Size matters for male woodlice. They prefer to mate with large females – but settle for smaller ones in times of danger, say researchers.
It’s a critical choice. They are likely to mate just once in their life, then spend the remainder of their time with their chosen partner and family of up to 70 baby woodlice.
Researchers at the Hebrew University of Jerusalem (HU) observed the mating behavior of male woodlice (or desert isopods) in two locations in the Negev Desert, in southern Israel.
One was close to the burrow of an Israeli gold scorpion, its natural predator, the other was further away in a safe area.
They found that large males note the proximity of a predator when choosing a mate. They were found to maintain their preference for larger females in safe areas, but less so in risky areas.
“This information is crucial in predicting how the fear of a predator may affect prey population dynamics and evolutionary processes in the creation of new species,” said Dr. Viraj Torsekar, one of the researchers who led the study.
“Using this manipulative field experiment, we found that desert isopods under risk of scorpion predation maintained ‘size assortative mating’, but that males that chose and fought over females were on average smaller for a given female size,” said Torsekar.
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They also found that the smaller males had often accepted second best and moved in with smaller females close to the lurking scorpion. Medium sized males choose between smaller females in safe places and larger females in risky places, demonstrating an equal fitness choice.
Desert isopods mate only once in their lifetime and spend the rest of their year-long life with their chosen mate and their family (of 60-70 offspring) in a single permanent burrow. Both parents take care of the brood, and all family members continue to excavate and clean the burrow together.
Female isopods initially dig the burrow, which is hard work in the dry compacted soil of the desert, so they are always on the lookout for holes that can make life a little easier. The HU researchers dug holes in two groups, one near the burrow of an Israeli gold scorpion and one further away.
Female isopods readily adopted the holes and excavated full-size burrows, however fewer isopod pairs took up residence in burrows near predators, despite it being virtually free real estate.
The researchers’ findings were published in the journal Ecology.