MORPHOMETRIC ADAPTATION OF THE HOUSEFLY, MUSCA DOMESTICA L., IN THE UNITED STATES

Evolutionary convergence in body shape obscures taxonomic diversity in species of the African Labeo forskalii group: Case study of L. parvus Boulenger 1902 and L. ogunensis Boulenger 1910

Labeo is the third most diverse genus of African cyprinids and is widely distributed across the continent. Labeo parvus, a small species originally described from the Congo basin, has been considered the only species of the L. forskalii group distributed across five African ichthyofaunal provinces (Nilo-Sudan, Congo, Cuanza, and Upper and Lower Guinea). However, morphological similarity between L. parvus and numerous congeners remains a central cause of taxonomic confusion within the genus. Here we employed a phylogenetic comparative approach to assess phenotypic convergence among species of the L. forskalii group, investigate the taxonomic status of L. parvus sensu lato (sl) in west Africa, and reevaluate the composition and distribution of L. parvus sensu stricto (ss). Our phylogenetic analysis provides no support for a sister relationship between L. parvus ss and any of the west African Labeo parvus-like species. Geometric morphometric and molecular phylogenetic data indicate that L. parvus ss is a Congo basin endemic, and seemingly ecologically equivalent species found in west Africa are L. ogunensis, L. obscurus and other undescribed or previously synonymized species. We discuss our findings in terms of convergent evolution using phylomorphospace and tests for phylogenetic signal.

A Theory of City Biogeography and the Origin of Urban Species

Many of the choices humans make with regard to infrastructure, urban planning and other phenomena have impacts that will last thousands of years. This can readily be seen in modern cities in which contemporary streets run along street grids that were laid out thousands of years prior or even in which ancient viaducts still play a role. However, rarely do evolutionary biologists explicitly consider the future of life likely to be associated with the decisions we are making today. Here, we consider the evolutionary future of species in cities with a focus on the origin of lineages and species. We do so by adjusting evolutionary predictions from the theory of island biogeography so as to correspond to the unique features of cities as islands. Specifically, the species endemic to cities tend to be associated with the gray habitats in cities. Those habitats tend to be dominated by human bodies, pet bodies and stored food. It is among such species where the origin of new lineages is most likely, although most research on evolution in cities has focused on green habitats. We conclude by considering a range of scenarios for the far future and their implications for the origin of lineages and species.

Global Size Pattern in a Group of Important Ecological Indicators (Diptera, Chironomidae) Is Driven by Latitudinal Temperature Gradients

Simple Summary

The size of animals is a result of the complex interactions between the evolution of a group, the environment in which the animal lives, and its physiology. It has been known for a long time that warm-blooded animals (such as birds or mammals) become larger in colder climates. This phenomenon is called “Bergmann’s rule”, and it is caused by the necessity of the animals to produce and preserve their heat in colder climates. This is easier for larger animals, as they have a lower ratio of body surface area to body volume. In cold-blooded animals, such as insects, similar patterns have been found in some cases, but their origin is less clear. In this paper, we show a strong negative relationship between size and temperature in a large group of aquatic insects (non-biting midges). We found that wings of non-biting midges are shorter by 32.4 µm for every 1 °C of mean annual temperature increase. This finding is important for use of non-biting midges in monitoring aquatic ecosystem health and tracking global climate change.

Abstract

Size is one of the most outwardly obvious characteristics of animals, determined by multiple phylogenetic and environmental variables. Numerous hypotheses have been suggested to explain the relationship between the body size of animals and their geographic latitude. Bergmann’s Rule, describing a positive relationship between the body size of endothermic animals and their geographic latitude, is especially well known. Whether or not insects exhibit a similar pattern has long been a subject for debate. We hypothesize that latitudinal size gradients are coupled to temperature variation affecting the metabolic rate of these merolimnic insects. We showcase a strong latitudinal size gradient in non-biting midges (Diptera: Chironomidae), based on the examination of 4309 specimens of these midges from around the world. Although phylogenetic position was a key predictor of wing length, we also found that wing length decreases by 32.4 µm per every 1 °C of mean annual temperature increase. This pattern was found across different taxa and could be detected in 20 of 24 genera studied. We discuss the reasons for this pattern origin and its palaeoecological implications.

Effects of photoperiod on life-history and thermal stress resistance traits across populations of Drosophila subobscura

INTRODUCTION

Organisms use environmental cues to match their phenotype with the future availability of resources and environmental conditions. Changes in the magnitude and frequency of environmental cues such as photoperiod and temperature along latitudes can be used by organisms to predict seasonal changes. While the role of temperature variation on the induction of plastic and seasonal responses is well established, the importance of photoperiod for predicting seasonal changes is less explored.

MATERIALS AND METHODS

Here we studied changes in life-history and thermal stress resistance traits in Drosophila subobscura in response to variation in photoperiod (6:18, 12:12 and 18:6 light:dark cycles) mimicking seasonal variations in day length. The populations of D. subobscura were collected from five locations along a latitudinal gradient (from North Africa and Europe). These populations were exposed to different photoperiods for two generations, whereafter egg-to-adult viability, productivity, dry body weight, thermal tolerance, and starvation resistance were assessed.

RESULTS

We found strong effects of photoperiod, origin of populations, and their interactions on life-history and stress resistance traits. Thermal resistance varied between the populations and the effect of photoperiod depended on the trait and the method applied for the assessment of thermal resistance.

PERSPECTIVES

Our results show a strong effect of the origin of population and photoperiod on a range of fitness-related traits and provide evidence for local adaptation to environmental cues (photoperiod by population interaction). The findings emphasize an important and often neglected role of photoperiod in studies on thermal resistance and suggest that cues induced by photoperiod may provide some buffer enabling populations to cope with a more variable and unpredictable future climate.

EFFECT OF AN EXPERIMENTAL BOTTLENECK ON MORPHOLOGICAL INTEGRATION IN THE HOUSEFLY

Three measures of multivariate integration were derived from both additive genetic covariance and correlation matrices estimated from parent-offspring covariances to investigate the effect of bottlenecks of different sizes on genetic integration of morphological traits in the housefly, Musca domestica L. Bottleneck lines were initiated with one, four, or 16 pairs of flies sampled from a natural outbred (control) population. Bottlenecks of intermediate size significantly increased the average genetic correlation among traits, resulting in nearly isomorphic variation among all traits in these lines. Single-pair bottlenecks significantly disrupted the trait interrelationships, and the suites of traits identified by principal components of the additive genetic correlation and covariance matrices for the control population were no longer evident in these bottleneck lines. The alteration of the genetic relationships among traits as a result of a bottleneck suggests that nonadditive components of genetic variation affecting these traits were present in the control line. We discuss the implications of nonadditive gene action, particularly epistasis, for speciation via bottlenecks.

Size relationships of different body parts in the three dipteran species Drosophila melanogaster, Ceratitis capitata and Musca domestica

Body size is an integral feature of an organism that influences many aspects of life such as fecundity, life span and mating success. Size of individual organs and the entire body size represent quantitative traits with a large reaction norm, which are influenced by various environmental factors. In the model system Drosophila melanogaster, pupal size and adult traits, such as tibia and thorax length or wing size, accurately estimate the overall body size. However, it is unclear whether these traits can be used in other flies. Therefore, we studied changes in size of pupae and adult organs in response to different rearing temperatures and densities for D. melanogaster, Ceratitis capitata and Musca domestica. We confirm a clear sexual size dimorphism (SSD) for Drosophila and show that the SSD is less uniform in the other species. Moreover, the size response to changing growth conditions is sex dependent. Comparison of static and evolutionary allometries of the studied traits revealed that response to the same environmental variable is genotype specific but has similarities between species of the same order. We conclude that the value of adult traits as estimators of the absolute body size may differ among species and the use of a single trait may result in wrong assumptions. Therefore, we suggest using a body size coefficient computed from several individual measurements. Our data is of special importance for monitoring activities of natural populations of the three dipteran flies, since they are harmful species causing economical damage (Drosophila, Ceratitis) or transferring diseases (Musca).

Polymorphism in the neurofibromin gene, Nf1, is associated with antagonistic selection on wing size and development time in Drosophila melanogaster

In many invertebrates, body size shows genetically based clines, with size increasing in colder climates. Large body size is typically associated with prolonged development times. We consider variation in the CNS-specific gene neurofibromin 1 (Nf1) and its association with body size and development time. We identified two major Nf1 haplotypes in natural populations, Nf1-insertion-A and Nf1-deletion-G. These haplotypes are characterized by a 45-base insertion/deletion (INDEL) in Nf1 intron 2 and an A/G synonymous substitution (locus L17277). Linkage disequilibrium (LD) between the INDEL and adjacent sites is high but appears to be restricted within the Nf1 gene interval. In Australia, the frequency of the Nf1-insertion-A haplotype increases with latitude where wing size is larger, independent of the chromosomal inversion In(3R)Payne. Unexpectedly, the Nf1-insertion-A haplotype is negatively associated with wing size. We found that the Nf1-insertion-A haplotype is enriched in females with shorter development time. This suggests that the Nf1 haplotype cline may be driven by selection for development time rather than size; females from southern (higher latitude) D. melanogaster populations maintain a rapid development time despite being relatively larger, and the higher incidence of Nf1-insertion-A in Southern Australia may contribute to this pattern, whereas the effects of the Nf1 haplotypes on size may be countered by other loci with antagonistic effects on size and development time. Our results point to the potential complexity involved in identifying selection on genetic variants exhibiting pleiotropic effects when studies are based on spatial patterns or association studies.

Genetic mapping of adaptive wing size variation in Drosophila simulans

Many ecologically important traits exhibit latitudinal variation. Body size clines have been described repeatedly in insects across multiple continents, suggesting that similar selective forces are shaping these geographical gradients. It is unknown whether these parallel clinal patterns are controlled by the same or different genetic mechanism(s). We present here, quantitative trait loci (QTL) analysis of wing size variation in Drosophila simulans. Our results show that much of the wing size variation is controlled by a QTL on Chr 3L with relatively minor contribution from other chromosome arms. Comparative analysis of the genomic positions of the QTL indicates that the major QTL on Chr 3 are distinct in D. simulans and D. melanogaster, whereas the QTL on Chr 2R might overlap between species. Our results suggest that parallel evolution of wing size clines could be driven by non-identical genetic mechanisms but in both cases involve a major QTL as well as smaller effects of other genomic regions.

Mitotic recombination inMusca domesticaL. and its influence on mosaicism, gynandromorphism and recombination in males

In the housefly, mosaics appear spontaneously but rarely. Sexual mosaics or gynandromorphs also appear in strains in which sex determination is based on autosomal sex factors. Rare cases of recombination in the male have been reported by some authors. In field and laboratory populations, mitotic plates with figures indicating exchange of chromatid segments are regularly observed in tissues of individuals of both sexes and at all stages of development. All these anomalies are interpreted as outward manifestation of the same phenomenon: mitotic recombination. The cytological basis of mitotic recombination, its relative frequency, its influence on linkage and genetic variability are discussed.

The nucleotypic effects of cellular DNA content in cartilaginous and ray-finned fishes

Cytological and organismal characteristics associated with cellular DNA content underpin most adaptionist interpretations of genome size variation. Since fishes are the only group of vertebrate for which relationships between genome size and key cellular parameters are uncertain, the cytological correlates of genome size were examined in this group. The cell and nuclear areas of erythrocytes showed a highly significant positive correlation with each other and with genome size across 22 cartilaginous and 201 ray-finned fishes. Regressions remained significant at all taxonomic levels, as well as among different fish lineages. However, the results revealed that cartilaginous fishes possess higher cytogenomic ratios than ray-finned fishes, as do cold-water fishes relative to their warm-water counterparts. Increases in genome size owing to ploidy shifts were found to influence cell and nucleus size in an immediate and causative manner, an effect that persists in ancient polyploid lineages. These correlations with cytological parameters known to have important influences on organismal phenotypes support an adaptive interpretation for genome size variation in fishes.

The evolution of body size in extant groups of North American freshwater fishes: speciation, size distributions, and Cope's rule

Change in body size within an evolutionary lineage over time has been under investigation since the synthesis of Cope's rule, which suggested that there is a tendency for mammals to evolve larger body size. Data from the fossil record have subsequently been examined for several other taxonomic groups to determine whether they also displayed an evolutionary increase in body size. However, we are not aware of any species-level study that has investigated the evolution of body size within an extant continental group. Data acquired from the fossil record and data derived from the evolutionary relationships of extant species are not similar, with each set exhibiting both strengths and weaknesses related to inferring evolutionary patterns. Consequently, expectation that general trends exhibited in the fossil record will correspond to patterns in extant groups is not necessarily warranted. Using phylogenetic relationships of extant species, we show that five of nine families of North American freshwater fishes exhibit an evolutionary trend of decreasing body size. These trends result from the basal position of large species and the more derived position of small species within families. Such trends may be caused by the invasion of small streams and subsequent isolation and speciation. This pattern, potentially influenced by size-biased dispersal rates and the high percentage of small streams in North America, suggests a scenario that could result in the generation of the size-frequency distribution of North American freshwater fishes.

Thermal evolution of growth efficiency in Drosophila melanogaster

Drosophila melanogaster shows geographic clines in body size, with genetically larger flies being found further from the equator and at higher altitudes. In the laboratory, evolution at lower temperatures results in genetically larger flies, and development at low temperature increases adult body size. This study demonstrates that when newly hatched larvae from laboratory temperature selection lines were raised on fixed amounts of food (yeast) at the same temperature, larvae from the lines with the cold evolutionary history required less food to produce a given size of adult. Larvae from both high- and low-temperature selection lines required more food, however, to make a given size of adult when grown in the cold than when grown in the hot. The opposite associations between growth efficiency and adult body size seen with evolution or development at low temperature are puzzling, and suggest that different mechanisms may underlie the size changes. Since environmental and evolutionary effects of temperature on body size seem to be widespread among ectotherms, some basic aspects of thermal physiology must be involved.

Genetic diversity at electrophoretic loci in the house fly, Musca domestica L

Vertical polyacrylamide gel electrophoresis was used to separate enzyme proteins at 73 putative loci in natural house fly populations sampled in central Iowa. Thirty-nine of the loci were polymorphic (53%). The mean effective number of alleles per polymorphic locus was 1.93 and 1.47 alleles among 68 scored loci. Observed and expected heterozygosities at 34 house fly loci were 0.1628 and 0.1834, respectively. No statistically significant differentiation was detected among nine central Iowa fly populations in 1989 or among nine Iowa and three Minnesota populations in 1990.

Natural selection and the heritability of fitness components

The hypothesis that traits closely associated with fitness will generally possess lower heritabilities than traits more loosely connected with fitness is tested using 1120 narrow sense heritability estimates for wild, outbred animal populations, collected from the published record. Our results indicate that life history traits generally possess lower heritabilities than morphological traits, and that the means, medians, and cumulative frequency distributions of behavioural and physiological traits are intermediate between life history and morphological traits. These findings are consistent with popular interpretations of Fisher's (1930, 1958) Fundamental Theorem of Natural Selection, and Falconer (1960, 1981), but also indicate that high heritabilities are maintained within natural populations even for traits believed to be under strong selection. It is also found that the heritability of morphological traits is significantly lower for ectotherms than it is for endotherms which may in part be a result of the strong correlation between life history and body size for many ectotherms.

Fecundity and longevity of houseflies after space flight

After 7 days of space flight house flies, Musca domestica, exhibited similar longevity, but a reduction in reproductive output as compared to earthbound controls. This reduction was not observed in later generations. These data suggest that space flight directly alters the rate of ovarian development, but that this effect is not genetically transmitted.