INTRA-UTERINE SELECTION DUE TO MATERNAL-FETALINCOMPATIBILITY OF BLOOD TYPES IN THE
WHALES*KAZUO FUJINO
Since its discovery, it had been generally considered that blood type was hereditarily neutral characteristics free from natural selection. Thereafter many observations were reported on the correlations between blood types and hemolytic
diseases in newborn or erythroblastosis foetalis and differential survival in intrauterine life such as rate of fertility and of miscarriage and in extra-uterine life forhuman and some other mammalian species (reviewed in Race and Sanger, 1959,
pp. 310-312). These knowledges have led to rise of discussions on natural selections relating to blood groups. Series of recent papers on human blood groups
by Matsunaga (1953, 1954, 1959), Matsunaga and Itoh (1953, 1954, 1958), Simmons et al. (I 960), Grubb and Sjostedt (1955), and Jakobowicz et al. (1961) furnish
more evidences from these view-points. Basing upon the results of the Antarctic
whaling investigation in 1960/61 season, Fujino (1962) describes that differential
percentage pregnancies by blood groups were seen in both species of the Antarctic
pigmy-blue and the fin whales, and that hemolytic antibodies were positively detected from isoserums of fin whales. Then he states that the facts in these observations strongly suggest incidence of miscarriages of fetuses caused by maternal-feta!
incompatibility of blood types in whales and that these frequencies of occurrence
will closely relate to gene frequencies of blood types of the population. Results offurther observations in 1961/62 Antarctic season (Fujino, unpublished data) confirm the differential rates of pregnancy stated above. In the present paper, atfirst are described the results of observation, that is a) differential apparent rates
of pregnancy by blood groups and b) hemolytic properties ofisoserums as the evidences suggesting intra-uterine selection in whales. Secondly, after basing upon knowledges about intra-uterine selection and its compensatory mechanism in human(Matsunaga, 1954), quantitative relationships between selection and fitness are
discussed, and the prenatal mortality rate is estimated for actual population ofwhales.
MATERIALS AND METHODS

Testing bloods All stages of testing bloods were performed on board for fresh
samples, and the methods of typing blood are same as that described in the previous
paper (Fujino, 1962). In addition, hemolytic antibodies were detected for isoserums
as follows. To each test-tube containing a series of successive dilutions of inactivated fresh isoserum was added equal volume of 2 % cell suspension, andmixtures were incubated at 37°C. Thirty minutes later, reading was made. In-* Dedicated to Professor T. Ogawa for his sixtieth birthday
53

54

K. FUJINO

direct Coomb's Test (1.C.T.) was undertaken as follows (refer Race and Sanger,
1959). To each tube containing two drops of a series of succesive dilutions of isoserum was added equal volume of 2 % cell suspension, and mixtures were incubatedat 37°C for one hour. After being washed three times with cool saline, two dropsof 1 : 10 diluted immune rabbit antiserum, prepared by injecting fin whale serum,
were added to the coated cells. Ten minutes later, results of reactions were observed.
Observing ovary and internal reproductive organ ef female whales As it is generally
considered that corpus albicans survive on ovary throughout life of female whale
even after diminishing in size (Mackintosh, 1929 and Laws, 1961), one can know
accumulated number of past ovulation for each individual by counting the ovarian
corpora. When carcases of female whales were treated on board, ovaries weretaken out and were observed. Individuals, of which existence of ovarian corpora
were positively detected, were recognized as sexually mature. Simultaneous
observations on uterine conditions were made to discriminate pregnancy or not.
Female, from which fetus was found in their uterus, always possesses functional
corpus luteum in the ovaries. Sometimes, however, observation encounters females
from which no fetus was found in spite of existence of functional corpus luteum
in their ovaries. These are generally interpreted to correspond with one of following three cases, that is, I) the corpus is originated from mere ovulation without
fertilization, 2) tiny embryo at a very younger stage of conception was missed or 3)
it has not passed so long time since fetus had been lost because of shock when killed
or of physiological factors. For some individuals of females additional observations
were made by author himself for intra-uterine conditions especially for degree ofcongestion of mucous membrane.
EVIDENCES SUGGESTING INTRA-UTERINE SELECTION
RELATING TO BLOOD GROUPSFirst of all, problems identifying breeding subpopulations should be discussed here.
After studying summarized results of marking return including those taken after
his previous work (Brown, 1954), Brown (1962) stated as follows. "Marks fromfin whales do suggest that fin whales from different breeding-populations may
intermingle on the feeding-grounds, and that the ' groups ' of whales within thewhaling Areas may include animals belonging to more than one breeding population. Thus, sector of area III which lies to the south of South Africa has beenshown to contain during the southern summer fin whales from the populations of
the South Atlantic and Indian Oceans." Fujino (1962) extends blood typing investigation, which was undertaken to identify breeding population of the North
Pacific fin whales (Fujino, 1960), to the Antarctic fin whales, and states that " Thefrequency of occurrence of Ju blood types of finbacks suggested that a portion of
the Atlantic population from area II migrates to area III and mingles with the
population there." Frequencies of occurrence of Ju2-positive types were estimatedapproximately as 2 per cent for the aboriginal population of the area III and as

55

INTRA-UTERINE SELECTION DUE TO BLOOD TYPE

30 per cent for the postulated Atlantic population which partly contribute to thestocks in the area III, and estimation of intermingling ratio between both populations were made for the sample taken from area III in 1960/61 season. Resultsof further investigation in 1961/62 confirm existence of geographical non-random
distribution of frequency of occurrence of blood types stated above, and suggest
existence of the additional different populations in the area IV of which frequencyof occurrence of Ju2-positive types reveals somewhat higher figure than that ofaboriginals in the area III (Fujino unpublished data). These might support
the already-cited knowledges which was noted by Brown (1962). When various
parameters for population study were obtained from area in which migratory
ranges of different populations overlapped each other, the figures should be separated
into those proper to each pure population. Figures for the postulated Atlantic
population in Table 1 were obtained by summarizing data on several days in whichdaily incidence of Ju2-positive blood types jumped up significantly (refer Fujino,1962).
TABLE 1.

FREQUENCY OF OCCURRENCE OF FIN WHALE Ju MAJOR
BLOOD TYPES IN THE AREA III OF THE ANTARCTIC*

Blood type

Postulated Atlantic
Population**

B

Geographical area***
A

c

69.7

91.2

95.4

98.0

25.0

7.5

4.0

2.0

5.3

1.3

0.6

0.0

132

734

350

104

J Ju!
J Jul·2J Ju2Percentage ofJu2-negative type
Percentage ofJul-2 heterozygote
Percentage ofJu2 homozygote

Total numbers of whales typed* Cited from Fujino (1962)* * Sum of the data of days in which the frequency of occurrence of Ju2-positive types jumped
to high frequencies of approximately 30 per cent.
* * * Arbitrarily divided as follows ; section A : 35 to 70 degrees east of south of 50 degrees south ;section B : 0 to 35 degrees east of south of same ; section C : north of 50 degrees south.

Here some results of observation can be adduced as evidences suggesting intra-uterine selection relating to blood groups. As already reported by Fujino (1962)
no significant differences was seen in frequency of occurrence of blood types between
both sexes, but marked differences in the percentage of pregnant whales among
mature females were recognized betweenJu2-positive andJu2-negative blood groups
in the pigmy-blue and the fin whales. These relationships were confirmed withresults of further investigationin 1961/62 season (Fujino, unpublished data). Table
2 shows these figures obtained in the season 1960/61 for different geographicalareas and for the postulated Atlantic population. Although fin whale bloods wereclassified into seven types in all by subgrouping J u2 antigen complex (Fujino, 1962),
in Table 2 comparisons of percentage incidence of pregnant female are shown forthree major groups alone, because of scantiness of data for subdividing. It can beseen from this table that percentage incidence of pregnant whales among mature

K. FUJINO

56

females reveals lower figure in Jul group than that in Ju2-positive groups. Similar
type of observations were reported for human already. For instance, basing uponhis observations on marked differences of rate of miscarriage between compatible
and incompatible matings for ABO blood groups, Matsunaga and Itoh (1954)
state that there should be differential natality rates between these two types of
TABLE 2.

DIFFERENCE OF PERCENT OF PREGNANCY BY BLOOD
TYPES AMONG ADULT FEMALE WHALES*
Fin whale

Blood
type

Postulated Atlantic
population

BA

Sum ofA and B

78.9(19) **63 .9(36)73.3(30)
61.6 (307)40.0(5)51.5(101)68.6(35)
59.1 (408)Ju2-positives
Ju2-negatives* Cited from Fujino (1962)

Pigmy-blue
whales71.4(7)32.8(61)**Figures in parentheses show number of samples typed.

matings. Basing upon data collected at maternity hospitals, Boorman (1950) and
Bryce et al. (1950) find with regard to compensatory mechanisms against intrauterine selection that rate of conception in mother population reveals the highest
figure in AB group than those in any other three groups belonging to ABO bloodgroup system. According to analogical construction from these phenomena inhuman being, above-stated observations in whales might suggest that there should
be significant differences by blood types in the rates offertilization or of miscarriage
or in both.
As alredy reported by Fujino (1962) most donors classified as Jul type homozygote have anti-Ju2 isoantibodies in their serum, and moreover isoantibodies are
positively detected with reference to three kinds of Ju2 specificities in fin whales.
TABLE 3.
cells of:
type
no.
Jui
Jul·2 3
Jul·2 2
Jul·2 1

313
394
403
349

cells of:
type
no.
Jui
Jul·2 3
Jui ·2 2
Jui ·2 1

1275
1279
1301
1348

TITRATION OF ISOAGGLUTININ OF FIN WHALE,NOT INACTIVATED*no. 313 serum**16 32 64 128 256+** ** * * +**** +
no. 1374 serum**4 8 16 32 64+*** * * *+ +**cells of:
type
no.
Jui
Jul·2 3
Jul·2 2
Jul·2 1

1275
1279
1301
1348

cells of:
type
no.
Jui
Jul•2 3
Jui ·2 2
Jui ·2 1

no. 1161 serum***
8 16 32 64 128

313
394
403
349

** + * +***no. 121 serum
I
2
4

*

+

no. 368 serum
I
2
4

* + +
**

* Blood types of these donors are Jui (nos. 313 and 1374), Ju l ·2 3 (nos. 368 and 1161)
and Ju 1·2 3 (no. 121).
** Specific hemolysis were observed up to dilutions I: 8 in no. 313 serum and I: 2 in no.
1374 serum against Ju 2 positive cells.
***Specific hemolysis was observed at dilutions I: I through 1: 4 against nos. 1301 and
1348 cells.

57

INTRA-UTERINE SELECTION DUE TO BLOOD TYPE

That is, Ju2 3 subtype donors had isoantibodies for Ju2 1 and Ju2 2, Ju2 2 donors had
isoantibody for Ju2 1 , while Ju2 1 had no isoantibody. Table 3 shows titrating
results for several examples of these isoserums. No isoserum for Jul has been discovered. Most fresh isoserums possessing antibodies specific to Ju2, derived from
Jul type donors, agglutinated Ju2 1 cells at dilutions ranging from I : 2 to I : 256and hemolysed at dilutions between I : I and I : 16 when not inactivated. However, two examples of isoserums taken from Jul type female donors (nos. 301
and 347), which have ovaries with functional corpus luteum and congested uterus
but lack fetus, revealed marked high titer. Table 4 shows comparisons of agglutinin
TABLE 4. COMPARISON OF AGGLUTININ TITER OF ISOANTIBODIES OF JU 1
TYPE OF FIN WHALES AT VARIOUS PHYSIOLOGICAL CONDITIONS,EXAMINED BY INDIRECT COOMB'S TEST (l.C.T.)
Physiological condition
male
femalematuremature,resting
pregnant
non-pregnant, butwith functional corp.
lutea, excluding nos.
301 & 347
no. 301 **no. 347**

no. of samples
examined

range of titer*

859

1 :4-1 :512
1 :4-1 :512
1: 4-1: 1024

11

1:4-1:1024
1: 2048
1: 4096* Tested against Ju2 1 homozygote cells. The rabbit serum prepared by injecting fin whale
serum does not agglutinate whale cells at dilution used.
* * Probable abortive 2 females out of 13 samples with a functional corpus luteum in their
ovary but lacking fetus.

titer by different physiological conditions for these anti-Ju2 isoantibodies derived
from Jui type donors. Titrations of isoserums were made by means of Indirect
Coomb's Test (I.C.T.). These observations suggest that titers of isoantibodies of
the Jui mothers have risen by isoimmunization between fetus and mother which
followed conception of Ju2-positive fetus and that subsequently the fetus seemed
to be miscarriaged by hemolytic diseases some time before the mother whale wascaptured.
No other anatomical observation has been made for this problem at present.
While it has not been solved yet how soon do the enlarged and congested
uterus regress and do functional corpus luteum diminish into corpus albicans. If
these physiological regression would be accomplished in a comparable shorter
interval, it might be reasonable to presume that a very limited number of miscarriages are anatomically confirmed at present, even if extensive observations areattempted.
Above-stated facts suggest that intra-uterine selections occur at fairly highfrequency in incompatible mating of Jul female x Ju2-positive male. Though nodirect evidence suggesting selection in another incompatible mating of Ju2 female x
Jul or Jul ·2 male has been obtained, it can be assumed that this selection might

58

K. FUJINO

occurs at lower frequency than in the former incompatible mating in the recruiting
generation in all, because 1) no isoantibody for Jul has been found in the serumsof Ju2 donors, and 2) Ju2 homozygote has very low frequency of occurrence in the
population.
In the case of human beings, differential natality rates between incompatible
and compatible matings can be observed after second conception of each individualfor Rh blood group system, but even in first conception already for ABO system.
It is thought to closely relate to these facts that natural isoantibodies for Rh factor
occur irregularly at low frequency, while those for A or B factor occur always inconnection with existence of erythrocyte antigens (Matsunaga, 1959). As alreadystated, most Jul type donors have isoantibodies specific to Ju2 in fin whales, so thatit can be surmised that intra-uterine selection in this species occurs already even in
first conception, although no available observation has been made so far.
RELATIONS BETWEEN FREQUENCIES OF OCCURRENCE OF BLOOD
TYPES AND OF INTRA-UTERINE SELECTION

Fujino (1962) states that prenatal mortality rate due to intra-uterine selection willclosely depend upon the frequency of occurrence of Ju blood groups. Analysisof these quantitative relationships will be attempted in this paragraph. First of
all genetic relationships should be discussed. After considering far lower figuresin relative frequency of occurrence of Jul ·2 heterozygote against those which are
expected from hypothetical two allelic system for random mating population andparentages between mother and fetus, Fujino (1960) proposed that three allelicgenes including a dominant or recessive gene will be involved in the Ju blood groupsystem for the north Pacific fin whale population. In the results of investigation
for the Antarctic fin whale population, however, observed figures of relative frequency for major three blood groups are well consistent with those which are expected from major two equal allelic genes for the random mating population (seeTable 1). Furthermore, it became to be obvious that Ju2 antigen was subdivided
into three kinds of subtypes, so that it can be assumed so far that four allelic genes
including one (jl) for Jul antigen and three (j2 1 ,j2 2 andj2 3 ) for Ju2 antigen complex
equal each other are involved for Ju blood group system of the Antarctic fin whales.
According to this hypothesis phenotype-genotype relationships can be expressed as
those in Table 5. As shown in Table 3, differential intensity in agglutination reaction
is observed among these three subtypes for the same reagent, and some evidences
have been obtained which suggest existence of subtypes among Ju2-positive groups
for the North Pacific whales also (Fujino, I 960, Table 7). These facts may leadneccesity in future to re-consider allelic system and biases in relative phenotypic
frequency which may be reflected by existence of subtypes and dosage effect. In
Table 5 are shown relative frequencies of three major phenotypes in the randommating population, where summarized frequency of allelic genes j2 1 , j2 2 and j2 3
controlling three specificities of Ju2 antigen complex is q and that of jl is p.
Secondly, should be noted definition of compatible-incompatible relationships

INTRA-UTERINE SELECTION DUE TO BLOOD TYPE

59

of pregnancy or mating in relation to blood groups of whales. According to Ma..
tsunaga (1959), incompatible pregnancy means a case which erythrocytes of cow
does not possess an antigen, which is hereditarily derived from bull and exists in fetal
blood. All other cases belong to compatible pregnancy. Incompatible mating is
the combination which may cause incompatible pregnancy, and other combinations
TABLE 5.

PHENOTYPE-GENOTYPE RELATIONSHIPS FOR THE ANTARCTIC
FIN WHALE JU BLOOD TYPES UNDER A HYPOTHETICAL
ALLELIC SYSTEM
Frequency of occurrence in*the population at HardyWeinberg's Equilibrium

Genotype

Phenotypep•

j 1 jlJu2-negative

jl j23
jl j2.
jl j21Ju2-positive

j23 j23
j23 j2., j22 j22
j23 j21' j22 j21' j21 j21* Freq. of occurrence of jl gene is p, summarized freq. of j2"j2 2 and j2 3 is q, and amount to 1.
belong to compatible mating. Table 6 shows these compatible-incompatible combinations related to major three phenotypes of Ju blood group system. As available data are not sufficient to analyse the problems under considering for subtypes,
following discussions in the present paper will be undertaken in accordance withcombinations in Table 6.
TABLE 6.

COMPATIBLE-INCOMPATIBLE PREGNANCIES AND MATINGSIN FIN WHALE JU MAJOR THREE BLOOD TYPES
pregnancy
incompatible____,,.___,

compatible....--.-....

mother
Jul
Ju2
Jul 2
Jul 2
Jul 2
0

0

0

mating

fetus
Jul
Ju2
Jul
Jul 2
Ju2
0

mother
Jul
Ju2

fetus
Jul·2
Jul•2

compatible,....--"-...

female male
Jul XJul
Ju2 xju2
Ju1·2Xjul
Jul ·2XJul ·2
Jul 2Xju2

incompatible,..-----..

female male
Jul xJul·2
Ju1 xJu2
Ju2xJul ·2Ju2 xJul0

Next problems to be considered are compensatory mechanisms against selection for heterozygotes. Phenotype to be selected disadvantageously by maternalfetal incompatibility of blood types is always heterozygous fetus to be born fromincompatible matings. This means that equal numbers of two kinds of major allelicgenes controlling antigens Jul and Ju2 eliminate from the population in each occasion of selection. If this phenomenon would merely progress, gene frequencyof the population should promptly shift and in consequence will be attained monomorphism consisting of one gene which had higher frequency at the ancestral population. In real natural populatl.on, however, polymorphism is generally maintained.

60

K. FUJINO

Regarding to these facts Matsunaga and ltoh (1954) state that the mortality rateof eliminating heterozygotes is so high that mutation could not sufficiently compensate the losses of genes in each generation. At present following several phenomenon are discussed in population genetics for human blood groups as the possible
mechanisms for maintaining polymorphism.
a) Excessive natality rate of heterozygous fetus in compatible mating: Afterreporting excessive natality of MN type child in the mating of MN mother x MN
father and of AB type child in the mating of AB mother x AB father in human,
Matsunaga (1954) states that heterozygous fetuses are disadvantageouly selected
in incompatible mating, while in compatible mating number of this type of childwhich are actually born exceeds expected figure. Though sufficient evidencessuggesting these similar phenomena have not been obtained yet in whales becauseof scantiness of data, it might be interpreted that differential rates of pregnancy
between Jul and Ju2-positive blood groups which was described in the previous
paragraph might consist of two elements of decline by intra-uterine selection in Jul
group cows and of excessive natality of Jul ·2 heterozygous calves in Jul ·2 heterozygous cows, if similar trends would be involved.
b) Selective interaction between different blood group systems : After partitioning the matings, that had produced miscarriages or stillbirths, by MN and
ABO incompatibility jointly of human blood groups, Matsunaga (1960) founda significant excess in the MN compatible, ABO incompatible mating and statesthat this might suggest that selection of heterozygous child due to ABO incompatible tend to occur more frequently in compatible mating than in incompatible mating
relating to MN blood group system. Although no information relationg to thesimilar type of facts has been available yet in whales, it must be important problem to be discussed in subsequent studies. Additional several observations werereported in relation to blood group and span of life for human being (Allan, 1953a, 1953 b), but sufficient observations have not been available yet in whales.
According to the above-stated discussions, there are some differences of relative
fitness in intra-uterine life between different phenotypes especially heterozygote
and homozygotes, and then it can be thought that gene frequencies of a population
are maintained by counterbalance between selection in incompatible mating andexcessive natality in compatible mating for heterozygotes. If interactions between
different blood group systems and some other factors could be thought to hardly
influence upon selective and compensatory mechanisms, selective value and relative
fitness could be calculated as follows. When selective value for heterozygous fetuses
in incompatible mating are given as k and k' for two cases of which blood groupsof cows are Jul and Ju2 homozygotes respectively and relative fitness is given as
I +K for heterozygote in compatible mating, incidence of intra-uterine selection
are expressed as q.k and p.k' for the former two cases and excessive natality rateis K/2 for the latter case, so that condition maintaining equilibrium for gene frequencies of a population is given by following formula.
[Jul] k.q+]Ju2] k'.p= [Jul·2] K/2 ........................... 1)

INTRA-UTERINE SELECTION DUE TO BLOOD TYPE

61

, where 1 ~ k, k' ~ 0, K~ 0, and [Jul ], [Jul ·2] and [Ju2] mean relative frequencyof occurrence for each phenotype, and amount to 1 in all. As survivor of fetuses
at the end of intra-uterine life are given by :[Jul] {Uul]+[Ju~· ](2-k)+[Ju2](1-k)} for Jul homozygote cows,

22[Jul. 2] + K
2.cior J u 1 • 2 h eterozygote cows,

2and [Ju2] {Uul](l-k')+[Ju~· ](2-k')+[Ju2J} for Ju2 homozygote cows
respectively, ratio between Pl and P2 which mean apparent rates of pregnancy in
Jul and Ju2-positive types of cows is expressed as follows.
{[Jul·2]+[Ju2]} {Uul]+ [Ju~·2

J (2-k)+[Ju2](1-k)}

Pl/P2 = [J l 2 ){[J l ]} ...... 2)
u ' (2+K)+[Ju2] [Jul)(l-k')+ u ' 2 (2-k')+[Ju2]22
As regards relations between k and k', it seems to be reasonable to assume as k ~ k',judging from the facts that anti-Ju2 isoantibody is positively detected from serumsof most Jul type donors while no isoantibody for Jul has been detected from Ju2
type donors. Then after applying the observed figures, which are shown in Tables
1 and 2, to Formulae 1 and 2, calculations were attempted for five cases of k' = k,l/2k, l/4k, l/8k and O<f..k. Parameters to be used in the present discussions shouldbe those which were obtained from a pure population. For this purpose figures
for the postulated Atlantic population of which Ju2-positive types occur in fairly
high frequency are most appropriate at present, that is, [Jul] = 0.697, [Jul ·2] =0.250, [Ju2] = 0.053,p = 0.822, q = 0.178 and Pl/P2 = 0.639/0.789 = 0.810. Percentage pregnancies for each blood group used here were obtained during Antarctic
pelagic whaling season in which whales migrate there for feeding. It is generally
accepted that pelagic whaling season does hardly overlap the seasons for copulationand parturition for the southern whales (Mackintosh and Wheeler, 1942, Laws,
1961). It may be thought therefore that this relative figure of percentage pregnancies between different blood groups obtained during whaling season approximately represent that of real population, even if female whales belonging to a
population somewhat segregate by age or some other physiological factors during
their migration to feeding grounds. The results of calculation are shown in Table
7. According to this table, figure of k shows an approximate constant of 0.37 forany cases of relations between k and k'. While, figure of k' fluctuates at ranges
between 0.000 and 0.373 and K at ranges between 0.368 and 0.500. This figureof k means that prenatal mortality rate of heterozygous fetuses expected from Jul
type mother whales at incompatible mating reach up to approximately 37 percent
for the postulated Atlantic population. This figure corresponds approximately
twice as the mortality rate of heterozygous A or B child at the matings of mother0 x father A or mother 0 x father B (Matsunaga and ltoh, 1954).

62

K. FUJINOTABLE 7. CALCULATED FIGURES OF VARIOUS PARAMETRES FOR
THE INTRA-UTERINE SELECTION OF FINBACK WHALES
relation between
k and k'
ii
iii
iv
v

k
k' =
k' = l/2k
k' = l/4k
k' = 1/sk
o=,.k' {'. k

k*

k'*

l+K**

0.373
0.371
0.370
0.369
0.371

0.373
0.186
0.093
0.046
0.000

1.500
1.433
1.401
1.384
1.368

* selective values of heterozygous fetuses expected from Jui and Ju2 mother whales at incompatible matings.
**relative fitness of heterozygous fetuses expected from Jui •2 mother whales at compatible
mating.

In the next place will be discussed general relationships between gene frequency and rate of intra-uterine selection of heterozygotes at incompatible mating
in a population which gene frequencies are given asp and q controlling Jul andJu2 antigens respectively, prenatal mortality rate (d) of heterozygous fetuses canbe expressed as the summarized figure for two cases which blood groups of cows
are Jul and Ju2 homozygotes.
d = [Jul] q.k+[Ju2] P·k' .................................... 3)

As the relations of p = 1-q, [Jul] = (1-q) 2 and [Ju2] = q2 can be adopted to arandom mating population, Formula 3 will be arranged for q as follows,d= q {(k-k')q 2 +(k'-2k)q+k} .............................. 4), where 1 ;;;; q>O.

When being differentiated by q, Formula 4 will bed' = 3(k-k')q2 +2(k' -2k)q+k ................................. 5)

Mortality rate d will take a maximum figure at a point of- 2k-k'-yk2-kk' +k' 2
q3(k-k')................................. 6 ), where 1;;;; q>O and 1;;;; k;;;; k';;;; 0.
Formulae showing relations between gene frequencies (p, q) and prenatal mortality rate (d) and figure of q at which d takes a maximum will be obtained from
Formulae 4 and 6 for five cases of relations between k and k', presented already, as
follows.
i)
ii)
iii)
iv)
v)

takes a maximum at q = 0.500
d = q(l-q)kWhenk' = k= 0.423= 1/2k, = q(l-q)(2-q)k/2""= 0.362= 1/4k, = q(l-q)(4-3q)k/4""= 0.355= 1/8k, = q(l-q)(8-7q)k/8"" 0 =o;: k' «::.k, = q(l-q) 2k= 0.333.

""... 7)

INTRA-UTERINE SELECTION DUE TO BLOOD TYPE

63

When figures of k in Table 7 are put into Formula 7, relations between d andq will be drawn as Fig. 1. According to Fig. I prenatal mortality rate takes amaximum figure at a point of q = 0.500 for a case of k = k' (curve I) and reaches
up to more than 9 percent of total recruiting generation of the population. In
the postulated Atlantic population (p = I-q = 0.822) the figure of d is approximately 5 percent for any cases of relations between k and k'. If various parameters in Table 7 could be available for the aboriginal population of area III
too, the figure of d might be es timated to not reach up more than 0.3 or 0.4
.100

:3"

-;"'

0.
0

0.
~

0

E

"'
k

g

.05

.e
k
0

E

.04

"""'

.03

:a
k

"'

.02
.01

1~q gene frequeny

Fig. I. Relation between blood type gene frequency and frequency ofoccurrence of intra-uterine selection of heterozygous fetuses in randon
mating ideal population of whales. Curves 1, 2, 3, 4 and 5 correspond to five cases of which relations between k and k' are k' = k,
= 1/ 2 k, = 1/ 4 k, = 1/ 8 k and~ O~k respectively.

percent for the population. These figures include mortality rate at intra-uterine
life only. Actually, however, perinatal mortality rate of recruiting generationmust be enhanced with postnatal death of infants which is observed in human as
fatal hemolytic diseases which follow incompatible pregnancies.
SUMMARY

Basing upon the results of blood typing investigation, the author stated in his previous paper (Fujino, 1962) that in the area III of the Antarctic distribute at least
two different breeding populations of fin whales which have different frequenciesof occurrence of blood type each other, and that this might support the results ofmarking investigation reported by Brown (1954). Furthermore after discussing

64

K. FUJINO

relations between blood groups and other items of investigation, he described thatsignificant differences were seen in the percentage pregnancy among mature femalesby blood groups. This suggest that intra-uterine selection caused by maternalfetal incompatibility of blood types, which has been reported for human beingsand some other mammalian animals, takes place in whales also.
In the present paper, at first results of serological observation, that is, existenceof natural isoantibodies, their hemolytic properties and marked ascending of titreof the isoantibody which seems to be caused by isoimmunization between fetus andmother are described as evidences relating to intra-uterine selection. Secondly,
after basing upon an assumption of compensatory mechanisms for intra-uterine
selection, quantitative relationships are discussed between frequency of occurrenceof blood types and relative rates of pregnancy by blood groups, and estimation for
the rate of incidence of the selection was made. Consequently, the author notedthat in the postulated Atlantic population approximate 37 percent of heterozygous
fetuses expected from Jui type females at incompatible mating were disadvantageously selected, and this figure correspond to approximate 5 percent of the recruiting
generation of the population and this does not reach up more than 0.3 or 0.4 percent in the aboriginal population of the area III.
ACKNOWLEDGEMENTS

The author is indebted to Dr. H. Omura, Director of the Whales Research Institute, Tokyo for orienting this study and to Dr. E. Matsunaga at the National Institute of Genetics, Mishima for his valuable comments. Dr. S. Tanaka at theTokai Regional Fish. Lab. gave the author pertinent advices in introducing theformulae. Thanks are also due to the officers and the crews of the whaling factory
ship, Kyokuyo-maru No. 2, who gave the author facilities and assistance.
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