The evolution of eye size in response to increased fish predation in Daphnia

Variation in eye size is ubiquitous across taxa. Increased eye size is correlated with improved vision and increased fitness via shifts in behavior. Tests of the drivers of eye size evolution have focused on macroevolutionary studies evaluating the importance of light availability. Predator‐induced mortality has recently been identified as a potential driver of eye size variation. Here, we tested the influence of increased predation by the fish predator, the alewife (Alosa pseudoharengus) on eye size evolution in waterfleas (Daphnia ambigua) from lakes in Connecticut. We quantified the relative eye size of Daphnia from lakes with and without alewife using wild‐caught and third‐generation laboratory reared specimens. This includes comparisons between lakes where alewife are present seasonally (anadromous) or permanently (landlocked). Wild‐caught specimens did not differ in eye size across all lakes. However, third‐generation lab reared Daphnia from lakes with alewife, irrespective of the form of alewife predation, exhibited significantly larger eyes than Daphnia from lakes without alewife. This genetically based increase in eye size may enhance the ability of Daphnia to detect predators. Alternatively, such shifts in eye size may be an indirect response to Daphnia aggregating at the bottom of lakes. To test these mechanisms, we collected Daphnia as a function of depth and found that eye size differed in Daphnia found at the surface versus the bottom of the water column between anadromous alewife and no alewife lakes. However, we found no evidence of Daphnia aggregating at the bottom of lakes. Such results indicate that the evolution of a larger eye may be explained by a connection between eyes and enhanced survival. We discuss the cause of the lack of concordance in eye size variation between our phenotypic and genetic specimens and the ultimate drivers of eye size.     

The outcome of the invasion of Florida lakes by Daphnia lumholtzi

1. We examined 7–12 years of monthly to quarterly historical data from 15 lakes in FL, U.S.A. to determine the extent and outcome of invasion by the alien cladoceran Daphnia lumholtzi Sars. 2. The alien species was found in 10 of the 15 lakes, including Florida’s three largest lakes: Okeechobee, George and Apopka. All the surveyed lakes had resident populations of the smaller native species Daphnia ambigua Scourfield. 3. In most of the lakes, D. ambigua occurred seven to ninefold more often in plankton samples than D. lumholtzi, and at 10‐ to 100‐fold higher maximal densities. One exception was a small lake in central Florida (Lake Jesup), where D. lumholtzi attained high densities on several occasions in the 10 years of sampling. 4. In Lake Okeechobee, where data were of sufficient quality and quantity to perform statistical analyses, the results of canonical correlation analysis indicated that high densities of D. lumholtzi were correlated with lower concentrations of suspended solids, high algal biomass and higher temperature, whereas the opposite conditions were correlated with high densities of D. ambigua. 5. Based on the majority of data, D. lumholtzi has successfully invaded many lakes in Florida, yet it has not become a substantive component of the zooplankton. Additional research is needed to determine whether resources, fish predation or some other factor is responsible for this outcome of invasion.     

A method for externally attaching radio transmitters to minimize dermal irritation

A method for externally attaching transmitters to fishes is described that reduces contact between the transmitter and the fish, thus reducing the potential for dermal irritation.     

中国西北部毛莨科新资料

本文发表了中国西北部毛莨科新资料, 即巴里坤毛莨Ranunculus balikunensis J.G.Liou, sp.nov.;髯毛蒙古白头翁Pulsatilla ambigua Turcz.ex pritz.var.barbata J.G.Liou, var.nov.。     

Movements of Macquaria ambigua, in the Murray River, south‐eastern Australia

A 2 year (2000–2001) radio‐tagging study was undertaken to investigate the movements of 51 golden perch Macquaria ambigua in the Murray River at Nyah in north‐western Victoria, Australia. During the winter of both years, golden perch did not undertake movements >5 km and displayed strong home range fidelity. In the first year of the study there was an increase in the distance of golden perch movement during late spring which coincided with increasing water temperature and river discharge. Nineteen golden perch were tracked during this period, of which 10 travelled downstream between 11 and 290 km. Seven of these fish moved to an area below the junction of the Murray and Wakool Rivers. Five golden perch travelled upstream between 13 and 35 km, four of which travelled to an area around the junction of the Murray River and Speewa Creek. The remaining four golden perch undertook localized movements of <5 km. Many of the long distance movements undertaken in spring 2000 were rapid and 53% of these golden perch returned to within 3 km of their release locations, indicating homing behaviour. Given that the rapid movements of golden perch in spring coincided with the known spawning season of this species, these long distance movements may be associated with reproductive strategy.     

Spatial and temporal dispersion patterns of golden perch, Macquaria ambigua, larvae in an artificial floodplain environment

Golden perch larvae were stocked into a pond and inundated floodplain system in south-eastem Australia to determine movement patterns of the larvae onto and off the floodplain area. A total of 428 larvae were caught moving from the floodplain into the pond whereas only 18 were collected moving in the reverse direction. Thirty one larvae were caught at open water sites in the pond and floodplain, but only three were collected from sites on the floodplain which provided shade, timber or water flow. Transect samples from the pond also yielded more larvae than samples from floodplain transects, indicating a distinct spatial dispersion pattern in favour of the pond.
Spatial dispersion patterns of golden perch larvae appear to correspond with gradients in water quality between the pond and floodplain habitats. Stratification occurred in the pond but did not develop on the floodplain. Water on the floodplain was cooler, harder and contained less oxygen than surface water from the pond. Die1 oscillations occurred in water temperature, pH, dissolved oxygen, carbon dioxide and acidity, but there was no significant corresponding pattern in the distribution of larvae.
Dispersion of golden perch larvae between pond and floodplain habitats is not random, and may be actively influenced by local-scale variations in water quality.     

Plasticity of flower longevity in Corydalis ambigua

We investigated the longevity of individual flowers of Corydalis ambigua Cham. et Schlecht. during different periods of pollinator activity and at different temperatures. To measure potential (unpollinated) flower longevity of C. ambigua, this study was conducted at forest islands where pollinator visits were scarce. The longevity of individual flowers of C. ambigua indicated high plasticity. The longevity of unpollinated flowers in natural pollination ranged from 2 to 25 days and continuously decreased with the date of flower opening. The temperature increased as the flowering season progressed. Furthermore, the greenhouse transplanting experiment showed that higher temperatures shorten the life span of flowers. The longevity of pollinated flowers subjected to hand pollination of newly opened flowers was shorter than that of unpollinated flowers in natural pollination regardless of the date of flower opening. These results showed that not only high temperature but also pollination shortens flower longevity. We discuss the role of plasticity in flower longevity for C. ambigua in relation to pollination success and reduction in the maintenance cost of the flowers.     

中国鹿花菌属志略

近年来,国外许多学者对鹿花菌属 Gyromitra Fr.的一系列研究导致该属传统的概念、范围发生了很大的变动。本文在接受了 Harmaja 将 Discina 和 Neogyromitra 合并在Gyromitra 名下的观点的基础上,报道了近年来作者在我国鹿花菌属研究中所确认的8个种。其中乳白鹿花菌 Gyromitra lactea 和新疆鹿花菌G.xinjiangensis 为新种,含糊鹿花菌G.ambigua、帚状鹿花菌 G.fastigiata 和亮鹿花菌 G.splendida 为我国首次报道。我国文献中所记载的鹿花菌 G.esculenta 在我国是否存在,尚需进一步调查。     

The influence of changes in food availability on the activities of key degradative and metabolic enzymes in the liver and epaxial muscle of the golden perch

This study investigated the influence of feeding frequency on the activities of important degradative enzymes and potentially rate-limiting enzymes in glycolysis and gluconeogenesis in the liver and white epaxial muscle of Macquaria ambigua . Adult animals were either fed daily to satiety (fed), deprived of food for up to 180 days (starved), or starved for 150 days then fed daily to satiety for 30 days (starved/fed). The activities of lipolytic, glycogenolytic and glycolytic enzymes in the livers of starved fish were maintained as long as liver energy stores were available, but became significantly reduced following their exhaustion indicating a decline in metabolism in response to prolonged starvation. The response of epaxial muscle metabolism to changes in food availability was different to that of the liver, as no significant change in the activities of muscle lipolytic or glycogenolytic enzymes were observed in response to starvation. Muscle tissue metabolism was reduced after 60–90 days of starvation, but then returned to prestarvation levels.