A new species of the genus Neometrypus collected in Cardoso Island in the Atlantic littoral of São Paulo State is described. The species is 2n=14 (male) – 14 (female) with a neoXY-XX sex determining mechanism originated in an X-autosome tandem fusion. Illustrations of the male and female specimens, male meiosis and drawings of the male genitalia sclerites are added.
The genus Neometrypus was erected by Desutter (1988) for a new species of cricket, Neometrypus amazonus, collected in the north west corner of the Neotropical region. The description was based on only two male specimens, one from Departamento de Loreto in Peru and the other from the Departamento de Amazonas, Colombia. The female of the species is unknown.
According to Desutter (1988, p 366) the tribes Tafaliscini and Neometrypini (Tafaliscinae) share among others, the following external morphological characters: hind tibia with four internal and five external spines, tympanum absent and ovipositor dorso-ventrally flattened. Species of the second mentioned tribe, that includes the single genus Neometrypus, have wings absent and show strongly reduced tegmina or are apterous.
The species here described was collected in salt marsh vegetation (restinga) of Cardoso Island in the south of the São Paulo Atlantic littoral and fits very well Desutter's description of the genus Neometrypus; but clearly it differs from N. amazonus in body color pattern, size and details of the phallic structure.
Several other undescribed species with similar generic characters occur in the Atlantic littoral forest, each one with a distinct color pattern.
The sex determining mechanism found in N. badius, originated in a X-A tandem fusion. A similar fusion previously described in three other species of orthopteran insects, one in an eumastacid (White et al. 1967) and two in tettigonids (Fernández-Piqueras et al. 1981; Warchalowska-Sliwa et al. 1998).
The inverted sequence of the reductional/equational first and second meiotic divisions, respectively, owing to the presence of X-A tandem fusions was reported by the above cited authors and is discussed in the present paper.
Neometrypus badius n. sp.
Holotype.— Male (specimen N° 1).
Measurements: femur III length: 10.5; femur III width: 3.4; tibiae III length: 9.0; metatarsum III length: 1.5; prontum length: 4.0; pronotum width: 3.6; distance between external borders of eyes: 3.1; head vertical length: 3.8. Brasil, São Paulo (Município de Cananéia), Cardoso Island, “Interpretative” trail, 13/XII/92 (Fig. 1a); specimen deposited Museum of Zoologia in the São Paulo State University (MZUSP).
Paratypes.— ♀ N° 2 (Fig. 1b) specimen deposited MZUSP, N° 5, and three nymphs, 13/XII/92. N° 8, “Morro das Almas” trail, 14/XII/92. N° 6 and N° 7, “Interpretative” trail, 13/III/93.
♂ ♂: N° 3 and N° 4, “Interpretative” trail, 13/XII/92.
All the specimens were collected in the same locality as the holotype by A. Mesa, P. García-Novo and E. Zefa. Adult ♀ ♀ N° 5, 8 and 7 and ♂ ♂ 3 and 4 will be deposited in the Dep. of Biology, UNESP, Rio Claro, Brazil.
Cardoso Island has an area of 151 km2 and extends between 45°53′48″- 48°05′42″W and 25°18′18″- 25°03′05″S, separated from the continent by the Arapira Channel.
Diagnosis.— Body color, tegmina and karyotype as reported in the description.
Description.— Ambisexual characters: body approximately 20 mm. Tegmina very short, rounded (approximately 2mm from their base to the rear border in males and slightly shorter in females), not touching at the midline. Wings absent. Tibiae III with one or two denticles between spines and 6–8 denticles before spines dorso-proximally.
Females: with dorso-ventrally flattened ovipositor. Head, thorax, and first two abdominal segments light reddish brown. Remaining abdominal segments very dark brown. Cerci and palps very light yellow. Eyes dark brown, same color at the distal end of the tibial spines, denticles and around tibial spine sockets. Antennae uniformly light yellow along their entire length.
Chromosome number (2n = 14) in both sexes with a XY(♂) – XX (♀) sex determinant mechanism.
Male: phallic sclerites - the proximal ectophallic sclerites (PECS) are two parallel bars (Fig. 5d).
The distal ectophallic sclerite (DECS) is a single sclerite that covers the dorsal and lateral faces of the apical phallic region (Fig. 5d) and narrows over its distal third. PECS and DECS are nearly equal in length.
The proximal endophallic sclerite (PENS) is represented by a single sclerite with two forwardly directed parallel projections (Fig. 5e).
The distal endophallic sclerites (DENS) are two parallel sclerites (Fig. 5e).
The stylet (S) is located in the midline of the ventral ectophallic membrane, as a poorly sclerotised elongate plate (Fig. 5e).
Measurements.— Ranges of several body measurements from three ♂ ♂ and five ♀ ♀ are given in Table 1.
Etymology.— Badius from brown color.
Karyotype.— The chromosome number of the species is 2n=14 in both sexes. The autosomes comprise a long pair, four medium size pairs and one small pair, all of them acrocentrics. The sex chromosomes are of the neoX-neoY type with both chromosomes acrocentric. During first prophase a median size bivalent becomes heterochromatic (see thick arrows in Fig 2a, b, d). The small bivalent is partially heterochromatic, as observed in the same figures (a and b, thin arrows). The sex bivalent shows the primitive X (XL) strongly heterochromatic (Fig. 2a–e) during first prophase stages. The XR segment remains euchromatic (see diakinesis of Fig. 2b) while the Y chromosome becomes heterochromatic from the middle of diplotene to diakinesis (Fig. 2e, i). During pachytene (Fig. 2b), the pairing of XRY occurs along most of their lengths (Fig. 2b, c), but from the middle diplotene it is clear that there are no chiasma between the XR and Y as seen in Fig. 2 e, i, h. The sex chromosomes instead seem to be connected by a single chiasma between the small arms as observed in the diakinesis of Fig. 2e and MI of Fig. 2f, g.
During MI the orientation of the centromeres of both X and Y seems to be amphitelic, and the XY bivalent goes through a true equational division during AI (Fig. 2k) and a reductional one at AII (Fig. 2m).
According to Desutter (1988) the tribe Neometrypini is comprised of the genus Neometrypus, with a single species described (N. amazonus), South American species of the genus Parametrypus and two new genera, mentioned but not described by her. Within Parametrypus only one species (aculeatus) is reported from South America (Otte 1994); it was described by Saussure in 1878. The locality for this species is “Le Brèsil, Sierra Giva” which probably means “Serra Geral”, an extense territory in the South and South East of Brazil. Saussure's description of P. aculeatus indicates that the ovipositor is “grêle” and is not specified to be dorso-ventrally depressed. For this reason the species cannot be included in the subfamily Tafaliscinae.
N. amazonus was described based on two males, one from Peru and the other from Colombia, the female being unknown. Desutter (1988) says that species of the tribe Neometrypini occur in the west of the Amazonian region, the Brazilian state of Rio Grande do Sul, the east coast of Brazil and the surroundings of Buenos Aires (Argentina); she does not mention the origin of this information.
The species N. amazonus and N. badius differ in several characters. The first, that N. amazonus is approximately 80% the size of N. badius (see Table 1). Though the phallic structure is basically the same, the species show differences in the proportion of the sclerites. The PECS and DECS are equal in length in N. badius while in N. amazonus PECS are approximately 80% the length of the DECS. The color of the species is clearly different when the written description of N. amazonus is compared. Several species of the genus Neometrypus collected by the authors of this paper in the Atlantic forest of the São Paulo State differ from each other in body color, size and karyotypes, but none of them show an X-autosome tandem fusion.
Desutter's diagnosis of the genus Neometrypus includes several body color characters. In consequence, each one of the species we collected in São Paulo State, differing among other characters in color pattern, should belong to different genera. We do not agree with this criterion and consider that in this case body color is only a good specific character within the genus.
The neo-X chromosome of N. badius originated in a tandem fusion between the distal region of a medium-size autosome and the proximal region of the primitive X, with the loss of the centromere of this chromosome.
The use of the terms “reductional” and “equational” in reference to the homologous chromosome behavior during the first and second meiotic divisions may be misleading. According to White (1973 Pp. 491–2) both terms are meaningless if applied to whole chromosomes because the terms mean separation of maternal and paternal strands. So only the centromere and segments of chromatids placed between that structure and the first crossing-over are reductional in the first division and equational in the second one. Beyond the first chiasmata maternal and paternal strands may separate reductionally or equationally depending on the number and position of each crossing-over.
In small pairs of acridid chromosomes, the presence of a distal heterochromatic segment is frequently seen (Fig. 4). When in heterozygote condition, two similar chromosomes, both with a short and long chromatid, go to opposite poles during first anaphase, due to the occurrence of a single chiasma in the proximal euchromatic segment. The centromeres divide and separate the unequal chromatids during AII. In this case, the first division is reductional with the centromeres arranged in a syntelic way at MI.
The three species with X-autosome tandem fusion reported, one eumastacid and two tettigonids, are similar to the above mentioned case, having a syntelic arrangment at MI and with a single chiasma taking place between XR and Y (see White et al. 1967, Fig. 6b; Fernández-Piqueras et al. 1981, Figs 3a, b and Warchalowska-Sliwa et al. 1998, Fig. 1j and this paper first row of Fig. 3).
In the species of cricket here studied the single crossingover seems to occur in the small arm of X and Y and the structure of the sex bivalent during first metaphase suggests an anphitelic orientation and the splitting of both centromeres to initiate AI, in a true equational first division (see Fig. 3, second row). The second division is then an authentic reductional division.
The presence of a heterochromatic Y chromosome during diakinesis could indicate that the X- tandem fusion in N. badius is relatively old. In the three previously published species, the fusion seems to be recent because of the presence of an interstitial chiasma between XR and Y. Moreover, in the case of the eumastacid (White et al. 1967, p.45), both XY and X free populations still exist, and the same happens in the tettigonid Callicrania seoanei (Fernández-Piqueras et al. 1981).
The unusual X-autosome tandem fusion observed in N. badius will be a definitive diagnostic character of this species in the event it is absent in N. amazonus, but for the present, the karyotype of this species remains unknown.
The authors are deeply indebted to Dr. Theodore Cohn who contributed valuable suggestions on the original manuscript. We also want to thank the Florestal Institute (Secretaria de Estado do Meio Ambiente de SP) for authorization to collect in Cardoso Island and Dr. Edson Zefa for his collaboration in the collection of specimens.