Population-genetic study of Balkan endemic nephropathy in Serbia

The study of Balkan Endemic Nephropathy (BEN) in the affected localities of southern Serbia shows population-genetic difference between samples of BEN affected individuals and control group consisting of non-affected individuals from the same localities. Detailed population-genetic study in village Chepure, which includes 20 large families where BEN is present in 646 (from first to fourth degree) relatives of probants, shows familial character of disease as well as significant genetic influences in expression of the illness. Our study of genetic homozygosity degree includes an analysis of the presence, distribution and individual combination of 20 to 30 selected genetically controlled morpho-physiological traits in the sample of BEN patients and in the control-healthy group. Assuming that BEN is genetically controlled disease, we made a hypothesis that an increased homozygosity level, as well as the changed variability among the patients, could be population-genetic parameter for the prediction of the illness. Taking into consideration our experience, as well as the experience of numerous scientists who studied the nature of the inheritance of mono- and oligo-genically controlled qualitative traits, we applied a methodology to estimate the proportion of such homozygously recessive characters (HRC-test). This population-genetic study did not only show statistically significant difference of the mean values of genetic homozygosity (BEN - 8.7 +/- 0.3; control - 7.6 +/- 0.3), but of the differences in the type of distribution too, as well as the differences in the presence of certain individual combinations of such traits.     

Morphogenetic variability and handedness in Montenegro and Serbia

This study tries to establish correlations between the types of handedness and several morphophysiological characteristics, controlled by one or a small number of genes with alternative dominant recessive manifestation. The population-genetic homozygosity degree study includes the analysis of the presence, distribution and individual traits combination in left-handed and right-handed persons. It was conducted at three localities in two states, Serbia (SRB) and Montenegro (MNE). Our hypothesis is that a possible genetic load due to increased recessive homozygosity, being a potential population-genetic parameter of left-handedness manifestation, may cause some change in other morpho-physiological characters. The average proportion of 23 studied homozygously-recessive characters (HRC’s) was similar among observed left-handed individuals in the studied localities. It varied from 10.5 ± 0.4 in Serbia to 10.7 ± 0.3 in MNE. The differences were somewhat bigger among right-handed persons, varying from 8.7 ± 0.3 in MNE to 9.1 ± 0.3 HRC’s in Serbia. However, in all localities the average homozygosity was significantly higher among left-handed school children. The number of HRC’s among 400 individuals varied from 2 to 16 among right-handed and from 4 to 19 among left-handed persons. There were no differences in scholar scores between left-handed and right-handed children, although small differences were found between two state samples.     

Genetic variability in the group of patients with congenital hip dislocation

Our study of genetic homozygosity degree includes an analysis of the presence, distribution and individual combination of 20 selected genetically controlled morpho-physiological traits in the group of patients (N = 93) with congenital hip dislocation (CDH) and in control sample consisting of school children from Belgrade (N = 200). Assuming that CDH is genetically controlled disease, we made a hypothesis that an increased homozygosity level, as well as the changed variability among the patients, could be population-genetic parameter for the prediction of the illness. Taking into consideration our experience, as well as the experience of numerous scientists who studied the nature of the inheritance of mono- and oligo-genically controlled qualitative traits, we applied a methodology to estimate the proportion of such homozygously recessive characters (HRC-TEST). This population-genetic study did not only show statistically significant difference of the middle values of genetic homozygosity (CDH-7.1+/-0.2; control - 5.2+/-0.1), but of the differences in the type of distribution too, as well as the differences in the presence of certain individual combinations of such traits. The described methodology can be used in further analyses, with hope that it can be applied as an early prognosis for decreased resistance to different diseases. The frequencies of ABO blood types in the sample of CDH patients were similar to the average value of Serbian population, while the percentage of blood group A is slightly increased. Comparing frequencies of Rh blood groups, there is no difference between tested samples.     

Genetic Variability in the Group of Patients with Congenital Hip Dislocation

Our study of genetic homozygosity degree includes an analysis of the presence, distribution, and individual combination of 20 selected genetically controlled morphophysiological traits in the group of patients (N = 93) with congenital hip dislocation (CDH) and in control sample consisting of schoolchildren from Belgrade (N = 200). Assuming that CDH is a genetically controlled disease, we made a hypothesis that an increased homozygosity level, as well as the changed variability among the patients, could be a population-genetic parameter for the prediction of the illness. Taking into consideration our experience, as well as the experience of numerous scientists who studied the nature of the inheritance of mono- and oligogenically controlled qualitative traits, we applied a methodology to estimate the proportion of such homozygously recessive characters (HRC-TEST). This population-genetic study did not only show statistically significant difference of the middle values of genetic homozygosity (CDH: 7.1 ± 0.2; control: 5.2 ± 0.1), but of the differences in the type of distribution too, as well as the differences in the presence of certain individual combinations of such traits. The described methodology can be used in further analyses, with hope that it can be applied as an early prognosis for decreased resistance to different diseases. The frequencies of ABO blood types in the sample of CDH patients were similar to the average value of the Serbian population, while the percentage of blood group A is slightly increased. Comparing frequencies of Rh blood groups, there is no difference between tested samples.__________From Genetika, Vol. 41, No. 8, 2005, pp. 1142–1146.Original English Text Copyright © 2005 by Cvjeticanin, Marinkovic.This text was submitted by the authors in English.     

Statistical models for trisomic phenotypes.

Certain genetic disorders are rare in the general population but more common in individuals with specific trisomies, which suggests that the genes involved in the etiology of these disorders may be located on the trisomic chromosome. As with all aneuploid syndromes, however, a considerable degree of variation exists within each phenotype so that any given trait is present only among a subset of the trisomic population. We have previously presented a simple gene-dosage model to explain this phenotypic variation and developed a strategy to map genes for such traits. The mapping strategy does not depend on the simple model but works in theory under any model that predicts that affected individuals have an increased likelihood of disomic homozygosity at the trait locus. This paper explores the robustness of our mapping method by investigating what kinds of models give an expected increase in disomic homozygosity. We describe a number of basic statistical models for trisomic phenotypes. Some of these are logical extensions of standard models for disomic phenotypes, and some are more specific to trisomy. Where possible, we discuss genetic mechanisms applicable to each model. We investigate which models and which parameter values give an expected increase in disomic homozygosity in individuals with the trait. Finally, we determine the sample sizes required to identify the increased disomic homozygosity under each model. Most of the models we explore yield detectable increases in disomic homozygosity for some reasonable range of parameter values, usually corresponding to smaller trait frequencies. It therefore appears that our mapping method should be effective for a wide variety of moderately infrequent traits, even though the exact mode of inheritance is unlikely to be known.     

A Systematic Approach to Mapping Recessive Disease Genes in Individuals from Outbred Populations

The identification of recessive disease-causing genes by homozygosity mapping is often restricted by lack of suitable consanguineous families. To overcome these limitations, we apply homozygosity mapping to single affected individuals from outbred populations. In 72 individuals of 54 kindred ascertained worldwide with known homozygous mutations in 13 different recessive disease genes, we performed total genome homozygosity mapping using 250,000 SNP arrays. Likelihood ratio Z-scores (ZLR) were plotted across the genome to detect ZLR peaks that reflect segments of homozygosity by descent, which may harbor the mutated gene. In 93% of cases, the causative gene was positioned within a consistent ZLR peak of homozygosity. The number of peaks reflected the degree of inbreeding. We demonstrate that disease-causing homozygous mutations can be detected in single cases from outbred populations within a single ZLR peak of homozygosity as short as 2 Mb, containing an average of only 16 candidate genes. As many specialty clinics have access to cohorts of individuals from outbred populations, and as our approach will result in smaller genetic candidate regions, the new strategy of homozygosity mapping in single outbred individuals will strongly accelerate the discovery of novel recessive disease genes.     

Divergent selection for antibody production in common carp (Cyprinus carpio L.) using gynogenesis

A base population (n = 101) of carp, consisting of a single hybrid cross, was immunized with the hapten-carrier complex DNP-KLH. to perform a divergent selection for antibody response. Measurement of the DNP-specific antibody response at 12 and 21 days postimmunization, allowed the classification of a low number of individual carp as early/high (10%) or late/low (13%) responders. Three individuals defined as early/high and three defined as late/low responding, were gynogenetically reproduced to obtain corresponding homozygous progenies within one generation only. Upon immunization with DNP-KLH, the antibody response was found to be significantly higher in the early/high responder homozygous offspring. Although the homozygosity of the offspring apparently caused a (s)lower antibody response (compared with the base population), the differences between the high and low responder offspring do indicate a genetic influence on the antibody response. The realized heritability (h2) for antibody production was estimated at 0.37 ± 0.36. The present study provides the basis for a divergent selection of homozygous inbred carp lines with a genetically controlled difference in antibody response. These inbred lines will allow us to investigate relationship(s) between immune responsiveness and resistance to infectious diseases in fish.     

A unifying study of phenotypic and molecular genetic variability in natural populations of Anadenanthera colubrina var. cebil from Yungas and Paranaense biogeographic provinces in Argentina

Anadenanthera colubrina var. cebil is a discontinuously distributed native tree species in South American subtropical forests. Thirteen quantitative traits and eight nuclear microsatellite loci were examined in individuals from two biogeographic provinces of Argentina to determine the number and composition of genetically distinguishable groups of individuals and explore possible spatial patterns of the phenotypic and genetic variability. Means of reproductive traits were higher in the Yungas than in the Paranaense biogeographic province, whereas five out of eight nonreproductive quantitative traits showed higher mean values in the latter. Variance coefficients were moderate, and there were significant differences between and within provinces. Three clusters were defined based on spatial model for cluster membership for quantitative traits. One cluster grouped the individuals from the Paranaense biogeographic province whereas the individuals from the Yungas biogeographic province grouped regarding its population of origin. Parameters of molecular genetic variability showed higher values in the Yungas than in the Paranaense biogeographic province. Observed heterozygosity was lower than expected heterozygosity in both biogeographic provinces, indicating an excess of homozygosity. The homozygosity test by Watterson and the exact test by Slatkin suggested diversifying selection for locus Ac41.1. Bayesian clustering spatial model for microsatellites loci data were performed for both all loci and for all loci excluding locus Ac41.1. In both analyses two clusters were inferred. Analysis of molecular variance revealed similar results for all genotypes and for all genotypes defined excluding locus Ac41.1. Most of the total variance is attributable to genetic variation within clusters. The presence of homogeneous clusters was detected for both the phenotypic and molecular genetic variability. Two Bayesian clustering analyses were performed according to molecular genetic data, and two clusters were inferred. Individuals were assigned to their provinces of origin. Genetic molecular variation was higher in the populations of the Yungas biogeographic province which translates into highly qualified populations for conservation. Populations from the Paranaense biogeographic province showed the highest mean value of number of seeds per fruit making them valuable as well with regard to the exploitation of management strategies as a means to recover the impacted areas where these populations are located.     

Inbreeding depression in a critically endangered carnivore

Harmful effects arising from matings between relatives (inbreeding) is a long‐standing observation that is well founded in theory. Empirical evidence for inbreeding depression in natural populations is however rare because of the challenges of assembling pedigrees supplemented with fitness traits. We examined the occurrence of inbreeding and subsequent inbreeding depression using a unique data set containing a genetically verified pedigree with individual fitness traits for a critically endangered arctic fox (Vulpes lagopus) population. The study covered nine years and was comprised of 33 litters with a total of 205 individuals. We recorded that the present population was founded by only five individuals. Over the study period, the population exhibited a tenfold increase in average inbreeding coefficient with a final level corresponding to half‐sib matings. Inbreeding mainly occurred between cousins, but we also observed two cases of full‐sib matings. The pedigree data demonstrated clear evidence of inbreeding depression on traditional fitness traits where inbred individuals displayed reduced survival and reproduction. Fitness traits were however differently affected by the fluctuating resource abundande. Inbred individuals born at low‐quality years displayed reduced first‐year survival, while inbred individuals born at high‐quality years were less likely to reproduce. The documentation of inbreeding depression in fundamental fitness traits suggests that inbreeding depression can limit population recovery. Introducing new genetic material to promote a genetic rescue effect may thus be necessary for population long‐term persistence.     

Migration as the main factor of the Russia’s urban population dynamics

This review summarizes the results of the long-term studies performed at the Institute of General Genetics, Russian Academy of Sciences, in the field of genetic demography of migration processes in Russia and its capital. The main population-genetic parameters of migration and their dynamics in Moscow over a hundred years are given. Sociodemographic and population-genetic implications of migration processes are considered. A model predicting the population gene pool dynamics under migration pressure for genes of different localization (autosomal, sex-linked, and mitochondrial), exemplified by predicting the allele frequency dynamics in the Moscow population of some gene markers, including genes accounting for monogenic pathology and genes associated with resistance to socially significant diseases, are presented. The paper discusses the selective character of migration processes, in particular, processes of emigration, with respect to some genetically significant ethnodemographic traits; the problem of adaptation of migrants; and adaptive strategies of consolidation of ethnoconfessional groups in the megalopolis (compact settlement over the urban territory and positive assortative mating with respect to demographic traits). It was shown that, owing to the intense influx of migrants and gene flows between ethnic groups, the population of the megalopolis is of mixed origin in terms of ethnic, anthropologic, and genetic aspects. The results of the study suggest the necessity to develop a specific strategy of genetic database formation for the population of megalopolises for the purposes of medical genetics and forensic medicine.     

Natural selection at genomic regions associated with obesity and type-2 diabetes: East Asians and sub-Saharan Africans exhibit high levels of differentiation at type-2 diabetes regions

Different populations suffer from different rates of obesity and type-2 diabetes (T2D). Little is known about the genetic or adaptive component, if any, that underlies these differences. Given the cultural, geographic, and dietary variation that accumulated among humans over the last 60,000 years, we examined whether loci identified by genome-wide association studies for these traits have been subject to recent selection pressures. Using genome-wide SNP data on 938 individuals in 53 populations from the Human Genome Diversity Panel, we compare population differentiation and haplotype patterns at these loci to the rest of the genome. Using an “expanding window” approach (100–1,600 kb) for the individual loci as well as the loci as ensembles, we find a high degree of differentiation for the ensemble of T2D loci. This differentiation is most pronounced for East Asians and sub-Saharan Africans, suggesting that these groups experienced natural selection at loci associated with T2D. Haplotype analysis suggests an excess of obesity loci with evidence of recent positive selection among South Asians and Europeans, compared to sub-Saharan Africans and Native Americans. We also identify individual loci that may have been subjected to natural selection, such as the T2D locus, HHEX, which displays both elevated differentiation and extended haplotype homozygosity in comparisons of East Asians with other groups. Our findings suggest that there is an evolutionary genetic basis for population differences in these traits, and we have identified potential group-specific genetic risk factors.     

Indirect genetic effects and inbreeding: consequences of BLUP selection for socially affected traits on rate of inbreeding

Background

Social interactions often occur among living organisms, including aquatic animals. There is empirical evidence showing that social interactions may genetically affect phenotypes of individuals and their group mates. In this context, the heritable effect of an individual on the phenotype of another individual is known as an Indirect Genetic Effect (IGE). Selection for socially affected traits may increase response to artificial selection, but also affect rate of inbreeding.

Methods

A simulation study was conducted to examine the effect of Best Linear Unbiased Prediction (BLUP) selection for socially affected traits on the rate of inbreeding. A base scenario without IGE and three alternative scenarios with different magnitudes of IGE were simulated. In each generation, 25 sires and 50 dams were mated, producing eight progeny per dam. The population was selected for 20 generations using BLUP. Individuals were randomly assigned to groups of eight members in each generation, with two families per group, each contributing four individuals. “Heritabilities” (for both direct and indirect genetic effects) were equal to 0.1, 0.3 or 0.5, and direct–indirect genetic correlations were −0.8, −0.4, 0, 0.4, or 0.8. The rate of inbreeding was calculated from generation 10 to 20.

Results

For the base scenario, the rates of inbreeding were 4.09, 2.80 and 1.95% for “heritabilities” of 0.1, 0.3 and 0.5, respectively. Overall, rates of inbreeding for the three scenarios with IGE ranged from 2.21 to 5.76% and were greater than for the base scenarios. The results show that social interaction within groups of two families increases the resemblance between estimated breeding values of relatives, which, in turn, increases the rate of inbreeding.

Conclusion

BLUP selection for socially affected traits increased the rate of inbreeding. To maintain inbreeding at an acceptable rate, a selection algorithm that restricts the increase in mean kinship, such as optimum contribution selection, is required.     

Genetic correlations between sides and heritability of asymmetry for nonmetric traits in rhesus macaques on Cayo Santiago

The use of nonmetric traits for estimation of biological distance is a long-standing practice in biological anthropology. Nonmetric traits can be scored using either the individual or the side of the individual as the unit of measure. If sides of the individual are genetically correlated the use of sides would produce redundant genetic information. For this reason, Korey (Am. J. Phys. Anthropol. 53:19-23, 1980) argues for the use of individuals as the unit of measure for nonmetric traits. Ossenberg (Am. J. Phys, Anthropol. 54:471-479, 1981), however, argues that bilateral occurrence of nonmetric traits indicates greater genetic liability for the trait and that therefore the sides are the more biologically correct unit of measure. Genetic correlations for 13 cranial nonmetric traits are estimated for a sample of rhesus macaque skeletons from Cayo Santiago. In addition, heritability of asymmetry is estimated for these 13 traits as a test of Ossenberg's contention that asymmetry is genetically influenced. Significant genetic correlations between sides support Korey's contention that nonmetric traits should be scored by individual. Only two asymmetry heritabilities were significantly different from zero, providing no significant support for Ossenberg's contention that asymmetry is genetically determined. Our results support the theory that asymmetry represents a measure of the ability of an organism to buffer stresses. Therefore, a measure of the heritability of asymmetry is a measure of the heritability of the ability to buffer stresses. This ability does not appear to be heritable in this sample.     

Consequences of inter-population crosses on developmental stability and canalization of floral traits in Dalechampia scandens (Euphorbiaceae)

Congruence between changes in phenotypic variance and developmental noise in inter-population hybrids was analysed to test whether environmental canalization and developmental stability were controlled by common genetic mechanisms. Developmental stability assessed by the level of fluctuating asymmetry (FA), and canalization by the within- and among-individual variance, were measured on several floral traits of Dalechampia scandens (Euphorbiaceae). Hybridization affected canalization. Both within- and among-individual phenotypic variance decreased in hybrids from populations of intermediate genetic distance, and strongly increased in hybrids from genetically distant populations. Mean-trait FA differed among cross-types, but hybrids were not consistently more or less asymmetric than parental lines across traits. We found no congruence between changes in FA and changes in phenotypic variance. These results suggest that developmental stability (measured by FA) and canalization are independently controlled. This study also confirms the weak relationship between FA and the breakdown of coadapted gene complexes following inter-population hybridization.     

Genes,psychological traits and civic engagement

Civic engagement is a classic example of a collective action problem: while civic participation improves life in the community as a whole, it is individually costly and thus there is an incentive to free ride on the actions of others. Yet, we observe significant inter-individual variation in the degree to which people are in fact civically engaged. Early accounts reconciling the theoretical prediction with empirical reality focused either on variation in individuals’ material resources or their attitudes, but recent work has turned to genetic differences between individuals. We show an underlying genetic contribution to an index of civic engagement (0.41), as well as for the individual acts of engagement of volunteering for community or public service activities (0.33), regularly contributing to charitable causes (0.28) and voting in elections (0.27). There are closer genetic relationships between donating and the other two activities; volunteering and voting are not genetically correlated. Further, we show that most of the correlation between civic engagement and both positive emotionality and verbal IQ can be attributed to genes that affect both traits. These results enrich our understanding of the way in which genetic variation may influence the wide range of collective action problems that individuals face in modern community life.     

Assessing the impact of hunting pressure on population structure of Guinea baboons (Papio papio) in Guinea-Bissau

Guinea baboons are heavily hunted for bushmeat consumption in Guinea-Bissau. We investigated whether hunting-driven mortality has affected population structure in this generalist primate using two genetic markers. Sampling was conducted in protected areas separated by anthropogenic landscape features. We predicted significant genetic differentiation between samples and investigated whether genetic discontinuities in the data were concordant with the location of human infrastructures. Genetic diversity was not significantly reduced when compared with a neighbouring population in Senegal and we inferred historically female-biased dispersal and recent contact between localities. Evidence was found for a contact zone between genetically differentiated populations where gene-flow is unidirectional, admixed individuals are at a higher proportion and individuals differentiated for both genetic markers co-exist within the same social units. Genetic discontinuities were, however, unrelated to anthropogenic dispersal barriers and we could not explain the existence of a contact zone by geographic distance, habitat type or the effect of social structure. We propose that hunting practices have affected the population structure by increasing dispersal distances, facilitating contact between previously separated gene pools within social groups. We suggest that hunting-related density sinks found in areas where the quality of the habitat remains adequate could precipitate the immigration of genetically distinct individuals from distant populations. Alternatively, migrants found in protected areas might be avoiding hunters, in locations they may perceive as less disturbed. This study suggests that hunting practices must be considered when investigating genetic patterns in primates and underlines the utility of molecular approaches to detect population perturbations due to bushmeat hunting.     

Increase of genetic variation over time in a recently founded population of great reed warblers (Acrocephalus arundinaceus) revealed by microsatellites and DNA fingerprinting

Genetic similarity within pairs of individuals was examined using both 10 polymorphic microsatellite loci and multi-locus DNA fingerprinting profiles in a semi-isolated population of great reed warblers at Lake Kvismaren, south Central Sweden, in 1987-1993. The population was founded by a few individuals in 1978, followed by a gradual increase in numbers until 1988, since when the population has remained relatively stable with about 60 breeding birds. We have previously found that high genetic similarity between pair-mates in the population during the early part of the study period reduced egg hatching success, and hence reproductive success. The measures of pairwise genetic similarity, microsatellite allele sharing and DNA fingerprinting band sharing, were highly correlated with pedigree-based relatedness. Both microsatellite and DNA fingerprinting similarities between pair-mates declined significantly over the study period, and the pattern was most pronounced in the DNA fingerprinting data. Analyses restricted to the microsatellite data showed that the average annual microsatellite similarity between pairwise combinations of individuals, as well as individual homozygosity in males, declined significantly over the study period, and that several immigrants carrying novel alleles entered the population during the study. Hence, the temporal decline in genetic similarity of mates in the population is probably a consequence of increased immigration, facilitated by the recent expansion of the species in the region. These results suggest that the population has now recovered genetically, or is in the process of recovering, from a recent founder event.     

Cunningham's skinks show low genetic connectivity and signatures of divergent selection across its distribution

Establishing corridors of connecting habitat has become a mainstay conservation strategy to maintain gene flow and facilitate climate‐driven range shifts. Yet, little attention has been given to ascertaining the extent to which corridors will benefit philopatric species, which might exhibit localized adaptation. Measures of genetic connectivity and adaptive genetic variation across species’ ranges can help fill this knowledge gap. Here, we characterized the spatial genetic structure of Cunningham's skink (Egernia cunninghami), a philopatric species distributed along Australia's Great Dividing Range, and assessed evidence of localized adaptation. Analysis of 4,274 SNPs from 94 individuals sampled at four localities spanning 500 km and 4° of latitude revealed strong genetic structuring at neutral loci (mean F_ST ± SD = 0.603 ± 0.237) among the localities. Putatively neutral SNPs and those under divergent selection yielded contrasting spatial patterns, with the latter identifying two genetically distinct clusters. Given low genetic connectivity of the four localities, we suggest that the natural movement rate of this species is insufficient to keep pace with spatial shifts to its climate envelope, irrespective of habitat availability. In addition, our finding of localized adaptation highlights the risk of outbreeding depression should the translocation of individuals be adopted as a conservation management strategy.     

Impact of living with kin/non-kin on the life history traits of Tetranychus urticae (Acari: Tetranychidae)

In many vertebrates and invertebrates, living in a group may influence the life history traits, physiology and behaviour of its individual members, whereas genetic relatedness affects social interactions among individuals in a group. The two-spotted spider mite Tetranychus urticae is characterised by a communal organization, in which silk production plays a key role. A silken web protects the colony against biotic and abiotic agents such as predators, competitors, humidity, wind, rain and acaricides. To evaluate the potential costs and benefits of being associated with genetically distant vs genetically close individuals in T. urticae, we assessed various fitness indicators (faecal pellet production, fecundity, death rate) in pure and mixed groups of two distinct populations of T. urticae: a red-form population from Tunisia and a green-form population from Belgium. If genetic origin had no influence, the values of fitness indicators in mixed groups composed of green and red individuals, would be intermediate between those of the pure green-form and red-form groups. Our results show that in a mixed group, faecal pellet production and death rate were statistically similar to the values obtained in the pure group of green-form individuals. Therefore, our study suggests that strain recognition ability may occur in T. urticae and that the genetic background of an individual may have a great impact on several of its life history traits.     

Evolutionary consequences of microhabitat: population-genetic structuring in kelp- vs. rock-associated chitons

Rafting has long been invoked as a key marine dispersal mechanism, but biologists have thus far produced little genetic evidence to support this hypothesis. We hypothesize that coastal species associated with buoyant seaweeds should experience enhanced population connectivity owing to rafting. In particular, invertebrates strongly associated with the buoyant bull-kelp Durvillaea antarctica might be expected to have lower levels of population-genetic differentiation than taxa mainly exploiting nonbuoyant substrates. We undertook a comparative genetic study of two codistributed, congeneric chiton species, assessing population connectivity at scales of 61-516 km, using ≥ 186 polymorphic AFLP loci per species. Consistent with predictions, population-genetic differentiation was weaker in the kelp-associated Sypharochiton sinclairi than in the rock-associated S. pelliserpentis. Additionally, while we found a significant positive correlation between genetic and oceanographic distances in both chiton species, the correlation was stronger in S. pelliserpentis (R(2) = 0.28) than in S. sinclairi (R(2) = 0.18). These data support the hypothesis that epifaunal taxa can experience enhanced population-genetic connectivity as a result of their rafting ability.