Abstract
Many species are expanding their ranges in response to climate changes or species introductions. Expansion-related selection likely drives the evolution of dispersal and reproductive traits, especially in invasive species introduced into novel habitats. We used an agent-based model to investigate these relationships in the red imported fire ant, Solenopsis invicta, by tracking simulated populations over 25 years. Most colonies of this invasive species produce two types of queens practicing alternate reproductive strategies. Claustral queens found new colonies in vacant habitats, while parasitic queens take over existing colonies whose queens have died. We investigated how relative investment in the two queen types affects population demography, habitat occupancy, and range expansion. We found that parasitic queens extend the ecological lifespan of colonies, thereby increasing a population’s overall habitat occupancy as well as average colony size (number of workers) and territory size. At the same time, investment in parasitic queens slowed the rate of range expansion by diverting investment from claustral queens. Divergent selection regimes caused edge and interior populations to evolve different levels of reproductive investment, such that interior populations invested heavily in parasitic queens whereas those at the edge invested almost entirely in claustral queens. Our results highlight factors shaping ant life histories, including the evolution of social parasitism, and have implications for the response of species to range shifts.
Highlights
Many species throughout the world are shifting or expanding their ranges in response to climate changes or species introductions (Parmesan et al 1999, Hickling et al 2006, Chen et al 2011)
In species practicing alternate life histories, range dynamics are likely affected by relative investment in different strategies
In our simulations of red imported fire ants, the production of parasitic queens resulted in larger average colony and territory sizes and higher habitat occupancy
Summary
Many species throughout the world are shifting or expanding their ranges in response to climate changes or species introductions (Parmesan et al 1999, Hickling et al 2006, Chen et al 2011). For example, colonies can produce two different types of queens from the same genome—an independent one that founds new colonies and a parasitic one that joins existing colonies of the same species (Bourke and Franks 1991, Rüppell and Heinze 1999) These alternate strategies result in dispersal differences, since only one queen type can colonize vacant sites while the other can reproduce only in occupied areas. Reproductive polymorphisms have been documented in many invasive ants (Yamauchi and Ogata 1995, Holway et al 2002, Tsutsui and Suarez 2003), and trait variability has been linked to invasion success in several other taxa (Richards et al 2006, Davidson et al 2011, Forsman 2014, González-Suárez et al 2015) It remains unclear how reproduction-dispersal polymorphisms in ants affect rates of range expansion, or how investment in different strategies responds to expansion-related selection
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