Coupling Between Heterotrophic Nanoflagellates and Bacteria in Fresh Waters: Does Latitude Make a Difference?

SEGOVIA, BIANCA; DOMINGUES, CAROLINA; MEIRA, BIANCA; LANSAC-TOHA; FERMANI, P; UNREIN, F.; LOBÃO, L; ROLAND, F.; VELHO, L.; SARMENTO, H.

Frontiers in Microbiology

Frontiers Research Foundation

Lugar: Lausanne; Año: 2016

1664-302X

Recent studies reported comparatively lower heterotrophic bacteria (HB) abundances in tropical regions, in dicating that factors in volved in bacterial losses could be morerelev an tin the tropics. Heterotrophic nanoflagellates (HN F) are considered the mainpredators of HB in aquat icecosystems, and one should expect higher abundancesin the tropics because of differences in the food web con figuration (absence of largedaphnids). However, there are no comprehensive studies comparing HB and HNF abundances in a latitudinal gradient. We hypothesiz ed 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 data set of HB and HNF abundances from tropical and temperate fresh water environments. We found that both HB and HNF abundances were lower in the tropical region, and that HNF-HB coupling doesnot 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 hav e an important role in tropical fresh waters. 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.