Genetic control over grain damage in a spring barley mapping population

A genetic map was constructed using DNA‐based markers in a barley mapping population derived from the cross ‘Tankard’בLivet’, that was developed to explore the genetic control over grain damage in spring barley cultivars. Quantitative trait loci (QTL) were located for husk skinning, gape between the lemma and palea and splitting of the fused pericarp/testa/aleurone tissues. The QTL accounted for 70% of the genetic variation in Split and 60% of the genetic variation in Gape and Skinning. The QTL were clustered on chromosomes 1H, 4H, 5H, 6H and 7H. QTL analysis indicates the possibility of transgressive segregation for grain splitting and so the breeding of lines with more extreme splitting. This is of concern to the malting industry as, without extensive phenotypic assessment, such lines could be commercialized, as was the case of Landlord, and put malting barley supplies at risk. These findings are discussed in relation to the genetic control over traits including grain length and width.     

Linking size‐based trophodynamics and morphological traits in marine fishes

The rule of thumb in marine trophodynamics indicates that the bigger an organism, the higher its trophic level (TROPH). This generalization leads to the assumption that fishes increase their TROPH with growth. However, a recent review showed that for many species, TROPH does not increase with body size, suggesting that size‐independent feeding is not rare in marine fishes. Here, we assessed some morphological traits of marine fishes that could potentially be used as indicators for the ability to vary TROPH with body size. Stable isotope values of nitrogen were used as a proxy TROPH. The specific objectives were as follows: (a) to evaluate the relationship between the oral gape and the trophodynamic trend and (b) to quantify the relevance of 11 external morphological traits in determining the size‐based trophodynamics. We used random forest models to identify the morphological traits that would help predict which species would have the potential to increase TROPH with growth and which would have not. The selected traits included the pelvic fin relative position, the dorsal fin shape, total length, and relative mouth size. Our results also showed a marked relationship between the rate of increase in the oral gape and TROPH. The analyses presented here provide the first comprehensive and quantitative review aiming at linking the trophodynamics of marine fishes with external morphological traits.     

Hypoxic conditions enhance refuge effect of macrophyte zone for small prey fish from piscivorous predators

Body size dependency of the refuge effects of gape limitation and differences in hypoxia tolerance between the predator largemouth bass Micropterus salmoides (Lacépède) and the prey fish, nigorobuna carp Carassius buergeri grandoculis Temminck & Schlegel, were modelled to simulate the relative effect of size and physiological refuges for prey inhabiting the hypoxic macrophyte zone along a lakeshore. The model simulation suggested that a physiological refuge, maintained by the difference in hypoxia tolerance, could protect far smaller prey than a size refuge that is based solely on predator gape size and prey body depth. The dissolved oxygen gradient observed in the macrophyte zone located in Yamanoshita Bay, Lake Biwa, Japan, which was extremely low at the inner part and higher offshore, was determined to provide a physiological refuge that would be effective in terms of space.     

中国多杜鹃寄生系统中同域分布的杜鹃雏鸟的鉴别(英文)

寄生者与宿主之间可形成一种类似军备竞赛的协同进化关系。杜鹃与其宿主之间的协同进化是迄今研究最多的一个寄生系统,但人们对亚洲杜鹃的了解却知之甚少。中国是亚洲寄生性杜鹃种类最丰富的国家,多种杜鹃鸟类,特别是形态非常相似的 Cuculus属杜鹃同域分布于某一地区,给杜鹃雏鸟的种类鉴别带来很大困难。这种情况在欧洲不存在,因为Cuculus属杜鹃在欧洲仅1种,即大杜鹃(Cuculus canorus)。本研究对同域繁殖于中国境内、外部形态特征非常相似的4种Cuculus属杜鹃,即大杜鹃、中杜鹃(C. saturatus)、小杜鹃(C.poliocephalus)和四声杜鹃(C. micropterus)雏鸟的重要形态鉴别特征进行了比较,并进一步通过采集雏鸟血样进行DNA分析加以确认。结果表明,Cuculus属4种杜鹃的雏鸟可通过嘴裂和羽毛两个重要形态特征加以区分。这是关于Cuculus属杜鹃雏鸟分子鉴定的首次报道。     

Episodic predation of mammals by stream fishes in a boreal river basin

Stream‐dwelling fish typically feed on small prey items, such as benthic invertebrates, but maintain the capacity to opportunistically feed on rare, large‐bodied prey when available. However, consumption of particularly large prey is typically viewed as isolated events that are not organised spatially or temporally across watersheds. We assessed the occurrence of small mammals in the stomach contents of rainbow trout (Oncorhynchus mykiss) and Arctic grayling (Thymallus arcticus) over 13 years in the Wood River basin, Alaska (59°34′N, 158°48′W). Shrews (Sorex spp.) were the dominant mammals observed episodically every 2–3 years in the stomach contents of fish. Notably, shrew consumption was correlated in both Arctic grayling and rainbow trout within individual streams, and across the river basin in several subwatersheds. Predators of shrews were usually the largest individuals within each population, suggesting that smaller fish are gape‐limited and that dominant fish monopolised mammal prey. On average, 24% (11–38%) of Arctic grayling >298 mm (fork length) and rainbow trout >290 mm contained mammal prey during peak years. Small mammal populations often cycle every 2–5 years with well‐known functional and numerical effects for terrestrial predators, a dynamic that may be reflected in our 13 years data set of diet contents for aquatic predators. Although numerically infrequent when averaged over time, small mammal subsidies to streams may be episodically important to the energy budgets of long‐lived consumers in freshwater environments.     

Physiological and behavioral responses to hypoxia in the bonnethead shark, Sphyrna tiburo: routine swimming and respiratory regulation

We examined the effect of hypoxia on the swimming speed, respiration rate (oxygen uptake), gape and ventilation volume of the bonnethead shark, Sphyrna tiburo. We used a sonic flowmeter developed for this study to examine swimming speed changes of sharks held in artificial lagoons during diurnal dissolved oxygen changes. Sharks were observed to swim at about 34 cm s^-1 during the day but increased to about 40 cm s^-1 at night when dissolved oxygen levels fell to < 3 mg l^-1. Using a closed system respirometer we examined changes in swimming speed, respiration rate and gape at four dissolved oxygen levels. Swimming speeds averaged 24 to 25 cm s^-1 under normoxic conditions but increased to 38 to 40 cm s^-1 during hypoxia. Similarly, respiration rate increased with increasing speed and decreasing dissolved oxygen. Gape averaged about 1.0 cm under normoxic conditions and increased to a maximum of about 3.5 cm during hypoxia. Using assumed oxygen extraction efficiencies of 25, 50 and 75% and observed respiration rates, we estimated that ventilation volumes of about 25 to 470 l h^-1, depending upon oxygen concentration, would be necessary for gill ventilation. These experiments suggest that changes in swimming speed and mouth gape are important for respiratory regulation in ram ventilating sharks.     

The role of gape‐limitation in intraguild predation between endangered Mohave tui chub and non‐native western mosquitofish

Intraguild predation (IGP) is a mechanism that may facilitate the co‐existence of native species with non‐native invasive species. We conducted laboratory predation trials to assess the role of predator gape‐limitation in the context of IGP between the endangered Mohave tui chub (Siphateles bicolor mohavensis) and invasive western mosquitofish (Gambusia affinis). Larval tui chubs had significantly lower (χ² = 74.74; P < 0.001) survival in the presence of female mosquitofish (10.0%) than in the presence of male mosquitofish (73.3%). Reciprocally, adult tui chubs preyed upon adult mosquitofish, causing a significantly lower (χ² = 11.33; P < 0.001) survival for male mosquitofish (60%) compared to female mosquitofish survival (96.7%). Vulnerability modelling revealed that mosquitofish with a body depth < 4.6 mm and a larval tui chub with a body depth < 1.2 mm were completely vulnerable to predation by adult Mohave tui chub and adult mosquitofish, respectively. IGP in this study system is size‐structured based on gape‐size limitation and may have some conservation implications for the recovery of endangered Mohave tui chub. Our findings also provide an important caveat to the dogmatic view of mosquitofish as a threat whenever they invade. It is important to note that many previous studies that reported negative impacts of mosquitofish involved native species with relatively small body sizes, often the same size as mosquitofish.     

Feeding selectivity in early life stages of Rhamdia voulezi under experimental conditions

The feeding selectivity of laboratory‐reared larvae of Rhamdia voulezi was assessed to investigate the preferred preys in early life stages. Three experiments were conducted at different larval development stages, starting soon after the absorption of the yolk sac (on fourth day after hatching – DAH), using zooplankton from fish ponds as food. Differences were detected in the patterns of prey selection among development stages. At first, the larvae prefer small preys, such as rotifers and cladocerans. Later, when they are more developed, they prefer to feed on large preys, such as copepods. On the fourth DAH, larvae in the pre‐flexion and initial flexion stage strongly selected rotifers and cladocerans (Diaphanosoma spinulosum, D. brevireme, Moina sp., M. micrura and M. minuta). At the other stages, cladocerans continued to be strongly selected. However, on the eighth DAH, larvae in flexion stage selected less strongly copepods Argyrodiaptomus azevedoi, Metacyclops mendocinus and Termocyclops decipiens. On the tenth DAH, larvae in postflexion stage selected more strongly copepods Argyrodiaptomus furcatus, Notodiaptomus cf. spinuliferus and M. mendocinus. As larvae grow, they tend to specialize in feeding of a particular prey. Prey selection of R. voulezi larvae was based both on species and zooplankton size. The size of the zooplankton ingested was related to the mouth gape size of larvae.     

Effects of seasonality and migratory prey on body condition of Cichla species in a tropical floodplain river

Abstract –  In this study we examine trends in body condition of three Cichla species native to the Cinaruco River, Venezuela. Specifically, we characterise the potential subsidy provided by migratory Semaprochilodus kneri to Cichla by comparing condition among species, hydrologic seasons and different size-classes (based on the ability to consume S. kneri assuming gape-limitation). All three species had lowest body condition during the rising-water season (following the reproduction period). Only Cichla temensis had greater body condition during the falling-water season than low-water season. During the falling-water season, C. temensis >300 mm SL had significantly greater condition than smaller conspecifics. Annual migration of S. kneri into the river during the falling-water season provides a resource subsidy to large C. temensis . Transfer of whitewater production into nutrient-poor rivers by migratory fishes appears to be a general phenomenon in the major Neotropical river basins and may partially account for high standing stocks of large piscivores in these unproductive ecosystems.