A new species and karyotype variation in the bordering distribution of Mepraia spinolai (Porter) and Mepraia gajardoi Frías et al (Hemiptera: Reduviidae: Triatominae) in chile and its parapatric model of speciation

SYSTEMATICS, MORPHOLOGY AND PHYSIOLOGY

A new species and karyotype variation in the bordering distribution of Mepraia spinolai (Porter) and Mepraia gajardoi Frías et al (Hemiptera: Reduviidae: Triatominae) in chile and its parapatric model of speciation

Daniel Frías-Lasserre

Instituto de Entomología, Univ Metropolitana de Ciencias de la Educación, 7760197, Santiago, Chile; [e-mail]

ABSTRACT

In the present study, the morphology, color pattern, chromosomal complement and aspects of meiosis in natural populations at the borders of the distributions of Mepraia gajardoi Frías et al and Mepraia spinolai (Porter) are described. The males of these bordering populations are brachypterous or macropterous, while females are always micropterous. Morphological and cytogenetic data indicated that the populations that border the distributions of M. gajardoi and M. spinolai, belong to a different species of parapatric origin.

Key words: Wing polymorphism, heterochromatin variation, vector of Chagas' disease

Mepraia spinolai (Porter) and Mepraia gajardoi Frías et al are two endemic Chilean Reduviidae. Mepraia gajardoi, originally considered as a population of M. spinolai, later came to be regarded as a distinct species (Frías et al 1998, Jurberg et al 2002). It is distributed along the northern coast of Chile, approximately between 18º and 26º S, while M. spinolai is distributed approximately between 26º S and 33º S (Frías & Atria 1998). Both species transmit the causal agent of Chagas' disease, Trypanosoma cruzi. Mepraia spinolai is adapted to sylvatic/peridomestic habitats, and M. gajardoi only to sylvatic habitats (Sagua et al 2000, Canals et al 2001, Carvajal et al 2007, Botto-Mahan et al 2008). This disease is important in the Neotropical region with nearly 16 million people infected, and another 90 million at risk of contracting the disease, especially in rural areas (Schofield et al 1982, Schofield 1994).

Mepraia gajardoi differs from M. spinolai in body color, morphology, genitalia and karyotype. Females of both species are invariably wingless (micropterous). Males of M. gajardoi are always winged (brachypterous), whereas males of M. spinolai may be winged (macropterous, brachypterous) or wingless (micropterous) (Mazza et al 1940, Neiva & Lent 1940, Lent & Jurberg 1967, Frías et al 1998). Reciprocal crossbreeding experiments showed that the two species are reproductively isolated (Frías et al 1998).

The karyotypes of both species are formed by 20 autosomes and an X1 X2 Y sex system. However, males of M. gajardoi have a large Y chromosome, whereas those of M. spinolai are polymorphic for a small neo-Y chromosome, which may have originated by a fracture of the large holocentric Y chromosome of M. gajardoi (Frías & Atria 1998). Also, a particular heteropycnotic chromocenter, typical of M. spinolai, differentiates this species from M. gajardoi. It is formed by sex chromosomes surrounded by several autosomal heteropycnotic dots. Other heteropycnotic regions outside this chromocenter can also be observed (Frías & Atria 1998, Perez et al 2004)

In the present study, I report the morphological traits of adults and the chromosomal complement of populations of Mepraia species bordering the distribution of M. gajardoi and M. spinolai, with a discussion of their mode of speciation.

Material and Methods

Populations studied. The specimens examined were collected during the summer of 1996 by D Frías and A Alviña, and during spring, in November 2002, by D Frías, from region III of Atacama and region II of Antofagasta (Fig 1). The former region is located in the Parque Nacional Pan de Azúcar: Pan de Azúcar Island, 3 km SW of Porto Pan de Azúcar (26º 92 053 S, 70º 402 533 W, 50 m a.s.l.): six males and two females; associated with Spheniscus humboldti (Humboldt penguin); in the coastal area of the mainland in the Caleta Pan de Azúcar (26º 92 013 S; 70º 402 013 W, 0 m a.s.l.): two females, two males associated with lizards; Cerro El Soldado, 3 km S of Porto Pan de Azúcar (26º 102 103 S, 70º 402 033 W, 231 m a.s.l.): one female and two males, associated with seagulls Larus dominicanus. Inca de Oro, Mina San Vicente, 16 km NE of Estación Chimbero (26º 452 013 S, 69º 542 063 W, 1600 m a.sl.): one female, three macropterous males, two micropterous males. The second was in the Caleta Bandurrias, 21 km S of Paposo (25º122 203 S, 70º 262 73 W, 0 m a.s.l.): one female, six males, associated with goats Capra hircus; Cachinales, 22 km S of Paposo (25º122 583 S, 70º 262 123 W, 0 m a.s.l.): two males associated with L. dominicanus. The specimens were transported to the laboratory in plastic boxes and maintained on live chicken.

Specimens collected in these studies were deposited in the Collection of the Institute of Entomology, Universidad Metropolitana de Ciencias de la Educación (IEUMCE), Santiago, Chile.

For comparative purposes, I utilized 168 specimens, 107 females and males of M. spinolai and 61 of M. gajardoi from different localities, collected between 18ºS and 33ºS, and those deposited at IEUMCE, Santiago, Chile. Specimens of M. gajardoi from region II and M. spinolai from region III were especially studied because they overlap parapatrically with the new species at some of these localities. Herein, I also redescribe M. spinolai and compare it to the new species and to M. gajardoi (Frías et al 1998, Jurberg et al 2002).

Characteristics of each locality. Pan de Azúcar Island and other coastal localities of regions II and III lie in a coastal-desert climate regime, with less than 200 mm of rain annually (Di Castri & Hajek 1976). Pan de Azúcar Island has been preserved as a national park because the Humboldt penguin Spheniscus humboldti and the sea otter Lutra feline reproduce on this island. The fauna and flora are similar to those of the coast, in the Atacama Desert. Cacti, marine birds, carrion birds, lizards and other marine mammals such as the sea lion Otaria flavescens are numerous on the island (Sagua et al 2000). Inca de Oro is a continental city located 1,600 m a.s.l., near the Domeyko Cordillera. This locality is in the most arid part of northern Chile. It has a desert climate with cold mountains and scarce and irregular rainfall during winter, rarely reaching 100 mm per year. The fauna that serves as a host to sylvatic M. spinolai is mainly composed by small rodents, such as Chinchilla lanigera, Lagidium viscacia, Oligoryzomys longicaudatus, Phyllotis darwini, Phyllotis xanthopygus, Abrocoma benetti and Octodon degus.

Morphology. I counted the number of wingless (micropterous) and winged (brachypterous and macropterous) males collected in each locality. Micropterous males, like females, have their hemelytra reduced to small suboval sclerites, not extending beyond the posterior margin of the mesonotum. Males with hemelytra shorter than the abdomen are considered brachypterous. Males having the hemelytra longer than or as long as the abdomen are considered macropterous.

The following measurements were taken for females and males: total length of the body (except the rostrum), head length (except the rostrum), maximum width of the head at the eye level, pronotum length and width (Fig 2a), hemelytra length (Fig 2b), abdomen length and width (Fig 2c). Body coloration and the color pattern of the connexivum of the abdomen were also analyzed. Terminology follows that of Lent & Wygodzinsky (1979).

The genitalia were dissected and treated overnight in 10% KOH. In males, the median process of the pygophore, parameres and phallus were studied following Lent & Jurberg (1967) and Jurberg et al (1998, 2002). In female genitalia, the gonocoxite 8 (Gc8), gonocoxite 9 (Gc9), gonapophysis 8 (G8) and gonapophysis 9 (G9) were particularly analyzed, following Lent & Jurberg (1967).

Cytological preparation. Chromosomes were obtained from the gonads of adults that were fixed in 3:1 ethanol-acetic acid. The gonads were crushed in 50% acetic acid, and frozen in liquid nitrogen. Coverslips were removed with a razor blade. Karyotypes were obtained by the classic lacto-acetic orcein method (Solferini & Morgante 1987). The barium hydroxide method of Sumner (1972) was used for C-Banding. Chromosome preparations were examined using an optical Leitz Laborlux K Microphoto microscope in addition to a laser scanning microscope 633 (Helium-Neon, Carl Zeiss, Inc. Model 210).

Mepraia parapatrica n. sp.

Holotype: Brachypterous male, region II of Antofagasta, Caleta Bandurrias, three November 2002, associated with goats, deposited at IEUMCE. Paratypes: one female and six males (one macropterous and five brachypterous), same data and locality as holotype. Cachinales, one female and two males (one brachypterous and one macropterous), associated with lizards, same data and locality as holotype. Collector D Frías.

Region III of Atacama, Parque Nacional Pan de Azúcar: Pan de Azúcar Island: two females and six males (one macropterous and five brachypterous), 5 November 2002, Caleta Pan de Azúcar, in coastal area of mainland: two females and two males (one macropterous and one brachypterous) associated with lizards, 6 November 2002, D Frías coll. Cerro el Soldado: one female and two brachypterous males, associated with sea birds, D Frías and A Alviña colls., 15 December 1996. The paratypes were deposited at IEUMCE.

Type locality. Caleta Bandurrias, region II of Antofagasta, 25° 122 202 2 S, 70° 262 072 2 W, 0 m a.s.l., 21 km S of Paposo city.

Distribution.Mepraia parapatrica n. sp. is distributed along the northern coast of Chile, region II of Antofagasta and region III of Atacama, in "desierto litoral" approximately between 25° 122 202 2 S,70° 262 072 2 W and 26º 102 103 S , 70º 402 033 W, 231 a.s.l. This species also occurs on Pan de Azúcar Island 26º 92 053 S, 70º 402 533 W, 50 m a.s.l. (Fig 1).

Diagnosis. Females: connexivum of second urotergite with two separate red spots, urotergites III to VII with small red spots at intersection with inter-segmental suture, urotergites VIII to X black; in ventral view, gonapophysis (G9) 0.60-0.70 mm long, slightly concave posteriorly, curved anteriorly, sharp and bifurcated at apex. Males: medial region of parameres with spiniform sclerotized area, basal plate of articulatory apparatus of phallus slightly sclerotized, 0.71-0.81 mm long, phallosome anteriorly, very small at apex, 0.11- 0.14 mm wide, phallotheca plate slightly sclerotized, rhomboid posteriorly, aedagus 1.29- 1.31 mm long.

System of sex determination X1X2Y. The Y chromosome is C positive and longer than the X chromosomes. Both X1 and X2 chromosomes are euchromatic with a small block of heterochromatin in one of their telomeres.

Description

Region III populations. Pan de Azúcar Island, Caleta Pan de Azúcar, and Cerro el Soldado.

Females. Black overall, micropterous, 18.40-22.40 mm long (Fig 3a). Head: length 4.22-4.78 mm, width 2.00-2.55 mm, black, strongly granulate, first and second segments of antennae black, first segment with short curved hairs, second segment with long hairs, third and fourth segments brown with long and short hairs. Rostrum, black with slender rostral segments. Eyes metallic gray, never reaching inferior level of head. Ocellus small, 0.16-0.21 mm in diameter, reddish or whitish. Neck shiny black. Thorax: pronotum subtrapezoidal, uniformly black, 2.00-3.00 mm long, 2.23-3.53 mm wide, anterior lobe conspicuously convex, posterior lobe rugose, shorter than anterior lobe, humerus and posterior margin of pronotum rounded. Anterolateral projections of pronotum conical, collar curved. Scutellum triangular, wider than long, heavily rugose, with median concavity. Hemelytra length 1.00-1.51 mm, reduced to small suboval sclerites. Legs uniformly black, except for dark-brown tarsi, femur with short curved hairs, tibia with short curved erect hairs, tarsus with long erect hairs. Abdomen: ovoid, black, 11.00-14.00 mm long, 7.00-10.00 mm wide; dorsally, first urotergite black, connexivum of second urotergite with two separate red spots, urotergites III to VII with small red spots on intersection of intersegmental suture, urotergites VIII, IX and X black (Fig 3a), in ventral view, urosternites I, II and III black or with tiny red spots, connexival membrane dark brown. Genitalia black overall (Fig 4a), and overall size smaller than M. spinolai and M. gajardoi (Fig 4d, ^g). Gonocoxite 8 (Gc8) rounded with numerous black bristles, gonapophysis 9 (G 9) 0.60-0.70 mm long, black, slightly concave posteriorly, curved anteriorly, with long bristles, sharp and bifurcated at apex (^{Fig 4b}); gonapophysis 8 (G 8) triangular, with long bristles (^{Fig 4c}), gonocoxite 9 (Gc 9) 0.90-1.00 mm long, concave, with external margin darker than central area, rounded at apex, with numerous long bristles anteriorly (Fig 4a). In M. spinolai and M. gajardoi these structures are very different, in particular gonapophysis 8 (^{Fig 4f-i}) and gonapophysis 9 (^{Fig 4e-h}).

Brachypterous male. Black overall, 15.50-19.00 mm long (Fig 3b). Head: 3.10-3.60 mm long, 2.3-2.7 mm wide (Fig 5a), black, strongly granulate, overall size smaller than M. spinolai (Fig 5b) and M. gajardoi (Fig 5c). First and second segments of antennae black, third and fourth segments brown, first segment with some short curved hairs, second, third and fourth segments with long and short hairs. Rostrum brown with slender rostral segments. Eyes metallic black or grayish, never reaching inferior level of head. Ocellus prominent, reddish or whitish, 0.19-0.27 mm in diameter. Neck shiny dark brown. Thorax: pronotum subtrapezoidal, black, 2.00-2.38 mm long, 3.00-3.53 mm wide, anterior lobe conspicuously convex, posterior lobe rugose, longer than anterior lobe, posterior margins of pronotum and humerus rounded. Anterolateral projections of pronotum conical, collar curved. Scutellum triangular, as wide as long, and heavily rugose with prominent median concavity. Hemelytra shorter than abdomen, 7.00-9.00 mm long, rounded at apex. Legs uniformly black except for dark-brown tarsi, femur of first, second, and third pairs of legs with short hairs, tibia and tarsus with long hairs. Abdomen: slightly ovoid, 8.70-10.00 mm long, 4.20-5.70 mm wide, black; connexivum with small red spots on urotergites II to VII extending onto inter-segmental sutures, black in ventral view, with small red spots. Spiracles black, parameres and pygophore black, median area of parameres spiniform, strongly curved anteriorly, rhombus-like and strongly sclerotized at apex (Fig 6a), parameres of M. spinolai and M. gajardoi lacking this spine-shaped area (Fig 6b,c); V-shaped median process of pygophere (Fig 6d) larger and broader than in M. spinolai and M. gajardoi (Fig 6e,f), basal plate of articulatory apparatus of phallus slightly sclerotized, 0.71-0.81 mm long, phallosome smaller than in M. gajardoi and larger than in M. spinolai, aedagus 1.29-1.30 mm long, longer than in M. spinolai and shorter than in M. gajardoi (Fig 7a,b,c), phallosome anteriorly, very small at apex, 0.11-0.14 mm wide, smaller than in M. spinolai and M. gajardoi (0.68-0.72 mm and 0.35-0.42 mm wide in M. spinolai and M. gajardoi, respectively) (Fig 7a-f). Phallotheca plate of M. parapatrica sclerotized, posteriorly rounded and rhombus-shaped (Fig 7d), whereas in M. spinolai this plate is posteriorly concave and rounded at its apex (Fig 7e), and in M. gajardoi the plate is rounded at its apex (Fig 7f). Endosome process in M. parapatrica anteriorly conical at apex and median area with small bristles (Fig 7g); in M. spinolai it is cylindrical (Fig 7h), and in M. gajardoi it is conical and larger than in M. parapatrica (Fig 7i).

Macropterous male. Similar to brachypterous males in color, but with larger body, 19.00-20.00 mm long (Fig 3c). Pronotum width 4.19-4.61 mm; hemelytra longer than those of brachypterous males, between 12.00 mmm and 13.00 mm, reaching to or past end of abdomen. Collar straight or slightly curved, in ventral view, spiracles reddish. Genitalia similar to those of brachypterous male.

Populations of region II. Caleta Bandurrias and Cachinales

Female. Similar to female of region III from Pan de Azúcar Island, Caleta Pan de Azúcar and Cerro el Soldado.

Brachypterous and macropterous males. These are morphologically similar to those described from region III.

Cytogenetics. The karyotype of the Bandurrias and Cachinales populations is formed by 20 autosomes and an X1, X2, Y system of sex determination. The Y chromosome is C positive and longer than the X1 and X2 chromosomes. All autosomes have constitutive heterochromatin in both telomeres. The X1 and X2 chromosomes are euchromatic, but have a small block of constitutive heterochromatin in one of their telomeres (Fig 8a,b). Specimens from Pan de Azúcar Island show a karyotype similar to specimens from Bandurrias (Fig 8c).

Etymology. The name of this species is related to its probable mode of speciation. The specific name refers to the Spanish word parapatrica, based on Articles 31.2.2 and 31.2.3 of the International Code of Zoological Nomenclature.

Redescription of Mepraia spinolai

Population of region III. Inca de Oro

Female. Overall dark brown, micropterous, 19.60-21.00 mm long. Head: 4.61-5.50 mm long, 1.97-2.00 mm wide, dark brown, strongly granulate, antennae brown, first segment with some short and curved hairs, second segment with long hairs, third and fourth segments with long and short hairs, rostrum dark brown with slender rostral segments. Eyes metallic black or grayish, never reaching inferior level of head. Ocellus reddish or whitish, 0.09-0.20 mm in diameter. Neck shiny brown. Thorax: pronotum subtrapezoidal, uniformly dark brown, 3.56-4.33 mm long, 3.05-4.07 mm wide, anterior lobe conspicuously convex, posterior lobe rugose and about as long as anterior, posterior margin of pronotum and humerus rounded. Scutellum triangular, wider than long, heavily rugose. Hemelytra length 1.25-1.50 mm, reduced to small suboval sclerites; legs uniformly brown, femur with short curved hairs, tibia and tarsus with long and short erect hairs. Abdomen: ovoid, black, 12.00-13.00 mm long, 8.00-9.00 mm wide, connexivum with dorsal red spots on each urotergite II to VIII. Second urotergite with dorsal continuous orange or red band on the edges; connexival sutures of urosternites I-VII with ventral red spots on intersection with inter-segmental suture, reddish connexival membrane. Genitalia black overall (Fig 4d), gonocoxite 8 with numerous long black bristles, gonapophysis 9 (G 9) 0.90-1.00 mm long, curved and rounded at apex, with long bristles anteriorly, concave posteriorly (^{Fig 4e}), gonapophysis 8 (G8) triangular, with long bristles (^{Fig 4f}); gonadocoxite 9 (Gc 9) 0.90-1.10 mm long, concave, with external margin darker than central area, numerous long bristles anteriorly, rounded at apex (Fig 4d).

Macropterous male. Brown overall, 19.00-20.00 mm long. Head: 4.5-4.62 mm long, 2.0-2.13 mm wide (Fig 5b), dark brown, strongly granulate, brown antennae, first segment with some short curved hairs, second, third and fourth segments with long and short hairs. Rostrum brown, with slender rostral segments. Eyes metallic brown or grayish, never reaching inferior level of head. Ocellus prominent, black, reddish or whitish, 0.20-027 mm diameter. Neck shiny brown. Thorax: pronotum subtrapezoidal and uniformly brown, 2.85-3.27 mm long, 4.00-4.70 mm wide, anterior lobe conspicuously convex, posterior lobe rugose and longer than anterior lobe, posterior margins of pronotum and humerus rounded. Anterolateral projections conical, collar curved. Scutellum triangular, wider than long, heavily rugose, with prominent median concavity. Hemelytra longer than abdomen or not exceeding its length, 14.00-15.00 mm long, rounded at apex. Legs uniformly brown, femur of first pair of legs with long erect and short curved hairs; femur of second and third pairs of legs with short and curved hairs, tibia and tarsus with long and short erect hairs. Abdomen slightly ovoid, 10.05-11.00 mm long, 6.00-8.00 mm wide, black, connexivum with dorsal red spots on urotergites II to VII in ventral view, black with red spots on urosternites II to VII, spiracles yellow, parameres strongly curved anteriorly, rhomboid and moderately sclerotized at apex, medial area not spiniform (Fig 6b), pygophore dark brown or black, median process of pygophore V-shaped (Fig 6e), basal plate of phallus articulatory apparatus heavily sclerotized 0.33-0.36 mm long, phallosome anteriorly, very broad at apex, 0.68-0.72 mm wide, aedagus 1.14-1.19 mm long (Fig 7b,e), phallotheca plate sclerotized, concave posteriorly and rounded at apex (Fig 7e), endosoma process anteriorly cylindrical, at apex and median area with small bristles (Fig 7h).

Micropterous male. Black overall, 18.50-19.00 mm long. Head: 3.90-4.33 mm long, 1.87-2.10 mm wide, black, strongly granulate, antennae brown, first segment with some short and curved hairs, second, third, and fourth segments with long and short erect hairs. Rostrum brown, with slender rostral segments. Eyes metallic black or grayish, never reaching inferior level of head. Ocellus prominent, reddish or whitish, 0.16-0.21 mm in diameter. Neck shiny brown. Thorax: Pronotum subtrapezoidal, uniformly brown, 2.21-2.97 mm long, 2.78-3.10 mm wide, anterior lobe conspicuously convex, posterior lobe rugose and about as long as anterior lobe, posterior margins of pronotum and humerus rounded. Anterolateral projections conical. Scutellum triangular, wider than long, heavily rugose, with pronounced median concavity. Hemelytra reduced to small suboval sclerites, 1.00-1.44 mm long. Legs uniformly brown, femur of first pair of legs with long erect hairs, femur of second and third pairs of legs with short curved hairs; tibia and tarsus with long and short erect hairs. Abdomen slightly ovoid, 9.45-10.00 mm long, 5.00-6.00 mm wide; black, connexivum with two dorsal red spots on urotergites II to VII on intersection of intersegmental suture, in ventral view black with red spots, spiracles yellow, parameres similar to Fig 6b, pygophore dark brown or black, median process of pygophore V-shaped, similar to Fig 6e; basal plate of phallus articulatory apparatus heavily sclerotized and shorter than 0.5 mm, phallosoma anteriorly very broad at apex, wider than 0.15 mm (similar to Fig 7b,e), aedagus length similar to macropterous male, phallotheca plate sclerotized, posteriorly concave and rounded at apex, similar to Fig 7e, endosoma process anteriorly cylindrical, with small bristles at apex and median area, similar to Fig 7h.

Cytogenetics. The karyotype of the Inca de Oro population is formed by 20 autosomes plus X1 X2 Y in males and X1 X1 X2 X2 in females (Fig 9a,b). All autosomes have C positive blocks on both telomeres; the X1 sex chromosome has one dot of heterochromatin in one of its telomeres, whereas the X2 chromosomes are totally euchromatic (Fig 9b). During metaphase II of meiosis (males), the tenth half bivalents form a ring-shaped configuration with three of the sex chromosomes in the center (Fig 9a). In anaphase II, the X1 and X2 chromatids segregate to the same pole, while the Y chromosome migrates to the opposite pole (Fig 9c). Therefore, the second division is reductional for sex chromosomes, as in other Hemiptera. The pachytene of prophase I has a particular heteropycnotic chromocenter formed by sex chromosomes surrounded by several autosomal heteropycnotic dots. Also, other heteropycnotic regions outside this chromocenter can be observed (Fig 9d). In one winged male (macropterous), different types of diakinesis plates were observed. In two of these plates the three sex chromosomes formed a chromocenter that seems to be attached to one bivalent autosome (Fig 10a,b). In another plate, one of the X chromosomes seems to be free, and in the other the X is attached to the Y chromosome and to one bivalent autosome (Fig 10c). The X chromosome also appears free, near a bivalent autosome (Fig 10d). This population has a chromosome complement similar to that of M. spinolai as described by Panzera et al (1998) and Frías and Atria (1998).

Discussion

Morphology. The population of M. parapatrica from region II (Bandurrias and Cachinales) and those from Parque Nacional Pan de Azúcar from region III differ from M. spinolai and M. gajardoi in their karyotype and morphology. The main differences are briefly summarized in Tables 1 and 2.

Males of M. parapatrica are always winged, brachypterous or macropterous, but never micropterous, whereas males of M. gajardoi are always brachypterous. Males of M. spinolai are polymorphic in the length of their wings, and can be micropterous, brachypterous or macropterous (Lent et al 1994, Frías & Atria 1998, Frías et al 1998). These wing differences are important, because it has been reported that the genes responsible for wing development are linked to the Y chromosome. Therefore the phenotypic differences described are inheritable (Frías & Atria 1998).

Chromosomes. The populations of M. parapatrica also show differences in their distinctive cytogenetic features in comparison to those occurring in M. gajardoi and M. spinolai (Table 2). All autosomes have blocks of heterochromatin in both telomeres; the X1 and X2 sex chromosomes have dots of heterochromatin in one of their telomeres (Fig 8a,b,c). This characteristic differentiates it from M. gajardoi, in which the autosomes and the X1 and X2 sex chromosomes are completely euchromatic. The Y chromosome in the new species is C-positive and is longer than the X chromosomes. This feature differentiates it from M. spinolai, which shows polymorphism in the number of Y sex chromosomes (Y1 and Y2), probably originating from a fracture of an ancestral longer Y chromosome of M. gajardoi (Frías & Atria, 1998).

It is probable that the association detected between sex chromosomes and one of the autosomes in the Inca de Oro micropterous males of M. spinolai correspond to a translocation, which allowed the fracture of the holocentric Y chromosome. This fracture would have originated the polymorphism in the number of Y chromosomes found in the M. spinolai population. This fragmentation of the original longer Y chromosome of M. gajardoi and M. parapatrica may be associated with the exceptional alary polymorphism detected in M. spinolai, especially regarding the origin of wingless males (Frías & Atria 1998, Jurberg et al 2002). Panzera et al (1998) found a similar association between each X chromosome and autosomes in a wingless male of M. spinolai.

Cytogenetic differences, mainly heterochromatinization, translocations and Y chromosome rupture with the formation of chromocenters (as described in M. spinolai) may indicate a post-zygotic reproductive isolation between Mepraia species in semi-geographical conditions.

Geographical distribution and biology.Mepraia parapatrica is apparently confined to Pan de Azúcar Island and also to the coastal border of regions II and III, approximately between 25º 12´ 20´´S, 70º 26´ 07¨W and 26 º 10´ 10¨S, 70º 40´ 03´´W. The presence of M. gajardoi in region II and M. spinolai in region III (Frías & Atria 1998, Frías et al 1998) may indicate that they cohabit with M. parapatrica in this area. However, the morphology of the female and male genitalia is very different from that of M. spinolai and M. gajardoi. Furthermore, the cytogenetic characteristics suggest that there is no gene flow between M. parapatrica and M. gajardoi and M. spinolai, indicating that M. parapatrica is a distinct species that had a parapatric origin. Also, these populations of M. parapatrica differ ecologically from the other two species. They feed on wild sea birds and lizards, similar to M. gajardoi, but they were also collected in a goat pen, therefore invading peridomestic environments as does M. spinolai. The latter is a wild or peridomestic species that normally feeds on small wild rodents, but also occasionally invades domestic habitats. However, it was never reported to feed on birds (Schofield et al 1982, Schofield 1994, Frias & Atria1998, Frías et al 1998).

These feeding differences may be related to the efficiency in the propagation of T. cruzi. Birds do not support the life cycle of T. cruzi (Schofield et al 1982). Sagua et al (2000) reported that in M. parapatrica, no T. cruzi infection was detected on Pan de Azúcar Island where this species is associated with the Humboldt penguin. The recently published information on T. cruzi infecting M. gajardoi indicates a natural association (11.8% infection in all analyzed insects; Botto-Mahan et al 2008). However, T. cuzi infection can reach up to 46.2% to 61% in M. spinolai in some areas of central Chile (Frías et al 1995, Botto-Mahan et al 2005).

Wing polymorphism and heterochrony during development. All females and males of Triatominae described are winged (Lent & Wygodzinsky 1979). It is probable that the gene for wing development in the ancestors of the genus Mepraia was located in an autosome. This would explain the existence of winged males and females in all Triatominae species. Cross-breeding of M. spinolai showed that the gene for wing development is linked to the Y chromosome (Frías & Atria 1998). This was probably the first step in the origin of the Mepraia complex (Fig 11). In an evolutionary framework, it is possible that M. gajardoi, with micropterous females and invariably brachypterous males, was the first ancestral species of the genus Mepraia in Chile.

The microptery observed in all species of Mepraia and in males of M. spinolai is an apomorphic trait (Schofield et al 1998), probably caused by heterochrony during the development (neoteny). Females are fertile, but their phenotype is similar to fifth instars (Mazza et al 1940). The break of the holocentric Y explains the origin of neo-Y chromosomes detected in M. spinolai; one form (Y1) bears genes for wings, while the other (Y2) lacks such genes, and this explains the origin of micropterous males (Frías & Atria 1998). The microptery in both males and females in M. spinolai shows that, in a parsimony model, M. spinolai is the most recent species in the evolution of the genus Mepraia in Chile, probably originating semi-geographically from M. parapatrica (Fig 11).

Longer wings of macropterous males, with hemelytra longer than the apex of the abdomen, as observed in M. parapatrica and M. spinolai, correspond to another phenotypic novelty in the Mepraia group. This is probably an atavistic trait, because this characteristic has been described in distant ancestors of Mepraia species, such as in some species of Triatominae belonging to the genus Rhodnius, and also in the genus Psammolestes (Lent & Wygodzinky 1979). However, this character is absent in their closest ancestors such as Triatoma breyeri Del Ponte and Triatoma erutyrusiformis Del Ponte as described by Lent & Wygodzinky (1979).

The probable origin of genus Mepraia. The species of the breyeri complex, formed by T. breyeri and T. eratyrusiformis, comprise a group related to the species of Mepraia (Carcavallo 2000), which occurs in desert and semi-desert areas of Argentina (Curto de Casas et al 1999) as do the species of Mepraia. Hypsa (2002), based on molecular studies using 16S and 12S rDNA, postulated that T. eratyrusiformis belongs to the genus Mepraia. This hypothesis does not accord with morphological studies by Caracavallo et al (2000). Comparing the phenotype of the antennae between M. gajardoi and M. spinolai, and T. eratyrusiformis and T. breyeri, Moreno et al (2005) found that Mepraia species and T. eratyrusiformis share similarities in bristles and receptors that are not present in T. breyeri. According to Moreno et al (2005), M. gajardoi and M. spinolai have a common ancestor, probably related to the breyeri complex.

It is possible that the origin of the genus Mepraia is related to the last uplifting of the Andes cordilleras during the Miocene, about 20 million years ago (Fig 11) (Solbrig 1976, Moreno et al 2005). This would have caused the separation of the breyeri group, which currently occurs in the dry areas of Argentina, along the eastern slope of the Andes (Lent & Wygodzinsky 1979). The speciation process in Mepraia would have occurred during the post-glacial Pleistocene about 10,000-8,000 years ago, when floristic, climatic, orogenic, volcanic,and Pacific Ocean-level changes occurred (Cecioni 1970, Vuilleumier 1971, Heusser 1974, Solbrig 1976, Paskoff 1977, Neghme 1982). In this period, Pan de Azúcar Island probably arose, where M. parapatrica is currently distributed. Chromosomal changes would have contributed to the reproductive isolation between these species, as described by Frías et al (1998). A significant cytogenetic change in the evolution of the Mepraia species was the heterochomatinization of telomeres of the autosomes and the X sex chromosomes, described here for M. parapatrica. This was a key genetic change that probably gave rise to M. parapatrica through meiotic barriers under semi-geographical conditions. Repetitive sequences are located within the constitutive heterochromatin (Gilbert 2003), and within these sequences non-transcriptional genes are found (Frías 2007). They have an important role in genetic regulation (Gatti & Pimpenelli 1992), telomere stabilization (Zakian 1998), DNA replication (Bell et al 1993) and chromosomal movement during cell division and chromocenter formation (Gatti & Pimpenelli 1992). Subsequently, in the evolution of Mepraia species, the large holocentric Y chromosome detected in M. gajardoi and M. parapatrica broke and originated the neo-Y chromosomes found in M. spinolai. According to the present distribution of these Mepraia species, it is likely that all these chromosomal and morphological changes occurred under semi-geographical conditions, similarly to the model described for the micropterous Morabinae grasshoppers in Australia (White 1968, 1978, Key 1974). Therefore, the most parsimonious model that explains the evolution of the Mepraia species in Chile is the parapatric model of phyletic speciation by negative heterosis.

Acknowledgments

I am grateful to the following persons: Ch. González for suggestions on the manuscript, Alejandro Vera for assisting me with the International Code of Zoological Nomenclature, and an anonymous reviewer for his valuable suggestions. I am grateful to CONAF-Chile for logistical aid in the Parque Nacional Pan de Azúcar. Supported by grants FONDECYT 1940753-1994 and DI, 1/09/ 2002 DIUMCE.

Received 08/I/09.

Accepted 01/VII/10.

Edited by Marcelo Duarte MZ/USP

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Publication Dates

• Publication in this collection
  14 Sept 2010
• Date of issue
  Aug 2010

History

• Received
  08 Jan 2009
• Accepted
  01 July 2010