f course, there were a few folks present at the volleyball picnic who were more interested in the opposite sex than in playing volleyball. Farmer Melanie’s roosters were definitely interested in showing off for the hens and in chasing each other away from the hens. Hens and roosters have pretty-much all the same parts in their reproductive systems as humans do, and those parts work pretty-much the same as they do in humans.

Reproductive System

Just like human males, roosters have testes in which sperm are produced. Also like human males, roosters’ testes produce lots of testosterone, and that, in turn, stimulates development of their secondary sexual traits. In the case of roosters, that typically includes the comb on top of their heads, the red wattles that hang down under their chins, big, arching tail feathers, and spurs on the inside edges of their feet. One big difference between roosters and human males is that roosters do not have an organ analogous to a man’s penis. In both roosters and hens, there is only one external opening called a cloaca, and the “ends” of the reproductive, excretory, and digestive systems all empty into the cloaca. Thus, when roosters mate with hens, they match up their cloaca with the hen’s cloaca for the few seconds they’re able to maintain that close of contact. More detailed information on the human reproductive system can be found on the Biol. 105 Reproductive System Web page (see link below).

Just like human females, hens have ovaries in which eggs are produced. Well, actully, if we’re going to be picky about details, we need to modify that a bit... it turns out that as little hens grow up, typically only the left ovary develops and eventually makes eggs. When a hen’s ovary makes eggs, they don’t start out like the chicken eggs you’re used to seeing. Initially, the egg is made of only the actual egg cell and the yolk. In humans, when a couple has sexual intercourse, the man’s sperm swim up her uterus and fallopian tubes to fertilize her egg near the far end of the fallopian tube. Similarly, in chickens, the rooster’s sperm must swim up her reproductive tract and fertilize the egg cell before her body adds all the other “stuff” around the outside. Then, her body adds the egg white (albumin) which is similar in function and chemical make-up to amniotic fluid in humans, and then, finally adds an egg shell around the outside. Human females don’t make, don’t need an egg shell because the embryo will be implanted and retained in the uterus as it develops. However, many people are surprised to find out that the chicken eggs they buy at the grocery store are not fertilized – the hens that laid those eggs never even saw a rooster. Again, this is very similar to what happens in human females. In a human female, approximately every 28 to 29 days or so (that’s a rough average, and individual women’s bodies vary a lot from that), an egg matures and bursts out of one of her ovaries, then starts to travel down that fallopian tube. That process will happen regardless of if that egg gets fertilized or not, and if it is not fertilized, she’ll have her period. Similar to that, but much more frequently (about every day or two), an egg is produced in a hen’s body, and her reproductive tract coats that egg with albumin and an egg shell, then passes it out, regardless of if it was ever fertilized or not. Thus, humans who “raise” eggs for profit have realized they don’t need to keep roosters around and pay to feed them (which, of course, eats into their profit margin).

In humans, if an egg is fertilized and successfully implants in the woman’s uterus a week later, the week-old new baby will continue to grow and develop, until nine months later, (s)he is born. Similarly, if a rooster’s sperm fertilize a hen’s eggs, and if she broods the eggs to keep them warm, in 21 days, little chicks will hatch out and continue to grow and develop.

In insects, too, the whole process is fairly similar: males and females mate, females lay fertilized eggs, and the eggs hatch into young. However, there are more species of insects in the world than all the rest of the plants and animals put together, so there is a wide variety of “details” involved. Males of most beetles have an intromittent (meaning, it goes inside) organ that fits into the female’s reproductive tract, while male grasshoppers, katydids, and butterflies have claspers that grab onto the entrance of the female’s reproductive system. In some insects, the male’s intromittent organ is specially modified to clean out or kill any sperm from a previous mating that might be present in the female’s reproductive system before depositing that male’s sperm.

Male katydids and crickets transfer their sperm in an external sack, and the sperm must swim from there into the female’s reproductive tract (before she turns around and eats the sack). Females of most insects have an organ called a seminal receptacle that’s part of their reproductive tract, and this organ is used to store sperm until needed to fertilize eggs. For example, a queen honeybee mates only once in her life, and from that one mating she stores enough sperm to fertilize all the eggs she’ll lay for the rest of her life (about another 3 to 4 years). If you’ve ever seen the inside of a bee hive, that’s a lot of worker bees! Females of some insects, such as Madagascar Hissing Cockroaches, hold the fertilized eggs within their body while the eggs develop, and then the eggs are laid as they hatch (or hatch as they’re laid?), so that the female gives birth to live young. The eggs of certain kinds of parasitic wasps can hatch into hundreds or thousands of young! That way, when a female has “one shot” at laying an egg in a host (most of these are parasites on other insects like caterpillars, not on humans), that egg can produce many offspring. Some kinds of walkingsticks and other insects can produce eggs by parthenogenesis, the ability of an unfertilized egg to develop and hatch. Often, those insects live in environments where there aren’t many mates around and they’re pretty spread out, so the chances of mating are slim. In that case, parthenogenesis allows the species to keep going even if a mate can’t be found. Interestingly, in honeybees, fertilized eggs hatch into females (workers and queens), while unfertilized eggs hatch into males (drones).

Background Information

Your Assignment
Continue Working

Keep on working on previous assignments to try to get them finished and submitted.

carterjs@uc.edu

Copyright © 2006 by J. Stein Carter. All rights reserved.
This page has been accessed times since 18 Nov 2006.