Chromosomal characteristics and karyotype evolution of Oxyopidae spiders (Araneae, Entelegynae).

Abstract

We made a cytogenetic analysis of four species of Oxyopidae and compared it with the karyotype data of all species of this family. In Hamataliwa sp, the mitotic cells showed 2n♂ = 26+X(1)X(2) and telocentric chromosomes. The 2n♂ = 28, which has been described for only one oxyopid spider, is the highest diploid number reported for this family. Peucetia species exhibited distinct karyotype characteristics, i.e., 2n♂ = 20+X(1)X(2) in P. flava and 2n♂ = 20+X in P. rubrolineata, revealing interspecific chromosome variability within this genus. However, both Peucetia species exhibited telocentric chromosomes. The most unexpected karyotype was encountered in Oxyopes salticus, which presented 2n♂ = 10+X in most individuals and a predominance of biarmed chromosomes. Additionally, one male of the sample of O. salticus was heterozygous for a centric fusion that originated the first chromosomal pair and exhibited one supernumerary chromosome in some cells. Testicular nuclei of Hamataliwa sp and O. salticus revealed NORs on autosomal pairs, after silver impregnation. The majority of Oxyopidae spiders have their karyotype differentiated by both reduction in diploid number chromosome number and change of the sex chromosome system to X type; however, certain species retain the ancestral chromosome constitution 2n = 26+X1X2. The most remarkable karyotype differentiation occurred in O. salticus studied here, which showed the lowest diploid number ever observed in Oxyopidae and the second lowest registered for Entelegynae spiders.

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©FUNPEC-RP www.funpecrp.com.br
Genetics and Molecular Research 10 (2): 752-763 (2011)
Chromosomal characteristics and
karyotype evolution of Oxyopidae spiders
(Araneae, Entelegynae)
L.M. Stávale1, M.C. Schneider2, A.D. Brescovit3 and D.M. Cella1
1Departamento de Biologia, Universidade Estadual Paulista, Rio Claro, SP, Brasil
2Departamento de Ciências Biológicas, Universidade Federal de São Paulo,
Diadema, SP, Brasil
3Laboratório de Artrópodes, Instituto Butantan, São Paulo, SP, Brasil
Corresponding author: M.C. Schneider
E-mail: maricb@rc.unesp.br
Genet. Mol. Res. 10 (2): 752-763 (2011)
Received September 29, 2010
Accepted November 24, 2010
Published May 3, 2011
DOI 10.4238/vol10-2gmr1084
ABSTRACT. We made a cytogenetic analysis of four species of
Oxyopidae and compared it with the karyotype data of all species
of this family. In Hamataliwa sp, the mitotic cells showed 2n♂ =
26+X1X2 and telocentric chromosomes. The 2n♂ = 28, which has
been described for only one oxyopid spider, is the highest diploid
number reported for this family. Peucetia species exhibited distinct
karyotype characteristics, i.e., 2n♂ = 20+X1X2 in P. flava and 2n♂
= 20+X in P. rubrolineata, revealing interspecific chromosome
variability within this genus. However, both Peucetia species
exhibited telocentric chromosomes. The most unexpected karyotype
was encountered in Oxyopes salticus, which presented 2n♂ = 10+X
in most individuals and a predominance of biarmed chromosomes.
Additionally, one male of the sample of O. salticus was heterozygous
for a centric fusion that originated the first chromosomal pair and
exhibited one supernumerary chromosome in some cells. Testicular
nuclei of Hamataliwa sp and O. salticus revealed NORs on autosomal
pairs, after silver impregnation. The majority of Oxyopidae spiders
have their karyotype differentiated by both reduction in diploid

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Genetics and Molecular Research 10 (2): 752-763 (2011)
Karyotype evolution of Oxyopidae spiders
number chromosome number and change of the sex chromosome
system to X type; however, certain species retain the ancestral
chromosome constitution 2n = 26+X1X2. The most remarkable
karyotype differentiation occurred in O. salticus studied here, which
showed the lowest diploid number ever observed in Oxyopidae and
the second lowest registered for Entelegynae spiders.
Key words: Chromosome fusion; Cytogenetic; Diploid number;
Nucleolar organizer region; Sex chromosome system
INTRODUCTION
Spiders are one of the most diverse orders of animals and are certainly the most abundant
terrestrial predators (Coddington and Levi, 1991). Cytogenetically, only about 1.5% (Král et al.,
2006) of the 41,719 species belonging to the order Araneae (Platnick, 2010) have been analyzed,
which showed a wide diversity of diploid chromosome number, ranging from 2n♂ = 7 to 2n♂ =
96, and different types of sex chromosome system, e.g., XY, X, X1X2, X1X2Y, X1X2X3, X1X2X3X4
(Araujo, 2007). In species of the monophyletic basal groups, the highest chromosome numbers were
verified, such as 2n♂ = 96 in the suborder Mesothelae and 2n♂ = 86 in the infraorder Mygalomor-
phae. In these groups, the karyotypes were composed of biarmed or uniarmed chromosomes (Su-
zuki, 1954; Srivastava and Shukla, 1986; Řezač et al., 2006). Among the derivative groups included
in the infraorder Araneomorphae, the spiders of the Haplogynae lineage presented a predominance
of low diploid chromosome numbers that varied between 2n♂ = 7 and 2n♂ = 37, a sex chromosome
system of the X type, and meta/submetacentric chromosomes. These features contrast with those
of the sister-group Entelegynae, which exhibited the highest number of species taxonomically de-
scribed and cytogenetically investigated (Araujo, 2007; Platnick, 2010). In entelegyne spiders there
is a conservation of the diploid number 2n♂ = 42, a sex chromosome system of the X1X2 type, and
chromosomes with acro/telocentric morphology (Araujo et al., 2005; Král et al., 2006).
After comparing the karyotype characteristics of the basal and derived species of Ara-
neae, Suzuki (1954) proposed that chromosomal evolution in this order has occurred through
reduction in the chromosome number. Later, Rowell (1990) suggested that in spiders there is a
peculiar form of karyotype evolution via “all or nothing” fusions. This proposition was based
on the fact that intermediate karyotypes that included both acro/telocentric chromosomes and
meta/submetacentric chromosomes are rarely encountered in this group. Král et al. (2006) ver-
ified that certain related species of entelegyne spiders differ with regard to the diploid number
but not in relation to chromosome morphology that is maintained as acro/telocentric. Thus, the
authors attributed the reduction in the chromosome number in these spiders to tandem fusions.
Within the Entelegynae lineage, the family Oxyopidae is very interesting because of its
predominance of the 2n♂ = 20+X. This karyotype includes a diploid chromosome number that
is relatively low when compared to those of other families of this group and a sex chromosome
system that was observed in only 12% of the entelegyne spiders. The chromosome morphology,
however, described for 11 species of a total of 21 studied is conserved as acro/telocentric (Table
1). Oxyopidae belongs to the group of spiders known as true lycosoids, whose monophyly is well
supported by morphological characters (Silva Davila, 2003). The families that constitute this group
form the clade [(Psechridae (Oxyopidae + Senoculidae)) + (Trechaleidae (Lycosidae + Pisauri-

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L.M. Stávale et al.
dae))] (Silva Davila, 2003). In order to gain a better understanding of the chromosomal character-
istics and processes of karyotype evolution of Oxyopidae, four species belonging to three different
genera were cytogenetically analyzed with standard staining and silver impregnation. It is worth
emphasizing that this is the first chromosomal record for oxyopids from Brazilian fauna.
MATERIAL AND METHODS
In this study, a sample of 23 individuals was analyzed, which included: two males
and one female of Hamataliwa sp, one male and three females of Peucetia flava Keyserling,
1877, nine males of P. rubrolineata Keyserling, 1877, and seven males of Oxyopes salticus
Species

Chromosomal
formula (2n males)
Chromosomal
morphology
Collection
locality
Reference
Hamataliwa sp
Nishina generosa Komatsu
(nonem nudum)
Oxyopes hindostanicus
Pocock, 1901
Oxyopes javanus Thorell, 1887
Oxyopes lepidus (Blackwall,
1864) under Oxyopes similaris
Oxyopes macilentus
L. Koch, 1878
Oxyopes pandae Tikader, 1969
Oxyopes ramosus
(Martini & Goeze, 1778)
Oxyopes ratnae Tikader, 1970


Oxyopes rufisternis Pocock, 1901
Oxyopes ryvesi Pocock, 1901
Oxyopes salticus Hentz, 1845
Oxyopes salticus Hentz, 1845


Oxyopes scalaris Hentz, 1845
Oxyopes sertatus L. Kock, 1877


Oxyopes shweta Tikader, 1970

Oxyopes sushilae Tikader, 1965
Oxyopes sp
Oxyopes sp
Oxyopes sp
Oxyopes sp
Oxyopes sp
Peucetia flava Keyserling, 1877 22=20+X1X2
Peucetia rubrolineata
Keyserling, 1877
Peucetia viridana (Stoliczka, 1869) 28=26+X1X2


A = acrocentric; M = metacentric; SM = submetacentric; T = telocentric; H = holocentric; B = supernumerary chromosome.
28=26+X1X2
21=20+X
26T+X1X2T
20A+XA
Brazil
Japan
Present study
Suzuki (1952)
21=20+X

23=22+X
21=20+X
20A+XA

22H+XH
20A+XA
India

Philippines
India
Bole-Gowda (1950),
Mittal (1961, 1970)
Barrion et al. (1989)
Bole-Gowda (1958)
21=20+X
23=22+X
21=20+X
21=20+X
20T+XT
22T+XT
-
20A+XM
Taiwan Chen (1999)
India
Finland
Srivastava and Shukla (1986)
Hackman (1948)
21=20+X


21=20+X
21=20+X
22=20+X1X2
11=10+X
12=11+X/
13=11+X+B
21=20+X
21=20+X


21=20+X

21=20+X
21=20+X
22=20+X1X2
22=20+X1X2
21=20+X
21=20+X
20T+XT


20A+XA
-
-
6M+2SM+2T+XSM
5M+2SM+4T+XSM/
5M+2SM+4T+XSM+BSM
-
20A/T+XA/T


-

-
-
-
20A+X1X2A
-
-
20T+X1X2T
20T+XT
India


India
India
-
Brazil
Datta and Chartterjee (1983, 1989),
Parida and Sharma (1987),
Sharma and Parida (1987)
Mittal (1961, 1970)
Sharma et al. (1960)
Painter (1914)
Present study
United States
Japan, Taiwan


India

India
India
India
India
India
India
Brazil
Brazil
Tugmon et al. (1990)
Suzuki (1950, 1952),
Igarashi and Kondo (1977),
Chen (1999)
Parida and Sharma (1987),
Sharma and Parida (1987)
Srivastava and Shukla (1986)
Sharma et al. (1960)
Mittal (1961)
Mittal (1970)
Srivastava and Shukla (1986)
Srivastava and Shukla (1986)
Present study
Present study 21=20+X
26A+X1X2A


India


Bole-Gowda (1950),
Parida and Sharma (1987),
Sharma and Parida (1987)


Table 1. Oxyopidae species cytogenetically analyzed.

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Hentz, 1845. All individuals were collected in Rio Claro (22°24’S, 47°33’W), State of São
Paulo (SP), Brazil. The voucher specimens were deposited in the Laboratório de Artrópodes,
Instituto Butantan (IBSP), city and State of São Paulo, Brazil. The chromosomal preparations
were obtained according to the procedure described by Araujo et al. (2008). Chromosome
spreads were stained with Giemsa solution (3% commercial Giemsa and 3% phosphate buffer,
pH 6.8, in distilled water) for 15 min and subsequently silver-impregnated (Howell and Black,
1980) to detect the nucleolar organizer regions (NORs). Mitotic and meiotic nucleus records
were performed using an Olympus BX51 microscope. The morphology of the chromosomes
was determined according to the nomenclature proposed by Levan et al. (1964).
RESULTS
Mitotic metaphase cells of Hamataliwa sp stained with Giemsa showed the diploid
numbers 2n = 28 for males and 2n = 30 for females, which were consistent with an X1X2/
X1X1X2X2 sex chromosome system (Figure 1A). All chromosomes revealed telocentric mor-
phology and decreased gradually in size. The sex chromosomes presented a high degree of
condensation; the X1 sex chromosome was slightly larger than the X2 chromosome, but both
possessed medium size. Early prophase I cells of male Hamataliwa sp revealed two blocks
that were highly condensed and positively heteropycnotic, which were interpreted as sex chro-
mosomes (Figure 1B). Diplotene and diakinesis nuclei showed 13II+X1X2 (Figure 1C,D), con-
firming the diploid number and type of sex chromosome system established through analyses
of mitotic cells. In these latter meiosis-phases, the autosomal bivalents showed one interstitial
or terminal chiasma and the X1 and X2 chromosomes always appeared as univalents and ar-
ranged side by side. In metaphase II cells, the haploid sets with n = 13+X1X2 and n = 13
chromosomes were observed (Figure 1E,F). All chromosome preparations of Hamataliwa sp
were subjected to silver impregnation but only diplotene and diakinesis nuclei revealed NORs,
which were located on the terminal region of one medium-sized bivalent and interstitial region
of one small-sized bivalent (Figure 1G,H).
Giemsa-stained spermatogonial metaphases of P. flava and P. rubrolineata dem-
onstrated the diploid chromosome numbers 2n = 22 and 2n = 21, respectively. The former
species presented a sex chromosome system of the X1X2 type while the latter showed a
system of the X type (Figure 2A,B). The karyotypes of both species were composed of telo-
centric chromosomes that gradually varied in size and sex chromosomes similar in size to
the smallest elements of the diploid complement. In pachytene cells of P. flava and P. rubro-
lineata, the autosomal bivalents were fully synapsed and the sex chromosomes appeared as
highly condensed and positively heteropycnotic univalents (Figure 2C,G). In diplotene and
diakinesis nuclei, the meiotic formulas 10II+X1X2 for P. flava and 10II+X for P. rubrolin-
eata were observed (Figure 2D,E,H,I). In both species, all autosomal bivalents showed one
interstitial or terminal chiasma, with the exception of some cells of P. flava that presented
one bivalent with two terminal and/or interstitial chiasmata. Metaphase II cells exhibited n
= 10+X1X2 and n = 10 in P. flava (Figure 2F) and n = 10+X and n = 10 in P. rubrolineata
(Figure 2J), confirming the regular segregation of all chromosomes during the preceding
anaphase. Although the chromosome preparations of the two Peucetia species have been
silver-impregnated, the presence of an argentophilic material corresponding to the NORs
was not verified in the sample of cells examined.

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Figure 1. Testicular cells of Hamataliwa sp Giemsa-stained (A-G) and silver-impregnated (H). A. Mitotic
metaphase with 2n = 26+X1X2 and telocentric chromosomes. B. Pachytene, showing positively heteropycnotic sex
chromosomes. C. D. Diplotene and diakinesis, exhibiting one interstitial (large arrows) or terminal (small arrow)
chiasma per bivalent. E. F. Metaphase II nuclei with n = 13+X1X2 and n = 13, respectively. G. Diakinesis. H. The
same cell as in G, revealing NORs (arrowheads) on terminal and interstitial regions of two bivalents. In detail,
bivalents with one terminal and interstitial NORs. Scale bar = 10 μm (A-H) and 5 μm (detail in H).