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Caterpillars lack a resident gut microbiome
#MMPMID28830993
Hammer TJ
; Janzen DH
; Hallwachs W
; Jaffe SP
; Fierer N
Proc Natl Acad Sci U S A
2017[Sep]; 114
(36
): 9641-9646
PMID28830993
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Many animals are inhabited by microbial symbionts that influence their hosts'
development, physiology, ecological interactions, and evolutionary
diversification. However, firm evidence for the existence and functional
importance of resident microbiomes in larval Lepidoptera (caterpillars) is
lacking, despite the fact that these insects are enormously diverse, major
agricultural pests, and dominant herbivores in many ecosystems. Using 16S rRNA
gene sequencing and quantitative PCR, we characterized the gut microbiomes of
wild leaf-feeding caterpillars in the United States and Costa Rica, representing
124 species from 15 families. Compared with other insects and vertebrates assayed
using the same methods, the microbes that we detected in caterpillar guts were
unusually low-density and variable among individuals. Furthermore, the abundance
and composition of leaf-associated microbes were reflected in the feces of
caterpillars consuming the same plants. Thus, microbes ingested with food are
present (although possibly dead or dormant) in the caterpillar gut, but
host-specific, resident symbionts are largely absent. To test whether transient
microbes might still contribute to feeding and development, we conducted an
experiment on field-collected caterpillars of the model species Manduca sexta
Antibiotic suppression of gut bacterial activity did not significantly affect
caterpillar weight gain, development, or survival. The high pH, simple gut
structure, and fast transit times that typify caterpillar digestive physiology
may prevent microbial colonization. Moreover, host-encoded digestive and
detoxification mechanisms likely render microbes unnecessary for caterpillar
herbivory. Caterpillars illustrate the potential ecological and evolutionary
benefits of independence from symbionts, a lifestyle that may be widespread among
animals.
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