Male orb-weaving spiders fight less in female-dominated colonies, study finds

Orb-weaving spiders weave interconnected webs in vast webs; In their colonies, individual spiders protect their webs from intruders and often fight each other for food and mates. Credit: Gregory Grether/UCLA

Birds do. Bees do. Even spiders in their webs do this: cooperate for more peaceful colonies.

This is one of the surprising findings of a new study by UCLA undergraduates on orb-weaving spiders in Peru.

The study also found that in colonies of orb-weaving spiders, males fight less with each other when there are more females than males, and females fight less with each other in female-dominated colonies than in male-dominated colonies, which is somewhat more peaceful. Spiders also showed little hostility to individuals from different colonies, a discovery that has not been previously documented for colonial spiders.

The research was published in the journal. Journal of Arachnology.

“We’re used to thinking about communal animals like honeybees and elephants,” said the paper’s senior author Gregory Grether, a professor of ecology and evolutionary biology at UCLA. “But spiders often live alone, so we were excited to study these colonial spiders and learn how they interact with their colony mates and individuals from other colonies.”

Globe-weaving spiders weave interlocking webs in large webs that are fixed to the surrounding vegetation. In colonies, individuals protect their nets from intruders and often fight each other for food and mates. When threatened, they withdraw to communal areas for protection, and some species defend communal areas.

Male orb-weaving spiders fight less in female-dominated colonies

Nihal Punjabi, a recent UCLA graduate, was one of four undergraduate co-authors of the study. Credit: Gregory Grether/UCLA

Four student writers—Catherine Wu, Chaiti Bhagawat, Modan Goldman, and Nihal Punjabi—were attending a field course that Grether led at the Cocha Cashu Biological Station in southeastern Peru. Their four-day journey to reach the field research station included a long, winding bus ride through the Andes and a boat trip down the Madre de Dios River and into one of its tributaries.

For 18 days, students studied 34 colonies of a species called Philoponella republicana to find out whether the location of the web, the ratio of male and female spiders, or the web or the spiders themselves affect the animals. aggression level. Alongside Grether, their work was overseen by UCLA assistant professor Debra Shier and social insect and spider researcher Roxana Arauco-Aliaga, who was then Cocha Cashu research coordinator and associate director.

They observed that although spiders do not share their food, they cooperate to build their webs and wrap their prey in silk – only one spider ate a particular prey item.

Students staged attacks by relocating spiders in different locations and relocating spiders from other colonies. Some spiders defended their orb webs against all intruders, but the spiders did not cooperate to repel the intruders.

When there were more females than males in colonies, males fought with other males and females fought less with males than in male-dominated groups, resulting in somewhat more peaceful colonies.

Male orb-weaving spiders fight less in female-dominated colonies

Cole Heramb (left), Catherine Wu and Chaiti Bhagawat observe orb-weaving spiders in Peru. Credit: Gregory Grether/UCLA

However, if colonies had many large and medium-sized females, those females snatched the most prey and formed slightly more aggressive colonies by fighting off the most captured insects.

After the students returned from the field, they learned from previous research that group-dwelling spiders are extremely rare – occurring in less than 0.1% of species. Despite this, several types of sociability are recognized by arachnologists. Collaborating in prey catching, web building, and brood maintenance, extraterritorial spiders are most similar to true social animals, such as ants, honeybees, and naked mole rats.

Territorial colonial spiders, which cooperate in building webs but also compete aggressively with other inhabitants of their colonies for food and mates, seem to have evolved from solitary species multiple times, possibly when ecological conditions favor group life. They occupy a position on a continuum of sociability similar to group-dwelling primates, including humans.

The student researchers all graduated from UCLA. Wu is currently studying outdoor education at UCLA Recreation, MA at Bhagawat Ghent University, and Goldman and Punjabi are medical students at Carle Illinois School of Medicine and Case Western Reserve University, respectively.

Since 2001, Grether has been taking groups of UCLA undergraduates to the tropical rainforest for field research training. He plans to return with a new group of students in January 2023 to reveal more of Cocha Cashu’s secrets.

More information:
Catherine Wu et al., Aggression in the Western Amazon colonial spider, Philoponella republicana (Araneae: Uloboridae), Journal of Arachnology (2022). DOI: 10.1636/JoA-S-20-093

Provided by the University of California, Los Angeles

Quotation: Male orb-weaving spiders fight less in female-dominated colonies, spider collaboration study (2022, Nov. 30) retrieved from https://phys.org/news/2022-11-male-orb-weaving- finds . spiders-female-domished-colonies.html

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