Guppy
The guppy, also known as the millionfish or rainbow fish, is a member of the family Poeciliidae and, akin to most New World members of the family, is considered a livebearer. Male guppies, which are smaller than females, have ornamental caudal and dorsal fins. Wild guppies generally feed on a variety of food sources, including benthic algae and the larvae of aquatic insects.
Originating from northeast South America, it has been introduced to many environments and are now found all over the world; guppies are now one of the world's most widely distributed tropical fish and one of the most popular freshwater aquarium fish species. They are highly adaptable and thrive in many different environmental and ecological conditions. Guppies are used as a model organism in the fields of ecology, evolution, and behavioural studies.
Taxonomy
Guppies were first described in Venezuela as Poecilia reticulata by Wilhelm Peters in 1859 and as Lebistes poecilioides in Barbados by De Filippi in 1861. It was named Girardinus guppii by Albert Günther in honour of Robert John Lechmere Guppy, who sent specimens of the species from Trinidad to the Natural History Museum in London. It was reclassified as Lebistes reticulatus by Regan in 1913. Then in 1963, Rosen and Bailey brought it back to its original name, Poecilia reticulata. While the taxonomy of the species was frequently changed and resulted in many synonyms, "guppy" remains the common name even as Girardinus guppii is now considered a junior synonym of Poecilia reticulata.Description
Guppies exhibit sexual dimorphism. While wild-type females are grey in body colour, males have splashes, spots, or stripes that can be any of a wide variety of colours. The development and exhibiting of colour patterns in male guppies is usually due to the amount of thyroid hormone that they contain. The thyroid hormones not only influence colour pattern, but control endocrine function in response to their environment. The size of guppies varies by gender, but males are typically long, while females are long.A variety of fancy guppy strains are produced by breeders through selective breeding, characterised by different colours, patterns, shapes, and sizes of fins, such as snakeskin and grass varieties. Many domestic strains have morphological traits that are very distinct from the wild-type antecedents. Males and females of many domestic strains usually have larger body size and are much more lavishly ornamented than their wild-type antecedents.
Distribution and habitat
Guppies are native to Antigua and Barbuda, Barbados, Brazil, Guyana, Trinidad and Tobago, and Venezuela. However, guppies have been introduced to many different countries on every continent except Antarctica. Sometimes this has occurred accidentally, but most often as a means of mosquito control. The guppies were expected to eat the mosquito larvae and help slow the spread of malaria, but in many cases, these guppies have had a negative impact on native fish populations. Field studies reveal that guppies have colonised almost every freshwater body accessible to them in their natural ranges, especially in the streams located near the coastal fringes of mainland South America. Although not typically found there, guppies also have tolerance to brackish water and have colonised some brackish environments. They tend to be more abundant in smaller streams and pools than in large, deep, or fast-flowing rivers. They also are capable of being acclimated to full saltwater like their molly cousins.Ecology
Wild guppies feed on algal remains, diatoms, invertebrates, zooplankton, detritus, plant fragments, mineral particles, aquatic insect larvae, and other sources. Algal remains constitute the biggest proportion of wild guppy diet in most cases, but diets vary depending on the specific conditions of food availability in the habitat. For example, a study on wild Trinidad guppies showed that guppies collected from an oligotrophic upstream region mainly consumed invertebrates, while guppies from a eutrophic downstream region consumed mostly diatoms and mineral particles. Algae are less nutritious than invertebrates, and the guppies that feed mainly on algae have poor diets.Guppies have also been observed eating native fishes' eggs, occasionally expressing cannibalism, also eating its own young, when kept in laboratory conditions.
Guppies' diet preference is not simply correlated to the abundance of a particular food. Laboratory experiments confirmed that guppies show 'diet switching' behaviour, in which they feed disproportionately on the more abundant food when they are offered two food choices. The result shows that different groups of guppies have weak and variable food preference. Diet preference in guppies could be related to factors such as the presence of competitors. For example, the lower Tacarigua River has a larger variety of species and competition for invertebrate prey is higher; therefore, the proportion of invertebrates is small in the diets of those guppies.
Guppies often forage in groups because they can find food more easily. Shoaling guppies spend less time and energy on antipredatory behaviour than solitary ones and spend more time on feeding. However, such behaviour results in food that is found being shared with other members of the group. Studies also show when an evolutionary cost exists, guppies that tend to shoal are less aggressive and less competitive with regards to scarce resources. Therefore, shoaling is preferred in high-predation regions, but not in low-predation regions. When guppies with a high tendency to shoal were isolated from high-predation regions and were relocated to predator-free environments, over time, they decreased their shoaling behaviour, supporting the hypothesis that shoaling is less preferred in low-predation environments.
Predation
Guppies have many predators, such as larger fish and birds, in their native range. Some of their common predators in the wild are Crenicichla alta, Anablepsoides hartii, and Aequidens pulcher. Guppies' small bodies and the bright colouration of males make them easy prey, and like many fish, they often school together to avoid predation. Schooling is more favoured by evolution in populations of guppies under high predation pressure, exerted either by predator type or predator density. Male guppies rely on schooling, in particular the behavioural responses of females, to make antipredator decisions. Colouration of guppies also evolves differentially in response to predation. Male guppies that are brighter in colour have an advantage in mating as they attract more females in general, but they have a higher risk of being noticed by predators than duller males. Male guppies evolve to be more dull in colour and have fewer, smaller spots under intense predation both in wild and in laboratory settings. Female guppies in a high-predation environment also evolve to prefer brightly coloured males less, often rejecting them.Predator inspection
When guppies encounter a potential predator, some of them approach the predator to assess danger. This behaviour, called predator inspection, benefits the inspector since it gains information, but puts the inspector at a risk of predation. To reduce the risk, inspectors avoid the predator's mouth area—called the 'attack cone'—and approach the predator from the side or back. They may also form a group for protection, the size of which is larger in high-predation populations. Although evidence indicates predators are less likely to attack an inspector than a non-inspector, the inspectors remain at higher risk due to proximity to the predator.Risk-taking behaviours such as predator inspection can be evolutionarily stable only when a mechanism prevents selfish individuals from taking advantage of "altruistic" individuals. Guppies may adopt a conditional-approach strategy that resembles tit for tat. According to this hypothesis, guppies would inspect the predator on the first move, but if their co-inspectors do not participate in the predator inspection visits or do not approach the predator close enough, they can retaliate by copying the defector's last move in the next predator inspection visit. The hypothesis was supported in laboratory experiments.