Electrophoretic Loci Research Articles

Geographic patterns of electrophoretic and morphological variation in the sagebrush least chipmunk (Tamias minimus scrutator)

Variation and differentiation among populations provide a framework to decipher how populations are, or are not, changing due to gene flow, genetic drift, and selection. The sagebrush least chipmunk (Tamias minimus scrutator) is distributed in arid and semi-arid habitats throughout much of the Great Basin and adjacent regions. The broad distribution and variation in elevation of populations make this a good system to assess population variation and the forces shaping differentiation. Here, we use allozyme and morphological datasets to: 1) assess the relative roles of geographic locality and elevation of populations in shaping population structure; 2) examine the level of differentiation of peripheral and isolated populations; and 3) compare the genetic and morphological signals of population variation and structure. We sampled 312 individuals from 12 T. minimus scrutator populations and other areas of their distribution. Individuals were measured for 27 genetic and 61 morphological traits. These datasets were analyzed to determine the distribution of variation and the differentiation among populations and tested for correlations with geographic distance and elevation. Multiple approaches were used to thoroughly compare the signals from each dataset. We found 13 polymorphic electrophoretic loci with most of the variation structured among populations within regions. Eight loci exhibited elevational heterogeneity but most high-elevation populations showed no heterogeneity among populations. Thirty-two morphological characters varied among populations but with no discernable trends across regions or elevations. Populations had varying levels of asymmetric distinctness in morphological characters, but there were no significant differences among populations. Morphological and genetic distance measures were correlated and there was some evidence of a correlation of genetic and geographic distance. We also found some correlation of asymmetric distances with morphological or genetic distances at smaller scales. There was substantial variation of genetic and morphological traits among sagebrush least chipmunk populations. Each population had a unique genetic signature and significant morphological differentiation. Our results suggest that genetic drift is contributing to the structure of these populations, with some evidence of selection shaping the distribution of variation at different elevations. The peripheral populations had mixed signals of isolation among the different datasets, with an overall signature suggesting that genetic drift is also driving the variation among these populations. The different measures of population variation yielded inconsistent signals of population structure, highlighting the need for multiple approaches to assess population variation. The variation among sagebrush least chipmunk populations is impacted by a variety of factors and contemporary investigations may reveal populations responding to alterations in habitat and climate.

Clustering of invasiveAspergillus ustuseye infections in a tertiary care hospital: A molecular epidemiologic study of an uncommon species

Aspergillus infections are being increasingly recognized as an important cause of morbidity and blindness. We report here the first cluster of Aspergillus ustus endophthalmitis cases which occurred in a large tertiary care hospital during the period October 2003 to June 2004. In three of the cases, the patients required enucleation following cataract surgery, while the fourth involved a fatal infection in a pediatric patient hospitalized for osteopetrosis. Patient charts from the four cases were reviewed retrospectively and indicated that postoperative signs of fungal endophthalmitis developed in the patients 1-11 weeks after surgery. The molecular characterization of the isolates and their epidemiological relatedness were evaluated by Random Amplification of Polymorphic DNA (RAPD). A source investigation of this mini outbreak was performed by environmental sampling, but no isolates of A. ustus were recovered from these studies. All A. ustus strains isolated from three patients with fungal endophthalmitis had the same RAPD pattern suggesting a common source. The strain from the pediatric patient differed from the ophthalmic isolates in five electrophoretic loci. The latter was included solely as an outbreak, unrelated control to evaluate the discriminatory power of the molecular typing method employed in the analysis of the ophthalmic strains. These cases illustrate the potential for uncommon species like A. ustus to cause high morbidity and mortality in some clinical settings. Aspergillus ustus endophthalmitis is a serious and devastating complication of ocular surgery. It is unknown whether ongoing hospital construction may have contributed to this cluster of cases. Random amplification of polymorphic DNA may give valuable clues about the clonality of A. ustus strains.

Genetic variability and phylogenetic relationships of Cnemidophorus parecis (Squamata, Teiidae) from Cerrado isolates in southwestern Amazonia

We investigated the genetic structure of Cnemidophorus parecis, and its phylogenetic relationships with other South American teiids using allozyme data. Because of southward expansion of Amazon Forest, populations of C. parecis presumably have been isolated in Cerrado enclaves during the last 3000 years. We scored 18 presumptive electrophoretic loci in Tupinambis merianae, Kentropyx altamazonica, Ameiva ameiva, Cnemidophorus ocellifer, and C. parecis, estimating genetic diversity through allelic richness, mean number of alleles per locus, proportion of polymorphic loci, and mean heterozygosity. To make interspecific comparisons independent of sample sizes, we also used a rarefaction analysis of allelic richness. C. parecis had relatively low values of genetic variability among the five studied species, but the results do not corroborate the hypothesis that enclave populations experienced a severe bottleneck. Therefore, geographic isolation affected the genetic variability of C. parecis, but Rondônia enclaves were apparently large enough to maintain adequate populations of this species, preserving some of the original genetic diversity. We also conducted a phylogenetic analysis adding data from Cnemidophorus lemniscatus and Cnemidophorus gramivagus previously reported in literature and using T. merianae as outgroup. Results indicated that C. parecis is more closely related to A. ameiva than to other congeneric species, corroborating the view that South American Cnemidophorus form a paraphyletic assemblage.

Genetic variability of South African fiscal shrikes (Lanius collaris) across an altitudinal gradient

An electrophoretic allozyme study of the fiscal shrike Lanius collaris, a widely distributed sub-Saharan passerine, was undertaken to investigate altitudinal variation in genetic structure within this species. It is a sedentary bird with limited dispersal so that subpopulations may be expected to show genetic isolation by distance, which may have been enhanced by Pleistocene glaciation effects. The study area was a linear altitudinal transect of four localities in the eastern half of South Africa, which ranged from sea level to an altitude of 1800 m, with the geographic distance between the furthest subpopulations being 300 km. Fourteen (40%) of the 35 electrophoretic loci examined were polymorphic. The mean percentage of polymorphic loci within populations, mean heterozygosity and mean number of alleles per locus were 0.519, 0.272 and 1.60, respectively. These values were much higher than those reported for most other avian species. The negative FIS and FIT values indicated a small excess of heterozygotes. The populations are only weakly differentiated genetically (FST = 0.076). Rogers’ (1972) mean genetic distance (D) was 0.094, and Nei’s (1978) mean unbiased genetic distance was 0.019. A phenogram (unweighted pair group method) and a phylogenetic tree (distance Wagner network), both based on Rogers’ (1972) distance, showed some degree of geographical subgrouping. The high mean value for the effective number of migrants (Nm) among demes indicated that 3.04 individuals were exchanged among demes per generation. The mean value for local genetic differentiation (FST) and Nm indicated levels of gene flow between the different localities of fiscal shrike subpopulations. The Mantel test indicated that there was no significant relationship between the FST values and the geographical distances between sample pairs. This study showed that the isolation-by-distance model of subpopulation structure is inappropriate for these birds. Juvenile natal dispersal distances, female divorce rates (every three years) and the distance of travel of females (although low) appear to be sufficient to maintain high levels of polymorphism and heterozygosity. These levels of polymorphism and heterozygosity, together with large amounts of gene flow and the general lack of spatial autocorrelation imply that the populations of L. collaris may be subject to high rates of random drift. High values of sample heterozygosity suggest that fiscal shrike subpopulations have been stable for a long period and that genetic diversity has accumulated within populations. The rates of migration suggest that the ‘subpopulations’ of fiscal shrike act more or less as a single population extending over at least 300 km.

Genetic Variability at Minisatellite and Allozyme Loci in Brown Trout (Salmo trutta)-A Comparison

Most of our present knowledge regarding the genetic structure of natural animal and plant populations has been derived from protein electrophoretic studies. New molecular techniques are evolving quickly, however, and increased attention is focused on the analysis of miniand microsatellite loci (e.g., PENA et al. 1993; QUELLER et al. 1993; AVISE 1994). Techniques for analyzing these types of loci are presumed to be of great interest to population biologists because of their high resolution power in relation to that of protein electrophoresis (AMOS and HOELZEL 1992; BRUFORD and WAYNE 1993a). It is important to evaluate the extent to which allozyme and mini-/ microsatellite data provide approximately the same overall picture of the population genetic parameters of interest ( CHAKRABORTY et al. 1992). To date, the number of studies comparing population genetic data for the same set of samples using both types of loci is still limited (e.g., CHAKRABORTY et al. 1992; BRUFORD and WAYNE 1993b; SCRIBNER et al. 1994). We have analyzed brown trout (Salmo trutta) samples using three minisatellite and 16 protein electrophoretic loci. The results indicate that although the minisatellite loci show higher levels of genetic variability, the two sets of markers are equally efficient in delineating genetic differentiation as evaluated from contingency tests for allele frequency homogeneity and gene diversity statistics (GST) in brown trout.

Geographical and altitudinal population genetic structure of two dung fly species with contrasting mobility and temperature preference

Local adaptation of populations requires some degree of spatio-temporal isolation. Previous studies of the two dung fly species Scathophaga stercoraria and Sepsis cynipsea have revealed low levels of geographic and altitudinal genetic differentiation in quantitative life history and morphological traits, but instead high degrees of phenotypic plasticity. These patterns suggest that gene flow is extensive despite considerable geographic barriers and large spatio-temporal variation in selection on body size and related traits. In this study we addressed this hypothesis by investigating genetic differentiation of dung fly populations throughout Switzerland based on the same 10 electrophoretic loci in each species. Overall, we found no significant geographic differentiation of populations for either species. This is inconsistent with the higher rates of gene flow expected due to better flying capacity of the larger S. stercoraria. However, heterozygote deficiencies within populations indicated structuring on a finer scale, seen for several loci in S. cynipsea, and for the locus PGM (Phosphoglucomutase) in S. stercoraria. Additionally, S. cynipsea showed a tendency towards a greater gene diversity at higher altitudes, mediated primarily by the locus MDH (malate dehydrogenase), at which a second allele was only present in populations above 1000 m. This may be caused by increased environmental stress at higher altitudes in this warm-adapted species. MDH might thus be a candidate locus subject to thermal selection in this species, but this remains to be corroborated by direct evidence. In S. stercoraria, no altitudinal variation was found.

Genetic and morphological relationships of the Berlenga wall lizard (Podarcis bocagei berlengensis: Lacertidae)

Six biometric characters and 15 electrophoretic loci of three known subspecies of Podarcis bocagei were studied. Contrary to biometric indications, Podarcis bocagei berlengensis showed a closer genetic relationship with Podarcis bocagei carbonelli than with the nominal subspecies. The biometric results were confounded by the relative large size of P. b. berlengensis. Post-glacial colonization from two different areas might explain the greater genetic differentiation between the P. b. bocagei and P. b. carbonelli populations (Nei's D - 0.158 - near the species threshold). It might also explain the known colonization of these two lizards through the islands off the west coast of the Iberian penninsula and their present distributions to the north of (Galicia; Northern Portugal) and to the south of the valley of river Douro (central Portugal, western and Sistema Central), respectively.

Genetic variation and reproductive isolation among phenotypically divergent amphipod populations

We examined the degree of reproductive isolation and patterns of genetic structure and diversification within and among seven populations of the freshwater amphipod Hyalella azteca. Hyalella occurs across ecologically dissimilar habitats in southeastern Michigan and exhibits substantial, and apparently adaptive, genetically based phenotypic variation among populations. Habitats with predatory centrarchid fish contain a small‐bodied Hyalella ecotype, whereas habitats lacking these predators contain a large‐bodied ecotype. Hierarchical F statistics showed that allele frequency variation at six electrophoretic loci is greater among populations within an ecotype than between ecotypes, a result also reflected in a cluster analysis based on genetic distances among the seven populations. Despite the lack of clear genetic differentiation between ecotypes, gene flow between ecotypes appeared restricted or absent. Physically adjacent large‐ and small‐ecotype populations in the same drainage differed appreciably in allele frequencies. Within‐population genetic structuring also differed between ecotypes. Whereas genotype frequencies never differed from Hardy‐Weinberg expectations in large‐ecotype populations, all small‐ecotype populations exhibited a significant deficiency of heterozygous genotypes at one or more loci. Interbreeding trials demonstrated that individuals from different populations of the same ecotype readily interbreed, but no interbreeding was observed in crosses involving individuals of dissimilar ecotypes. Interbreeding results, considered together with between‐ecotype differences in allele and genotype structure, suggest that Hyalella ecotypes in southeast Michigan form at least two separate species. Furthermore, the lack of distinct allelic differences and the relative levels of allele frequency differentiation within and between ecotypes suggest recent local speciation in this taxon.

Electrophoretic Evidence for Tetrasomic Inheritance in the Dioecious Tree Maclura pomifera (Raf.) Schneid

Although polyploidy is recognized as an important feature of chromosomal evolution, natural autopolyploids rarely occur compared to allopolyploids. Enzymes coded by four electrophoretic loci (Lap, Pgm-1, Pgi-2, and Tpi-2) in adults and full-sib progeny indicate tetrasomic inheritance in the dioecious tree Maclura pomifera, strongly suggesting that this species is an autopolyploid. This study is the first to document tetrasomic inheritance in a dioecious tree. Five of 19 segregation arrays deviated significantly from expected tetrasomic ratios, whereas 11 of 19 deviated significantly from digenic disomic expectations. We observed 22 double-reduction genotypes, which provides a likely source of deviation from expected tetrasomic frequencies. We suggest that unusual patterns of sexual expression in this species are related to autopolyploidy through production of unbalanced sex chromosome ratios.

GEOLOGICALLY DATED SEA BARRIERS CALIBRATE A PROTEIN CLOCK FOR AEGEAN WATER FROGS.

Reliable estimates of phylogenetic relationships and divergence times are a crucial requirement for many evolutionary studies, but are usually difficult because fossils are scarce and their interpretation is often uncertain. Frogs are fresh water animals that generally are unable to cross salt water barriers (their skin is readily permeable to both salt and water). The geologically determined ages of salt water barriers that isolate related frog populations thus provide an independent measure of the minimum date of genetic divergence between pairs of such populations. For the genetically well-studied western Palearctic water frogs (Rana esculenta group), the Aegean region provides an ideal area for determining the relationship between genetic divergence and time of spatial isolation, using a nested set of geologically determined isolation times (12,000 yr, 200,000 yr, 1.8 Myr, 2-3 Myr, and 5.2 Myr). Using 31 electrophoretic loci for 33 pairs of neighboring frog populations, a linear relationship between geologically determined isolation time and Hillis' modified Nei genetic distance was found: D*Nei = (0.04 ± 0.01) + (0.10 ± 0.01) isolation time [Myr] corresponding to an average divergence rate ("molecular clock" pace) of 0.10 D*Nei /Myr (0.10 DNei /Myr). This rate is in the range of previous estimates reported for protein electrophoretic data; the value is conservative because relatively few of the loci used are "fast evolvers" (13%; sAAT, ALB, EST-5, MPI). Removing these fast evolvers from the analysis results in 0.08 D*Nei /Myr (0.08 DNei /Myr). The confidence limits for estimation of the divergence time given the genetic distance are large, but unusually narrow for this kind of study; they permit us to estimate divergence times during the Pliocene and Miocene. Few previous studies, including sequence analyses, have provided reasonable estimates of divergence time for the Pliocene. A test using the outgroup taxa Rana perezi and Rana saharica (also isolated for 5.2 Myr by the Strait of Gibraltar) fits the calibration well: observed genetic Nei distance D*Nei = 0.55, expected D*Nei = 0.56. The calculated divergence times, based on this absolute molecular clock, suggest a series of speciation events after the Messinian (5.2 Myr), possibly triggered by the rapid ecological changes accompanying the desiccation and refilling of the Mediterranean Basin.

Small Genetic Distances among Populations of Green Lacewings of the Genus Chrysoperla (Neuroptera: Chrysopidae)

Seven populations of four species of green lacewings of the genus Chrysoperla were examined for variation at 17 electrophoretically detectable loci. Objectives were (1) to determine the degree of genetic differentiation, if any, that has occurred between two cryptic sibling species, C. plorabunda (Fitch) and C. johnsoni (Henry et al.), which can be distinguished only by differences in their courtship songs and their behavioral reproductive isolation; and (2) to compare those two species with the closely related C. downesi (Smith) and the more distantly related C. harrisii (Fitch). Most of the genetic differentiation in these populations was caused by differences between the cryptic species C. plorabunda and C.johnsoni on the one hand and each of the other two species. Nei's and Roger's genetic distances among all populations were not significantly different. The only significant node was that separating C. harrisii from the other populations. Phenograms from unweighted pair-group method using arithmetic averages (UPGMA) did not resolve the cluster of populations of C. plorabunda and C.johnsoni. These cryptic sibling species are genetically very similar, suggesting recent speciation. Examination of more variable electrophoretic loci, or use of an alternative method such as mtDNA restriction site analysis, might provide enough differences to separate these otherwise good biological species.

WHEN MORPHOLOGY MISLEADS: INTERPOPULATION UNIFORMITY IN SEXUAL SELECTION MASKS GENETIC DIVERGENCE IN HARLEQUIN BEETLE-RIDING PSEUDOSCORPION POPULATIONS.

Differences in secondary sexual characteristics of males often provide the most conspicuous means of distinguishing between closely related species. Does this therefore imply that the absence of differentiation in exaggerated male traits between allopatric populations provides evidence of a single, genetically cohesive species? We addressed this question with a comprehensive investigation of two populations (French Guiana and Panama) of the harlequin beetle-riding pseudoscorpion, Cordylochernes scorpioides. This highly sexually dimorphic pseudoscorpion is currently described as a single species, ranging throughout the Neotropics. Our morphometric analyses detected minimal differentiation between the two populations in all nine external morphological characters measured, including sexually dimorphic traits in males. Only in traits of the spermatophore was there any appreciable level of differentiation. Behavior differentiation and prezygotic reproductive isolation were also limited: 78.3% of males successfully transferred sperm to "foreign" females, and in 63.9% of these cases, females' eggs were successfully fertilized. By contrast, extensive divergence existed in two of nine electrophoretic loci, including an essentially fixed-allele difference at the Ldh locus. Most significantly, postzygotic reproductive isolation was complete, with heteropopulation zygotes invariably aborting early in development. These results strongly suggest that the two populations are, in fact, sibling species, a conclusion supported by our recently published findings on their marked divergence in minisatellite DNA. How can such interpopulation homogeneity in male sexually dimorphic traits exist in the face of strong genetic divergence? We propose that sexual selection, oscillating between favoring small and then large males, maintains such high levels of male variability within each population that it has obscured a speciation event in which genetic divergence and postzygotic incompatibility have clearly outpaced the evolution of prezygotic reproductive isolation.

Allozyme and RFLP heterozygosities as correlates of growth rate in the scallop Placopecten magellanicus: a test of the associative overdominance hypothesis.

Several studies have reported positive correlations between the degree of enzyme heterozygosity and fitness-related traits. Notable among these are the correlations between heterozygosity and growth rate in marine bivalves. Whether the correlation is the result of intrinsic functional differences between enzyme variants at the electrophoretic loci scored or arises from non-random genotypic associations between these loci and others segregating for deleterious recessive genes (the associative overdominance hypothesis) is a matter of continuing debate. A prediction of the associative overdominance hypothesis, not shared by explanations that treat the enzyme loci as causative agents of the correlation, is that the correlation is not specific to the type of genetic marker used. We have tested this prediction by scoring heterozygosity at single locus nuclear restriction fragment length polymorphisms (RFLPs) in a cohort of juvenile scallops (Placopecten magellanicus) in which growth rate was known to be positively correlated with an individual's degree of allozyme heterozygosity. A total of 222 individuals were scored for their genotypes at seven allozyme loci, two nonspecific protein loci of unknown function and eight nuclear RFLPs detected by anonymous cDNA probes. In contrast to the enzyme loci, no correlation was observed between growth rate and the degree of heterozygosity at the DNA markers. Furthermore, there was no relationship between the magnitude of heterozygote deficiency at a locus and its effect on the correlation. The differences observed between the effects of allozyme and RFLP heterozygosity on growth rate provide evidence against the associative overdominance hypothesis, but a strong case against this explanation must await corroboration from similar studies in different species.

Contribution of genetic distances studies to the taxonomy ofAteles, particularlyAteles paniscus paniscus andAteles paniscus chamek

We studied 20 electrophoretic loci in two populations ofAteles (Ateles paniscus paniscus andAteles paniscus chamek). We observed intrapopulational variation at the following loci: esterase D, glyoxalase 1, adenosine deaminase (A. p. chamek) and carbonic anhydrase 2 (A. p. paniscus). The two populations share the most frequent alleles at 17 loci, but we noted great differences in glyoxalase 1, adenosine deaminase and phosphoglucomutase 1.A. p. paniscus is monomorphic for theGLO1*1 allele, which has a frequency of 6% inA. p.chamek. They did not share alleles in relation to the ADA and PGM1 loci. We found a CA2 allele, named hereCA2*1, which has not been described previously in other neotropical primates (Sampaio et al., 1991a), inA. p. paniscus. The present results suggest that the geographical isolation represented by the Rio Amazonas has lasted long enough to support this level of divergence. These observations taken together with chromosomal findings, led us to endorse the proposal of two distinct species:Ateles paniscus andAteles chamek.

Effect of a founder event on variation in the genetic sex-determining system of the fire ant Solenopsis invicta.

Effects of a recent founder event on genetic diversity in wild populations of the fire ant Solenopsis invicta were studied, with particular attention given to the genetic sex-determining system. Diploid males are far more common relative to haploid males in introduced populations than in native populations of fire ants, and queens that produce diploid males account for a significantly larger proportion of the mated queens in introduced than in native populations. Differences between native and introduced populations in attributes of the mating systems (i.e., queen mating frequency or level of inbreeding) can be excluded as factors contributing to these different levels of diploid male production. Thus, we conclude that diploid males have increased in frequency in introduced populations because of a loss of allelic diversity at the sex-determining locus (loci). This loss of sex alleles has generated a substantial increase in the estimated segregational genetic load associated with production of sterile diploid males in introduced populations over the load in native populations. The loss of allelic diversity in the sex-determining system in introduced S. invicta is paralleled by a loss of electrophoretically detectable rare alleles at protein-encoding loci. Such concordance between these different types of markers is predicted because each of the many sex alleles present in the native populations is expected to be rare. Estimates of expected heterozygosity (Hexp) based on 76 electrophoretic loci do not differ significantly between the native and introduced fire ant populations, illustrating the lack of sensitivity of this measure for detecting many types of bottlenecks.

Gene Diversity in Natural Diabrotica barberi Smith & Lawrence Populations (Coleoptera: Chrysomelidae)

A survey of electrophoretic loci in Diabrotica barberi Smith & Lawrence showed that 21 of 27 loci were polymorphic. Mean gene diversity at the polymorphic loci was 0.274 ± 0.051 and 0.213 ± 0.041 among all 27 loci. Gene frequencies were heterogeneous among collections of adult beetles from 14 farms in five counties in northwestern Iowa. About half the variance in gene frequencies was partitioned among farms in counties and half among the counties. Wright’s F statistics showed that most departures from random mating occurred within populations; departures from random mating among populations were insignificant. The data show much gene flow among D. barberi populations.

Estimates of heterozygosity in two social insects using a large number of electrophoretic markers

An extensive electrophoretic survey of enzyme and protein markers was conducted for a haplodiploid eusocial insect, the red imported fire ant (Solenopsis invicta), and for a diploid communal insect, the eastern tent caterpillar (Malacosoma americanum). This survey resulted in the discovery of 110 electrophoretic loci for S. invicta (15 of which were polymorphic at the 95 per cent level) and 37 electrophoretic loci for M. americanum (seven polymorphic). Expected heterozygosities (mean Hexp±S.E.) were 0.051 ± 0.013 and 0.092 ± 0.030 for S. invicta and M. americanum, respectively. Although these values do not differ significantly, they are consistent with the frequently reported pattern of low gene diversity in the eusocial Hymenoptera relative to non-eusocial diploid insects. This pattern persists when a large number of markers is scored in different life stages and castes, as in S. invicta in this study, and when a direct comparison is made using data generated in a single laboratory.

VARIATION IN MATING CALL ACROSS THE HYBRID ZONE BETWEEN THE FIRE-BELLIED TOADS BOMBINA BOMBINA AND B. VARIEGATA.

Three components of mating call (pulse duration, cycle length, and fundamental frequency) were measured and six diagnostic enzyme loci scored across the hybrid zone between the toads Bombina bombina and B. variegata. All three call components differ significantly, but only cycle length is diagnostic. The clines in call coincide with those for enzymes, and have similar widths. This suggests that there is no strong selection on any of these characters. There are significant correlations between electrophoretic markers and call components, but these are no stronger than would be expected if the electrophoretic loci and the genes causing mating call were neutral. The selection differential on the call is no greater than 6% of the difference in mean cycle length between the two taxa. There is a substantial increase in the variance of cycle length in the center of the zone, suggesting that a small number of loci are involved (≈ three). Recombination between these loci will hinder the evolution of reinforcement and may partly be responsible for the lack of premating isolation between B. bombina and B. variegata.

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

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

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.