Meiosis in the Grasshopper: Chiasma Frequency After Elevated Temperature and X-Rays

Abstract

rasshoppcrs \rere given an acute dose of X-rays, injected with Ht b n~i d i n e and thereafter lnaintained at 42°C. Autoradiographic analysis of testicular tubules taken at daily intervals after injection gave meiotic stage durations. T h e mean chiasll~a frequency n.as reduced 4 days after the hoppers \vere placed at +lo, in both X-rayed and non-irradiated aninials, and remained low in the non-irradiated animals throughout the experiment. In the X-rayed animals the chiasma frequency rose to control levels on the 6th day and dropped again thereafter. Analysis of the data indicates a period ending approxi~nately at zygotene during 15-hich chiasma frequc~lcy can be reduced by high temperature. T h e chiasma frequency can be increased by irradiating leptotene-zygotene. T h e end of the heat and X-ray sensitive stages are ternporally d~s t~n c t . Univalents \ \ w e never produced by the hear treatment. Changes in chiasma frequency are restrictetl to the four pairs of larger chromoson~es where multiple chiasniata are com~nonly found. Hence, the presence o r abscncc of chiasniata sho\vs a con~ples interaction \vith the physical environment.Little is known about thc mechanism of gcnctic crossing-over in higher organisms. In fact, thcre is e\.en disagrecmcnt as to thc time during ~nciosis when crossing-over occurs (Grcll and Chandlcy, 1965;Henderson, 1966). Since chiasma formation and gcnetic recombination are usually considered to be manifestations of the same cvcnt (Brov n and %ohar\r, 1955), an understanding of chiasma formation should clucidatc the problcn; of crossing-otrcr.Production of chiasmata is affected b y both y-:111d X-radiation (La~vrcnce, 196 la, 1961 b; i\lathcr, 1934; Westerman, 1967). At lcast thrcc radioscnsitive periods affecting chiasma formation occur during meiosis and one during premeiotic mitoses. 1,awrence (1961) demonstrnted a decrcasc in chiasma frequency whcn ./-radiation was applied during the prc-inciotic D N A synthetic pcriod and an increase when the treatment was given during latc zytotcne or early pachytene in both Liliz~7/1 1 0 1 1 g i f l o~~1~~1 and Tmdescn/lti;l pnl[~dosn. Similar results werc obtained by Westerman ( 1 9 6 7 ) using X-radiation on thc dcscrt locust, Schistoce~ca greynr-in, with the exception that the increase occurrcd when the trcatmcnt nlas given during leptotcnc-zygotenc. ,\/lather (1934) and Wcsterman (1967) also notcd a significant increasc in chi:islna frcqucncy \vhen X-radiation was applied during pre-mciotic mitoses.Heat shock also affccts chiasma production in S. ,yrega~in (tlenderson, 1962, 1963, 1966) and in a grasshopper, Go?linen nzlstrnlinsiae (Peacock, 1968).A drastic decreasc in chiasma frequency occurs when cither S. gre,qar-in or G. azcstrnliasiae is subjected to a temperat;rc of 4 0°C . 'The heat-sensitive period appears to be latc ygotenc-early pachvtenc.

Meiosis in the grasshopper

“…The results of this investigation are strikingly similar to those obtained from similar experiments performed with males of the same species (Church and Wimber, 1969). In both sexes chiasma frequencies were lowered in response to high temperatures.…”

“…Church and Wimber (1969) determined this time to be 8 days in males as compared to 5 days observed for females in the present investigation. However, the experiments are not strictly comparable since they were carried out on male adults and female nymphs.…”

“…The mean chiasma frequency per cell in M. femur-rubrum males was approximately l35 (Church and Wimber, 1969). The mean chiasma frequency observed for females was approximately 1 52 per cell.…”

“…However, I have determined that the ovaries of nymphal stages of a grasshopper Melanoplus femur-rubrum display some diplotene cells from which chiasma frequencies can be obtained. In addition to the technical reasons, Melanoplusfemur-rubrum females were chosen for the study because information is available from similar studies carried out in the male of this species (Church and Wimber, 1969) and a basis for comparison between the sexes is available.…”

The effect of X-irradiation on chiasma frequency in Chorthippus brunneus

“…It is likely that they also agree in showing an increase following irradiation of leptotene-early zygotene, though in Chorthippus the increase is small and seen only on day +6k-(t = 25365 P 0.02-0.01). Using another grasshopper species, Melanoplus femur-rubrum, Church and Wimber (1969) have also noted an increase in chiasma frequency following irradiation at this time. In their experiment the increase was seen in spite of an overall reduction in chiasma frequency brought about by a 42° C. temperature regime.…”