bluuebunny/crossref_metadata_2025 huggingface dataset:
Inheritance of body size in the Barnacle Goose under different environmental conditions
Authors: Larsson Kjell
Published: December 2004

Heritabilities, genetic variances and covariances for body size traits, i.e. tarsus length, head length and body mass, were estimated under different environmental conditions in a Barnacle Goose (Branta leucopsis) population. Under poor growth conditions, that is, when average body size of fully grown offspring in a given cohort was small, the offspring‐parent regressions and full‐sib analyses yielded heritability estimates not significantly different from zero. By contrast, when growth conditions were normal or good the heritability estimates were generally significantly positive. Comparisons of genetic covariance estimates indicated that they also differed across the analysed environmental conditions. This result, together with similar results obtained in studies of passerine birds, suggests that genotype‐environment interactions might be frequent within the range of environments normally encountered by birds in natural populations. If general, such results might question the validity of assuming approximate constancy of additive genetic variances and covariances over time and environments in evolutionary models.
Evolution of the alternation of haploid and diploid phases in life cycles. II. Maintenance of the haplo‐diplontic cycle
Authors: Richerd Sophie , Couvet Denis , Valéro Myriam
Published: December 2004

The relative duration of the haploid and the diploid phases during the reproductive cycle varies greatly between organisms. This paper addresses the question of the evolution of haploid, diploid, and haplo‐diplontic life cycles. When the life span of haploid and diploid individuals is constant whatever their cycle, we show that the haplo‐diplontic cycle has an advantage, which depends on the sex‐ratio in anisogamous species and on the probability of fertilization in isogamous species. This is because meiosis and fertilization occur half as often in the haplo‐diplontic cycle as in haploid or diploid cycles, for the same number of generations of individuals. This argument is demonstrated using a model which considers a genetic determination of the cycle, and fixed haploid and diploid fitnesses. The relevance of measures of fitness of haploid and diploid individuals in predicting the evolution of life cycles is discussed. Measures obtained in algae are compared with theoretical predictions.
Initiation of maternal effects in Lymantria dispar: Genetic and ecological components of egg provisioning
Authors: Rossiter Mary Carol , Cox‐Foster Diana L. , Briggs Michelle A.
Published: December 2004

Resources supplied by mothers to offspring through the egg are known to significantly influence offspring life history traits in the gypsy moth, Lymantria dispar. The purpose of this research was to determine the relative contribution of genetics (based on familial contribution) and the nutritional environment of the parents to the mean and variance of resources supplied to the eggs. Vitellogin, the dominant egg storage protein in the gypsy moth, was selected as the focus of the study. The amount of vitellogin in individual eggs from 48 mothers reared on one of four host species, quaking aspen, chestnut oak, red oak, or pitch pine was quantified with an immunoassay. Results of a nested analysis of variance show that both genetics and parental nutritional experience make significant contributions to egg vitellogin levels. When parents were reared on quaking aspen, vitellogin levels were highest and the expression of familial variation was greatest. This study shows that polyphagy can amplify phenotypic variance in reproductive traits through the interaction between genotype and nutritional environment. To the extent that egg resources influence offspring vigor, the fitness of offspring can include a time‐lagged component which arises from the interaction between the parental genotype and the parental environment. The time‐lagged expression of such a maternal trait is capable of influencing the rate and direction of character evolution and the stability of local population dynamics.
Multiple origins of self‐fertilization in tristylous Eichhornia paniculata (Pontederiaceae): Inferences from style morph and isozyme variation
Authors: Husband Brian C. , Barrett Spencer C. H.
Published: December 2004

Populations of Eichhornia paniculata (Pontederiaceae) exhibit a wide range of mating systems, from predominant outcrossing to high levels of self‐fertilization. The origin of self‐fertilization in this tristylous species is associated with the loss of style‐length morphs from populations and the spread of self‐pollinating, floral variants. We examined geographic variation in style morph and allozyme frequencies to determine whether the loss of style morphs and transition to selfing could have multiple origins in E. paniculata. Surveys of floral variation in 167 populations from six states in northeastern Brazil revealed that at least one style morph was absent from 29.3%. Non‐trimorphic populations occurred in all states and ranged in frequency from 9% in Ceará to 68% in Alagoas. Selfing variants occurred in 8.5% and 55% of trimorphic and non‐trimorphic populations, respectively, and were distributed among five of six states with primary concentrations in Alagoas and Pernambuco. A comparison of electrophoretic variation at 24 isozyme loci in 28 trimorphic, 13 dimorphic and 3 monomorphic populations indicated that non‐trimorphic populations contained 84% of the allelic variation present in trimorphic populations and were markedly differentiated from one another. Analyses of genetic distance and the distribution of rare alleles indicated that non‐trimorphic populations were often more similar to neighbouring trimorphic populations than to one another. Populations with selfing variants occurred at low frequency in three genetically distinct parts of the range. These results, in combination with genetic and morphological evidence suggest that style morphs are lost repeatedly from populations of E. paniculata and that selfing variants may have originated on at least three separate occasions in northeastern Brazil.
Reproductive energetics of the role reversing bushcricket, Kawanaphila nartee (Orthoptera: Tettigoniidae: Zaprochilinae)
Authors: Simmons L. W.
Published: December 2004

Theory predicts that sexual differences in reproductive strategies arise because of differences in the magnitude of investment made by males and females in reproduction. In some bushcrickets, the typical sex role of competitive male and choosy female is reversed when populations are subject to nutrient stress. Here I present an energetic analysis of reproduction for the role reversing bushcricket, Kawanaphila nartee, that supports the contention that this sex role reversal is a consequence of reversal in the pattern of relative reproductive investment. When fed ad libitum, males spent 16% of their daily energy reserves on the spermatophore compared with 26% spent on calling to attract a mate. Females spent 29% of their daily energy reserves in producing and laying eggs. However, when allowed only limited access to food, female expenditure in eggs was reduced to 23% of daily reserves while male expenditure remained unchanged. After accounting for the incorporation of male nutrients into eggs, female energy expenditure in reproduction exceeded male expenditure when animals were fed ad libitum, but male expenditure exceeded female expenditure when diet was limited. This role reversal in relative energy expenditure that is associated with courtship role reversal supports classical and contemporary theories on the control of sexual selection.
Origin of European rabbit (Oryctolagus cuniculus) in a Mediterranean island: Zooarchaeology and ancient DNA examination
Authors: Hardy Chris , Vigne Jean‐Denis , Casañe Didier , Dennebouy Nicole , Mounolou Jean‐Claude , Monnerot Monique
Published: December 2004

Mammalian species presently living on Mediterranean islands have been brought in by man. The question of their geographical origin and of the time of their introduction is often a matter of debate. We studied this problem using a population of rabbits (European rabbit: Oryctolagus cuniculus) living in Zembra, an island off Tunisia. Archaeological surveys show that rabbit has been introduced to the island by Bronze Age or Roman people, between the IIIrd Millenium B.C. and the IIIrd century A.D. Part of the 16S‐rRNA gene of mitochondrial DNAs from fossil bones of different ages (dated back to 130–390 A.D.) was characterized and compared to that of present day rabbits of differing geographical origin. The data suggest that animals present on Zembra in late Roman times belonged to the same maternal lineage as present populations from Northern Spain and Southern France.
Molecular biogeography: using the Corsica‐Sardinia microplate disjunction to calibrate mitochondrial rDNA evolutionary rates in mountain newts (Euproctus)
Authors: Caccone Adalgisa , Milinkovitch Michel C. , Sbordoni Valerio , Powell Jeffrey R.
Published: December 2004

Mitochondrial DNA (mtDNA) sequence variation was examined in the three species belonging to the newt genus Euproctus: E. asper, E. montanus, and E. platycephalus, and in three other species belonging to the same family: Triturus carnifex, T. vulgaris and Pleurodeles waltl. The Euproctus species inhabit mountain streams in the Pyrenean region, Corsica, and Sardinia, respectively. This vicariant distribution is believed to be a result of the disjunction and rotation of the Sardinia‐Corsica microplate from the Pyrenean region and suggested dates for each cladogenetic event are available. A total of 915 bp from 12S and 16S ribosomal rRNA genes were compared for each taxon. These are the first mt‐rDNA sequence data for salamanders. Sequences were used to reconstruct phylogenetic trees, investigate evolutionary rates for these genes, calibrate them with absolute time since divergence, and compare rates with published ones.

Using P. waltl as the outgroup, all phylogenetic methods used (parsimony, maximum likelihood, and Neighbor Joining) produced trees with identical topologies and similar bootstrap values associated with each node. These sequence data cannot unambiguously resolve the splitting events leading to the main radiation of the genus Triturus and the origin of the genus Euproctus. These events may well have occurred very close in time, consistent with other sorts of data. Although it is unlikely strict linearity holds for all kinds of substitutions, relative rate tests of the molecular clock hypothesis could not reject clock‐like behavior of sequence changes along Euproctus lineages. Estimates of absolute rates of base changes are 0.35% per Myr since divergence for all substitutions and 0.14% per Myr for transversions; these estimates are similar to other vertebrate estimates. A comparison with distance measures from allozyme studies agrees quite well with regard to relative divergences of the three Euproctus species.
Selecting for floral character associations in wild radish, Raphanus sativus L.
Authors: Stanton Maureen , Young Helen J.
Published: December 2004

ESS models of reproductive allocation have been used extensively to explain patterns of floral diversity in angiosperms. These theoretical explorations assume that proportional allocation to pollen, ovules, and seeds, as well as to secondary features such as showy petals and nectar rewards, can evolve independently within the limits set by total resource availability. In populations of California wild radish, we have shown previously that petal size, a strong determinant of visitation by honey bee pollinators, is positively correlated with both pollen and nectar production, but not with ovule or seed number per flower. These phenotypic associations may reflect selection, environmental correlation, and/or genetic constraint. By exerting selection on the petal size : pollen number ratio over two generations, we eliminated the positive correlation between petal size and pollen production, with both characters showing significant change after a single selection episode. Once these two floral traits became uncoupled, nectar sugar production was significantly correlated only with petal size. Our results suggest that natural selection could readily alter reproductive allocation in these flowers, and that the phenotypic correlations observed in nature may be maintained by selection for effective reproductive phenotypes.
Evolution of clutch size in insects. I. A review of static optimality models
Authors: Wilson Kenneth , Lessells C. M.
Published: December 2004

Abstract This paper reviews the importance of constraint assumptions to the predictions of static optimality models of insect clutch size. This allows us to identify predictions that distinguish between models embodying different constraints on female oviposition behaviour and hence to determine which resources or other factors limit clutch size evolutionarily. We conclude that while some models may be distinguished using qualitative criteria, others require the testing of quantitative predictions. In a companion paper (Wilson 1994) these models are tested using the bruchid beetle Callosobruchus maculatus.
Population structure of Leptothorax ambiguus, a facultatively polygynous and polydomous ant species
Authors: Herbers Joan M. , Grieco Sarah
Published: December 2004

We examined the genetic and spatial structure of Leptothorax ambiguus in a Vermont site. Nests of this tiny ant species have variable queen number and comprise larger polydomous colonies, as do their closest relatives in North America. Nests are patchily distributed in the forest, and sometimes occur in local abundance. We collected 121 nests in four years from plots in which all nests were mapped; furthermore, we subjected nests collected in two separate years to starch gel electrophoresis and estimated relatedness according to the Queller—Goodnight (1989) algorithm. Queens that share a nest site also share 33% of their alleles on average, and relatedness among worker nestmates is about 0.5. The existence of diploid males and nonzero F‐values demonstrate inbreeding in this species, an unusual phenomenon for social insects in general. Mapping data showed that nests with like genotypes tended to cluster in space, forming polydomous colonies. Colonies consisted of 1–6 nest subunits, and about half of all colonies were polygynous. We compare these features of L. ambiguus to its close relative L. longispinosus and a European congener L. acervorum. These comparisons allow us to conclude that an interplay between ecological and genetic factors produces the observed pattern of multiple queening and nest spatial distribution in this species.
Inbreeding depression and mating‐distance dependent offspring fitness in large and small populations of Lychnis flos‐cuculi (Caryophyllaceae)
Authors: Hauser Thure P. , Loeschcke Volker
Published: December 2004

The spatial structure of four Lychnis flos‐cuculi populations, varying in size and degree of isolation, was studied by comparing the fitness of offspring resulting from self‐pollination and pollinations by neighbouring plants, plants within the same population, and plants from other populations. Selfed offspring had the lowest fitness of the four offspring groups. No significant difference was found between the performance of offspring from pollinations by neighbouring plants and offspring pollinated by plants further apart but within the same population. A lower fitness of offspring from pollinations between neighbours would be expected if these matings, on average, yielded inbred offspring which suffered from inbreeding depression. These results imply that either a tight neighbourhood structuring is not present, or that the inbreeding depression for offspring by neighbours is too low to detect, although these are inbred. Crossings between populations produced offspring with a significantly higher fitness than offspring sired within populations. There were no significant differences in response to inbreeding among the populations, and differences in mean fitness among populations had no clear relation to the population size or degree of isolation. A reduced fitness of small populations due to inbreeding depression or a less severe response to experimental inbreeding due to purging of deleterious alleles is therefore not supported by our results.
Thermal evolution of pre‐adult life history traits in Drosophila melanogaster
Authors: Partridge L. , Barrie B. , Fowler K. , French V.
Published: December 2004

Replicated lines of Drosophila melanogaster were allowed to evolve in population cage culture at 16.5° C or 25° C for five years. Their larval and pupal development times, larval growth rates, larval critical weights for pupariation and pre‐adult survival rates were then measured at both temperatures. Pre‐adult survival showed evidence of adaptation of the lines to their thermal selection regimes, with each set of lines showing superior survival when tested at the temperature at which they had been evolving. Pupal periods were similar for all lines when growing at 16.5° C but, at 25° C, the low temperature lines had the longer pupal periods. Irrespective of experimental temperature, low temperature lines grew faster and had shorter larval development periods than the high temperature lines. Larval critical weights for pupariation were higher in the low temperature lines at the low experimental temperature, and higher in the high temperature lines at the higher experimental temperature. The correlations between these traits induced by thermal evolution were in general different from or opposite to the genetic correlations found within a single temperature.
Morphometric variation in a hybrid zone of two subspecies of Gerris costae (Heteroptera: Gerridae) in the Maritime Alps
Authors: Largiadèr Carlo Rodolfo , Klingenberg Christian Peter , Zimmermann Manfred
Published: December 2004

Two morphologically distinct subspecies of Gerris costae form a contact zone extending from the Maritime to the Western Alps. Within this area canonical trend surface analysis revealed a geographic pattern of morphometric variation consistent with topography. From North to South, and from high to low elevation there was a transition from G. c. costae‐like phenotypes to phenotypes resembling pure G. c. fieberi. The same pattern was confirmed with canonical variate analysis not taking geographic location into account; it is therefore not an artifact of trend surface analysis.

Comparisons of the pattern of morphometric variation of laboratory‐reared offspring with the pattern of their parents sampled from natural populations show that geographic variation is mostly determined genetically. Intermediate individuals from field populations probably are natural hybrids between the two subspecies, because laboratory‐reared hybrids were intermediate between the offspring of pure strains.

We did not find increased morphometric variation within the contact zone. This suggests unimpeded introgression and is in contrast with an increase in size variability that is predicted to be associated with a transition between uni‐ and bivoltine forms.
Life history adaptation along a latitudinal cline in the water strider Aquarius remigis (Heteroptera: Gerridae)
Authors: Blanckenhorn W. U. , Fairbairn D. J.
Published: December 2004

We addressed the general hypothesis that life history differences among eastern populations of the North American water strider, Aquarius remigis (Heteroptera: Gerridae), along a north‐south gradient are manifestations of genetic differentiation due to natural selection. We raised offspring of two field‐caught populations from each of three latitudes in a common laboratory environment at 20° C and two photoperiods. Nearly all Quebec (PQ) individuals (ca. 46° N) entered diapause to reproduce the following spring (univoltine life cycle), while intermediate proportions of New York (NY; ca. 43° N) and New Jersey (NJ; ca. 41° N) individuals reproduced directly, producing a second generation (bivoltine life cycle). PQ females were smaller, developed faster, and laid smaller eggs than NY and NJ individuals; NY and NJ populations differed little in these variables. NY females had longer life spans than either PQ or NJ females, but lower oviposition rates. Total reproductive output did not differ across latitudes. Photoperiod affected body length, development time, and reproductive pathway, resulting in a latitude by environmental interaction. PQ individuals reproduced directly under 15L : 9D (summer) conditions only, while the NY and NJ populations exhibited more direct reproduction under 13L : 11D (spring or fall) conditions. Some life history characters of the NY and NJ populations displayed the higher variability indicative of phenological transition zones. These results indicate local adaptation of populations to long‐term climatic patterns. Water striders appear to adapt to longer seasons by extending development, growing larger, and breeding directly. Larger body size and extended or rapid development are associated with bivoltinism and increase in egg size, but not necessarily with higher fecundity or oviposition rate. The phenological transition zone appears to be unrelated to a transition zone a little further south established by allozyme data and morphology, as all populations studied here could be electrophoretically identified as northern "type".
The genetic basis of female mate preferences
Authors: Bakker Theo C. M. , Pomiankowski Andrew
Published: December 2004

We review the evidence for genetic variation in female and male mate preferences. Genetic differences between species and partially isolated races show that preferences can evolve and were genetically variable in the past. Within populations there is good evidence of genetic variation, both of discrete genetic effects (8 cases) and quantitative genetic effects (17 cases), from a diverse range of taxa. We also review evidence for the presence of genetic covariance between mate preferences and sexual traits in the other sex. The 11 studies go a long way to validating the theoretical prediction of positive genetic covariance. The few negative results are best explained by a lack of appropriate experimental design. One unresolved question is whether genetic covariance is due to linkage disequilibrium between unlinked genes or physical linkage. Some evidence points to linkage disequilibrium but this is not yet conclusive.
Introduced Swedish Canada geese (Branta canadensis) have low levels of genetic variation as revealed by DNA fingerprinting
Authors: Tegelström H»kan , Sjöberg Göran
Published: December 2004

The Swedish, Finnish and Norwegian population of Canada geese (Branta canadensis), now amounting to some 30–50 000 birds, was founded by only five individuals. We used DNA fingerprinting to assess the level of genetic variability in minisatellite loci of Swedish Canada geese from two northern areas. For comparison, we estimated the minisatellite variability in lesser white‐fronted geese (Anser erythropus), barnacle geese (Branta leucopsis) and a reintroduced stock of Canadian giant Canada geese (Branta canadensis maxima).

The mean similarity between Swedish Canada geese was 0.76 ± 0.15, which is higher than recorded for any other natural bird population. The high similarity implies that a fourfold increase of homozygosity has taken place in this population. The probable cause for the loss of variation is the low number of birds originally introduced and a history of repeated translocations, leading to a sequence of founder events. As a consequence of the high similarity, it has not been possible to use DNA fingerprinting for determination of parenthood in the population studied.
Temporal stability in hybridization between Bufo microscaphus and Bufo woodhousii (Anura: Bufonidae): Behavior and morphology
Authors: Sullivan Brian K.
Published: December 2004

I analyzed temporal variation in hybridization between the southwestern toad (Bufo microscaphus) and Woodhouse's toad (Bufo woodhousii) along the Virgin River in southwestern Utah and northwestern Arizona. Bufo woodhousii is largely restricted to the floodplain of the Virgin River from southern Nevada to the vicinity of St. George, Utah. By contrast, B. microscaphus is confined primarily to the tributaries of the Virgin River, only occupying the Virgin River proper exclusive of B. woodhousii along its upper reaches east of La Verkin Creek. As in all other zones of sympatry for these bufonids, behavior and morphology provide clear evidence of hybridization at a number of sites along the Virgin River. Analysis of morphology and behavior indicates that the distribution of these taxa and their hybrids is largely unchanged relative to that documented forty years ago by Blair (1955). Comparisons of morphological hybrid index scores reveal slight shifts in relative numbers of parental taxa at only one site. Hybridization between these anurans has been relatively stable geographically, and may be related to the nature of the riparian habitat available for breeding.
Sex‐ratio distortion in Drosophila simulans: co‐occurence of a meiotic drive and a suppressor of drive
Authors: Merçot Hervé , Atlan Anne , Jacques Micheline , Montchamp‐Moreau Catherine
Published: December 2004

A sex‐ratio distortion factor was found at high frequency in D. simulans strains from Seychelles and New Caledonia. This factor is poorly or not expressed within those strains which are resistant to it. Its presence was detected by crossing females from New Caledonia or the Seychelles with males from a different geographic origin. Most of the F1 males obtained produced an excess of females (up to 99%) in their progeny. The two strains are infected with Wolbachia, but these micro‐organisms are not involved in the sex‐ratio distortion. The sex‐ratio factor is shown to be an X‐linked meiotic driver; nuclear resistance factor(s) act by suppressing the drive. It is likely that the same X‐located driver invaded the two populations, which subsequently developed resistance factor(s) against it.
Why pollinators visit only a fraction of the open flowers on a plant: The plant's point of view
Authors: Iwasa Y. , De Jong T. J. , Klinkhamer P. G. L.
Published: December 2004

We analyze the so‐called ‘exponential decay’ model of pollen transfer for the case in which pollinators visit a fraction of the open flowers on a plant. The analysis is limited to the simplest case of a self‐incompatible species, in which self pollen does not interfere with seed set. Plants can manipulate the number of flowers visited per pollinator approach by adjusting attractiveness of flowers so as to maximize pollen export (male fitness). In the model the length of the visitation sequence that is optimal for the plant f̂ always decreases with pollen deposition rate k1, pollen uptake rate k2, and the number of pollinator approaches to the plant X, but increases with the total number of flowers F. We assume that the average number of pollinator approaches X increases with the total number of flowers F, but slower than proportionality. It then follows that the optimal fraction of flowers a pollinator visits after arriving on the plant (f̂/F) decreases with the total number of flowers F. Furthermore, the male fitness gain per flower generally decreases with number of flowers, except for the condition of ‘inefficient’ pollen transfer with very small values of k1, k2, and X, or when the plant has only a few flowers. The latter conditions should favour high nectar production and mass blooming. The known range of parameters suggests that male fitness increases with the total number of flowers slower than proportionality.
Acetic acid tolerance in Drosophila is a prerequisite for ethanol tolerance
Authors: Th. Eisses Karel , Den Boer Ar A.
Published: December 2004

Acetic acid tolerance compared with ethanol tolerance of Drosophila simulans and six Drosophila melanogaster strains shows a curvilinear relation with apparent asymptotic hyperbolic profile. The upper limit of acetic acid tolerance is lower than that for ethanol. We compared strains which had pairwise identical alcohol dehydrogenase (ADH) coding regions but different genetic backgrounds. A positive regression existed for ethanol tolerance on ADH activity. Adh‐null mutants with very low ethanol tolerances had appreciable acetic acid tolerances and as a consequence did not fit the curve. ADH‐F and ADH‐S strains selected for high ethanol tolerances had the ability to tolerate high ethanol concentrations even after selection had been relaxed for several years. These selected lines tolerated higher acetic acid concentrations than the non‐selected original strains. We propose that intake of high concentrations of ethanol and oxidation into acetic acid induces esterification of ethanol and acetic acid into ethylacetate. This cannot take place after the intake of acetic acid only, which also gives a lower energy yield.
Epistatic selection opposed by immigration in multiple locus genetic systems
Authors: Slatkin Montgomery
Published: December 2004

A model of “complete” epistatis is considered in which all “plus” alleles must be present in an individual before the adaptive phenotype is expressed. The conditions under which the plus alleles and hence the adaptive phenotype can increase and reach a stable equilibrium in the presence of immigration of gametes carrying minus alleles are found. In haploids and diploids in which the plus alleles are recessive, frequencies of the plus alleles are the same at all loci, regardless of the linkage relationships. Tight linkage favors the existence of a locally stable polymorphic equilibrium, but the equilibrium with only minus alleles is locally stable unless there is very tight linkage or very strong selection. Thus, this kind of epistasis, which provides a simple model for a character that requires several components to be present at the same time, is very sensitive to even a small amount of immigration. Hence, the evolution of such characters is likely only in completely rather than partially isolated populations.
An easy method for preserving nucleic acids in field samples for later molecular and genetic studies without refrigerating
Authors: Laulier M. , Pradier E. , Bigot Y. , Périquet G.
Published: December 2004

The nucleic acids in field collected samples of viruses, bacteria, yeasts, invertebrates and vertebrates were well preserved in buffered solution of 4M guanidium‐thiocyanate. This method is particularly suitable for population, epidemiological and parasitological molecular studies. The DNA and RNA from samples kept up to 41 days without refrigeration in this way were suitable for PCR and reverse transcription PCR.
Genetic variation and plasticity of thorax length and wing length in Drosophila aldrichi and D. buzzatii
Authors: Barker J. S. F. , Krebs R. A.
Published: December 2004

Reaction norms across three temperatures of development were measured for thorax length, wing length and wing length/thorax length ratio for ten isofemale lines from each of two populations of Drosophila aldrichi and D. buzzatii. Means for thorax and wing length in both species were larger at 24 °C than at either 18 °C or 31 °C, with the reduction in size at 18 °C most likely due to a nutritional constraint. Although females were larger than males, the sexes were not different for wing length/thorax length ratio. The plasticity of the traits differed between species and between populations of each species, with genetic variation in plasticity similar for the two species from one locality, but much higher for D. aldrichi from the other. Estimates of heritabilities for D. aldrichi generally were higher at 18 °C and 24 °C than at 31 °C, but for D. buzzatii they were highest at 31 °C, although heritabilities were not significantly different between species at any temperature. Additive genetic variances for D. aldrichi showed trends similar to that for heritability, being highest at 18 °C and decreasing as temperature increased. For D. buzzatii, however, additive genetic variances were lowest at 24 °C. These results are suggestive that genetic variation for body size characters is increased in more stressful environments. Thorax and wing lengths showed significant genetic correlations that were not different between the species, but the genetic correlations between each of these traits and their ratio were significantly different. For D. aldrichi, genetic variation in the wing length/thorax length ratio was due primarily to variation in thorax length, while for D. buzzatii, it was due primarily to variation in wing length. The wing length/thorax length ratio, which is the inverse of wing loading, decreased linearly as temperature increased, and it is suggested that this ratio may be of greater adaptive significance than either of its components.
Heritable allometric variation in bumble bees: opportunities for colony‐level selection of foraging ability
Authors: Owen R. E. , Harder L. D.
Published: December 2004

Different characters of an organism may be correlated if genes control the allometric relationship between them. If genetic variation exists for such genes then the allometric relation itself is potentially subject to change by selection. In social insects allometric relations represent colony‐level characters. If colonies differ in these relations and this variation leads to differential productivity among colonies, then selection on allometric relations can operate at the level of the colony. We assessed the extent of heritable, between‐colony variation for the allometric coefficients relating proboscis ( = glossa) length to wing length for two bumble bee species (Bombus huntii and B. occidentalis). We found that in both species colonies did not differ significantly in slope (b) but did differ significantly in intercept (a) of the regression of glossa length on wing length. Within‐colony variation of the intercept was estimated by randomly constituting groups of five workers from each colony and calculating the regression for each group. The intraclass correlation was then calculated from the between‐ and within‐colony mean squares. We found significant intraclass correlations in both species, giving heritabilities of 0.5 ± 0.3 in B. hunti and 0.7 ± 0.3 in B. occidentalis. If this allometric relation affects colony foraging success and foraging environments vary geographically, then the intercept should exhibit corresponding geographic variation. We tested this prediction by comparing intercepts calculated using wild‐caught B. vagans workers from Alberta, Ontario and Maine. We found that the intercepts did differ significantly between sites, with the bees from Alberta having a significantly smaller intercept than the bees from eastern North America. Our results illustrate the opportunity for selection on an allometric relation that directly affects the foraging success of individual bumble bee colonies.
Analysis of the relationship between allozyme heterozygosity and fitness in the rare Gentiana pneumonanthe L.
Authors: Oostermeijer J. G. B. , Van Eijck M. W. , Van Leeuwen N. C. , Den Nijs J. C. M.
Published: December 2004

Especially for rare species occurring in small populations, which are prone to loss of genetic variation and inbreeding, detailed knowledge of the relationship between heterozygosity and fitness is generally lacking. After reporting on allozyme variation and fitness in relation to population size in the rare plant Gentiana pneumonanthe, we present a more detailed analysis of the association between heterozygosity and individual fitness. The aim of this study was to test whether increased fitness of more heterozygous individuals is explained best by the ‘inbreeding’ hypothesis or by the ‘overdominance’ hypothesis. Individual fitness was measured during 8 months of growth in the greenhouse as the performance for six life‐history parameters. PCA reduced these parameters to four main Fitness Components. Individual heterozygosity was scored for seven polymorphic allozyme loci.

For some of these loci (e.g. Aat3, Pgm1 and 6Pgdh2) heterozygotes showed a significantly higher relative fitness than homozygotes. To test the inbreeding model, regression analyses were performed between each Fitness Component and the number of heterozygous loci per individual. Multiple regressions with the adaptive distance of five loci as independent variables were used to test the overdominance model. Only the inbreeding model was a statistically significant explanation for the relationship between heterozygosity and fitness in G. pneumonanthe.

The number of heterozygous loci was significantly negatively correlated with the coefficients of variation of three of the six initially measured fitness parameters. This suggests a lower developmental stability among more homozygous plants and may explain the higher phenotypic variation in small populations of the species observed earlier. The importance of the results for conservation biology is discussed.
Non‐selectivity in extinction of bivalves in the Late Cretaceous of the Atlantic and Gulf Coastal Plain of North America
Authors: McClure M. , Bohonak A. J.
Published: December 2004

It has been suggested that the biogeographic and clade‐level characteristics of marine invertebrate groups important in survival through mass extinctions are different from those important in survival during normal times. The role played by ecologically important characters in survival across mass extinctions, however, has not been well‐studied. We obtained information from the literature about the feeding mode and morphology, burrowing habits, size and depth below sea‐level inhabited, temperature range, shell thickness, species richness and abundance of bivalve genera present in the Late Cretaceous of the Atlantic and Gulf Coastal Plain of North America. Non‐parametric analysis revealed that there were no significant associations between any of these characteristics and survival across the Cretaceous‐Tertiary boundary. This lack of selectivity may be due to varying local conditions, which favor different ecological characteristics in each area and produce no overall pattern of selectivity. It might also be indicative of the severity of this extinction on bivalves — differences in ecological habits may have been virtually irrelevant to survivorship through this event.
A genetic metapopulation model for reef fishes in oceanic islands: the case of the surgeonfish, Acanthurus triostegus
Authors: Planes S. , Galzin R. , Bonhomme F.
Published: December 2004

Allozyme data on a surgeonfish, Acanthurus triostegus, were analysed from 10 islands in French Polynesia. We compared estimates of gene flow according to the hypothesis of an equilibrium between genetic drift and migration, and estimated genetic divergence times assuming complete genetic isolation without gene flow since foundation. The significant correlation between genetic divergence and geographic distance, at the within‐archipelago level (r = 0.709, P = 0.024) indicates exchange of individuals mainly between neighbouring populations. The correlation was, however, not significant at the among‐archipelagoes level (r = 0.325, P = 0.330), suggesting that long distance migrations are more sporadic. This addresses the problem of scale in population biology. According to the spatial scale of analysis, results can change from an island model, with no relation between genetic differentiation and geographical distances between archipelagos, to an isolation‐by‐distance model within an archipelago.

These factors lead us to propose a “patchy population” model, in which all patches are occupied and reproductively active, though with few successful migrations between neighbouring populations. This model describes a subdivided population that is stable through time, with an amount of gene flow small enough to allow significant local differentiation in neutral gene frequency, but high enough to prevent differential fixation in the long term, and therefore preserving the genetic cohesion of the species.
Frequency dependent selection: I. Rare male phenomenon in D. subobscura dependent on the proportion of Amy genotypes and substrate composition
Authors: Terzić T. , Andjelković M. , Marinković D. , Stamenković‐Radak M.
Published: December 2004

Analysis of the rare male mating advantage in D. subobscura, as a type of frequency dependent selection on maltose and starch media, was done by applying different statistical approaches (χ2, cross‐product ratio, variance and regression analysis). They reveal that mating occurs at random when proportions of prospective mates are equal, and that mating success of the males homozygous for Amy‐locus genotypes (S/S and F/F) depends on their proportion. Regression analysis showed that the F/F males are sexually more active (have higher vigour) than S/S males. Rare male effect is one‐sided and appears in F/F males that partake in more heterogamic matings. Comparison of the number of observed and expected homo‐ and heterogamic matings shows that homogamic matings are more frequent. Multifactorial analysis of variance shows that the number of matings are different for nine pairs of lines and four possible mating types (SfSm, SfFm, FfSm, FfFm). The rare male phenomenon is not dependent on different food composition, but is associated with variations in individual genotypes.
Hybrid zones between two genetically differentiated forms of the pond frog Rana lessonae in southern Italy
Authors: Santucci F. , Nascetti G. , Bullini L.
Published: December 2004

Two distinct population groups of the pond frog Rana lessonae were detected in peninsular Italy and Sicily by multilocus electrophoresis: one group inhabits the peninsula down to northern Calabria, the second occurs in southern Calabria and on Sicily. Fixed alternative alleles distinguish the two groups at 5 of the 25 loci examined; marked allele frequency differences were observed at two additional loci. On average, the two groups differ by a Nei's standard genetic distance of 0.4. A wide hybrid zone (about 120 km) occurs between the two groups, with high genotypic diversity and absence of pure parental genotypes in central Calabria. Patterns of allozyme variation suggest that at least two distinct contact and hybridization events occurred, one in the Catanzaro, the other in the Crati‐Sibari plains, about 70 km to the north. Geological evidence indicates that these areas correspond to two main marine‐flooded grabens that would have repeatedly interrupted or reduced genetic exchange during Plio‐Pleistocene times. The finding of a fixed difference at the Mdhp‐1 locus between Sicilian and Calabrian R. lessonae witnesses their continuing differentiation following their last separation by definitive opening of the Strait of Messina, about 50 000 years ago. The wide hybrid zone, the diversity of genotypes and the agreement with Hardy‐Weinberg expectations suggest complete hybrid fertility. Different patterns of introgression were observed at the various loci. The pattern of allelic variation at loci in R. lessonae is paralleled by the pattern of variation in lessonae genomes of the sympatric hemiclonal hybrid Rana esculenta, into which lessonae genomes are introduced each generation as a result of hybridogenesis.
Hypericum cumulicola demography in unoccupied and occupied Florida scrub patches with different time‐since‐fire
Authors: Quintana‐Ascencio Pedro F. , Dolan Rebecca W. , Menges Eric S.
Published: December 2004

1 Metapopulation models predict that unoccupied, but suitable, patches will exist for species subject to extinction and colonization dynamics. We compared the demographic responses of Hypericum cumulicola, a rare herbaceous species almost entirely restricted to Florida rosemary scrub, when transplanted to occupied or unoccupied patches.

2 Seedlings were transplanted and seeds buried into Florida rosemary scrub patches differing in time since last fire, and in the presence or absence of H. cumulicola. We used a replicated, factorial design to place the transplants and seeds in the field, and monitored their performance for 18 months.

3 Neither time‐since‐fire nor prior H. cumulicola site occupancy affected survival of transplants. Only time‐since‐fire affected growth. Time‐since‐fire, H. cumulicola occupancy, and their interaction affected reproductive effort, but these effects were not consistent between years.

4 Flowering and seed production led to subsequent seedling recruitment near transplants, mainly in recently burned sites. Genetic screening of transplants and seedlings showed that transplants in occupied sites could have crossed with nearby resident plants, but that offspring in sites previously unoccupied were likely to have been parented only by nearby transplants.

5 Seeds buried, and later exhumed, germinated after 1 or 2 years of burial, demonstrating a persistent soil seed bank from which populations could recover after fire. Neither time‐since‐fire nor H. cumulicola occupancy affected seed dormancy or germination.

6 Similar demography in unoccupied and occupied patches suggests that the patchy pattern of site occupancy by H. cumulicola is probably due to limited dispersal and periodic extinction, especially associated with long fire‐free intervals. Conservation measures need to protect unoccupied patches to allow metapopulation dynamics and persistence.
Analysis of reticulate relationships within the Daphnia longispina species complex. Allozyme phenotype and morphology
Authors: Gießler S.
Published: December 2004

A two‐step method is proposed to get reliable associations between morphology and genotype in clonal assemblages in which more than two predominantly parthenogenetic species are thought to coexist with hybrids. In dataset 1, the genetic relationships among clones of the Daphnia longispina hybrid complex from seven prealpine lakes in southern Germany were studied based on the variation at 21 enzyme loci. The spatial arrangement in the multidimensional scaling plot revealed a reticulate pattern among three presumably parental species, D. cucullata, D. galeata and D. hyalina, and three hybrid groups, D. cucullata/galeata, D. cucullata/hyalina and D. galeata/hyalina. The Got1 locus was believed to be a discriminating factor between species and hybrids (cf. Wolf and Mort, 1986). However, this locus is more variable, and 57% of the clones would have been misidentified using it. Moreover, the morphological variation within genetically defined groups is also higher than previously assumed. In dataset 2, the revision of morphological and genetic markers greatly improved the association between morphology and genotype in newly collected animals. The spatial arrangement of clones in multidimensional scaling plots and morphological asymmetries to parents suggest both, different degrees of introgression and bidirectional hybridization. Most unexpected genotypes were found in the cxh hybrid group, suggesting that F1‐hybrids are fertile.

The results showed (1) that the clonal diversity was very high (2) that detailed analyses of multiple morphological and allozyme markers are necessary to resolve taxonomic relationships within clonal assemblages consisting of multiple species, hybrids and differently introgressed backcrosses, and (3) that the three original species seem to have sufficient within‐species recombination and a low enough rate of backcrossing to allow taxonomic identification. It must remain undecided if the present situation is locally restricted, if it is stable or represents a transient situation which could lead to either a consolidation of the three species by gradual elimination of the hybrids, to a taxonomic breakdown, or to hybrid speciation.
A note on the timing of tradeoffs in discrete life history models
Authors: Doebeli M. , Blarer A.
Published: December 2004

We discuss the timing of tradeoffs in discrete life history models. With a simple mathematical example we show that different assumptions about the temporal order of costs and benefits resulting from a reproductive effort can lead to qualitatively different predictions. We examine two models taken from the literature, in which an implicit assumption is that benefits from reproductive efforts are received before the corresponding costs are paid. We show that the reverse assumptions would have led to very different results. Since there is no biological basis for a bias towards a particular set of assumptions, we conclude that a more flexible approach should be used when studying optimality problems that are based on discrete life histories.