''Poeciliopsis monacha'', or the headwater livebearer, is a species of freshwater
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
in the family
Poeciliidae
The Poeciliidae are a family of freshwater fishes of the order Cyprinodontiformes, the tooth-carps, and include well-known live-bearing aquarium fish, such as the guppy, molly, platy, and swordtail. The original distribution of the family was t ...
. It is
endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
to
Mexico
Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
.
Distribution and habitat
''Poeciliopsis monacha'' is
endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
to northwestern Mexico where it is present in the upper reaches of streams and
arroyos
Arroyo often refers to:
* Arroyo (creek), an intermittently dry creek
Arroyo may also refer to:
People
* Arroyo (surname)
Places United States
;California
* Arroyo Burro Beach, a public beach park in Santa Barbara County, California
* Arroyo ...
on the western side of the
Sierra Madre Occidental
The Sierra Madre Occidental is a major mountain range system of the North American Cordillera, that runs northwest–southeast through northwestern and western Mexico, and along the Gulf of California. The Sierra Madre is part of the American C ...
mountain range. Some of these watercourses dry up during the summer and the fish may have to survive in springs and pools. Conditions are harsh in winter in the headwaters of the streams at altitudes of around ; there may be frosts and snow may fall. The fish become torpid at temperatures below about , but there are some hot springs, and water exposed to the sun may warm up during the day. In the summer, no precipitation occurs, much of the water evaporates, and fish may have to survive in dwindling pools where temperatures above about will be lethal.
Ecology
In addition to the stress factors induced by trying to survive in summer in decreasing and warming waters, some pools have very low oxygen levels, exacerbated at night by the lack of the
photosynthetic
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...
oxygen produced by plants, and often lower at the pool base where the fish feed, or under the mats of algae that tend to accumulate. Under these circumstances, the fish may resort to "surface skimming", a behaviour that allows them to obtain enough oxygen at the interface of water and air.
[
''P monacha'' is a ]viviparous
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the m ...
species of fish with the young developing in an outgrowth of the female's pericardial sac
The pericardium, also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong connective tissue (fibrous pericardium), and an inner layer made of ...
.[ After mating, sperm is stored in folds in the ovary lining, and several clutches of young can develop simultaneously at different stages of development.]
''P. monacha'' hybridises with ''Poeciliopsis lucida
''Poeciliopsis lucida'', the clearfin livebearer, is a species of small freshwater fish in the family Poeciliidae. Reproduction is viviparous, and the female can have several clutches of young developing internally at the same time. It is one of ...
'' and ''Poeciliopsis occidentalis
The Gila topminnow or charalito (''Poeciliopsis occidentalis'') is a species of fish in the family Poeciliidae. It is found in Mexico and the United States.
Description
The Gila topminnow has an elongated curved body. Males are rarely over and ...
''. When a female of ''P. monacha'' mates with a male of either of these two species, the offspring are invariably female.[ In fact this all-female breeding line can be maintained indefinitely in the laboratory by repeatedly back-crossing the offspring to males of ''P. lucida'' and ''P. occidentalis''.] In the headwaters of the Fuerte River
The Fuerte River is a river in the state of Sinaloa, in northwestern Mexico. It flows from headwaters in the Sierra Madre Occidental to the Pacific Ocean in the Gulf of California.
Course
It begins at the junction of the Rio Verde (also called ...
in northwestern Mexico, it is found that only the bisexual form of ''P. monacha'' is present in the highest waters, and the proportion of unisexual individuals increases progressively downstream from here.
''P. monacha'' are highly cannibalistic
Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species
In biology, a species is the basic ...
and the juvenile fish
Fish go through various life stages between fertilization and adulthood. The life of a fish start as spawned eggs which hatch into immotile larvae. These larval hatchlings are not yet capable of feeding themselves and carry a yolk sac which ...
es tend to hide from their mother close to the substrate. ''P. lucida'' is the reverse, and the young swim beside their mother. Hybrids between the two species are intermediate between these two behaviours.
''Poeciliopsis monacha'' sometimes exhibits black spot disease, caused by parasitic trematode
Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host ...
larvae. The parasites burrow into the body wall of the fish and forms tiny cysts. Some authorities consider that infection reduces reproductive success while other authorities believe that fecundity is unaffected.[
]
Ancient clonal lineage
The unisexual (all female) hybridogenetic fish ''Poeciliopsis monacha—occidentalis'' is an ancient clonal lineage that appears to be more than 100,000 generations old. ''P. monacha'' was the maternal ancestor of this lineage and ''P. occidentalis'' was the paternal ancestor. In these hybridogenetic fish only the haploid maternal ''P. monacha'' genome (M), but not the paternal genome, is transmitted to ova (''hemiclonal'' reproduction). The paternal ''P. occidentalis'' genome (O) is excluded during a pre-meiotic cell division, thus avoiding synapsis and crossing-over. Fertilization of haploid (M) eggs by O sperm occurs during mating with ''P. occidentalis'' males. This fertilization restores diploidy and results in expression of maternal and paternal traits in somatic tissue. These findings indicate that clonal reproduction in a vertebrate lineage is not necessarily transient, but can achieve a substantial evolutionary age
References
{{Taxonbar, from=Q2243288
monacha
''Monacha'' is a genus of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the subfamily Trochulininae Lindholm, 1927 of the family Hygromiidae, the hairy snails and their allies. MolluscaBase eds. (2021). MolluscaBase. Mo ...
Endemic fish of Mexico
Freshwater fish of Mexico
Fish described in 1960
Taxa named by Robert Rush Miller
Taxonomy articles created by Polbot