Exophenotypic effects of chromosomal change: the case of Leptysma argentina (Orthoptera)

Abstract

Most of the literature about phenotypic effects of chromosomal change has dealt with its effects on chiasma frequency and/or distribution, whereas whether or not they affect the exophenotype has received less attention and has remained controversial. In the present paper morphometrical variables of the species Leplysma argentina were analysed in connection with chromosome polymorphisms for a centric fusion and a supernumerary segment.The centric fusion between pairs 3 and 6 (fusion 3/6) and a supernumerary segment in the smallest pair of the complement (s1) were consistently proved to have effects on chiasma frequency and position; preliminary analyses had shown, however, that fusion 3/6 could be correlated with some effects on body size (Colombo, 1989). In the present paper the analysis of femur, tibia, prothorax and total length as well as prothorax height on larger samples were consistent in showing that both polymorphisms are positively correlated with increasing total length; in the case of the supernumerary segment, however, this effect is not constant over all the populations sampled.An adaptive change in body size may be achieved through selection on: (i) genetic factors that affect this trait; or (ii) chromosome polymorphisms with exophenotypic effects. This latter case would be more effective, because genetic factors are usually polygenic and hence their response to selection would be slow. It is tempting to say that this could be the case for L. argentina, because in grasshoppers increased body size can be related to tolerance to cold or dry environments.

The significance of body size in the Orthoptera: a review

“…Moreover, in this species, body size-related variables were larger in fusion homozygotes than in unfused homozygotes; the effect over heterozygotes was variable (Table 4). This trend is clear both in males (Colombo 1989;1997) and in females (Colombo et al 2001; all over the geographical gradient.…”

“…The correlation of fusion 3/6 frequency with body size-related variables was stunning (Colombo 1989;1997), but it should be recognized that, superimposed on the fusion 3/6 effect, there was a within-karyotype latitudinal effect (Colombo 1997). It could be affirmed, with considerable care given the limited extent of the gradient (latitude 31°S to 34°S), that L. argentina showed a positive Bergmann's effect (r = 0.9297, P = 0.0221) (Fig.…”

“…Four hundred and forty-nine individuals from 9 populations of L. argentina located in central-eastern Argentina assessed for Robertsonian translocation and body size-related traits were considered in order to analyze simultaneous patterns of chromosome and body length variation (Colombo 1989(Colombo , 1997.…”

Karyotypic analysis, constitutive heterochromatin and NOR distribution in five grasshopper species of the subfamily Leptysminae (Acrididae)

“…The B chromosome present in Stenopola dorsalis is similar to the X in terms of size and pycnotic behavior. Indeed B chromosomes and extra segments have also been found in some leptysmines such as Cylindrotettix obscurus, C. santarosae and Leptysma argentina (CONFALONIERI and BIDAU 1986;COLOMBO 1989COLOMBO , 1997BIDAU and HASSON 1984).…”

“…Leptysminae, in turn, occurs only in the neotropical region and chromosomal studies of this subfamily are scarce, most of them involving standard staining (MESA et al 1982). Among the 22 Leptysminae species studied, 19 showed basic 2n=23,XO karyotypes (MESA et al 1982;MESA and FONTANETTI 1983;BIDAU and HASSON 1984;CONFALONIERI and BIDAU 1986;COLOMBO 1989;LORETO and SOUZA 2000). However, Stenopola pallida, Leptysma argentina (21,XO) and Tetrataenia surinama (19,XO) presented karyotypic reductions due to centric autosomal fusions (MESA et al 1982;BIDAU and HASSON 1984).…”