The Hine's Emerald Gallery Page 2
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Clasper details Reproduction and copulation Eggs to larvae
The cerci of Hine's Emerald males are more highly modified than those of the female, and they are shown below in detail. Figure A shows a male oriented such that the clasper, with its two dorsal cerci, can be seen, and the inset is an enlargement of the clasper.
A good way to visualize the clasper is to place your thumb just below the first and second fingers of your hand, with the two fingers separated from the thumb by an inch or so. The thumb represents the epiproct, the lower member of the clasper, while the two fingers are the cerci. Muscles within can close the cerci on the epiproct, allowing the clasper to act as a clamp-like structure. The male dragonfly can also move the cerci laterally.
Side views of claspers are shown in Figs. B and C above. Note that the claspers of all S. hineana males are identical in appearance. In fact, claspers of dragonflies are species specific, and one of the surest ways to identify a male Hine's Emerald is to look at the tip of the abdomen for the characteristic shape of the clasper. During copulation, the tip of the epiproct and tips of the cerci index with specific depressions on the upper aspect of the head of the female. This coupling can be considered a kind of "lock and key" arrangement. A typical male is shown below, with the clasper further enlarged in the inset.
Dragonflies as a group can be considered living fossils, for those seen today are remarkably similar to those that appeared on our planet over 300 million years ago (during the Carboniferous Period). Someone has said that much of their evolution must have been spent trying to perfect their copulation strategy, which is most unusual.
In the male, the testes are located in the posterior half of the abdomen, and sperm can be discharged through an opening on the underside of abdominal segment #9. Prior to mating, the male swings its abdomen down and forward during flight and transfers sperm to a chamber inside segment #2 (referred to as part of the male's "accessory genitalia"). This segment in the male is expanded ventrally to form a spout-like structure involved in transferring sperm from the chamber within to the female.
After the male dragonfly has transferred sperm, or sperm packets, to the chamber in abdominal segment #2, it is ready to copulate. It does so by flying over a female and using its legs to grasp the female's head and thorax; then the male curves its abdomen downward and forward such that its clasper engages the back of the dorsal (top) aspect of the female's head. In response, the female swings abdomen forward and fits the underside of segment #8, with its opening to the ovaries and eggs within, to the male's secondary genitalia (segment #2), which contains sperm within. Thus the male and female, while in flight, become linked in a circular configuration, sometimes called the "wheel position," as shown at the left.
Although copulating individuals can fly, mostly due to the efforts of the uppermost male, once linkage is established the male grasps a twig or evergreen branch from which the pair remains suspended as sperm transfer to the female occurs. If undisturbed, a copulating pair may remain linked for up to an hour or so.
The thumbnail image below shows the head of the male and the posterior portion of the abdomen of the attached female. Click on the image to enlarge the photograph.
Click thumbnail image for enlarged view
The next enlargement shows the anterior end of the upside-down female. Note the manner in which the clasper is locked to the head of the female, while the female tightly grasps the abdomen of the male for support. Once transfer of sperm is completed, the male and female disengage. Soon thereafter the female returns to nearby water and begins to lay fertilized eggs, while the male patrols the area to chase away competing dragonflies. Females lay eggs in flight by dipping the ends of their abdomens in water as the hover close to the surface.
Click thumbnail image for enlarged view
The eggs overwinter and hatch into larvae the next spring. After about three years, and with growth and molting, larvae develop to a point where they are prepared to transform from aquatic predators to aerial predators. They crawl out of the water onto vegetation, work their way out of the larval exoskeleton, and become airborne carnivores.
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