Douglas Araujo

Sex Chromosomes and Meiosis in Spiders:A Review

According to Platnick (2011), the order Araneae possesses 110 families, 3,849 genera, and 42,473 species. It is divided into two suborders: Mesothelae, consisting of only one family (Liphistiidae), and Opisthothelae. The latter suborder is divided into two infra-orders: Mygalomorphae, consisting of spiders with paraxial chelicerae, and Araneomorphae, consisting of spiders with diaxial chelicerae. The latter infra-order is divided into the basal clades (Hypochilidae and Austrochiloidea), Haplogynae, and Entelegynae, which includes the majority of extant spiders (Coddington & Levi, 1991) (Fig. 1).

CHROMOSOMAL DATA OF TWO PHOLCIDS (ARANEAE, HAPLOGYNAE): A NEW DIPLOID NUMBER AND THE FIRST CYTOGENETICAL RECORD FOR THE NEW WORLD CLADE

Abstract Mesabolivar luteus (Keyserling 1891) and Micropholcus fauroti (Simon 1887) specimens were collected in Ubatuba and Rio Claro, both in the state of São Paulo, Brazil. Mesabolivar luteus showed 2n (♂) = 15 = 14 + X and 2n (♀) = 16 = 14 + XX in mitotic metaphases and 7II + X in diplotenic cells. During late prophase I, all bivalents presented a ring shape, evidencing two chiasmata per bivalent. In this species, some diplotenic cells appear in pairs, maybe due to specific characteristics of the intercellular bridges. The metaphases II showed n = 7 or n = 8 = 7 + X chromosomes. Micropholcus fauroti evidenced 2n (♂) = 17 = 16 + X in spermatogonial metaphases and 8II+X in diplotenic cells, with only one chiasma per bivalent, contrasting with M. luteus. In both species, all chromosomes were metacentrics. The sexual chromosome X was the largest element and appeared as a univalent during meiosis I. These are the first cytogenetical data for the genera Mesabolivar and Micropholcus. Additionally, M. luteus is the first chromosomally analyzed species of the New World clade and the observed diploid number for M. fauroti had not yet been recorded in Pholcidae.

Chromosomes of Theridiidae spiders (Entelegynae): interspecific karyotype diversity in Argyrodes and diploid number intraspecific variability in Nesticodes rufipes

Theridiidae is a derived family within the Araneoidea clade. In contrast to closely related groups, the 2n(male) = 20+X1 X 2 with acro/telocentric chromosomes is the most widespread karyotype among the theridiid spiders. In this work, the cytogenetic analysis of Argyrodes elevatus revealed original chromosome features different from those previously registered for Theridiidae, including the presence of 2n(male) = 20+X with meta/submetacentric chromosomes. Most individuals of Nesticodes rufipes showed family conserved karyotype characteristics. However, one individual had a 2n(male) = 24 due to the presence of an extra chromosome pair, which exhibited regular behavior and reductional segregation during meiosis. After silver staining, mitotic cells exhibited NORs localized on the terminal regions of the short arms of pairs 2, 3, and 4 of A. elevatus and on the terminal regions of long arms of pair 4 of N. rufipes. The comparative analysis with data from phylogenetically related species allowed the clarification of the origin of the interspecific and intraspecific chromosome variability observed in Argyrodes and in N. rufipes, respectively.

Comparative Cytogenetics of Seven Ctenidae Species (Araneae)

The present study elevates the number of cytogenetically analyzed ctenid species and genera from two to eight and six, respectively, presenting comparisons between chromosomal data obtained and the phylogenetic hypothesis proposed in the literature. Six ctenid species presented 13 autosomal pairs, exhibiting either X1X2O (Ctenus ornatus, Ctenus sp., Parabatinga brevipes and Phoneutria nigriventer) or X1X2X3O sex chromosome systems (Nothroctenus sp. and Viracucha andicola). Asthenoctenus borellii showed 2n ♂ = 20 + X1X2O. In all species, the chromosomes were telocentric. Some cells of one C. ornatus specimen exhibited one extra chromosome that, considering the behavioral similarities between the two chromosomes, can be considered to be supernumerary, derived from or giving rise to a sex chromosome. Silver impregnation revealed nucleolar organizer regions on one autosomal pair of C. ornatus and P. nigriventer (Cteninae) and two pairs of V. andicola (Acanthocteninae). Chromosomal data suggests that the X1X2X3O system arose several times in the evolution of entelegyne spiders, and that conversion of an X1X2O system into an X1X2X3O system and vice-versa has been a relatively common event in spiders. All the chromosomal data corroborate the close relationship between Ctenus and Phoneutria, the placement of P. brevipes within Cteninae, the placement of Anahita in a separated branch within Cteninae, and the inclusion of A. borellii in a distinct group within the ctenids (Viridasiinae), all of which are as proposed by phylogenetic hypotheses available in the literature.

Cytogenetical characterization of six orb-weaver species and review of cytogenetical data for Araneidae

Abstract The family Araneidae is the third largest among spiders and the third most studied from a cytogenetical point of view. In spite of this, only 2% of all araneids have been karyotyped. The majority of araneids analyzed possess 2n  =  24 chromosomes in males; however, the study of additional species could reveal unusual karyotype characteristics. Thus, the aim of this work is to analyze chromosomally, for the first time, six species belonging to three araneid genera from Brazil. The specimens of Alpaida leucogramma (White 1841), Alpaida truncata (Keyserling 1865), Alpaida veniliae (Keyserling 1865), Parawixia kochi (Taczanowski 1873), Parawixia velutina (Taczanowski 1878) and Wagneriana sp. were collected in Parque Nacional de Ilha Grande and in the municipality of Rio Claro. The gonads were treated with colchicine and hypotonic solution before fixation with Carnoy I solution. The results were 2n♂  =  24 (11II+X1X2) in A. leucogramma and P. velutina, and 2n♂  =  22 (10II+X1X2) in A. truncata, A. veniliae, P. kochi and Wagneriana sp. When the chromosomal morphologies were established, we observed telocentric chromosomes in all specimens save one female specimen of P. velutina. The univalent sex chromosomes were easily recognized on diplotenes. The unpaired metacentric element found in one female specimen of P. velutina with 2n  =  25 probably arises by centric fusion/fission. Araneidae is a megadiverse family composed of ∼3000 species distributed mainly in the tropics; thus the analysis of more species may provide new insights about orb-weaver chromosome evolution.

Mesabolivar brasiliensis (Moenkhaus 1898) and Mesabolivar cyaneotaeniatus (Keyserling 1891) (Araneomorphae, Pholcidae): close relationship reinforced by cytogenetic analyses

Abstract Pholcidae is the most diverse family among haplogyne spiders but only 15 species have been analyzed cytogenetically. These studies revealed that the diploid number varies from 2n  =  15 to 2n  =  32, that there are three types of sex chromosome systems in males (X, X1X2 and X1X2Y), and that the chromosomes are predominantly biarmed. Within the genus Mesabolivar, only Mesabolivar luteus (Keyserling 1891) has been karyotyped, and it showed 2n  =  15  =  14 + X, with all chromosomes being metacentric. In the present work, we characterize the mitotic and meiotic chromosomes of Mesabolivar brasiliensis (Moenkhaus 1898) and Mesabolivar cyaneotaeniatus (Keyserling 1891). Male mitotic metaphases of the two species showed the diploid number 2n  =  17  =  16 + X; oogonial cells of M. brasiliensis showed 2n  =  18  =  16 + XX. In both species, the chromosomes were exclusively biarmed, and the X chromosome was the largest element of the karyotype. Diplotene spermatocytes of the two species exhibited 8II + X and the occurrence of only one terminal or interstitial chiasma per bivalent. In M. cyaneotaeniaus, metaphases II with n  =  9  =  8 + X and n  =  8 were found, indicating the regular segregation of all chromosomes during meiosis I. Mitotic metaphases of M. brasiliensis stained with CMA3/DA/DAPI revealed GC-rich chromatin in the terminal region of almost all autosomes, especially in pair 2. An earlier revision of the New World pholcids grouped M. brasiliensis and M. cyaneotaeniatus in a “southern group” and placed M. luteus in a “miscellaneous group.” A molecular study showed a closer relationship between M. brasiliensis and M. cyaneotaeniatus than between M. luteus and either of these two species. The 2n  =  17 found in M. brasiliensis and M. cyaneotaeniatus corroborates this hypothesis, given that M. luteus has a diploid number of 2n  =  15.

The Chromosomes of Phlugis proxima Bruner (Orthoptera, Tettigoniidae) and Discussion on Chromosomal Patterns in Meconematinae

ABSTRACT: The first cytogenetic analysis of Phlugis Stål, 1861, Phlugis proxima Bruner, 1915, revealed 2n♂ = 27, X0 and 2n♀ = 28, XX. Some tribe-specific chromosomal patterns are assigned to Meconematinae: 1) In Phlugidini, the X chromosome is metacentric and the largest chromosome of the karyotype; 2) In Phisidini, the X chromosome is telo/acrocentric, and largest element only in species with exclusively telocentric autosomes; 3) In Meconematini, three genera have an acrocentric X element and members of Xiphidiopsis Redtenbacher, 1891 exhibit a metacentric X chromosome; 4) The Australian Phlugidini showed 2n♂ = 29 and the Neotropical P. proxima 2n♂ = 27; 5) Phisidini, except one species, is characterized by lower diploid numbers (2n♂ = 19, 21 or 23); 6) Meconematini, except one presumed parthenogenetic species, is characterized by higher diploid numbers (2n♂ = 33, 31 or 27). No telomeric interstitial sites were observed, indicating a possible ancient chromosome fusion in the origin of the P. proxima karyotype

Chromosomal similarities between Nephilidae and Tetragnathidae indicate unique evolutionary traits among Araneoidea

Abstract Nephilid systematics has been subject to several changes in the last years, and the use of non-classical characters could be useful for evolutionary considerations. In this study, we analyzed the mitotic chromosomes of two nephilid spiders, Nephila clavipes and Nephila sexpunctata, using standard staining, silver nitrate impregnation and C-banding techniques, aiming to discuss the chromosomal similarities of Nephilidae and Tetragnathidae, and chromosome evolution within Nephila and Nephilingis. The basic karyotype characteristics observed in these two species (2n♂ = 22 + X1X20 and monoarmed chromosomes) were similar to those registered for most araneoid families, i.e., Araneidae, Linyphiidae, Nephilidae, Nesticidae and Tetragnathidae. However, the occurrence of both prominent secondary constrictions and nucleolar organizer regions (NORs) is a shared characteristic between Nephilidae and Tetragnathidae, considering that these regions were not observed in any other Araneoidea species cytogenetically examined. Furthermore, in the present study we showed that within Nephila and Nephilingis species, change in the number and location of NORs as well as in the quantity and distribution of constitutive heterochromatin were the main events responsible for chromosome evolution, and that these differences can be useful in the cytotaxonomy of this group.

Small pholcids (Araneae: Synspermiata) with big surprises: the lowest diploid number in spiders with monocentric chromosomes

Abstract Even though less than 2% of pholcid species have been karyotyped, previous studies documented a wide diversity of diploid numbers and sex chromosome systems. Here, we increase the number of native Brazilian cytogenetically investigated pholcid species from three to eight and discuss implications of chromosome evolution in this group. The species analyzed here share a X0/XX sex chromosome system and biarmed chromosomes, but vary in diploid numbers, i.e., 2n♂ = 17 in Mesabolivar spinulosus (Mello-Leitão, 1939) and Mesabolivar togatus (Keyserling, 1891), 2n♂ = 15 in Carapoia sp., and 2n♂ = 9 in Micropholcus piaui Huber, Carvalho & Benjamin, 2014 and Micropholcus ubajara Huber, Carvalho & Benjamin, 2014. Chromosomal data indicate that most Mesabolivar species share a 2n♂ = 17, X0, while Mesabolivar luteus shares with Carapoia sp. a 2n♂ = 15, X0. This lends further support to the idea that M. luteus is in fact misplaced and more closely related to Carapoia González-Sponga, 1998. The diploid number of the two Micropholcus species is the lowest reported so far for spiders with monocentric chromosomes. The 2n♂ = 9, differs strongly from the 2n♂ = 17 previously reported for Micropholcus fauroti (Simon, 1887). As the number of autosomes of M. piaui and M. ubajara is exactly half of that found in M. fauroti, we hypothesize that the reduction occurred by an “all or nothing” fusion event. The low diploid number observed in M. piaui and M. ubajara is the first morphological synapomorphy that would support the establishment of a new genus to allocate the New World Micropholcus species.

Comparative cytogenetic analysis among filistatid spiders (Araneomorphae: Haplogynae)

Abstract The family Filistatidae is considered sister to Synspermiata or sister to Hypochilidae. Cytogenetic knowledge of this family could be useful for understanding the mechanism of chromosome evolution that has occurred within the group. In this work, two filistatid species belonging to distinct subfamilies, Kukulcania hibernalis (Hentz, 1842) (Filistatinae) and Misionella mendensis (Mello-Leitão, 1920) (Prithinae), were investigated using standard and differential chromosome staining. Analysis of mitotic and meiotic cells revealed the diploid 2n♂ = 25 for K. hibernalis and 2n♂ = 21 for M. mendensis. Both species exhibited a sex chromosome system of the X1X2Y type and metacentric/submetacentric chromosomes. In prophase I cells, the sex chromosomes were in a trivalent configuration with all elements associated without chiasma through their terminal regions. Both species revealed six nucleolar organizer regions on the terminal region of three autosomal pairs. In K. hibernalis, constitutive heterochromatin was located mainly in the terminal regions of autosomes and sex chromosomes while in M. mendensis, the heterochromatin occurred in the pericentromeric region of all chromosomes. Despite the scarcity of cytogenetic information for Filistatidae, the available results show the occurrence of high variability in the diploid number but with the maintenance of the X1X2Y sex chromosome system. Additionally, the karyotype differentiation in the species of this family seems to have involved not only the number of autosomes but also specific chromosomal sites, such as the constitutive heterochromatic regions.