Genomic markers confirm introgressive hybridization in Cichla (Teleostei) in an invaded coastal system

Abstract

Hybridization seems frequent among Cichla species (peacock bass), as studies have reported hybrids in populations within and outside their natural range (the Amazon and Orinoco river basins). Cichla kelberi and C. monoculus were introduced to the São João river (Southeast Brazil) more than 20 years ago, where they successfully colonized different environments. In this system, specimens have coloration and morphology that differ from patterns observed in their native range, indicating that the contact between C. monoculus and C. kelberi eliminated reproductive isolation, leading to introgressive hybridization. In this context, we used the LWS and dlx2 genes and the random amplified polymorphic DNA technique to characterize Cichla species in the São João river and to detect possible hybridization processes. The genetic markers identified here showed mismatches between mitochondrial and nuclear DNA in C. monoculus and C. kelberi, sampled both in the reservoir and in the estuarine stretch. Fragments of nuclear DNA from both species, as well as the presence of mitochondrial DNA from one species associated with the nuclear genome of the other, provide strong evidence of hybridization associated with bidirectional genetic introgression. Because hybrids may be more resistant, competitive, and aggressive than their parental species, these invaders may pose a significant threat to native biodiversity in this and other coastal rivers of the region.

Global distribution of the South American peacock bassesCichlaspp. follows human interference

“…The potential for hybridization for peacock basses is another issue related to the sympatry of these species. Although not commonly found in natural habitats, there are several examples of hybrid peacock basses from introduced populations or in reservoirs located within their native ranges (Almeida-Ferreira et al, 2011;Diamante et al, 2020;Oliveira et al, 2006). Among the consequences of this process, when hybrids are reproductive and ecologically viable, they may present lower (inbreeding depression), equivalent or even higher fitness levels (hybrid vigour) than their parental species (Good et al, 2010;Rosenfield et al, 2004).…”

“…The efforts allocated in taxonomy and systematics of peacock basses on the last decades changed substantially the number of valid species (see Kullander & Ferreira, 2006;Sabaj et al, 2020;Willis et al, 2012;Winemiller et al, 2021) S1). Recent molecular and phylogenetic analyses have also revealed high levels of introgressive hybridization in both native, but especially in non-native regions (Diamante et al, 2020 ;Oliveira et al, 2006;Willis et al, 2007Willis et al, , 2012. Despite the known adverse impacts caused by peacock basses, introductions of this species are increasingly common in tropical freshwaters (Daga et al, 2016), often through intentional releases for recreational or commercial purposes (Hall & Mills, 2000;Santos et al, 2001;Zaret & Paine, 1973), and especially in reservoirs (Franco et al, 2021).…”