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| From out of the Pond, water pumps up the hillside. |
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| Three (3 1/2?) pairs of damselfly doing their thing near our submerged water pipe. |
So the following excerpt was too good not to reproduce again here:
Damselfly Mating Game Turns Some Males Gay |
| James Owen for National Geographic News |
| June 21, 2005 |
| Disguises used by female damselflies to avoid unwanted sexual advances can cause males to seek out their own sex, a new study suggests. Belgian researchers investigated why male damselflies often try to mate with each other. The scientists say the reason could lie with females that adopt a range of appearances to throw potential mates off their scent. In an evolutionary battle of the sexes, males become attracted to a range of different looks, with some actually preferring a more masculine appearance. The study, published recently in the journal Biology Letters, says such evolutionary selection pressures could also explain homosexual behavior seen in males of other animals whose females assume a variety of guises. Such "polymorphic" species are seen in dragonflies, butterflies, hummingbirds, and lizards. Female blue-tailed damselflies (Ischnura elegans) assume different color forms, or morphs, in adulthood: green-brown, yellow-brown, and blue. The blue form closely matches the male in both body coloration and pattern. The study team found the sexual preference of male damselflies was influenced by the company they keep. Males that were housed together before being introduced to females tended to seek out their own gender afterward. But males kept in mixed-sex living quarters later preferred all three female forms when choosing a mate. This suggests male damselflies are likely to become attracted to other males only when females are absent or scarce. Yet a minority of males still showed an innate preference for male mates. The team's findings were reflected in mating behavior observed in the wild, says study author Hans Van Gossum, an evolutionary biologist at the University of Antwerp, Belgium. Van Gossum says around 17 percent of males in wild populations appear to favor same-sex pairings, while about one in six males in the lab experiments showed the same tendency despite exposure to females. "This behavior can be considered homosexual," he said. Sexual Selection But why should any males choose to mate with each other instead of with females? Such behavior apparently goes against theories of sexual selection, which predicts the optimization of reproductive success. Homosexual damselflies, however, aren't going to sire too many babies. Homosexuality has been recorded in a wide range of animals, including beetles, sheep, fruit bats, dolphins, and monkeys. In many such cases explanations have been put forward to explain this behavior. Consider, for example, the beetle known as the sugarcane rootstalk borer weevil. U.S. and Israeli researchers suggest the reason why females of the species mount other females is that the behavior attracts big males with good genes. Puny males seem to shy away from such antics. Female Japanese macaques also engage in intimate sexual acts with one another. U.S. primatologist Amy Parish and other researchers say female macaques may enhance their social position and form alliance partners through such intimacy which in turn can boost breeding success. Van Gossum and his colleagues propose a new explanation for homosexuality in animals like the blue-tailed damselfly. When males face strong evolutionary pressures to be flexible about their idea of what a female should look like, males may end up also fancying their own sex. Males damselflies need to be adaptable because their female counterparts are adaptable. Numbers of the three main female color forms, or morphs, fluctuate over time. Van Gossum, the study author, says most researchers agree such polymorphism most likely results from sexual conflict, with females evolving traits to avoid excessive harassment. While plenty of sex might suit male damselflies, this isn't the case for females. Joan Roughgarden is a professor of biological sciences at Stanford University in California. She writes, "Copulation ranges from over one hour to over six hours, averaging three hours. While a long copulation might seem like great fun, this can waste a whole day and be too much of a good thing, especially if carried out day after day over a life span that is only a few days long." Roughgarden adds that female damselflies collect all the sperm they need to reproduce from a single mating. Aviodance Tactics "Males go for quantity and females for quality," Van Gossum said. "As a consequence, females may wish to avoid excessive male attention. One way of doing so is by looking different from what a male thinks a female to be." The blue female form may accomplish this by mimicking the appearance of males. But Van Gossum says an alternative theory is that male harassment also leads to other morphs. "The minority female morph in a population"—whether blue or another form—"is the one that benefits, by receiving less male harassment," he added. In turn, it's likely that males have developed a flexible "search-image" that matches the majority female fashion of the day. This boosts a male's chances of finding a mate. "Males with a search-image that can be changed if the minority female morph becomes the majority morph are probably out-competing males that are less flexible," Van Gossum said. Such flexibility may also lead to genuinely homosexual damselflies. Van Gossum says such behavior could arise when a male is still young. A preference developed in male damselflies before reaching maturity, he says, is probably less prone to change in later life. The Belgian researcher adds that evolutionary pressures that shape damselfly mating behavior may also explain homosexuality seen in other male animals, including butterflies and hummingbirds, whose females similarly adopt a range of colorful guises. http://news.nationalgeographic.com/news/pf/48026386.html |
This excerpt is also too good not to copy and paste:
"Damselflies, like all odonates, have a very interesting breeding system. Before they actually copulate, males and females of many groups spend some considerable time in physical contact with one another, presumably in an effort to assess their potential mate. . . . This physical contact is made by the male clasping the female's thorax with the four terminal appendages on the end of his abdomen. [Note in our photograph above each male holding its potential mate with its terminal appendage (and in the one somewhat more interesting case, the male holding the other male's abdomen.]
"The male's terminal abdominal appendages consist of two superior cerci and two inferior paraprocts. The [left] figure [below] is a computer generated model of the tenth abdominal segment of a male E. ebrium viewed from the posterior. These four appendages grasp the female's thorax while they are in tandem. The [right] figure is a computer generated model of the females thorax viewed from above. The male's paraprocts contact her prothorax and the male's cerci fit into the two plates on the anterior surface of her mesothorax - the mesothoracic plates. These mesothoracic plates are thought to be used by the female to assess the species identity and potentially the suitability of the male that is grasping her in tandem.
"Field studies have shown that females discriminate among males based on cerci shape (Paulson 1974, Robertson and Paterson 1982, Fincke et al. 2006). Also, males with experimentally altered cerci are rejected by conspecific females (Robertson and Paterson 1982). Thus, the morphologies of these male and female structures seem to be critical for mate recognition, and so the evolution of these structures may play a vital role in speciation in Enallagma. These structures are akin to a lock-and-key mechanism, with each sex potenitially evaluating the fit between the male's cerci with the contours of the female's mesothoracic plates."
http://www.enallagma.com/cerci/damselflyMating.html
Immature damselflies (known as naiads), live in the stream for a year or so until one emerges into the world of air and becomes the light-weight flying thing that resembles a dragonfly. The adult version will live for a few weeks to a few months, during which time its only real purpose is to mate. The articles above tell the first part of this story. The other part begins with the male arching his long abdomen over to his own abdomen where he will deposit sperm on the underside of about the second segment. (Some sources say that the male deposits his sperm onto this accessory sex organ before searching for a female.) He then clasps onto the female behind her head and she arches her abdomen under and around to retrieve the sperm. She, then, will lay her fertilized eggs on the surface of waters, bits of plant emerging from the water, in the mud, drilled into plant stems, or let go in the warm summer or autumn air itself .
Here's a drawing of part of the Act:
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| From the Pond, past the 3 1/2 pairs of damselflies, across the Stonefield, and to the old Ruth Berry pressure pump. |
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| And then up Whitman's Rough. |
I focused mainly on the cedar elms along the east slope of Whitman's Rough above the home site. Buckeyes, junipers, persimmons, and other trees are dying, too. While I was sitting in a thin patch of shade beside the hose, a three-inch long lizard appeared on a water-spattered boulder. He went from one wet spot to the next, "lapping" up moisture as if in a frenzy. I don't know where he and other animals could possibly be getting enough water to survive.
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| With no creek flowing into it, the Pool warms and evaporates, shrinking the universe for dozens of fish, tens of thousands of insects, and gazillions of smaller invertebrates. |
