Oviposition site selection and embryo mortality in perch

Egg strands of perch Perca fluviatilis around the margins of a lake were associated significantly with submerged vegetation. The proportion of dead embryos was significantly higher in egg strands deposited directly on the lake bottom than those on submerged vegetation.     

Novel molecular approach demonstrates that turbid river plumes reduce predation mortality on larval fish

Turbidity associated with river plumes is known to affect the search ability of visual predators and thus can drive ‘top‐down’ impacts on prey populations in complex ecosystems; however, traditional quantification of predator–prey relationships (i.e. stomach content analysis) often fails with larval fish due to rapid digestion rates. Herein, we use novel molecular genetic methods to quantify larval yellow perch (YP) in predator stomachs in western Lake Erie to test the hypothesis that turbidity drives variation in larval predation. We characterize predator stomach content DNA to first identify YP DNA (single nucleotide polymorphism) and then quantify larval YP predation (microsatellite allele counting) in two river plumes differing in turbidity. Our results showed elevated larval YP predation in the less turbid river plume, consistent with a top‐down impact of turbidity on larval survival. Our analyses highlight novel ecological hypothesis testing using the power of innovative molecular genetic approaches.     

Individual feeding success of juvenile perch is consistent over time in aquaria and under farming conditions

Juvenile (0+ year) perch Perca fluviatilis , held in tanks (1 m³) for 8 months under constant temperature (17° C) and light (12L : 12D) conditions, were weighed monthly. Individually marked fish from the tanks were placed in aquaria in groups of four and tested for feeding success, assessed as individual share of a group meal in three identical short‐term aquarium experiments separated in time (January, May and June). The groups consisted of the same individuals in each of the three experiments. In tanks, growth (thermal growth coefficient, G _T) was used as a measurement of feeding success. Individual G _T in tanks was consistent over time, and individual share of a group meal in aquaria was consistent between consecutive months. There was no connection between individual feeding success in aquaria and G _T in tanks in May and June, and in January the factors were negatively correlated. The condition factor at the start of aquarium experiments and feeding success in aquaria were negatively correlated in June and tended to be so also in May. Boldness in aquaria was negatively correlated with growth in tanks. Thus, individuals that were successful in one environment seemed to be less successful in the other. There was a seasonal change in G _T, with an increase from March to April and from April to June despite constant day length and temperature.     

Isolation over 35 years in a heated biotest basin causes selection on MHC class IIß genes in the European perch (Perca fluviatilis L.)

Genes that play key roles in host immunity such as the major histocompatibility complex (MHC) in vertebrates are expected to be major targets of selection. It is well known that environmental conditions can have an effect on host–parasite interactions and may thus influence the selection on MHC. We analyzed MHC class IIß variability over 35 years in a population of perch (Perca fluviatilis) from the Baltic Sea that was split into two populations separated from each other. One population was subjected to heating from cooling water of a nuclear power plant and was isolated from the surrounding environment in an artificial lake, while the other population was not subjected to any change in water temperature (control). The isolated population experienced a change of the allelic composition and a decrease in allelic richness of MHC genes compared to the control population. The two most common MHC alleles showed cyclic patterns indicating ongoing parasite–host coevolution in both populations, but the alleles that showed a cyclic behavior differed between the two populations. No such patterns were observed at alleles from nine microsatellite loci, and no genetic differentiation was found between populations. We found no indications for a genetic bottleneck in the isolated population during the 35 years. Additionally, differences in parasitism of the current perch populations suggest that a change of the parasite communities has occurred over the isolation period, although the evidence in form of in‐depth knowledge of the change of the parasite community over time is lacking. Our results are consistent with the hypothesis of a selective sweep imposed by a change in the parasite community.     

伊犁鲈微卫星位点的筛选及近缘物种通用性

为开发伊犁鲈(Perca schrenkii)分子标记用于鲈属鱼类种质资源保护,以伊犁鲈为材料,应用磁珠富集法进行了微卫星标记的筛选.从伊犁鲈尾鳍提取总DNA,进行酶切、接头连接、PCR扩增,再采用生物素标记(CA)15探针及生物素标记(TG)15探针对扩增产物进行杂交富集,经再次PCR扩增及T-A克隆,成功构建了伊犁鲈基因组微卫星富集文库.采用重复序列引物筛选获得阳性克隆,随机选取48个阳性克隆进行测序,测得序列46个,其中38个克隆含有微卫星序列,41个位点的微卫星重复数在8次以上.根据测得序列设计17对微卫星引物,均能在伊犁鲈群体中扩增获得目的条带.采用该17对引物对河鲈(P.fluviatilis)及黄金鲈(P.flavescens)群体样本进行扩增,10对引物具有通用性,其中6对在河鲈中具有高度多态性(PIC>0.5),5对在黄金鲈中具有高度多态性.     

Environmental factors regulate the effects of roach Rutilus rutilus and pike Esox lucius on perch Perca fluviatilis populations in small boreal forest lakes

In this study of 18 small boreal forest lakes, the effects of abiotic and biotic factors (roach Rutilus rutilus and pike Esox lucius) on various population variables of perch Perca fluviatilis were examined. As a single variable, the gillnet catch per unit effort (CPUE) of R. rutilus was negatively related to the mean mass of small (< 200 mm) and the growth rate of young (1–2 years) P. fluviatilis. The mean mass of large (≥ 200 mm) P. fluviatilis was the highest at intermediate CPUE of R. rutilus. Redundancy analysis including environmental factors and P. fluviatilis population variables suggested that ‘predation–productivity–humus' gradient affected P. fluviatilis populations by decreasing the CPUE and mean mass of small individuals but increasing these variables of large individuals. The CPUE of R. rutilus and lake area had a negative effect on small and a positive effect on large P. fluviatilis growth rate. In small boreal forest lakes, P. fluviatilis populations are affected by the partially opposite forces of competition by R. rutilus and predation by E. lucius, and the intensity of these interactions is regulated by several environmental factors.     

基于多变量形态度量学和线粒体Cytb序列的鲈属鱼类分类探讨

鲈属鱼类的分类在学术界尚存在很多争议。本文通过鲈属鱼类32个多变量形态学参数和1134bp的线粒体DNA细胞色素b序列的比较,对鲈属鱼类分类问题做了探讨。结果显示河鲈和伊犁鲈之间的形态距离为0.15,黄金鲈和伊犁鲈为0.14,河鲈和黄金鲈为0.09,在形态上黄金鲈和河鲈较接近,而伊犁鲈与前两者差异明显;主成分2(16.09%)对主成分1(21.71%)作图结果显示黄金鲈和河鲈有重叠区,而伊犁鲈与其它二种鲈有较大差距;细胞色素b同源序列差异百分比为河鲈与伊犁鲈13.08%、黄金鲈与伊犁鲈10.68%、黄金鲈与河鲈11.47%,鲈属鱼类间的碱基差异属于种间的遗传差异。MP、NJ和ML三种系统发育树在河鲈、黄金鲈和伊犁鲈三个种或亚种之间的拓扑结构一致,显示黄金鲈与伊犁鲈的演化关系较河鲈为近。根据20个样本的细胞色素b基因序列的遗传差异和系统发育树以及地理分布上的繁殖隔离,我们进一步认定黄金鲈和河鲈是不同的种,鲈属鱼类包括伊犁鲈、河鲈和黄金鲈三个种。     

Genetic divergence and phylogeographic relationships among european perch (Perca fluviatilis) populations reflect glacial refugia and postglacial colonization

We used the widely distributed freshwater fish, perch (Perca fluviatilis), to investigate the postglacial colonization routes of freshwater fishes in Europe. Genetic variability within and among drainages was assessed using mitochondrial DNA (mtDNA) D-loop sequencing and RAPD markers from 55 populations all over Europe as well as one Siberian population. High level of structuring for both markers was observed among drainages and regions, while little differentiation was seen within drainages and regions. Phylogeographic relationships among European perch were determined from the distribution of 35 mtDNA haplotypes detected in the samples. In addition to a distinct southern European group, which includes a Greek and a southern Danubian population, three major groups of perch are observed: the western European drainages, the eastern European drainages including the Siberian population, and Norwegian populations from northern Norway, and western side of Oslofjord. Our data suggest that present perch populations in western and northern Europe were colonized from three main refugia, located in southeastern, northeastern and western Europe. In support of this, nested cladistic analysis of mtDNA clade and nested clade distances suggested historical range expansion as the main factor determining geographical distribution of haplotypes. The Baltic Sea has been colonized from all three refugia, and northeastern Europe harbours descendants from both eastern European refugia. In the upper part of the Danube lineages from the western European and the southern European refugia meet. The southern European refugium probably did not contribute to the recolonization of other western and northern European drainages after the last glaciation. However, phylogenetic analyses suggest that the southern European mtDNA lineage is the most ancient, and therefore likely to be the founder of all present perch lineages. The colonization routes used by perch probably also apply to other freshwater species with similar distribution patterns.     

Laboratory evaluation of two bioenergetics models applied to yellow perch: identification of a major source of systematic error

Laboratory growth and food consumption data for two size classes of age 2 year yellow perch Perca flavescens , each fed on two distinct feeding schedules at 21° C, were used to evaluate the abilities of the Wisconsin (WI) and Karas–Thoresson (KT) bioenergetics models to predict fish growth and cumulative consumption. Neither model exhibited consistently better performance for predicting fish body masses across all four fish size and feeding regime combinations. Results indicated deficiencies in estimates of resting routine metabolism by both models. Both the WI and KT models exhibited errors for predicting growth rates, which were strongly correlated with food consumption rate. Consumption-dependent prediction errors may be common in bioenergetics models and are probably the result of deficiencies in parameter values or assumptions within the models for calculating energy costs of specific dynamic action, feeding activity metabolism or egestion and excretion. Inter-model differences in growth and consumption predictions were primarily the result of differences in egestion and excretion costs calculated by the two models. The results highlighted the potential importance of parameters describing egestion and excretion costs to the accuracy of bioenergetics model predictions, even though bioenergetics models are generally regarded as being insensitive to these parameters. The findings strongly emphasize the utility and necessity of performing laboratory evaluations of all bioenergetics models for assurance of model accuracy and for facilitation of model refinement.