related to their original strain, suggesting there is symbiont fidelity driven by ant
behavior (Mueller et al. 2004). Therefore, permissible habitats within hosts can be
feasible in three colonist pool scenarios: when the microbes have little influence on
the host’s fitness (Louca et al. 2016a), when the variability in microbial composition
is inconsequential for function (such as redundant communities) or when variability
is beneficial for its diversity in functions (upon dietary changes, for example,
Davenport et al. 2014). This reasoning indicates that, to further our understanding
with respect to the role of dispersal on microbial function in the context of hosts, we
should consider the functional characteristics of the colonist pool as well as the
assembly processes that control local diversity and function.
17.4 Conclusions
Understanding how different species come together and deliver a functional outcome
that impacts host fitness is central to our understanding of host-associated microbial
communities. Given the broad range of microbial communities that can contribute to
host function, I believe this is an opportunity to challenge the way we look at
diversity–function relationships. We should consider the mechanisms through
which species contribute to a specific function and how the specific functions
contribute to broader functions. This type of conceptual framework could lead to a
more predictive study of host-associated microbial function. Moreover, we should
also consider the ecological mechanisms that result in microbial diversity and
function, namely, host–microbe and microbe–microbe interactions, as well as microbial dispersal and colonization. A clearer understanding of host-associated microbial
diversity and function will improve our ability to predict the effect of environmental
change on microbiomes (for example, in coral reefs, Ainsworth et al. 2010) and to
manage microbes for the benefit of human health (Kamada et al. 2013) and agriculture (Grover et al. 2011; Munoz-Ucros et al. 2020).
Ultimately, we should be able to understand when a host needs to select for low
diversity microbial communities (Fig. 17.3, black arrows represent host feedback).
Based on the proposed framework, we could say that hosts should invest (evolutionarily or ecologically speaking) in filtering mechanisms when either: (1) only
relatively few species are functionally efficient but these are poor competitors
(function corresponds to the negative selection BEF model), or (2) the colonist
pool contains ineffective species or dangerous potential pathogens. Similarly,
hosts should have fewer filtering constraints and allow for permissive and diverse
communities when either: (1) functions are complementary, (2) broad functions have
specific functions in parallel, or (3) the colonist pool is redundant and functionally
efficient. Interestingly, it is possible that filtering to prevent disease results in
decreased function in other areas of the microbiome, reflecting trade-offs and
revealing the limits of microbial benefits to fitness. Eventually, a broader picture
can emerge, where ecological processes that shape microbial communities also result
in functions that can benefit the host’s fitness. A constant dialog between microbes
17 Diversity–Function Relationships and the Underlying Ecological Mechanisms in. . .
315
behavior (Mueller et al. 2004). Therefore, permissible habitats within hosts can be
feasible in three colonist pool scenarios: when the microbes have little influence on
the host’s fitness (Louca et al. 2016a), when the variability in microbial composition
is inconsequential for function (such as redundant communities) or when variability
is beneficial for its diversity in functions (upon dietary changes, for example,
Davenport et al. 2014). This reasoning indicates that, to further our understanding
with respect to the role of dispersal on microbial function in the context of hosts, we
should consider the functional characteristics of the colonist pool as well as the
assembly processes that control local diversity and function.
17.4 Conclusions
Understanding how different species come together and deliver a functional outcome
that impacts host fitness is central to our understanding of host-associated microbial
communities. Given the broad range of microbial communities that can contribute to
host function, I believe this is an opportunity to challenge the way we look at
diversity–function relationships. We should consider the mechanisms through
which species contribute to a specific function and how the specific functions
contribute to broader functions. This type of conceptual framework could lead to a
more predictive study of host-associated microbial function. Moreover, we should
also consider the ecological mechanisms that result in microbial diversity and
function, namely, host–microbe and microbe–microbe interactions, as well as microbial dispersal and colonization. A clearer understanding of host-associated microbial
diversity and function will improve our ability to predict the effect of environmental
change on microbiomes (for example, in coral reefs, Ainsworth et al. 2010) and to
manage microbes for the benefit of human health (Kamada et al. 2013) and agriculture (Grover et al. 2011; Munoz-Ucros et al. 2020).
Ultimately, we should be able to understand when a host needs to select for low
diversity microbial communities (Fig. 17.3, black arrows represent host feedback).
Based on the proposed framework, we could say that hosts should invest (evolutionarily or ecologically speaking) in filtering mechanisms when either: (1) only
relatively few species are functionally efficient but these are poor competitors
(function corresponds to the negative selection BEF model), or (2) the colonist
pool contains ineffective species or dangerous potential pathogens. Similarly,
hosts should have fewer filtering constraints and allow for permissive and diverse
communities when either: (1) functions are complementary, (2) broad functions have
specific functions in parallel, or (3) the colonist pool is redundant and functionally
efficient. Interestingly, it is possible that filtering to prevent disease results in
decreased function in other areas of the microbiome, reflecting trade-offs and
revealing the limits of microbial benefits to fitness. Eventually, a broader picture
can emerge, where ecological processes that shape microbial communities also result
in functions that can benefit the host’s fitness. A constant dialog between microbes
17 Diversity–Function Relationships and the Underlying Ecological Mechanisms in. . .
315