THE CHROMOSOMES OF NORTIEST PULMONATE SNAILS
by
JAMES MARSHALL 1«)RD
A TiiESIS
submitted to
ORFJON STATE UNIV13ITY
tri partial fulfillment of the requirements for the degree of
DOCTOS OF PHILOSOPHY
June 1962 APPROVED: Redacted for privacy
Professor of Zoo]4gj'and Ch&irrnan of the Department
In Charge of Major Redacted for privacy
Chairman of Schoo1Graduate Committee
Redacted for privacy
Dean of Graduate Scioo1
Date thesis is presented May 12, 1962
Typed by Nancy Kerley ACNOLEDWJLNTS
I wish to express sincore gratitude to
Dr. Ernst J. Dornfeld, my major professor, for his ever willing help and patient guidance in the preparation of this thesis. Dr. Albert G.
Canaris provided assistance in the collection and identification of specimens for which I azi grateful.
An expression of thanks is duo Superintendent
"eridell T. Phips and President George A. Hodson of Skagit Valley College where much of the research and writing was done.
I also appreciate t1 effective help of my wife, Frances, and four children, Brian,
Douglas, Jean and Stuart, who cheerfully and busily gathered snails for this stndy. TABLE OF CONTENTS
Pt.ga
IPTRODUCTION ...... , . . . . a . . . I
WFTHODS AND ATYI1I ALS ...... a 7
OLSERVATIONS. . . . . a ...... 12
flonadenia f idolis ...... a s a s 1)4
Tr1oc1opss germana ...... 35
Alloßorla tc'Wn3endjn.a s e s s a s e 17
Vepericolt? co1uibiana e s . . s . s a . s 18
Iiaplotreiaa vncouveren3e ...... 20
Tar3.otremc. corte11a , , . . . 21
DISCUSSION S S S S S 5 S 5 5 s a s s s a
SUMMARY , s s s s s s i s s s s a s s s s 3 1
BI BLI O G RA PuY s s s s s s s s s s a J L.
PtAT};S . s S S S S S S S S S 5 5 5 S S S s s 39 TIlE CHROMOES OF NORTH'"EST PULMONATE SNAILS
I NT RODIJ C T ION
The value of chroraosorno studies in understanding certain evolutionary and taxonomic relationships in living organisms has been noted since the early years of this century by such cytologists as C. E. McClung, w. R. B. Roburtscin, R. Matthey, S. Makino, C. D. Darlington and M. J. D. Thite. Every species i considered to possess a unique genetic system based, along with other characteristics, on the chromosome number and chiasma frequency (the caryotype) and on the meiotic pattern.
Since this gertic system has evolved in the evolutionary process, it beco.as important to know something about the chromosome characteristics of all organisms. When it is considered that external features of the phenotype, as traditionally used by taxonomists, are conditioned by the chromosomal constitution, the relation- ship between cytology and taxonomy bocones apparent. Cytological studios have aided taxonomic studios in many casos, but the full use of caryolocy in this respect has been limited.
In 1916, Robertson, (L.1, p. 179-331) in his work dth the chromosomes of orthopterans, made the following statement: 2
tA certain doroe of parallelism oxists between chromosome structure and those characters of the body which systematists recognize as of use in determining the relationships of species, genera and families. The degree of relationship may be recotnized as precisely tri gern-coll structures as in any other part of the body. Conditions in Orthoptera confirm this view. From the evidence displayed in the series of chromosomes, descent by variation from a common ancestral saris s of chromosomes may certainly be inferred, and the degree of variation shown in these ehromosomes is paralleled by the degree of variation exhibited by sonatic structures, vihich sytematists have m&de use of in showing the relationship of species, genera, subfamilies, etc.t'
Matthoy (2t, p. 229-237), in a 1932 essay on chromosomes and systematics, str6ssed the value of chromosome numbers and forms in determining t'xonomie relationships between such larger families and orders. Dar1inçon (C, p. 8ll-3]i.) at this time also pointed out that species anal7sls could gain refinement by attention to caryolo:y.
3iflCO the time of these early expressions of the advisability of correlating cytological ar1 taxonomical studies, considerable progress has been made in thia direction. This is evidenced by the numerous lists and atlases of chromosome numbers in plants and by similar compilations for animals (Mcclung, 28; Makino, 22;
Matthey, 25). Despite those accomplIshments many animals have not boon submitted to cytoloica1 investigations and 3 considerable work remains to be done in this area of animal biology. '1-iere cytological analyses have been made, the judgements of the taxonomists and evolutionists have often been mutually supported. In other casos, however, problems which have defied taxonomists have been elucidated arid new evolutionary relationships have been proposed on the basis of information derived from the chroraosorie set. Chi'omosome cytology may therefore not only confirm the work of tl systernatist but it may shed new light on species relationships, help to recognize and separate closely related species, aid in deto.L'mining taxonomLc relationships botwoen and within families and ordo's, and in addition, re'ioal pattorns of ovolutonary divergence. Tho present study represents a caryological investigation of sono pulinonate gastropods with respect to their taxonomic relationships. Various gastropods were investigated in the early 1900's with most of the interest concentrated on the dovolopment of the germ cells and the fertilization process. In sorne cases chromosome counts were attempted as a secondary aspect of the problem, but accuracy in counting was not stressed and many discrepancies can be noted in the literature. However, some chromosome studies per se on pulinonate snails were undertaken. The 11. chromosomes of a few terrestrial 2ulrnonates, especially in the genus Iilîx, received considerable attention and the dozen or more papers pu)lished were reviewed by Navilla
p. 3S3-3C3) and 2crrot (39, p. L7-.66). In 1930,
Ponriypacker (36, p. L.]5-14.53), in a study of the germ cells of ?olygyra appressa, adc chromosome counts in that genus and presented excollent pictures of tI chromosomes. About the same time Hicnari (16, p. 2I3-289) counted the chromo- somes in Succinea ovalis while studying spormioenesis in that species. Iore recently (l9L6-l9S3) Husted and ?. R.
Bureh (17, p. Li.l0-429; 18, p. 62-61j) concentrated on the family Polygyr&dae, tudying the four genera Stenotrema,
esodon, Triodopsis and Allogona. Chromosome studios on Helix poniatia were revived in 1960 by Evans (l!, p. 129-138) when he discovered two populations containing supernumerary chromosomes. Aquatic pulmonatos have alzo received some
very recent cytological attention by J. G. Durch (Ii.., p. 9-10) and iataranjan (33, p. 103-107).
Most of t1 pulmonato enora have apparently escaped cytolo:ical investigations, as is 3hown by the fact that
White (L15, p. 171. and 20S) reports chromosome counts from only 72 of the approximately ,000 species. These 72, which largely represent the terrstria1 family Helicidae, include several aquatic species. It seems like a meager amount of information when we recognize that pulnonate gastropods are of unuaual interest to students of varitt1on, distribution and evolution. The haploid chromosome numbers considered as reliable in the Pulmonata includo i6, 17, 18, 20, 21, 22, 23, 2L.,
25, 26, 27, 28, 29, 30 and 31. White (1,5, p. 205) believes that this series does not suest polyp].oidy. Naville
(3L.., p. 353-382), howevor, suspected a polyploid develop- ment in sorno racas of Helix poinatia and proposed a scheme to elain such an occurrence. In any case, the seriation of chromosome numbers sugosts a succession of structural rearrangeraenta accompanied by duplications and deletions. The value of addirt, cytological data as a criterion for the classification of gastropods was recently voiced again (1952) by ßguayo (1, p. 2-Li..) when he noted that as many elements as possible should be utilized: not only the shell, the radu].a, the sexual apparatus, the ecology, but also, in the near future, cytogenetics. Because the soft parts are often influenced by the environment and the sexual apparatus changes greatly during development, any classification scheme based solely on theso criteria is not completely satisfactory. A chromosome study of a ,roup of terrestrial pulmonate snails common to the Northwest coastal region of the United States was undertaken in this study. The genera 6
(representing three fimilies) which are commonly found in this area are Monadonia, Alloona, Vesporicola, Triodopsis and Haplotrema. While some information on the chromosomes of Allogona arid Triodopsis from the eastern part of the
United States was available from Husted and k. R. Burch
(17, p. J4O-129; 18, p. 62-4), no references to
cytolo5ical work on the other three onera could be found,
The snails used in ihis study are classified according
to Pilsbry (0) as follows:
Class: Gastropoda Sub Class: Pulmonata
Order : Stylornmatophora Sub Order: Sigmurethra Family: Helminthoglyptidae Monadenia f idelis (Gray)
Family: Polygyridae Allogoria bownsendiana (Lea) Vespericola colubiana (Lea) Triodopsiigena (Gould)
Family: Haplotrematidae Haplotrenia vancouverense (Lea) Haplotrema sportella (Gould) 7
ME'rHODs AND MATERIALS
All ix spccie3 w3 identified on the basis of their shells. The descriptions provided by Pilsbry (L..0) were useful in this respect. The deterniinations offered no difficulty except in the genus Haplotrema where differentiation between t two species at first proved troublesome. After some experience, and with the assistance of Dr. A. G. Canaris, these species distinctions wore resolved by closer attention to lip shape and sculpture characteristics. The shells of all species are shown in dorsal and ventral view in 21a tes IV and V. The best colleotinij areas were well-drained wooded slopes covered with deciduous and coniferous trees and sword ferns. Both species of Haplotre were cinonly found in the sword ferns. In western Oregon, ilonadenia fidelis, Vespericola columbiana, Haplotreina vancouverense and Haplotreina sportella were all collected on such wooded slopes while Allogona townsendiaria was found in moist grassland pasture. In western Thshintofl, all six species were collected from leaf litter on wooded slopes. Except for Triodopsis ;ernana, each species was represented by specimens from at least two different areas. Table I shows the number of specimens examined from each collectiní area. TABLE I
Number of Specinens Collected and Collecting Sites
Burnt Woods McDonald Mount Woods, Creek, F'est, Canby, Morton, Vernon, Lincoln Bonton Benton Clackaxias Lewis Skagit County, County, County, County, County, County, Total Species Oregon Oregon Oregon Oregon Wash. Wash. Specimens
M. f idolis 3 t1. 1 3 11
T. gerniana 10 lO
A. townsendiana 12 2 34
V. columbiana 2 8 34
H. vancouverense 12 2 34
H. sportella 111. 2 The collected specimens were placed under refriGeration
(tO° F) until they could be examined. If the period between collection and oxamin8tion was loníer than about five days, the animals were kept in suitable containeri in a cool room at approximately 63° F.
Since iciot1c figures were examined, thu ovotestis was used in this study. after breaking the shell with a pair of pliers, the ovotestis was removed with fine forceps and placed in distilled water for about u-lO minutes. This operation was done under a binocular dissecting microscope at lOx magnification. The tissue was either prepared for smearing or for sectioning. The smears which gave the bettAr results were produced by a modification of the aceto-orcein suasìi method for chromosomes as outlined by Darlirton and La Cour (11, p. j5). A portion of the ovotestis was :emovod from the distilled water into a pool of i per cent aceto-orcein solution on a glass slide. After QOUb five minutes of stain action the tissue was minced very finely. The larger unminced particles were removed and an albuminized cover slip was applied with pressure to produce the smear. Permanent slides wore made by soaking the cover slip freo in 15 per cent acetic acid, dehydrating, clearing and mounting in balsam. In preparing the tissue 202.' sections a method lo used by llu.sted and P. 1. Durch (17, p. l2) was modified.
Tho ovotesti, which was usually renoved in fragment8, was fixed in Sanfolico's mixture for four to five hours, washed in five changes of 70 pox' csnt thy1 aloohol, dehydi'ae in dioxaa, c1ex'od in j1o1 and erbedded in ?araffin.
Seøtjo wert made at 12 or 114. mIcrons and staird ;;lth either the ircn ìernatoxy1tn or the Feulgen nethod. These sections, whIle not, as satisfactory for studying the chronosomes as the smears, retained cellula? orientation within the ovotestis.
Atterpts viere made to observe mitotic chronosones th other tissuc3 in order to vorify the chromosome counts obtained from meiosis. &iall piocos of tho zaantlo v.ore clipped and sr.ieared b:r the aceto-orcoin method. SquasLles of developing eiibryos wore s mi1ar1y examined. These tissues did not permIt tho oborvation of aiiy clear initotic fiuros. iltoses were observed in the spez'matogoiiia of all species however, and the chromosonie counts made on these satisfactorily supplemented those obtained from the raeiotic figes.
Microscopic observations at 970x and 1145Sx were made with a Leitz Labolu.x resoarch microscope and an Pxúerican Optical Microstar resea.'c'. microscope. Photographs were taken of selected nuclol on mlcrofile (high contrast) film 11 with a 35 mm camera. Drawinrs of chroniosotios were made with aid of a Zeiss draw1n' attachriont or a Leitz camiera lucida.
Althouçh the observations and tI data collected were primarily on t1 chromosomes, some note was taken of t1 general structure of the ovotestis and its developmontal condition at various times of the year.
Chromosome counts were made from meiotic diploteno and diakinetic figures, and from mitotic anaphases. Diplotone stares were employed to study chromosome shapes and sizes and to determine chiasma frequencies. 12
O BSEE VAT 10 NS
In Table II the charactoristic, or most commonly found, haploid chromosome number for each species is presented. The chromosomes of those snails can be cate;orized into four different size classes which are 'epreserìted in the table in microns. The number of chromosories in each class is shown for each specios. Average chiasma frequencies aro also presented. Pable II
Comparison of Chromosome Numbers, 1ize C1asss arti hisma Frrguencies
liaploid Average Chroin. Class i Class 2 Class 3 Class t. Chiasma Species I!umber 7..l0 ' 5-6.5 j 3-1.5 ,,' 1-2. , FrAquenoy
Rs].rninthogiyptidae 6 L fidelis 29 3. 22 73 Polygyri dae T.grmana 31 6 2 77
A. townsendtana 26 2 5 19 67
V. co1biana 30 2 t. i6 8 7i
Hapiotreinatidae H. vancouverense 30 1 5 2L. 67
H. sportoila 29 9 20 68
Detailed data for each species aro provided in the paragraphs which follow.
7-, 114.
Monadenia fidelis (family Helminthoglyptidae) Plate I, Fig. 1; Plate II, Fis. 1 and 2
Haploid Nunibors Dip].oid Numbers Specimen No. 27 28 29 30
i (Burnt ":oods, Ore.) o 0 3 0 o o i o
¿4 o 2( ) o o O o o o
14. o o o o 3 ( 't ) 19 22 7
6 o 2 0 0 L. (Canby, Ore.) 1 2 o
5 (Morton, Wash.) O 0 9 0 O O O O
lt O O ) O O Li. O O O
7 (Woods Creok, Ore.) O 0 8 o O O i O
o o o o 8( 't ) O 1 S o
n ) O 0 lO O O O O O
10 (Morton, .ash.) 1 2 8 0 o o o o
1]. (1oOds Creek, Ore.) 0 0 7 0 o o o o
A variable haploid chrornosorie number was observed in four specimens of this species. The other seven showed a constant count of n 29 or 2n 58. Since n 29 ws the most frequently recorded figure, this is probably the basic haploid count while t1 numbers 27, 28 and 30 represent deviations.
Twenty-two chromosomes fall within the Class 3 range; six are smaller and one larger (cf. Table II). In cells with reduced or incroasod haploid number, the chromosome is loss or gain comas from the smaller elements. An average chiasma frequency of 73 was recorded (basod on 12 measure- ments). t'ith the exception of three small rods, the chromosomes have either a median or a submedian centromere.
Triodopsis ßormana (family Polygyridae) Plate I, Fig. 2; Plate III, Fig. i Haploid Numbers Diploid Numbers Specimen
3. (Mt. Vernon, V]ash.) 1 1 11 3. 0 0 i O
2( ) 0 0 3 0 0 0 0 0
0 0 2 0 0 0 3. 0
) O O L. O O O O O
) 1 1 2 0 0 0 0 0
6( ) 0 0 3 0 0 0 1 0
tt 7( ) 0 1 2 1 0 0 0 0
) 0 2 3 1 0 0 0 0
9( ) O O o o o o o
l0( " ) O i t. O O O O O
In half of the specimens ox' T. germana studied, variable haploid chromosome counts were recorded, though 31 was the number most frequently observed. The haploid counts of 29, 30 and 32 appear to represent nuclei in which chromosomes have been lost or :aird in the process of celi division. of the 33. chromosomes, six large ones fall into i6
Class 2, 23 into Class 3, and two small ones into Class L.
In cells which howec1 deviit1ons from 31, the loss or gain in chromosomes came from Class 3 or Class I, Twenty-three chromosomes were observad to be neta- centric or submetacentric and eight were acrocentric. In each nucleus one of the two small chroniosonies did not oxcoed l. microns in length, whereas the other measured
2. microns. All of the bivalents displayed at least two chiasmata oxcept the smallest chromosome which formed only one. Lioro than two chiasmata wore usually noted in the 1arer members of the set. The chiasma frequency per nucleus averaod 77 (based on six cell counts). 17
Alioona townsoncliana (family Polyyridae) Plate I, 3; Plato III, Pies. 2, 3 and t.
IIaploid Numbers Diploid Numbers
Spec irie No. 26
i (Burnt Woods, Oro.) 3 0
2( ) 2 0
3( ) 14. 0
) iS O
't ) 3 1
6( ) 2 o
0 7( t, ) 8
12 14.
9( ) 1 0
¶1 l0( ) 3 0
ll( " ) 3 0
" 12( ) C o
13 (Morton, Vlash.) 3 o
iJ4.( ) 5 1
The only haploid number ob;erved in A. townsondiana was 26. The chromosomes were 1arer in this species than in the other pulmonates investigated and no representatives
of Class 14. were scored. Two chromosomes measured 10 microns at diploter. Five of the chromosomes fall in the Class 2 range and nineteen in Class 3, The average chiasma frequency of 67 per nucleus (13 cell counts) was lower than that recorded for T. germana and V. columbiana in the same f ainlly. The two very large chromo- somes each showed four to six chlasmata, and the large and medium sized chroniosoies hd two or three chiasmata per bivalent. All of tho chromosomes are metacentric or subnetacentric. Vespericola columbiana (family Polyyr1dae) Plate I, kig. L; Plate III, Figs. and Ci Itaploid Numbers Diploid Numbers SpeciienNo. 3O CiO62
i (Burnt Víood, Ore.) O 2 0 0 0 0
1 2( ) 3 Ì4 o o o o 0 2 0 0 0 0
O lo O O O
(McDon. For., Ore.) 1 0 14. 1 0 0
6( ) 2 L o O i O
7 (iit. Vernon, ash.) 0 6 0 0 2 0
) 6 1 2 o o
9( ) i 5 3. 2 0 0 lO( ) 0 3 0 0 0 0
O 1l( ) 14- 0 1 2 o
12( ) 0 9 0 0 1 0
) O 5 0 0 1 0
n ) O O 0 0 2 0 1
Varyiní chroriooiio counts rc observed in this species, but the haploid nuriibr 30 oecurs iwt frAq&ent1y, Chromo8omes from every ¿1ze c1.z were ipi'eserted with 1) of the 30 e1eexits fa111r in the Cla$3 3 croup. Two very 13'ge met.centric chromosomes, simtDr to the large chromosortes of A. townsendiaria, ere &.served. Four
1arge chromoories be1on to Class 2 while eiht Class L e!eriients were present. Thtì chromosomes were all metacontric or submetacontric except f s i small rods.
In 'el1s containing 29 or 31 chromosomes, th loss o gain involves eleLlents from Glass ..
The two very larçe bivalents each displayed four t jx chiasLlata. Tho largo ar riediuiri-sized bivalents usually showed three, and the small bivalents f orid a tuo chiasmata associa;ion. The avorae chiasma frequency was 7t. (based on seven coli counts). 20
Haplotrema vancouverense (family Haplotreniatidae) Plate I, Fig. 5; Plate II, Figs. 3 and t1. Haploid Numbers Diploid Numbers Specimen No, 30 60
i (Burnt oods, Ore.) 2 0
2( ) i O
0 3( 't ) 37
ti ) i
) 10 0
0 6( ) 10
0 7( " ) 11
8( ) 5 0
6 0 9( ) lO( ) 2 0
0 il( ) 10
12( ) 10 0
13 (::t. Vernon, 'ash.) 3 2
iI( " ) S O
The haploid number 30 was consistent for t hli. specimens of H. vancouverense investigated. Twenty-four are small and of the Class 1. range, five fall in Class 3, and only one in Class 2. Two chiasniata per bivalent were recorded except in the six larger chromosomes wre tÀree to four were noted. The average chiasma frequency (based 2].
on eight cell counts) was 67. Classified by centromere position, the chromosonies of this species distribute as follows: one large metacentric, five medium and five small metacentrics, one small sub'ietacentric and 18 srnnll acrocentrics. Haplotrenia sportella (family liap].otrematidae) Plate I, Fig. 6; Plate II, Figs. and 6 ilaploid Numbers Diploid Numbers
Specimen A2t ..2 i (Burnt :oods, Ore.) 2 0
ti 3.6 2( ) 0
n 3( ) 6 0
Ij( n 2 0
( ,, ) 6 0
6( f' ) 8 0
Il 7( ) t_ o
t ) lS 1
't 9( ) 6 0
1O( I' ) 12 0
1l( " ) 8 1
12( ) 10 0
13( " ) 12 0
n 5 0
15 (Mt. Vernon, 'nash.) 10 1
16( " ) L. i. 22
H. ortella speciiions provided a consistent haploid number of 29 with Class L. size chroniosos making up 20 of these; nino fall in Class 3. Two chiasniata pox' bivalent wero usual in this species except in the nine larger members of the set which showed three to four. An average chiasma frequency similar to that of II. vancouveronse was noted (based on 1]. cell counts). Nineteen of the chromo- sornes are !netacentric and ten of the small ones aro aci'ocentric. Sorne observations on the hIstology of tho ovotestos were made from the prepared sccioris and deserve comment. An ovotestis is a compound acinar Gland in which each lobule, or acinus, is surrounded by a singlo layer of nuclei contained in a syncytial envelope. Sperm develop :5n the interior of the lobule while the egcs are produced around the periphery. A cross-section of an ovotestis shows the acini in varying stages of rturation, but in a given acinus the Canietes are all at the same stage of development. This histological description applies to all six species studied. In the SpGCimOflS prepared in t1 months of December and January, only a vestige of the ovotestis was found. Apparently this orean de'enerates after the reproductive season and develops again the following breeding season. 23
Th5s ìLtorn 's apai'ent i aU p;cLos. In i. fde1is and .! c.uabiana the ¿onc1 shoîd a re.ì.ictton in size in Au3t in1 30ptibor nd n1nc to dc1ino throh
October' a;d ovrib', 13r Deceraber, only ve3tLgtal, non-funotoua1 stricturo rtaained. The nmturatlon prt.o :iRs f3PCß1 fl these two species and in T. ¿erriana by p1acinr them in a i'eonhousa tn Decombør and .fanu,rr.
In Fohrury and ch sperm production cs tkin placo. 2L.
:jisci SSION
In considerinr the caryotypos of the snails studied
here, the first comparison might be xiiade between the three
families. M. fidelis, a member of the Helminthoglyptidae,
has only ono 1are chromosome while most of the chromosorne8
be1on to the Class 3 group (3-4.5 microns). The
representativos of the Polygyridae, T. germana, A.
townsendlana and V. columbiana, show a greater number of
larve chromosomes (Classes i and 2) than either the
Helmintholyptidae or the Haplotrematidae; moreover, the
caryotypes of tse three ¿enera resemble each other more
than they do the genera of the other families. The two
very large chromosomes of A. townsendiana and V. columbiana
are conspic: usly larger than any in the other two families.
In the Haplotrernatidae, represented hero by H.
vancouvereno arid H. sportolla, most of the chromosomes
are of the Class Lj. rango (1-2.5 microns), this small size
class beine poorly represented in the He1mintholyptidae or Polygyridae.
The family Haplotrematidao has the lowest average
chiasma frequency, 67-68, which may be expected because
of the preponderance of small chromosomes. A. townsendiana (Polygyridae) possessiny distinctly 1arer chromosomes, shows a siLnilar frequency, but its haploid number is only 26. ,.'.
The soiewhat higher chiama frequency of M. fde1is (73) of IIo1mintho1î2tida3 reseib1os those or T. oxiana (77) ar V. co1umbi.i:a (7t) in th Polygyridao. .A1thouh the chrornosoni nux.bor varies in the .o1ygyrid goncra tuded 'ore, the number of ch'omosome arr, obtained by countinr each 1etace;2tric olemerit as two arms and each crocentric elenerit as one axm, as sugestod by obertson (I1, p. 293-302), is siiii1ar for the three genra. Thua, T. geana, which possesses L6 metacentric or subnietacentric chromosomes an i6 aocentric elements, has 108 arms. In A. townsendiana, with 2 matacentric or submetacentric chromosomes, the number of chromosone arms ic 1014... V. coluinbiana, which has i8 nietacentric or subnetacentric elements and 12 acrocentrc chromosomes, has 108 arîn. This suggests that either fusion or dissoci- ation of chromosomes has occurred in this family. iusted and P. R. :surch (18, p. 6261), after their studios on AlloCona profunda, whose haploid number is 26, assumed that ovo1utonary chance occurred in the polygyrids through a radua1 increase n chromosome number and consequently regarded Al1ojona as a primitive genus since it has a low chromosome number. This viewpoint, however, cannot be well defended since evolutionary change may involve decrease as well as irrease of chromosome number. Matthey
(2S, p. 35) considers the lower chromosotne numbers to be 1e38 primitivo in ciio vrtebrato farnj11cs duo to the occuri'ence ci' csntrl c fus t on (a -r'an10 at. on inVOiVlJlL.
btei'm.nai breaks in two arocontric ciroznosoie to Cor a ¡netaceatric). WhIte (, p. (.6 ar1 19].) notes that a dcz'a2e in 1')ìUO8O nuxiibez' thxouh centric fusion can be a.ccomplished with greater ease than tho disciat1on of a c1-ìrouooi (one, tacenttc to two tcrocentrics) which would probably requiro a pernîorary eiemt. The pre3enee of ruported supeinuinerary chromosomes in the pulmonates, hosever, might enhance the issocia1ioi process, resulting in an lrzcroa.e in chromosome nunbers.
Rusted and P. R. Burch (17, p. I.1O-I.29) round the typca1 haploid numbei of the genus Triodopsis from
virginia to be 29. Inforn.tion on contromere position in tl chromosries was not prasentcd and consequently, a chromosome az comparison between the western T. germana, with the prsdminant haplold number of 31, and the eastern forLis is not possible at this time. The genus Haplotrerna is divided into four roups by Pilsbry (Lo, vol. 2, p. 202-231). H. vancouverense is placed in th h. caelatum group while H. sportella is in the I. spore11a group. Vancouverense and sportella show a real dfferonce in their haploid chromoso number (30 vs. 29), which Is not obscured òy variability. SInce the 27 two chromosome sets ì1so differ in size characteristics, the problem of their homologies cannot bo clearly resolved without such evidence as may be derived from synaptic patterns of interspecific hybrids, if such are produceable. One riay conjecture frorri the extent and distribution of the size differences that a considerable nuner of structural rearrangements have occurred in t evolutionary divergence of theso two species. The nuclear analysis of othor species of the ¿enus (which occur mostly in California; one group is in the eastern and central UnIted States) could presumably add information of value in deciphering these caryological relations. The variability of chromosoms counts obsorved in the three species, M. fidelis, T. germana and V. columbiana, deserves some attention, The literature, as reviewed by Husted and P. R. Durch (17, p. Ì4l), reveals that considerable aneuploidy exists in the Pulmonata, with varying chromosome numbers occurring between individuals of the same species. Husted and ?. R. Durch (17, p. Ll3) found a variation in chromosome number in L..o per cent of the specimens of Triodopsis fraudulenta (2n 58) since specimens with diploid nuclei of S9, 60, 61 and 62 vr. recorded. Evans (15, p. 129-138) observed this sanie type of variation between individuals of Helix pomatia an also 23 noted 3perinatogonial variations witlilu individuals as found in the present study. Jixcept for intraindividual variations, these cases of apparent aneuploidy could represent supernumerary chroiuosomos as suç(estod by hito
(L5, p. 162) and Jvnrìs (ls, p. 129-138). in the pu].uonates of tho present study, the variation in chromosome nu.nibors, where it occurs, exists entirely within the individual and involves - as far' as a deoartui'e from the basic number is concerned - a minority of the spermatocytes, most of which still retain the basic chromosome number. This suggests that the deviations are due to mechanical accidents during cell division, such as non-disjunction or dislocrtion of the chromosomes from the spindle though neither of these aborration was directly observed. This typo of chroinosomal varlabion is apparently cozrunon in those pulnonatos and could conceivably, under appropriate conditions, play a rolo in the origin of races with fixed chan{e in the chromosome nwrter. This may have occurred in ?o1yyra aprossa (a member of the Po1yyridae) since Husted and P. R. I3urch (17, p. L27) recorded specimens from
Virpinia with haploid counts of 29 while Ponnypacker (36, p. Il5-I53) observed specimens from ew Jersey with 31 haploid e1onents. Apparently members or the Pulmonata can tolerate duplications and deletions ol' certain 2
c1roiD3a1 1intu ciw3 .i.1Lo i1 aocoipany1ig
3trictuia1. In thi i'ooe oC sjooia!on.
Suci pothis vouLi ')d 1r 1i.re v;.t' he obrvtc1
or'ri.on of ono.oiu u biY3 !n th j)U1c1cna*3s (1i..te,
3. 17h) acd bho tion b wh10 ('+L., p. 132-133) that the hronosorn nunbf-3r tri pubnonte species baa been a1tere raìuai1y br to thp1icat1on ii' e1iin.riattrn of oxi3tîri, hromoo'ios rather thri h po].yploidy.
The 1sck of evidence for po1yp1oiy In hts croup of he'naphocUtIc nLna13 has arouoed eonsiclei'ahle interest.
Herma?hrodttic anLia1 o ould tho ofet Lcally produCe
totraploic't offprtng sthco the psttLn of . sex cirouo-
3OO :icintsri te riot tflVOiVA(I. O possibi1It of po1r
)1oid.y in Helix poaatta had been considered by Nnville in
1923 (31;., p. 33-33) when he reported races with haplold fltlrnbor:3 of 9, 18 nd 27. iowever, P*rrot and rrot (38, p. 203-209) in their sudiea on the sìme pecis, fro the seime localitIes, :ere unable to 'ind a count t}at vnried frorr n 27. 'vans (1, P. 129-138) in rec&nt ohervat1ons of T1 pceti found no polyploid spocmrnens, but found that one to two per cent of the prirry spermatccyt were tetraploid and sttempted to explain this on the bacis of nuclear f!3son. In the present study polyploidy was not observed In any cells of species. ThEa que3tion of sex chroiìosor1i ..n 3sveï'ai p1ìonates has JorL ¡ai8ed d such ,oi'e doscr1bd by J. L. Pe'rot
(37, p. 3í)7.43!.). it Is difficulb to see how sueh a
uic1iariirn could function in hrraaphroditic organisrs, aiiC
White p. 278) foo1 that irwe io1'3 wlw cIaiì to iìavo seen sex chromocors in puLiionates vare mistaken In tkieir obsorations or in hc Ir intorpretatlon. evidence was found for sex chroriiosomos ifl the pulxuionat.e species involved in this st1dy, since netthor heteronorphic pairs nor unlvalonts wore observed. 31
ix species of ilorthwest pulnionate snails wore exaiined cyto1o'ica11y and the following haploid chronosouo natbers were recorded: Family: !Ie1mintho1yptidae i:onadenia fidelis ...... 29 1aiui1y: k>olyfyridae
Triodopsis erntana ...... 31 A11oLona towusnciax.a . . . . . 2G Vosporicola columbiana . . . . 30 í'1arnily: llaplotreraatidao
Haplotrema vancouverense . . . 30 llap1otroa sportuila . . . . . 29
As a furthsr means of coruparizon, the chromosomes of each spocies were classified into size croups. Class i chromosolEes ir.cluäd those 7-10 iiicrons in 1enth; Class 2,
5_6.; microns; Class 3, 3-.5 :aicrona; and Glss L, 1-2.5 microns. . fidelLs possesscd mostly chx'oirLosories of tne
Class 3 type and an average chiasrna freq'ncy of 73 2er nucleus. The Fo1ygyrid sp2cies characteristically shoJv3d Lix to seven large Ci.fOOSOfliO5 of Gla.ses 1 anc 2, rerraented oy only c.rìe e1eneni in ths other two families.
.4veeae chiasizia freqencis wei 77 nd 7L. for T. -eraana and V. eo1umbian rspectivo1y, bi nly G7 foi' A. townsendiana vihich had fewez' cm1or..oso:s, The cironcsones 32
of Ii. a:id H. jorte11&. vee rriain]' f tJias L.
3:-:e sv th, ave'.' ch!ari £:'Iuoriciì3 were 7 an! 68
A1thou-'h thr*e 3pc1t3r3 of th Po1yyridae ha
chÓr.vo:.9 thSt d1fÍ'x'ed tn number (26, 30, 1) ariz in
size c&.strihu±iorL, the rtunthr of cioaore ais (deti'.td.ned by a coInpwTßon of imetacentric, sibretcentrJ.c an'
'crocentr1c 1eints) ?!.8 closoly similar. Thts iugests
thRt 9i(hr ñsion er di3ociatior1 ÖÇ chr000rto h taken pi8ee.
Two Of the fou.r 3pi ccaploxes withizi the genus
Erap:ot1e11L aro rpreontd ii thc tudr jr H. vancoiiverone ad porte11a. Theie two specie8 aa'e d.stinutshab3.e o.1 n ca'yo1oica1 basis, conES itnt1y In nuiber
iz dlstr.tbution of thfl cr(tOsox1Os.
In three species, variable chrornosie ourt were rcorad within indivic1w18, Jperniatocyti of M. fi1s11 had hp1od nuiber of 27, 2(, ?9 and 30. Counts *f ?9
30, 31 and 32 were scored in T. ;ermana cthi1 in 'T. co1iimbian the variation vw. hetwon ¿9, 31) and 31. The@ va:iation riay i'epreent the resu1t of fa1ty call
&vûin meohanisius. Howover, the ton.tency toward this varIation in ChrnrnO8orae ni..wtber, which ILas boen observed
fl ot;!tei' puimonato sectes may hvt Implications in the zj:c!a5io:. p_'cez. The du1ict!.oux r eliui:atin of
Oi OZ tJO Lt tLLe, o1od ith croma1
y account for bhe apparent cradu'].
xLc2o.:i or docrcao inì chrio ribor2 in t
1ro:4íLt z.
Po1y1od zpentoto wex'e r.ot obsrvei In ths
na:.1$, and tb cquence of hap1od nnbr, 26, 9, 30
ad 31, roerd here cìoc n that any of these
peci 1i th result of polyplo.d thve1opent.
k evidence W&8 found foi sex chromosories, as would have be,n 1ndcated b7 unìilents or heteroiorijc bjtlent,, hich dId nt occur in any of the spueie.
:i ii ovotostis, a copo'ìr acin.r land, srn r3 produced In th lumen of each acthu3 .nd es dovlor
c,und the porlphery. Tho Gonad apparently declines after
the reproductive season and reoierct.e.s the foliow.tn
as on, 3)..
BIBLIOGL{ !PHY
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le?. 'Ihitney, U. . T herrnaphroditc 1and and gorI1 cells of Val) onia puichella Mull. Papers of the ¡(Ichigan Academy of cionce, Arts and Letters 26:31l-38. l9O. APPENDIX PLATJ I
The ilaploid Cb.roinosoms at Late Diplotene (ail figures x 1000)
Fig. i - Monadenia fidelis n 2° (fcri1y He1nhintho)lyptidae)
Fig. 2 - Triodopsis germana n - 3]. (fnii1y Po1yyrdae)
Fig. 3 - A].logona towneendlana n 2- (family Polygyridae)
Fis. 14. - Ve8pex'icola co1unbiana n 30
( tmi1y Po1yyridae)
Fie. 5 - Haplotrerna vQncoiverense n 30 (ri1y !Iap1otreatidae)
Fig. 6 - Ilaplotrenia sportella n 29 (f azuily Iiaplotrematidae) tj.0 , 4s s' e f 1.. es.. 5 7 0 . i .O a s
FIG. I FIG. 2 4'.'... ô.r.I,l4,O.. cPjS
. t' bs s
FIG. 3 FIG. 4
0 I ØK' 11. . s $ .3e. 'e te.Sc., ( o. 4)
FIG. 5 FIG. 6 t'TrR1? f L Mejotic Chromosoues of {e1minthnL1yptidae and Haplotrematidae (all 1.ure z 1000)
Fig. i - Monadsxiia fidelis - 1itt (iplotene; 25 OhPOmOBOm6S
Fig. 2 - L1owcieria flce1iz -m6bap&se i
Fig. 3 - Hapiotrema vancoi.vcrerise i&te ipio',o; two ends1t of ton 'break off of one t'valent are siov:n.
Fig. I. -Hpiotreraa vancouverense - metaphaße 3.
Fi;. S - 9lt' portei1a - late dtpiotne
Fig. 6 - liapiot'enia sperteiia diakinezis Ò e , 0, - 4 O ) g)
FIG. I FIG. 2
FIG. 3 FIG. 4 O,.
s.l. I t 's s e, t
FIG. 5 FIG. 6 ?LI.TE III
reiottc Chroocomec cf Pclygyrid&e (al]. figures x 1000)
Fig. i TrLodopzis germana late dipiotene; .0 CflO!!tOOflZ
Fig. 2 - Allogona townzendiana - early anaphae i
Fig. 3 - Aliogona townsoniana - anap'c.ase i
Fig, Iii. - Ailogona towrsendiana - ciplctene figures
Fig. -Veperco1 coluzubiara - late dipiotene; 31 chromo.ornes
Fig. 6 - Vespericola columbiana - anaphase 2 .;
f,. 4J
O .'."T*- e
FIG. I FIG. 2
0 ,ea .1 O b. G ' b (1 e
FIG. 3 FIG. 4
w ¿s
s
FIG. 5 FIG. 6 PLAT:: IV
Zhells of Northwest Pulmonato Snails - Dorsal View (t'-11 fic.re nat'r3. siz)
Fig. i - 1Tonadenia f idelis
Fig. 2 - Triodop6is germana
Fig. 3 - Allogor1a townsendian&
Fig. 14. -Vesporcola coluibiara
Fig. ' -Rapiotrea vncouverense
Fig. 6 - piotreira sjorte11a s
FIG. 2
n
FIG. 3 FIG. 4
O
FIG. 5 FIG. 6 of Jorthwest Pulmonate Sra1l - (all figures natural size)
i - Toriadenia fideii
- l'riodopsis germana
3 - Allogona townsendiana
Vespericola c olumbiana
5 - Hap1otreni vancouverense
6 -Hplotreri sportella I.I
C. r --
r ,- I- ç L'.
F1G 5 FiGe, 6