Chromosomal variation, macroevolution and possible parapatric speciation in Mepraia spinolai (Porter) (Hemiptera: Reduviidae)

Abstract

Mepraia spinolai is an endemic species in Chile that lives in wild and domestic habitats. It is the only species of the Reduviidae family that shows alate polymorphism; females are always wingless, but males can be found with and without wings. The M. spinolai karyotype consists of 10 pairs of autosomes and a complex sex determination system. Males from the northernmost regions I and II (latitude 18°-26° South) are always winged (braquipterous) and are X1X2Y, with a large Y chromosome. From region III to the metropolitan region (latitude 26°-33° South), males may be either winged or wingless but appear to be polymorphic for a small neo-Y chromosome, which may have originated by fracture of the large holocentric Y chromosome found in populations from farther north. Experimental crosses suggest that the genes for wings are linked in the Y chromosome and also that there are two cytologically indistinguishable types of neo-Y chromosomes. One form (Y1) bears a gene or genes for wings while the other (Y2) lacks such genes. Males that are X1X2Y1, X1X2Y1Y1 and X1X2Y1Y2 are winged, while the absence of Y1 (X1X2Y2 and X1X2Y2Y2 ) results in a wingless male. These chromosomes and morphological changes are correlated with a shift of the southern population into more arid habitats of the interior in the metropolitan region and region III.<br>Mepraia spinolai é uma espécie endêmica no Chile que mora em habitats domésticos e silvestres. É a única espécie da família Reduviidae que apresenta polimorfismo de asas: as fêmeas são sempre sem asas, mas os machos podem ou não tê-las. O cariótipo de M. spinolai consiste de 10 pares de autossomos e um sistema complexo de determinação do sexo. Os machos das regiões mais setentrionais, regiões I e II (latitude 18o-26o S), sempre têm asas (braquíteros) e são X1X2Y, com um grande cromossomo Y. Da região III à região metropolitana (latitude 26o-33o S), os machos podem ou não ter asas, mas parecem ser polimórficos para um pequeno neo-cromossomo Y que pode ter se originado por fratura do grande cromossomo Y holocêntrico encontrado nas populações mais ao norte. Cruzamentos experimentais sugerem que os genes para asas estão ligados no cromossomo Y e também que há dois tipos citologicamente indistinguíveis de neo-cromossomo Y: uma forma (Y1) é portadora de um gene ou de genes para asas, enquanto que a outra (Y2) não apresenta tais genes. Os machos que são X1X2Y1, X1X2Y1Y1 e X1X2Y1Y2 têm asas, enquanto que a ausência de Y1 (X1X2Y2 e X1X2Y2Y2 ) resulta em um macho sem asa. Esses cromossomos e as modificações morfológicas correlacionam-se com uma mudança da população do sul para habitats mais áridos do interior da região metropolitana e da região III

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

“…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).…”

“…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. …”

“…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).…”

“…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. These wing differences are important, because it has been reported that the genes responsible for wing development are linked to the Y chromosome.…”

“…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.…”