Evidence Of Geographic Variation Research Articles

Use of a density equalizing map projection in analysing childhood cancer in four California counties.

In this study, 401 cases of childhood cancer in four California counties in 1980-1988 were analysed with the innovative methodology of density equalizing map projections. The data were originally collected and analysed by the California State Department of Health Services (DHS). In addition to the new analytic technique, the present analysis used population data more detailed and more accurate than those in the DHS analysis. The geographic boundaries of the 259 census tracts in the study area were adjusted according to population at risk so as to make population density everywhere constant; then the 401 case locations were plotted on the density equalized map. If risk is everywhere equal, the resulting distribution of cases should be uniform except for statistical variation. The metric used was a measure of the variability of the density of cases on the density equalized map. The same metric was calculated for independent samples of artificial cases, generated under the null hypothesis of equal risk. The slight geographic non-uniformity observed among the real cases is well within the limits of variation observed in the samples of artificial cases. In agreement with results published by DHS, we conclude that there is no evidence for geographic variation of risk among the cases studied. Subsets of the data, selected by age, sex, race, time period and cancer site, yielded similar negative results.

Applicability of external measurements to sexing of the Cape petrel Daption capense at within‐pair, within‐population and between‐population scales

AbstractSexual size dimorphism in the Cape petrel Daption capense was analysed to improve methods for sexing live birds in field studies. Samples originated from two geographically distant study populations in the Antarctic: Nelson Island, South Shetland Islands (sample N: 83 M, 89 F), and Ardery and O'Connor Islands, Windmill Islands (sample A: 36 M, 27 F). Using single characters with cut points calculated from sexed individuals, about 59–76% (N; best separator tarsus length) and 61–86% (A; best separator tube length) of birds could be assigned to the correct sex. Combination of characters improved performance of sample‐specific discriminant functions to a maximum of 84% in the N‐sample (five characters) and 95% in the A‐sample (four characters). The most useful character sets as well as ranking of individual characters (their weights) differed between samples. At the same time, cross‐testing revealed asymmetry in the applicability of sample‐specific functions to the other sample. Hence, the method of a generalized discriminant (Auk110: 492–502, 1993) was implemented and tested to develop a species‐specific discriminant for the Cape petrel. For all examined character sets, results of their cross‐application to the other sample were improved by using character weights estimated from combined samples instead of weights derived only from the original sample. The generalized function (tube length + 1.05*bill depth at tube + 0.72*culmen length + 0.07*wing length) combined with a cut point calculated from a distribution of discriminant scores (assumed mixture of two normal distributions with possibly unequal variances) is suggested as currently the best compromise for sexing Cape petrels in populations for which specific functions are not yet available: comparison with our best sample‐specific functions shows a decrease in accuracy by only 1% to 3%. However, examination of other promising characters (head length, bill depth at gonys, mid‐toe length) is recommended to improve further a generalized discriminant. In all cases a larger percentage (N: 87–89%, 38 pairs; A: 100%, 27 pairs) of individuals was correctly sexed by within‐pair comparison of discriminant scores than according to the sample‐specific cut point. No clear evidence for assortative mating with respect to body size has been found in this study. Available biometric data show little evidence for geographical variation in the Cape petrel, which suggests good applicability of generalized sex‐discriminants in other populations.

Applicability of external measurements to sexing of the Cape petrel Daption capense at within-pair, within-population and between-population scales

Sexual size dimorphism in the Cape petrel Daption capense was analysed to improve methods for sexing live birds in field studies. Samples originated from two geographically distant study populations in the Antarctic: Nelson Island, South Shetland Islands (sample N: 83 M, 89 F), and Ardery and O'Connor Islands, Windmill Islands (sample A: 36 M, 27 F). Using single characters with cut points calculated from sexed individuals, about 59–76% (N; best separator tarsus length) and 61–86% (A; best separator tube length) of birds could be assigned to the correct sex. Combination of characters improved performance of sample-specific discriminant functions to a maximum of 84% in the N-sample (five characters) and 95% in the A-sample (four characters). The most useful character sets as well as ranking of individual characters (their weights) differed between samples. At the same time, cross-testing revealed asymmetry in the applicability of sample-specific functions to the other sample. Hence, the method of a generalized discriminant (Auk110: 492–502, 1993) was implemented and tested to develop a species-specific discriminant for the Cape petrel. For all examined character sets, results of their cross-application to the other sample were improved by using character weights estimated from combined samples instead of weights derived only from the original sample. The generalized function (tube length + 1.05*bill depth at tube + 0.72*culmen length + 0.07*wing length) combined with a cut point calculated from a distribution of discriminant scores (assumed mixture of two normal distributions with possibly unequal variances) is suggested as currently the best compromise for sexing Cape petrels in populations for which specific functions are not yet available: comparison with our best sample-specific functions shows a decrease in accuracy by only 1% to 3%. However, examination of other promising characters (head length, bill depth at gonys, mid-toe length) is recommended to improve further a generalized discriminant. In all cases a larger percentage (N: 87–89%, 38 pairs; A: 100%, 27 pairs) of individuals was correctly sexed by within-pair comparison of discriminant scores than according to the sample-specific cut point. No clear evidence for assortative mating with respect to body size has been found in this study. Available biometric data show little evidence for geographical variation in the Cape petrel, which suggests good applicability of generalized sex-discriminants in other populations.

Evidence of Geographic Variation in Lethal Temperature but Not Activity Temperature of a Lizard

[Extract] Species that occur over large geographical areas must tolerate, or adapt to, a range of climatic conditions. The response of ectotherms to a range of environmental temperatures is particularly interesting, because temperature has important effects on performance in these species (Hues and Stevenson, 1979).

The interaction between behavior and physiology in determining life history patterns in Atlantic salmon (Salmo salar)

Atlantic salmon (Salmo salar) exhibit extreme diversity in the age of smolt migration and sexual maturation, both within and among populations. Theoretical analyses reveal the adaptive significance of such variation, but models of the underlying physiological and behavioral mechanisms are also needed. I summarize one such proximate model that suggests that smolting and maturation are only triggered if expected performance trajectories exceed threshold levels during sensitive periods. The probability of a threshold being exceeded is therefore dependent on an individual fish's ability to acquire and utilize resources efficiently, which in turn depends on a range of physiological and behavioral traits. Spatial variation in life histories is chiefly caused by differences in growth opportunity, although there is evidence of geographical variation in genetically determined expected growth trajectories. Simulations show that small changes in young fry growth rates can have pronounced effects on mean smolt age and sex ratio, by influencing the proportion of males that fail to exceed the threshold for early smolting and mature as parr (and so are less likely to survive to smolting). More sophisticated proximate models should allow powerful predictions of smolt production based on simple environmental parameters, due to their influence on growth trajectories and hence life history decisions.

Banding Reference Areas and Survival Rates of Green-Winged Teal, 1950-89

The green-winged teal (Anas crecca carolinensis) is an important harvest species, yet we know relatively little about its population ecology. We investigated aspects of green-winged teal population ecology of potential importance to waterfowl managers. We used recoveries of green-winged teal banded during winter (1950-89) to establish banding reference areas and estimate survival and band recovery rates. We used cluster analysis based on similarities in recovery patterns to group banding degree blocks into 8 minor and 5 major reference areas describing the principal wintering range of green-winged teal in North America. We then estimated survival and recovery rates of green-winged teal banded in these areas. Mean annual survival rate estimates across years and reference areas were similar (P > 0.05) for males (0.55, SE = 0.022) and females (0.51, SE = 0.057). Mean annual recovery rate estimates were larger for males (0.033, SE = 0.0017) than for females (0.024, SE = 0.0024) (P < 0.01). There was little evidence of temporal variation in survival or recovery rates for most datasets. There was evidence of geographic variation in survival rates among major reference areas for males (P = 0.04) but not for females (P = 0.30). We recommend that analyses be conducted on green-winged teal banded during preseason to further investigate possible sex specificity of survival rates and to address questions about the relationship between harvest rates and survival.

Arsenic in plaice ( Pleuronectes platessa) and whiting ( Merlangius merlangus) from the North East Irish Sea

Total arsenic has been quantified in muscle tissue of plaice and whiting from the NE Irish Sea. The highest mean values of 20.5 mg kg −1 in plaice and 6.2 mg kg −1 in whiting were recorded, respectively, on the Sludge Disposal Ground in Liverpool Bay and towards the Isle of Man. Sites to the north of the Mersey Estuary and close to the English coast such as Walney, Fleetwood and Lune Deep were all fairly similar with mean values for plaice of less than 7.5 mg kg −1. Concentrations of arsenic in whiting were much lower than for plaice with most site mean values <4 mg kg −1, and with less evidence of geographical variation or patterns across the study area. Inorganic arsenic is only a very minor component of the total arsenic present and on this basis there is no direct cause for concern as regards human health. The arsenic is thought to be present as refractory organoarsenic compounds of low mammalian toxicity.

Acclimation for desiccation resistance in Drosophila: Species and population comparisons

In previous work, it was found that Drosophila melanogaster females became more resistant to desiccation after prior exposure to a non-lethal desiccation stress. Here, this acclimation response is shown to occur in three other widespread Drosophila species: D. simulans, D. immigrans and D. serrata. However, such acclimation was unsuccessful in D. birchii, a sibling species of D. serrata found in rainforest habitats. An acclimation response in all the widespread species was evident after a prior exposure period of a few hours, and acclimation was still evident after more than 24 h. Two D. serrata populations, one originating from a tropical location (Townsville) and one from a cooler coastal area (Forster) had a similar acclimation response. Although D. melanogaster and D. simulans populations originating from a tropical site (Cairns) were less resistant to desiccation than conspecific populations from a temperate site (Melbourne), the populations had similar acclimation responses. Hence, there was no evidence for geographic variation in acclimation ability.

SEX RATIOS AND CONDITIONS REQUIRED FOR ENVIRONMENTAL SEX DETERMINATION IN ANIMALS

Conclusions and SummaryEnvironmental sex determination (ESD) is a system of sexual determination that is influenced by a variable environment. Once sex is determined it is then fixed for life. The model of Charnov &amp; Bull (1977) proposes that ESD is favoured by natural selection when an individual's fitness as a male or female is strongly influenced by environmental conditions and when the individual has little control over which environment it will experience. Adaptive sex ratio variation is considerably easier for organisms with ESD, and this feature is the ultimate cause for the evolution and maintenance of ESD. ESD is taxonomically widely expressed, and more cases are likely to be discovered. Both environmental and genotypic sex determination mechanisms are found in closely related species. Evidence of geographical variation in the degree and in the critical environmental values of ESD within the same species has also been discovered, e.g. in the fish Menidia menidia and in the crustacean Gammarus duebeni.The factors causing sex determination in invertebrates include temperature, daylength, nutrition, density, humidity, ionic composition of the environment, pH, carbon dioxide, UV light, metabolic products, parasites, exposure to the opposite sex of the same species, and in parasitoids also host size, age and type. In vertebrates temperature is the dominant factor causing sex determination, though in fish also pH, salinity, light, water quality and nutrition, and in turtles water potential of the substrate have some effect on the sex expression. Most of these factors influence growth through resource availability or developmental speed. In most cases of ESD in invertebrates and fish, the environmental factor has a gradual effect on the sex expression, in contrast to the typical steep threshold mode found in reptiles. These differences might be due to the fact that invertebrates exhibiting ESD are commonly parasitic or confined to aquatic environments, where less spatial microhabitat differentiation exists. Sex ratio data available from nature for animals with ESD are quite limited, except for reptiles. In the laboratory sex ratios can be varied more widely than what is observed in nature.There are a number of characteristic features some of which are found in each species exhibiting ESD: (1) Patchy environments, (2) variable sex ratios, (3) parthenogenesis in addition to bisexuality, (4) parasitism, (5) aquatic habitats, (6) sexual dimorphism, (7) females larger than males, and (8) local mate competition.

Site selection in a polymorphic mangrove snail

Three species of littorinid snail live on mangroves of the genus Rhizophora on the north coast of Papua New Guinea. They have recently been placed in the genus Littoraria. The species are L. scabra and L. intermedia, which are monomorphic and cryptic and live on bark, and L. pallescens which is polymorphic and lives in foliage. Littoraria intermedia was found mostly on mangroves facing on to partially fresh water, while L. scabra occurred only at sites facing on to the sea; L. pallescens occurs at both types of site. When kept together in plastic containers, L. pallescens shows a greater propensity to climb than the other two species. The morphs of L. pallescens are principally yellow, orange or dark. Orange is present at a frequency of 0–9% and yellow at 10–50%. There is little evidence of geographical variation in frequency over 80 km of coast, although one central locality has a significantly higher frequency of yellow than sites to the north or south of it. Throughout the tropics where the species occurs, orange is the rarest and yellow usually the next rarest morph. Larger individuals are on average higher in the foliage than smaller ones, and there is a higher frequency of yellows among larger shells than smaller ones. As the air temperature increases, a progressively larger fraction of a sample was found to be on the under-surfaces of leaves rather than on the upper epidermis or on flower or leaf buds. When over 30% of a sample is situated on lower surfaces there is a significant excess of yellows and a deficiency of darks on the upper surfaces. This indicates that individuals selectively take up different positions depending on morph colour, resulting in a degree of optimal background matching. Such a choice of location may be of direct relevance to the maintenance of the polymorphism. A difference in morph frequency between the same sites examined in 1979 and 1984 is interpreted as being a result of site selectivity.

Variation in Wing Length of the African Armyworm, Spodoptera exempta in East Africa During 1973-74

SUMMARY Wing lengths of nearly six thousand Spodoptera exempta adults have been measured in samples caught at light-traps at various sites in East Africa between December 1973 and July 1974. There were systematic variations in mean wing length between different populations at different times and places. A sampling unit called the station-month is defined as all the moths of one sex caught at one particular station in one particular month. The variance between station-months was greater than that between days within station-months, but less than that between observations within days. In general, wing length was at a minimum in February and rose to reach a maximum at the end of the season in July. In any one month wing lengths were usually larger at more northerly stations. A sample from one particular night at Ilonga (Tanzania) consisted of moths whose wing length and sex ratio differed significantly from those caught there at other times; this suggests that there was an influx of moths from a different geographical source on this night. Measurements were also made on samples from emergence sites in Kenya, and the results compared with the main analysis: they provide further evidence for geographical variation. Possible causes and consequences of the variation are discussed.

Biogeographic Range Comparisons and Evidence of Geographic Variation in Host‐Parasite Relations

A test for judging whether a parasite's geographic range is as extensive as that of its host is described. Suppose hosts have been examined at M / N sites and infested specimens have been found at only M of them. Let a map of the area be divided into blocks by drawing boundary lines through the N clean sites. Each block contains one or more infested sites, or is empty; but a block cannot contain any clean sites since, owing to the method of block construction, all clean sites are on block boundaries. Now count the number of empty blocks. One may compute the probability of finding at least as many empty blocks on the null hypothesis that the risk of a host's infestation is independent of its geographic location, and hence tests the hypothesis. The test is then applied to data on the ranges of several aphid species that attack species of Solidago (goldenrod) in Nova Scotia and Prince Edward Island (NS / PEI). Data on plant—aphid relations obtained in NS / PEI are compared with previously collected data from southeastern Ontario. One of the Solidago species constitutes an empty niche in Ontario, either because the aphids that attack it in NS / PEI have small geographic ranges, or because Ontario plants of the species are aphid—resistant. One of the aphid species, with greater geographic range than its three host species, attacks different (though closely related) Solidago's in the different regions.

Melanin pigmentation in the dorsal plumage of New Zealand oystercatchers

Feather samples gathered from the mantle of breeding birds of the three New Zealand species of oystercatcher were analysed spectrophotometrically to evaluate melanin pigmentation parameters. The only statistically significant difference in these parameters was among individuals, indicating that melanin pigmentation is a conservative character of little systematic value. There is no evidence for geographic variation in melanin pigmentation of black phase Haematopus unicolor, and thus there is no justification for considering southern black birds specifically distinct from their northern counterparts on the basis of dorsal plumage colour.

Studies on the relationship between soil-borne viruses of the ringspot type occurring in Britain and Continental Europe

Plant-protection and serological tests showed that raspberry yellow dwarf virus is closely related to, and should be considered a strain of, arabis mosaic virus. Cherry trees affected by diseases of the rasp-leaf type in England, Germany, and Switzerland contained either arabis mosaic or raspberry ringspot viruses, but a virus from cherry with Eckelrader disease in the Netherlands was unrelated to either of these viruses. Arabis mosaic virus was also isolated from wild elder ( Sambucus nigra L.) trees and from horse radish ( Armoracia rusticana Gaertn.). No common antigens were detected in raspberry ringspot and tomato black ring viruses although the two viruses often occur together in fields. As with tomato black ring virus, there was much evidence of geographical variation between isolates of raspberry ringspot virus from Scotland, England, and Continental Europe, but isolates of arabis mosaic virus from different countries were scarcely distinguishable.

Incidence of urinary calculi among patients in general hospitals, 1948 to 1952.

• A questionnaire enlisting the cooperation of medical record librarians was used to determine the incidence of urinary calculi among patients admitted to or discharged from general hospitals. For the country as a whole it was estimated that 9.47 persons per 10,000 population were admitted with this diagnosis during the year 1952. Evidence of geographical variation was obtained, with rates of 19.25 and 18.42 from South Carolina and Georgia at one extreme and 5.81 and 4.31 from Wyoming and Missouri at the other. There were also significant differences within states, the incidence in the northern part of Alabama, for instance, being less than half that in the southern part. The incidence of calculous disease was lower among Negroes than among whites and lower among children than adults.