Maternal provisioning of an obligate symbiont

Abstract

Vertical transmission of microbial symbionts is interpreted as all offspring within a clutch being provided a similar number of symbionts irrespective of reproductive output (fecundity). This interpretation, however, stems primarily from oviparous insects and, thus, has yet to consider other major reproductive strategies. We used the viviparous sponge Halichondria panicea and its obligate symbiont Candidatus Halichondribacter symbioticus to test the hypothesis that offspring receive quantitatively similar numbers of its obligate symbiont. This quantitative strategy of vertical transmission was not observed. Instead, we find that H. panicea has a maternal pool of Ca. H. symbioticus that is partitioned proportionally to reproductive output and allometrically by offspring size. Moreover, Ca. H. symbioticus could not be experimentally reduced in larvae by antibiotics, while the total bacterial community could be depleted. The ability to undergo metamorphosis was unaffected by this perturbation. Together, this demonstrates that the obligate symbiont Ca. H. symbioticus is maternally provisioned and, thus, provides an additional strategy for how microbes can be vertically transmitted.

Microbes as manipulators of developmental life-history

“…Fitness for each egg size bin was a product of fertilization success (Equation 5), larval survival based on egg size (Equation 6), and the settlement constant ( L per m 2 ). To account for a potential for microbial abundance to influence the relationship between egg size and offspring survival, we additionally modeled scenarios of enhanced growth (g > 0), where egg size influenced the effective B parameter (Bv) because larger eggs would have higher microbial abundance [28][29][30] .…”

“…Constant variation was assumed for each generation, and iterations were performed until the mean egg size reached a stable point. Bacterial abundance (i.e., titer) also scales allometrically with offspring size [28][29][30] and, therefore, we established the V parameter to account for the possibility that microbial abundance influences the relationship between egg size and offspring survival (i.e., the effective B parameter) (Fig. S4).…”

Dynamics, diversity, and roles of bacterial transmission modes during the first asexual life stages of the freshwater sponge Spongilla lacustris

“…This intermediate transmission mode was initially named "leaky vertical transmission" [12], or "mixed-mode transmission" [13]. While VT was con rmed for a large diversity of sponge models [14][15][16][17][18], it appears insu cient to explain the origin of the overall bacterial community [8,19,20]. For example, larvae of eight Mediterranean sponge species shared only 17% of the bacterial ASVs with their parents, on average [8].…”