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Video and images: To sooth the female during copulation bouts the male N. pilipes spider gently spreads fine silk upon the dorsum of the female. It is the touch of the male that soothes the female most of all a team of researchers recently learned through a series of laboratory tests. Click photos to enlarge. (Images courtesy Shichang Zhang, National University of Singapore)

To appease the female and make her more receptive to the multiple copulation sessions that are common among these spiders, the male N. pilipes spins a fine silk which he gently spreads about the female’s dorsum or backside—a behavior scientists call “mate binding.”

Now, a new study by a team of scientists from the Smithsonian’s National Museum of Natural History, the National University of Singapore, Hubei University, and the Slovenian Academy of Sciences and Arts have unlocked the secret to this little-studied behavior, and revealed just how it calms the female. Essentially, the scientists write in a recent paper, mate binding might be more descriptively termed “mate massaging,” as it is the tactile communication between the male and female N. pilipes, not the silk or chemical pheromones in the silk, that is the most important calming factor in this process.

In a series of laboratory experiments, the scientists—Shichang Zhang from the National University of Singapore, Daiqin Li of the National University of Singapore and Hubei University in China and Matjaž Kuntner of the Slovenian Academy of Sciences and Arts and a research associate at the Smithsonian’s National Museum of Natural History—blocked the tactile feeling on the dorsum of one group of female spiders with a thin layer of glue, and blocked the chemical receptors on the forelegs and palps (appendages near the mouth) of other females. In a third group of females they blocked both of these senses.

In addition, on a number of males they blocked the spinnerets used to spin the fine silk used in mate binding.

Next, they placed male spiders on the webs of the females and observed their mating behavior. What they learned, the scientists write, is that mate binding is not an obligatory behavior that always precedes mating, but rather, it always “occurred after females had interrupted copulations and became aggressive towards their suitors.”

Tactile communication caused by the male spider moving around the dorsum of the female with his spinnerets rubbing against her was the most important calming factor in mate binding behavior, they determined. Chemical signals embedded in the silk also appeared to have a calming influence on the females, but are secondary to the tactile feel of the male moving around the female’s dorsum. Silk production is but a by-product of the mate binding behavior.

Mate binding “enables the male to mate with the female multiply,” reducing her resistance and aggression, prolonging copulation bouts and maximizing the male’s paternity, the scientists conclude.

“Mate binding: male adaptation to sexual conflict in the golden orb-web spider (Nephilidae: Nephila pilipes)” appeared in a recent edition of the journal Animal Behaviour.

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Image left: A honeybee pollinates and apple blossom.

“Invertebrate conservation is hard to justify when many people see each insect as a potential pest or each spider as a potential health threat,” write the paper’s authors, who include entomologists Terry Erwin and Pedro Cardoso of the Smithsonian’s National Museum of Natural History. In general the public is unaware of the critical role invertebrates play in the health of the ecosystem or the conservation threats that these creatures now face.

In addition, policymakers are often poorly informed about the details of invertebrate conservation, the scientists say. “Many assume that in protecting a single large animal, that animal will serve as an ‘umbrella species’ protecting all the other species—including invertebrates—in its habitat. “This view is however largely unsupported and untested,” the scientists say.

Image right: The tree-nesting tropical ant Cephalotes atratus (Stephen Yanoviak)

Remarkably, most of the world’s invertebrates remain unknown and have never been studied or described by scientists. The vast majority of species now going extinct due to human activities—about 3,000 a year—belong mainly to understudied groups of invertebrates, ‘the little things that run the world,’ the scientists write.  “Because most invertebrates are undescribed, their geographic distribution is unknown as is their abundance, ways of life and sensitivities to pollution and habitat change.” Basic science for the study of invertebrates is scarce and underfunded.

Image left:  Bonaire box jelly fish, St. Vincent Island, Caribbean (Photo by Ned DeLoach)

To remedy the problem the scientists offer a number of suggestions, including:  More invertebrates should be placed on red lists of endangered species and in environmental impact statements; a stronger link must be made in the public imagination between invertebrate conservation and human well-being; sampling and analytical methods for biodiversity assessment and monitoring should be improved; and long-term ecological studies should be initiated to monitor ecosystem change.

“Invertebrate conservation is only possible with the preservation of ecosystems and their structure, function and processes,” the scientist’s conclude. “Only by preserving all species and guaranteeing interactions and ecosystem services may we reach the goal of overall biodiversity conservation.”

Photo right: A living colony of cupuladriid bryzoans, tiny coral-like marine organisms. (Photo by Aaron O’Dea)

“The seven impediments in invertebrate conservation and how to overcome them,” appeared in the journal Biological Conservation, and is authored by Pedro Cardoso, Terry Erwin, Paulo Borges of the Azorean Biodiversity Group, Portugal, and Tim New of La Trobe University, Australia.

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Image left: A single gene controls the repeated evolution of red color patten mimicry in passion-vine butterflies.

Now several research teams that include Smithsonian scientists in Panama, have discovered that Heliconius butterflies mimic each other’s red wing patterns through changes in the same gene.

Not only does this gene lead to the same red wing patterns in neighboring species, it also leads to a large variety of red wing patterns in Heliconius species across the Americas that result when it is turned on in other areas of the wings.

Because different butterfly species evolved red wing patterns independently, resulting in a huge variety of patterns we see today, researchers thought that different genes were responsible in each case.

Image right: Heliconius butterflies were reared in butterfly houses at the Smithsonian Tropical Research Institute’s facilities in Gamboa, Panama.

“The variety of wing patterns in Heliconius butterflies has always fascinated collectors,” said Owen McMillan, geneticist at the Smithsonian Tropical Research Institute, “People have been trying to sort out the genetics of mimicry rings since the 1970’s. Now we put together some old genetics techniques and some newer genomics techniques and came up with the very surprising result that only one gene codes for all of the red wing patterns. The differences that we see in the patterns seems to be due to the way the gene is regulated.”

First the team used genetic screens to look for genes that are turned on differently in butterflies with red wing patterns and lacking in other butterflies without this pattern. When they discovered a promising gene, they used stains to show where this gene was expressed on butterfly wings showing different patterns. They found the gene to be expressed exactly where red pigment occurs in the wings in every case. The match was so perfect that they could identify subtle differences in red patterns between species using these stains.

They combed genetic libraries—gene banks— to see if the gene they found matched genes characterized in other studies. “We found that the same gene that codes for the red in Heliconius wings was already identified as a gene called optix that is involved in eye development in other organisms,” said co-author Heather Hines, “It is intriguing that the ommochrome pigments that color these wings red are also expressed in the eye. How the optix gene codes for wing color raises a host of new questions.”

“Tropical biologists have been striving for centuries to explain what it is that makes life in the tropics so biologically diverse,” said STRI Director, Eldredge Bermingham, “Now this group has discovered that a single gene underlies one of the most spectacular evolutionary radiations in nature! Perhaps the genetic basis for diversity will turn out to be far more simple than we expected.”

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This short video shows frame-by-frame views of the movements of an ant (Cephalotes atratus) suspended in the updraft of a wind tunnel chamber.  The three images are from above and two sides, and all are synched. These tree-dwelling ants are capable of a directed aerial descent (DAD) should they fall from high-up in the tree canopy. DAD is a defensive behavior that allows an ant to glide backwards and steer itself toward and land on the trunk of the tree from which it fell. In this way it is saved from the distant, hostile and unfamiliar terrain of the forest floor. (Video credit Yonatan Munk, UC Berkeley.)

Directed aerial descent (DAD) is a defensive behavior that allows an ant dislodged from the tree canopy to glide toward and land back on the trunk of the tree from which it fell. In this way it is saved from the distant, hostile and unfamiliar terrain of the forest floor.

This video was created to compare a non-gliding and a gliding ant, both dropped from a tree. Videos courtesy of Steve Yanoviak.

One of the most challenging aspects of this research is simply studying these insects as they are falling, says Yanoviak, a tropical arthropod ecologist at the University of Arkansas, Little Rock, and colleagues, Robert Dudley of the Smithsonian Tropical Research Institute, and Yonatan Munk, University of California, Berkeley. Small body size, rapid descent, and the long distances that they can fall, make accurate data taking a challenge, they write in a recent paper published in the journal of Integrative and Comparative Biology summarizing their research.

Still, the team has discovered many new and interesting aspects to the directed aerial descent of different species of ants:

• DAD has multiple evolutionary origins in ants, the researchers say, occurring independently in numerous genera in the subfamilies Myrmicinae, Formicinae and Pseudomyrmecinae.

• Wind tunnel videos reveal that as they fall, gliding C. atratus ants hold their legs elevated and outstretched above the main body, and their gaster (the bulbous posterior body segment) fixed slightly below the main body axis. This configuration is aerodynamically stable and creates a force that pushes the ant backwards in a controlled glide. These ants steer by changing the position of their hind legs, mid legs and gaster.

Images above and below: C. atratus by Stephen Yanoviak

• Ants with hind legs, mid legs and gaster removed are unable to steer or glide effectively.

• Only tree-nesting ant species are capable of directed aerial descent. Some species are capable of righting themselves as they fall and rotating so their heads point toward the trunk of the tree from which they fell, but are not capable of horizontal movement. This suggests a transitional period in which these ants are evolving a gliding behavior.

• Ground nesting ant species may forage in the tree canopy but they cannot glide.

• Morphologically, ant species that can glide look no different from ant species that cannot.

• Gliding ants that are active both day and night, cannot glide at night, mainly due to their inability to see a target in the darkness.

• Gliding ants that fall into the leaf litter or into water are frequently attacked and killed by other ants, insects and fish. The mortality of ants that fall to the forest floor varies depending on environment.

Given the wide diversity of arboreal ants in the world, the researchers say, a broader study of directed aerial descent in these social insects promises a deeper understanding of the origin and evolution of this unusual behavior.

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