A latitudinal diversity gradient in planktonic marine bacteria

Area of Science:

• Microbial Ecology
• Biodiversity Science
• Oceanography

Background:

• A long-standing debate in biology concerns the drivers of latitudinal biodiversity gradients, with productivity, temperature, and historical factors proposed.
• Previous studies suggested unicellular organisms might lack these gradients due to high abundance and dispersal, challenging existing theories.
• Bacteria, being the most abundant and smallest organisms, were hypothesized to exhibit no latitudinal diversity patterns.

Purpose of the Study:

• To investigate the presence and drivers of latitudinal diversity gradients in marine bacterial plankton.
• To evaluate competing hypotheses for biodiversity gradients using bacterial communities.
• To determine if bacteria, despite their characteristics, conform to general biodiversity patterns.

Main Methods:

• Employed amplified ribosomal intergenic spacer analysis (ARISA) for whole-assemblage genetic fingerprinting.
• Quantified bacterial species richness in 103 near-surface marine plankton samples.
• Collected samples across a latitudinal range from tropical to polar regions in both hemispheres.

Main Results:

• A significant latitudinal gradient in marine bacterial species richness was identified.
• Species richness showed strong correlations with latitude and temperature.
• Correlations with productivity (chlorophyll, primary productivity, bacterial abundance) and other factors (salinity, distance to shore) were weak.

Conclusions:

• Marine bacteria exhibit geographic patterns of species diversity comparable to other life forms.
• The findings support the hypothesis that metabolic kinetics, influencing the pace of life, significantly impacts diversity.
• Latitudinal biodiversity gradients are not exclusive to macroscopic organisms and are influenced by factors like temperature and metabolic rates.