Phenotypic pattern over centric fusion clinal variation in the water-hyacinth grasshopper, Cornops aquaticum (Orthoptera: Acrididae)

Abstract

The water-hyacinth grasshopper, Cornops aquaticum, occurs in the New World between latitudes 23°N, in Mexico, and 35°S in Central Argentina and Uruguay following the distribution of its host plants, i.e. different species of water-hyacinths (family Pontederiaceae) (Adis et al., 2007;Capello et al., 2010). The recent worldwide expansion of the water-hyacinth Eichhornia crassipes as a serious freshwater weed in tropical and subtropical, and even temperate, regions of the world (Center et al., 2002) has led to the use of C. aquaticum as a biological control agent (Oberholzer & Hill, 2001;Coetzee et al., 2011;Bownes et al., 2013). Its basic karyotype consists of 22 acrocentric autosomes, with an X0/XX sex determination system (França Rocha et al., 2004). The cytological study of natural populations have revealed the presence of three centric fusion poly-

Spatial population structure: patterns of adaptation in populations of the water hyacinth grasshopper Cornops aquaticum (Bruner 1906)

“…Although the strong negative association of fusion frequencies with maximum temperature, as well as the consistent repetition of clines along the Paraná and Uruguay River Basins, suggests an adaptive nature to the clinal variation in C. aquaticum populations (Colombo and Remis, 2018), it must be considered that clinal patterns can be also produced by neutral processes (Endler, 1973;Storz, 2002). For this reason, we have taken pains to perform additional analyses that further demonstrate a non-neutral explanation to the parallel clines, namely, a population pairwise differentiation study between the frequency of centric fusions and that of neutral microsatellite pattern.…”

“…Earlier studies in this region including populations located from 27 to 34°S latitude revealed that C. aquaticum has a rich chromosomal variability, with three polymorphic centric fusions whose frequencies increase from north to south (Colombo, 2008;Colombo and Remis, 2018). Even though the potential of polymorphic chromosomal inversions in facilitating local adaptation has been widely examined, just a few studies started to deal with the role of centric fusions in microevolution (Dumas and Britton-Davidian, 2002;Bidau et al, 2012;Colombo, 2013;Guerrero and Kirkpatrick, 2014;Wellband et al, 2018), which adds relevance to the results obtained in this study.…”

“…The most southwardly marginal populations show the highest chromosomal differentiation and are simultaneously the most divergent ones from the genetic standpoint. Moreover, combined chromosomal and morphometric studies revealed that the fusions are associated with an increase of body size-related variables (Romero et al, 2014;Colombo and Remis, 2018).…”

“…Values of variables are given as mean and standard deviation (±). Samples marked with * and # were described inColombo and Remis (2018) and inRomero et al (2014) respectively, and those marked with + were resampled and measured (to analyse larger sample size), and (N ) the unmarked ones belong to the current study.…”

C-banding characterization of centric fusion and heterochromatin polymorphisms in the water-hyacinth grasshopper, Cornops aquaticum (Orthoptera: Acrididae)

“…Cornops aquaticum (Bruner 1906), another Neotropical grasshopper, also bears a system of polymorphic centric fusions that is second only to D. pratensis in complexness despite the relatively small area involved (Colombo 2007, 2008, 2009, Romero et al 2014, 2017, Colombo and Remis 2015, 2018, Colombo et al 2021). It is a semiaquatic grasshopper that lives, feeds, and lays eggs exclusively on floating plants of the family Pontederiaceae, or water-hyacinths, between latitudes 23° N (Southern Mexico) and 35° S (Central Argentine and Uruguay) (Adis et al 2007).…”