VOCAL DIALECTS AND THE STRUCTURE OF GEOGRAPHIC VARIATION IN MORPHOLOGICAL AND ALLOZYMIC CHARACTERS IN THE RUFOUS-COLLARED SPARROW,ZONOTRICHIA CAPENSIS

The geographical patterns of variation shown at 20 allozyme and non-enzymatic protein-coding loci, in 8 external, and in 12 skeletal morphological characters in the rufous-collared sparrow, Zonotrichia capensis, were analyzed in order to test the local (genetic) adaptation hypothesis regarding the origin and maintenance of vocal dialects in birds. Approximately 20 males were collected from each of four sites within each of six different dialect zones. There was significant variability in both external and skeletal morphology among all 24 sites and among dialect groups. Average Wright's corrected fixation coefficient (F_ST) was 0.118, indicating significant genetic differentiation among all sites, regardless of dialect. Hierarchical F statistics indicated that only 50% of among site variability was due to a dialect effect. Puna dialect sites were highly differentiated from all other sites with respect to both morphology (external and skeletal measures) and allozyme frequencies. Heterogeneity at the PGM-1 locus among puna scrub sites was the major cause of the high average F_ST across all sites, and within the puna scrub dialect. Average genetic differentiation among non-puna sites (F_ST = 0.018) was similar to differentiation among sites within each of the five non-puna dialect groups (mean F_ST = 0.0132 ± 0.0069). Hierarchical F statistics indicated that none of the among-site differentiation in this subset of samples was due to a dialect effect. These observations are not consistent with the local adaptation hypothesis. All significant genetic heterogeneity occurred among sites in mountainous habitats, and we suggest that topography and patchiness of habitat may have been major factors involved in population differentiation, rather than vocal dialects.     

MIGRATION-SELECTION BALANCE AND LOCAL ADAPTATION OF MITOCHONDRIAL HAPLOTYPES IN RUFOUS-COLLARED SPARROWS (ZONOTRICHIA CAPENSIS) ALONG AN ELEVATIONAL GRADIENT

Variable selection pressures across heterogeneous landscapes can lead to local adaptation of populations. The extent of local adaptation depends on the interplay between natural selection and gene flow, but the nature of this relationship is complex. Gene flow can constrain local adaptation by eroding differentiation driven by natural selection, or local adaptation can itself constrain gene flow through selection against maladapted immigrants. Here we test for evidence that natural selection constrains gene flow among populations of a widespread passerine bird ( Zonotrichia capensis ) that are distributed along an elevational gradient in the Peruvian Andes. Using multilocus sequences and microsatellites screened in 142 individuals collected along a series of replicate transects, we found that mitochondrial gene flow was significantly reduced along elevational transects relative to latitudinal control transects. Nuclear gene flow, however, was not similarly reduced. Clines in mitochondrial haplotype frequency were strongly associated with transitions in environmental variables along the elevational transects, but this association was not observed for the nuclear markers. These results suggest that natural selection constrains mitochondrial gene flow along elevational gradients and that the mitonuclear discrepancy may be due to local adaptation of mitochondrial haplotypes.     

NOTES ON THE OCCURRENCE OF MALES IN POPULATIONS OF POTAMOPYRGUS JENKINSI

Freshwater prosobranch snails of the genus Potamopyrgus arerenowned for being extremely variable and for reproducing parthenogenetically;in addition they are among the very few animals which appearto have successfully colonized Europe from the Antipodes (seeFretter & Graham, 1978, and Winterbourn, 1972 for reviewsand references). During investigations into the genetics and sex ratios of P.antipodum (or antipodarum) (Gray) in New Zealand, a period ofleave allowed some comparisons to be made with the AustralianP. nigra (Quoy & Gaimard), which is the subject of a separatenote (Wallace, 1978) and the European P. jenkinsi(Smith) discussedhere. (Received 10 March 1978;     

TEMPORAL AND SPATIAL VARIATIONS IN EXPLOITED AND NON- EXPLOITED POPULATIONS OF THE INTERTIDAL LIMPET CELLANA CAPENSIS

Temporal and spatial variations in the density, size compostionand growth of exploited and non-exdploited populations of theintertidal limpet Cellana capensis from the Transkei coast ofsouthern Africa, between 1989 and 1991, are described. The timingand intensity of recruitment varied between shores and amongstsites within shores. Recruitment success was relatively poorand, in fact, at some of the protected sites no recruitmentwas recorded until July 1991. Juvenile and adult limpets wereboth significantly more abundant at the exploited than at theprotected sites. The gradual decline in density of limpets observedat the latter sites reflected poor recruitament as well as senescenceof older individuals. The extent of variations in density amongstshores was also found to vary from censius to census. Limpetsat the exploited sites tended to be much smaller than thosefound at the protected sites. Although there were initiallyno differences in the size of limpets amongst sites withingshores marked differences became apparent during the courseof the study. This finding, together with the observation ofmarked annual differences in population size compostion at severalof the study sites highlighted the temporal instability of thesepopulations. Such results have profound implications for comparativestudies of population size composition. The absence of significant differences in growth rate amongstshores suggests that differences in the intensity of competitiveinteractions may have been offset by the higher microalgal productionat the exploited shore. It is also suggested that upshore migrationof largter individuals may counter the intense competition experiencedat mid-tidal levels on the exploited shore. Differences in therate of recritment could also account for some of the observeddifferences in population characteristics. Both of these explanationsare viable alternatives to an earlier proposal which attributeddifferences solely to the effects of size-selective predationby man. (Received 30 May 1992; accepted 10 December 1992)     

眼镜蛇甲状腺结构的年周期变化律

本文报道眼镜蛇甲状腺结构的年周期变化规律;发现：（１）眼镜蛇甲状腺的滤泡、滤泡柱状上皮和吞饮泡的总数均值皆近似单峰曲线的年周期变化。滤泡、滤泡柱状上皮和吞饮泡的总数均值的高峰时间分别为６月１７日、５月２７日和５月３０日。眼镜蛇甲状腺结构３项指标总数均值的高峰期处于血浆ＴＳＨ浓度高峰期后,血浆Ｔ３,Ｔ４浓度高峰期前。     

DIALECTS AND GEOGRAPHICAL VARIATION IN THE SONG OF THE SPLENDID SUNBIRD NECTARINIA COCCINIGASTER

The male Splendid Sunbird has only one song type, each note of which has a simple frequency/time profile. An analysis of the songs of males from several localities near Legon (5^.63° N, 0.19° N) showed that there are clear-cut song dialects characterizing each population. Those parts of the song giving rise to dialects are the time interval between consecutive pairs of notes (the time interval pattern) and the frequency/time profile of each note.
The dialects were preserved over a period of three years (the duration of the study) and there was little variation in the song of a ringed bird over a period of two months. The boundary between dialects is apparently quite sharp, occurring perhaps within a distance of 50 m.
Marked geographical variation in the song occurs, and is expected because of the mosaic of dialects that presumably exist throughout the sunbird's range in southern Ghana. For dialects to be effective in keeping populations together, those characteristics of the song which give rise to dialects should be readily and quickly discerned and need not require a statistical demonstration. This condition holds for the song of the Splendid Sunbird.
The results are compared with the ideas of Nottebohm (1964) and Thielcke (1969) on the maintenance and usefulness of song dialects.     

云南松居群核型变异及其分化研究

在分析研究6个云南松居群核型变异的基础上,应用常规统计方法和巢式分析方法,在常规染 色体水平上探讨云南松居群间、个体间和细胞间的变异式样及其分化。结果如下:(1)云南松居群核型 变异不显著,6个居群的核型公式均为2n=24m(6～10SAT),核型类型均为1A。(2)云南松居群仅相 对长度系数、臂比和次缢痕数目及其分布有小的变化。6个居群染色体相对长度系数(I．R．L)分别为: 滇中居群P1=16M₂+6M₁+2S;滇东南居群P2=14M₂+8M₁+2S;滇西居群P3=12M₂+10M₁+2S; 地盘松居群P4=14M₂+8M₁+2S;细叶云南松居群P5=14M₂+8M₁+2S;云南松与思茅松渗入杂交 居群P6=10M₂+12M₁+2S。(3)巢式方差等级分析表明,云南松染色体结构变异有10％左右来源于居群间,有90％左右来源于居群内个体间或细胞间。     

THE MAINTENANCE OF POLYGENIC VARIATION IN FINITE POPULATIONS

Models of the maintenance of genetic variance in a polygenic trait have usually assumed that population size is infinite and that selection is weak. Consequently, they will overestimate the amount of variation maintained in finite populations. I derive approximations for the equilibrium genetic variance, in finite populations under weak stabilizing selection for triallelic loci and for an infinite “rare alleles” model. These are compared to results for neutral characters, to the “Gaussian allelic” model, and to Wright's approximation for a biallelic locus under arbitrary selection pressures. For a variety of parameter values, the three-allele, Gaussian, and Wrightian approximations all converge on the neutral model when population size is small. As expected, far less equilibrium genetic variance can be maintained if effective population size, N, is on the order of a few hundred than if N is infinite. All of the models predict that comparisons among populations with N less than about 10⁴ should show substantial differences in . While it is easier to maintain absolute when alleles interact to yield dominance or overdominance for fitness, less additivity also makes more susceptible to differences in N. I argue that experimental data do not seem to reflect the predicted degree of relationship between N and . This calls into question the ability of mutation-selection balance or simple balancing selection to explain observed . The dependence of on N could be used to test the adequacy of mutation-selection balance models.     

THE INFLUENCE OF INTRASPECIFIC VARIATION IN DISPERSAL STRATEGIES ON THE GENETIC STRUCTURE OF PLANTHOPPER POPULATIONS

The hypothesis that levels of gene flow among populations are correlated with dispersal ability has typically been tested by comparing gene flow among species that differ in dispersal abilities, an approach that potentially confounds dispersal ability with other species-specific differences. In this study, we take advantage of geographic variation in the dispersal strategies of two wing-dimorphic planthopper species, Prokelisia marginata and P. dolus, to examine for the first time whether levels of gene flow among populations are correlated with intraspecific variation in dispersal ability. We found that in both of these coastal salt marsh–inhabiting species, population-genetic subdivision, as assessed using allozyme electrophoresis, parallels geographic variation in the proportion of flight-capable adults (macropters) in a population; in regions where levels of macroptery are high, population genetic subdivision is less than in regions where levels of macroptery are low. We found no evidence that geographic variation in dispersal capability influences the degree to which gene flow declines with distance in either species. Thus, both species provided evidence that intraspecific variation in dispersal strategies influences the genetic structure of populations, and that this effect is manifested in population-genetic structure at the scale of large, coastal regions, rather than in genetic isolation by distance within a region. This conclusion was supported by interspecific comparisons revealing that: (1) population-genetic structure (G_ST) of the two Prokelisia species correlated negatively with the mean proportion of flight-capable adults within a region; and (2) there was no evidence that the degree of isolation by distance increased with decreasing dispersal capability. Populations of the relatively sedentary P. dolus clustered by geographic region (using Nei's distances), but this was not the case for the more mobile P. marginata. Furthermore, gene flow among the two major regions we surveyed (Atlantic and Gulf Coasts) has been substantial in P. marginata, but relatively less in P. dolus. The results for P. marginata suggest that differences in the dispersal strategies of Atlantic and Gulf Coast populations occur despite extensive gene flow. We argue that gene flow is biased from Atlantic to Gulf Coast populations, indicating that selection favoring a reduction in flight capability must be intense along the Gulf. Together, the results of this study provide the first rigorous evidence of a negative relationship within a species between dispersal ability and the genetic structure of populations. Furthermore, regional variation in dispersal ability is apparently maintained by selective differences that outweigh high levels of gene flow among regions.     

MORPHOLOGICAL AND ALLOZYMIC VARIATION IN POPULATIONS OF MYTILUS GALLOPROVINCIALISFROM THE AEGEAN SEA

Eight populations of Mytilus galloprovincialis from differentcoasts of the Northern and Central Aegean Sea have been investigatedat the morphological and allozymic level. A significant degreeof variation was found within and among the populations. Theaverage degree of heterozygosity ranges from 0.085 to 0.14 andit is lower than those reported for other populations of thesame species. No correlation was found between the degree ofheterozygosity and the morphological variability among the populationsexamined. (Received 14 May 1992; accepted 1 October 1992)