Reproductive biology

Tadpole shrimps may reproduce sexually with populations composed of separate sexes (males and females), males and hermaphrodites, or solely hermaphrodites. The latter either self-fertilize or cross-fertilize one another. In most species,

A shield shrimp (Triops australiensis) in drying mud in an ephemeral lake, near Charleville, western Queensland, Australia. (Photo by B. G. Thomson/Photo Researchers, Inc. Reproduced by permission.)

females or hermaphrodites also reproduce parthenogeneti-cally, which is the most common means of reproduction in the Notostraca. During mating, the male holds the female above it while swimming in an upside-down position. Tadpole shrimps breed throughout their adult life.

The female or hermaphrodite carries the fertilized eggs in a brood pouch for several hours before dropping them in the water. These eggs are drought- and freeze-resistant and may remain dormant for up to several decades. Furthermore, through a mechanism that is not yet understood, a small percentage of these eggs may hatch shortly after being laid, while another portion may need only one period of drought before hatching, and some others may need two or more drought periods to hatch. In this way, tadpole shrimps increase the chances of their offspring surviving if any given pool should not last long enough to complete their development. In addition, the eggs are sensitive to light, osmotic pressure, and temperature, which allows them to hatch only in new (temporary) freshwater pools where predators can be avoided.

Tadpole shrimps hatch as nauplius larvae, and their development is extremely rapid, going through larval molts in as little as 24 hours if conditions are optimal. After each molt, the individual gains a pair of appendages. In most species, sexually mature tadpole shrimps may be found a couple of weeks after hatching.

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