Daphnia lumholtzi
Encyclopedia
Daphnia lumholtzi is a small, invasive water flea
that originates in the tropical and subtropical lakes of Africa, Asia, and Australia. As an invasive species
, Daphnia lumholtzi disrupts aquatic habitats by spreading throughout the warmer waters of lakes and reservoirs.
that is 2–3 mm in length. It has a large helmet and a long tailspine, usually longer than the length of its body, that fluctuates in size. Its body structure is arched, extending to a sharp point. There are roughly 10 prominent spines on the margin of the abdominal shield covering
.
s at 26–31 °C (78.8–87.8 F), producing large amounts of microscopic offspring. Studies have shown that population density and water surface temperature are positively correlated. Once favorable temperatures are reached, such as those in the late summer, the previously deposited eggs hatch. It shows a much lower reproductive capacity and lower survival rates in temperatures below 10 °C (50 °F).
pattern, moving upward as the sun sets and downward as the sun rises. This behavior leads to large population densities close to the water surface at night and also occurs in the absence of a suggested predator threat.
ranging from 1 to 25 micrometers in size, but will also eat foods that contain organic detritus
, bacteria
, and protist
s which provide an excellent source of nutrients.
s in 1991 and has since been found in more than 16 states and over 125 lakes and reservoirs. Studies have shown that the ability of D. lumholtzi to disperse widely is most likely due to human activity. Heavy boat traffic on lakes and reservoirs during warmer seasons when D. lumholtzi thrive enable them to expand into other nearby bodies of water. The long spines and hairs on eggs act as hooks and enable attachment to boats, facilitating dispersal. The presence of D. lumholtzi in smaller ponds is atypical; however it is unlikely that non-human dispersal mechanisms, such as smaller invertebrate
s moving between bodies of water, have contributed to its widespread distribution.
for long periods of time. The eggs are characterized by long spines and hairs that act as hooks. Ephippia are protective shells that cover the egg until favorable conditions occur, such as warmer temperatures or a larger amount of resources. D. lumholtzi is capable of producing 10 times more ephippia than other daphnid species. In temperatures above the optimal temperature for reproduction, 25°C, the rate of egg development decreases. In temperatures below 25°C, egg development slows.
s living in these conditions. It has been suggested that D. lumholtzi’s more tropical origins may have enabled it to live in these higher temperatures. This advantage allows them to be a better competitor and ultimately out-compete other species, specifically native zooplankton
species, within the same habitat and come out as a successful invader. In accordance with the competitive exclusion principle
, no other species can inhabit the same late summer niche as D. lumholtzi; another factor that allows it to have higher survivorship than other Daphnia species and is ultimately a better invader. It is important to note, however, that high survivorship and reproduction are not the only factors that make D. lumholtzi an invasive species
.
Competition between D. lumholtzi is increased in habitats that favor the high light intensity of shallow waters. D. lumholtzi showed greater survivorship than other Daphnia species (specifically D. pulex
), which made them a stronger competitor for light reception and resources in bodies of water receiving high light intensity. It was found to out-compete other species in areas with high light intensity which in turn contributes to its invasive success.
D. lumholtzi is capable of producing 10 times more ephippia than other daphnid species, which can remain dormant until favorable conditions occur. This egg bank gives them an advantage over other species whose eggs cannot withstand desiccation
or lower temperatures, enabling them to produce more offspring that survive longer. The reproductive rate also increases with a higher concentration of food. Areas exhibiting high food abundance will therefore attract more D. lumholtzi, and in turn result in a higher rate of reproduction. The greater number of offspring puts pressure on the habitat’s resources and other competitors.
D. lumholtzi is highly plastic
, meaning it has the ability to morphologically adapt to factors within the environment by developing structures that enable it to successfully avoid predation
. A long tail spine, large helmet, and additional spines on the abdomen are produced in response to predator kairomone
s, which are predator hormones, within the water. D. lumholtzi does not produce these protective structures when there are no predators present, and looks morphologically similar to other Daphnia species. When predators are detected, D. lumholtzi responds by producing a tail spine, helmet, abdomen spines for protection; other Daphnia species do not adapt this way to predator threats. With the development of these morphological features, predators have a more difficult time preying on D. lumholtzi. This excess energy the predators put into eating D. lumholtzi lessens predator efficiency, making the predators more likely to choose another prey. This prey-switching
puts an extra strain on other native zooplankton species, reducing predation on D. lumholtzi and allowing it to outperform other competitors.
Cladocera
Cladocera is an order of small crustaceans commonly called water fleas. Around 620 species have been recognised so far, with many more undescribed. They are ubiquitous in inland aquatic habitats, but rare in the oceans. Most are long, with a down-turned head, and a carapace covering the apparently...
that originates in the tropical and subtropical lakes of Africa, Asia, and Australia. As an invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
, Daphnia lumholtzi disrupts aquatic habitats by spreading throughout the warmer waters of lakes and reservoirs.
Description
Daphnia lumholtzi is a small crustaceanCrustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
that is 2–3 mm in length. It has a large helmet and a long tailspine, usually longer than the length of its body, that fluctuates in size. Its body structure is arched, extending to a sharp point. There are roughly 10 prominent spines on the margin of the abdominal shield covering
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
.
Temperature
D. lumholtzi is typically found in the warm, shallow regions of bodies of water with larger surface areas. It survives in water temperatures above and around 25 °C (77 °F), and reaches maturity more quickly at higher temperatures. D. lumholtzi spawnSpawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
s at 26–31 °C (78.8–87.8 F), producing large amounts of microscopic offspring. Studies have shown that population density and water surface temperature are positively correlated. Once favorable temperatures are reached, such as those in the late summer, the previously deposited eggs hatch. It shows a much lower reproductive capacity and lower survival rates in temperatures below 10 °C (50 °F).
Behavior
Both adult and juvenile D. lumholtzi exhibit a vertical migrationDiel vertical migration
Diel vertical migration, also known as diurnal vertical migration, is a pattern of movement that some organisms living in the ocean and in lakes undertake each day. Usually organisms move up to the epipelagic zone at night and return to the mesopelagic zone of the oceans or to the hypolimnion zone...
pattern, moving upward as the sun sets and downward as the sun rises. This behavior leads to large population densities close to the water surface at night and also occurs in the absence of a suggested predator threat.
Diet
Daphnia lumhotzi mostly feeds on phytoplanktonPhytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
ranging from 1 to 25 micrometers in size, but will also eat foods that contain organic detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
, bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, and protist
Protist
Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...
s which provide an excellent source of nutrients.
Dispersal
Daphnia lumholtzi was originally restricted to the tropical lake and pond regions of southwest Asia, Australia, and most of Africa. The exact location of geographic origin in the United States has not been identified, but scientists believe the introduction of exotic African fish to lakes most likely caused the distribution. It was first detected in Missouri and Texas reservoirReservoir
A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...
s in 1991 and has since been found in more than 16 states and over 125 lakes and reservoirs. Studies have shown that the ability of D. lumholtzi to disperse widely is most likely due to human activity. Heavy boat traffic on lakes and reservoirs during warmer seasons when D. lumholtzi thrive enable them to expand into other nearby bodies of water. The long spines and hairs on eggs act as hooks and enable attachment to boats, facilitating dispersal. The presence of D. lumholtzi in smaller ponds is atypical; however it is unlikely that non-human dispersal mechanisms, such as smaller invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s moving between bodies of water, have contributed to its widespread distribution.
Reproduction
D. lumholtzi deposits eggs in lake sediment that can remain dormantDormancy
Dormancy is a period in an organism's life cycle when growth, development, and physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions...
for long periods of time. The eggs are characterized by long spines and hairs that act as hooks. Ephippia are protective shells that cover the egg until favorable conditions occur, such as warmer temperatures or a larger amount of resources. D. lumholtzi is capable of producing 10 times more ephippia than other daphnid species. In temperatures above the optimal temperature for reproduction, 25°C, the rate of egg development decreases. In temperatures below 25°C, egg development slows.
Predators
The main predators of D. lumholtzi are fish and small invertebrate species. Larger fish are almost always successful in their encounters with D. lumholtzi. Small invertebrate predators are less efficient than large fish in catching D. lumholtzi.As an Invasive Species
D. lumholtzi exhibits higher survivorship and reproduction in the late summer, under high heat conditions, when compared to other crustaceanCrustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s living in these conditions. It has been suggested that D. lumholtzi’s more tropical origins may have enabled it to live in these higher temperatures. This advantage allows them to be a better competitor and ultimately out-compete other species, specifically native zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
species, within the same habitat and come out as a successful invader. In accordance with the competitive exclusion principle
Competitive exclusion principle
In ecology, the competitive exclusion principle, sometimes referred to as Gause's law of competitive exclusion or just Gause's law, is a proposition which states that two species competing for the same resources cannot coexist if other ecological factors are constant...
, no other species can inhabit the same late summer niche as D. lumholtzi; another factor that allows it to have higher survivorship than other Daphnia species and is ultimately a better invader. It is important to note, however, that high survivorship and reproduction are not the only factors that make D. lumholtzi an invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
.
Competition between D. lumholtzi is increased in habitats that favor the high light intensity of shallow waters. D. lumholtzi showed greater survivorship than other Daphnia species (specifically D. pulex
Daphnia pulex
Daphnia pulex is the most common species of water flea. It has a cosmopolitan distribution: the species is found throughout the Americas, Europe and Australia. It is a model species, and was the first crustacean to have its genome sequenced.-Description:...
), which made them a stronger competitor for light reception and resources in bodies of water receiving high light intensity. It was found to out-compete other species in areas with high light intensity which in turn contributes to its invasive success.
D. lumholtzi is capable of producing 10 times more ephippia than other daphnid species, which can remain dormant until favorable conditions occur. This egg bank gives them an advantage over other species whose eggs cannot withstand desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
or lower temperatures, enabling them to produce more offspring that survive longer. The reproductive rate also increases with a higher concentration of food. Areas exhibiting high food abundance will therefore attract more D. lumholtzi, and in turn result in a higher rate of reproduction. The greater number of offspring puts pressure on the habitat’s resources and other competitors.
D. lumholtzi is highly plastic
Phenotypic plasticity
Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...
, meaning it has the ability to morphologically adapt to factors within the environment by developing structures that enable it to successfully avoid predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
. A long tail spine, large helmet, and additional spines on the abdomen are produced in response to predator kairomone
Kairomone
A kairomone is a semiochemical, emitted by an organism, which mediates interspecific interactions in a way that benefits an individual of another species which receives it, without benefiting the emitter. This "eavesdropping" is often disadvantageous to the producer...
s, which are predator hormones, within the water. D. lumholtzi does not produce these protective structures when there are no predators present, and looks morphologically similar to other Daphnia species. When predators are detected, D. lumholtzi responds by producing a tail spine, helmet, abdomen spines for protection; other Daphnia species do not adapt this way to predator threats. With the development of these morphological features, predators have a more difficult time preying on D. lumholtzi. This excess energy the predators put into eating D. lumholtzi lessens predator efficiency, making the predators more likely to choose another prey. This prey-switching
Prey switching
Prey switching is frequency-dependent predation, where the predator preferentially consumes the most common type of prey. The phenomenon has also been described as apostatic selection, however the two terms are generally used to describe different parts of the same phenomenon. Apostatic selection...
puts an extra strain on other native zooplankton species, reducing predation on D. lumholtzi and allowing it to outperform other competitors.