Chromosomal C-band variation inAllium schœnoprasum (Liliaceae) in eastern North America

Variation in C-banding was studied in seven populations ofAllium schnoprasum from eastern N. America, including populations referable to var.sibiricum, var.laurentianum, and ± intermediate. 23 bands were recognized on five pairs of chromosomes, and were treated as 23 loci. No banding site was monomorphic throughout the plants studied. The level of polymorphism per population was >60%, and the average heterozygosity values varied from 0.21 to 0.27. The various banding patterns of chromosomes were shown to depend on the random combination of individual bands. Nei's genetic distances between populations varied from 0 to 0.070 (mean: 0.033). The matrix of genetic distances was analysed by non-metric multidimensional scaling, and the results showed a significant relationship between longitude and population scores on the ordination. The chromosomal data did not clearly discriminate between the two native varieties ofA. schnoprasum, but were interpreted as a longitudinal cline. It is suggested that studies of C-banding variation in vascular plants should focus on individual banding sites, rather than on whole chromosome banding patterns.     

Whistle variability of Guiana dolphins in South America: Latitudinal variation or acoustic adaptation?

A previous comparison of whistles using data sampled at 48 kHz suggested that certain frequency parameters vary along a latitudinal gradient. This geographical pattern may be biased because whistles sampled at higher frequencies could potentially have very different frequency contents. The current study compared the acoustic parameters of Guiana dolphin (Sotalia guianensis) whistles recorded at a higher sampling rate (96 kHz) and from groups occupying two never before sampled sites, Benevente Bay, Espírito Santo, Brazil, and Formosa Bay, Rio Grande do Norte, Brazil, with recordings of other populations in South America. By only considering data sampled at a rate of at least 96 kHz, we aimed to detect differences in whistles across locations. Contrary to previous findings, our analyses do not indicate any clear separation between northern and southern populations based on whistles, and do not corroborate the hypothesis of latitudinal acoustic variation in this species. The variation in Guiana dolphin whistle parameters found here appears to be influenced by latitude to some extent, but several other factors, including sampling method, environmental fluctuations, and social influence on vocal learning, may be confounding the detection of a geographic pattern in these whistle samples.     

Prevalence of wood characters in eastern North America: what characters are most promising for interpreting climates from fossil wood?

The frequency of wood-anatomical characters in the eastern North America dicotyledonous tree flora shows spatial variance that can be related to climate (40% of the variation in 18 characters is explained by temperature and precipitation). Percent of taxa with rings varies with mean annual temperature, but the relationship is weak and the difficulties in making determinations as to presence or absence of rings make this character a problematic climatic indicator. Significant climate sensitivity is seen among characters pertaining to: a) vessel size and density (in diffuse-porous woods); 2) vessel arrangement; 3) parenchyma types; and 4) rays. Overall, the anatomical variables can be used to represent 82% of the variance in total precipitation and 91% of the variance in mean annual temperature within the study area. These results demonstrate the possibility of deriving a multivariate representation of the response of wood to climate that will be useful in climate reconstruction and comprise a source of information similar to that obtainable from leaf morphology and permitting estimates of precipitation as well as temperature.     

Are secondary sex traits, parasites and immunity related to variation in primary sex traits in the Arctic charr?

Primary and secondary sex traits are influenced by the same sex hormones, and the expression of secondary sex traits may consequently signal males' capacity for sperm production. Sperm quality may also be influenced by immune activity, as sperm are non-self to the male. Parasite infections alter immune activity and may thus reduce ejaculate quality. In the Arctic charr (Salvelinus alpinus) the red abdominal colour is considered an ornament that signals important information in mate choice. We captured and individually caged sexually mature male Arctic charr during the spawning period. Afterwards we estimated abdominal colour, parasite infections, gonad mass and several spermatological and immunological variables. Intensity of abdominal colour was positively correlated to testes mass, milt mass and sperm cell numbers produced. Additionally, males with low parasite intensities had high testes mass and produced milt with high sperm density, indicating a trade-off between parasite resistance and development of primary sex traits. Our measures of immunity were, however, not related to primary sex traits. We conclude that females evaluating male abdominal coloration may obtain information about differences between males in fertilization potential and parasite resistance.     

The association between parasite infection and growth rates in Arctic charr: do fast growing fish have more parasites?

Trophically transmitted parasites are known to impair fish growth in experimental studies, but this is not well documented in natural populations. For Arctic charr [Salvelinus alpinus (L.)], individual growth is positively correlated with food consumption. However, increased food consumption will increase the exposure to trophically transmitted parasites. Using a correlative approach, we explore the association between parasite abundance and the individual growth of Arctic charr from five lakes within the same watercourse. The studied parasite species differ in their life cycles and cost to the host. We predicted a positive association between parasite abundance and fish growth for parasites of low pathogenicity reflecting high consumption rates, and a negative association at higher parasite abundances for more costly parasites. We found no direct negative associations between parasite abundance and fish growth. The relationship between parasite abundance and growth was linearly positive for the low costly Crepidostomum sp. and concave for the more costly Eubothrium salvelini. In natural fish populations, the negative effects of parasites on fish growth might be outweighed by the energy assimilated from feeding on the intermediate host. However, experimental studies with varying food consumption regimes are needed to determine the mechanisms underlying our observations.

     

Latitudinal variation in litter size of polar bears: ecology or methodology?

I used data reported in the scientific literature to examine latitudinal variation in litter size of polar bears in 18 different populations. No relationship was found between litter size and latitude using non-weighted regression. Regression weighted by sample size indicated a negative relationship with latitude. However, sampling biases caused by latitudinal differences in the timing of sampling and cub mortality after den emergence could produce a latitudinal cline. Stratifying analyses by sampling area, at dens or away from dens, revealed no latitudinal trend in litter size. Observed differences in litter size among populations may result from variation in demography and ecosystem productivity that is not simply related to latitude. I conclude that available data do not provide support for a biologically significant latitudinal cline in polar bear litter size. Accepted: 25 May 1999     

Does global warming threaten the dynamics of Arctic charr in Lake Geneva?

In France, the Arctic charr (Salvelinus alpinus) is native in only two lakes (Lakes Bourget and Geneva), in the most southerly part of its distribution area. It is a profundal morph living at depths of between 30 and 100 m in Lake Geneva. Following considerable stocking of Lake Geneva with juvenile Arctic charr and some good results during the 1980s, catches are currently declining. Several hypotheses have been proposed to explain this decrease, but the potential influence of warming of the lake in the 1990s has not been considered. This article studies the relationship between the strength of the cohorts and the temperature in Lake Geneva from 1992 to 2002, and discusses the various potential causes of the population collapse observed. The findings reveal close correlation between water temperature and the strength of the cohorts. It is concluded that the recent warming of Lake Geneva may have a significant direct or indirect impact on the Arctic charr population.     

Does the Arctic charr Salvelinus alpinus produce sounds in a captive setting?

Arctic charr Salvelinus alpinus did not appear to invest in acoustic communication during courtship and agonistic interactions in captivity. Salvelinus alpinus did, however, produce four different types of sounds which were found to be associated with three different types of air exchange behaviours which probably have a swimbladder regulation function. Since air passage sounds appear to be common among Salmonidae, it is suggested that the potential of passive acoustics techniques for behavioural and ecological monitoring should be further investigated in future field and laboratory investigations.     

Cannibalism in Arctic charr: do all individuals have the same propensity to be cannibals?

By comparing large Arctic charr Salvelinus alpinus , which had shown a persistent cannibalistic response varying from zero to very high in succeeding laboratory trials, with their individual cannibalistic behaviour after release into a natural lake inhabited by small Arctic charr, it was found that all Arctic charr had the potential to become cannibalistic, irrespective of their laboratory behaviour. More specifically, Arctic charr that never fed on prey fishes when offered them in the tank experiments turned to cannibalism when released in the lake, highlighting the potential difficulties in extrapolating laboratory results to natural settings. This was also true for naive fish that had no prior experience of eating live food. Since no significant increase in the number of prey consumed during each of the succeeding laboratory trials was found, and naive fish showed a response under natural conditions similar to that of their counterparts, the training of the Arctic charr (or experience or learning) probably had no effect upon the piscivorous or cannibalistic response after stocking. Thus, the study appeared to demonstrate that most variations in cannibalism in Arctic charr was simply a function of environmental conditions, depending on the density of conspecifics v . alternative prey, and the relative size difference between predator and prey, rather than any genetic influence.     

Limited differentiation in microsatellite DNA variation among northern populations of the yellow warbler: evidence for male‐biased gene flow?

Comparisons of the patterns of differentiation among genetic markers with different modes of inheritance can provide insights into patterns of sex-biased dispersal and gene flow. Here, we compare the patterns of differentiation in six microsatellite loci among eight northern breeding populations of the yellow warbler (Dendroica petechia) with results obtained with mitochondrial DNA. Significant but low levels of differentiation (overall FST = 0.014; overall RST = 0.015) were present across all populations. The level of differentiation is substantially less than that observed in the same samples based on mitochondrial DNA control region variation. The presence of low population imbalance index values and significant isolation-by-distance relationships for both FST and RST suggests that these populations are at evolutionary equilibrium and that the high degree of similarity between populations may be due to high levels of male-biased gene flow. This suggests that there may be significant but previously unappreciated differences in the long-distance and/or episodic dispersal behaviour of males and females in these birds.     

Is there more insect folivory in warmer temperate climates? A latitudinal comparison of insect folivory in eastern North America

1.  It is generally believed that warmer climate forests suffer more herbivory, as a proportion of leaf area, than cooler climate forests. However, standardized studies using the same methodology have rarely been performed.
2.  We carried out a study on scattered forest-edge populations of four widespread tree species ( Quercus alba , Acer rubrum , Fagus grandifolia and Liquidambar styraciflua ) spanning 17° of latitude in North America.
3.  We sampled early summer sun leaves (12 weeks after bud break) at each latitude in 2 years. Total insect folivory damage was estimated from the percentage area damaged in fresh leaves on forest edges, using a scanner-linked software.
4.  The percentage area damage per leaf of all four species in both years shows a significant latitudinal trend, with less damage in lower latitude areas of eastern North America. This is contrary to what would generally be expected according to current ecological thinking. Among the four studied species, only A. rubrum showed a significant difference between the 2 years.
5.   Synthesis . The observation of an inverse latitudinal trend may have wider implications for the study of community functioning, suggesting that strength of 'biotic' interaction between plants and herbivores might actually be no less important, or in fact more important, in cool temperate climates compared with warm temperate climates.     

Can Coyotes Affect Deer Populations in Southeastern North America?

ABSTRACT The coyote (Canis latrans) is a recent addition to the fauna of eastern North America, and in many areas coyote populations have been established for only a decade or two. Although coyotes are known predators of white-tailed deer (Odocoileus virginianus) in their historic range, effects this new predator may have on eastern deer populations have received little attention. We speculated that in the southeastern United States, coyotes may be affecting deer recruitment, and we present 5 lines of evidence that suggest this possibility. First, the statewide deer population in South Carolina has declined coincident with the establishment and increase in the coyote population. Second, data sets from the Savannah River Site (SRS) in South Carolina indicate a new mortality source affecting the deer population concurrent with the increase in coyotes. Third, an index of deer recruitment at SRS declined during the period of increase in coyotes. Fourth, food habits data from SRS indicate that fawns are an important food item for coyotes during summer. Finally, recent research from Alabama documented significant coyote predation on fawns there. Although this evidence does not establish cause and effect between coyotes and observed declines in deer recruitment, we argue that additional research should proactively address this topic in the region. We identified several important questions on the nature of the deer—coyote relationship in the East.     

Sex ratio variation and mixed pairs in roe deer: evidence for control of sex allocation?

Sex allocation has provided rich ground for the development of evolutionary theory. The dominant models in vertebrates have provided predictions of sex ratio based on asymmetry in variance in breeding success between sexes in the breeding system, and the relative effect of local competition. In ungulates, empirical work has provided some support for these models, but has also generated apparently contradictory observations. Recent models have provided some predictions for both individual and population sex ratio, showing that the availability of high-quality habitat patches and dispersal rates can critically affect both population- and individual-level expectations. We explore patterns in offspring sex ratio among a large sample of roe deer, a species with some interesting aspects of the breeding system. We found that in singleton pregnancies (the minority) there was an excess of male embryos, which was more marked in does in good condition at most sites. While the sex ratio among twins was close to parity, and unaffected either by average condition among populations or by individual condition within populations, we observed a clear excess of mixed pregnancies (sub-binomial variance, SBV). The excess was greater where the average condition was high. Within sites, population changes in average condition were associated with changes in SBV: in populations declining in condition, SBV also declined. There was no tendency for mixed twins to be more likely in individuals in better condition within a population. We conclude that condition-dependent allocation of sex does occur in roe deer. We suggest that in these "income breeders", mixed pairs might offer the greatest opportunity to optimize maternal investment during lactation, when conditions will be unpredictable, and that this is increasingly the case when average condition is poor.     

Microgeographic variation in metabolic rate and energy storage of brown trout: countergradient selection or thermal sensitivity?

We examined the influence of habitat size, growth opportunity, and the thermal conditions experienced during early development on the standard metabolic rate (SMR) of juvenile brown trout (Salmo trutta) from six natural populations to contrast the hypothesis of countergradient selection in metabolic rate. The study populations differed significantly in SMR. Population means for SMR changed in response to the temperature experienced during the yolk-absorption stage, when the risk of oxygen deficit increases and the vulnerability to hypoxia is highest. We also found a strong negative correlation between the temperature experienced during the first 2 months after yolk resorption and SMR, which supports the hypothesis of countergradient variation. Moreover, we detected a strong negative correlation between an index of growth opportunity and relative lipid content, suggesting that the risk of energy shortfall could be a major force in the evolution of storage strategies. Our results suggest that temperature can shape the evolution of metabolic rate during the yolk-absorptive stage or the first feeding stage, while energy storage levels may be more sensitive to thermal constraints acting on growth rates.     

Facultative primary sex ratio variation: a lack of evidence in birds?

The facultative control of primary sex ratio by breeding birds has become a major focus in evolutionary biology in recent years. A combination of well-developed theoretical literature and rapid publication of empirical results has created considerable confusion, with controversial claims for both extreme control of primary sex ratio versus no control around inherent random variability. We present a robust and quantitative summary of published empirical literature to assess clearly the body of evidence for female birds to control sex assignment in their offspring. Our meta-analytical approach reveals that published studies do not exhibit any variability beyond that which could be expected owing to sampling error. Therefore, we conclude that facultative control of offspring sex is not a characteristic biological phenomenon in breeding birds.     

High genetic variation in resting‐stage production in a metapopulation: Is there evidence for local adaptation?

Local adaptation is a key process for the maintenance of genetic diversity and population diversification. A better understanding of the mechanisms that allow (or prevent) local adaptation constitutes a key in apprehending how and at what spatial scale it occurs. The production of resting stages is found in many taxa and reflects an adaptation to outlast adverse environmental conditions. Daphnia magna (Crustacea) can alternate between asexual and sexual reproduction, the latter being linked to dormancy, as resting stages can only be produced sexually. In this species, on a continental scale, resting‐stage production is locally adapted—that is, it is induced when the photoperiod indicates the imminence of habitat deterioration. Here, we aimed to explore whether selection is strong enough to maintain local adaptation at a scale of a few kilometers. We assessed life‐history traits of 64 D. magna clones originating from 11 populations of a metapopulation with permanent and intermittent pool habitats. We found large within‐ and between‐population variation for all dormancy‐related traits, but no evidence for the hypothesized higher resting‐stage production in animals from intermittent habitats. We discuss how gene flow, founder events, or other forms of selection might interfere with the process of local adaptation.     

Modeling landscape condition for biodiversity assessment—Application in temperate North America

Conservation decisions are well supported by predictive spatial models that indicate the relative ecological condition of a given place. The intent of this 90 m pixel landscape condition model is to use nationally available spatial data from the USA, Mexico, and Canada to express assumptions regarding the relative ecological effects of land uses on terrestrial natural communities and species. This approach emphasizes and updateable and transparent design which takes advantage of empirical biodiversity data from the USA to both calibrate and validate the model. Map layers depicting infrastructure, land use, and modified vegetation were each scored for site impact and distance decay, and then combined into one map surface. Field observations from Natural Heritage Programs, each scored for relative ecological condition (in categories A = excellent to D = poor), were used to calibrate distance decay parameters. Some 90,000 observations for at-risk species, invasive plant species, and natural communities were used for model validation. Statistically significant distinctions in ecological condition among validation samples were predicted by the resultant spatial model. Variation in landscape condition was then summarized by regional U.S. Landscape Conservation Cooperatives (LCCs) in terms of areas approximating A–D condition. Montane and desert LCCs scored on average much higher in area approximating “A” and “B” landscape condition, while LCCs with more substantial agricultural and urban footprints scored overwhelmingly within the “D” range of condition. Similar analyses illustrated range-wide scoring of landscape condition for major vegetation types across temperate North America.