Do host‐associated microbes show a contrarian latitudinal diversity gradient? Insights from Mytilus californianus, an intertidal foundation host

Abstract

Aim The latitudinal diversity gradient (LDG) is one of the most pervasive large‐scale trends in biodiversity. However, whether microbial taxa also conform to this pattern remains poorly known. This study uses the gill and shell‐surface microbiomes of the marine bivalve Mytilus californianus to test whether the diversity of host‐associated microbial communities declines with increasing latitude, as predicted by the LDG. Location Northeastern Pacific coast, ranging from Sitka, AK to La Jolla, CA, USA (spanning 24.12 degrees of latitude). Taxon Bacteria and Archaea associated with M. californianus gills and shell‐surfaces. Methods We amplified and sequenced the 16S rRNA gene from M. californianus gill and shell‐surface samples. We used linear and quadratic regressions, accounting for spatial autocorrelation when needed, of average alpha and gamma diversities of the whole microbiome, as well as individual microbial clades, to determine whether these taxa conformed to the traditional LDG. We also used permutational multivariate analysis of variance to determine the level of compositional differentiation among sampling sites. Results Gill and shell‐surface microbiota show differing latitudinal diversity patterns, with both micro‐environments exhibiting high levels of compositional differentiation along latitude. Individual microbial clades within each micro‐environment also show different latitudinal trends, most likely due to differing ecologies and life histories. Main conclusions Mytilus californianus‐associated microbial taxa show a flat, hump‐shaped or contrarian LDG, suggesting that a steep decline in diversity with increasing latitude may not be a universal pattern across different domains of life.

The biogeography of host‐associated bacterial microbiomes: Revisiting classic biodiversity patterns

“…Studies in anemones (Morelan et al, 2019) and fruit flies (Corby‐Harris et al, 2007) spanning limited latitudinal ranges (8 and 10°, respectively) found no differences in bacterial microbiome diversity. In contrast, geographical patterns were found in the California blue mussel across a latitudinal range of 24° (Neu et al, 2021). However, results depended on the tissue type, diversity metric and taxonomic scale, and they varied across bacterial clades (Neu et al, 2021).…”

“…Microbiome diversity could also be structured differently across varying spatial scales, ranging from a few kilometres across elevations to potentially thousands of kilometres across latitudes. Latitudinal diversity gradients of bacterial microbiomes are commonly investigated across hundreds to thousands of kilometres, but ranges vary substantially among studies (e.g., between 8 and 24 degrees of latitude in the studies by Morelan et al, 2019; Neu et al, 2021), and variation across such studies could be leveraged to test whether geographical scale affects the likelihood of observing biogeographical microbiome patterns. Dispersal rates also vary considerably across host species, raising the question of whether stronger microbiome structuring along environmental gradients might be expected for hosts with lower dispersal.…”

“…It has also been argued that by studying diversity patterns for whole bacterial communities, one might overlook patterns in certain bacterial clades (Neu et al, 2021). One approach to overcome this issue would be to determine microbiome biogeography for certain microbial lineages rather than at the overall community level.…”

“…Knowledge of microbial biogeography thus far has largely been limited to free‐living communities (reviewed by Dickey et al, 2021; Martiny et al, 2006), and studies have shown that microbial abundance, composition and diversity vary along environmental gradients (e.g., Bryant et al, 2008; Ladau et al, 2013). Yet, host‐associated microbial communities (hereafter referred to as “microbiomes”) have been mostly neglected, with very few studies having explored microbiome biogeography (e.g., Morelan et al, 2019; Neu et al, 2021). This is particularly true for bacteria, whereas we have a better understanding for other microbes, such as plant‐associated fungi (Kivlin et al, 2017).…”

Latitude variations of soil bacterial community diversity and composition in three typical forests of temperate, northeastern of China

“…performed at different scales, are inconsistent (Tedersoo et al, 2014;Neu et al, 2021). Even under the same environmental conditions can the distribution of soil microorganisms be inconsistent (Han et al, 2015;Li et al, 2019;Tian et al, 2022).…”