Characteristics of Chordata Reproduction

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Phylum Chordata includes an incredible variety of species that are found all over Earth. In this lesson, we'll look at the different methods for how these animals reproduce, some of which may surprise you!

Chordates Share Unique Features

What do an alligator, a fish, a human, and a small marine animal that looks like a pouch called a tunicate all have in common? They are all part of phylum Chordata! That's right, even though we look very different on the outside, we are all classified as chordates because we share a few common features, at least during some point in our lives. These four features are a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. In animals like vertebrates (those with a backbone), the notochord develops into the vertebral column, while in other animals like fish, the pharyngeal slits develop into gills.

Though they may not look like it, tunicates are your long, long, LONG lost relative!
light bulb tunicate

But these four features are pretty much where the similarities end, because the diversity of chordates is immensely broad. Some lay eggs, while others have live births. Some have skin, others feathers, and still others have scales. Some have legs, some have wings, and some have fins. Locomotion, feeding habits, body plans, and everything in between come in all shapes and sizes in this phylum, and reproduction, which is the focus of this lesson, is no exception.

Similarities in Chordata Reproduction

Since there are so many differences, let's start with the similarities in how chordates reproduce. For the most part, reproduction among members of this phylum is sexual, meaning that an egg is fertilized by a sperm. There are a few animals in this group that reproduce asexually, ''a'' meaning ''without sex.'' For example, some tunicates (those pouch-like organisms I mentioned before) reproduce by budding off a part of themselves, and that bud, which is genetically identical to the parent, develops into a new individual. Additionally, some fish and reptiles reproduce through parthenogenesis. This is a form of asexual reproduction in which an embryo develops without being fertilized.

Also, most chordates are dioecious, meaning that the males and females of species are different (''di'' for ''two''). For example, humans and other mammals, most fish, birds, and reptiles, etc., have males and females that have distinctly different reproductive organs. But some chordates are hermaphroditic, meaning that they have both male and female reproductive structures. This doesn't necessarily mean that they can self-fertilize, as the two do not always go hand in hand. Remember our friend the tunicate? Some of these guys are hermaphroditic, and to reproduce they will send both sperm and egg out into the water, where one will fertilize the other.

Male clownfish may change gender if something happens to the breeding female of the group.
clownfish

Want to get even weirder? Some chordates, like many fish species, are hermaphroditic, but they will actually change their sex at some point in their lives! To see this, we need to look no further than our famous friend the clownfish, which initially develop as males and then switch to females later in life. Why does this happen? Well, in the group, there is only one breeding male and one breeding female; the rest of the fish are non-breeding males. If something happens to the female, one of the non-breeding males has to step up by switching to a female so that the group can continue to reproduce. The reverse situation also occurs in other species, where from a group of females a leader will arise in the event that something happens to the original breeding male.

Differences in Sexual Reproduction

Since most chordates reproduce sexually, we're now going to switch to talking about the differences in how this is accomplished. We know that through this type of reproduction an egg is fertilized by a sperm, but there are different ways that this can occur, as well as different paths that the egg may take after fertilization.

There are two ways that eggs themselves are fertilized. Most terrestrial species will employ internal fertilization, where the egg is fertilized inside the body, while most aquatic species will employ external fertilization, which -- you guessed it -- is fertilization that occurs outside the body.

After fertilization, there are different ways that embryos develop. Animals that develop in eggs outside of their mother's body are called oviparous (''ovi'' for ''egg'' and ''parous'' for ''giving birth''). Think of fish, birds, reptiles, amphibians, and the like, where eggs are laid with all the nourishment they're going to get already provided inside that shell. For some species, they will simply lay their eggs and leave them to fend for themselves, like many fish and amphibians. Others, like many birds, will put in a good deal of effort to protect their eggs from harm until they hatch.

Chickens hatch from an egg outside the body of their mother, making them oviparous.
chicken with egg

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