and _P. prolifica_ group. These three fish are very matrotrophic. In 1947, C. L. Turner said the follicular cells of _P. turneri_ were "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."

Scientists argue about why Poeciliid fish developed to give their young eggs food chemicals inside their bodies.  There are two groups of ideas, adaptive hypotheses and conflict hypotheses. Adaptive ideas, including the locomotor hypothesis, Trexler-DeAngelis Model (reproductive allotment), and life-history facilitation, say that the fish's placenta evolved to help another advantage to evolve. The conflict hypothesis says the placenta is a nonadaptive byproduct of genetic tug-of-war between the mother and the eggs.

## Subfamilies and tribes

The family has the following subfamilies and tribes:

- Subfamily Aplocheilichythinae <small>Myers, 1928</small> (Banded lampeyes)
    - Genus _Aplocheilichthys_ <small>Bleeker, 1863</small>
- Subfamily Procatopodinae <small>Fowler, 1916</small> (Lampeyes)
    - Tribe Fluviphylacini <small>Roberts, 1970</small>
        - Genus _Fluviphylax_ <small>Whitley, 1920</small>
    - Tribe Procatopodini <small>Fowler, 1916</small>
        - Genus _Laciris_ <small>Huber, 1981</small>
        - Genus _Micropanchax_ <small>Myers, 1924</small>
        - Genus _Lacustricola_ <small>Myers, 1924</small>
        - Genus _Poropanchax_ <small>Clausen, 1967</small>
        - Genus _Platypanchax_ <small>Ahl, 1928</small>
        - Genus _Lamprichthys_ <small>Regan 1911</small>
        - Genus _Pantanodon_ <small>Myers, 1955</small>
        - Genus _Hypsopanchax_ <small>Myers, 1924</small>
        - Genus _Procatopus_ <small>Boulenger, 1904</small>
        - Genus _Plataplochilus_ <small>Ahl, 1928</small>
        - Genus _Rhexipanchax_ <small>Huber, 1999</small>
- Subfamily Poeciliinae <small>Bonaparte, 1831</small> (Livebearers)
    - Tribe Alfarini <small>Hubbs, 1924</small>
        - Genus _Alfaro_ <small>Meek, 1912</small>
    - Tribe Gambusini <small>Gill, 1889</small>
        - Genus _Belonesox_ <small>Kner, 1860</small>
        - Genus _Brachyrhaphis_ <small>Regan, 1913</small>
        - Genus _Gambusia_ <small>Poey, 1854</small>
        - Genus _Heterophallus_ <small>Regan, 1914</small>
    - Tribe Heterandriini <small>Hubbs, 1924</small>
        - Genus _Heterandria_ <small>Agassiz, 1853</small>
        - Genus _Neoheterandria_ <small>Henn 1916</small>
        - Genus _Poeciliopsis_ <small>Regan 1913</small>
        - Genus _Priapichthys_ <small>Regan 1913</small>
        - Genus _Pseudopoecilia_ <small>Regan 1913</small>
        - Genus _Xenophallus_ <small>Hubbs, 1924</small>
    - Tribe Poeciliini <small>Bonaparte, 1831</small>
        - Genus _Limia_ <small>Poey, 1854</small>
        - Genus _Micropoecilia_ <small>Hubbs, 1926</small>
        - Genus _Pamphorichthys_ <small>Regan, 1913</small>
        - Genus _Phallichthys_ <small>Hubbs, 1924</small>
        - Genus _Poecilia_ <small>Bloch & Schneider, 1801</small>
        - Genus _Xiphophorus_ <small>Heckel, 1848</small>
    - Tribe Cnesterodontini <small>Hubbs, 1924</small>
        - Genus _Cnesterodon_ <small>Garman, 1895</small>
        - Genus _Phalloceros_ <small>Eigenmann, 1907</small>
        - Genus _Phalloptychus_ <small>Eigenmann, 1907</small>
        - Genus _Phallotorynus_ <small>Henn, 1916</small>
        - Genus _Tomeurus_ <small>Eigenmann, 1909</small>
    - Tribe Scolichthyini <small>Rosen, 1967</small>
        - Genus _Scolichthys_ <small>Rosen, 1967</small>
    - Tribe Xenodexini <small>Hubbs, 1950</small>
        - Genus _Xenodexia_ <small>Hubbs, 1950</small>