It’s nice to read about the couples that’ve met through PATC in this issue. Ah, love!
Cupid shoots his love darts and we fall in love. How beautiful and simple, yet, how totally misleading. Would you believe that Cupid has its basis in the reproductive strategy of the common garden snail? And, it’s neither a beautiful nor a simple story.
Snails are hermaphroditic, meaning they have both male and female parts. Many snails and slugs have what are called ‘love darts’; calcified or chitinous projectiles that are used to spear their partners during foreplay. Sometimes one or both partners are killed since the darts can penetrate the heart or brain. These love darts are shot prior to copulation and do not carry sperm. The dart is coated with a special mucus, which contains a hormone-like substance that contracts the female half of the reproductive system of the snail that is struck with the dart. This allows many more sperm to survive, significantly increasing the likelihood of a successful fertilization.
Cupid, known as Eros in Greek mythology, fired love darts. The Greeks, being excellent naturalists, certainly were aware of the love darts used by the common garden snail. Thus, it is easy to make the connection between Cupids arrows and the love darts of snails.
Use of these love darts appears limited to certain species of snails and slugs, while hermaphroditey is found in worms, barnacles and a few other invertebrates.
A variation of this theme is found in species of flatworms. Such flatworms mate hypodermically; one must jab its partner with its penis. When two flatworms meet, they rear up, sticking their penises out and try to stab each other. This penis-fencing duel can last an hour. The flatworm that successfully stabs its mate gets to fertilize eggs, while the worm being stabbed has to bear the cost of healing its wounds as well as producing the offspring. Some species have sperm so aggressive that it eats its way through the body tissues of the recipient until it finds the ovaries. Such recipients can have gaping holes from the sperm, losing up to two-thirds of their body mass.
Ah, love. One might wonder if there’s a way to avoid such conflicts while maintaining the ability to reproduce. Enter the parthenogenic species; species whose females can reproduce without ‘input’ from males. The introduced woolly hemlock adelgid, responsible for the decimation of our hemlock trees, are strictly females – as are the woolly balsam adelgids, responsible for the loss of balsam firs in the Great Smoky Mountains NP.
Parthenogenesis occurs naturally in some invertebrate animal species (e.g. crayfish, aphids, nematodes, some bees, some scorpion species, and parasitic wasps), and vertebrates (e.g. some reptiles – whiptail lizards and geckos, fish, and very rarely birds). Komodo dragons and hammerhead sharks have recently been added to the list. While there are no known cases of naturally-occurring mammalian parthenogenesis, parthenogenesis has been induced with rabbits and mice.
There are numerous variations of parthenogenic reproduction, just as there are virtually unlimited methods of ‘normal’ sexual reproduction practices.
It always seems the opossum finds ways to be unique. Males have a forked penis, which matches the paired lateral vaginae of the female. In other more advanced mammals, the female reproductive tube fuses in the middle to form a single canal. In fact, the opossums produce paired sperm. As a pair, the sperm swim in a straight line, but if separated, they swim in circles. Copulation involves the male grabbing the female by the nape of the neck and both falling over to the right side. On occasion when they may fall to the left, or remain upright, copulation is likely to be unsuccessful.
Among shrews, like reptiles and birds, both genital and urinary tracts merge into a single opening called a cloaca. A study of European shrews show that when two males meet, they engage in a squeaking contest. If neither backs away, they will rise up on their hind feet and continue squeaking. If still a stalemate, they will roll over on their backs, with one grabbing the tail of the other and throwing him, judo style. Hence, the winner finally emerges.
The phrase, “Mad as a March hare” comes from the springtime mating antics of female hares, sizing up the courting males. Females stand up on their hind legs and cuff males in the face and ears. Female hares and rabbits are normally larger than males, indicative of the evolution of selection for combative females.
Regarding the courtship behavior of lagomorphs, the following describes the snowshoe hare, “The male snowshoe approached the female, sniffed her and jumped into the air. After landing, the male urinated on the female and left. The male re-approached the female, and the female jumped into the air twice, after which the male left. The male returned, jumped into the air and urinated on the female. Both snowshoes then went into the bushes, where more jumping occurred.”
So, how do porcupines mate? Of course, the answer is – very carefully! In fact, they do mate carefully, with the male learning at an early age to move the females’ bristly tail to the side!
Ain’t love grand?