Extreme Ecological Niche Differences Lead to Extreme Postzygotic Ecological Isolation: A Case of Hybridization Between Carnivorous and Herbivorous Cyprinidae Fishes

Haoran Gu Key Laboratory of Freshwater Fish Reproduction and Development (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, School of Life Sciences, Southwest University, Chongqing 400715฀ China Yuanfu Wang Southwest University School of Life Sciences Haoyu Wang Southwest University School of Life Sciences You He Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Shanghai 201204, China Sihong Deng Liangshan Kehua Water Ecology Company Limited, Xichang 645000, China Xingheng He Sichuan Lubei Biotechnology Company Limited, Chengdu 610011, China Yi Wu Sichuan Lubei Biotechnology Company Limited, Chengdu 610011, China Kaiyan Xing Xichang Agriculture and Rural Affairs Bureau, Xichang 615000, China Xue Gao Xichang Agriculture and Rural Affairs Bureau, Xichang 615000, China Xuefu He Southwest University School of Life Sciences Zhijian Wang (  wangzj1969@126.com ) Key Laboratory of Freshwater Fish Reproduction and Development (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, School of Life Sciences, Southwest University, Chongqing 400715, China)

of genetic isolation between them also increases. Will the increase in parental 23 ecological niche differences also lead to the increase in ecological isolation performance for parental resources, and these hybrids could hardly forage for 34 parental resources. The poor foraging performance of these hybrids for parental 35 resources was caused not only by the decline in the foraging ability of these 36 hybrids but, more importantly, by the decrease in foraging activity. Interestingly, 37 these hybrids initially showed a high interest in foraging small fishes; however, 38 after the first successful capture, these hybrids had difficulty ingesting fish and 39 spit them out, which led to the subsequent decrease in foraging activity. We isolation. Then, will the increase in ecological niche differences also lead to the 85 increase in ecological isolation intensity? The current research cannot easily 86 answer this question due to the lack of hybridization cases of extreme 87 ecological niche parents. Therefore, we put forward two hypotheses. The external morphology of age-two SW (n=30), PP (n=30) and PS (n=30) 129 was studied, and the examination standards are shown in Supplementary Table   130 1. Then, we selected 10 fish individuals for quantification of skeletal morphology.    where 1 represents body weight, and 2 represents chyme weight. 152 2.5 Hybrid vs P. pingi in foraging fish 153 We compared the foraging capacity of PP (n=15) and PS (n=18) for small 154 fishes (S. taeniatus) (Fig. 4a). Specific experimental methods are described in   Interestingly, we found a large amount of small fish debris in the PS 287 aquarium tank (Fig. 3c), while little debris was noted in the tanks with SW and 288 PP, suggesting that one of the reasons why fish intake by PS intake was low 289 was spitting of fish. than that of SW (Fig. 4d), the FL was extremely significantly lower (P=0.002) 297 than that of SW (Fig. 4e), and the FE was significantly lower (P=0.037) than 298 that of SW (Fig. 4f) (Fig. 4h); and the AF of PS was extremely significantly lower (P<0.01) than 306 that of PP (Fig. 4i). In summary, PS showed greater interest in first foraging for 307 fish but had a high SR, which caused PS to be negative in later predation.   (Fig. 6i). However, the SR of fish meat was significantly lower (P<0.01) than 321 that of small fish (Fig. 6j), suggesting that the spitting behaviour was not caused 322 by bad taste but by chewing difficulty, which may be caused by pharyngeal tooth 323 structure, prey size, and the maximum opening width between pharyngeal teeth.

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Therefore, the SR of PS to different sizes of meat and fish was quantified. The 325 small fish weighed the same as small-sized meat, and the medium fish weighed 326 the same as medium-sized meat. The results showed that PS did not spit on 327 large, medium and small meat and had a low SR for small fish but a high SR 328 for medium fish (Fig. 6k).

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Next, the details of the pharyngeal teeth were compared, and we found that  The quantitative results support the above morphological description. The

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MOWPT of PP was extremely significantly higher (P<0.01) than that of SW and 342 PS, and no significant difference was observed between them (P≥0.05, Fig.   343 6l). The DDHPT of PP was extremely significantly higher (P<0.01) than that of 344 SW and PS, and PS was extremely significantly higher (P<0.01) than SW (Fig.   345 6m). The GSAPH of SW was extremely significantly higher (P<0.01) than that   Table 2). Interestingly, for PP and SW, the sharp horny front jaw is an invisible 365 trait, which is not exhibited by PS (Fig. 1)  Written informed consent for publication was obtained from all participants.

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The datasets used or analysed during the current study are available from 463 the corresponding author on reasonable request.

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Competing interests 465 All authors declare that they have no competing interests.        vs PP in the SRFA (success rate of the rst attack), SRTA (success rate of the total attacks) and SR (spitting rate). (h) PS vs PP in the FAT, FST ( rst success time) and FAT2 ( rst attack time after the rst successful capture). (i) PS vs PP in the AF (attack frequency). The scale is 1 mm. The numbers above the columns give the P-value based on Tukey test, the height give the mean, the thick lines give the medians and whiskers indicate mean ± SE.

Figure 5
The

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