Nuptial Gifts and Other Romantic Gestures of the Bug World
By Adrienne Antonsen
On Valentine’s Day across the globe, people often offer presents to their loved ones. Many insects are also gift-givers. Known as nuptial gifts, these treats can help attract a partner and improve reproductive success.
In honor of this day of romance, here’s a look at recent entomological research on how some insects and other arthropods woo one another with gifts.
Nursery Web Spiders Give Big Gifts, But They May Be Partially Used
Nursery web spiders (family Pisauridae) are well known for their mating ritual in which males often present females with a silk-wrapped prey item before beginning copulation. These nuptial gifts lower the likelihood that females will eat the males, increase the length of time females permit copulation, and improve fertilization success.
A recent study investigated what size of gift Pisaura mirabilis males prefer to present to females and whether or not they feed on the prey item before giving it away. To test this, male spiders of variable body condition were presented with either a large or small cricket nymph in an environment with or without female pheromones. The researchers found that, regardless of body condition, males preferred to produce large nuptial gifts over small ones, indicating an energetically costly gift ultimately pays off better than cutting corners with a smaller gift. However, if the males were in poor bodily condition, they were more likely to feed on the gift before offering it to a female. But hey, it’s the thought that counts, right?
Long-Tailed Dance Flies Seek the Heaviest Partners They Can Hold On To
When it comes to romance, Rhamphomyia longicauda, often known as the long-tailed dance fly, switches things up. Most often in the animal world it’s the females who do the choosing and the males who do the wooing, but those roles are reversed for dance flies. Females don’t hunt, so they rely completely on nuptial gifts provided by males for nutrition. The females fly in groups at dusk and dawn waiting for males to bring food to them. To make themselves appear more desirable, females fill their abdomens with air to advertise their eggs as being more mature than they may truly be, a characteristic that males seek out.
Mating takes place in flight, and males bear the weight of both the nuptial gift and the female while she feeds upon it. So, just how large can a female get without becoming too heavy to hold onto in flight? To test this question, researchers studied a wild population to see whether the wing loading of males (i.e, wing area relative to body mass) was related to the mass of the female dance flies they ultimately mated with. Contrary to their hypothesis that males with higher wing loading would select smaller females, the researchers found the opposite. This indicates that male long-tailed dance flies don’t experience the same load-lifting constraints that other dance flies do. When it comes to long-tailed dance flies finding a date, being bigger is better.
Nitrogen is a Game-Changer for Cabbage White Butterfly Mating and Reproduction
In imported cabbageworm butterflies (Pieris rapae), also known as cabbage white butterflies, nitrogen plays an important role in mate selection. The nutrient makes up a significant amount of the nuptial gift passed from males to females during copulation, an important source of energy for female butterflies. Nitrogen is also used in wing pigmentation, a cue the butterflies can use to visually assess mate quality. Researchers wondered how variable nitrogen availability, specifically due to anthropogenic influences, might affect cabbage white mating behavior and physiology. To test this, they compared cabbage white butterflies from a non-agricultural population with a population from an agricultural setting where fertilizer has significantly increased nitrogen availability.
Several differences became apparent between the two populations. First, while females from the non-agricultural site typically mated with more than one male, agricultural females tended to mate only once, thus receiving fewer nuptial gifts. The agricultural females were also less choosy when selecting a mate. Second, the toothed structures used to break down nuptial gifts were reduced in agricultural females’ reproductive tracts, indicating a reduced need for the nutrients. Third, both males and females from the agricultural population had increased wing pigmentation. Altogether these results suggest that changes in nitrogen availability can affect cabbage white reproductive behavior and physiology in a multitude of ways. As the world changes, so do the rules of romance for these butterflies.
Hawaiian Swordtail Cricket Males That Give More Gifts Produce More Offspring
To reproduce, male insects will often transfer their genetic material to females via a protein capsule known as a spermatophore. Sometimes, however, these capsules may contain only nutrients and no genetic material. These are called microspermatophores and serve as nuptial gifts. Males of the cricket species Laupala cerasina, also known as the Hawaiian swordtail cricket, typically present females with anywhere from one to nine of these nuptial gifts before transferring the final capsule that contains their genetic material. (See a male and female L. cerasina pair in the image at the top of this article.) This process can take several hours. Why do these crickets go to all this effort of producing capsules without any reproductive material inside? As it turns out, the nuptial gifts improve the amount of genetic material successfully transferred from the final spermatophore to the female.
Researchers wanted to find out if the number of nuptial gifts a male Hawaiian swordtail cricket presents to a female affects the number of future offspring that are sired. To test this, the researchers paired a female cricket with two males: one that mated earlier in the day with a different female and one that did not. Males that had mated earlier transferred fewer microspermatophores to the female during the second mating. Using DNA sequencing, it was then possible to directly compare both the number and paternity of the offspring produced. As it turned out, females had a higher number and higher proportion of offspring with the males that offered a greater number of nuptial gifts. So, these crickets better not be stingy with their gifts when it’s time for love!
Take a cue from these creatures and get your gifts in order for the love bugs in your life this Valentine’s Day.
Adrienne Antonsen is a graduate student in entomology at North Dakota State University. Email: firstname.lastname@example.org