bluuebunny/crossref_metadata_2025_split huggingface dataset:
Population divergence and morphometric integration in the greenfinch (Carduelis chloris) – evolution against the trajectory of least resistance?
Authors: Merilä  , Björklund  
Published: March 2003

Abstract
Theory predicts that genetic and phenotypic correlations among traits may direct the process of short-term evolution by limiting the directions of variation available to natural selection to act on. We studied correlations between 14 skeletal traits in 10 geographically distinct and relatively young greenfinch (Carduelis chloris) populations to unravel whether the divergence among populations has occurred into directions predicted by the within-population correlations (cf. drift/correlated responses models), or whether it is better explained by ‘adaptive’ models, which predict no necessary association between within- and among-population correlations (allometries). We found that the within-population character correlations (or covariances) did not predict character divergence between populations. This was because the first eigenvector of the among-population correlation/covariance matrix, summarizing the major dimension of divergence, was a bipolar body:beak dimension, and distinct from the (≈ isometric) first eigenvector of within-population matrix. Hence, as the divergence among greenfinch populations cannot be satisfactorily accommodated by drift/correlated response models, an adaptive basis for divergence is suggested. The second major axis of within-population variation was a classical ‘group size’ factor revealing that beak size was more or less free to vary independently of body size. Consequently, even if the divergence among populations cannot be simply accommodated to expectations of drift and correlated response models, it is striking that the most pronounced size-independent (nonallometric) changes had occurred along the second largest dimension of variance. This could mean that selection pressures which shape integration within populations are the same as those that cause divergence among populations. A relaxed beak:body integration could also occur as a result of species level selection favouring taxa in which independent evolution of beak and body is made possible.
Mate search and aggregation behaviour in the Galician hybrid zone of Littorina saxatilis
Authors: Erlandsson J. , Kostylev V. , Rolán-Alvarez E. 
Published: March 2003

Abstract
In Galician rocky shores two ecotypes of the snail L. saxatilis can be found in sympatry. A ridged and banded ecotype (RB-morph) and a smooth and unbanded ecotype (SU-morph) overlap in midshore with the production of some hybrids. The distinct morphs mate assortatively and there is evidence of a partial reproductive barrier between them. This sexual isolation is caused by a nonrandom microdistribution and mate choice behaviour. Mucus trail-following, movement rate and aggregation behaviour were studied to determine their roles in the mating behaviour and sexual isolation of this species. Morph-specific mucus trail-following could not, in our experiments, explain either of these two processes. The reasons for the aggregation of morphs were investigated by Monte Carlo simulations of data from natural populations, which showed that size aggregation (refuge sizes fit different sized morphs differently) could explain only about 36% of the morph aggregation in adult snails. In the laboratory, morph aggregation was still present, and simulations suggested that size aggregation was the possible explanation. Thus, morph aggregation in Galician L. saxatilis has to be explained also by other causes in addition to size aggregation. These may be a combination of contrasting preferences for barnacle and mussel patches in the two morphs, and possibly longer copulation and pair formation time with similar sized snails of the same morph. Thus aggregation behaviour, but not trail-following, contributes to incipient reproductive isolation and perhaps sympatric speciation in Galician L. saxatilis populations.
Ecology and evolution of extravagant feather ornaments
Authors: Cuervo J. J. , Møller A. P. 
Published: March 2003

Abstract
The ancestral conditions that permit the evolution of extravagant secondary sexual characters are of considerable theoretical and empirical interest because they allow identification of necessary ecological conditions, but also allow empirical tests of models of female mate preferences. We investigated the ancestral and derived state of a range of ecological and evolutionary variables that might have been implicated in the evolution of secondary sexual characters. Extravagant feather ornaments have evolved independently at least 70 times in birds, and the context of these evolutionary events was investigated statistically. The acquisition of feather ornaments was significantly associated with a change in social mating system from monogamy to polygyny or lekking. This association is consistent with the Fisherian mechanism of sexual selection. However, very often also the acquisition of feather ornaments occurred without change in mating system. Therefore, ornamentation can develop for reasons other than polygyny. We did not find any indication of male parental care, kind of food, foraging mode, coloniality, nest site, migration or body mass being significantly associated with a change in the state of ornamentation.
Rate of deleterious mutation and the distribution of its effects on fitness in vesicular stomatitis virus
Authors: Elena  , Moya  
Published: March 2003

Abstract
Despite their importance, the parameters describing the spontaneous deleterious mutation process have not been well described in many organisms. If mutations are important for the evolution of every living organism, their importance becomes critical in the case of RNA-based viruses, in which the frequency of mutation is orders of magnitude larger than in DNA-based organisms. The present work reports minimum estimates of the deleterious mutation rate, as well as the characterization of the distribution of deleterious mutational effects on the total fitness of the vesicular stomatitis virus (VSV). The estimates are based on mutation-accumulation experiments in which selection against deleterious mutations was minimized by recurrently imposing genetic bottlenecks of size one. The estimated deleterious mutation rate was 1.2 mutations per genome and generation, with a mean fitness effect of –0.39% per generation. At the end of the mutation-accumulation experiment, the average reduction in fitness was 38% and the distribution of accumulated deleterious effects was, on average, left-skewed. The magnitude of the skewness depends on the initial fitness of the clone analysed. The implications of our findings for the evolutionary biology of RNA viruses are discussed.
Optimal timing of first reproduction in parasitic nematodes
Authors: Gemmill  , Skorping  , Read  
Published: March 2003

Abstract
The time between infection and the onset of reproduction (maturation time) is a key determinant of body size, fecundity and generation time in parasitic nematodes. An optimality model for maturation time is developed centred on prematurational growth, the duration of which has opposing consequences for fecundity and for survival to reproductive age. The maturation time favoured by natural selection is found to be inversely proportional to prematurational mortality rate. The product of maturation time and mortality rate is predicted to be an invariant number equal to the allometric slope linking daily fecundity to maturation time. Predictions are tested using comparative data on mammalian gastrointestinal nematode taxa. Half the cross-species variation in prepatent period (the time from infection until propagules are shed from the host) is accounted for by this adaptive trade-off hypothesis, even though many biological details are not explicitly modelled. These results are discussed in the light of previous studies and in the context of general models of life history evolution.
Pollinator behaviour and the evolution of Louisiana iris hybrid zones
Authors: Wesselingh  , Arnold  
Published: March 2003

Abstract
Pollinator preference may influence the origin and dynamics of plant hybrid zones. Natural hybrid populations between the red-flowered Iris fulva and the blue-flowered Iris brevicaulis are found in southern Louisiana. The genetic structure of these populations reflects a lack of intermediate genotypes. We observed pollinator behaviour in an experimental array with five plants each of I. fulva, I. brevicaulis, their F1, and the first backcross generation in each direction, to obtain data on flower type preferences and transitions between flower types. The most abundant visitors were Ruby-throated Hummingbirds (Archilochus colubris) and workers of the bumblebee Bombus pennsylvanicus. Hummingbirds visited I. fulva twice as often as I. brevicaulis and visited hybrids at intermediate frequencies. Bumblebee workers preferred the purple-flowered F1s and visited plants of I. fulva and the backcross to I. fulva more often than I. brevicaulis and its backcross. Overall, F1 flowers were visited most frequently. Both hummingbirds and bumblebees visited nearest neighbours in almost 80% of the interplant movements. This meant that a majority of movements were between different flower types, rather than between plants of the same type. Findings from the present study suggest that pollinator preference is not a major causal factor for the lack of intermediate genotypes in natural iris hybrid populations. Instead, pollinator behaviour in our array promoted mixed mating between flower types belonging to different pollination syndromes. However, owing to predominant nearest-neighbour visitation, the spatial distribution of parental and hybrid genotypes (in concert with pollinator behaviour) will have a strong influence on mating patterns and thus the genotypic structure and evolution of Louisiana iris hybrid zones.
High-prevalence male-killing Wolbachia in the butterfly Acraea encedana
Authors: Jiggins  , Hurst  , Dolman  , Majerus  
Published: March 2003

Abstract
Inherited bacteria which kill males during early development are widely distributed throughout the insects, but have been little studied outside of a single family of beetles, the Coccinellidae. We have investigated a male-killing bacterium discovered in the butterfly Acraea encedana. This bacterium belongs to the genus Wolbachia and is identical in wsp gene sequence to a male-killer in the closely related butterfly A. encedon, suggesting that it has either recently moved between host species or was inherited from a common ancestor of the butterflies. The prevalence of Wolbachia is remarkably high, 95% of females are infected and only 6% of wild caught butterflies are male. Measurements of the vertical transmission efficiency were used to calculate that this high prevalence is the result of infected females producing at least 1.79 times the number of surviving daughters as uninfected females (lower confidence limit is 1.25).
Mass-dependent reproductive strategies in wild bighorn ewes: a quantitative genetic approach
Authors: RÉale  , Festa-Bianchet  
Published: March 2003

Abstract
In the Ram Mountain bighorn sheep (Ovis canadensis) population, ewes differing by more than 30% in body mass weaned lambs with an average mass difference of only 3%. Variability in adult body mass was partly due to additive genetic effects, but inheritance of weaning mass was weak. Maternal effects could obscure genetic effects in the phenotypic expression of weaning mass, particularly if they reflected strategies of maternal expenditure that varied according to ewe mass. We performed a quantitative genetic analysis to assess genetic and environmental influences on ewe mass and on maternal expenditure. We used the mean daughters/mother regression method and Derivative Free Restricted Maximum Likelihood models to estimate heritability (h2) of ewe mass and indices of maternal expenditure. We found additive genetic effects on phenotypic variation in maternal mass, in lamb mass at weaning (absolute maternal expenditure) and in weaning mass relative to maternal mass at weaning (relative maternal expenditure). Heritability suggests that maternal expenditure has the potential to evolve. The genetic correlation of ewe mass and absolute maternal expenditure was weak, while ewe mass and relative maternal expenditure were strongly negatively correlated. These results suggest additive genetic effects on mass-dependent reproductive strategies in bighorn ewes. Mass-dependent reproductive strategies could affect lamb survival and phenotypic variation in adult mass. As population density increased and reproduction became costlier, small females reduced maternal expenditure more than large females. Constraints on reproductive strategy imposed by variations in resource availability are therefore likely to differ according to ewe mass. A general trend for a decrease in maternal expenditure relative to maternal size in mammals suggests that size-dependent negative maternal effects may be common.
Temporal and microspatial variation in the intensities of natural and sexual selection in the yellow dung fly Scathophaga stercoraria
Authors: Jann P. , Blanckenhorn W. U. , Ward P. I. 
Published: March 2003

Abstract
Studies of phenotypic selection in natural populations often concentrate only on short time periods and do not quantify selection intensities. We quantified temporal and microspatial variation in the intensities of natural and sexual selection for body size in the yellow dung fly over 2 years. Female fecundity selection intensity remained approximately constant over the season with an overall mean ± SE of 0.187 ± 0.014. Selection intensity for male reproductive success, defined as eggs obtained by mating males, did not differ from zero, indicating there was no assortative mating by size. Sexual selection intensity for male mating success favouring large males was variable but overall strong in the two years (0.499 ± 0.053 and 0.510 ± 0.051). As theoretically expected for male–male competition, sexual selection intensity increased with competitor density and reached an asymptote at about 250 males per pat; it also decreased with time in spring and increased again in autumn as a function of density. Small males had the best chance of obtaining a female at very low male densities. Greater selection intensity for large size in males than females is consistent with, and might be responsible for, the observed sexual size dimorphism in this species, as males are larger. The seasonal pattern of mean male body size (smallest at the beginning and end of the season) most likely reflects mere environmental (primarily temperature) influences on phenotypic size.
The paternal-sex-ratio (PSR) chromosome in natural populations of Nasonia (Hymenoptera: Chalcidoidea)
Authors: Beukeboom L. W. , Werren J. H. 
Published: March 2003

Abstract
Selfish genetic elements may be important in promoting evolutionary change. Paternal sex ratio (PSR) is a selfish B chromosome that causes all-male families in the haplodiploid parasitic wasp Nasonia vitripennis, by inducing paternal genome loss in fertilized eggs. The natural distribution and frequency of this chromosome in North American populations of N. vitripennis was investigated using a combination of phenotypic and molecular assays. Sampling throughout North America failed to recover PSR except from populations in the Great Basin area of western North America. Extensive sampling of Great Basin populations revealed PSR in frequencies ranging from 0 to 6% at different collection sites, and extended its distribution to Idaho and Wyoming. Intensive sampling in upstate New York did not detect the chromosome. Frequencies of the maternal-sex ratio distorter (MSR), son killer (SK) and virgin females ranged from 0 to 12%. Paternal sex ratio may be restricted to the Great Basin because its spread is hampered by geographical barriers, or because populations in other areas are not conducive to PSR maintenance. However, it cannot be ruled out that PSR occurs in other regions at very low frequencies. The apparent limited distribution and low frequency of PSR suggest that it will have relatively little impact on genome evolution in Nasonia.
Experimental analysis of an early life-history stage: avian predation selects for larger body size of hatchling turtles
Authors: Janzen F. J. , Tucker J. K. , Paukstis G. L. 
Published: March 2003

Abstract
One common life-history pattern involves an elevated rate and nonrandom distribution of neonatal mortality. However, the mechanisms causing this pattern and the specific traits that confer a survival benefit are not always evident. We conducted a manipulative field experiment using red-eared slider turtles to test the hypothesis that diurnal avian predators are a primary cause of size-specific neonatal mortality. Body size was a significant predictor of recapturing hatchlings alive and of finding hatchlings dead under natural conditions, but was unimportant when diurnal predators were excluded from the field site. Overall recapture rates also more than doubled when predators were excluded compared to natural conditions (72.4 vs. 34.9%). We conclude that birds are an important cause of size-specific mortality of recently emerged hatchling turtles and that ‘bigger is better’ in this system, which has important implications for life-history evolution in organisms that experience size-specific neonatal mortality.
Macroevolution of hoverflies (Diptera: Syrphidae): the effect of using higher-level taxa in studies of biodiversity, and correlates of species richness
Authors: Katzourakis A. , Purvis A. , Azmeh S. , Rotheray G. , Gilbert F. 
Published: March 2003

Abstract
We test a near-complete genus level phylogeny of hoverflies (Diptera: Syrphidae) for consistency with a null model of clade growth having uniform probabilities of speciation and extinction among contemporaneous species. The phylogeny is too unbalanced for this null model. Importantly, the degree of imbalance in the phylogeny depends on whether the phylogeny is analysed at the genus level or species level, suggesting that genera ought not to be used uncritically as surrogates for species in large-scale evolutionary analyses. Tests for a range of morphological, life-history and ecological correlates of diversity give equivocal results, but suggest that high species-richness may be associated with sexual selection and diet breadth. We find no correlation between species-richness and either body size or reproductive rate.
Genotype-by-environment interaction and the Dobzhansky–Muller model of postzygotic isolation
Authors: Bordenstein S. R. , Drapeau M. D. 
Published: March 2003

Abstract
The Dobzhansky–Muller (D–M) model of reproductive isolation (RI) posits that hybrid sterility and inviability result from negative epistatic interactions between alleles at a minimum of two genes. This standard model makes several implicit assumptions, including a lack of environmental effects and genotype-by-environment interactions (GEI) involving hybrid sterility and hybrid inviability loci. Here we relax this assumption of the standard D–M model. By doing so, several patterns of the genetic architecture of RI change. First, a novel single-locus model of postzygotic RI emerges. Several indirect lines of evidence are discussed in support of the model, but we conclude that this new single-locus model is currently no more supported than previous ones. Second, when multilocus D–M models incorporating GEI are considered, we find that the number of potential negative epistatic interactions increases dramatically over the number predicted by the standard D–M model, even when only the most simple case of two-allele interactions are considered. Third, these multilocus models suggest that some previous generalizations about the evolutionary genetics of postzygotic RI may not necessarily hold. Our findings also suggest that the evolution of postzygotic RI may be more likely when the expression of traits driving speciation is affected by the environment, since there appears to be a greater spectrum of potential hybrid incompatibilities under the D–M model incorporating GEI.
DNA variation at the rp49 gene region in Drosophila madeirensis and D. subobscura from Madeira: inferences about the origin of an insular endemic species
Authors: Khadem M. , Rozas J. , Segarra C. , Aguadé M. 
Published: March 2003

Abstract
An ~1.6-kb fragment spanning the rp49 gene was sequenced in 16 lines of Drosophila subobscura from Madeira and in 22 lines of the endemic species D. madeirensis. Nucleotide diversity in D. subobscura from Madeira (π=0.0081) was similar to that in lines from Spain carrying the O3+4 chromosomal arrangement (π=0.0080). No significant genetic differentiation was detected between insular and continental O3+4 lines of D. subobscura. These results are compatible both with a rather recent and massive colonization, and with multiple colonization events from the continent. Nucleotide diversity in D. madeirensis (π=0.0076) was similar to that in D. subobscura, which deviates from the expectation, under strict neutrality, of a lower level of variation in an insular species with a small population size. The observed numbers of shared polymorphisms and of fixed differences between D. madeirensis and D. subobscura are compatible with the isolation model of speciation, where shared polymorphisms are due to common ancestry.
Combining mitochondrial DNA sequences and morphological data to infer species boundaries: phylogeography of lanceheaded pitvipers in the Brazilian Atlantic forest, and the status of Bothrops pradoi (Squamata: Serpentes: Viperidae)
Authors: Puorto G. , Da Graça Salomão M. , Theakston R. D. G. , Thorpe R. S. , Warrell D. A. , Wüster W. 
Published: March 2003

Abstract
Phylogeographic studies using mitochondrial DNA sequence information are frequently used as the principal source of evidence to infer species boundaries. However, a critical analysis of further evidence is essential to test whether different haplotype clades identify different species. We demonstrate a hypothesis-testing approach, using a combination of phylogeographic methods, multivariate morphometrics and matrix association tests, to investigate species boundaries in eastern Brazilian pitvipers conventionally assigned to the species Bothrops leucurus and B. pradoi. Two basal haplotype clades with partly overlapping geographical distributions are identified, which could either represent two partly sympatric species, or multiple haplotypes within one organismal lineage. We use partial Mantel matrix association tests to verify whether generalized morphology, or any of four supposedly diagnostic characters for the two species, show any association with mtDNA variation. Negative results lead to the conclusion that the haplotype clades do not denote independently evolving organismal lineages, and do not constitute separate species under any criterion.
Sexual selection on phenotypic traits in a hybrid zone of Littorina saxatilis (Olivi)
Authors: Cruz R. , Rolán-Álvarez E. , García C. 
Published: March 2003

Abstract
Step clinal transitions in inherited character(s) between genetically distinct populations are usually referred to as hybrid zones. An example is found in the population of the intertidal snail Littorina saxatilis in Galicia (NW Spain). We studied the shape of the overall fitness surface for sexual selection in this hybrid zone, and the position of hybrids and pure morphs on this surface. We found that sexual divergent selection acted on a combination of phenotypic traits separating the pure morphs, and therefore that sexual selection contributed to morph differentiation. The average fitness of hybrids as a group was not significantly different from that of the pure morphs, but they did show divergent sexual selection in some traits. These results are in agreement with a model of divergent selection favouring both the pure morph as well as those hybrids most resembling each morph. The finding of divergent selection is remarkable because quadratic selection gradients are usually weak in nature.