Hobbies And Interests
Classification
Phylum: Arthropoda
Class: Crustacea
Order: Cladocera
Species: Daphnia
Ecology and Habitat
Daphnia live in a wide range of habitats. They inhabit ephemeral pools, like puddles, as well as lakes. Depending on their environment, their hemoglobin production changes to cause daphnia to range in color from completely clear to bright red. Daphnia eat phytoplankton--microscopic water organisms--such as microscopic algae. They are preyed upon by roaches, perches and invertebrates such as bug larvae.
Eggs and Embryos
Daphnia females have a brood chamber between their body wall and the top surface of their carapace to carry eggs. They produce eggs in the summer that form in the ovaries. The eggs are squeezed out of the ovaries into the brood chamber hours after the female molts. While in the brood chamber, the eggs change shape and becomes more spherical. Each egg grows into an embryo inside the chamber before birthing as live young. All females produce female embryos asexually, but some produce male embryos asexually and others produce "resting eggs" in membrane pouches that require fertilization.
Asexual Embryos
A female daphnia creates eggs that are exact copies of itself. This cloning process allows females to reproduce without the help of males. Daphnia molt, or shed their shell, as they grow. After each molt, the female can put up to twenty eggs in their brood chamber. Unfertilized eggs grow into females. This form of reproduction preserves favorable genes, and allows for fast maturation and high fertility rates.
Sexual Embryos
Sometimes, the daphnia switch to bisexual reproduction. When daphnia are under environmental stress, some embryos will develop into small males and fertilize a couple of the eggs. In this case, two "resting eggs" wrapped in an epiphium (membrane structure) rest on the female's back. Daphnia shed the epiphium when they molt, allowing the eggs to remain dormant and protected for many years before developing into embryos.
Juveniles and Adults
Called neonates during the first instar or phase between molts, fully developed juveniles are only .004 inches long. They go through four moltings before reaching the fifth instar and becoming a sexually mature adult. First reproduction takes place between five and forty days old. Fully mature daphnia range in size from .02 to .06 inches. Daphnia do not live longer than a year, but they can die sooner depending on food availability, temperature and habitat. According to Geochembio, a shorter lifespan seems to be advantageous in frequently changing environmental conditions, while a longer lifespan where reproduction comes later or lasts longer is better in stable environmental conditions.