Marcelo O. Gonzaga
By Brian Owens
Species: Manogea porracea
Habitat: lower branches and leaf litter of Eucalyptus species in neotropics from Panama to Argentina
Most male spiders bail out after mating – if they make it through the process alive, that is, as females of many spider species cannibalise their mates.
But not this spider. Male Manogea porracea in South America not only help with childcare, they often end up as single dads.
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The male of the species builds a dome-shaped web above the female’s and sets about helping to maintain a “nursery” web. This is built between the two domes and holds the egg sacs (see photo, below).
The males also defend the eggs from would-be predators and even remove water from the surface of egg sacs on rainy days.
Lone parenthood
But their presence really pays off if the female disappears.
By the end of the mating season, 68 per cent of egg sacs are taken care of by males alone, says Rafael Rios Moura, an ecologist at the Federal University of Uberlândia in Brazil, whose team studied the spiders in the wild.
Single dads improve the odds of offspring surviving compared with those who lose both their parents. Once the female is gone, the male moves closer to the egg sacs by moving to the female’s web (see photo, top). Moura found that significantly more hatchlings emerge from egg sacs taken care of by the males than those that had no parents around.
When Moura set up experiments with predators, more hatchlings survived when the male was present, then when not, probably because they move aggressively towards intruders, fending off attacks.
Marcelo O. Gonzaga
Four other spider species have been seen invading the M. porracea webs and attacking the egg sacs.
The sheer volume of predators that M. Porracea have to deal with is likely what’s driving the males to help defend their eggs, says Linda Rayor, an entomologist at Cornell University in Ithaca, New York. “The male risks losing his entire investment if he doesn’t defend the eggs.”
Moura isn’t sure why the females often disappear. The males might naturally have longer lifespans, or the females might be preferentially targeted by predators. “Some predators might prefer prey with more lipids, which the larger females have, and that could affect survival,” he says.
Either way, the fact that males often outlive females has probably contributed to its evolving to take on paternal duties – the first such known case in solitary species. The only other male spiders known to defend youngsters from predators are a social species from Africa, Stegodyphus dumicola.
Paternity test
“This was my first time studying spiders, and we found this amazing system,” says Moura.
Most male spiders don’t provide parental care because they don’t live as long as females, or they can’t be sure that they are really the father, and are evolutionarily better off looking for other females to mate with.
M. porracea males, though, are unique in both respects. Building a web above that of the female means they can be fairly confident in their paternity. And as they tend to live longer than the females, there are fewer females around for them to mate with.
Journal reference: Animal Behaviour, DOI: 10.1016/j.anbehav.2016.09.018
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