Text|Little Tiger History Talk
Editor|Little Tiger History Talk
There are differences in breeding timing in many bird populations, but how this change is maintained is not obvious because timing has substantial adaptive consequences. Daily energy expenditure (DEE) during spawning increases as temperature decreases, so perhaps only females who are able to lay eggs at low energy costs will lay their eggs at low temperatures early in the season.
This test was performed whether the daily energy expenditure of late spawning females during spawning was higher than that of spawning preterm females by comparing the DEE of early females in the spawning sequence with the DEE of early females in the spawning sequence on the same day.
The classic explanation for the difference in breeding time is that there is a variation in the local food supply time during the chick stage, so the birds adjust the breeding time according to the local food supply time. Differences in the average breeding dates of populations may reflect adaptive evolutionary differences.
Early breeding occurs where the peak of food is greatest in chickling, while variation within populations may reflect a combination of genetic differences and adaptive plasticity.
Another explanation for the change in adaptation of breeding time is that the spawning date is influenced by the pre-spawning food conditions. Spawning is energy-expensive, as indicated by the increase in the metabolic rate of egg-laying females.
To match the time of maximum food demand with the time of maximum food supply, eggs must be laid 5 weeks before the food peak. As a result, eggs are laid in cold weather conditions, with low foraging efficiency and high energy costs. It has long been thought that resource constraints set the earliest spawning date within a year, and that birds don't lay eggs earlier simply because they can't get enough resources.
This resource limitation hypothesis can also be seen as a trade-off between costs and benefits. Early spawning may allow for a better match with the chicks' food peaks, but laying eggs in harsh conditions early in the season can lead to increased energy costs, which can negatively impact current and future reproductive success with the increased fitness costs of the workload.
Experimentally increased costs of female little black-backed gulls during spawning reduce the ability to raise offspring at the chick stage, resulting in fledgling weight loss. Experimentally increasing the cost of breeding within 1 year affects the breeding time in the second year – the increased cost of female large begins to lay eggs in the second year after manipulation.
As ongoing costs increase during the breeding cycle, female survival also decreases at the expense of future reproductive success. Some females may lay eggs later than the time when chick needs and food conditions are best matched during chick feeding to increase the chances of future reproductive success.
As an income feeder, the energy expenditure of female great collecting enough food for spawning may vary depending on the local food supply before and during spawning. According to this hypothesis, differences in spawning dates may be due to differences in the timing or abundance of food supplies at the territorial level in the period prior to spawning.
If there are differences between females in terms of the energy expenditure required to lay eggs, differences in spawning dates may occur, which may be due to inherent differences in the quality of females.
The daily energy expenditure of females during egg laying was investigated. Differences in female DEEs indicate that something is different in their environment or physiology. As environmental conditions improve in season, those females who are able to lay eggs at low cost will be able to lay eggs in poorer environmental conditions and will therefore reproduce earlier.
Comparing the DEE of early breeding females with late females is difficult because the factors that affect DEE vary in seasons and daily variations. The DEEs of females with different first spawning dates were compared on the same day, thus avoiding daily changes in conditions by taking advantage of overlapping spawning periods.
DEE in late female spawning sequence in early females was compared with DEE in late females in early spawning sequences during overlapping spawning period. By comparing within a day, we do not need to correct for the effects of temperature and food availability.
Double labeled water technology with eggs as samples
Double-label water technology allows us to enriche in the animal's body water by measuring 2H and 18O by injection. Instead of measuring the elimination rate of the O isotope in the 2H and 18 blood samples, the elimination rate in the egg protein produced was measured.
The time period for which DEE was measured using this method depended on the exact time when water molecules could not move freely between the female body's pool and the water in the egg, and studied the relationship between barn swallow protein and isotopic concentrations in the blood, and found that the average time for the pool separation of females and eggs was about 2245 hours.
While this time is unknown in the great, what matters is the timing of the female separation on consecutive eggs. There is no evidence that this timing differs between successive eggs in the female's spawning sequence.
The DEE values found in the data are comparable to those found by Stevenson and Bryant during spawning and are approximately 2.5 times the BMR.
Nest boxes are inspected twice a week from early 2011 to monitor nest construction, and once the bottom of the box is covered with nest material, the nest is inspected daily to determine the exact spawning date. The eggs are numbered on the day they are laid.
Female great are caught when they leave the nest box early in the morning, using a makeshift "box net" shortly after laying eggs. Immediately after capture, 0 μl DLW is injected intraperitoneally using a 33.12 ml syringe with a 0.3×0 mm needle.
After injection, females are weighed to the nearest 1.10 g and released. Early females are captured and injected with DLW on the morning of laying their sixth egg, while late females are injected on the morning of laying their second egg.
The day after the injection, the third egg from the late stage and the seventh egg from the early woman are collected. The next day, we collected the fourth and eighth eggs of these females.
Because females can only be captured the morning after the first egg is detected, the earliest measurements of DEE are between the third and fourth egg production.
For early females, we chose the eighth egg as the last sample, as not all females can produce more than eight eggs. All eggs collected as samples are immediately replaced with sterile eggs from nearby study sites to prevent the production of replacement eggs.
About 12 h after collection, the length, width, and quality of the eggs are measured, the yolk and egg whites are isolated and weighed in the laboratory to the closest mg. Homogenize the protein by hand and transfer three ~15 μl samples into a non-heparinized 25 μl capillary for immediate flame sealing.
The Isotope Research Center analyzed the isotopes using methods detailed elsewhere. The protein in the capillary tube is distilled in a vacuum tube and brought into a standard vial where it is automatically injected into the isotope ratio mass spectrometer system.
Local water quality standards (2H- and 18O-water prepared from pure water) covering the entire enrichment range of protein samples for calibration purposes. Actual 18O and 2 H measurements of automated batches are performed using a high-temperature pyrolysis unit coupled with a GVI isotope ratio mass spectrometer for actual isotope analysis.
The temperature was retrieved from Deelen, the location of the Royal Netherlands Meteorological Institute. Both study sites are inland and there is no reason to believe there is a temperature difference between the two sites. Since the timing of the separation of the eggs from the female TBW is largely unknown.
Three different 24-hour average temperatures were tested. The results do not vary depending on the time period of the average temperature, but since midnight-midnight temperature explains most of the change, average temperature results for this period are presented.
To test the hypothesis that there is no consistent difference in DEE in female spawning sequences, we isolated egg numbers using the "centered" procedure in a linear mixed model. The significance of female egg count on DEE was tested in a mixed model using DEE as the response variable and mean temperature, female weight, average egg number, and average egg number deviation measured by each DEE as explanatory variables.
The latter variable is of the most interest. We also included temperature and female weight, as these variables appeared to be important in the analysis of the full dataset.
Use a linear hybrid model to explain the fact that multiple females are measured in a single day. The starting model with DEE as the response variable included the average temperature, study area, female weight, number of eggs laid after final sample eggs, amount of yolk and protein in the final sample, date, final clutch size, and interaction of egg number with temperature.
In women who were measured twice, a randomly selected measurement was included in the analysis. Starting with the interaction, the least important terms are removed from the model, resulting in a final model with only valid variables.
We used two separate tests to test for DEE differences between early and late spawning females. First, we ran a 2-factor ANOVA with DEE as the response variable and date as the factor and egg quantity. Use the date as a factor to explain all possible differences that occur between dates.
As another way to answer the same question, a linear hybrid model was run with DEE as the response variable, date as a random variable and the interaction between temperature, female weight, number of eggs, and temperature and number of eggs.
The daily energy expenditure of female great during spawning decreases with ambient temperature. The slope of the effect of temperature on DEE did not differ between the two study areas, but at a given temperature, Oosterhout females consumed more energy than Hoge Veluwe females.
DEE increases with weight gain. After the DEE measurement date, various egg characteristics, clutch size, date or remaining egg production have no effect on the DEE.
There may be differences in fitness costs incurred by females for sexual energy, which may explain the change in spawning dates. There are many examples where an increase in workload can negatively affect the survival of parents. In order to optimally explain the maintenance of spawning date changes, fitness costs must be individually different due to increased energy expenditure.
The data results showed that Oosterhout's female big consumed more energy during spawning than Hoge Veluwe females. This difference may be caused by genetic differences between populations in Osterhout, and not one of the 3,376 known species birds in Osterhüt was born at Hogvilüwe, and only two known Hogvehué breeders were born in Osterhout.
Site-to-site differences in energy expenditure may be due to differences in timing of caterpillar food peaks. In contrast to the sandy soil of Hoge Veluwe, the Oosterhout population is located on fertile river clay.
The difference in soil type is likely why trees in Oosterhout lose their leaves earlier compared to Hoge Veluwe, causing caterpillar food peaks earlier.
This means that Osterhout females must lay eggs earlier and thus consume more energy. Since the great does not store a lot of fat, the maximum energy expenditure will directly depend on energy intake.
From radio-tracking data from the first two populations of spawning, we know that females in Oosterhout often use large amounts of supplemental bird food from nearby villages, a source of which is not available to the Hoge Veluwe population.
We have seen that females often visit for supplementary food, after which they fly back to their territory and jump into the canopy of trees to feed, most likely in search of insects.
conclusion
Complementary foods are used only as fuel and help forage for protein-rich foods. Compared to Hoge Veluwe females, they are able to work harder and therefore consume more energy. Choices are influenced by and may alter these costs and benefits throughout the reproductive cycle.
Understanding how energy costs differ in females not only during spawning but also during other periods of the reproductive cycle will help to gain insight into patterns of phenotypic selection in natural populations.
bibliography
[1] Avery MI, Krebs JR (1984) Great (Parus major) Successful hunting spider temperature and foraging. Crested Ibis 126: 33-38
[2] Daan S, Dijkstra C, Drent RH, Meijer T (1989) Annual time of food supply and bird breeding. Int Avia 19: 392–407
[3] Daan S, Masman D, Groenewold A (1990) Basal metabolic rate in birds – their association with body composition and energy expenditure in nature. Natl Physiol 259: R333–R340