Anne-Marie Dutrillaux

High chromosomal polymorphism and heterozygosity in Cyclocephala tridentata from Guadeloupe: chromosome comparison with some other species of Dynastinae (Coleoptera: Scarabaeidae).

Very distinct karyotypes have been observed in two Cyclocephala species from Guadeloupe, considered as very close and possibly vicariant: C. insulicola with only metacentric and C. tridentata tridentata with many acrocentric autosomes. This prompted us to study the karyotype of a few other neotropical Dynastinae belonging to four of the eight existing tribes, to find out which one of these two species had the most divergent chromosomes from their ancestral condition. In the four additional species studied, i.e., Cyclocephalamaffafa, Strategus syphax, Ligyrus cuniculus and Megasoma actaeon, a karyotype composed of 20 chromosomes, including 18 meta- or submetacentric autosomes was found, as it was in C. insulicola. Thus, the karyotype of C. t. tridentata, in which most of the 18 autosomes were acrocentric, is apomorphic. In addition, it was highly polymorphic, with six different karyotypes observed among the ten specimens studied. All had one to four heterozygous chromosome pairs formed by one acrocentric and one submetacentric carrying a large juxta-centromeric heterochromatic component. This heterozygosity did not seem to impair either meiotic synapsis or chiasma formation and chromosome segregation. Such high rates of chromosome heterozygosity and polymorphism are infrequent and never described in beetles. This suggests that C. t. tridentata undergoes an active process of chromosome evolution. A possible relationship with insularity and/or pesticide exposure is briefly discussed.

X-Y-autosome translocation, chromosome compaction, NOR expression and heterochromatin insulation in the Scarabaeid beetle Dynastes hercules hercules.

The karyotype of the giant beetle Dynastes hercules hercules is composed of only 16 autosomes and large sex chromosomes. Meiotic studies in the males showed that a large part of the sex chromosomes undergo synapsis at pachynema similarly to autosomes, demonstrating that both derived from an autosome-gonosome translocation. Therefore, karyotype formula is 18,neoXY. The heterochromatisation of the neoX short arm at pachynema indicates that it corresponds to the ancestral X. It carries the nucleolar organizer region (NOR) in its proximal part, which is undercondensed, especially in male mitotic and meiotic cells. In female mitotic cells, both NOR staining and undercondensation were more difficult to observe in the neoX short arms. In somatic interphase nuclei, NOR expression strongly varies with the sex. Two separated compact groups of silver dots were observed in female nuclei, while a single dispersed and large group of silver deposit exists in the males. Both the lower condensation and the higher NOR expression of the single neoX of the males, compared to each of the two neoXs of the females, is interpreted to be a consequence of dosage compensation, a mechanism not yet described in Coleoptera. In mammals as well as in Coleoptera, the carriers of gonosome-autosome translocations not exhibiting deleterious phenotypes show constitutive heterochromatin at the autosome-gonosome junction. Thus, heterochromatin may play an important universal role by clearly separating chromosome segments with different regulations of gene expression, such as inactivation or dosage compensation of the X chromosome on the one side and a conventional autosomal structure on the other side.

Chromosome Analysis of 82 Species of Scarabaeoidea (Coleoptera), with Special Focus on NOR Localization

The aim of this study was the identification of the ancestral location of the nucleolus organizer region (NOR) in the Scarabaeoidea superfamily, and its evolutive trends in the karyotypes. For this purpose, the mitotic and meiotic chromosomes at pachynema of 82 species belonging to 4 families and 8 subfamilies, including 49 species without any published data, were examined after Giemsa staining, C-banding and NOR staining. It could be perceived that most karyotypes are composed of 18 nonacrocentric autosomes, an acrocentric X and a punctiform Y. NORs are frequently located on the X independent of its morphology. In contrast, autosomal NORs are frequently on the rare acrocentric short arms. Thus, it could be shown that the ancestral karyotype was very probably composed of 18 metacentric/submetacentric autosomes, an NOR carrier acrocentric X and a punctiform Y. The NOR translocation on autosomes parallels the passage to their acrocentric morphology. It is proposed that the frequent location of the NOR on the X of beetles, and possibly other insects, is made possible by their mode of dosage compensation of the X chromosome, consisting in the overexpression of the unique X of the males.

Evolution of European Cockchafers (Melolonthinae: Scarabaeidae: Coleoptera): a morphological, molecular and chromosomal study of intra- and inter-specific variations

In cockchafers of the genus Melolontha, there is a marked intraspecific polymorphism for morphological characters, making some specimens of one species resemble another. A cytogenetic and molecular (mitochondrial COI gene sequence) study of typical and atypical forms of M. melolontha and M. hippocastani, captured at the same period and area, was performed. Karyotypes and haplotypes clearly characterize each taxon, placing atypical specimens in one or the other species unambiguously. This formally discards the role of hybridization in phenotypic resemblance, as usually proposed. Karyotypes and haplotypes were compared to those of M. pectoralis and Phyllophaga pleei, a more distantly related Melolonthinae, and some Dynastinae species, to reconstruct their ancestral karyotype. The karyotype of M. melolontha is the most derivative and that of P. pleei the most conserved among the Melolonthinae studied, which fits with the phylogeny established by COI gene analysis. Both karyotypes and COI haplotypes demonstrate the proximity of M. pectoralis and M. melolontha. The karyotype of M. melolontha is polymorphic, without relationship with morphological variations. Finally, the existence of similar morphological variations in different Melolontha species and chromosomal polymorphism in M. melolontha is discussed in relation with a network (reticulated) mode of speciation.

Etude chromosomique de seize espèces ou sous-espèces de Cetoniini (Coleoptera: Scarabaeidae: Cetoniinae) d’Europe

Résumé L’établissement du caryotype de seize espèces ou sous-espèces de Cetoniini d’Europe montre que toutes possèdent une formule chromosomique à 20, Xyp, à l’exception de Tropinota (Epicometis) hirta qui porte un chromosome B surnuméraire et un néo-chromosome X. Le caryotype des espèces du genre Cetonia se caractérise par la présence de nombreux chromosomes acrocentriques, alors que celui des espèces des genres Protaetia, Oxythyrea et Tropinota est constitué uniquement de méta- ou sub-métacentriques. Chaque espèce possède son propre caryotype, et les différences interspécifiques résultent principalement de la survenue d’inversions, c’est à dire, de remaniements intra-chromosomiques. Les données chromosomiques concordent bien avec la systématique actuelle.

Recherches sur la phylogénie du genre Saga (Orthoptera: Tettigoniidae): données chromosomiques

Résumé L’analyse cytogénétique de quatre espèces européennes de Saginae, dont les caryotypes n’avaient jamais été étudiés, la ré-investigation de celui de Saga pedo (Pallas 1771), la prise en compte des données publiées, et le résultat d’investigations sur le terrain, permettent de proposer une reconstitution de leur phylogénie. Les caryotypes les plus ancestraux semblent être ceux de Saga ornata Burmeister 1839 et de Saga cappadocica Werner 1903, publiés antérieurement, dont tous les autosomes seraient acrocentriques. La fusion de deux paires de leurs chromosomes aboutirait aux caryotypes de Saga natoliae Serville 1839 et de Saga hellenica Kaltenbach 1967, comportant une paire de grands submétacentriques. Ces deux caryotypes se différencient par une inversion péricentrique touchant ces grands chromosomes, probablement chez S. natoliae. Saga campbelli Uvarov 1921 et Saga rammei Kaltenbach 1965, ont acquis une fusion chromosomique de plus et possèdent donc deux paires de grands submétacentriques. Le caryotype de S. rammei détient en plus une particularité de son hétérochromatine. Enfin, le caryotype de S. pedo est tétraploïde, probablement formé de la juxtaposition de deux génomes diploïdes par hybridation. La particularité de l’hétérochromatine de S. rammei se retrouve chez S. pedo sur deux chromosomes différents. Alors que l’on pourrait attendre des quadruplets ou des doublets de chromosomes, il existe une grande diversité de chromosomes en copie unique. Ceci démontre qu’un fort taux de remaniements chromosomiques a modifié le caryotype de S. pedo, postérieurement à son passage à la tétraploïdie. Cette accumulation de remaniements, aboutissant à une forte hétérozygotie, peut s’expliquer par l’absence de filtre méiotique chez cette espèce parthénogénétique. Nos dernières prospections terrain dans le sud des Balkans, nous ont amené à découvrir une zone probable d’intergradation entre Saga pedo et certains taxons sexués affines. L’analyse chromosomique des individus de cette région va sans doute se révéler d’une importance essentielle pour la poursuite de nos recherches.

Cyclocephala (Coleoptera: Scarabaeidae: Dynastinae) evolution in Lesser West Indies indicates a Northward colonization by C. tridentata.

A dual cytogenetic and molecular analysis was performed in four species of Cyclocepala (Coleoptera: Scarabaeidae: Dynastinae) from Lesser Antilles (Martinique, Dominica and Guadeloupe). Two species/sub-species, C. mafaffa grandis and C. insulicola, are endemic to Guadeloupe. They have their own non-polymorphic karyotype and a fairly homogeneous haplotype of the COI gene. C. melanocephala rubiginosa has a distinct karyotype. Its COI haplotype is homogeneous in Guadeloupe and heterogeneous in Martinique. Finally, C. tridentata has highly different karyotypes and haplotypes in the three islands. In Martinique, its karyotype, composed of metacentrics, is monomorphic while its haplotype is fairly heterogeneous. Both are close to those of other Cyclocephala and Dynastinae species, thus fairly ancestral. In Guadeloupe, its karyotype is highly polymorphic, with many acrocentrics, and its haplotype fairly homogeneous. Both are highly derived. In Dominica, both the karyotype and the haplotype represent intermediate stages between those of Martinique and Guadeloupe. We conclude that several independent colonization episodes have occurred, which excludes that C. insulicola is a vicariant form of C. tridentata in Guadeloupe. Both chromosome and COI gene polymorphisms clearly indicate a recent colonization with a northward direction for C. tridentata.

Chromosome Polymorphism and Fanconi-Like Instability in the Scarabaeid Beetle Macraspis tristis from Guadeloupe

The karyotype of Macraspis tristis Laporte is described. It is composed of 18 chromosomes. C-band positive heterochromatin is very abundant and is located at centromeric regions and, for some chromosomes, at telomeric regions. There is a high inter-individual chromosomal polymorphism for the presence and extension of telomeric heterochromatin. In one of the 8 specimens studied, 2 populations were observed in testicular cells. Besides groups of normal metaphases, other groups displayed multiple chromatid and chromosome alterations such as breaks, exchanges (radials), deletions and translocations, resembling those described in Fanconi anemia. The insect had a normal phenotype, but its gametogenesis did not reach the spermatocyte II stage, and was quite poor in spermatocytes I. The clonal character of the chromosome instability was obvious owing to the incomplete cytodiaeresis of germ cells which remain associated by cytoplasmic bridges. This may be the first example of chromosome instability observed in animals from nature.

Présence d’un caryotype très original à 53–54 chromosomes chez Vesperus xatarti Mulsant 1839 (Coleoptera : Cerambycidae : Vesperinae)

Résumé Après description de techniques permettant ďétablir avec précision le caryotype des coléoptères, I’analyse cytogénétique du Vesperus xatarti est rapportée. Son caryotype est tout à fait particulier, puisqu’il possède 53–54 chromosomes à I’état diploïde, un nombre bien supérieur à ce qui a été rapporté jusqu’ici chez les Coléoptères. Ceci indique qu’une évolution importante, probablement par fissions chromosomiques multiples, en est à I’origine. Utilisation de marquage chromosomique en bandės permet de montrer que la variation de nombre est liée au sexe : 54 chez la femelle et 53 chez le mâle. Cette différence est due au fait que la femelle possède deux pairęs de petits autosomes, et le mâle deux autosomes uniques et un autre chromosome résultant de leur fusion ou de leur maintien non fissionné. Cette particularité, décrite chez ďautres coléoptères comme un système à chromosomes sexuels multiples, n’avait jamais été encore observée chez les Cerambycidae. Ces particularités chromosomiques mériteraient ďêtre prises en compte pour une éventuelle révision de la position systématique des Vespėrus.

Parthenogenetic reproduction demonstrated in the diploid Spasalus puncticollis (Le Peletier & Serville 1825), n. stat ., from the Antilles (Coleoptera, Scarabaeoidea, Passalidae)

Only females were observed in Spasalus crenatus (Mac Leay 1819) in the Antilles, from Puerto Rico to Saint-Vincent, whereas both sexes are in Trinidad and on the continent. No difference in endo- and ectodermic female genitalia could be noticed between the two populations. Chromosomes of specimens from Guadeloupe reveal a 26,XX karyotype, as in females of various sexual species of Passalini, which demonstrates its diploidy. Breedings were developed with isolated immature stages. After nine years, descendants from a single female are demonstrating their parthenogenetic reproduction. This is the first recorded parthenogenesis in Passalidae and a rare telytoky in diploid insects. Relationships between parthenogenesis, diploidy and insularity are discussed in the scheme of geographical parthenogenesis. No discriminant morphological character on adults could be found between the two populations, except the total length. The modes of reproduction distinguishing the two geographically separated populations suggest the presence of two taxa: S. crenatus on the continent and Trinidad; the parthenote S. puncticollis (Le Peletier & Serville 1825), n. stat., on the Arc of the Antilles.