Drift Samples Research Articles

Effect of gene conversion on variances of digenic identity measures

The variances and covariances of digenic descent measures are studied for a two-locus model incorporating mutation, gene conversion, recombination, drift, and finite sampling. Gene conversion can occur between allelic pairs of genes or between non-allelic pairs on the same or different gametes within individuals. Most interest therefore centers on pairs of genes, and five digenic identity measures are required. The behavior over time of these measures is studied, with an emphasis on the effects of gene conversion. Because of the stochastic nature of the forces of drift, recombination, mutation, and conversion, the actual identity status of gene pairs can vary from expectation among replicate populations. To study this variation we compute the expected variances and covariances of the measures, and show that this requires the introduction of trigenic and quadrigenic measures. Allowing for conversion between genes on different gametes requires a large number of these higher-order measures.

Effects of aerial spraying of insecticides on nontarget macrobenthos in a mountain stream

The effects of aerial spraying of an insecticide were investigated in a mountain stream using a drift net. The concentration of fenitrothion (organophosphorus insecticide) in the river water increased to ca. 20 μg liter −1 3 hr after the spraying and decreased exponentially to half the peak value after 2 hr. A large number of aquatic insects were found drifting after the spraying. The total number of individuals which drifted in the daytime after spraying reached nine times the number found the previous night. The total number of species which drifted during the 24 hr following the spray increased to 43 from 17 on the previous day. Before the insecticide spraying, the drifting benthos were almost entirely made up of three species of Baetis (Ephemeroptera). However, many individuals of several species of Heptageniidae (Ephemeroptera), Apsilochorema sutshanum (Trichoptera), and Chironomidae (Diptera) drifted in addition to Baetis after the spray. A large number of young Baetis, which had not been seen in the natural night drift samples, were found drifting due to the insecticide. Natural night drift almost disappeared from the day folowing insecticide spraying. At the second insecticide spraying, conducted 20 days after the first, the number of individuals which drifted during the 24 hr following spraying decreased to only 0.85% of that in the first spraying although changes in insecticide concentration showed a similar pattern. Several species of Ephemeroptera were dominant among the fauna in the studied stream, and the causal relationships of this are discussed.

Diel Feeding Chronology and Diet Selection of Rainbow Trout (Oncorhynchus mykiss) in the Henry's Fork of the Snake River, Idaho

Concurrent rainbow trout (Oncorhynchus mykiss) stomach contents and invertebrate drift samples were collected during three 24-h periods in summer 1987. Feeding was discontinuous through the day on all dates. Mean stomach content weight was minimal after 0400 MST and sharply increased between 1000 and 1200 MST on all three dates. Feeding apparently did not occur after twilight. Mean stomach content weight was correlated with water temperature on two dates and was never correlated with invertebrate drift density for non-age-0 trout. Daily ration (wet weight) was 7% of live weight for non-age-0 trout and 21% for age-0 trout. Trichoptera, Ephemeroptera, and Diptera were most important in the diet; terrestrial insects and aquatic vertebrates were rare. The degree of selectivity varied through 24 h and the interpretation depended on the method of analysis used. Occurrence of low-drift cased Trichoptera larvae in stomachs was correlated with amount of filamentous algae ingested, indicating a degree of epibenthic foraging, although no diel pattern could be reliably discerned. Mean length of prey items in stomachs was larger that the drift in 83% of the samples. Our findings support experimentally derived decision rules-of-thumb for foraging trout: select larger prey items, select vulnerable prey, and relax selectivity when hungry.

An assessment of short-term depletion of stream macroinvertebrate benthos by drift

A study was conducted to determine if emigration of drifting macroinvertebrates from a stream riffle which was blocked for one week from immigration by upstream colonists significantly reduced the abundance of drift collected from the tail of the riffle. The head of a 9 m long riffle of a 2nd order stream in Maryland (USA) was blocked from incoming drift by a 250 μm mesh weir. Upstream immigration of invertebrates into the riffle was largely prevented by a partition placed at the tail of the riffle which held the drift nets. Benthos and drift samples were collected from the riffle prior to weir placement and following its removal, and drift was collected at dusk on each day. No difference in drift or in benthic abundance between the beginning and end of the study was observed. This is largely attributed to recruitment of immature insects (primarily hatching of eggs present at the outset), particularly of Dolophilodes distinctus and species of Tanytarsini, from within the riffle. Results suggest that recruitment of riffle species is of sufficient magnitude to more than compensate for short-term riffle depletion due to drift. Samples of drifting and non-drifting (benthic) animals were held without food for 12 h after collection and mortality within each group was determined. The mortality of drifting animals was three-fold that of benthic animals.

Prey selection byGalaxias vulgarisin the Hawkins River, New Zealand

Abstract To determine the extent of prey selection by the nocturnally active fish Galaxias vulgaris, samples of fish, drift, and benthos were collected over a 24‐h period in summer in a stream draining the foothills of the Southern Alps in New Zealand. Feeding started after sunset, peaked by midnight, and virtually ceased by midday. Both drifting and benthic foods were consumed, and timing of peak feeding was synchronous with the period of greatest abundance of aquatic drift. Larvae of Austrosimulium spp., Deleatidium spp., and Aoteapsyche colonica comprised the major proportion of the prey eaten. Prey selection was indicated by the over‐representation of Austrosimulium spp. and under‐representation of both the smaller size classes of Deleatidium spp. and other aquatic invertebrates in the diet of fish. With the exception of the coleopteran Costelytra zelandica, terrestrial organisms were not eaten by fish, but several aquatic taxa were. Foraging by Galaxias vulgaris on drift and benthos may provide fish with greater prey options for feeding efficiently throughout the night.

Feeding in a Nocturnally active fish, Galaxias brevipinnis, in a New Zealand stream

To determine the diel feeding periodicity and diet of a lake-inlet population of Galaxias brevipinnis in New Zealand, samples of benthos, drift and fish were collected over a 24-h period in summer. Both numerically and gravimetrically, fish stomach contents revealed that feeding started some time after sunset, peaked towards midnight, and virtually ceased after sunrise. Benthic invertebrates were consumed almost exclusively, with ephemeropterans, trichopterans, and dipterans constituting 95% of the total foods eaten, a major proportion being chironomid larvae. Size of prey eaten compared with size of invertebrates in the benthos differed significantly during the night; this indicated that some size-selective feeding occurred. The benthic feeding habit of Galaxias brevipinnis appears to allow it to forage on relatively small prey during the night, a phenomenon that has been reported for other bottom-dwelling native fish species in New Zealand.

The neutral theory of molecular evolution and the world view of the neutralists.

The main tenet of the neutral theory is that the great majority of evolutionary changes at the molecular level are caused not by Darwinian selection but by random fixation of selectively neutral (or very nearly neutral) alleles through random sampling drift under continued mutation pressure. The theory also asserts that the majority of protein and DNA polymorphisms are selectively neutral, and that they are maintained in the species by mutational input balanced by random extinction rather than by "balancing selection." The neutral theory is based on simple assumptions. This enabled us to develop mathematical theories (using the diffusion equation method) that can treat these phenomena in quantitative terms and that permit theory to be tested against actual observations. Although the neutral theory has been severely criticized by the neo-Darwinian establishment, supporting evidence has accumulated over the last 20 years. In particular, the recent burst of DNA sequence data helped to strengthen the theory a great deal. I believe that the neutral theory triggered reexamination of the traditional "synthetic theory of evolution." In this paper, I review the present status of the neutral theory, including discussions of such topics as "molecular evolutionary clock," very high evolutionary rates observed in RNA viruses, a deviant coding system found in Mycoplasm together with the concept of mutation-driven neutral evolution, and the origin of life. I also present a worldview based on the conception of what I call "survival of the luckiest."

The permanent effect of reproductive events on blood prolactin levels and its relation to breast cancer risk: a population study of postmenopausal women

In each of two population-based studies conducted on the Island of Guernsey between 1967–1976 and 1977–1984, respectively, single specimens of blood were taken from over 5000 normal women. From these two studies there were 1173 and 946 postmenopausal women in whom blood prolactin was determined and multivariate analysis was used to establish the association between blood prolactin concentration and possible determinants of risk of breast cancer. Since prolactin levels were log-normally distributed these analyses were done on log-transformed data. The age at menarche or menopause, age at first or last childbirth, length of reproductive life (i.e. time from menarche to menopause) or post-menopausal life (i.e. time from menopause to time of blood sampling), contraceptive use and history of breast cancer were not significantly associated with blood prolactin concentration. Of significance were age, parity, time of blood sampling and assay drift. Ponderosity (Quetelet's Index) was positively associated with prolactin concentration and this was significant using a one-tail criterion. Women with a mammographic pattern designated DY by Wolfe had significantly higher prolactin levels than those with N 1 patterns. However, the main finding to emerge was that after standardizing for all the other variables increasing parity was related to a step-wise reduction in blood prolactin levels. Since this had occurred in women who had had their last child up to 35 years previously it implies this effect is permanent. It could therefore be that the protective effect on breast cancer risk of multiparity and early first pregnancy could be mediated by such a life-long reduction in blood prolactin levels.

A model to estimate the increase of genetic variability due to electrophoretically cryptic alleles.

To consider the problem of the increase of genetic variability due to electrophoretically cryptic alleles, the equally degenerate electromorph model is proposed. Mutation, random sampling drift and selection can be incorporated in this model. Simple formulas are obtained to show how genetic variability increases when cryptic alleles are distinguished. This model is extended to a two-population system to see the effect of cryptic allele variation on genetic differentiation.

Leaf litter in two southern Tasmanian creeks and its relevance to palaeobotany

Benthic and drifting leaf litter were examined in two parallel creeks in mixed forest in southern Tasmania, and the occunence of whole leaves recorded. Nothofagus cunninghamii leaves were dominant in both the benthic and drift samples, Atherosperma moschatum occuned in the drift but only in trace quantities in the benthic samples, Phy!locladus aspleniifolius occurred in the benthos but only in trace quantities in the drift samples, and whole Eucalyptus obliqua leaves were absent from all samples. Otherwise most species occurred in similar proportions in both creeks and for both sampling strategies. It is concluded that the processes of litter input, leaf buoyancy, and leaf breakdown will result in an unequal potential for fossilisation of the leaves of different species; accordingly, attempts to reconstruct vegetation using macrofossils need to be approached with caution.

A method for subsampling unsorted benthic macroinvertebrates by weight

A simple method for subsampling unsorted benthic macroinvertebrates by weight is described for different types of samples obtained from lentic and lotic environments. It is especially useful for samples containing large amounts of filamentous algae that preclude the use of conventional subsampling methods. The method provided random dispersions of individuals in the original samples. Overall variability of the subsamples was low for artificial substrate and catastrophic drift samples. Variability was higher for regular drift samples, which had the lowest numbers of individuals of the three sample types. The method produced considerable savings in time spent sorting. Subsampling approaches for community level studies are discussed.

Occurrence of Glochidia in Stream Drift and on Fishes of the Upper North Fork Holston River, Virginia

Occurrence of glochidia in stream drift, and prevalence and intensity of glochidial infestations on host fishes were recorded in the upper North Fork Holston River near McCrady, Virginia, between June 1981 and June 1982. Glochidia of Lampsilinae were collected in drift samples year-round, peaking in abundance during June and July. Glochidia of the Ambleminae were in the drift from June to midAugust. Of 4800 fish (41 species) examined for infestations, 147o carried encysted glochidia. Eleven fish species in the Centrarchidae, Cottidae and Percidae were infested with lampsiline glochidia, with prevalence highest in March. Amblemine glochidia occurred only in 12 species of the Cyprinidae, with prevalence highest in July. Prevalence and intensity of infestations were highest in fish hosts of the Ambleminae. Previous accounts of host specificity, based on laboratory experiments with naiades, were corroborated by field observations.

Choice of trap exposure time for collection of invertebrate drift samples : Zadorina, V.M., 1987. Hydrobiol. J. (a translation of Gidrobiol. Zh.), 23(2):82–86. Polar Res. Inst. of Mar. Fish. and Oceanogr., Ministry of Fish., Acad. of Sci., Murmansk, USSR

Choice of trap exposure time for collection of invertebrate drift samples : Zadorina, V.M., 1987. Hydrobiol. J. (a translation of Gidrobiol. Zh.), 23(2):82–86. Polar Res. Inst. of Mar. Fish. and Oceanogr., Ministry of Fish., Acad. of Sci., Murmansk, USSR

Susceptibility of Young-of-the-Year Fishes to Downstream Displacement by Flooding

Abstract I examined downstream displacement of young-of-the-year fishes (primarily centrarchids and cyprinids less than 25 mm total length, TL) by field sampling of drift during floods and by an experiment conducted in a 4.9-m-long artificial stream channel. The pattern of drift during a June 1985 flood (stage increase of 3.2 m) in Brier Creek, Oklahoma, indicated that both centrarchids and cyprinids smaller than 10 mm TL were extremely susceptible to downstream displacement. Drift rates of larger fish (10–25 mm) during both the June flood and a smaller flood (stage increase of 0.4 m) in July 1985 suggested that these fishes were much less susceptible to displacement. The rapid decline in susceptibility to displacement with increase in size from the field study coincided with results obtained in the artificial channel. These results suggest that the effects of floods on stream fish communities can depend on small differences in the timing of reproduction and of flooding.

Drift and upstream movement in Yuccabine Creek, an Australian tropical stream

Drift and upstream movement were monitored over 14 months in a seasonal upland tropical stream in northeastern Australia. There were distinct seasonal pulses in the drift with variable peak levels in the summer wet season and low more stable levels during the dry season. Drift density ranged from 0.36 to 3.98 animals per m3 (monthly mean = 1.26). There was no correlation between drift density and either benthic density or stream discharge. In the absence of catastrophic drift, drift was dispersive, not depletive in the wet season. A total of 121 taxa were caught in the 14 drift samples. Most taxa had nocturnal maximum drift levels with a peak immediately after sunset, a pattern apparently related to level of light and not temperature. Compensation for drift by upstream-moving nymphs and larvae was least during the wet season and increased during the dry season to a peak of 27% by numbers. Mean compensation was 8.2%. It is suggested that apart from in the wet season when an animal may drift substantial distances, most riffle animals will spend their larval lives in one small stretch of stream.

Speciation and the “shifting balance” in a continuous population

Shifts between adaptive peaks, caused by sampling drift, are involved in both speciation and adaptation via Wright's “shifting balance.” We use techniques from statistical mechanics to calculate the rate of such transitions for a population in a single panmictic deme and for a population which is continuously distributed over one- and two-dimensional regions. This calculation applies in the limit where transitions are rare. Our results indicate that stochastic divergence is feasible despite free gene flow, provided that neighbourhood size is low enough. In two dimensions, the rate of transition depends primarily on neighbourhood size N and only weakly on selection pressure (≈ s k exp(− cN)), where k is a number determined by the local population structure, in contrast with the exponential dependence on selection pressure in one dimension (≈exp(− cN √ s)) or in a single deme (≈exp(− cNs)). Our calculations agree with simulations of a single deme and a one-dimensional population.

The probability of peak shifts in a founder population

We have analysed the role of sampling drift in inducing shifts between alternative adaptive peaks, in small and rapidly growing populations. Using a simple model of disruptive selection on a polygenic character, we calculate the net probability of a peak shift. If the growth rate is high, the probability of a shift in a growing population is insensitive to selection on the character. Assuming that the character is effectively neutral during the brief initial increase, we find that the probability of a peak shift is given by the probability of finding a standard normal variate greater than √2ΔV where ΔV is the reduction in additive genetic variance during the growth period. This result holds for arbitrary pattern of increase in size, provided that the rate of increase is high enough for selection to be negligible, and the character depends on a large number of loci. Comparing the probability of peak shifts in founding populations with the rate of shifts in static and allopatric populations it appears that although strongly selected shifts are only likely to occur in a growing population, a static population is a more congenial setting for adaptive shifts.

Food and Feeding Preferences of Rainbow and Brown Trout in Southern Appalachian Streams

The stomach contents of Age 1 and older rainbow (Salmo gairdnert) and brown trout (S. trutta) in five southern Appalachian soft-water streams were compared with concurrent drift samples. A wide range of food items was consumed, and no prey genus comprised an average of more than 2.5% by number of the diet of either trout species. Seasonal changes in composition of drift from June to November were generally mirrored by shifts in trout diets. The contribution of terrestrial organisms to drift and to diets was highest in late summer and autumn. Averaged over all sam- ples, terrestrial taxa comprised 36, 45 and 50% of the drift, rainbow and brown trout diets, respectively. Both trout species exhibited statistically significant feeding prefer- ences for particular taxa (notably terrestrial organisms), but most prey were con- sumed in proportions similar to their abundance in the drift. Opportunistic feeding lends stability to trout populations in streams with relatively low autochthonous food production by allowing trout to capitalize on terrestrial input. Our findings empha- size the importance of both protecting riparian vegetation (which is a source of terres- trial prey) and considering aquatic habitat elements in which trout can efficiently capture surface drift when determining minimum stream flow requirements for water-diversion projects.

Comparison of Encounter Model Predictions with Observed Size-Selectivity by Stream Trout

Observed size-selective predation on the amphipod Gammarus pseudolimnaeus by trout was compared with encounter model predictions based on drift and benthic samples over seven months. The generalize...

Quantitative genetic models of sexual selection: a review.

Quantitative genetic models of sexual selection have disproven some of the central tenets of both the handicap mechanism and the 'sexy son' hypothesis. These results suggest that the 'good genes' approach to sexual selection may often lead to erroneous results. Runaway sexual selection seems possible under a wide variety of circumstances. Quantitative genetic models have revealed runaway processes for sexually selected attributes expressed in both sexes and for attributes of parental care. Furthermore, the runaway could occur simultaneously in a series of populations that straddle an environmental gradient. While the models support the feasibility of runaway processes, empirical studies are needed to evaluate whether runaways actually happen. Estimates of critical genetic parameters are particularly needed, as well as measures of natural and sexual selection acting on the same population. The models also show that sexual selection has tremendous potential to produce population differentiation, particularly in epigamic traits. Differentiation is promoted by indeterminancy of evolutionary outcome, transient differences among populations during the final slow approach to equilibrium, sampling drift among equilibrium populations, and the tendency of sexual selection to amplify geographic variation arising from spatial differences in natural selection. Recent work with two- and three-locus models of sexual selection has produced results that parallel the results of the polygenic models (Kirkpatrick, 1982, 1985, 1986; Seger, 1985). Thus the feature of indeterminate equilibria (outcome dependent on initial conditions) is common to both types of model.