PMC

(A) Mean starting symbiont density of A. hyacinthus colonies across Palau is negatively correlated with the fraction of symbionts retained after heat stress. Colonies with lower symbiont population densities (fraction of symbiont cells per coral cells) tend to show higher retention after 2 days of standardized heat stress (r² = 0.080, p = 9.063 × 10^–4). (B) Annual growth (2018–2019) is higher for colonies with higher symbiont loads (r² = 0.026, p = 0.0398). Accompanying source data are available as .data.
Figure 3—source data 1.Colony by colony measurements of symbiont load, retention and growth.

Localization of the bacterial symbionts in the abdomen of Antestiopsis thunbergii. In the fluorescence in situ hybridization (FISH) images, blue, green, and red signals indicate insect nuclear DNA, the gut symbiont, and the Sodalis, Spiroplasma, or Rickettsia symbiont, respectively. (A) FISH of a tissue section of the posterior midgut, in which crypt cavities are filled with the gut symbiont cells. (B) FISH of a tissue section of the posterior midgut from another insect, wherein the Sodalis symbiont cells are sporadically located in gut epithelia and fat body cells in addition to the gut symbiont cells in crypt cavities. (C) The Sodalis symbiont cells in a fat body cell. (D) FISH of a tissue section of the posterior midgut region without staining of the gut symbiont, wherein the Spiroplasma symbiont cells are sporadically detected in fat body cells. (E) The Spiroplasma symbiont cells in a fat body cell. (F) The Rickettsia symbiont cells in midgut epithelial cells. Abbreviations: fb, fat body; G, gut symbiont; mgc, midgut crypt; R, Rickettsia symbiont; Sd, Sodalis symbiont; Sp, Spiroplasma symbiont.

In vivo localization of the alpha-symbiont visualized by fluorescent in situ hybridization. (A to D) Disymbiotic strain NpFky002 of Nysius plebeius infected with the alpha-symbiont in addition to the primary Schneideria symbiont. Red, green, and blue signals indicate the alpha-symbiont, the Schneideria symbiont, and host insect DNA, respectively. (A) Bacteriocytes making up a bacteriome. (B) Tip region of an ovariole. (C) Anterior pole of an oocyte. (D) Midgut epithelium. (E to G) Trisymbiotic strain NpTsk002 of N. plebeius infected with the alpha-symbiont, the Wolbachia symbiont, and the Schneideria symbiont, Red, green, and blue signals indicate the alpha-symbiont, the Wolbachia symbiont and host insect DNA, respectively, while the Schneideria symbiont is not visualized except for the DNA staining. (E) Bacteriocytes constituting a bacteriome. (F) Tip region of an ovariole. Signals of the Wolbachia symbiont are particularly concentrated in the germarium region, which mainly consists of nurse cells and also contains somatic and germ line stem cells (). (G) Developing oocytes, wherein the Wolbachia symbiont and the alpha-symbiont colocalize and form a cluster at the anterior pole. (H and I) Trisymbiotic strain KrOkn001 of Kleidocerys resedae infected with the alpha-symbiont, the Wolbachia symbiont, and the primary Kleidoceria symbiont. Red, green, and blue signals indicate the alpha-symbiont, the Wolbachia symbiont, and host insect DNA, respectively, while the Kleidoceria symbiont is not visualized except for the DNA staining. (H) Bacteriocytes constituting a bacteriome. (H) Midgut epithelium. Abbreviations: a, signal of the alpha-symbiont; f, follicle cell; g, germarium mainly consisting of nurse cells; iz, infection zone in germarium (); n, nucleus of bacteriocyte; o, oocyte; ob, ovarial bacteriocyte in infection zone (); s, signal of the Schneideria symbiont; w, signal of the Wolbachia symbiont. The arrows pointing up and down indicate the anterior poles and posterior poles of oocytes, respectively.

Hitchhiking or selection? Key for (co-)infection context deconstruction and its use in interpreting the symbiont dynamics shown in later figures. (A) Possible pattern expected if: there is positive selection on aphids with Symbiont A due to the symbiont’s fitness/phenotypic impacts, and if Symbiont B rarely lives with Symbiont A, showing, thus, no response via hitchhiking. (B,C) Patterns consistent with selection on aphids with one symbiont and hitchhiking by another. Under this scenario, selection acts on the phenotypic effects conferred by Symbiont A. This symbiont commonly lives with Symbiont B, which does not strongly impact Symbiont A’s fitness/phenotypic impacts, and which does not, itself, alter fitness at the given time. Symbiont B’s frequency dynamics, thus, extend from selection acting on its co-infecting Symbiont A partner. (D) Pattern expected if selection acts on a phenotype conferred due to the joint actions of two co-infecting symbionts. In this case, it is the co-infection that is under selection (only positive selection scenario shown for panel (D)—as done also for panel (A)). The boxed legend at the bottom decodes the line -color and -dashing schemes used to illustrate symbiont and (co-)infection context frequencies in (A–D). Note that y-axes represent the frequency of each symbiont or the particular (co-)infection type. Colored circles on the x-axis represent different sampling times.