Esko Suomalainen

Evolution of Parthenogenetic Insects

Even though fertilization is one of the basic processes of life, many organisms reproduce without a union of gamete nuclei. In parthenogenesis the egg cell develops into a new individual without fertilization. Parthenogenesis is a fairly common phenomenon in the animal kingdom, so that parthenogenetically reproducing forms occur in most animal groups. There is no need to enumerate all the groups in which parthenogenesis has been found; for details the reader is advised to consult Vandel’s (1931) review. Among the insects, a large number of parthenogenetic forms are known. It is to be noted, however, that parthenogenesis has so far not been found in such important orders as Odonata or Hemiptera.

On the sex chromosome trivalent in some Lepidoptera females

In four of the moth species investigated, viz. Witlesia murana, Scoparia arundinata (Pyraloidea), Bactra furfurana and B. lacteana (Tortricoidea) the metaphase plates of the first meiotic division of their oocytes show a trivalent in addition to the normal bivalents. It evidently has its rise in a transverse break in one of the conjugated chromosomes. Two sex chromatin bodies can be seen in the female somatic cells of three of these species, whereas other species with a normal XY bivalent have only one. These two sex chromatin bodies are unequal in size, and their sizes bear approximately the same relation to each other as do those of the two smaller chromosomes of the trivalent. The “broken” chromosome is evidently the Y chromosome. The sex chromosome designation for the four above-mentioned species is thus XY1Y2 for the females and XX for the males. The sex chromosomes of the four species are among the biggest of the respective complements. This supports the view that the big chromosome to be found in several Lepidoptera species is the sex chromosome. It seems that in animals with holokinetic chromosomes an excessive fragmentation is hindered, at least in the case of the sex chromosomes, by its deleterious effect on the balance of sex-determining genes.

On the chromosomes of the geometrid moth genus Cidaria

Summary1.The oogenesis of 44 (48) species of the Geometrid moth genus Cidaria has been studied. Spermatogenesis has been studied in two species only.2.The most common (haploid) number among the Cidaria species so far investigated is 30, which is likewise the number second in commonness among the Lepidoptera as a whole. Most (33, or 75 percent) of the species have a chromosome number between 29 and 32, like most of the other groups of Lepidoptera.3.No species has more than 32 chromosomes, whereas eleven have less than 29. The smaller chromosome numbers found are 28, 27, 25, 20, 19, 17, 13 and 12.4.The great differences in chromosome numbers between closely related species are of interest. Such discrepancies are found in the subgenera Thera (variata and obeliscata 13, firmata 19, cognata 20 and juniperata 30), Lampropteryx (minna 17 and suffumata 32), and Hydrelia (testaceata 13 and flammeolaria 30).5.The chromosomes are clearly bigger in the species with a low chromosome number than in those with a high one. In the chromosome sets of most Cidaria species studied the chromosomes are approximately equal in size.6.Photometric measurements revealed that the DNA-content of closely related species is almost equal, in spite of great differences in chromosome numbers. This is also true of the subgenera investigated. This indicates that one chromosome in a species with a low number of chromosomes corresponds to two or more chromosomes of another one with a high chromosome number.7.The discrepancies in the chromosome numbers among Lepidoptera have not arisen from polyploidy or differences in the degree of polyteny. They are due to “fragmentations” or “fusions”, which are rendered easier by the diffuse kinetochore.8.It is obvious that in animals with a diffuse kinetochore some mechanism, possibly the location of sex-determining genes, reduces the role of chromosomal rearrangements in chromosomal evolution from what the diffuse kinetochore otherwise would allow.9.Contrary to earlier assumptions of the author, chiasmata are not formed in the bivalents during oogenesis in the Lepidoptera. This is especially evident in preparations stained with Feulgen, when the elimination chromatin contained by the bivalents in the female remains unstained.

Genetic polymorphism and evolution in parthenogenetic animals : Part 9: Absence of variation within parthenogenetic aphid clones.

SummaryThe enzyme gene variability within parthenogenetic clones of Acyrtosiphon pisum has been followed by gel electrophoresis. No variation was observed within any clone. One enzyme locus was found to vary between clones. No evidence was found to support gene recombination due to the alleged endomeiosis. This hypothesis is proven to be also theoretically untenable. The low average heterozygosity in aphids is explained as a result of directional selection operating upon the parthenogenetic aphid clones, as a consequence of which the heterozygosity is lowered.

Achiasmatische Oogenese bei Trichopteren

No chiasmata are formed in the oogenesis of the caddis flies Limnophilus decipiens and L. borealis. In the Trichoptera, in likeness to what has been found in earlier cytologically analysed cases, the achiasmatic meiosis is confined to the heterogametic sex. The orders Trichoptera and Lepidoptera share the following cytological features: a) The female is heterogametic. b) No chiasmata are formed in oogenesis. c) Chromatin elimination takes place in the first meiotic division in the egg. d) In the Lepidoptera the chromosomes are holokinetic. This seems to be the case in the Trichoptera, too. e) Apyrene sperms are common. f) The most frequent chromosome number is practically the same: 31 in the Lepidoptera and 30 in the Trichoptera. These cytological similarities obviously originate from a period preceding the divergence of Trichoptera and Lepidoptera; this branching took place at the latest before the tertiary period. The preservation of these cytological similarities for at least 60 to 70 million years is an indication of the great stability of such cytogenetic system.

Zur Zytologie der parthenogenetischen Curculioniden der Schweiz

ZusammenfassungIn der vorliegenden Untersuchung werden die Chromosomenverhältnisse von 6 bisexuellenOtiorrhynchus-Arten und 16 parthenogenetischen Curculioniden aus den UnterfamilienOtiorrhynchinae undBrachyderinae näher behandelt. Das Untersuchungsmaterial stammt aus verschiedenen Orten in der Schweiz.Alle untersuchten bisexuellenOtiorrhynchus-Arten haben dieselbe Chromosomenzahl (2n=22). Sie sind also durchgehend diploid mit der Grundzahl 11. Das Geschlechtschromosomenpaar besteht beim Männchen aus einem X- und einem kleinen Y-Chromosom.Alle untersuchten parthenogenetischen Curculionidenarten sind polyploid. Triploid sind 11 Arten:Otiorrhynchus chrysocomus, O. pauxillus, O. salicis, O. singularis, O. subcostatus, O. sulcatus, Barynotus moerens (pentaploid in den österreichischen Kalkalpen),Polydrosus mollis (diploid in Finnland und Polen),Sciaphilus asperate, Strophosomus melanogrammus undTropiphorus carinatus. Tropiphorus cucullatus ist tetraploid undOtiorrhynchus anthracinus pentaploid.Zwei von den untersuchten Arten,Otiorrhynchus rugifrons undO. niger, weisen in der Schweiz sowohl eine diploide bisexuelle als auch eine triploide parthenogenetische Basse auf.Drei Arten,Otiorrhynchus scaber, O. subdentatus undPeritelus hirticornis, haben in der Schweiz sowohl eine triploide als auch eine tetraploide parthenogenetische Rasse.Im Ovarium eines triploiden parthenogenetischenOtiorrhynchus scaber-Weibchens wurde ein hexaploides Ei mit etwas mehr als 60 Chromosomen gefunden. Der hexaploide Chromosomensatz in diesem Ei ist offen-bar durch Verdoppelung der triploiden Chromosomengarnitur entstanden.Ein Größenvergleich der zytologisch verschiedenen Rassen bei vier Cureulionidenarten zeigt, daß die Polyploidie auch bei den Curculioniden eine Größenzunahme der Tiere mit sich bringt.Ziehen wir sämtliche vorläufig zytologisch untersuchten parthenogenetischen Rüsselkäferarten und -rassen, insgesamt 30, in Betracht, so ergibt es sich, daß nur eine von diesen (Polydrosus mollis in Finnland und Polen) diploid ist. 21 sind triploid, 6 tetraploid und 2 (Otiorrhynchus anthracinus in der Schweiz undBarynotus moerens in den österreichischen Kalkalpen) pentaploid. Die große Mehrzahl der parthenogenetischen Curculioniden ist also triploid. Die vorläufig zytologisch untersuchten parthenogenetischen Curculioniden und ihre Polyploidiegrade sind auf S. 644–645 verzeichnet.In allen genauer untersuchten Fällen, in denen eine Curculionidenart entweder sowohl eine bisexuelle als auch eine parthenogenetische Rasse oder mehrere, dem Grad ihrer Polyploidie nach verschiedene parthenogenetische Rassen hat, weisen diese Rassen eine verschiedene Verbreitung auf. Die wichtigste Ursache zu der verschiedenen Verbreitung der betreffenden Rassen ist offenbar die Polyploidie, und zwar wahrscheinlich dadurch, daß sie anscheinend zu einer Veränderung der Reaktionsnorm und des Lebensoptimums der in Frage stehenden Rassen geführt hat.Der relative Anteil der polyploiden parthenogenetischen Formen in der GattungOtiorrhynchus ist in Fennoskandien bedeutend größer als in der Schweiz und in den österreichischen Kalkalpen.

Genetic polymorphism and evolution in parthenogenetic animals. IV. Triploid Otiorrhynchus salicis Ström (Coleoptera: Curculionidae)

The genetic variability at 20 enzyme loci in natural populations of Otiorrhynchus salicis Strom was studied by starch gel electrophoresis. Altogether 135 weevils were analyzed. The samples originated from a diploid bisexual population in Austria, from four triploid parthenogenetic populations in the Carpathian mountains, and from three triploid parthenogenetic populations in central Sweden. Altogether 16 different genotypes were found in triploid parthenogenetic populations. Two major types, comprising 39 out of the 76 parthenogenetic individuals, occur both in Scandinavia and in central Europe. The less frequent types can be derived from these through mutations. O. salicis is a flightless insect, which has been assumed to have overwintered the Wurm glaciation in icefree refugia in Scandinavia. The overall genetic similarity found in the material suggests that the parthenogenetic race spread to its isolated Scandinavian area in postglacial times.

The mode of meiosis in the Psyllina

Summary1.The spermatogenesis of six psyllids and the oogenesis of Psylla försteri have been studied. The haploid number n=13 was found in 4 species, all with an XO system of sex determination. 13 may well be the modal haploid number in the genus Psylla.2.The chromosome complement of the only XY species, Psylla corcontum, with n=11, is probably the result of two chromosomal rearrangements which have led to the formation of a neo-XY pair.3.Psylla försteri is an XO species in which the haploid set consists of only 8 chromosomes, one of which is very large. As the amount of DNA in this species is approximately equal to that in the 13-chromosome species P. sorbi, the large chromosome obviously corresponds to 5 or 6 chromosomes of P. sorbi.4.A diffuse stage, which leads to a considerable increase of nuclear size, is typical of late pachytene to late diplotene of spermatogenesis.5.In contrast to the other cytologically studied Homoptera Sternorrhyncha, the bivalents of psyllids co-orientate at the first metaphase of spermatogenesis. The following anaphase is therefore prereductional.6.In the oogenesis of Psylla försteri the bivalents always seem to have auto-orientation, which means morphological postreduction at first anaphase.7.The karyological picture is that of an organism with a diffuse kinetochore.8.The Hemiptera and the plant genus Luzula both have diffuse kinetochores. The reason that the chromosome numbers in Hemiptera vary far less than in the genus Luzula may lie in the existence in the Hemiptera of a delicate system of sex determination sensitive to any change in chromosome number and structure.9.Cytologically, the Psyllina lie between the suborders Sternorrhyncha and Auchenorrhyncha.

The solenobiinae species of Finland (Lepidoptera: Psychidae), with a description of a new species

The Finnish Solenobiinae are revised. This subfamily is represented in Finland by two genera and seven species of which three are parthenogenetic: Solenobia triquetrella (Hubner) (also reported from Denmark, Norway and Sweden), Solenobia lichenella (Lin.) and Solenohia fennicella n. sp., which is described here. Of the remaining species, Solenobia charlottae Meier (also recorded from S) and Siederia rupicolella Sauter (also recorded from S) are eartier known only from the mountains of Central Europe. Solenobia furnosella Heinemann (recorded also from D, N and S) and Siederia pineti (Zeller) (also from D and S) are bisexuals earlier known from Finland. – Notes for identifying each species and their distribution are given.

Chromosome number variation within Philaethria butterflies (Lepidoptera: Nymphalidae, Heliconiini)

The haploid chromosome number of the South American butterfly Philaethria dido varies from 12 to 88. Eight different numbers have been found in this species complex. The related Ph. pygmalion and Ph. wernickei usually show only n=29, a very frequent number in the Lepidoptera; numbers of n=15 and n=21 for these species need confirmation. The most common chromosome number for Ph. dido is also the highest, n=88, and is found in many parts of northern and central Brazil on the Amazon river and its tributaries, as well as adjacent parts of other countries. The other numbers were observed mainly in northern South America and along the east coast. Two very different numbers were found together in four localities. We did not find specimens with meiotic features suggesting hybridization between individuals with different chromosome numbers. The diverse numbers in Ph. dido may belong to good sibling species, distinguishable externally by very minor characters. Since Ph. dido is a very primitive species in the tribe Heliconiini, dating probably from the early Tertiary, it probably has had many opportunities to undergo divergent chromosome evolution in isolation. Its strong, high flight and broad ecological valence would then permit rapid spreading out and coexistence of different chromosome forms, which in some cases have been noted to show diverse behaviour in the field.