Lovebirds and Love Darts: The Wild World of Mating
for National Geographic News
|February 13, 2004|
Valentine's Day Special Report
Valentine's Day may have its origins in what ancient civilizations saw as the courting rituals of the animal world. But among cupid fish, lovebirds, and "love dart"-firing snails, mating is apparently anything but an affair of the heart.
The winged god-child known to the ancient Greeks as Eros and to the Romans as Cupid, had an eye for mischief. Anyone whose heart he pierced with his arrows fell deeply, immediately, and irrevocably in love.
So how did a carnivorous freshwater fish with a reputation for being solitary and aggressive come to be called Cupid? The Cupid cichlid's (Biotodoma cupido) cousins are named green terror, Jack Dempsey, convict, and black beltdistinctly more appropriate for fish that aquarium dealers recommend be kept only in a tank of similar-sized fish that can defend themselves.
"The Cupid cichlid is named after the Cupido Creek or River which feeds into another river in Surinam," said Douglas J. Sweet, adding that the information comes from the Catalog of Fishes by William N. Eschmeyer. Sweet is curator of fishes at the Belle Isle Aquarium in Detroit, Michigan. "The fish is not named after Cupid but the river the specimens were captured from."
In the Middle Ages people believed that birds found their mates for life on February 14, and Valentine's Day cards frequently depict lovebirds. But do lovebirds deserve their loving rep?
Lovebirds (Agapornis) acquired their name because it looks like they're constantly cuddling, sitting in pairs, preening each other's feathers. The ancient Greeks and Romans believed that lovebirds couldn't live without their mates.
Few Birds Are Faithful
The lovebird in the wild is one of the rare creatures that is monogamous, and "so the perfect couple exists," said Dirk Van den Abeele, laughing. Van den Abeele has written several books on lovebirds and is president of the Belgian Lovebird Society.
"However, when a mate is lost they waste no time in searching and achieving the securing of a new mate," said Al Decoteau, a director of the Society of Parrot Breeders and Exhibitors. Until the advent of genetic testing in the late 1980s, 90 percent of bird species were thought to be monogamous. DNA analysis of nestlings put the kibosh on that idea. Roughly 90 percent of bird species pair-bondhook up for a breeding season and raise chicks together. But few are faithful and many males wind up raising other males' babies.
"Extra-pair copulations"the scientific way to say "infidelity"serve a purpose for both the male and female in the animal kingdom. Each wants to produce as many offspring as possible.
Infidelity ups the male's chance to produce more offspring because individual females are limited in the number of babies they can produce. The catch to individual evolutionary fitness is that quality counts as much as quantity; producing lots of babies that die before they reproduce doesn't count.
Females benefit from promiscuity by improving the genetic quality of their young. A good provider is not necessarily the best sperm donor, so while the female builds a nest with her mate, she may sneak out and go sperm shopping for a male with brighter feathers, bigger body size, or a more glorious singing voiceall indicators of good health.
This widespread lack of fidelity led scientists to coin a new term: social monogamyliving in pairs but sexually unfaithful.
While genetic testing shattered the halos of birds as monogamous creatures, they were not the only species revealed as promiscuous. Only about 3 percent of mammals are thought to be monogamous, mating and bonding with one partner for life. Humans are not one of these naturally monogamous animals. Black vultures, termites, and prairie voles are.
Dueling Love Darts
But back to the arrow-shooting Cupid. Garden snails (Helix aspersa) use "love darts" to get their point across.
The hermaphroditic snails have both male and female characteristics, but do not self-fertilize. Courtship, which could take anywhere from 15 minutes to several hours, consists of circling one another to get in the best position to shoot a love dart but not be shot.
"Love is coming down to war in a way," said Ronald Chase, a biologist at McGill University in Montreal. "Sexual conflict plays out, even though both members of the mating pair are hermaphrodites."
Once the love darts are firedand about one-third of the time they missthe snails transfer sperm to one another in a separate process that lasts as long as six hours. What's the point of the love dart if hitting or missing makes no difference to whether the pair copulates?
The mucus covering the dart causes part of the recipient's female reproductive tract to contract, resulting in a significant increase in the amount of sperm stored. Successful dart shooters father more babies than do snails that miss with their darts.
"Successful dart shooting seems to only benefit the dart shooter, not the recipient," Chase said. "It causes damage"although Chase has seen snails shot through the brain and still live"it hurts, and it increases the number of babies the shooter is going to get."
Does Cupid enter the picture?
"I believe the myth of Cupid and his arrows has its basis in this snail species, which is native to Greece," Chase said. "The Greeks probably knew about this behavior because they were pretty good naturalists and observers."
The marine flatworm Pseudobiceros hancockanus takes the mating fight one step further, in what scientists call penis fencing. Each flatworm is a hermaphrodite with two penises. The mating ritual consists of dueling penises, each flatworm trying to pierce the skin of the other with its sharp-tipped organ. The winnerthe stabbertransfers its sperm. The loser gets what scientists call the burden of motherhood: the considerable energy costs of caring for the developing eggs.
Finally, is there anything in the animal world that parallels the "opposites attract" theory of romance in humans? Yes, according to recent bird research.
A study of the mating habits of great tits (Parus major) in the wild, conducted by scientists at the Netherlands Institute of Ecology, found that the offspring of parents with opposing personalities had much higher rates of survival than the chicks of parents with similar "extreme" personalities.
Niels Dingemanse and Christiaan Both found that when two birds with "extreme" personality traitsvery fast and aggressive or very slow and cautiousmated, they produced chicks with more extreme behaviors. These chicks tended to die early and reproduce less. The "average types" resulting from a fast and aggressive bird mating with a slow and cautious bird had the highest survival and reproduction rates.
More Valentine's Day Specials
Read "Finding a Valentine Can Be Tough for Animals Too, Cameras Show"
Watch National Geographic Presents: When Animals Attract on Fox TV tonight at 9 p.m. ET.
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