Patterns of bacterial generalists and specialists in lakes and reservoirs along a latitudinal gradient

Abstract

AimThe geographical distribution of bacteria is an important, but poorly understood, topic in microbial ecology. A major question is how broadly distributed generalist taxa, and limitedly distributed specialist taxa, vary across a latitudinal gradient in freshwater ecosystems. We predict that: (a) generalists and specialists exhibit latitudinal diversity gradient with different patterns; (b) their community assemblies are mainly driven by stochastic processes; and (c) generalists coexist through niche differences, while specialists coexist through fitness differences.LocationSixty lakes and reservoirs in China, ranging from 18° N to 50° N.Time PeriodJuly–August in 2012 and 2018.Taxa StudiedBacterioplankton.MethodsWe clustered zero‐radius operational taxonomic unit (zOTU) (subspecies‐like level) into operational taxonomic unit (OTU) (species‐like level) and calculated the intra‐specific variation and spatial asynchrony of OTU. We examined the relative effects of environment versus space (latitude) on bacterial community and quantified the community assembly processes of generalists and specialists, respectively. The binary‐state speciation and extinction (BiSSE) model has been used to estimate the evolutionary characteristics. The abundances of the top zOTUs within each OTU were identified to reveal their niche preferences (distribution patterns at different sites).ResultsWe found that bacterial generalists had a higher intra‐specific variation, greater asynchrony and wider niche width than the specialists. With increasing latitude, bacterial diversity decreased with abundance variations in generalists and occurrence variations in specialists, respectively. Diversification in stochastic processes was the main driving factor in both groups, though deterministic processes showed greater effects on specialists than generalists in local communities. Bacterial generalists coexisted through niche differences, whereas specialists coexisted through average fitness differences.Main ConclusionsWe demonstrated distinct latitudinal distribution patterns of bacterial generalists and specialists. These results highlight differences in biogeography of microbial generalist and specialist taxa mediated by intra‐specific variation and emphasize their distinctly vital roles mediated by differing mechanisms in freshwater ecosystems.

Microbiome analysis in Asia’s largest watershed reveals inconsistent biogeographic pattern and microbial assembly mechanisms in river and lake systems

“…Moreover, as a widely studied alpha diversity pattern, 28 species diversity decreases with increasing latitude. 29 However, in the present study, the microbial diversity of the lakes did not increase from the upstream to downstream of watershed. Although the lake was connected with the rivers, the independence between the lakes was strong, and the lakes in upstream can hardly interact hydrologically with the lakes downstream.…”

Increased host diversity limits bacterial generalism but may promote microbe-microbe interactions

“…This contrast may point to a fundamental difference in host filtering compared to free-living bacterial community assembly. However, these systems, like ours (Figure 2), showed that generalist bacterial lineages are more geographically structured than specialists (Liao et al 2016;Hu et al 2019;Luo et al 2019;Zuo et al 2023).…”

“…This difference is likely driven by the absence of highly prevalent and host generalist Proteobacteria ASVs in high diversity host communities (Figure 2, Table S2), contradicting our hypothesis that high host diversity would drive ASVs to become either highly specialist, or highly generalist. Our data show patterns that directly contrast with free-living bacteria assemblages, in which generalist microbes are more diverse at southern latitudes (Zuo et al 2023). This contrast may point to a fundamental difference in host filtering compared to free-living bacterial community assembly.…”

“…As the number of host lineages increase, we expect the number of specialist bacterial lineages to increase as well, as has been observed in host-specific parasite lineages (Bordes et al 2011; Clark 2018). In further support of this idea, free-living generalist bacteria are more diverse toward the tropics (Zuo et al 2023). Second, we hypothesize that microbes in high diversity host communities will either be specialized on specific host lineages or highly generalist (Sant et al 2021), with fewer lineages showing midrange generalism.…”

Urbanization alters the diversity, assembly and complexity in microbial generalist and specialist community of a subtropical river system

“…For instance, the community assembly of generalists and specialists in the sedimentary habitats of Lake Tibetan was been found to be dominated by stochastic processes [30]. However, study [31] pointed out that the community assembly of specialists in upland lakes is controlled only by deterministic processes, which is consistent with the results of studies on generalists and specialists in lakes and reservoirs at different latitudes in eastern China [32].…”