Extensive fragmentation of the X chromosome in the bed bug Cimex lectularius Linnaeus, 1758 (Heteroptera, Cimicidae): a survey across Europe

Abstract

Variation in the number of chromosomes was revealed in 61 samples of Cimex lectularius Linnaeus, 1758 from the Czech Republic and other European countries, hosted on Myotis Kaup, 1829 (4) and Homo sapiens Linnaeus, 1758 (57). The karyotype of all the specimens of Cimex lectularius analysed contained 26 autosomes and a varying number of the sex chromosomes. The number of sex chromosomes showed extensive variation, and up to 20 fragments were recorded. Altogether, 12 distinct karyotypes were distinguished. The male karyotypes consisted of 29, 30, 31, 32, 33, 34, 35, 36, 37, 40, 42 and 47 chromosomes. The females usually exhibited the number of chromosomes which was complementary to the number established in the males from the same sample. However, 11 polymorphic samples were revealed in which the karyotypes of females and males were not complementary each other. The complement with 2n = 26+X1X2Y was found in 44% of the specimens and 57,4% samples of bed bugs studied. The karyotypes with higher chromosome numbers as well as individuals with chromosomal mosaics were usually found within the samples exhibiting particularly extensive variation between individuals, and such complements were not found within samples contaning a few or single specimen. The occurrence of chromosomal mosaics with the karyotype constitution varying between cells of single individual was observed in five specimens (4.3%) from five samples. We assume that polymorphism caused by fragmentation of the X chromosome may result in meiotic problems and non-disjunction can produce unbalanced gametes and result in lowered fitness of individuals carrying higher numbers of the X chromosome fragments. This effect should be apparently enhanced with the increasing number of the fragments and this may be the reason for the observed distribution pattern of individual karyotypes in the studied samples and the rarity of individuals with extremely high chromosome numbers. The assumed lowering of the fitness of individuals carrying higher numbers of the X chromosome fragments could affect population dynamics of variable populations.

Comparison of different cytogenetic methods and tissue suitability for the study of chromosomes in Cimex lectularius (Heteroptera, Cimicidae)

“…The numbers of C. lectularius X chromosomes can differ among different populations (localities), or among specimens within one population. Even a single specimen can contain cells with different numbers of X chromosomes (Ueshima 1966, 1979, Sadílek et al 2013. Preliminary study has also indirectly indicated the possibility of a variable number of X chromosomes in an obligatory bat parasite Cimex pipistrelli Jenys, 1839 (Sadílek et al 2013).…”

“…Even a single specimen can contain cells with different numbers of X chromosomes (Ueshima 1966, 1979, Sadílek et al 2013. Preliminary study has also indirectly indicated the possibility of a variable number of X chromosomes in an obligatory bat parasite Cimex pipistrelli Jenys, 1839 (Sadílek et al 2013). Therefore, it seems possible that intraspe-cific variability of X chromosomes could be a general feature of the genera Cimex and Paracimex Kiritshenko, 1913, or even possibly a wider spectrum of Cimicidae species.…”

“…Traut (1976) developed other modifications of the spreading for lepidopteran chromosome analysis. Recently, this method has been used more frequently not only for study of chromosomes of various insect taxa , van't Hof et al 2011, Paladino et al 2013, Sadílek et al 2013, Chirino et al 2015 but also for all other main arthropod evolutionary lineages such as arachnids (e.g. Šťáhlavský and Král 2004, Forman et al 2013, Adilardi et al 2014, Sadílek et al 2015, myriapods (e.g.…”

“…Darlington 1939, Slack 1939, Ueshima 1966, Sadílek et al 2013). In the family Cimicidae, the sex is determined by the presence of an XX/XY (female/male) simple sex chromosome system in 53 cytogenetically analysed species.…”

“…In the family Cimicidae, the sex is determined by the presence of an XX/XY (female/male) simple sex chromosome system in 53 cytogenetically analysed species. Most cimicid species, including the majority of Cimex species, also possess a multiple sex chromosome system X 1 X 1 X 2 X 2 / X 1 X 2 Y (except C. antennatus Usinger & Ueshima, 1965, C. latipennis Usinger & Ueshima, 1965and C. incrassatus Usinger & Ueshima, 1965 with the basic XX/XY system) (Poggio et al 2009, Grozeva et al 2010, Sadílek et al 2013. Four cimicid species possess constantly three X chromosomes (X 1 X 2 X 3 Y, male) (Paracimex capitatus Usinger, 1966, P. inflatus Ueshima, 1968, P. philippinensis Usinger, 1959and Hesperocimex coloradensis List, 1925 and two species four X chromosomes (X 1 X 2 X 3 X 4 Y, male) (Cimex adjunctus Barber, 1939 andC.…”