Evolutionary dynamics of ecological niche in three Rhinogobio fishes from the upper Yangtze River inferred from morphological traits

In the past decades, it has been debated whether ecological niche should be conserved among closely related species (phylogenetic niche conservatism, PNC) or largely divergent (traditional ecological niche theory and ecological speciation) and whether niche specialist and generalist might remain in equilibrium or niche generalist could not appear. In this study, we employed morphological traits to describe ecological niche and test whether different niche dimensions exhibit disparate evolutionary patterns. We conducted our analysis on three Rhinogobio fish species (R.typus, R.cylindricus, and R.ventralis) from the upper Yangtze River, China. Among the 32 measured morphological traits except body length, PCA extracted the first four principal components with their loading scores >1.000. To find the PNC among species, Mantel tests were conducted with the Euclidean distances calculated from the four principal components (representing different niche dimensions) against the pairwise distances calculated from mitochondrial cytochrome b sequence variations. The results showed that the second and the third niche dimension, both related to swimming ability and behavior, exhibited phylogenetic conservatism. Further comparison on niche breadth among these three species revealed that the fourth dimension of R.typus showed the greatest width, indicating that this dimension exhibited niche generalism. In conclusion, our results suggested that different niche dimensions could show different evolutionary dynamic patterns: they may exhibit PNC or not, and some dimensions may evolve generalism

Life history traits and implications for conservation of rock carp Procypris rabaudi Tchang, an endemic fish in the upper Yangtze River, China

Rock carp is an endemic fish in the upper Yangtze River basin. Its populations have dramatically declined in the recent years due to human activities, such as overfishing and damming. In the present study, with the aim to give suggestions for better conservation, we investigated age, growth, and reproductive biology of the rock carp using samples collected between 2007 and 2013 from the Chishui River. The results indicate that there are no significant differences between the length-weight relationships of females and males (W = 0.015SL(3.155)). The von Bertalanffy growth curves computed by the observed length-at-age data could be expressed as L (t) = 64.9(1 - e(-0.101(t+0.217))). The estimated length at 50 % sexual maturity for males is 24.2 cm (approximately aged 4) and 37.0 cm for females. Female gonad analysis suggests that rock carp is a batch spawner, which can spawn at least twice during the reproductive season, from April to August. Standard length and age of 86.5 % individuals were below 25 cm and 4 years, respectively, indicating that the exploitation is too intensive and that populations are undergoing miniaturization. These data corroborate that a combination of natural and anthropogenic factors has caused a sharp decline in wild populations during recent years, calling for immediate design and implementation of conservation measures for this species

Effects of Environmental Factors on Natural Reproduction of the Four Major Chinese Carps in the Yangtze River, China

The four major Chinese carps are commercially important fish species with high production in China. However, their recruitment decreased sharply in the Yangtze River since the late 20th century. In the present study, to reveal the relationships between spawning activities of the four species and environmental factors, drifting eggs were collected at Yidu City, in the middle reaches of the Yangtze River, from May to July each year between 2005 and 2010. Classification and regression trees (CART) analysis was applied to identify the key factors associated with spawning activities of the four carp species. Twelve predictor variables (hydrological and meteorological variables) and one response variable (egg presence or number of egg) were included in the CART. Our CART analysis showed that water temperature and the diurnal increase of water level were the two most significant factors for the spawning activities. When water temperature was between 18 degrees C and 24 degrees C, especially in association with the diurnal increase of water level greater than 0.55 m.d(-1), spawning activities was always favored. Unlike the hydrological factors, meteorological factors seemed to have no influence on initiating the spawning activities. The density of drifting eggs of the four species was mainly influenced by the diurnal variation of water level, the diurnal variation of water discharge, water temperature, humidity, and air pressure. We then related our results to the ecological regulation of the Three Gorge Reservoir in the middle reaches of the Yangtze River. We suggested that, when water temperature was between 18-24 degrees C from May to July, to ensure the successful spawning of the four carp species, the ecological regulation should be managed to create flood peaks and make the diurnal increase of water level greater than 0.55 m.d(-1).The four major Chinese carps are commercially important fish species with high production in China. However, their recruitment decreased sharply in the Yangtze River since the late 20th century. In the present study, to reveal the relationships between spawning activities of the four species and environmental factors, drifting eggs were collected at Yidu City, in the middle reaches of the Yangtze River, from May to July each year between 2005 and 2010. Classification and regression trees (CART) analysis was applied to identify the key factors associated with spawning activities of the four carp species. Twelve predictor variables (hydrological and meteorological variables) and one response variable (egg presence or number of egg) were included in the CART. Our CART analysis showed that water temperature and the diurnal increase of water level were the two most significant factors for the spawning activities. When water temperature was between 18 degrees C and 24 degrees C, especially in association with the diurnal increase of water level greater than 0.55 m.d(-1), spawning activities was always favored. Unlike the hydrological factors, meteorological factors seemed to have no influence on initiating the spawning activities. The density of drifting eggs of the four species was mainly influenced by the diurnal variation of water level, the diurnal variation of water discharge, water temperature, humidity, and air pressure. We then related our results to the ecological regulation of the Three Gorge Reservoir in the middle reaches of the Yangtze River. We suggested that, when water temperature was between 18-24 degrees C from May to July, to ensure the successful spawning of the four carp species, the ecological regulation should be managed to create flood peaks and make the diurnal increase of water level greater than 0.55 m.d(-1)

Reproductive behaviour of female rosy bitterling Rhodeus ocellatus in response to a female-biased operational sex ratio

While the effect of Operational Sex Ratio (OSR) on reproductive behaviour of males has been studied extensively, little is known of the response of females facing a female-biased OSR. We investigated the effect of different OSRs on female reproductive behaviour using the rosy bitterling, Rhodeus ocellatus, a freshwater fish that lays its eggs inside the gills of living freshwater mussels. Three levels of OSR (male/female ratio 1:1, 1:3 and 1:5) were tested. We demonstrated that inspection of the mussel (spawning substrate) by individual females increased with increasingly female-biased OSR, but that the rate of following territorial male decreased. Aggression towards other females was not affected by the OSR. Interestingly, when a male bitterling led a non-dominant female towards the mussel, the dominant female would become aggressive to the male and chase the non-dominant female away. Aggression towards male followed a bell-shaped pattern and was highest at an OSR of 1:3. In both the female-biased OSRs examined, almost 50% of dominant females tended to chase away other females and defend the mussel, showing territoriality in a similar manner to males. These observations suggest that female reproductive behaviour is strongly affected by the OSR, and their reproductive tactics during courtship change from a passive role in courtship (following a male) to an active role in courtship (approaching a male), with presence of female territorial behaviour as the OSR becomes increasingly female-biased. This study provides strong evidence that a female-biased OSR has an important effect on female reproductive behaviour.While the effect of Operational Sex Ratio (OSR) on reproductive behaviour of males has been studied extensively, little is known of the response of females facing a female-biased OSR. We investigated the effect of different OSRs on female reproductive behaviour using the rosy bitterling, Rhodeus ocellatus, a freshwater fish that lays its eggs inside the gills of living freshwater mussels. Three levels of OSR (male/female ratio 1:1, 1:3 and 1:5) were tested. We demonstrated that inspection of the mussel (spawning substrate) by individual females increased with increasingly female-biased OSR, but that the rate of following territorial male decreased. Aggression towards other females was not affected by the OSR. Interestingly, when a male bitterling led a non-dominant female towards the mussel, the dominant female would become aggressive to the male and chase the non-dominant female away. Aggression towards male followed a bell-shaped pattern and was highest at an OSR of 1:3. In both the female-biased OSRs examined, almost 50% of dominant females tended to chase away other females and defend the mussel, showing territoriality in a similar manner to males. These observations suggest that female reproductive behaviour is strongly affected by the OSR, and their reproductive tactics during courtship change from a passive role in courtship (following a male) to an active role in courtship (approaching a male), with presence of female territorial behaviour as the OSR becomes increasingly female-biased. This study provides strong evidence that a female-biased OSR has an important effect on female reproductive behaviour

Molecular Phylogeny and Conservation Priorities of the Subfamily Acheilognathinae (Teleostei: Cyprinidae)

It is increasingly accepted that conservation work should consider the evolutionary history of target species. Fishes in the subfamily Acheilognathinae, family Cyprinidae, are, with the exception of three species exclusively distributed in Europe, restricted to Asia and show a distinct spawning behavior in laying their eggs in gill chambers of freshwater mussels. At present, many of the 70 species recognized in this group are facing with serious population decline in China and Japan, and their phylogenetic relationships are not well resolved. In the present study, based on mtDNA cyt b and 12S rRNA gene sequences, we reconstructed a more detailed species-level phylogenetic tree of this group, and assessed species conservation priorities based on their evolutionary distinctiveness. Molecular phylogenetic analyses showed that the Acheilognathinae contains two major clades: Acheilognathus clade and Tanakia-Rhodeus clade. Based on this phylogenetic result, conservation priority analyses were conducted using ED (evolutionary distinctiveness)/HED (heightened evolutionary distinctiveness), and EDGE (evolutionary distinctiveness and global endangeredness)/HEDGE (heightened evolutionary distinctiveness and global endangeredness) methods. The results suggested that T. himantegus, T. lanceolata, A. gracilis, A. imberbis, T. tanago, and A. longipinnis should be ranked as the top-priority species for conservation. According to our results, we also discussed the current conservation efforts of the bitterling fishes and gave suggestions for future work.It is increasingly accepted that conservation work should consider the evolutionary history of target species. Fishes in the subfamily Acheilognathinae, family Cyprinidae, are, with the exception of three species exclusively distributed in Europe, restricted to Asia and show a distinct spawning behavior in laying their eggs in gill chambers of freshwater mussels. At present, many of the 70 species recognized in this group are facing with serious population decline in China and Japan, and their phylogenetic relationships are not well resolved. In the present study, based on mtDNA cyt b and 12S rRNA gene sequences, we reconstructed a more detailed species-level phylogenetic tree of this group, and assessed species conservation priorities based on their evolutionary distinctiveness. Molecular phylogenetic analyses showed that the Acheilognathinae contains two major clades: Acheilognathus clade and Tanakia-Rhodeus clade. Based on this phylogenetic result, conservation priority analyses were conducted using ED (evolutionary distinctiveness)/HED (heightened evolutionary distinctiveness), and EDGE (evolutionary distinctiveness and global endangeredness)/HEDGE (heightened evolutionary distinctiveness and global endangeredness) methods. The results suggested that T. himantegus, T. lanceolata, A. gracilis, A. imberbis, T. tanago, and A. longipinnis should be ranked as the top-priority species for conservation. According to our results, we also discussed the current conservation efforts of the bitterling fishes and gave suggestions for future work

Hydroacoustic survey on the spatial distribution pattern and day-night rhythmic behaviour of fishes in the Xiaonanhai reach of the upper Yangtze River

To understand the spatial distribution patterns and fish behaviour in the Xiaonanhai reach of the upper Yangtze River at the end of the Three Gorges Reservoir, four acoustic surveys were carried out over longer periods in 2011 and 2012, which included two boat surveys and two fixed-station horizontal detections. The results showed that fish assemblages were unevenly distributed in the investigated areas, and were mainly concentrated in the section from Funiuxi to Gaojiatuo. Fish behaviour was found to show a night-time activity peak. Additionally, fish moved much closer to the riverbank at night than during the day. Considering the intense human activities in this area, some suggestions are offered to mitigate the negative effects of shipping and hydrodam construction by using design and operational logistics to support future fish conservation.To understand the spatial distribution patterns and fish behaviour in the Xiaonanhai reach of the upper Yangtze River at the end of the Three Gorges Reservoir, four acoustic surveys were carried out over longer periods in 2011 and 2012, which included two boat surveys and two fixed-station horizontal detections. The results showed that fish assemblages were unevenly distributed in the investigated areas, and were mainly concentrated in the section from Funiuxi to Gaojiatuo. Fish behaviour was found to show a night-time activity peak. Additionally, fish moved much closer to the riverbank at night than during the day. Considering the intense human activities in this area, some suggestions are offered to mitigate the negative effects of shipping and hydrodam construction by using design and operational logistics to support future fish conservation

Environmental cues for natural reproduction of the Chinese sturgeon, Acipenser sinensis Gray, 1835, in the Yangtze River, China

For effective conservation, it is important to explore the environmental cues initiating the spawning activities of a fish species. Based on monitoring data gathered between 1998 and 2011, the relationships between spawning activities of the Chinese sturgeon, Acipenser sinensis, and several environmental cues were analyzed using the rare events logistic regression Relogit' method, which indicated that water temperature, 1-day -discharge, and atmospheric pressure were among the key spawning cues for A.sinensis (P<0.05). It is suggested that Chinese sturgeon might have an optimal environment window of 17-20 degrees C water temperature, high day-to-day discharge increase, and low atmospheric pressure for spawning. In support of Chinese sturgeon reproduction, suggested modifications to the operational procedures for the Three Gorges Reservoir (TGR) to trigger spawning are: lowering the downstream water temperature to below 20 degrees C before mid-October and expanding the period with water temperatures of between 17 and 20 degrees C; to create a day-to-day intermittent increase in the discharge to an optimal spawning water temperature; and to regulate flow at nights with a low atmospheric pressure.For effective conservation, it is important to explore the environmental cues initiating the spawning activities of a fish species. Based on monitoring data gathered between 1998 and 2011, the relationships between spawning activities of the Chinese sturgeon, Acipenser sinensis, and several environmental cues were analyzed using the rare events logistic regression Relogit' method, which indicated that water temperature, 1-day -discharge, and atmospheric pressure were among the key spawning cues for A.sinensis (P<0.05). It is suggested that Chinese sturgeon might have an optimal environment window of 17-20 degrees C water temperature, high day-to-day discharge increase, and low atmospheric pressure for spawning. In support of Chinese sturgeon reproduction, suggested modifications to the operational procedures for the Three Gorges Reservoir (TGR) to trigger spawning are: lowering the downstream water temperature to below 20 degrees C before mid-October and expanding the period with water temperatures of between 17 and 20 degrees C; to create a day-to-day intermittent increase in the discharge to an optimal spawning water temperature; and to regulate flow at nights with a low atmospheric pressure

Global climate change will severely decrease potential distribution of the East Asian coldwater fish Rhynchocypris oxycephalus (Actinopterygii, Cyprinidae)

Global climate change has been suggested to cause decrease of distribution area of many species. However, this has not been tested for East Asian inland coldwater fish. Chinese minnow (Rhynchocypris oxycephalus) is a small typical coldwater fish, which is endemic to East Asia and generally inhabits stream headwaters. Due to its occurrence in temperate south China, there is growing concern about its future fate in the face of global warming. In this study, we employed maximum entropy approach to analyze how distribution of this species would be impacted by future climate change. We collected data of 310 independent distribution points and 20 environmental variables, and conducted modeling under three general circulation models assuming two gas emission scenarios for 2020s, 2050s, and 2080s. The results showed that the Min temperature of coldest month was the most important climatic variable for potential distribution of the Chinese minnow. Modeling predicted geographical distribution of the Chinese minnow would shrink over time and become much more limited in all the situations especially in South-eastern China, and there would be little suitable habitat left in this region by 2080s. Our results confirm that climate change clearly poses a severe threat to the Chinese minnow, and we suggest that conservation efforts should focus on lower temperature areas within the current range, because these areas will remain relatively cool and may be still suitable for the Chinese minnow even under the most drastic climate change scenarios.Global climate change has been suggested to cause decrease of distribution area of many species. However, this has not been tested for East Asian inland coldwater fish. Chinese minnow (Rhynchocypris oxycephalus) is a small typical coldwater fish, which is endemic to East Asia and generally inhabits stream headwaters. Due to its occurrence in temperate south China, there is growing concern about its future fate in the face of global warming. In this study, we employed maximum entropy approach to analyze how distribution of this species would be impacted by future climate change. We collected data of 310 independent distribution points and 20 environmental variables, and conducted modeling under three general circulation models assuming two gas emission scenarios for 2020s, 2050s, and 2080s. The results showed that the Min temperature of coldest month was the most important climatic variable for potential distribution of the Chinese minnow. Modeling predicted geographical distribution of the Chinese minnow would shrink over time and become much more limited in all the situations especially in South-eastern China, and there would be little suitable habitat left in this region by 2080s. Our results confirm that climate change clearly poses a severe threat to the Chinese minnow, and we suggest that conservation efforts should focus on lower temperature areas within the current range, because these areas will remain relatively cool and may be still suitable for the Chinese minnow even under the most drastic climate change scenarios