title: Coupling Between Heterotrophic Nanoflagellates and Bacteria in Fresh Waters: Does Latitude Make a Difference?
abstract: Recent studies reported comparatively lower heterotrophic bacteria (HB) abundances in tropical regions, indicating that factors involved in bacterial losses could be more relevant in the tropics. Heterotrophic nanoflagellates (HNF) are considered the main predators of HB in aquatic ecosystems, and one should expect higher abundances in the tropics because of differences in the food web configuration (absence of large daphnids). However, there are no comprehensive studies comparing HB and HNF abundances in a latitudinal gradient. We hypothesized that HB abundance would be lower in the tropics because HNF abundance would be higher, resulting in a tighter HNF-HB coupling. To test this hypothesis, we compiled a large dataset of HB and HNF abundances from tropical and temperate freshwater environments. We found that both HB and HNF abundances were lower in the tropical region, and that HNF-HB coupling does not differ between temperate and tropical regions. The lower HNF abundance and lack of coupling may be explained by a strong top-down control on HNF and/or their herbivory preference. Besides, no relationship was found between bacterial specific growth rate and either chlorophyll-a and HB abundance, indicating that bacterial losses may have an important role in tropical freshwaters. Thus, we found that HNF is likely not the main controllers of HB abundance, and that grazing by ciliates and cladocerans, together with the physiological effects of higher temperatures, may explain the high bacterial loss rates in the tropics.
authors.affiliation: Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Universidade Estadual de Maringá Maringá, Brazil.
authors.forename: Bianca T
authors.initials: BT
authors.lastname: Segovia
authors.affiliation: Departamento de Botânica, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil.
authors.forename: Carolina D
authors.initials: CD
authors.lastname: Domingues
authors.affiliation: Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Universidade Estadual de Maringá Maringá, Brazil.
authors.forename: Bianca R
authors.initials: BR
authors.lastname: Meira
authors.affiliation: Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Universidade Estadual de Maringá Maringá, Brazil.
authors.forename: Fernando M
authors.initials: FM
authors.lastname: Lansac-Toha
authors.affiliation: Instituto Tecnológico de Chascomús, Universidad Nacional de San Martín Chascomús, Argentina.
authors.forename: Paulina
authors.initials: P
authors.lastname: Fermani
authors.affiliation: Instituto Tecnológico de Chascomús, Universidad Nacional de San Martín Chascomús, Argentina.
authors.forename: Fernando
authors.initials: F
authors.lastname: Unrein
authors.affiliation: Departamento de Ecologia, Universidade Federal de Juiz de Fora Juiz de Fora, Brazil.
authors.forename: Lúcia M
authors.initials: LM
authors.lastname: Lobão
authors.affiliation: Departamento de Ecologia, Universidade Federal de Juiz de Fora Juiz de Fora, Brazil.
authors.forename: Fabio
authors.initials: F
authors.lastname: Roland
authors.affiliation: Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Universidade Estadual de Maringá Maringá, Brazil.
authors.forename: Luiz F M
authors.initials: LF
authors.lastname: Velho
authors.affiliation: Departamento de Hidrobiologia, Universidade Federal de São Carlos São Carlos, Brazil.
authors.forename: Hugo
authors.initials: H
authors.lastname: Sarmento
keywords: bacterioplankton; cladocera; latitude; predation; protist