inheritance of dichromatism in lina and gastroidea

1NHERITANCE OF DICHROMATISM IN LINA AND GASTROIDEA

BY

ISABEL McCRACKEN

In a series of experiments with the dichromatic species of beetle, Lina lapponica, as described in a previous paper,l it was deter- mined by breeding through a series of four generations that the behavior in heredity of the alternate characters of the species

spotted-brown ” and (‘black ” follows, in general, Mendelian behavior.

This was evidenced by the fact that the broods from a first cross between spotted individuals and black individuals are either wholly spotted or the broods are made up of individuals, some of which (and the majority) are spotted, and some are black. I n other words, it appeared that spotted-brown” was either completely or partially dominant, depending upon unknown causes.

T h a t black is a recessive character was evidenced by the fact that it frequently did not appear in a first cross between S and B, in which case it was extracted in the next generation and thereafter bred true.

T h e proportions between alternate characters from hybrids in Lina showed no parallelism with typical Mendelian proportions, however, and called for further experimentation.

‘6

“

EXPERIMENTS WITH LINA

I have during the past season (1905), sought to determine the exact proportion of dominant to recessive in successive generations bred each generation from hybrid dominant parents. T h e individuals used as parents in each generation were spotted individuals, from broods composed of both spotted and black individuals, that had

Inheritance of Dichromatism in Lina lapponica, Journal of Experimental Zoology, vol. ii, pp. 119-136.

JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 111, No. z.

322 I sabd McCracken

proven their hybrid character by producing black as well as spotted offspring.

Diagram I shows character of matings and color character of offspring throughout four generations from hybrid parents. S standing alone signifies a brood in which S was completely dominant, S B standing side by side signifies a brood consisting of both spotted and black individuals, the spotted being present in larger numbers (or partially dominant).

s x s 1 1

I S and S B

s x s 1 . J

I S and S B

I S R

I S and S B

S B I

S and S I3

I S and S B

Diagram I . Showing pedigree through four generations from hybrid S.

I n the past year’s experiments, as in the previous ones, the hybrid S parents of the first generation produced two sorts of broods, broods in which S was completely dominant and broods in which S was partially dominant. I n 1904, by breeding consecutively from completely dominant S broods, pure S broods were obtained in the third generation. Breeding in 1905 consecutively from hybrid S parents chosen from broods in which S dominated partially, in each generation both sorts of broods were obtained, that is, completely dominant S broods and partially dominant S broods. I n the partially dominant S broods the proportion of dominant to recessive gradually increased through the fifth generation when hibernation began.

It may be noted here that last year (1905) there occurred in broods both from dominant and recessive parents, an occasional wholly melanic individual, thorax as well as wing covers being totally black. Such individuals were utilized for a study of (6 sport-variation ” in heredity.

Inheritance of Dtchromatisrn 323

First generation . . . , . , . . . . . Second generation . . . , . . . . . Third generation . . . . . . . . . . Fourth generation. . . . , . . . . .

Table I gives a summary of the data in each generation from S x S parents, including total number of broods, number of broods in which S dominated completely, number of broods in which S dominated partially (designated as " mixed broods"), total number of melanic or sport individuals, total number of individuals and proportion of S to B in partially dominant S broods.

I 18 45

142 19

TABLE I

Total No. of Broods.

pletely Domi- nant S

Broods.

16

Total No. of Mixed Broods.

' 0 5 18 21

3

Total No. of Melanic Sports.

Total No. of Indikid-

uals.

3442 I050

549 4736

Propor- tion of S : B

in Mixed Broods.

3 . 8 : I

6 . 1 : I

8 . 7 : 1

26 : I

The increasing proportion of spotted individuals produced in successive generations shows a progressive dominance of the S character. T h a t B might eventually be excluded from the partial dominant S line seems highly probable, but conclusive evidence cannot be obtained on this point until success attends hibernation.

It seems, however, that we may consider S as dominant in a greater sense than that denoted by Mendelian terminology. It is progressively dominant in a way not accounted for by Mendelian law.

EXPERIMENTS W I T H GASTROIDEA

The relation of dominant to recessive in alternative characters of the kind studied is more clearly brought out in the following series of experiments with Gastroidea dissimilis.

Gastroidea dissimilis is a dichromatic species belonging to the same family of beetles as Lina lapponica, the Chrysomelida.

When an adult of this species first issues from its pupal case, the wing covers are soft and yellow. During the process of harden-

324 Isabel McCracken

ing all individuals become at first a smoky brown and later black. From this black condition the individual color-development pro- ceeds gradually in one of two directions. In one series of individuals there is a gradual deepening of the pigment to a shiny permanent deep blue-black condition. In the other series there is a passing from the black condition to a shiny permanent bright green condition. T h e color is fixed in each series within two or three hours of issuing.

We find, therefore, in Gastroidea, in its color-development, the same condition found in Lina, that is, a primary condition through which all individuals pass (and in which one series of individuals remains), and a secondary condition into which one series of individuals only passes.

T h e two colors, black and green, are therefore represented in the species, no intermediates having been observed during the course of the experiment involving the handling of many thousands of individuals (about 26,000). T h e beetle is small, about 5 mm. long, feeds on dock or rhubarb and breeds from late in February until early in September, producing normally five or six generations in a year. Under laboratory conditions the breeding season was prolonged through December and seven generations were reared from a lot collected March 16, 1905.

T h e experiment began with two hundred adults, one hundred black, one hundred green. These had been mating out of doors, blacks and greens promiscuously, and ovipositing had begun. I t was comparatively certain that there were no pure bred individuals in the collection, since presumably crossmating had been going on ever since dichromatism had been established in the species.

These hatched March 24 and issued as adults April 23. At this season, therefore, mature adults were obtained in less than forty days from the egg. Females oviposited five or six days after maturing, each female ovipositing ten to fifteen egg masses during the following few weeks with from twenty to thirty eggs in a mass, frequently run- ning as high as fifty eggs in the mass. With this material as a nucleus, I sought to determine whether there was a behavior of

T h e first eggs were obtained March 16.

Inheritance of Dichromatism 325

Color Number Character of

of Green Matings. Broods.

__

B X B 0

the color-alternatives in heredity corresponding to that of Lina lapponica. My plan was to breed successively from completely dominant hybrids, if such were found to be present, to breed successively from partially dominant hybrids, and, finally, from recessives that had from one to several pair of dominant ancestors.

In the following tables results in total are tabulated for seven generations of laboratory reared lots.

Table I1 gives the data of the first generation reared from out- door collected adults. Individuals used as parents for these data were confined in the laboratory with mates of similar color. Since it is altogether possible that some or all of the females had mated with individuals of alternate color before laboratory isolation, the results indicated give little more than known parentage for second generation data.

I Number Number 1 Total No. '

Black ~ Mixed 1 Indi- , Broods. 1 Broods. 1 viduals. i

Proportion of B : G in Mixed Broods.

of of

I ____- 1

o I 6* 580 1 I B in each of six G broods. 2 I 19 I207 1 . 2 : I

T A B L E I1

First Generation

*One B individual in each six broods.

T h e single black individuals occurring in otherwise green broods of G x G are possibly due to earlier matings of the female parents. T h e data from the B x B matings seemed to point to B as the dominant type, the actual results being presumably somewhat modified by uncontrolled matings previous to collection.

In succeeding generations the same method of mating was followed as with Lina lapponica in 1904, that is, females of one brood were confined in a breeding-jar with males of another and v i c e versa.

326 Isabt-1 McCrackm

For second generation data five categories of matings were established as follows :

No. Black Broods.

A-G X G, each parent from broods of B X B parentage that had produced mixed broods. B-G X G, each parent from broods of G X G parentage that had produced broods of green only. C-B X B, each parent from a mixed brood of B parentage. D-B X B, each parent from broods of B X B parentage that had produced broods of black only. E-G X B or B X G, the G parent from a pure G brood, the B parent from a completely dominant

B brood.

No. of Mixed

Brood?

Table 111 gives a summary of the data of these matings.

0 ~ 0 0 0

5 2 5 I 0

I ' 5

T A B L E I11

Second Generarion

337

7 4 0 98

22

3 8 4

~-

Mating Cate- gory.

____ A B C D

E

Grand- parents. Parents.

No. Green Broods.

Total No. of Individ-

uals.

Proportion of B : G i n

Mixed Broods.

1 . 2 : I

But I brood reared.

3 . 6 : I

m1 in parenthesis means that the individuals mated were from mixed broods. cd? in parenthesis means that the individuals mated were from broods in which B was completely

dominant.

This data shows that the recessive greens (G) breed true under either condition A or condition B. T h e dominant blacks (B) produce, under condition C, either broods in which B dominates completely or mixed broods in which B dominates partially. Since but a single brood was reared under condition D, the data are insufficient. B x G produces either completely dominant B broods or mixed broods.

For third generation data five categories of matings were established as indicated by Diagrams 2, 3, 4, 5 and 6.

Inheritance of Dichronzatism 327

Diagram 2. Mating category A.

First matings ............ B x B B x B B x B B x B I L ! I L ! I / __ I I

I I I I First gen ................. B-BG B-BG B-BG B-BG

I I I r I Secmd gen G

I ! I

Third gen G

1 G ..............

................

Diagram 3. Mating category B.

First matings ........... B x B B x B B x B B x. B I I LA I! II

~ I- I I I

1 , I 1 , I First gen .................. B-BG B-BG B-BG B-B-G

Second gen ....... I

B-BG I

B-BG

I G

Diagram 4. Mating category C.

First matings. .......... B x B B x B B x B B x B II I_..._!! I I I

I I I I I L-_ . .I

I I

I I

First gen ................. B-BG B-BG B-BG B-BG

B-BG Second gen .............. B-BG

1 B-BG

Diagram 5. Mating category D.

First matings ............ B x B B x B B x B B x B I 1 i.i I 1 ~ I I i I 7 I

I I I I First gen.. ................ B-BG B-BG B-BG B-BG

I B-BG

I Second gen ............... B-BG

I I !

B-BG

328

K O .

Black Broods.

Isabel McCracken

No. Mixed

Broods. - - _ ~

Diagram 6 . Mating category E.

First matings ........... B x B G x G B x B G x G I-! I J I--! I I

I I First gen .................. B G B

I

i-___i I G

I Second gen.. ............ B B

I I

Third gt=n ............... B G

Inspection of these diagrams shows that the original black parents (B x B of the first matings, except in Diagram 6) may be considered hybrids inasmuch as they produce both black and green individuals.

Table IV gives a summary of the results of third generation mat i ngs.

T A B L E IV

Third Generation

Ma- ting Cate-

F F Y .

Great- grand-

parents.

Parents. Grand- ' parents. 1

-

No. Green Broods.

29 27 0

0

Total No. of Indi-

,iduals

733

688

420

653

5'8

'roportion of B : A in

Mixed Broods.

2.76 : I

4 .2 : I

2 : I

*One B individual in a brood of nineteen, otherwise G individuals.

Comparing categories A and B, we find, with the single exception of one individual, that broods of green individuals only are produced by G x G matings, whether there are one (Category B) or two (Category A) generations of green parentage.

Comparing Categories C and D, we find that under each of these conditions, that is, whether the B parents are chosen from broods in which B dominates completely, or from mixed broods,

Inheritance of Dlchromatisrri 329

Ma- ring

care- RO‘Y.

two kinds of broods result, broods in which “black” dominates compIetely, and mixed broods. T h e comparative number of broods in which “black ” dominates completely is, however, much greater in Category D than in Category C, and the comparative number of black individuals in mixed broods is much greater in Category D than in Category C. This shows a decided difference in the influence of the black character in these two categories.

In the fourth generation, ten categories of matings were established as indicated in Table V. This table gives a summary of the results of these matings.

G-great-

parents. grand-

TABLE V

Fourth Generation

A B C

E F G

I

’

B X B B X B B X B B X B‘\ G X G I B X B B X B B X B B X B\ G X G I B X B‘\ G X G I B X B\ G X G (

Grand- parents.

__-___ G X G G X G(m) B X B (m)

B X B (m)

B X B (m) B X B (m) B X B (cd)

B X B (cd)

B X B (m)

B X B(cd)\ G X G

Parents.

G X G G X G G X G (m)

G X G(m)

G X G (m) B X B B X B

B X B (m)

B X B (m)

B X G

NO.

G’n rood!

I7 I7 6

8

4 0

0

0

0

0

No. 3lack ,rood

0

0

0

0

0

5 9

0

2

2

lo. 0

Rl’d lroodi

0

0

0

0

0

8 0

3

8

I

457 404

69

322

73 250

‘99

52

=93

76

‘ r o b of B:G in Mixed Broods.

5 . 5 : I

3 . 8 : I

5 : 1

4 : r

Comparing Category D of Table IV with Category G of Table V we find, as in Lina lapponica, that by selecting individuals in which there is complete dominance, the recessive character is eventually eliminated. I n other words, the fourth generation from hybrid parents, along the line of complete dominance, breeds true to the dominant character, no recessives appearing in the offspring.

Isabel McCracken 330

Comparing Categories A, B, C, D and E in Table V we find G x G breeding true in the fourth generation whether the immediate parents only are green or there has been a lineage of green for one, two or three generations.

I n the fifth generation, seven categories of matings were established as indicated in Table VI. This table embodies a summary of these matings.

TABLE VI

Fifth Generation _- Ma- ting Cate gory,

A B C D D E F

G

GGG-’ grand-

parents.

G G- grand- parents.

G X G B X B B X B B X B B X B B X B (E) B X B (cd B X B(cd)\ G X G 1

~~

Great- grand-

parents.

G X G G X G B X B B X B B X B B X B (m‘ B X B (cc BX B(cd)i G X G J --

Grand- parents.

G X G G X G G X G B X B B X B B X B (m) B X B (cd B X B(cd)\ G X G

?arents.

G X G G X G G X G G X G G X G B X B B X B

G X B - .

I

32 24.

5 ‘4 14 0

0

o

0

0

0

0

0

35 ‘5

2

~

JO.

[ix. d’:

_- 0

0

0

0

0

8 0

6 ~

__

Total ro. oi ‘ndi- rid’s.

‘529 679 I20

3 7 0 370

397

24”

‘336

?rap. of S : G in Mixed Broods.

8 : s : ’

6 : 1

’The letter G in this connection indicates “great.”

Data in Table VI shows G x G continuing to breed true in Categories A, B, C and D, that is, whether there has been a line of green parentage for four generations or the immediate parents only are green. Comparing Category F of Table V with Category E of Table VI we find an increasing proportion of broods in which black is wholly dominant and an increasing proportion of black individuals in the broods in which black is but partially dominant. I n Category F, Table VI (compare Category G, Table V) black in the completely dominant line continues to breed true.

I n the sixth generation six categories of matings were established as indicated in Table VII. This table embodies a summary of the results of these matings.

I FE

ommtdmmow xxxxxxxx

OmmmmWoO xxxxxxxx


T h e data in Categories A and B show single black individuals in each of three otherwise green broods out of a total of forty-four broods, and a total of I 3 1 7 individuals of G x G parents. Unless this can be attributed to a mishap due to accident in the handling of breeding jars (a possibility where hundreds of breeding-jars are being daily cleaned and cared for) this is a return of latent B in normally recessive G. It will be noticed that such an exception to the general behavior in G x G matings was also recorded in Table IV (third generation).

Comparing data in Category F, Table VI, with data in Category D, Table VII, we find a discrepancy in the behavior of what was apparently pure B, that is likewise unaccounted for unless by accident or reversion. Table VII, Category D, records the presence of a recessive G (possibly a latent G in Castle's termi- no1ogy)l in each of six broods from pure B parentage.

Otherwise the behavior of G and B in the sixth generation is consistent with their behavior in preceding generations in similar categories.

I n the seventh generation, nine categories of matings were established, as indicated in Table VIII.

'Castle, W. E., 1905: Heredity of Coat-color in Guinea pigs and Rabbits. Carnegie Inst. Pub.,No. 23.

TA

BL

E VIII

Seve

nrh

Gsn

erat

ion

Mat

ing

Cat

e-

gory

.

GG

GG

G-

gran

d-

pare

nts.

B X

B(m

) B

XB

BX

B

BX

B

BX

B

BX

B

BX

B 1

GX

G

BX

B

BX

B

GG

GG

- gr

and-

pa

rent

s.

--_

__

~

B X

B

(m)

B X

B(m

) B

XB

\

GX

G 1

BX

B \

GX

G 1

GG

G-

gran

d-

pare

nts.

GX

G

B X

B (

m)

BX

B 1

GX

G 1

BX

B \

GX

G

1

GG

- gr

and-

pa

rent

s.

~~

GX

G

GX

G

BX

B \

GX

G 1

BX

B 1

>X

G 1

BX

B 1

GX

G

1 B

X B

(m)'l

BX

B 1

GX

G

/ B

X B

(cd:

B

X B

(cd:

B x

B(m

)(

Gre

at-

Gra

nd-

pare

nts.

GX

G

GX

G

GX

G

~G

XG

B

XB

1

GX

B

GX

B

BX

B(m

)

B X

B(c

d)\

B X

B(c

d)\

B Y

B (m

)(

B X

B(c

d)l

GX

B

,BX

B(

m)

B X

B(c

d)

B X

B(c

d)

B X

B

(cd)

B

X B

(cd)

Pare

nts.

__

__

GX

G

GX

G

GX

G

BX

B

GX

G

BX

B

BX

B

BX

B

BX

B

No.

of

Gre

en

3roo

ds.

71 9 37 0

34

0

0 0

0

-

I

No.

of

No.

of

Bla

ck

~ M

ixed

B

rood

s.

0

0

37

0

0

Bro

ods.

__

__

0

0

0

49

0

10

22.

~ 4:

21

0

34

I

Tot

a1

No.

of

ndiv

id

2013

223

944

1638

976

333

1678

559

976

~

Prop

'n

on

B:G

M

ixed

+

B

rood

s. a 2-

LY 2 <

b

2-

3.4:

I 2 3 a, -3 N

.

a -.

N. :

4:'

w

w

w


Total No. of Broods.

Categories A, B, C and E show consistent behavior of recessives. Category F shows the possibility of complete domination of B

even from a line of partially dominant ancestry. The proportions in Categories D and G remain consistent with

proportions in corresponding categories of previous tables. Table IX embodies a comparison of broods of seven generations

reared successively from B x B in which the parents were partial dominants, that is, black individuals from mixed broods con- taining a larger number of black than green individuals. This table shows the proportion of B : G (of dominant to recessive) in successive generations, and the rate of increase from generation to generation of the dominant €3.

This data shows a progressive dominance of B, which either reduces G to a latent in the seventh generation or wholly eliminates

~ Total No. 1 Broods B

Individs. 'Completell Dominant.

Total No. of

it.

4' 3 0 27

'3 43 '4 10

TABLE IX

I 207

740 868

250

4'9 333

'336

First generation (Table 11). . . . . . . . . . . , Second generation (Table I11 G ) . . . , . . Third generation (Table IV C) . . . . . . . Fourth generation (Table V F) . . . . . . , Fifth generation (Table VI E) . . . , , . . . Sixth generation (Table VII E) . . . . , . . Seventh generation (Table V I I I F)' . . . .

Total No. Broods B Par:ially

Dominant.

39 25

'9 8 8 6 0

Prop'n o f B : G

in Mixed

Broods.

1 . 2 : '

I . I z : I

2 . 7 6 : ' 5 . 5 : ' 8 . 5 : '

16 : I

All B

'Not absolutely, but practically, comparable with categories of other generations with which it is compared.

COMPARISON OF RESULTS I N LINA A N D GASTROIDEA

T h e fact that in one species (Gastroidea) black is the dominant character, while in the other species (Lina) black is the recessive

Inher i tance o f D ichromat i sm 335

character, shows that there is nothing in the character as such that makes for its actual behavior.

T h a t green is the final color in the color-development of the individual in Gastroidea has already been pointed out. In the paper previously referred to, it was pointed out that black is the final color in the color-development of individuals in Lina lapponica. We have, therefore, a similarity of behavior in the estab- lishment of the definitive color in the two-color series in each species. T h a t is, we have in each species a primary color-condition through which all individuals pass and in which one series remain (“black” in Gastroidea, “spotted” in Lina). We have in each species a secondary color-condition into which some of the individuals pass and there remain (“green” in Gastroidea and “black” in Lina). It has been shown that it is the final or secondary color-condition that becomes the recessive character in each species.

If it could be shown that the primary or first condition into which each species enters represents the older or ancestral condition, we would then have in Lina and Gastroidea a condition found by Castle in pigmented versus albino and long versus short-coated guinea pigs; that is, a dominance of the ancestral or older character.

SUMMARY OF RESULTS

I . In Gastroidea dissimilis “black” is dominant, “green” is recessive. I n Lina lapponica “black” is recessive and “spotted- brown” is dominant, though not typically so. In each species the dominant color is that appearing first in the color-development of the maturing adult, and the recessive color is that appearing last in the color development.

I n each species the recessive character breeds true at once (with the possibility of the recurrence of the latent dominant). The dominant character breeds true in the third or fourth generation from a hybrid through the completely dominant line (with the possibility of a recurrence of the latent recessive).

I n each species there is progressive or accumulative dominance from generation to generation through the partially dominant line.

2.

3 .

3-36 isa Gel Mc Cr ac Re ri

I n conclusion it is evident that under the conditions of the breeding experiments with Lina lapponica and Gastroidea dissimilis, the heredity of the ahernate characters in dichromatic species differs materially from typical Mendelian heredity of alternate characters. I n the latter, the relation between dominant and recessive characters is a perfectly stable one, assuming the definite numerical proportion of 3 : I . In the former, there is apparently an actual prepotency of the dominant character that in the long run effectually eliminates or reduces the recessive character to a latent one.

Entomological Laboratory, Stanford University, December, 1905

inheritance of dichromatism in lina and gastroidea

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