Males of the species protect chicks and eggs from predators even without knowing whether they are actually their parents.
The males of some species of spiders often cannibalize the offspring of competitors or simply abandon their offspring when they cannot be sure of paternity. But, in the case of Manogea porracea, the practice is to take care of any young or oothecae (sets of eggs wrapped in silk) that are found in webs characteristic of the species.
This paternal care behavior, unprecedented among solitary spiders, was observed in M. porracea for the first time in 2016. Now, researchers have demonstrated that males of the species protect offspring and eggs against predators even without knowing whether they are actually their fathers.
The findings were published in the journal Ethology by researchers from the universities of the State of Minas Gerais (UEMG), the Federal University of Uberlândia (UFU) and the State University of Campinas (Unicamp).
“The males make a web above that built by the sexually immature female. When she becomes fertile, they copulate. The male can remain in the web protecting his partner against competitors or leave to try to mate again, which does not guarantee that other males will not also mate with the female he left behind. When his partner, for some reason, dies, he descends into her web and takes care of the young. In our experiment, they took care of their offspring even when we placed them in a web with the offspring of another couple”, explains Rafael Rios Moura, professor in the Department of Biological Sciences at the State University of Minas Gerais (UEMG), in Ituiutaba.
Moura carried out the work during a post-doctoral internship in the Postgraduate Program in Animal Biology at the Institute of Biology (IB) at Unicamp, with a scholarship from FAPESP and supervision by professor João Vasconcellos Neto https://bv.fapesp.br/pt/pesquisador/2208, one of the co-authors of the work.
Researchers have not yet been able to determine why most females of the species disappear after laying their eggs, but they believe that, because they accumulate a lot of lipids during the reproductive period – and, therefore, are chubbier –, they may attract more predators than males.
“On the other hand, males of this species build a web above their partner's web and can continue to feed during adulthood. This behavior is also rare in spiders and may increase the longevity of male M. porracea. The scenario creates opportunities for males to care for the young. In the absence of parents, offspring survival is very low. Therefore, paternal care is an important evolutionary innovation for the species”, says Moura, who coordinates the Center for Extension and Research in Ecology and Evolution (NEPEE) at UEMG and carries out scientific dissemination in the “Rios de Ciência” project on social media. .
The behavior had only previously been described in an African species of spider (Stegodyphus dumicola), which lives in large communal webs in which several males and females care for both their own offspring and eggs and those of other couples, which is called alloparental care. .
In the study published in 2017, which described paternal care for the first time, Moura's team showed that, at the end of the reproductive season, 68% of oothecae were cared for by males and that a significantly greater number of offspring were born from eggs watched over by these males. individuals, compared to those who did not receive any care.
Father is the one who takes care
M. porracea occurs from Panama to Argentina, in very different ecological scenarios. The population studied by the group of Brazilian researchers, however, lives in eucalyptus plantations surrounded by native Cerrado areas at Fazenda Nova Monte Carmelo, in Estrela do Sul, Minas Gerais. The webs are built close to the ground, using branches and the layer of leaves on the ground (litter) as support.
In the laboratory, the researchers observed 40 males, 57 females and 87 oothecae. All males were found in the wild, in webs with these sets of eggs. In the laboratory, the females were placed in transparent boxes with eucalyptus branches and cotton balls (to maintain humidity) for at least 24 hours, so that they could build the webs. Then, each one was removed and replaced with a male and an ootheca that was not necessarily his.
To check whether males protect their adopted offspring from predators, spiders of two species (Faiditus caudatus and Argyrodes elevatus, both from the Theridiidae family), known for consuming M. porracea eggs and adults, were placed in the boxes. Observations were carried out for ten days. In some of the boxes, used as controls, the predators were placed without the protective male and ate the eggs. In others, males were observed taking a protective position over the oothecae and offspring and scaring away predators when they approached. In one of them, the predator was killed by the male.
“The number of offspring that left the oothecae was two and a half times greater in treatments in which males were present, even without being able to verify paternity. And both biological and adoptive parents were equally effective in protecting against predators,” says Moura.
In addition to scaring away predators, the researchers observed in other experiments two more behaviors that characterize paternal care in the species: males constantly suck the oothecae when they are wet, probably removing excess moisture that could attract fungi or harm the development of eggs. Furthermore, they rebuild the web's supporting threads, which, without this care, could fall to the ground and expose the eggs to ants and other predators. Future work will describe these behaviors in detail.
The spider's strategy of protecting any offspring of the species, therefore, can be summarized by the last lines of the poem “Ode on a Distant Prospect of Eton College”, by the English poet Thomas Gray (1716-1771), which Moura uses in the title of the article : “Where ignorance is bliss, it is folly to be wise.”
The article "Where ignorance is bliss, 'tis folly to be wise”: Indiscriminate male care in a neotropical spider, by Rafael Rios Moura, Isabella Dias Oliveira, João Vasconcellos-Neto and Marcelo Oliveira Gonzaga, can be read by subscribers at: https://onlinelibrary.wiley.com/doi/abs/10.1111/eth.13112.
original article published on the Agência Fapesp website.
