Plains topminnows (Fundulus sciadicus) are small minnows that are found in several microhabitats of the Nearctic region. They are found in the northern and western margins of the Ozarks from Lost and Shoal Creeks in southwestern Missouri and into direct tributaries of the Missouri River. They are also found in Nebraska, northeastern Colorado, eastern Wyoming, southern South Dakota, northeastern Oklahoma, in the Red River in Minnesota, and in western Iowa. (Cope, 2009; Helt, et al., 2003; Koupal and Pasbrig, 2010; Pflieger and Smith, 1997)
Plains topminnows have the most limited range of all of the Fundulus species due to their habitat requirements. Attempts have been made to reintroduce plains topminnows into several rivers in Missouri, where they are believed to have been historically extant. (Rahel and Thel, 2004)
Plains topminnows seem to prefer shallow waters with little or no current that have sandy substrates and abundant vegetation. Evidence suggests that sandy locations with vegetation are important for nesting behavior. Vegetation provides cover from potential predators and prevents the eggs from washing downstream. Plains topminnows also gravitate towards areas that are sheltered from the wind and lakes featuring gradually sloping bottoms. ("Development, Growth and Reproduction of Plains Topminnow, Fundulus sciadicus, in a Broodstock Pond Located at Sacramento-Wilcox Management Area", 2010; Koupal and Pasbrig, 2010)
Plains topminnows generally prefer to live near the water's surface. This provides a much higher oxygen content, as well as the ability to avoid predators. Plains topminnows cannot survive in distilled water, which may be an adaptation due to human development. They are adapted to freshwater and slightly saline water, allowing them the ability to live in slightly brackish water. They are also very dependent on the area to which they are individually adapted. Due to habitat fragmentation from ditching and draining of rivers, lakes, and streams, they tend to specialize in their own form of water only and can not be transported from habitat to habitat very well. (Koupal and Pasbrig, 2010; Rahel and Thel, 2004; SUMNER, 1911; Smith and Hoboken, 1912)
Outside the breeding season, female and male plains topminnows have identical dark green coloration with black sides and silvery white stomachs. During the breeding season, the female's color does not change while the male adopts an orange and yellow belly, presumably to attract a mate. Most of the year, their fins lack vertical bars or other distinct markings. Adult plains topminnows have one dorsal and one anal fin. The anal fin rays are 12 to 14 inches long with 12 to 15 spines. The dorsal fin rays, however, are shorter at 10 to 11 inches with 9 to 12 spines. The heads of plains topminnows are broad and flat, giving their mouth an upturned look. Due to their small size, they are not adapted for sustained swimming in high currents, even though this is necessary to move through drainage networks to recolonize new habitats after a severe drought. (Cope, 2009; Pflieger and Smith, 1997; Rahel and Thel, 2004)
Plains topminnows are viviparous. Females lay many eggs with a coating of mucus around them and oil inside, which provides nutrients. Gestation typically lasts 8 to 10 days. Eggs most likely hatch once the water temperature reaches 21 degrees Celsius. Newly hatched minnows are approximately 7.6 mm in length. Minnows feed immediately on the first day out of the egg, and develop predator avoidance techniques 2 to 4 days after hatching. Only 0.42% of the eggs will survive to maturity. Plains topminnows exhibit indeterminate growth. (Glaser, 1912; Kinney and Lynch, 1991; Koupal and Pasbrig, 2010; Pflieger and Smith, 1997; Rahel and Thel, 2004)
The mating strategy of plains topminnows is similar to other members of the Fundulus genus. The breeding season occurs between May and June. The water temperature needs to be around 21 degrees Celsius before spawning can occur. Females mostly decide mates, determined by competition among males. Two males line up next to each other and swim in circles until one of the males ends up biting the tail of the other male. The female witnesses this display, and then proceeds to swim very closely to the ground. This allows her anal fin to dig into the sand, which creates a place for her to deposit her eggs. Once this small trench is dug, she swims back and deposits her unfertilized eggs into the trench. The male then immediately swims past her eggs, depositing sperm onto them. This system ensures that most of the eggs are fertilized by the dominant male. Satellite males swim by after the first male and fertilize the remainder of the eggs. This is a very effective method for reproduction that creates only a small chance that the eggs will wash downstream and not survive. Males also have multiple mates. Although mating behavior in plains topminnows has been observed extensively, it is only speculated that it is what causes the female to mate with the male. This is a result of laboratory observation, where no deposition of eggs have been observed, despite eggs being found after this behavior happens. (Kinney and Lynch, 1991; NEWMAN, 1909; Rahel and Thel, 2004)
Plains topminnows breed once a year in early spring and summer. Females lay many eggs with a coating of mucus around them and oil inside. The eggs are sealed from the outside and none of their chemicals leach out into the environment. They are surrounded in mucous that attaches the eggs to vegetation. The oil inside the egg is used for sustenance until the egg hatches. Eggs laid in warmer water have a thinner coat of mucus, and this mucus layer becomes thicker as water temperature increases. There is also a strong positive correlation between the age of the mother and the amount of oil and mucus produced. Older minnows produce more, and presumably their eggs have a higher survival rate. Of the 200 to 400 eggs that are laid, only about 25 to 50 eggs survive to birth as a result of the low level of parental care. Only about 0.42% survive to maturity. (Glaser, 1912; Kinney and Lynch, 1991; Koupal and Pasbrig, 2010; NEWMAN, 1909; Pflieger and Smith, 1997; Rahel and Thel, 2004)
Gestation typically lasts 8 to 10 days. Eggs most likely hatch when the water temperature is at 21 degrees Celsius. When the minnows hatch, they are approximately 7.6 mm long. The minnow immediately feeds on the first day out of the egg, and develops predator avoidance techniques 2 to 4 days after hatching. (Glaser, 1912; Kinney and Lynch, 1991; Koupal and Pasbrig, 2010; M.L., et al., 2009; NEWMAN, 1909; Pflieger and Smith, 1997; Rahel and Thel, 2004)
Females provide the egg with mucus so it can adhere to the ground and the vegetation where it is laid. Inside of the mucus coating, there is an oil that is used as a nutrient source for development of the embryo. After eggs are laid, their is no additional investment by either parent. (M.L., et al., 2009; NEWMAN, 1909; Pflieger and Smith, 1997; Rahel and Thel, 2004)
Plains topminnows have been identified that are 4 years of age, even though they were not tracked from juvenile stages to adult stages. (Rahel and Thel, 2004)
There are typically low numbers of adult plains topminnows, which suggests low levels of intraspecific competition. There appears to be an increase in observations and activity of this minnow when the temperature of the water is increased. There is little other information about their behavior besides their mating pattern. ("Development, Growth and Reproduction of Plains Topminnow, Fundulus sciadicus, in a Broodstock Pond Located at Sacramento-Wilcox Management Area", 2010; Koupal and Pasbrig, 2010; Pflieger and Smith, 1997; Rahel and Thel, 2004)
There is little known about the the territory sizes of individual plains topminnows. It is suspected that there are low amounts of intraspacific competition due to the low abundance of adults. (Cope, 2009; Koupal and Pasbrig, 2010; Pflieger and Smith, 1997; Rahel and Thel, 2004)
Plains topminnows are not schooling minnows like many others in the genus Fundulus. They perceive their environment using their eyes and lateral line. The lateral line in any fish runs along the middle of their body from the opercle to the beginning of the caudal fin. Its functions include water current sensation and vibration detection. ("Development, Growth and Reproduction of Plains Topminnow, Fundulus sciadicus, in a Broodstock Pond Located at Sacramento-Wilcox Management Area", 2010; Rahel and Thel, 2004)
There have been no studies published on the feeding behavior of plains topminnows in the wild. Several papers have proposed that they are sustained by a diet of fly larvae (Diptera), specifically nonbiting midges (Chironomidae) and black flies (Simuliidae), plankton skimmed from the surface, crustaceans (Crustacea), and snails of the genus Physa. These assumptions are based on the habitat of the minnow and the morphology of the jaw, which is adapted for feeding at the surface of the water. In labs, plains topminnows are fed a diet of insects. ("Development, Growth and Reproduction of Plains Topminnow, Fundulus sciadicus, in a Broodstock Pond Located at Sacramento-Wilcox Management Area", 2010; Pflieger and Smith, 1997; Rahel and Thel, 2004)
There is only speculation in regards to predators of plains topminnows, due to lack of study. It is assumed that various species of pisciviorus fishes, green sunfish (Lepomis cyanellus), creek chubs (Semotilus atromaculatus), birds (Aves), and black bullheads (Ameiurus melas) are the main predators. These species live in the same habitat as plains topminnows and prey upon similar species. (Rahel and Thel, 2004)
Plains topminnows contribute to the foodweb as predators and prey, though their food habits and predators are not well understood. A fair amount of evidence suggests that populations of plains topminnows declined after the introduction of western mosquitofish (Gambusia affinis). Western mosquitofish, which have very similar habitat requirements, were introduced with the intent of reducing mosquito populations, motivated by fear of West Nile virus. In laboratory settings, extreme aggression by western mosquitofish is observed against plains topminnows. (Pflieger and Smith, 1997; Rahel and Thel, 2004)
Plains topminnows are host to two species-specific parasites. The flatworm Salsuginus yutanensis infects the gills, and is ingested as the minnow takes in oxygen. Plains topminnows are also affected by the trematode Phyllodistomium funduli, which infects the urinary blander and the ureters of the minnow. The Phyllodistomium funduli is suspected to be ingested by the eating of small clams, which are the intermediate host of this parasite. There is no evidence that either of these parasites kill their host. (Ferdig, et al., 1991; Helt, et al., 2003; Rahel and Thel, 2004)
Plains topminnows are aquarium fish and bait fish. They make a very hardy addition to most aquariums, despite being a very aggressive fish that often attacks other fish. Plains topminnows are used quite often as a bait, though this not legal in all states due to their low numbers. For example, it is illegal to possess these minnows as bait fish in the state of Colorado. (Pflieger and Smith, 1997; Rahel and Thel, 2004)
Western mosquitofish (Gambusia affinis) have been introduced into several habitats of the plains topminnow as a way to help control mosquito populations and provide economic benefit to humans. Because plains topminnows compete heavily with western moquitofish, there is an indirect negative economic impact on humans. (Rahel and Thel, 2004)
Plains topminnows are assumed to be stable across their home range. They are not considered a threatened, endangered or sensitive species by the federal government. They are considered rare in South Dakota, and a sensitive species within United States Forest Service Region 2. These statuses are a result of their limited habitat and slowly declining numbers. Declining numbers are a result of ditching, and draining for irrigation to be used to water crops, as well as the introduction of the western mosquitofish (Gambusia affinis). Some other ways that the habitat is being lost is through sedimentation from agricultural runoff, and pollutants being introduced into the habitat. A recent study in Nebraska showed that plains topminnows have disappeared from 75% of the 643 historic sites in Nebraska. Some conservation efforts exist. In 1994, the state government of Colorado attempted restoration efforts to the habitat of plains topminnows, reintroducing the species back into where it was thought to have been previously inhabited. (Cope, 2009; Koupal and Pasbrig, 2010; M.L., et al., 2009; Rahel and Thel, 2004)
Plains topminnows suffers from severe habitat fragmentation, which causes a lot of diversity among this species. This makes gene flow impossible, and causes a large amount of genetic variation. A sample of this species showed a 61% variation among males and 83% variation among females. This variation has caused the species to be discovered several different times within a short period of time by accident. Despite the severe differences, this species lacks a subspecies designation due to extreme genetic homogeneity within and between populations, possibly a result of the bottleneck effect. (Li, et al., 2009; O’Hare, 1985; Rahel and Thel, 2004)
Jonathan Zwart (author), Minnesota State University, Mankato, Robert Sorensen (editor), Minnesota State University, Mankato, Catherine Kent (editor), Special Projects.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
uses smells or other chemicals to communicate
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
fertilization takes place outside the female's body
parental care is carried out by females
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
mainly lives in water that is not salty.
Animals with indeterminate growth continue to grow throughout their lives.
An animal that eats mainly insects or spiders.
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
the business of buying and selling animals for people to keep in their homes as pets.
an animal that mainly eats plankton
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
uses sight to communicate
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
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