Abstract
Karyotypes are presented for 10 species of Gyrinus Geoffroy, 1762: Gyrinus minutus Fabricius, 1798, Gyrinus caspius Ménétriés, 1832, Gyrinus paykulli Ochs, 1927, Gyrinus distinctus Aubé, 1836 var. fairmairei Régimbart, 1883, Gyrinus marinus Gyllenhal, 1808, Gyrinus natator (Linnaeus, 1758), Gyrinus opacus Sahlberg, 1819, Gyrinus substriatus Stephens, 1869, Gyrinus suffriani Scriba, 1855, Gyrinus urinator Illiger, 1807 and for Orectochilus villosus (Müller, 1776) (Coleoptera: Gyrinidae). The 10 Gyrinus species have karyotypes comprising 13 pairs of autosomes plus sex chromosomes which are X0 (♂), XX (♀), with the X chromosomes the longest in the nucleus. Orectochilus villosus has 16 pairs of autosomes plus X0, XX sex chromosomes. The data obtained by Saxod and Tetart (1967) and Tetart and Saxod (1968) for five of the Gyrinus species are compared with our results. Saxod and Tetart considered the X chromosome to be the smallest in the nucleus in all cases, and this is considered to result from confusion arising from uneven condensation of some of the chromosomes. Small differences between the chromosomes of different Gyrinus species have been detected, but not between Greenland and Swedish populations of Gyrinus opacus, nor between typical Gyrinus distinctus from France and Gyrinus distinctus var. fairmairei from Kuwait.
Highlights
The Gyrinidae appear to be the first coleopteran family to be subjected to chromosomal analysis using air-drying of inflated cells on glass slides (Saxod and Tetart 1967, Tetart and Saxod 1968)
Relative Chromosome Lengths (RCL, the length of each chromosome expressed as a percentage of the total haploid autosome length in the nucleus) are given as approximate values, without any statistical analysis–the data are insufficient for statistical testing
The X chromosome, clearly the longest in the nucleus, has a RCL of about 20 and is metacentric. This is the longest X chromosome encountered in the present study
Summary
The Gyrinidae appear to be the first coleopteran family to be subjected to chromosomal analysis using air-drying of inflated cells on glass slides (Saxod and Tetart 1967, Tetart and Saxod 1968). The first account of an acetic acid dissociation, air-drying technique for use on insect cells was by Crozier (1968) He used hypotonic saline to inflate living cells prior to fixation, whereas Tetart (1969) began by dissecting out gonads in an isotonic saline solution and placing small pieces of tissue on slides and there fixing them briefly, with a fixative comprising absolute alcohol (70%) and glacial acetic acid (30%). After a minute or so the fixative is poured off and replaced with a swelling solution comprising 40% absolute alcohol, 30% glacial acetic acid and 30% distilled water. This causes tissue swelling and cell dissociation, monitored under a microscope. Treatment with hydrochloric acid (concentration and time not given) prevents cytoplasmic staining, and the chromosomes are stained with Giemsa
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