Mosquito oviposition and larvae development in response to kairomones originated by different fish

Predator‐released kairomones indicating the presence of predatory fish are known to alter the behaviour and life‐history traits of several aquatic herbivores. Culex mosquitoes (Diptera: Culicidae) respond to such cues by altering oviposition habitat selection and larval development time. These responses differ among fish species indicating composition differences among fish‐released cues, but the recognition pattern is not clear. This study tested the dependence of fish recognition to co‐evolution and the level of threat to larvae. We compared Culex responses to three fish, the invasive larvivorous Gambusia affinis (Cyprinodontiformes: Poeciliidae), the native larvivorous Aphanius mento (Cyprinodontiformes: Cyprinodontidae) and the native algivorous Garra rufa (Cypriniformes: Cyprinidae). The effects of cues released by the three fish on Culex oviposition and life‐history shifts were compared in field mesocosms and lab tests. Our results showed that ovipositing females were significantly repelled only by cues originated from G. affinis, while developing larvae response was a more general one. Our results support the idea that fish‐released kairomones differ in composition or quantities among different species.     

Factors affecting the horizontal migration of the amphipod Pontoporeia affinis Lindström. I. Pacording method and response to water currents

Pontoporeia affinis Lindström was subjected to slow horizontal water currents in narrow aquaria 3 m long and its swimming activity recorded by pairs of photocells. A relationship was established between the number of animals and activity level. By dividing the aquaria with intersecting walls during the day, when the animals hid in the sediment, the activity recorded in separate sections during subsequent nights revealed that Pontoporeia migrates upstream. This migration probably takes place only at the very beginning of the light period or just before it. The experimental method is explained in detail.     

Comparative gut content analysis of invasive mosquitofish from Italy and Spain

Eastern mosquitofish (Gambusia holbrooki) are among the most widely introduced freshwater species globally. To gain a better understanding of feeding patterns in non‐native populations, and which local factors may influence them at the population level, we carried out gut content analysis on 163 specimens from nine invasive populations in Italy and Spain. Based on previous studies, we predicted that (a) mosquitofish are omnivores with a preference for detritus and cladocerans; (b) they display size‐ and population‐specific differences in gut morphologies and diet, with larger fish feeding more intensively over a wider range of prey items; and (c) some of the variation would be associated with differences in local environmental and climatic factors. Our results confirmed our first prediction, because mosquitofish fed on a variety of diet items, among which detritus and Cladocera dominated. However, not a single diet item was shared among all populations. Congruent with our second prediction, we further identified size‐ and population‐specific differences in the occurrence of some diet items and gut morphologies. However, observed patterns in dietary habits did not seem to be driven by the environmental and climatic variables we had quantified. The fairly variable diet likely aids invasion success and helps explain the ubiquity of invasive mosquitofish across Italy and Spain, as mosquitofish seem to be able to rely on whatever a local habitat provides. We further propose that size‐specific differences likely capture the substantial sexual size dimorphism (males are smaller than females), while population‐specific differences are likely the result of differences in local prey abundance. The lack of an influence of temperature on dietary habits suggests that mosquitofish feeding ecology may be less impacted by rising temperatures than other freshwater fish species. If true, then this suggests climate change‐induced effects may further exacerbate the competitive superiority of mosquitofish over native species in the future.     

Impact of mass mortality of a mosquito fish,Gambusia affinison the ecology of a fresh water eutrophic lake (Lake Naini Tal,India)

Between 28th March and 4th April, 2000 a fungal infection killed >80% of the most abundant planktivorous fish, Gambusia affinis in Lake Naini Tal, Uttaranchal, India. In response to this mortality, planktonic communities and some eutrophication-related parameters viz., primary productivity, phosphate–phosphorus, nitrate–nitrogen and transparency of the water, were considerably changed. Total zooplankton number more than doubled, phytoplankton number reduced nearly to half, primary production and phosphate-phosphorus was dramatically reduced, while nitrate–nitrogen and water clarity increased. The phytoplankton decline was caused by increased zooplankton grazing (top-down control) rather than phosphorus deficiency (bottom-up control). After 3 months, Gambusia and planktonic communities and nutrient levels reverted back almost to their pre-mortality state. Thus removal of G. affinis could improve water quality of Lake Naini Tal.     

Overcoming challenges to morphological and molecular identification of Empidonax flycatchers: a case study with a Dusky Flycatcher

Flycatchers in the genus Empidonax are among the most difficult avian taxonomic groups to identify to species. Observers often rely on calls or songs in the field or detailed morphometrics in the hand to identify species. In January and February 2013, we twice captured an Empidonax flycatcher at the Virginia Zoo in Norfolk, Virginia. After being unable to identify the flycatcher to species level using morphometrics and photographs, we extracted DNA from two tail feathers collected during the second encounter to identify the individual genetically. Comparison of cytochrome c oxidase I (COI) with reference sequences in the Barcode of Life Database (BOLD) suggested that the specimen had a >99.8% probability of placement as a Dusky Flycatcher (Empidonax oberholseri). Additional comparisons of NADH dehydrogenase subunit 2 (ND2) to reference sequences in GenBank, however, suggested that the specimen was a Pine Flycatcher (Empidonax affinis), a species not represented in BOLD and confined geographically to a small area in Mexico and Guatemala. After analyzing both COI and ND2 from additional vouchered specimens, the bird caught in Virginia was determined to be a Dusky Flycatcher. We also suspect that some of the sequences in GenBank might derive from incorrectly identified specimens or otherwise could represent overlooked pseudogenes. Because the putative identification, based on GenBank sequences, would have represented the first record of Pine Flycatcher from the United States, our results reinforce the need for carefully vetted and taxonomically comprehensive molecular databases to allow definitive conclusions about sample identity. Further molecular phylogeographic review of this genus is warranted to resolve haplotype ambiguities.     

Lesser Scaup Nest Success and Duckling Survival on the Yukon Flats,Alaska

Abstract: Over the last 20 years scaup numbers have declined, and these declines have been greatest in the northern boreal forests of Canada and Alaska where most lesser scaup (Aythya affinis) nest. We studied nest success and duckling survival of lesser scaup over 3 field seasons, 2001–2003, on the Yukon Flats National Wildlife Refuge in northeastern Alaska, USA. Daily survival rate (DSR) of nests on our study area across all 3 years was 0.943 (n = 177 nests, 95% CI: 0.930–0.954), corresponding to a nest success of only 12.3%, considerably lower than published estimates of an average nest success as high as 57% for lesser scaup in the northern boreal forest. With Mayfield logistic regression, we investigated effects on nest survival of year, clutch initiation date, and nesting habitat type (large wetlands >10 ha, small wetlands <10 ha, and wooded creeks). Neither year nor clutch initiation date influenced nest survival; however, the odds of nest success on large wetlands was 49% lower than on wooded creeks (odds ratio = 0.512, 95% CI = 0.286, 0.918). Based on the model that used only habitat type for estimation, DSR on large wetlands was 0.931 (corresponding nest success = 7.6%), DSR on small wetlands was 0.941 (nest success = 11.1%), and DSR on wooded creeks was 0.963 (nest success = 26.2%). To estimate duckling survival, we monitored 10 broods (n = 75 ducklings) over 3 field seasons by radiotagging hens at nest hatch. Most duckling mortality (94%) occurred in the first 10 days after hatch. Average duckling survival during 1–10 days was 0.321 (95% CI: 0.122–0.772), during 11–20 days was 0.996 (95% CI: 0.891–1.040), and during 21–30 days was 0.923 (95% CI: 0.769–1.041). Three of 10 hens moved all or part of their broods overland between nesting and brood-rearing wetlands for distances of 0.3–1.6 km. Our estimates of lesser scaup nest success and duckling survival on the Yukon Flats were among the lowest ever reported for ducks nesting at northern latitudes, even though the study site was in pristine boreal forest. Estimating and comparing scaup demographic rates from different geographic areas can contribute to improved conservation. Given the scarcity of information on scaup nesting in the boreal forest, basic nesting parameters are important to those trying to model scaup population dynamics.     

Chromium and Selenium in Invertebrate Prey of Lesser Scaup

Abstract: The combined lesser scaup (Aythya affinis) and greater scaup (A. marila) population in North America has steadily declined from an average of 7.5 million breeding birds in the 1970s to an all-time low of 3.39 million in 2005. Bioaccumulation is widely known as the means of elevated levels of toxins in vertebrates. Our goal was to determine whether chromium and selenium were factors contributing to the continental scaup population decline by identifying wetlands used by scaup that potentially contain dangerous concentrations of chromium and selenium. We hypothesized that zebra mussels (Dreissena polymorpha) would contain the highest concentrations of selenium and chromium because they are filter feeders, whereas amphipods would contain the lowest concentrations because of their short life span. We collected zebra mussels, fingernail clams (Sphaerium transversum), chironomid larvae, snails (Gastropoda), and amphipods on randomly selected traditional lesser scaup staging and breeding wetlands. We found higher chromium concentrations in zebra mussels from Iowa, USA, than in those from Wisconsin, USA (P = 0.0074). In addition, selenium concentrations in zebra mussels from Wisconsin were higher than in those from Iowa (P < 0.0001). Higher selenium concentrations in amphipods were associated with sampled wetlands surrounded by developed land. Invertebrates with >5 μg/g selenium and >1 μg/g chromium are potentially hazardous for scaup. Chromium concentrations in Iowa were the highest for most species examined, whereas they were the lowest in Minnesota, USA. Based on our results, lesser scaup probably accumulate the highest concentrations of selenium on Lake Onalaska, Wisconsin, whereas they probably accumulate the lowest concentrations in Iowa. Waterfowl biologists are searching for explanations to the scaup decline; we propose chromium and selenium concentrations in amphipods and fingernail clams may be a factor.     

HYBRID ZONE DYNAMICS ARE INFLUENCED BY GENOTYPE-SPECIFIC VARIATION IN LIFE-HISTORY TRAITS: EXPERIMENTAL EVIDENCE FROM HYBRIDIZING GAMBUSIA SPECIES

Results from two experiments are presented that contrast differences in life-history traits and population dynamics between two species of live bearing fishes (Gambusia affinis and G. holbrooki) that hybridize across portions of the southeastern United States. Progeny from parental holbrooki and holbrooki-affinis F₁ crosses exhibited larger lengths at birth, at 15 days, and matured earlier, and at larger size than did progeny from parental affinis and affinis-holbrooki F₁ crosses. Comparisons of experimental populations of affinis, holbrooki, and mixed (affinis + holbrooki) species composition followed over two years revealed that affinis populations consistently exhibited smaller population size, lower carrying capacity, lower recruitment, and larger over-winter mortality than did holbrooki or mixed populations. Evidence for density-dependent reductions in fecundity and concomitant increases in juvenile mortality rates were observed in all populations, but were most pronounced for affinis populations. Genotype-specific differences in life-history traits appear to confer differential advantage to offspring of parental holbrooki origin and F, progeny of holbrooki maternal parentage given the resource availability and the age structure and densities experienced during these experiments. Results have direct implications regarding the rate and direction of evolution within hybrid zones formed by these two species.     

Biological control of Culicidae with the copepod Mesocyclops aspericornis and larvivorous fish (Poeciliidae) in a village of French Polynesia

The copepod Mesocyclops aspericornis Daday and the larvivorous fishes Gambusia affinis (B. & G.) and Poecilia reticulata R. & B., were released into mosquito breeding sites in Tuherahera village, Tikehau atoll, French Polynesia, to control larvae of Aedes aegypti (L.), Ae.polynesiensis Marks, Culex annulirostris Skuse and Cx quinquefasciatus Say. Treatments were completed within a week, in January 1990. Fish quickly eliminated mosquito larvae from the open breeding sites (ponds, wells). The impact of copepods in water tanks, drums and covered wells was inconsistent, apparently depending on the availability of microfaunal diet for growth of copepod nauplii. As the biting rate of adult Ae.aegypti seemed to be unaffected by the biological control of larvae, this village-scale experiment was judged to be unsuccessful as a means of vector control.     

Recent discovery of widespread Ixodes affinis (Acari: Ixodidae) distribution in North Carolina with implications for Lyme disease studies

Ixodes affinis, which is similar morphologically to Ixodes scapularis, is widely distributed in North Carolina. Collections have documented this species in 32 of 41 coastal plain counties, but no piedmont or mountain counties. This coastal plain distribution is similar to its distribution in Georgia and South Carolina, where it is considered an enzootic vector of Borrelia burgdorferi sensu stricto. An updated list of hosts for I. affinis in the U.S.A. is included, increasing the number to 15 mammal and one bird species. The presence of questing adults of I. affinis from April to November reinforces the need for confirmed identifications of suspected tick vectors of Borrelia spirochetes collected during warm months.