Distribution patterns of the two genetic groups of Corbicula fluminea in a lotic-lentic system.

Differences in local habitat conditions are often implicated as drivers for morphological and genetic divergence in natural populations. However, there are still relatively few studies regarding how divergent habitats influence patterns for morphotypes and genetic lineages in aquatic invertebrates. In this study, we explored the morphological patterns, genetic divergence, and distributions of a bivalve, Corbicula fluminea, in a lotic-lentic system. Sampling locations included lotic, ecotone, and lentic habitats. First, we found two lineages (Lineages A and B) with significant genetic divergence that primarily corresponded to two morphotypes (Morphs D and C) of C. fluminea. Lineage A consisted of 88.68% Morph D (shell sculpture: 8-14 ridges/cmsh) and 11.32% Morph C (shell sculpture: 15 ridges/cmsh) individuals and had genetic similarity to invasive populations. Lineage B consisted of only Morph C (shell sculpture: 15-23 ridges/cmsh). Second, we revealed clear effects of habitat on the spatial distribution patterns for the two lineages of C. fluminea. Lineage A was dominant in lotic habitats, with a significantly higher density than that of Lineage B in these locations. Lineage B was dominant in lentic habitats. However, both lineages had their highest densities in the ecotone habitat, without clear dominance and no significant difference in density between groups. Individuals of Lineages A and B are different in shell morphology, which may be related to a benefit trade-off between shell shapes that allow for rapid burrowing and holding position in different flow conditions. The distribution patterns indicate that Lineages A and B may not prefer uniquely lotic and lentic habitats, but each lineage is more tolerant to one habitat type, respectively. Generally, our study established a correlation among morphotypes, lineages, and different habitats for C. fluminea along a lotic-lentic gradient system, which has important implementations for fisheries management units and for understanding the role of habitat preference for this species in monitoring for pioneer dispersal in invasive species management.

Investigations of Fish Assemblages Using Two Methods in Three Terminal Reservoirs of the East Route of South-to-North Water Transfer Project, China.

The terminal reservoirs of water transfer projects directly supply water for domestic, agricultural, and industrial applications, and the water quality of these reservoirs produce crucial effects on the achievement of project targets. Typically, fish assemblages are monitored as indicators of reservoir water quality, and can also be regulated for its improvement. In the present study, we compared traditional fish landing (TFL) and environmental DNA (eDNA) metabarcoding methods for monitoring fish assemblages in three terminal reservoirs of the East Route of the South-to-North Water Transfer Project, China. Results of TFL and eDNA showed similar assemblage structures and patterns of diversity and spatial distribution with obvious differences in fish composition across three examined reservoirs. Demersal and small fish were dominant in all reservoirs. In addition, a strong association between water transfer distance and assemblages and distribution of non-native fish was found. Our findings highlight the necessity of the fish assemblage monitoring and managing for water quality and revealed the impact of water diversion distance on the structure of fish assemblages and dispersal of alien species along the water transfer project.

Interpopulation trophic niches and ontogenetic shifts of a mangrove fish predator.

Fish trophic niches reflect important ecological interactions and provide insight into the structure of mangrove food webs. Few studies have been conducted in mangrove fish predators to investigate interpopulation trophic niches and ontogenetic shifts. Using stable isotope analysis and two complementary approaches, the authors investigated trophic niche patterns within and between two ontogenetic groups (juveniles and sub-adults) of a generalist predator (Acentrogobius viridipunctatus) in four mangroves with heterogeneous environmental conditions (e.g., tidal regimes, salinity fluctuations and mangrove tree community). The authors hypothesized that the trophic niche between populations would vary regionally and trophic position would increase consistently from juvenile to sub-adult stages. The results revealed that both δ13 C and δ15 N values varied greatly across populations and between ontogenetic groups, and complex spatio-ontogenetic variations were expressed by Layman's metrics. They also found some niche separation in space, which is most likely related to resource availability in spatially diverse ecosystems. In addition, trophic niche position increased consistently from juveniles to sub-adults, indicating ontogenetic feeding shifts. The isotopic plasticity index and Fulton's condition index also showed significant spatial-ontogenetic variation, which is consistent with optimal foraging theory. The findings highlight that trophic plasticity has a high adaptive value for mangrove fish predators in dynamic ecosystems.