Analysis of asymmetries in the African fruit bats Eidolon helvum and Rousettus egyptiacus (Mammalia: Megachiroptera) from the islands of the Gulf of Guinea. I. Variance and size components of bilateral variation

A set of cranial characters was examined in the fruit bats Rousettus egyptiacus and Eidolon helvum to compare trends and relative importance of major components of bilateral morphometric variation, and their relationship with character size. Using two‐way, sides‐by‐individuals ANOVA , four components of variation were estimated for each bilateral variable: individual variation (I), directional asymmetry (DA), non‐directional asymmetry (NDA) and measurement error (E). Both species exhibit similar major trends of variation in asymmetry across characters, as shown by principal component analysis, using variance components as variables. Degree of interspecific congruence among characters was confirmed by a two‐way ANOVA with species and variance components as fixed factors. Congruence of asymmetry patterns between species suggests that the concept of population asymmetry parameter (PAP) could be extended to higher hierarchies. PAPs above the species level may result from common mechanisms or similar developmental constraints acting on species’ buffering capacities and morphological integration processes.     

Geography of fluctuating asymmetry in the greenfinch, Carduelis chloris

Levels of fluctuating asymmetry (FA) in 12 bilateral skeletal traits were estimated from 12 populations of greenfinches (Carduelis chloris) collected along a north‐south gradient across Europe. Average FA of measured traits was positively correlated with latitude indicating that the younger and genetically less diverse northern European populations are developmentally less stable than the older and genetically more diverse southern populations. Levels of FA differed significantly between different traits being lowest for functionally important traits (limb and wing bones) and highest for functionally less important traits such as foramina (apertures through bones)– a pattern that was highly concordant across different populations. Males tended to exhibit higher levels of FA than females, a finding consistent with the suggestions that males are more prone to developmental perturbations than females. Age differences in levels of FA were relatively clear, but inconsistent across traits with different degree of functionality. Individual heterozygosity – as enumerated from variation in allozyme loci – was unrelated to individual FA. No evidence for existence of individual asymmetry parameter (IAP) was found although traits related to locomotion indicated some degree of integration, which was expressed by correlations in the signed asymmetry. Nevertheless, an individual's overall asymmetry was poorly predicted by asymmetry of individual characters. Evidence for existence of population asymmetry parameter (PAP) was clear since all traits exhibited a similar degree of association with latitude. That the latitudinal cline of increasing FA towards north coincided with decreasing levels of genetic variability across the cline could be indicative of break down of developmental stability in the recently established and genetically impoverished populations. To what extent a reduced heterozygosity, the break up of co‐adapted gene complexes and/or environmental differences contributed to this process cannot be distinguished from our data.     

Adaptive evolution of lateral plates in three‐spined stickleback Gasterosteus aculeatus: a case study in functional analysis of natural variation

The three‐spined stickleback Gasterosteus aculeatus is a model species for studying questions in ecology and evolution. The rapid diversification of G. aculeatus in post‐glacial freshwater environments, combined with recently developed molecular tools, provides a unique opportunity to study the functional basis of fitness variation in natural populations. In derived freshwater populations, a number of morphological traits have diverged in parallel from the marine ancestral state, including the number of lateral armour plates. Evolution of reduced armour in freshwater populations is due to positive selection from both abiotic and biotic mechanisms. The major effect gene (ectodysplasin‐A or Eda), along with several minor effect genetic regions, has recently been shown to control lateral plate variation. Field experiments have further determined the fitness consequences of allelic variation at the major effect locus. This work helps elucidate the mechanisms connecting genetic variation with phenotypic variation and fitness in the wild, a synthesis that should be applicable to many other phenotypic traits and species of fishes.     

Habitat‐related specialization of lateral‐line system morphology in a habitat‐generalist and a habitat‐specialist New Zealand eleotrid

An investigation of intraspecific habitat‐related patterns of variation in oculoscapular lateral‐line superficial neuromasts (SN) identified a decrease in the ratio of total SNs to pores, and a trend towards decreased asymmetry in SNs in the habitat‐generalist common bully Gobiomorphus cotidianus from fluvial habitats compared to lacustrine habitats, suggesting habitat‐related phenotypic variability. A greater ratio of pores to SNs, as well as less variation in the total number and asymmetry of SNs observed in the fluvial habitat‐specialist redfin bully Gobiomorphus huttoni may provide further evidence of variations in the oculoscapular lateral‐line morphology of fluvial habitat G. cotidianus individuals serving as adaptations to more turbulent environments.     

Homozygosity at a class II MHC locus depresses female reproductive ability in European brown hares

The link between adaptive genetic variation, individual fitness and wildlife population dynamics is fundamental to the study of ecology and evolutionary biology. In this study, a Bayesian modelling approach was employed to examine whether individual variability at two major histocompatibility complex (MHC) class II loci (DQA and DRB) and eight neutral microsatellite loci explained variation in female reproductive success for wild populations of European brown hare (Lepus europaeus). We examined two aspects of reproduction: the ability to reproduce (sterility) and the number of offspring produced (fecundity). Samples were collected from eastern Austria, experiencing a sub‐continental climatic regime, and from Belgium with a more Atlantic‐influenced climate. As expected, reproductive success (both sterility and fecundity) was significantly influenced by age regardless of sampling locality. For Belgium, there was also a significant effect of DQA heterozygosity in determining whether females were able to reproduce (95% highest posterior density interval of the regression parameter [−3.64, −0.52]), but no corresponding effect was found for Austria. In neither region was reproduction significantly associated with heterozygosity at the DRB locus. DQA heterozygotes from both regions also showed a clear tendency, but not significantly so, to produce a larger number of offspring. Predictive simulations showed that, in Belgium, sub‐populations of homozygotes will have higher rates of sterile individuals and lower average offspring numbers than heterozygotes. No similar effect is predicted for Austria. The mechanism for the spatial MHC effect is likely to be connected to mate choice for increased heterozygosity or to the linkage of certain MHC alleles with lethal recessives at other loci.     

Asymmetric size and shape variation in the Central European transect across the house mouse hybrid zone

We studied asymmetric variation of the mandible in the Central European portion of the hybrid zone between two house mouse subspecies, Mus musculus musculus and Mus musculus domesticus. Within introgression classes, defined by the share of diagnostic allozymes, we quantified the directional and fluctuating component of asymmetric variation, as well as skewness and kurtosis of individual asymmetry distributions. Furthermore, in the same manner we re‐analysed asymmetric variation of the ventral side of the skull. According to the quadratic polynomial model, the mandible shape‐fluctuating asymmetry, but not size‐fluctuating asymmetry, was significantly decreased in the centre of the hybrid zone (with a minimum predicted for a hybrid index of 0.41). On the contrary, the skull shape‐fluctuating asymmetry non‐monotonically increased towards the musculus side of the hybrid zone (with a peak predicted for a hybrid index of 0.86). Thus, the impact of hybridization on fluctuating asymmetry is trait‐specific in this portion of the house mouse hybrid zone. The only general feature of asymmetric variation we observed was the shift towards the platykurtosis of asymmetry distributions in the centre of the hybrid zone. Taken together, we suggest genetic variability for right–left asymmetries to be generally increased, but the developmental instability of mandible shape to be decreased, by hybridization. We hypothesize the decrease of developmental instability to be caused by overdominant effects on developmental dynamics rather than by increased heterozygosity. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 13–27.     

Evolutionary history shapes the association between developmental instability and population‐level genetic variation in three‐spined sticklebacks

Developmental instability (DI) is the sensitivity of a developing trait to random noise and can be measured by degrees of directionally random asymmetry [fluctuating asymmetry (FA)]. FA has been shown to increase with loss of genetic variation and inbreeding as measures of genetic stress, but associations vary among studies. Directional selection and evolutionary change of traits have been hypothesized to increase the average levels of FA of these traits and to increase the association strength between FA and population‐level genetic variation. We test these two hypotheses in three‐spined stickleback (Gasterosteus aculeatus L.) populations that recently colonized the freshwater habitat. Some traits, like lateral bone plates, length of the pelvic spine, frontal gill rakers and eye size, evolved in response to selection regimes during colonization. Other traits, like distal gill rakers and number of pelvic fin rays, did not show such phenotypic shifts. Contrary to a priori predictions, average FA did not systematically increase in traits that were under presumed directional selection, and the increases observed in a few traits were likely to be attributable to other factors. However, traits under directional selection did show a weak but significantly stronger negative association between FA and selectively neutral genetic variation at the population level compared with the traits that did not show an evolutionary change during colonization. These results support our second prediction, providing evidence that selection history can shape associations between DI and population‐level genetic variation at neutral markers, which potentially reflect genetic stress. We argue that this might explain at least some of the observed heterogeneities in the patterns of asymmetry.     

Temporal genetic changes between cohorts in a natural population of a marine fish, Diplodus sargus

Temporal changes at 17 allozyme loci in the Diplodus sargus population of Banyuls sur Mer (Mediterranean Sea, France) were monitored within a single population among ten year‐classes (cohorts) sampled over a 6‐month period. The genetic survey was combined with evaluation of the demographic structure of the population by determining variation of abundance between cohorts. The population showed variation in abundance among cohorts ranging from 16 to 214 individuals. Significant divergences in genetic structure were observed between cohorts (P < 0.0001) despite very low values of F_ST (multilocus F_ST over all cohorts = 0.0018). The heterozygosity of each cohort, as well as the F_IS values, was significantly correlated with the abundance of each cohort, with abundant cohorts showing lower heterozygosity and a significant deficit of heterozygotes (positive F_IS values). Finally, multilocus temporal genetic variance (F_k) computed between successive cohorts was higher in low abundance cohorts. Change of heterozygosity between cohorts, distribution of year‐class genetic structure, and change in the genetic structure within a cohort appear to be affected mostly by the abundance of the cohort and are therefore driven by genetic drift. We propose that the Diplodus sargus cohorts are built up from the mixing of families during the pelagic stage or later during recruitment, and that the decrease in heterozygosity leading to a deficit of heterozygotes is characteristic of a Wahlund effect. Such a Wahlund effect would derive from the mixing of the progeny of families made up of few individuals, but exhibiting high fecundity and high variability of reproductive success. Therefore, although cohorts derived from poor recruitment would only group a few families and would exhibit limited deficit of heterozygotes (higher heterozygosity values), they would lead to high genetic drift and appear more divergent (higher mean temporal genetic variance) than cohorts with high abundance. While not demonstrating directly the family structure of marine populations, our survey provides evidence of highly structured populations. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76 , 9–20.     

MULTIPLE EVOLUTIONARY PATHWAYS TO DECREASED LATERAL PLATE COVERAGE IN FRESHWATER THREESPINE STICKLEBACKS

Adaptation to novel environments can be based either on standing genetic variation or variation attributable to new mutations. When standing genetic variation for a functional adaptation is lacking, and variation due to new mutations is not yet available, adaptation is possible only through alternative functional solutions. Reduction in the number of bony lateral plates as an adaptation to freshwater colonization by marine threespine sticklebacks (Gasterosteus aculeatus) has occurred in numerous independent cases through allelic substitution in the ectodysplasin‐a (Eda) gene. Studying the phenotypic and genetic variation in plate number and size in five marine and six freshwater threespine stickleback populations, we found that when variation in Eda was limiting (i.e., alleles associated with the low‐plate morph were missing or in extremely low frequency), plate number reduction did not take place in freshwater populations, but reduced lateral plate coverage was achieved by a reduction in the size of lateral plates. Our results suggest that this phenotypically and genetically discrete "small‐plated" threespine stickleback—which is the dominant form in three northern European freshwater populations—may be functionally equivalent to the low‐plated morph and hence, serve as an example of convergent evolution toward functional similarity in the face of genetic constraints.     

Spatial patterning of bone stiffness in the anterior mandibular corpus of Macaca fascicularis: Implications for models of bone adaptation

Elastic modulus of bone from the anterior mandibular corpus was determined via microindentation in a mixed-sex ontogenetic sample (N = 14) of Macaca fascicularis. This investigation focused on the hypothesis that material heterogeneity in the macaque mandibular symphysis—provided an accounting of age and sex variation—is explicable as a means to homogenize strains in this region. Experimental data and theoretical models of masticatory loading indicate that in the absence of material compensation, large strain gradients exist in the anterior mandibular corpus of macaques, particularly between lingual and labial cortical plates owing to the effects of lateral transverse bending. Microindentation data indicate that juvenile macaques possess less stiff bone than their subadult and adult counterparts; however, sex differences in elastic modulus are not apparent. Anisotropy variation is idiosyncratic; that is, there is not a common pattern of variation in stiffness sampled among orthogonal planes across individuals. Similarly, differences in stiffness between lingual and labial cortical plates, as well as differences among alveolar, midcorpus, and basal regions are inconsistently observed. Consequently, we find little evidence in support of the hypothesis that spatial variation in bone stiffness functions to homogenize strains in the anterior corpus; in fact, in some individuals, this spatial variation serves to exacerbate, rather than to minimize, strain gradients. The mechanical benefit of elastic modulus variation in the macaque mandibular symphysis is unclear; this variation may not confer adaptive benefit in terms of structural integrity despite the fact that such variation has discernible functional consequences. Am J Phys Anthropol 156:649–660, 2015. © 2014 Wiley Periodicals, Inc.     

Genetic variation within and between populations of hermaphroditic <Emphasis Type="Italic">Bulinus truncatus</Emphasis> tetraploid freshwater snails of the Albertine Rift,East Africa

Genetic variability within and among Bulinus truncatus of the Albertine Rift freshwater bodies were assessed to investigate the degree of inbreeding and gene flow in the snail populations. The effect of ploidy on the genetic structuring of B. truncatus is also described. We characterized the genetic structure of seven B. truncatus populations from Lake Albert, Lake Kivu, and Katosho swamp in Tanzania using five polymorphic microsatellite loci. Genetic differentiation was quantified using pairwise FST values and Nei’s standard genetic distances. Different alleles were observed across all loci and genetic diversity was low although it varied greatly across populations; observed heterozygosity was, however, higher than the expected heterozygosity in three of the populations studied. Significant heterozygote deficiencies were observed coupled with significant linkage disequilibria in five populations for all the five loci examined in this study. We found significant genetic differentiation among the seven freshwater bodies; private alleles were observed across all loci indicating restricted or absence of gene flow between populations. Limited snail dispersal and the reproductive biology of B. truncatus are the major forces shaping the genetic variation observed. Low genetic variation within B. truncatus populations exposes them to a high parasite infection risk as predicted in the Red Queen hypothesis.     

Genetic variation and spatial structure in sugar maple (Acer saccharum Marsh.) and implications for predicted global-scale environmental change

Current ecosystem model predictions concerning the effects of global temperature increase on forest responses do not account for factors influencing long‐term evolutionary dynamics of natural populations. Population structure and genetic variability may represent important factors in a species' ability to adapt to global‐scale environmental change without experiencing major alterations in current range limits. Genetic variation and structure in sugar maple (Acer saccharum Marsh.) were examined across three regions, between two stands within regions, and among four to five open‐pollinated families within stands (total N = 547 genotypes) using 58 randomly amplified polymorphic DNA (RAPD) markers. Differences within open‐pollinated families account for the largest portion of the total variation (29%), while differences among regions represent less than 2% of the total variation. Genetic diversity, as indicated by estimates of percent polymorphic loci, expected heterozygosity, fixation coefficients, and genetic distance, is greatest in the southern region, which consists of populations with the maximum potential risk due to climate change effects. The high level of genetic similarity (greater than 90%) among some genotypes suggests that gene flow is occurring among regions, stands, and families. High levels of genetic variation among families indicate that vegetational models designed to predict species' response to global‐scale environmental change may need to consider the degree and hierarchical structure of genetic variation when making large‐scale inferences.     

Polymorphic microsatellite loci in Lithophragma maximum (Saxifragaceae), an endemic plant of San Clemente Island

In this paper, we report the isolation of 11 polymorphic microsatellite loci from Lithophragma maximum (Saxifragaceae), a rare species restricted to San Clemente Island, California. We found moderate levels of allelic variation (mean N_A= 5.5) and high levels of expected heterozygosity (mean H_E= 0.531) across sampled individuals. However, eight loci showed a significant absence of heterozygous individuals, which we attribute to small population size and demographic history of the species.     

Lateral plate asymmetry,diet and parasitism in threespine stickleback

Individuals with random left–right departures from bilateral symmetry are predicted to exhibit fitness reduction including increased parasitism. In an insular lake population of stickleback (Gasterosteus aculeatus) from the Queen Charlotte Islands, Western Canada, phenotypes with high or low number of lateral bony plates exhibited increased plate asymmetry relative to modal phenotypes. Asymmetric lateral plate phenotypes had increased prevalence and to a lesser extent intensity of parasitism relative to symmetric individuals, suggesting that differences in genetic resistance to pathogens contributed to unequal parasitism. The effect occurred mainly in the larger adults and during the warmest season, which may be due to the high metabolic costs incurred during the summer breeding season. Dietary differences between symmetric and asymmetric phenotypes were also detected and could contribute to unequal infection rates by mediating exposure to infected prey items. Our study, which is one of the first long‐term field assessments of asymmetry and parasitism, yields results that are consistent with studies linking asymmetry to reduced fitness and indicate that lateral plate asymmetry can be an indicator of poor individual quality, despite its apparent directionality.     

Evolutionary consequences of ecological factors: pollinator reliability predicts mating‐system traits of a perennial plant

The reproductive‐assurance hypothesis predicts that mating‐system traits will evolve towards increased autonomous self‐pollination in plant populations experiencing unreliable pollinator service. We tested this long‐standing hypothesis by assessing geographic covariation among pollinator reliability, outcrossing rates, heterozygosity and relevant floral traits across populations of Dalechampia scandens in Costa Rica. Mean outcrossing rates ranged from 0.16 to 0.49 across four populations, and covaried with the average rates of pollen arrival on stigmas, a measure of pollinator reliability. Across populations, genetically based differences in herkogamy (anther–stigma distance) were associated with variation in stigmatic pollen loads, outcrossing rates and heterozygosity. These observations are consistent with the hypothesis that, when pollinators are unreliable, floral traits promoting autonomous selfing evolve as a mechanism of reproductive assurance. Extensive covariation between floral traits and mating system among closely related populations further suggests that floral traits influencing mating systems track variation in adaptive optima generated by variation in pollinator reliability.     

Latitudinal shifts in body size of Enallagma cyathigerum (Odonata)

Aim Survey of the latitudinal body size pattern for populations of Enallagma cyathigerum (Odonata) across a south‐north transect. Location A transect covering the whole distribution range from south to north across Europe was sampled. Methods Newly emerged adults were collected from five major sites across Europe and one to four localities were sampled within each site. In total 253 adults were collected from fourteen localities. Body size was measured using thorax length, length of right front wing and length of right hind tibia. These body size estimates were thereafter related to latitude and mean temperature in January and July. Results Body size showed a U‐shaped pattern with latitude, being large at low and high latitudes and small at intermediate latitudes. The same U‐shaped pattern was found for mean January and July temperature, with large animals at low and high temperatures. Conclusion The U‐shaped relationship between body size and latitude is suggested to be a combination of two effects: (1) the length of the season favourable for growth and development, and (2) variation in life cycle length with latitude.     

Morphometric and genetic variation of small dwarf honeybees Apis andreniformis Smith, 1858 in Thailand

The small dwarf honey bee, Apis andreniformis, is a rare and patchily distributed Apis spp. and is one of the native Thai honey bees, yet little is known about its biodiversity. Thirty （27 Thai and 3 Malaysian） and 37 （32 Thai and 5 Malaysian） colonies of A. andreniformis were sampled for morphometric and genetic analysis, respectively. For morphometric analysis, 20 informative characters were used to determine the variation. After plotting the factor scores, A. andreniformis from across Thailand were found to belong to one group, a notion further supported by a cluster analysis generated dendrogram. However, clinal pattems in groups of bee morphometric characters were revealed by linear regression analysis. The body size of bees increases from South to North but decreases from West to East, although this may reflect altitude rather than longitude. Genetic variation was determined by sequence analysis of a 520 bp fragment of the mitochondrial cytochrome oxidase subunit b （cytb）. DNA polymorphism among bees from the mainland of Thailand is lower than that from Phuket Island and Chiang Mal. Although two main different groups of bees were obtained from phylogenetic trees constructed by neighbor-joining and unweighted pair-group method using arithmetic averages programs, no clear geographic signal was present. Thus, while the minor group （B） contained all of the samples from the only island sampled （Phuket in the south）, but not the southem mainland colonies, it also contained samples from the far northem inland region of Chiang Mai, other samples of which were firmly rooted in the major group （A）.     

Contrasting heterozygosity‐fitness correlations across life in a long‐lived seabird

Selection is a central force underlying evolutionary change and can vary in strength and direction, for example across time and space. The fitness consequences of individual genetic diversity have often been investigated by testing for multilocus heterozygosity‐fitness correlations (HFCs), but few studies have been able to assess HFCs across life stages and in both sexes. Here, we test for HFCs using a 26‐year longitudinal individual‐based data set from a large population of a long‐lived seabird (the common tern, Sterna hirundo), where 7,974 chicks and breeders of known age were genotyped at 15 microsatellite loci and sampled for life‐history traits over the complete life cycle. Heterozygosity was not correlated with fledging or post‐fledging prospecting probabilities, but was positively correlated with recruitment probability. For breeders, annual survival was not correlated with heterozygosity, but annual fledgling production was negatively correlated with heterozygosity in males and highest in intermediately heterozygous females. The contrasting HFCs among life stages and sexes indicate differential selective processes and emphasize the importance of assessing fitness consequences of traits over complete life histories.     

MHC,mate choice and heterozygote advantage in a wild social primate

Preferences for mates carrying dissimilar genes at the major histocompatibility complex (MHC) may help animals increase offspring pathogen resistance or avoid inbreeding. Such preferences have been reported across a range of vertebrates, but have rarely been investigated in social species other than humans. We investigated mate choice and MHC dynamics in wild baboons (Papio ursinus). MHC Class II DRB genes and 16 microsatellite loci were genotyped across six groups (199 individuals). Based on the survey of a key segment of the gene‐rich MHC, we found no evidence of mate choice for MHC dissimilarity, diversity or rare MHC genotypes. First, MHC dissimilarity did not differ from random expectation either between parents of the same offspring or between immigrant males and females from the same troop. Second, female reproductive success was not influenced by MHC diversity or genotype frequency. Third, population genetic structure analysis revealed equally high genotypic differentiation among troops, and comparable excess heterozygosity within troops for juveniles, at both Mhc‐DRB and neutral loci. Nevertheless, the age structure of Mhc‐DRB heterozygosity suggested higher longevity for heterozygotes, which should favour preferences for MHC dissimilarity. We propose that high levels of within‐group outbreeding, resulting from group‐living and sex‐biased dispersal, might weaken selection for MHC‐disassortative mate choice.