Vertically transmitted microbiome protects eggs from fungal infection and egg failure

Background Beneficial microbes can be vertically transmitted from mother to offspring in many organisms. In oviparous animals, bacterial transfer to eggs may improve egg success by inhibiting fungal attachment and infection from pathogenic microbes in the nest environment. Vertical transfer of these egg-protective bacteria may be facilitated through behavioral mechanisms such as egg-tending, but many species do not provide parental care. Thus, an important mechanism of vertical transfer may be the passage of the egg through the maternal cloaca during oviposition itself. In this study, we examined how oviposition affects eggshell microbial communities, fungal attachment, hatch success, and offspring phenotype in the striped plateau lizard, Sceloporus virgatus, a species with no post-oviposition parental care. Results Relative to dissected eggs that did not pass through the cloaca, oviposited eggs had more bacteria and fewer fungal hyphae when examined with a scanning electron microscope. Using high throughput Illumina sequencing, we also found a difference in the bacterial communities of eggshells that did and did not pass through the cloaca, and the diversity of eggshell communities tended to correlate with maternal cloacal diversity only for oviposited eggs, and not for dissected eggs, indicating that vertical transmission of microbes is occurring. Further, we found that oviposited eggs had greater hatch success and led to larger offspring than those that were dissected. Conclusions Overall, our results indicate that female S. virgatus lizards transfer beneficial microbes from their cloaca onto their eggs during oviposition, and that these microbes reduce fungal colonization and infection of eggs during incubation and increase female fitness. Cloacal transfer of egg-protective bacteria may be common among oviparous species, and may be especially advantageous to species that lack parental care.

Monitoring of Unhatched Eggs in Hermann’s Tortoise (Testudo hermanni) after Artificial Incubation and Possible Improvements in Hatching

The causes of embryonic mortality in Hermann’s tortoises (Testudo hermanni) during artificial incubation were determined. Total egg failure at the end of the hatching period was investigated. The hatching artefacts represented 19.2% (N = 3557) of all eggs (N = 18,520). The viability rate of incubated eggs was 80.8%. The eggs, i.e., embryos, were sorted according to the cause of unsuccessful hatching and subsequently analyzed. Some of the eggs were divided into two or more groups. Unfertilized eggs were confirmed in 61.0%, infected eggs in 52.5%, and eggs in various stages of desiccation in 19.1%. This group also included mummified embryos. Pseudomonas aeruginosa, Bacillus sp., Purpureocillium lilacinum, and Escherichia coli were frequently confirmed in infected eggs. Embryos were divided into three groups: embryos up to 1.0 cm—group 1 (2.2%), embryos from 1.0 cm to 1.5 cm—group 2 (5.4%) and embryos longer than 1.5 cm—group 3 (7.3%) of all unhatched eggs. Inability of embryos to peck the shell was found in 1.3%. These tortoises died shortly before hatching. Embryos still alive from the group 2 and group 3 were confirmed in 0.7% of cases. Dead and alive deformed embryos and twins were detected in the group 3 in 0.5% and 0.1% of cases, respectively. For successful artificial hatching, it is important to establish fumigation with disinfectants prior to incubation and elimination of eggs with different shapes, eggs with broken shells, and eggs weighted under 10 g. Eggs should be candled before and periodically during artificial incubation, and all unfertilized and dead embryos must be removed. Heartbeat monitor is recommended. Proper temperature and humidity, incubation of “clean” eggs on sterile substrate and control for the presence of mites is essential. Monitoring of the parent tortoises is also necessary.

Partitioning Risk Among Different Causes of Nest Failure

Nest predation and nest parasitism receive the most attention as causes of nest failure for North American songbirds. Yet for many populations, interspecific competition, adverse weather, abandonment, nestling starvation, and egg failure may also be significant causes of nest failure. Despite the long interest in differential failure, serious challenges remain in the estimation of separate probabilities of nest failure from different causes. Apparent rates of failure suffer from at least two sources of bias: heterogeneous ages at discovery and classification error. We developed maximum-likelihood estimators for cause-specific daily probabilities of nest failure. We further show how the estimators can be extended to include classification error, if known. Finally, we demonstrate a simple application to Loggerhead Shrikes (Lanius ludovicianus), Tree Swallows (Tachycineta bicolor), Violet-green Swallows (T. thalassina), and Western Bluebirds (Sialia mexicana). Daily probabilities of survival were lower for the Loggherhead Shrike (0.978 ± 0.004) than for any of the three cavity-nesting species (range: 0.989 ± 0.002 − 0.993 ± 0.001). Weather was an important cause of nest failure for Loggerhead Shrikes (0.15 ± 0.05 overall). Conversely, competition among secondary cavity-nesters was not an important contributor to nest failure (range: 2–5% of nest failures) for bluebirds or swallows. Our estimator differs from others by allowing multiple fates to be modeled as separately estimated parameters rather than as covariates to a single estimated failure probability. Thus, our estimator should be viewed as an important complement to existing methods. División del Riesgo Entre Diferentes Causas de Fracaso Durante la Nidificación

Cloacal Microbes in House Sparrows

We examined the communities of bacteria and fungi associated with the cloaca of adult House Sparrows (Passer domesticus) to investigate whether microbes could be transferred during copulation and thus represent a cost to mating. The levels of microbes in the cloacae of the male and female of eight breeding pairs were significantly correlated. The levels of microbes on the rim of the cloacal protuberance, which comes into direct contact with another bird during copulation, were similar to those inside the cloaca. These findings are consistent with microbes being transferred during copulation. Females could also receive non-cloacal pathogens during copulation, given that two of five males sacrificed had microbes within their testes, which could be incorporated into the ejaculate. Undeveloped eggs were screened for the presence of microbes, although only a low proportion (18%) was contaminated. It seems unlikely that microbial contamination is a general cause of egg failure in this species.

Nesting ecology of Blanding's turtle (Emydoidea blandingii) in Nova Scotia, the northeastern limit of the species' range

This study was conducted to obtain accurate information on the reproductive ecology of the threatened population of Blanding's turtle (Emydoidea blandingii) in Nova Scotia. In 1994, 1995, and 1996, beaches and roadways in Kejimkujik National Park were surveyed for nesting turtles; all nests observed were covered with wire-screen cages to prevent predation and facilitate the collection of data on incubation and nest success. Nesting lasted from mid-June until early July. In each year, 80% of nesting occurred during a 10-day period in the third and fourth weeks of June. Turtles nested in the evening and predominantly on lakeshore cobble beaches. Site fidelity is high in this population: 73.3% of multiparous females returned to nest on the same beach in all years. No female produced more than one clutch per season, and most females (67.9%) nested less than annually. Mean clutch size was 10.6 eggs. Hatchlings emerge in September and October. Incubation times ranged from 80 to 128 days (mean = 94 days, SD = 11.7 days; n = 26 nests). In 1994 and 1995, most protected nests were productive; that is, 76.4 and 93.3% of protected nests produced at least one live hatchling in 1994 and 1995, respectively. In 1996, only 18.1% of protected nests were productive. Between 50 and 75% of productive clutches contained unhatched eggs and, on average, between 1.0 and 1.2 eggs failed per productive clutch. Total annual egg failure ranged from 26.5 to 94%. In the absence of nest predation, lower temperatures during incubation and nest flooding appear to be major cause of egg failure in this population. More effective means of reducing nest failure and bolstering recruitment must be implemented if efforts to aid the recovery of this threatened population of Blanding's turtle are to be successful.

The Biology of the Ground Parrot, Pezoporus wallicus, in Queensland. II. Spacing, Calling and Breeding Behaviour

The spacing, calling and breeding behaviour of ground parrots in Cooloola National Park was studied over three years. Despite having overlapping home ranges, individual parrots maintain a solitary existence, the inter-bird distance averaging 106 m. No aggressive behaviour was ever recorded. Calling was restricted to before sunrise and after sunset; it comprised whistling notes mostly in variable ascending scales. Four call types were used throughout the year, and three others only in the breeding season. Light intensity appears to be the main factor determining when calling starts and finishes; parrot density influences the rate of calling by individuals. Calling may be used to advertise dominance status and location of an individual. The formation of a dominance hierarchy would enable several birds to use the same area, individual rank determining priority of access to the spatially and temporally variable seed resources. Ground parrots bred in spring, the clutch size was either three or four. Nests were found only on the ground under vegetation in dry parts of heathlands that had not been burnt for at least 3-4 years. Minimum nest density ranged between 1.0 and 1.3 nests per 10 ha. Only the female incubated the eggs, the male provided all food to both the female and chicks. On average a pair produced 1.9 fledglings per nest each year. An unusually high rate of egg failure (22-31%) appears to be typical for this species.

Factors affecting the reproductive success of common tern (Sterna hirundo) colonies on the lower Great Lakes during the summer of 1972

The breeding biology of five common tern (Sterna hirundo) colonies in the lower Great Lakes was studied between May and August 1972. Frequent visits were made to each colony and data collected on nests within large artificially enclosed areas. The objective was to identify factors that influence the reproductive success of common tern colonies on the Great Lakes. Hatching success was significantly dependent on clutch size and time of clutch initiation, whereas fledging success was independent of clutch size. The most common category of egg failure was disappearance from the nest. One colony (Port Colborne) realized a significantly higher hatching and fledging success than the others, among which there were no significant differences in prehatch or posthatch success rates. Factors that contributed to differences in reproductive success are presented and their relative contributions to the reproductive success of the tern colonies are discussed. The factors include the relative proportion of three-egg clutches, incubation time as a measure of 'parent attentiveness,' numerical size of the colony, predation, competition for nesting sites by gulls, food availability, flooding, and toxic chemicals. We conclude that no single factor can be readily correlated with reproductive success and suggest that caution should be exercised when considering the relationships between reproductive success and factors influencing it.