The ultrastructure of the eye of the mosquitofishGambusia affinis

Summary The ultrastructure of the tissue components of the eye ofGambusia affinis, excluding the sensory cells, is described. The cornea consists of two different sections of collagenous layers of different density. The choroid includes an argentea composed of- and-melanophores, lipopterinophores and a choriocapillaris associated with the rete mirabile of the choroid body. Bruch's membrane, underlying the retinal pigment layer, can develop complex associations with fibroblasts delimiting the choriocapillaris. The outer section (stroma) of the iris includes several cell types that are not found in the inner or vitread section. In adultGambusia the lens capsule is well developed, but in twoweek-oldSarotherodon larvae the lens epithelium is covered only by a glycocalyx.     

Gut morphology and function in Atherinops affinis (Teleostei: Atherinopsidae), a stomachless omnivore feeding on macroalgae

The marine silverside Atherinops affinis has a short, simple gut and no obvious stomach or physical mechanisms for breaking down algal cells even though its diet in many estuarine habitats is primarily green macroalgae. Silverside from the Upper Newport Bay estuary in southern California had: (1) assimilation efficiencies from a green algal diet of 54% (total organic material), 74% (carbon), 84% (nitrogen), 89% (protein) and 81% (energy), values typical for marine herbivorous fishes; (2) an alkaline gut and no pepsin activity, thus confirming that the fish lacks a stomach; (3) relatively high amylase activity and low trypsin and lipase activities, a digestive enzyme profile expected in a fish consuming a high-carbohydrate, low-protein and low-lipid diet. The fish appears to be capable of functional herbivory and can be classified tentatively as a type III herbivore based on its possible use of pharyngeal jaws for lysis of algal cells.     

The conservation status of athalassic lakes in New South Wales,Australia

To provide an overview for the State Pollution Control Commission of NSW, 102 lakes were visited throughout the state during the 1988–9 summer to ascertain their ecological condition. The sites chosen covered a spectrum of geomorphic types in approximate proportion to their perceived relative abundance. Field work concentrated on some physicochemical parameters and on zooplankton and littoral invertebrates. A summary of these features of the lakes of NSW is given.The most widespread problem is eutrophication, though for many lakes changes in trophic status could be part of wider changes in lakes since European settlement. A significant number of lakes suffer eroded shorelines and sedimentation. The introduced mosquito fish, Gambusia affinis, is associated with decreased diversity mainly in coastal lakes where also alien plants may be pestiferous. A few lakes in western areas have their flooding regime altered, while a number in the east are drained. With few exceptions there are no management programs to improve the conservation status of degraded lakes in NSW.     

Ephemeroptera from Central and South America: New Species of the Farrodes bimaculatus Group with a Key for the Males

The genus Farrodes was recently revised, and two species groups were delimited: Farrodes caribbianus and Farrodes bimaculatus. In that paper the species of the F. caribbianus species group were described or redescribed. In the F. bimaculatus species group eight undescribed species were treated but not described. In the present paper, these new species of the F. bimaculatus species group are described and discussed and a key for the separation of all the species known from male imagines in this group is provided.     

Laboratory evaluation of predation on mosquito larvae by Australian mangrove fish

A series of laboratory experiments compared predation rates of three native eastern Australian mangrove fish species (Psuedomugil signifer, Hyseleotris galii, Pseudogobius sp.) and the exotic Gambusia holbrooki on 2^nd and 4^th instar Aedes vigilax larvae, in order to determine their potential as mosquito control agents in mangrove forests. All four species preyed on significant numbers of both 2^nd and 4^th instar larvae. All showed a similar pattern of larval consumption, gorging on larvae in the first hour of each experiment, before reducing to a relatively constant background feeding rate. Gambusia holbrooki showed the highest larval consumption rates, but is unsuitable as a mosquito control agent due to it being an exotic pest species in Australia. Of the three native species, P. signifer showed the greatest potential as a mosquito control agent, having consumption rates comparable to G. holbrooki, and was the only species that did not show a significant reduction in larval consumption in the night experiments.     

Plasticity of the mate choice mind: courtship evokes choice‐like brain responses in females from a coercive mating system

Female mate choice is fundamental to sexual selection, and determining molecular underpinnings of female preference variation is important for understanding mating character evolution. Previously it was shown that whole‐brain expression of a synaptic plasticity marker, neuroserpin, positively correlates with mating bias in the female choice poeciliid, Xiphophorus nigrensis, when exposed to conspecific courting males, whereas this relationship is reversed in Gambusia affinis, a mate coercive poeciliid with no courting males. Here we explore whether species‐level differences in female behavioral and brain molecular responses represent ‘canalized’ or ‘plastic’ traits. We expose female G. affinis to conspecific males and females, as well as coercive and courting male Poecilia latipinna, for preference assays followed by whole‐brain gene expression analyses of neuroserpin, egr‐1 and early B. We find positive correlations between gene expression and female preference strength during exposure to courting heterospecific males, but a reversed pattern following exposure to coercive heterospecific males. This suggests that the neuromolecular processes associated with female preference behavior are plastic and responsive to different male phenotypes (courting or coercive) rather than a canalized response linked to mating system. Further, we propose that female behavioral plasticity may involve learning because female association patterns shifted with experience. Compared to younger females, we found larger, more experienced females spend less time near coercive males but associate more with males in the presence of courters. We thus suggest a conserved learning‐based neuromolecular process underlying the diversity of female mate preference across the mate choice and coercion‐driven mating systems.     

Have introduced fish initiated piscivory among the long-fingered bat?

During the winter of 2003–2004 feces were collected from a winter colony of the long-fingered bat (Myotis capaccinii) in the Hazorea cave (north-west Israel). Of the 1913 feces that were examined, 234 contained scales of Gambusia affinis – a small fish that had been introduced to Israel around 1920 in order to control mosquito larvae. The remains of spiders and five insect orders were also represented in the feces. This is the first report of a piscivorous bat in the Middle East and the first finding of fish remains in the feces of M. capaccinii. The findings show that in the north of Israel this species does not hibernate but remains active throughout the winter. It appears that the consumption of G. affinis reflects a change in the diet of these bats from insectivory to semi-piscivory.     

低温胁迫对番茄种子萌发的影响

在人工气候箱中模拟3个低温处理(24h最低/最高温度分别设定为7℃/12℃、5℃/10℃和3℃/8℃),分析了播种后不同天数低温胁迫对番茄种子萌发的影响。结果表明:与对照(18℃/25℃)相比,低温胁迫处理的温度越低影响越大,当日最低温度达到5.0℃、日均温低于10.0℃(相当于低温胁迫处理7℃/12℃)时,对番茄种子萌发的影响较为严重;播种后越早经受低温影响越大,播种后3d内经受低温胁迫,番茄种子发芽势、发芽指数和萌发率均有较大的下降,播种6d后低温胁迫对其萌发指标的影响较小;低温胁迫影响种子萌发的原因主要是低温导致了α-淀粉酶活性下降,相对离子渗漏率增加,从而减缓了番茄种子贮藏物质的降解,影响了番茄种子萌发初期的物质与能量代谢,并增强了细胞膜的透性,导致外渗物增多。     

模拟氮沉降对华西雨屏区慈竹林土壤活性有机碳库和根生物量的影响

从2008年1月起,对华西雨屏区慈竹(Neosinocalamus affinis)人工林进行了模拟氮沉降试验,氮沉降水平分别为对照(CK,0 g.m-.2a-1)、低氮(5 g.m-.2a-1)、中氮(15 g.m-.2a-1)和高氮(30 g.m-.2a-1)。在模拟氮沉降1.5 a后,按土层深度取土样和根样,测定不同深度土壤活性有机碳含量和根生物量。结果表明,华西雨屏区慈竹林土壤有机碳、微生物量碳、浸提性溶解有机碳和活性碳含量均随土层深度的增加而减少。氮沉降显著减少了土壤微生物量碳和活性碳含量,显著增加了浸提性溶解有机碳含量,并使得土壤碳库管理指数减小。同时,慈竹林根密度在氮沉降条件下减少了12%-14%。说明氮沉降的增加减少了土壤有机碳中的活性部分,增加了土壤有机碳的淋溶流失,降低了慈竹林土壤碳库质量。同时,根系生物量的减少,间接影响了土壤微生物活动和土壤碳周转过程。在未来氮沉降持续增加的背景下,慈竹林土壤对碳的保持能力可能会下降。     

Prefledging Growth and Recruitment of Female Lesser Scaup

Annual variation in juvenile recruitment is an important component of duck population dynamics, yet little is known about the factors affecting the probability of surviving and breeding in the first year of life. Two hypothesized mechanisms to explain annual variability are indirect carry-over effects (COEs) from conditions experienced during the prefledging period and direct effects from climatic conditions during the postfledging period. We used Cormack-Jolly-Seber models to estimate apparent survival and detection rates of 643 juvenile female lesser scaup (Aythya affinis) marked just prior to fledging at Red Rock Lakes National Wildlife Refuge in southwestern Montana, USA, 2010–2018. We evaluated COEs from hatch date, a hatch date × spring phenology interaction, and conspecific duckling density in addition to a direct climatic effect of winter conditions (indexed by the El Niño Southern Oscillation [ENSO]) and spring habitat conditions on the study area. We used growth data from a subset (n = 190) of known-aged ducklings to estimate the influence of hatch date and conspecific density on prefledging growth to help identify mechanisms underlying COEs. Prefledging growth and juvenile apparent survival were negatively related to measures of conspecific duckling density. We found evidence that detection probability varied annually for juvenile (but not adult) scaup, possibly representing decisions to delay breeding and not return to or remain at the study site in their first year of life. Like with apparent survival, there was suggestive evidence that detection probability decreased with increasing duckling density in the previous year. Hatching date was weakly negatively related to detection probability, but unrelated to apparent survival, whereas neither vital rate was related to winter ENSO index. Our results are consistent with a process where density-dependent growth rates in the prefledging period carry over to influence fitness in subsequent life-cycle stages. If this pattern generalizes to other systems, this density COE may have important implications for our understanding of duck population dynamics and reaffirms the importance of maintaining abundant brood-rearing habitats in conservation and management of ducks. © 2021 The Wildlife Society.