Adaptive microbiota in scale-eating pupfish
Fish scales are composed of a deep layer that is mostly collagen type I
(Harikrishna et al. 2017); therefore, we predicted that any adaptive
microbes within the scale-eater gut would have collagen degrading
properties. This includes Bacillus , Clostridium , andVibrio taxa, which are well-known for microbial collagenase
enzymes (Duarte et al. 2016). We found a significant reduction ofVibrio taxa within the scale-eater gut from both lake populations
(Figs. 3-4). Although it is not clear why there are fewer taxa, the
significant shift in a major collagenase-producing group suggests the
potential for an adaptive scale-eater microbiome, even in the absence of
dietary scales (except perhaps incidental aggression and ingestion of
scales among tankmates). We also found significant enrichment of the
family Burkholderiaceae in both scale-eater populations (Figs.
3-4). Burkholderiaceae is a family of proteobacteria which
contains many human and animal pathogens (diCenzo et al. 2019), plant
and insect symbionts (Gyaneshwar et al. 2011; Takeshita and Kikuchi
2017), and can be found in soil, water, and polluted environments
(Coenye and Vandamme 2003; Estrada-de los Santos et al. 2016). They also
include some collagenase-producing bacteria, such as Burkholderia
pseudomallei (UniProtKB - A3P3M6; Rainbow et al. 2004), which is the
causative agent of melioidosis in humans (Holden et al. 2004).
In contrast to a microbiome study of the adaptive radiation of
Tanganyikan cichlids (Baldo et al. 2015), we found no evidence ofClostridia enrichment in scale-eaters nor a reduction of
microbial diversity in this carnivorous species. This may be due to the
very young 10 kya age of the scale-eating pupfish relative to the
comparatively ancient 12 Mya Tanganyikan radiation and Perissodus
scale-eating clade (Koblmueller et al. 2007; Martin and Wainwright
2013).