Nonnative African jewelfish are more fit but not bolder at the invasion front: a trait comparison across an Everglades range expansion
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Invasive species present a global threat to natural ecosystems and native biodiversity. Previous studies have shown that invasive range expansion is often related to the invader’s life histories and dispersal behavior. Among behavioral traits, boldness is a key trait that may aid species in performing well in novel environments. Thus, along a species’ invaded range, individuals from the invasion front should be bolder, better dispersers, and have life histories that maximize population growth relative to established populations. We tested these hypotheses with the invasion of the African jewelfish Hemichromis letourneuxi in Everglades National Park (ENP). Jewelfish entered ENP in 2000, and since then they have expanded their range rapidly but traceably. Our study examined variation in reproductive investment, body condition, gut fullness, boldness, and dispersal behavior across six wild-caught populations of African jewelfish. Boldness and dispersal were tested using an emergence-activity test and an emergence-dispersal test in large, outdoor experimental setups. We dissected fish from the six populations to assess life histories. Populations from the invasion front (western ENP) had higher reproductive investment, higher gut fullness, and better body condition, but they were not relatively bolder nor better dispersers than inner populations (eastern ENP). As the invasion progressed, lower intraspecific density at the invasion front may have relaxed competition and allowed for higher fitness and reproductive investment. Understanding underlying behavioral and life-history mechanisms of an invasion is key for the development of management strategies that aim to contain current invaders and prevent the spread of future ones.