Disruption of the termite gut microbiota and its prolonged consequences for fitness

Abstract

The disruption of host-symbiont interactions through the use of antibiotics can help elucidate microbial functions that go beyond short-term nutritional value. Termite gut symbionts have been studied extensively, but little is known about their impact on the termite's reproductive output. Here we describe the effect that the antibiotic rifampin has not only on the gut microbial diversity but also on the longevity, fecundity, and weight of two termite species, Zootermopsis angusticollis and Reticulitermes flavipes. We report three key findings: (i) the antibiotic rifampin, when fed to primary reproductives during the incipient stages of colony foundation, causes a permanent reduction in the diversity of gut bacteria and a transitory effect on the density of the protozoan community; (ii) rifampin treatment reduces oviposition rates of queens, translating into delayed colony growth and ultimately reduced colony fitness; and (iii) the initial dosages of rifampin had severe long-term fitness effects on Z. angusticollis. Taken together, our findings demonstrate that the antibiotic-induced perturbation of the microbial community is associated with prolonged reductions in longevity and fecundity. A causal relationship between these changes in the gut microbial population structures and fitness is suggested by the acquisition of opportunistic pathogens and incompetence of the termites to restore a pretreatment, native microbiota. Our results indicate that antibiotic treatment significantly alters the termite's microbiota, reproduction, colony establishment, and ultimately colony growth and development. We discuss the implications for antimicrobials as a new application to the control of termite pest species.

Fig. 1.

Diagrammatic representation of the protocol. Incipient colonies of Z. angusticollis were established by paring dealates inside petri dishes lined with filter paper and wood on day zero. Arrows indicate the days at which rifampin was added to the experimental colonies. Control colonies received distilled water only on these same days. In subsequent censuses, colonies were sprayed with distilled water as needed. Pd indicates that incipient colonies were housed in petri dishes. Q and K denote queen and king, respectively. See text for details.

Fig. 2.

Survival distributions of control (solid lines) and rifampin-treated (dashed lines) male and female Z. angusticollis reproductives originating from colonies BDTK17 (a) and BDTK19 (b) during the first 2 years of colony life. Filled and open circles represent the percent survival of control and rifampin-treated individuals at each of the major census dates (indicated by the arrows), respectively. These percentages differed significantly on days 465 and 730 postestablishment (Pearson's χ², P < 0.004). * and NS, significant and insignificant differences in the median survival time at each of the census dates, respectively (MW test; see text). Additional survival parameters are shown in Table 2.

Fig. 3.

Percentages of established control (□) and rifampin-treated () colonies in relation to the number of eggs (a), larvae (b), and soldiers (c) produced at 150 days postestablishment. Kolmogorov-Smirnov tests and their associated Z score were used to test for differences in the locations and shapes of the distributions and whether the two treatments had equal distributions. Note that a higher percentage of control colonies produced the highest number of eggs, larvae, and soldiers.

Fig. 4.

Numbers of eggs (a), larvae (b), and soldiers (c) produced by control (□) and rifampin-treated () Z. angusticollis reproductives at each of the major census days. Each box plot shows the median value and interquartile range. The outliers, identified by small circles, included cases with values between 1.5 and 3 box lengths from the upper edge of the box. The number below each of the box plots represents the number of colonies. Reproductive parameters were compared between treatments within each census day by MW test.

Fig. 5.

Number of days elapsed to first oviposition (a) and first hatching (b) for Z. angusticollis colonies headed by untreated (□) and rifampin-treated () reproductives. Each box plot shows the median value and interquartile range. The outliers, identified by small circles, included cases with values between 1.5 and 3 box lengths from the upper edge of the box. Reproductive parameters between treatments were compared using MW test.

Fig. 6.

Maximum number of eggs, maximum number of larvae, and number of larvae recorded on day 150 after colony establishment for control (□) and rifampin-treated () R. flavipes reproductives. Each box plot shows the median value and interquartile range. The number below each of the box plots represents the number of colonies. Reproductive parameters were compared between treatments using a nonparametric Mann-Whitney U test.