Contrasting ecological niches lead to great postzygotic ecological isolation: a case of hybridization between carnivorous and herbivorous cyprinid fishes

Abstract

Background Postzygote isolation is an important part of species isolation, especially for fish, and it can be divided into two aspects: genetic isolation and ecological isolation. With the increase in parental genetic distance, the intensity of genetic isolation between them also increases. Will the increase in parental ecological niche differences also lead to the increase in ecological isolation intensity between them? This question is difficult to answer based on the current literature due to the lack of hybridization cases of contrasting ecological niche parents. Results Cyprinid fish parents (Schizothorax wangchiachii and Percocypris pingi) with contrasting ecological niches (herbivorous and carnivorous) and their F1 hybrids were used as research objects. Fish and periphytic algae were selected as food corresponding to different parental resources. The foraging-related traits of these hybrids are generally the same between parents; however, the intermediate foraging traits of hybrids did not result in intermediate foraging performance for parental resources, and these hybrids could hardly forage for parental resources. The poor foraging performance of these hybrids for parental resources was caused not only by the decline in the foraging ability of these hybrids but, more importantly, by the decrease in foraging activity. Interestingly, these hybrids initially showed a high interest in foraging small fishes; however, after the first successful capture, these hybrids had difficulty ingesting fish and spit them out, which led to the subsequent decrease in foraging activity. We designed a series of experiments to explore the mechanism of the fish spitting of these hybrids, excluding the taste and the size of prey, and found that the decrease in their pharyngeal tooth puncture ability may be the reason. Conclusions This study was the first to demonstrate that these parents with contrasting ecological niches will produce great postzygotic ecological isolation for parental resources. The poor foraging performance of these hybrids for parental resources is mainly due to the decrease in foraging activity. Interestingly, these hybrids have obvious fish-spitting behaviour, which is a typical example of the incompatibility between intermediate traits and genetic behaviors.

Examining differentiation of sympatricSchizothoraxfishes reveals low differentiation in internal compared to external feeding traits

“…SHL/HL is an indicator defined in this study, it represents the location of the mouth, which is related to feeding habits. External traits and pharyngeal bone data and figures of PP and SW have been used in our previous papers (Gu et al., 2019; Gu et al., 2021).…”

“…The structure of the pharyngeal bones and teeth (important feeding organs in cyprinid fishes) is related to the ingestion of prey. For example, the pharyngeal bones of carnivorous fishes are generally long and narrow and have developed hooked teeth, which help to stabilize and puncture prey; the pharyngeal bones of herbivorous fishes are generally short and wide, and have compressed or grinding teeth, which help to grind and cut food (Gu et al., 2021; Zeng & Liu, 2011). Digestive traits are mainly related to the digestion of prey.…”

The Himalayan uplift and evolution of aquatic biodiversity across Asia: Snowtrout (Cyprininae: Schizothorax) as a test case

“…In contrast, the converse is true for different species in the same drainage [ 16 , 78 ]. This can reflect incomplete lineage sorting [ 21 , 77 ]; hybridization (intergeneric: [ 5 , 93 ], intrageneric: [ 94 ]); rapid diversification [ 5 ]; and/or convergent evolution (e.g., juxtaposition of trophic and spatial niches across species; [ 95 , 96 ]). None can be resolved using mtDNA [ 22 ].…”

Interspecific differences and ecological correlations between scale number and skin structure in freshwater fishes

“…They play an important role in mechanical protection ( Torres et al 2008 ), acting as armor to protect fish from piscivorous predators and scrapes from rocks and branches. Fish scales can resist piscivorous predators’ bites to a certain extent ( Meyers et al 2012 ; Zhu et al 2013 ; Yang et al 2014 ), but most piscivorous predators tend to swallow their prey whole ( Mcgee et al 2015 ; Gu et al 2021 ), which indicates that the resistance to piscivorous predators is a secondary role of the scales. Another important role of scales is their resistance to pathogenic microorganisms.…”