成長する鳥類胚における心拍数解析 : 成長モードと卵質量の効果(「動物の心拍リズム」国際シンポジウム発表論文選集)

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Bird embryos may be regarded as developing in their thermo-neutralzone, at rest, and stay in the egg for a fixed period of time untilhatching. It is therefore interesting to investigate if they followthe same "rule" set for adult homeotherms, which states that, within ataxonomically or functionally defined category such as mammals orbirds, the number of heart beats throughout the life span (sL) is moreor less constant. This rule stems from the allometric relationshipsbetween heart rate(HR) and body mass (mB) and between sL and mB.As a step towards understanding the general allometric nature ofavian embryonic physiology we analyzed the HR values of avianembryos in relation to their incubation span (sI).Data from 30 species were selected from the scientific literaturefor the analyses. Values obtained from invasive methods which werejudged to grossly alter natural incubation conditions, or fromundefined or unmatched temperature conditions were not used. Theseinclude most values obtained below the first 30% of the incubation.Also, data obtained after internal pipping were discarded sincehatching activity influences them. Values for sI and egg mass (mE) asrepresentative of embryonic mass were also collected.Embryonic HR was normalized to 70.1-80% sI. At 20.1-30% sI it wasonly 85% of the value at 70.1-80% sI and increased to a plateau atabout 50.1-60% sI. It was almost constant among species between 50.1-60% sI and pre-internal pipping(PIP) time and thus, the mean HR valuebetween 50.1-60% sI and 90.1-100% excluding pipped eggs (MHR) was takenas a representative value for each given species. The MHR(bpm) and thecorresponding sI (d) values for the 30 species, scaled with mx (g) asfollows: MHR=371.1 mE'-0.112' and: sI=12.29 mE'+0.209'. Both powers weresignificantly different from 0. The product of MHR and sr(MHR ・ sr),representing the total number of heartbeats throughout the incubation,scaled with mE, for the entire data set as follows: MHR sr = 6.565 ・10+6 ・ mE+0.096, where the + 0.096 power is significantly different fram 0.Vaiues for MHR ・ sI, from embryos of altricial birds tended toconcentrate at the low mE end of the plot while those of the precocialones tended towards the high end. Separate analyses showed that the mEpower for the combined altricial and semi-altricial species (ASA), andthe combined precocial and semi precocial species (PSP), of log MHR ・sr against log mE regressions, were both insignificantly different from0. Thus, means of MHR ・ sI for ASA and PSP were calculated. The meanASA value of 7.27 ・ 10+6 heartbeats for MHR ・ sr, was significantlydifferent from the mean PSP value of 10.93 ・ 10+6. The difference of3.66 ・ 10+6 (33.5%) heart beats can be attributed to either the moreadvanced stage of the PSP hatchlings at hatch, to the larger mE valuesof these hatchlings, to the difference on water fractien of thehatchlings or all. The result of a linear regression of MHR ・ sI (in d-1units) against the rate of sI compietion (the inverse of incubationspan, fI; d-1) was: MHR ・ 10-6 = 0.205 + 3.940 ・ fI. Thus, the faster isthe average rate of development accomplished per day (shorterincubation) the higher is daily heart rate. Data tended to clustersuch that large eggs, mostly of the PSP type with reiatively low MHR,complete 2 to 4% of their incubation per day, whiｌe small, ASA typeeggs with relatively high MHR, complete 6 to 8% of their incubationtime per day.We conclude that, at this stage of knowledge, the data isinsufficient to resolve whether the different modes of hatch stagealone can explain differences in the total number of heartbeatsthroughout embryonic life among all bird species, or egg mass andwater content differences contribute variability. This should beinvestigated on a larger sample of species in more depth.
室蘭工業大学の論文
1999-11-30

成長する鳥類胚における心拍数解析 : 成長モードと卵質量の効果(「動物の心拍リズム」国際シンポジウム発表論文選集)

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