Bacterial symbionts support larval sap feeding and adult folivory in (semi-)aquatic reed beetles

Abstract

Symbiotic microbes can enable their host to access untapped nutritional resources but may also constrain niche space by promoting specialization. Here, we reconstruct functional changes in the evolutionary history of the symbiosis between a group of (semi-)aquatic herbivorous insects and mutualistic bacteria. Sequencing the symbiont genomes across 26 species of reed beetles (Chrysomelidae, Donaciinae) spanning four genera indicates that the genome-eroded mutualists provide life stage-specific benefits to larvae and adults, respectively. In the plant sap-feeding larvae, the symbionts are inferred to synthesize most of the essential amino acids as well as the B vitamin riboflavin. The adult reed beetles' folivory is likely supported by symbiont-encoded pectinases that complement the host-encoded set of cellulases, as revealed by transcriptome sequencing. However, mapping the occurrence of the symbionts' pectinase genes and the hosts' food plant preferences onto the beetles' phylogeny reveals multiple independent losses of pectinase genes in lineages that switched to feeding on pectin-poor plants, presumably constraining their hosts' subsequent adaptive potential.

Multiple concurrent and convergent stages of genome reduction in bacterial symbionts across a stink bug family

“…While most of the extremely reduced genomes of symbionts are from intracellular symbionts, which are carefully protected within host cells, extracellular symbionts have additional constraints that likely impede further genome reduction. However, these can be overcome if there is significant investment from the host on structures that guarantee housing and transmission of its bacterium 85 – 87 . Stink bug symbionts are housed in separate gut compartments (or crypts) developed with a complex morphogenetic process from birth to adulthood 26 and they are externally transmitted 17 , 23 , 37 , although it is unclear to what degree these symbionts are impacted by abiotic conditions outside of the host (i.e.…”

In their sister’s footsteps: Taxonomic divergence obscures substantial functional overlap among the metabolically diverse symbiotic gut communities of adult and larval turtle ants

“…This suggests that symbiont abilities to degrade pectins in adult turtle ants vary across host colonies, and plausibly among species. Such variability could be indicative of symbiont responses – plastic or evolved – to short- or long-term changes in host diet – quite possibly due to differing fractions and forms of pectins [21, 170]. While turtle ants are believed to consume wind-dispersed fungal spores and pollen [48,98,139], little is known about dietary variation across Cephalotes species.…”

Wolbachia Endosymbionts of Fleas Occur in All Females but Rarely in Males and Do Not Show Evidence of Obligatory Relationships, Fitness Effects, or Sex-Distorting Manipulations

“…This implies that males may experience a secondary loss of infection during their development, which could be indicative of a facultative nutritional role of Wolbachia, since females have greater nutritional needs than males in blood sucking arthropods (e.g., Krasnov, 2008;Ben-Yosef et al, 2020). Second, the dominant occurrence of Wolbachia in the Malpighian tubules of S. cleopatrae females (Figure 2) may further support a nutritional role (Ben-Yosef et al, 2020;Reis et al, 2020) or indicate that these organs may store Wolbachia for other beneficial functions (Faria and Sucena, 2013). Altogether, this evidence may suggest that under restricted conditions, e.g., low nutrient availability for the larvae, anemic hosts for adult fleas, or exposure to pathogens, some potential Wolbachia fitness advantages to females may be expressed.…”

“…In addition, we characterized the location of these endosymbionts within female fleas, as this may hint at their function. For example, endosymbiont occurrence in the gut and gut appendages may suggest a nutritional role (Ben-Yosef et al, 2020;Reis et al, 2020).…”