Climate change is affecting the courtship behavior of male spiders in areas with low predictability in rainfall and temperature, causing them to give up on traditional gifts of fresh insect meat and instead offer inedible items such as seeds and plant stems. This weakening of a courtship signal has significant implications for reproduction.
Evolutionary biologist Maria José Albo of Universidad La República in Montevideo, Uruguay, has been studying the courtship behavior of spiders since 2015. Her team focused on species that flirt mostly in evenings and nights among rocks and pebbles in rivers of Uruguay and southern Brazil.
Gift-giving is a common practice among certain spider species, where males present females with small gifts wrapped in silk. The best gifts are nuggets of fresh insect meat, which the female can feed on while the male inserts sperm. This allows the male to deliver more sperm and increase his chances of becoming the father.
However, Albo’s team found that in areas with low predictability in rainfall and temperature, males were giving up on their traditional gifts. At two study sites, over half of the gifts analyzed were inedible silk-wrapped trash, including seeds, broken insect exoskeletons, and bits of plant stems.
The weakening of a courtship signal due to climate stress has significant implications for reproduction. Albo notes that “it shows how variation in climate can affect something very essential — which is reproduction.”
Behavioral ecologist Michelle Beyer, who works with Europe’s best-known gift-giving spider, the nursery web spider Pisaura mirabilis, suggests that mercurial weather could change not just the contents of males’ gifts but also the important silk wrapping.
Gift giving in courtship has been described in only 15 or 20 of the world’s more than 50,000 known species of spiders. Since 2015, researchers have focused on spiders that flirt mostly in evenings and nights among the rocks and pebbles of rivers of Uruguay and southern Brazil.
