Cornops aquaticum

Colombo, Pablo César & Remis, María Isabel, 2015, Morphometric variation in chromosomally polymorphic grasshoppers (Orthoptera: Acrididae) from South America: Bergmann and converse Bergmann patterns, Florida Entomologist 98 (2), pp. 570-570 : 570-

Cornops aquaticum

In C. aquaticum , the chromosomal polymorphism consisted of 3 Robertsonian rearrangements that increased in their frequency southwards ( Colombo 2008). The chromosomally studied area was small compared with the continental distribution of the species (latitude 23°N to 35°S) but not negligible at all. Thus, it extended from Corrientes (27°S) in northeastern Argentina to Tigre (34°S) in central-eastern Argentina. The Corrientes population was monomorphic without fusions; Santa Fe had 0.12 fusions per individual (fpi); in Rosario, this value remained small (0.11) and then it rose southwards ( San Pedro: 1.25 fpi; Zarate: 3.07 fpi; Tigre: 5.14 fpi). The maximum possible (6 fpi, i.e., complete fixation) was never attained, at least in the studied populations. In an isolated sample, sent from Trinidad and Tobago (10°N), this population was also monomorphic without fusions; moreover, a study of C. aquaticum that aimed to establish its karyotype ( Rocha et al. 2004) failed to detect the centric fusions in a population from São Lourenco da Mata, Pernambuco, Brazil (latitude 8°S), so at the moment the only described chromosome rearrangements are those found in Argentina. Nevertheless,we know that these fusions were also present in Uruguay because there was a previous chromosome study mention- ing them ( Mesa 1956), and that was the first report ever of Robertsonian rearrangement polymorphisms in Orthoptera .

In Romero et al. (2014), we studied the relationship between morphometric variables and chromosomal constitution, and we found that body size–related variables positively correlated with the number of fused chromosomes from an intra-population point of view. Populations of C. aquaticum sited in the middle and lower course of the Paraná River were polymorphic for 3 centric fusions (1/6, 2/5, and 3/4). The relationship between the karyotype and the phenotype was analyzed in 2 populations (Zárate and San Pedro) where we found a representative number of individuals of each karyotypic class ( Table 5). Males with fusion 1/6 were bigger than standard males. The Kruskal– Wallis analysis showed significant differences between the different numbers of fusion 1/6 for the tegmen length variable (H = 7.280, P = 0.026*) ( Table 5, as in Romero et al. 2014). Because fusion frequency is also correlated with latitude, southern populations would be expected to have a bigger size than northern ones.

With respect to a broader geographic point of view, we found no relationship between body size and geography in our own data, but we later merged them with those of the morphometric study by Adis et al. (2007) on a continental scale, going from Trinidad and Tobago (latitude 10°N) in the north to Montevideo (latitude 35°S) in the south. We had to limit the analysis to tegmen length, because it was the only variable that Adis et al. (2007) and we had measured in the same way. The results are shown in Table 6 and Figures 1C and 1D . It turns out that, at least for tegmen length, there is a clear positive Bergmann effect in both sexes (r = 0.7790, P = 0.0079 in males and r = 0.9067, P = 0.0003 in females). Hence, in this species the morphometric chromosome effects also are correlated with the geographic tendency .

COMMON PATTERNS AND DIFFERENCES

Previous reviews showed different species within a main group (e.g., Orthoptera ) may exhibit various phenotypic variations with respect to latitude ( Shelomi 2012). Moreover, in some species, such as Dichroplus elongates Giglio-Tos ,contrasting patterns of body size variation with respect to latitude were observed generating Bergmann and converse Bergmann patterns along about 1,000 km ( Rosetti & Remis 2013).With respect to Bergmann’s rule, it is clear that L. argentina and C. aquaticum show a positive Bergmann effect, while T. pallidipennis follow a negative one. However, with respect to this rule, it is clear that its author devised it for endotherms, and that perhaps its extension to ectotherms produces these paradoxes. Perhaps the trends of ectotherms regarding latitude and/or altitude are governed by different needs, such as the length of breeding season (which would lead to a negative Bergmann effect) or the reduction in the number of genera- tions in a year. Hence, we take the Bergmann’s law in ectotherms with extreme care, treating each species as a special case.

As for chromosome polymorphisms and their morphometric effects, we noticed a common pattern in all 3 species studied: they were coher- ent with their geographical distribution ( Colombo 1989; 2008; Colombo & Confalonieri 1996). In fact, in all cases the chromosome polymorphisms were associated with body size enlargement (the chromosome rearrangement in question was associated with enlarged body size–related variables in all 3 species).Effectively, in C. aquaticum and L. argentina the Robertsonian rearrangement(s) were more frequent in southern populations ( Colombo 2014), and these 2 species follow a Bergmann’s pattern. Conversely, in T. pallidipennis populations sited at lower altitudes tend to support larger individuals,where pericentric inversions are more frequent ( Colombo 2014). Apparently, this may be an adaptive effect of chromosome polymorphisms, which probably support genes that cause increased body size in the appropriate environments. This would be another evidence of adaptive effects associated with chromosome polymorphisms, of which abundant evidence has been provided in the past ( Colombo 1993; Colombo & Confalonieri 1996; Norry & Colombo 1999; Colombo et al. 2004; Romero et al 2014). Current molecular studies may shed more light on these patterns.

and their karyotype composition. UU: Unfused homozygotes; UF: heterozygotes; FF: fused homozygotes. N: number of individuals sampled.

Adis J, Sperber CF, Brede EG, Capello S, Franceschini MC, Hill M, Lhano MG, Marques MM, Nunes AL, Polar P. 2008. Morphometric differences in the grasshopper Cornops aquaticum (Bruner, 1906) from South America and South Africa. Journal of Orthoptera Research 17 (2): 141-147.

Bergmann C. 1847. Über die Verhältnisse der Wärmeökonomie der Thiere zu ihrer Grösse. Göttinger Studien. Pt. 1: 1847: 595-708.

Berner D, Blanckenhorn WU. 2006. Grasshopper ontogeny in relation to time constraints: adaptive divergence and stasis. Journal of Animal Ecology 75: 130-139.

Berner D, Körner C, Blanckenhorn WU. 2004. Grasshopper populations across 2000 m of altitude: is there life history adaptation? Ecography 27: 733-740.

Bidau CJ, Martí DA. 2007 a. Dichroplus vittatus (Orthoptera: Acrididae) follows the converse to Bergmann’s rule although male morphological variability increases with latitude. Bulletin of Entomological Research 97: 69-79.

Bidau CJ, Martí DA. 2007 b. Clinal variation of body size in Dichroplus pratensis (Orthoptera:Acrididae): inversion of Bergmann’s and Rensch’s rules. Annals of the Entomological Society of America 100 (6): 850-860.

Blanckenhorn WU, Demont M. 2004. Bergmann and converse Bergmann latitudinal clines in arthropods: two ends of a continuum? Integrative and Com- parative Biology 44: 413-424.

Butlin RK, Read JL, Day TH. 1982. The effects of a chromosomal inversion on adult size and male mating success in the seaweed fly, Coelopa frigida. Heredity 49: 121-128

Colombo PC, Confalonieri VA. 1996. An adaptive pattern of inversion polymorphisms in Trimerotropis pallidipennis (Orthoptera). Correlation with envi- ronmental variables: an overall view. Hereditas 125: 289-296

Colombo PC. 1989. Chromosome polymorphisms affecting recombination and exophenotypic traits in Leptysma argentina (Orthoptera). Heredity 62: 289- 299.

Colombo PC. 1993. Chromosome polymorphisms and natural selection in Leptysma argentina (Orthoptera). II. Gametic phase disequilibrium and differ- ential adult male viability. Heredity 71: 295-299.

Colombo PC. 1997. Exophenotypic effects of chromosomal change: the case of Leptysma argentina (Orthoptera). Heredity 79: 631-637.

Colombo PC. 2002. Chromosome inversion polymorphisms influence morphological traits in Trimerotropis pallidipennis (Orthoptera). Genetica 114: 247- 252.

Colombo PC. 2008. Cytogeography of three parallel Robertsonian polymorphisms in the water-hyacinth grasshopper, Cornops aquaticum. European Journal of Entomology 105: 59-64.

Colombo PC. 2014. Micro-evolution in grasshoppers mediated by polymorphic translocations. Journal of Insect Science 13: 43.

Colombo PC, Pensel SM, Remis MI. 2001. Chromosomal polymorphism, morphometric traits and sexual selection in Leptysma argentina (Orthoptera). Heredity 87: 480-484.

Colombo PC, Pensel SM, Remis MI. 2004. Chromosomal polymorphism, morphometric traits and mating success in Leptysma argentina (Orthoptera). Genetica 121: 25-31.

Hasson ER, Fanara JJ, Rodriguez C, Vilardi JC, Reig OA, Fontdevila A. 1992. The evolutionary history of Drosophila buzzatii. XXIV. Second chromosome inversions have different average effects on thorax length. Heredity 68: 557- 563.

Mesa A. 1956. Los cromosomas de algunos acridoideos uruguayos (Orthoptera, Caelifera, Acridoidea). Agros, Revista de la Asociación de Estudiantes de Agronomía, Montevideo 141: 32-45.

Norry FM, Colombo PC. 1999. Chromosome polymorphisms and natural selection in Leptysma argentina (Orthoptera): external phenotype affected by a centric fusion predicts adult survival. Journal of Genetics 78: 57-62.

Rocha MF, Souza MJ, Moura RC. 2004. Karyotype analysis, constitutive hetero- chromatin and NOR distribution in five grasshopper species of the subfamily Leptysminae (Acrididae). Caryologia 57: 107-116.

Romero ML, Colombo PC, Remis MI. 2014. Morphometric differentiation in the semiaquatic grasshopper Cornops aquaticum: associations with sex, chromosome and geographic conditions. Journal of Insect Science 14: 164.

Rosetti MEN, Remis MI. 2013 Latitudinal clines in the grasshopper Dichroplus elongatus: coevolution of the A genome and B chromosomes? Journal of Evolutionary Biology 26: 719-732.

Shelomi M. 2012. Where are we now? Bergmann’s rule sensu lato in insects. The American Naturalist 180: 511-519.

Werle SF, Klekowski EDG. 2004. Inversion polymorphism in a Connecticut river Axarus species (Diptera: Chironomidae): biometric effects of a triple inversion heterozygote. Canadian Journal of Zoology 82: 118-129.

White MJD, Andrew LE. 1960. Cytogenetics of the grasshopper Moraba scurra V. Biometric effects of chromosomal inversions. Evolution 14: 284-292.

White MJD, Lewontin RC, Andrew CE. 1963. Cytogenetics of the grasshopper Moraba scurra VII: geographic variation of adaptative properties of inversions. Evolution 17: 147-162.

Whitman DW. 2008. The significance of body size in the Orthoptera: a review. Journal of Orthoptera Research 17: 117-134.

Figures

Fig. 1. A) Trimerotropis pallidipennis: Tegmen length (in mm) against altitude; B) Leptysma argentina: Total body length in mm against latitude; C) Cornops aquati- cum: Tegmen length in mm against latitude in males; and D) Cornops aquaticum: Tegmen length in mm against latitude in females.