Host Reproductive Phenology Drives Seasonal Patterns of Host Use in Mosquitoes

Seasonal shifts in host use by mosquitoes from birds to mammals drive the timing and intensity of annual epidemics of mosquito-borne viruses, such as West Nile virus, in North America. The biological mechanism underlying these shifts has been a matter of debate, with hypotheses falling into two camps: (1) the shift is driven by changes in host abundance, or (2) the shift is driven by seasonal changes in the foraging behavior of mosquitoes. Here we explored the idea that seasonal changes in host use by mosquitoes are driven by temporal patterns of host reproduction. We investigated the relationship between seasonal patterns of host use by mosquitoes and host reproductive phenology by examining a seven-year dataset of blood meal identifications from a site in Tuskegee National Forest, Alabama USA and data on reproduction from the most commonly utilized endothermic (white-tailed deer, great blue heron, yellow-crowned night heron) and ectothermic (frogs) hosts. Our analysis revealed that feeding on each host peaked during periods of reproductive activity. Specifically, mosquitoes utilized herons in the spring and early summer, during periods of peak nest occupancy, whereas deer were fed upon most during the late summer and fall, the period corresponding to the peak in births for deer. For frogs, however, feeding on early- and late-season breeders paralleled peaks in male vocalization. We demonstrate for the first time that seasonal patterns of host use by mosquitoes track the reproductive phenology of the hosts. Peaks in relative mosquito feeding on each host during reproductive phases are likely the result of increased tolerance and decreased vigilance to attacking mosquitoes by nestlings and brooding adults (avian hosts), quiescent young (avian and mammalian hosts), and mate-seeking males (frogs)

Fish assemblage recovery along a riverine disturbance gradient

Artificial fluctuations in streamflow have been documented to alter the composition andstructure of stream communities. This study tests the hypothesis that a spatial recovery gradientin fish assemblage structure exists downstream of a hydroelectric dam, and that recovery can be identified by the presence and abundance of species largely restricted to flowing-water habitats(fluvial specialists). A longitudinal gradient of change in a shoreline fish assemblage wasquantified in a 66-km reach of a mid-sized, species-rich river (Tallapoosa River, Alabama) withdaily flow fluctuations from hydropower generation. The shoreline fish assemblage in a nearbyand similar river (Cahaba River, Alabama) was quantified as a regional reference for theoccurrence of fish assemblage gradients. Fish were collected with prepositioned areaelectrofishers in 240 randomly located sampling sites, and physical habitat was quantified. Usingdistributional and habitat use information, fish species were categorized as fluvial specialists ormacrohabitat generalists (species that occur in a wide variety of aquatic systems). Sampledhabitats were similar between rivers and along each study reach. The longitudinal pattern ofspecies occurrence and fish abundance was consistent in the free-flowing river. A longitudinalgradient of increasing abundance and richness of only fluvial specialist species existeddownstream of the hydroelectric dam. No similar spatial gradient existed for macrohabitatgeneralists in either river. Although a fish community recovery gradient was identified, a recoveryendpoint was not evident because assemblage change was gradual and possibly incomplete.The preservation and management of riverine fish faunas will partly depend on incorporatingspatial recovery into decisions about permitting and siting of anthropogenic changes like hydroelectric dams. http://dx.doi.org/10.2307/194192