Water Fleas: Look Weird, Adapt Weirder

Summary

Water fleas, despite their name, are not insects but small crustaceans called Cladocerans, with Daphnia being the most commonly observed. Known for their flea-like appearance and jumping ability, water fleas play a crucial role in aquatic ecosystems as filter feeders. They adapt to environmental changes through behaviors like diel vertical migration and adjust their reproduction strategies based on cues from predators or environmental conditions. The video highlights their unique biology, including their large compound eye, hemoglobin-based oxygen transport, and their remarkable ability to switch between asexual and sexual reproduction when faced with survival challenges.

Takeaways

• 🦐 Water fleas, or Cladocerans, are crustaceans, not insects, with over 600 known species.
• 🐜 They got their name due to their resemblance to fleas and their ability to jump.
• 👁 Daphnia, a common genus of water fleas, have a large compound eye that develops from two eye spots in their embryonic stage.
• 🌡️ Their heart rate is temperature-dependent, beating faster in warmer conditions and slower in colder ones.
• 🦑 Water fleas use hemoglobin to transport oxygen, increasing its concentration by 20-fold when oxygen is scarce, turning them red.
• 🌊 They practice diel vertical migration to avoid predators, staying in darker, deeper waters during the day and rising at night to feed.
• 🐟 The presence of predator signals, called kairomones, can change the size of their offspring, making them smaller or larger depending on the threat.
• 🦷 Some Daphnia species can grow protective features like 'neck-teeth' to defend against predators like the phantom midge.
• 🥚 Daphnia primarily reproduce asexually but switch to sexual reproduction when environmental conditions worsen, producing males and resting eggs for survival.
• 📦 Daphnia are often sold as fish food in aquarium stores but play a crucial role in filtering algae and bacteria in aquatic ecosystems.

Q & A

What are water fleas, and how do they differ from actual fleas?

Water fleas, also known as Cladocerans, are small crustaceans, whereas fleas are insects. They share some superficial similarities like jumping, but water fleas belong to a completely different group of organisms.

Why are water fleas called 'fleas' if they are crustaceans?

Water fleas got their name because they somewhat resemble fleas and can jump in a way that reminds people of fleas, despite being crustaceans, not insects.

How large are water fleas compared to other microscopic organisms?

Water fleas are considered large in microcosmic terms, ranging from 0.5 mm to 6 mm long, making them quite large compared to many other microorganisms.

What is the function of the two sets of antennae on water fleas?

One set of antennae is used for sensing their environment, while the other set is used for swimming.

How do Daphnia's eyes develop, and what is unique about their vision?

Daphnia start with two brown eye spots as embryos, but these merge to form a single large compound eye during development. They also have a smaller photosensitive organ called the naupliar eye between their compound eye and mouth.

How do Daphnia survive in low oxygen environments?

Daphnia can increase the concentration of hemoglobin in their bodies up to 20-fold, allowing them to transport more oxygen in low-oxygen environments, which can turn their bodies a more vivid red.

What is diel vertical migration, and why do Daphnia perform it?

Diel vertical migration is a strategy where Daphnia move to lower depths during the day to avoid predators and then rise to the surface at night to feed when it's safer.

How do chemical signals called kairomones affect Daphnia's behavior and size?

Kairomones are chemical signals that alert Daphnia to the presence of predators. Fish kairomones cause them to birth smaller offspring to avoid detection, while midge kairomones cause them to grow larger and even develop defensive structures like neck-teeth.

What is the reproductive cycle of Daphnia, and how do environmental factors influence it?

Daphnia typically reproduce asexually, producing genetically identical offspring. However, under tough environmental conditions, they switch to sexual reproduction, producing males and creating opportunities for gene exchange. This ensures survival in changing environments.

How does the ephippium function in Daphnia's reproductive cycle?

The ephippium is a saddle-like structure produced after sexual reproduction that holds resting eggs. These eggs can survive harsh conditions, lying dormant for years until the environment becomes favorable for hatching.