| The embryonic stage is the most sensitive and vulnerable period to the environment in birds’ life history.Its adaptation to the environment is an important part of biology and evolutionary ecology.Study on embryonic development of tropical bird,however,was quilt shortage in China.To understand embryonic development characteristics and differences of breeding birds in tropical areas and reveal birds’ embryonic physiological mechanism adapting to the environment.From April to July 2021,i investigated embryonic development of morphology and physiology of four common breeding birds,Red-whiskered Bulbul(Pycnonotus jocosus),Yellow-bellied Prinia(Prinia flaviventris),Yellow-bellied Warbler(Seicercus superciliaris),and Whitebrowed Piculet(Sasia ochracea),in northern tropical limestone Area,Southern China.The eggs were incubated artificially under the same conditions.Supplemented by an oxygen bomb calorimeter,infrared embryo heart rate meter and Clark temperature controlled oxygen electrode device,morphological and physiological indexes such as incubation period,egg morphology,yolk content and energy,embryonic heart rate,mitochondrial respiration,and cytochrome C oxidase(COX)activity were studied.The results are as follows:(1)The incubation period of the Red-whiskered Bulbul was(12.31±0.11)d,and that of the Yellow-bellied Prinia was(13.14±0.17)d.The incubation period of the Yellow-bellied Warbler is(14.25±0.25)d,and that of the White-browed Piculet is(13.75±0.25)d.The incubation period of Red-whiskered Bulbul was significantly shorter than Yellow-bellied Prinia(P=0.000).It suggests that Redwhiskered Bulbul may have a faster embryonic development rate than Yellowbellied Prinia.(2)The average of clutch size of Red-whiskered Bulbul was(3.037 ±0.113),and egg mass was(2.647 ± 0.198)g.The average of clucth size of Yellow-bellied Prinia was(4.444±0.123),and egg mass was(1.000±0.051)g.There were significant differences in average of clutch size and egg mass between Red-whiskered Bulbul and Yellow-bellied Prinia.The average of clucth size of Yellow-bellied Warbler was(3.667 ± 0.211),and fresh egg mass was(0.892 ± 0.072)g.The average of clucth size of White-browed Piculet was(2.800 ± 0.200),and egg mass was(1.193± 0.159)g.During the incubation period,egg mass of the four birds decreased gradually with embryonic development.These reflect the differences in the reproductive investment of different birds,which directly affect the embryonic development rate.(3)The body mass and visceral organs(heart and liver)of newborn of Redwhiskered Bulbul are larger than those of the other three birds,with significant differences.Among them,newborn body mass of Red-whiskered Bulbul is(2.023±0.251)g,heart mass is(0.020±0.001)g,and liver mass is(0.057±0.003)g.The newborn body mass of Yellow-bellied Prinia is(0.714±0.067)g,heart mass is(0.007 ± 0.000)g,and liver mass is(0.014 ± 0.001)g.The newborn body mass of Yellow-bellied Warbler is(0.740±0.027)g,heart mass is(0.006±0.000)g,and liver mass is(0.014±0.000)g.The newborn body mass of White-browed Piculet was(0.867±0.045)g,heart mass was(0.007±0.000)g,and liver mass was(0.015±0.003)g.The function is compatible with the structure,and the larger organ is one of the important factors to strengthen the function.(4)Initial and residual yolk mass of Red-whiskered Bulbul is significantly different from other three birds,and there is a significant difference with Yellow-bellied Prinia.Considering the difference of egg mass,there was no significant difference in the relative yolk content between Red-whiskered Bulbu and Yellow-bellied Prinia.After burning the dried yolk,it was found that the total yolk energy of Red-whiskered Bulbul was closer to Yellow-bellied Prinia,Yellow-bellied Warbler and White-browed Piculet.However,yolk energy per unit mass of Red-whiskered Bulbul was lower than that of the other three birds,and there was a significant difference between Red-whiskered Bulbull and Yellow-bellied Prinia.It shows that species with small egg mass may make up for the lack of egg mass by increasing the energy per unit yolk.(5)The embryonic heart rate of birds showed an upward trend during hatching.There was a negative correlation between the egg mass of the four birds and maximum embryonic heart rate and embryonic heart rate at 80% of the incubation period,but the intraspecific correlation was not significant.Although the embryonic heart rate of Yellow-bellied Prinia is lower than that of Yellowbellied Prinia,its heart mass is significantly greater than that of Yellow-bellied Prinia,and its heart output is also greater.It shows that Red-whiskered Bulbul may increase the output of blood pumps to the whole body by increasing heart mass,strengthening material transportation and oxygen-carrying,and improving the metabolic rate.(6)There are species differences in mitochondrial respiratory intensity(State 3 and State 4)in the liver of newborn birds.Among them,the unit mass mitochondrial respiration(State 3 and State 4)in the newborn liver of the Redwhiskered Bulbul was significantly lower than that of Yellow-bellied Prinia,but overall mitochondrial respiration(State 3 and State 4)in liver of Red-whiskered Bulbul was higher than the other three birds.The mitochondrial protein concentration in Red-whiskered Bulbul’s liver was close to that of Yellowbellied Prinia,while COX activity was greater.Therefore,the total metabolic rate of Red-whiskered Bulbul is higher than that of Yellow-bellied Prinia.In conclusion,birds in the Nonggang area may have different embryonic development patterns to adapt to the special environment of tropical limestone.The total yolk energy of red eared Bulbul is close to that of other three birds.But the larger heart and liver may improve the metabolic capacity of the Redwhiskered Bulbul at the individual level,so it has a faster embryonic development rate and shorter incubation period.The results suggest that the embryonic stage of birds is a key period in birds’ life history.In the northern tropical limestone area with a high nest predation rate as a strong driving force,understanding characteristics and physiological mechanism of embryonic development is particularly important to explore the environmental adaptation of breeding birds in the tropics. |
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