Humans aren’t the only ones who grow tired of the social scene and look to settle down with a mate in a secluded area. This, according to new research presented during the annual conference of the Society for Integrative and Comparative Biology in West Palm Beach, Florida.
In the study, researchers from the University of California-Berkeley set out to investigate the practices of monogamy and biparental care of offspring. While natural selection suggests having a greater number of partners and a genetically diverse group of offspring would be most beneficial, some creatures still opt to settle down with a single partner to raise a family.
While single-partner families is rare in nature, experts have wondered why it even evolved at all. Dr. Molly Wright of UC-Berkeley explained that the most commonly discussed reason is a need for biparental care, meaning that both sexes tend to take care of their young.
These relationships tend to produce fewer or less genetically diverse offspring, but they often have a better chance to survive to maturity, she explained. While the trade off may make sense, scientists have only found evidence of it in a narrow range of creatures, including mammals.
Dr. Wright and her colleagues looked to investigate this phenomenon by looking at a unique type of monogamous creature, the mantis shrimp. These crustaceans, which are also known as stomatopods, have primarily been studies for their complex eyes and their claws, which are capable of delivering the fastest punches in the animal kingdom.
However, in a statement, she explained that the creatures also practice social monogamy. She and her colleagues said that they found that the stomatopods “were living at higher densities farther away from coral heads, and that wasn’t what we were expecting.”
What they anticipated was to see more burrows near the coral, where there is a greater abundance of the small fish and invertebrates upon which mantis shrimp feed. The fact that the shrimp seem to prefer living far away from their food source led Wright and her associates to discover that the corals where the prey live are also home to many of its predators.
Avoiding these dangerous creatures could be particularly important for socially monogamous mantis shrimp species, they said, because they have a less armored shell than some of their more promiscuous relatives.
Dr. Wright said that the results made her wonder what role that evading predators played in shaping the social monogamy and mating systems of the stomatopods. She and her colleagues tested two competing ideas to determine if avoiding predators might have been the true catalyst for the evolution of monogamy.
If biparental care evolved early in the monogamous mantis shrimp, either at the same time or just prior to the evolution of monogamy, then the classic hypothesis would apply to mantis shrimp. However, if social monogamy evolved along with a sedentary lifestyle designed to avoid predation, it would indicate that monogamy was linked to the desire of the mantis shrimp to avoid becoming prey.
They tested each idea by mapping life history traits onto an evolutionary history of mantis shrimps, and found that they went strongly against the classic hypothesis since biparental care evolved after social monogamy.
Based on those findings, Dr. Wright suggests that the shrimp would have been most vulnerable to predators when they ventured out to find a mate, so they opted instead to settle down with one partner in a safe place far away from the dangerous coral reefs.
“I generally try to be careful about what I say about human mating systems,” the professor said, it is easy to draw parallels to human marriage and the sedentary lifestyles of the mantis shrimp. She hopes that her research will eventually clarify how mating systems evolve in different species throughout the animal kingdom.
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