DRAGONFLIES LIVE FOR SEX

Well, don't we all? By "all," I mean all living things that reproduce sexually. When you think of it mechanistically, an organism's adaptations are primarily directed toward getting its genes into the next generation. Eat, sleep, avoid predators, grow up and reproduce—what else is there? Well, besides keeping in touch through Facebook.

For dragonflies, it's a long larval life in the water, as they eat and try to avoid being eaten. Then the magic of metamorphosis when they leave the water to become an adult winged insect. After that, more feeding and predator avoidance and, most of all, attempting to reproduce.

Male dragonflies spend much of their time at the water. Think of a singles bar, where the males are hanging around in hopes of meeting someone of the opposite sex. That's why those males head for the water. As the larvae are aquatic, the females have to lay their eggs in the water. Because the females have to come to the water to do this, males have a better chance of meeting one there.

Because so many males are at the water, the sex ratio can be extremely skewed there, with dozens to even hundreds of males for every female. Thus for a male there can be extreme competition for mates, and some males never mate in their lifetime. One way to alleviate that is for a male to defend a territory large enough, keeping other males out of his air space, so that he has access to any female that approaches. Many kinds of dragonflies do just this.

When a male damselfly sees a female, he immediately attempts to grab her for mating. He flies up to her, lands on her head and bends his abdomen forward to clasp her "neck" (prothorax) in two pairs of clasping appendages at the end of the abdomen. As soon as he has a good grip, he brings his abdomen forward and transfers sperm from the tip of his abdomen, where they are produced, to a storage chamber called a seminal vesicle in his second segment. From there, the spermatozoa can be transferred to his copulatory organ.

He then signals the female his readiness to mate by swinging her forward. The tip of her abdomen contacts his second segment, and structures on both of them form a firm connection. His genital ligula (penis) then transfers the sperm to the female's vagina, where it is moved to the spermatheca, another storage organ.

They then disconnect from that point, and she is ready to lay eggs. Her eggs travel from her ovary down her oviduct and are fertilized as they pass the spermatheca. She then can insert them into plant tissue with a specialized ovipositor, and the cycle begins again.

Dragonflies do about the same thing as damselflies, but the male fills his seminal vesicle before mating, and he clasps the female's head with three clasping appendages. The majority of dragonflies lay their eggs directly into the water rather than inserting them into plant tissue. See Odonate Oviposition, November 3, 2011, on this blog site.

Dennis Paulson

RUDDY DUCKS ARE ODD DUCKS

Most ducks of the North Temperate Zone mate in the winter, then the pair flies to their breeding grounds, where the female builds a nest and lays eggs. When she begins to incubate the eggs, the male deserts her, and there is no pair bond until the next fall, when the cycle begins again.

Ruddy Ducks (Oxyura jamaicensis) are quite different, and this might have been predicted, as they are the only northern ducks in which males molt in the spring into a bright breeding plumage, much as many shorebirds and passerines do. This is the rich red color that gives the species its name. The male bill, gray during winter, turns intense sky blue from structural changes.

There is no courtship or mating on the wintering grounds, but as soon as the birds arrive on their breeding grounds in spring, intense mating activity takes place. The males display actively at each other and at nearby females. The display consists of the male bumping its bill on its chest rapidly, creating bubbles in the water around it. This Bubbling Display is usually followed by a rush across the water in Display Flight, looking and sounding like a little motor boat. The loud noise accompanying the latter is made by the feet.

Male Ruddy Ducks are fiercely aggressive to one another and to other waterfowl when in mating mode. Females also can be very aggressive. Grebes and coots are not happy sharing ponds with Ruddy Ducks, and vice versa. They are not territorial, but the male stays very close to the female with which he is mated, even if only temporarily. Many males form a monogamous pair bond with a single female, some form pair bonds with a second and rarely a third female, and some appear to form no pair bonds at all, merely attempting to mate with any receptive female.

Now, about duck breeding. Most birds copulate by the male and female pressing the opening of their cloacas together, during which time sperm is transferred. But some male birds, including ducks, have a copulatory organ, the penis. This organ is not homologous to the mammalian or reptilian penis but is an erectile extension of the cloacal opening, as if a glove were turned inside out.

Ducks mate in the water, and cloacal appression might not be adequate for effective sperm transfer in the aquatic medium, so the evolution of a copulatory organ would have been an appropriate adaptation. The unequal sex ratio in ducks, with intense male competition for females, might also play a part in this adaptation. The penis is corkscrew-shaped, and the female vagina is similarly shaped in the opposite direction, so most mating attempts, especially between unmated birds in which the female does not cooperate, may be unsuccessful.

The Lake Duck (Oxyura vittata) of South America apparently has the longest penis in relation to its size of any vertebrate. It may be up to 40 cm, as long as the body. This species is closely related to the Ruddy Duck, which – as far as the present record books show – can develop a penis only about 25 cm long. A very interesting recent finding is that in a given wetland, only certain males develop the longest organs, and these are dominant to the others and the most successful breeders.

There is plenty more of interest about this odd duck. Ruddy Ducks lay the largest eggs with respect to body size of any duck, the average clutch of 7 eggs weighing about as much as the female herself. Thus the young hatch in a very precocial stage, grow quickly, and are abandoned by the female when about three weeks old, before they can fly. Speaking of flying, Ruddies are the poorest fliers among the ducks, rarely seen performing this activity. They apparently move around between wetlands and migrate entirely at night.

They are very highly adapted divers, with big feet that propel them under water, a compact body, and a long tail that may provide steering. They seem to be specialists on midge larvae, which make up the majority of their diet wherever studied. Because their prey is abundant and often evenly distributed, Ruddies can aggregate in large flocks that can find enough to eat even though there are many of them. They feed by diving to the bottom and slurping through the mud to strain out the larvae. They can feed actively for a while, fill up with midges, and then sleep, so our encouters are often with sleeping flocks.

Dennis Paulson

DUCK MATING GOES ON AND ON AND ON

It’s nowhere near spring, but believe it or not, there are many Pacific Northwest birds in the throes of intense mating behavior. Those birds are ducks. Ducks have a peculiar mating system, unique among birds. They form a strong pair bond, but it is mostly during the nonbreeding season!

Males of most temperate-zone ducks have bright, species-specific plumages, quite different from the drab plumages of females, many of which look very similar to one another. But these bright feathers are displayed from fall to early summer, and they are replaced during midsummer by a dull, female-like basic plumage (often called “eclipse” plumage). Displaying “breeding” plumage in fall, winter and spring and “nonbreeding” plumage in summer seems quite reversed from the situation in other birds, and in fact it is.

Most temperate-zone ducks are migratory, moving from breeding grounds in marshy freshwater wetlands to larger ponds and lakes and the ocean itself after breeding. Some duck species arrive on their wintering grounds while still in basic plumage, and the males molt fairly quickly into their beautiful alternate plumage. Other species, later migrants, molt farther north and arrive already in full color.

Almost as soon as the flocks arrive on their wintering grounds, the urge to mate kicks in, and the males begin to court the females. Those that arrive early wait until they have molted, but those that arrive late can begin the process immediately. Male ducks all have distinctive displays, which, coupled with their bright, species-specific colors, produce a dazzling show. Behavior involved in mating, both aggression and courtship display, is at its best in groups, with multiple individuals of both sexes.

Most male dabbling ducks have bright, contrasting markings around the head and breast and additional bright markings around their rear end. As soon as you see them display, you realize these color patterns are incorporated into the display. The displays are quite stereotyped, male Mallards, for example incorporating distinct display behaviors called Grunt-Whistle, Head-Up-Tail-Up, and Down-Up. Distinct behaviors are usually capitalized when written about in scientific literature.

Female Mallards perform head movements, bill-jabbing behavior, and characteristic vocalizations to indicate interest in copulating with a particular male. Females of most species will show aggression to males other than their mates. Copulation between pairs starts in the fall and continues through the winter into spring, when the birds return to their breeding grounds. Maintaining the pair bond seems to be the important function of this activity, which of course does not result in eggs being formed.

Displays in goldeneyes and mergansers are among the fanciest. In male goldeneyes, the head is thrown back almost onto the back, with a big splash when the feet kick back and an accompanying throaty note. In Red-breasted Mergansers, the male ends its display with tail down, back up, breast sinking into the water and neck extended upward with open beak, the whole thing reminiscent of some reptilian ancestor.

Some ducks rush along the water or fly short distances in their courtship. Buffleheads bob their heads violently up and down, fly just over the female and land by skiing on their bright pink feet, and cock both wings forward, exposing their big white patches. As part of their display, male Black Scoters also rush along the surface but with head down. A male Surf Scoter flies for 20-30 feet, wings whistling loudly, then drops feet-first into the water with wings raised. These display components are stereotyped in form and the order in which they are presented.

Because there is heavier predation on females when they are nesting, there are more male than female ducks in winter. Thus by spring there are still many unmated males. Courtship becomes even more intense, as gangs of male ducks roam around trying to find unmated females and spending much time harassing pairs to try to separate them (usually unsuccessfully). A lone female may be harassed by numerous males, and forced copulations are common at that time.

Finally, it’s time to make something of all that time spent mating. The pair heads off to wherever it is they breed, still maintaining that bond. They arrive, and the male has a fresh bunch of rivals to deter. The female quickly constructs a nest and lays her clutch of eggs, all the while shadowed by her mate. As soon as she begins to incubate, he leaves the scene and begins to hang out with other males in the same state. They typically move out into deeper water, begin their molt into basic plumage, and drop their flight feathers in preparation for growing a new set. It’s a new year in the odd annual cycle of a male duck.

Dennis Paulson