Reproductive strategies of males and females are different, which creates a conflict of interest between the sexes. Reproductive success of a male is generally proportional to his ability to mate with the maximum number of females and spreading as many copies of his genome as possible while investing as little efforts and resources as possible to each connection. The evolutionary mission of females is to attract as many males as possible in order to choose the best partner (or the best genes!) and get from him some resources to secure the survival of themselves and the offspring. This conflict of interests often leads to the development of bizarre adaptations that help both males and females to manipulate their partners to achieve their reproductive goals. Numerous examples of these amazing adaptations are described in the book of evolutionary biologist Olivia Judson, “Sex for survival”.

Males of some spiders and insects present valuable ‘wedding gifts’ to females before mating. Usually, these gifts are freshly caught prey that female would eat during copulation. Sometimes males cheat and bring to their girlfriends inedible objects such as petals, seeds and even their own feces. In order to increase the effect and distract the female for longer time, male spiders wrap the gift in a bright fluffy cocoon of spider web. Female spiders Pisaura mirabilis are equally willing to mate with males who offer either edible or symbolic gifts, while rejecting those that have no gifts at all. In case if the female received an inedible gift, she interrupts intercourse sooner, which reduces the reproductive success of the ‘cheating’ males: they have less time and give less sperm to the female than the rivals who have spent time and effort in obtaining nutritious gifts. Apparently, this explains the fact that the majority of male P. mirabilis spiders still prefer to give edible gifts to females. Sometimes males-cheaters temporarily win the race and the cheap gifts become widespread. When the females win the race, more expensive, hard to find gifts are in fashion in the population of spiders.

Like many people, females of P. mirabilis apparently believe that the most valuable gift is the one in a good packaging. The packaging has three useful functions for the male. First, the packaging itself attracts and predisposes the female. Second, the packaging itself does not allow a female to see immediately what’s inside, that gives the male additional time to approach female and start intercourse. Third, it is much easier for a male to get hold of the gift wrapped in a web as females often try to prematurely terminate copulation and get away before the male can fill special seminal receptacle on the bottom side of the abdomen of female. Male spiders are smaller and weaker than females and cannot retain them by force, so they use tricks to over-smart females. When the female interrupts the copulation and tries to escape, the male spreads legs around the wrapped gift and pretends to be dead. The female cannot shake off the “dead” boyfriend hanging on the gift, so she drags him along. As soon as she starts to eat the meal again, the male “wakes up” and resumes copulation.

Scientists developed genetically modified silkworms that produce a spider silk protein that incorporates into silk fibers and makes them much stronger than natural silk fibers and as tough as spider web. This approach allows producing spider silk fibers on an industrial scale for a range of biomedical, military and textile applications such as wound dressings, artificial ligaments, tendons, artificial blood vessels, tissue scaffolds, microcapsules and even the body armor.

Despite the great demand of the spider fibers and numerous benefits it can offer, it is impossible to farm spiders because of territorialism and cannibalism between spiders. To get around this problem, recombinant spider silk proteins have been produced in other hosts such as bacteria, yeast, baculovirus, mammalian cells, and transgenic plants and animals. However, all these approaches are expensive, hard to scale up, and lack natural spinning of silk fibers. Silkworms represent the perfect host for spider silk production. Their silk glands naturally produce silk fibers. Gene encoding natural silk protein can be replaced with recombinant spider silk protein that can be targeted to the silk gland using a tissue-specific promoter.

In the attempt to generate transgenic silkworms, scientists created a vector that encodes the synthetic spider silk protein A2S814 and targeted its expression to the silkworm’s silk gland as well as an enhanced GFP (EGFP) tag for visual monitoring of the recombinant protein expression. They injected the vector into eggs and selected transformed larvae using EGFP as a marker of A2S814 expression.

Further analyses of silk extracted from the cocoons confirmed that chimeric silkworm/spidersilk proteins expressed by the transgenic larvae and incorporated into chimeric silk fibers. Importantly, the composite fibers were on average stronger than the parental fibers and more extensible than parental silkworm and native dragline spider silk. “These results demonstrate that the chimeric silkworm/spider silk proteins can significantly improve the mechanical properties of composite silk fibers.