Human-induced habitat change leads to physical and behavioral change in mosquitoes
Bahamian mosquitoes in habitats fragmented by human activity are more willing to explore their surroundings, more stressed by change, and have smaller brain regions associated with a fear response than mosquitoes in unaffected habitats. The new study from North Carolina State University shows that these fish have adapted quickly in specific ways to human-induced changes, and cautions that environmental restoration projects should understand these changes so as not to damage adapted populations.
The Bahamian mosquito is a small species of coastal fish that frequently inhabit tidal coves – shallow, tidal-influenced marine ecosystems. In the 1960s and 1970s, road building in the Bahamas caused many of these habitats to “fragment”, or largely cut off from the ocean.
“Mosquitoes in these fragmented areas suddenly found themselves in a very different environment than before, in terms of predation and tidal dynamics,” says Brian Langerhans, associate professor of biology at NC State and corresponding author of the study. “We set out to determine how natural variation in habitat structural complexity and human-induced fragmentation influenced exploration behavior, stress response and brain anatomy.”
Langerhans and a team of researchers from the state of North Carolina observed about 350 mosquitoes from seven different populations: three fragmented and four unfragmented. The habitats varied in complexity, ranging from simple mud-bottomed spaces to those that included a large number of rocks and vegetation, such as mangroves.
“We were testing predictions based on our understanding of natural selection,” Langerhans explains. “For example, in a fragmented space with fewer natural predators, we hypothesized that these fish would be more exploratory, as exploratory behavior might be rewarded in terms of competition for food. We also wanted to see if there is had physiological changes in areas of the brain that are associated with these and other similar behaviors. “
The team measured stress response and exploration behavior by temporarily placing mosquitoes in a different environment and observing changes in breathing and their willingness to explore. They also compared the brain sizes of fish from different habitats.
They found that overall, fish in a more complex environmental habitat were more willing to explore new environments. But for a given level of habitat complexity, fish from fragmented sites were more exploratory than those from unfragmented sites. In addition, fish from fragmented habitats have a higher response to stress to change.
“These results were in line with our expectations,” said Langerhans. “Exploration behavior can reward fish in habitats with few predators by helping them compete for food, and can give fish in complex habitats an advantage in locating safe and hard-to-find food resources. As for the stress response, fish in unfragmented tidal streams. with many predators and high tidal dynamics have a higher daily stress level than those in more static and predator-free habitats. The change will be much more stressful for the fish in these latter areas, as they are less stressed initially. “
They also noted that although there was no overall difference in brain size between fish from different habitats, fish from fragmented environments had a smaller telencephalon – the region of the brain associated with the reaction of fear, while fish in complex environments had larger optic tectum and cerebellum. , the regions of the brain associated with the response to visual stimuli, motor skills and associative learning.
“Brain tissue is expensive for an organism to produce,” explains Langerhans. “While fish in fragmented or simple environments no longer experience major demands for behaviors such as avoiding predation or navigating complex situations, seeing changes in these brain areas is not so surprising.”
The study also highlights how quickly organisms adapt to new environments and how these environments affect the biological makeup of their inhabitants – something that planners of restoration projects should keep in mind when attempt to restore habitats to their ancestral state.
“Anything humans plan to do in these environments needs a lot of forethought,” Langerhans says. “If local adaptations occurred over a 50-year period in response to an altered environment and we quickly restored it to ‘normal’, you could do more harm than good to some of its inhabitants.”
The search appears in the Journal of Animal Ecology, and was supported by the WM Keck Center for Behavioral Biology of the State of North Carolina, the Helge Axson Johnson Foundation and the Swedish Research Council (Grant 2015-00300). NC State graduate student Matthew Jenkins is the first author. North Carolina State undergraduate students John Cummings and Alex Cabe, fishing and wildlife professor Nils Peterson and former North Carolina State postdoctoral researcher Kaj Hulthén also contributed to the work.
Note to editors: A summary follows.
“Natural and anthropogenic sources of habitat variation influence exploration behavior, stress response, and brain morphology in coastal fish”
DOI: 10.1111 / 1365-2656.13557
Authors: Matthew R. Jenkins, John M. Cummings, Alex R. Cabe, Kaj Hulthén, M. Nils Peterson, R. Brian Langerhans, North Carolina State University
Posted: Journal of Animal Ecology
Abstract: Evolutionary ecology aims to better understand how ecologically important traits respond to environmental heterogeneity. Environments vary both naturally and as a result of human activities, and investigations that simultaneously examine how natural and human-induced environmental variations affect various types of traits are becoming increasingly important as human activities result in the endangerment of species. Here, we examine how habitat fragmentation and habitat structural complexity affect disparate trait types in the Bahamian mosquito (Gambusia hubbsi) inhabiting tidal streams. We tested a priori predictions of how these factors might influence exploratory behavior, stress responsiveness, and brain anatomy. We examined approximately 350 adult Bahamian mosquitoes from seven tidal stream populations across Andros Island, Bahamas, which varied both in terms of human-caused fragmentation (three fragmented, four unfragmented ) and complexity of natural habitat (eg 5-fold variation in rocky habitat). Populations that had undergone severe human-induced fragmentation, and hence restriction of ocean tidal exchanges, exhibited greater exploration of a new environment, stronger physiological stress responses to a mildly stressful event and a smaller telencephalon (relative to body size). These changes were consistent with adaptive predictions based primarily on 1) reduced risk of chronic predation and 2) decreased navigation demands in dynamic tidal habitats. Populations at sites with greater habitat structural complexity showed a greater propensity for exploration and relatively larger optic tectum and cerebellum. These models matched adaptive predictions related to increased navigation demands in complex environments. Our results demonstrate environmental variations, including recent anthropogenic impacts (
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