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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Illuminating the evolution of social parasite ants    
      
     Date:   
         March 3, 2023   
     Source:   
         Rockefeller University   
     Summary:   
         The findings offer a new way to understand how some ants become   
         total layabouts.   
      
      
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   FULL STORY   
   ==========================================================================   
   Ants are known as hard workers, tirelessly attending to their assigned   
   tasks - - foraging for food, nurturing larvae, digging tunnels, tidying   
   the nest. But in truth, some are total layabouts. Called workerless social   
   parasites, these rare species exist only as queens, and they die without   
   workers to tend to them. To survive, parastic ants infiltrate a colony of   
   closely related ants, where, as long as they keep their numbers relatively   
   low, they and their offspring become the leisure class of the colony.   
      
      
   ==========================================================================   
   It's long been thought that these determinedly lazy insects likely   
   evolved their queenly characteristics one by one, through a series of   
   mutations, in an isolated setting. Now scientists in the Laboratory of   
   Social Evolution and Behavior at The Rockefeller University, together   
   with their collaborators at Harvard University, have a new theory. As   
   they report in Current Biology, they've discovered queen-like mutants --   
   parasitic ants that spontaneously appeared in colonies of clonal raider   
   ants, which are typically queenless.   
      
   "This mutant is like the precursor to other parasitic species," says   
   Waring Trible, lead author of the study. "It's a new way of understanding   
   how ants evolve to become socially parasitic."  Delving into the genetics   
   of these unique ants could be a way to better understand the molecular   
   mechanisms behind caste differentiation, or how an ant develops into a   
   worker or a queen, which remain unknown. It could also help illuminate   
   biological development in organisms in general.   
      
   Hiding in plain sight Among the more than 15,000 identified ant species   
   are hundreds that qualify as social parasites. Born inside a host colony,   
   a parasitic ant will leave the colony, use a sex pheromone to attract a   
   male from another colony to mate with, and once pregnant, will infiltrate   
   the original colony or find another nearby.   
      
   She'll often use subterfuge to sneak past colony guards. The shampoo ant,   
   for example, will snatch a few ants just outside a nest entrance, lick   
   them to acquire the colony's signature chemical scent, and then lick   
   herself all over to transfer it to her own body. Chemically cloaked,   
   she then can slip inside to live out her life and reproduce both new   
   queens and males who mate outside the colony. The males die, and the   
   queens begin the cycle again.   
      
   Because of their uniqueness, they've been studied extensively by   
   biologists since Charles Darwin, still there's been a sticking point   
   in a prevailing theory of their evolution, says Daniel Kronauer, the   
   Stanley S. and Sydney R.   
      
   Shuman Associate Professor at Rockefeller University, and head of the lab.   
      
   They're closely related to their hosts, but if they had to acquire   
   these parasitic traits over time, they would need to be isolated during   
   reproduction, otherwise interbreeding with their hosts would wash out   
   their unique traits.   
      
   But no one has found intermediately evolved ants -- ones with some social   
   parasite traits but not others -- in the wild, says Kronauer.   
      
   When queen-like ants suddenly appeared among the clonal raider ants   
   in Kronauer's lab in 2015, Trible -- who was looking to investigate   
   genetic mechanisms behind caste differentiation -- took notice. Because   
   clonal raider ants typically have no queens and reproduce asexually,   
   the queen-like mutants stood out: they were born with wings, larger eyes   
   and ovaries, and as adults showed a general indifference towards labor.   
      
   But it turned out they were nothing new -- they'd had been hiding for   
   years in dense colonies whose numbers obscured their presence. Genetic   
   analysis revealed that they had mutated into existence inside the colony   
   in which they were first detected -- a community of otherwise normal ants   
   that Kronauer had collected in Okinawa, Japan, in 2008, and that still   
   lived in the lab. It was a clue that the typical story of parasite ant   
   invasion might need rethinking.   
      
   The researchers then ran a series of experiments and genetic analyses. One   
   of the first experiments was to isolate them to see whether the phenotype   
   was heritable. Because clonal raider ants reproduce asexually, they   
   didn't have to worry about interbreeding with other ants.   
      
   The queen-like mutants lay eggs that developed into copies of   
   themselves. "We knew we had something cool," Kronauer says.   
      
   They also tested behavior. Foraging parties composed entirely of   
   queen-like mutants were half the size of those of worker ants, and they   
   were far less likely to try to enlist other ants to track down food. These   
   behaviors were a sort of intermediary between the diligence of worker   
   ants and the dependence of queens, and allowed the mutant ants to avoid   
   the dangers inherent to leaving the safety of the colony.   
      
   Despite laying twice as many eggs as their hosts, the ants self-regulate   
   their head count. As long as their numbers stay below about 25 percent   
   of the host population, they do well. More than that and they run into   
   trouble. Queens need help from workers to free their wings as they emerge   
   from the pupae, and if there are too many queens for the workers to look   
   after, they'll die entangled in their pupal skin.   
      
   "They seem to have the ability to regulate their own reproduction so that   
   they don't drive their host colony extinct, which is a very smart thing   
   for a parasite to do," says Trible, a former member of Kronauer's lab who   
   now runs his own lab at Harvard studying these and other mutants. "This   
   provides these mutants the capacity to survive for long periods of time."   
   The influence of hormones Whole-genome sequencing revealed that the   
   parasitic queens have a mutation in chromosome 13, which is structurally   
   similar to chromosomes that regulate colony social structure in other   
   ants. This mutant chromosome seems to contain a "supergene," a set   
   of genes that work together to create a phenotype. In this case, the   
   supergene contains more than 200 individual genes, a disproportionate   
   number of which assist in the metabolism of hormones. These include   
   genes that code for cytochrome p450 enzymes, which are required to   
   synthesize hormones in both ants and humans, and may play a role in   
   the creation of these highly unusual mutants. (This enzyme family may   
   be familiar to anyone who has been warned to not drink grapefruit juice   
   while taking certain medications because the juice inhibits the enzymes   
   from detoxifying the drugs.)  It appears that with this single mutation,   
   "their form, the higher egg production, the behavior -- it can all shift   
   in a single mutational step," Kronauer says.   
      
   And if that's the case, Trible says, "it would be a way that it's actually   
   possible to go from a normal ant to a parasite within a single species."   
   That idea -- that two very different forms of an animal can arise in a   
   single species -- gets at the heart of the mystery of ant castes. Because   
   workerless social parasites arise from a very specific type of mutation   
   affecting ant caste development, studying the queen-like mutants has the   
   potential to reveal insights into the still-unknown molecular mechanisms   
   that allow ant larvae to develop distinct caste morphologies. "It provides   
   a very comprehensive framework in which to study their evolution,"   
   says Kronauer.   
      
   Size matters The findings could also lead to further research on an   
   important process of development known as allometric scaling that happens   
   in all animals, including humans, Trible says. Allometric scaling keeps   
   the tissues of an organism proportional to its body size as it grows.   
      
   Its mechanisms are unknown, but understanding them likely has relevance to   
   many aspects of human biology, including disease, says Trible. Perhaps   
   queen-like mutants can provide a new avenue of investigation. "We   
   don't have good examples of mutations in fruit flies or mice or human   
   genetic disorders that break allometric scaling in such a dramatic way,"   
   he says. "We think this queen-like mutant will be a powerful tool for   
   understanding caste development, and caste development is in turn an   
   ideal model to investigate these larger questions about how allometric   
   scaling works."   
       * RELATED_TOPICS   
             o Plants_&_Animals   
                   # Insects_(including_Butterflies) # Evolutionary_Biology #   
                   Invasive_Species # Mating_and_Breeding   
             o Earth_&_Climate   
                   # Exotic_Species # Ecology # Environmental_Awareness #   
                   Sustainability   
       * RELATED_TERMS   
             o Fire_ant o Ant o Wood_Bison o Bee   
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             Anticonvulsant o Red-cockaded_Woodpecker   
      
   ==========================================================================   
   Story Source: Materials provided by Rockefeller_University. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Waring Trible, Vikram Chandra, Kip D. Lacy, Gina Limo'n, Sean K.   
      
         McKenzie, Leonora Olivos-Cisneros, Samuel V. Arsenault, Daniel J.C.   
      
         Kronauer. A caste differentiation mutant elucidates the evolution   
         of socially parasitic ants. Current Biology, 2023; DOI: 10.1016/   
         j.cub.2023.01.067   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/03/230303105250.htm   
      
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