Introduction history overrides social factors in explaining genetic structure of females in Mediterranean mouflon

Fine‐scale spatial genetic structure of populations results from social and spatial behaviors of individuals such as sex‐biased dispersal and philopatry. However, the demographic history of a given population can override such socio‐spatial factors in shaping genetic variability when bottlenecks or founder events occurred in the population. Here, we investigated whether socio‐spatial organization determines the fine‐scale genetic structure for both sexes in a Mediterranean mouflon (Ovis gmelini musimon × Ovis sp.) population in southern France 60 years after its introduction. Based on multilocus genotypes at 16 loci of microsatellite DNA (n = 230 individuals), we identified three genetic groups for females and two for males, and concurrently defined the same number of socio‐spatial units using both GPS‐collared individuals (n = 121) and visual resightings of marked individuals (n = 378). The socio‐spatial and genetic structures did not match, indicating that the former was not the main driver of the latter for both sexes. Beyond this structural mismatch, we found significant, yet low, genetic differentiation among female socio‐spatial groups, and no genetic differentiation in males, with this suggesting female philopatry and male‐biased gene flow, respectively. Despite spatial disconnection, females from the north of the study area were genetically closer to females from the south, as indicated by the spatial analysis of the genetic variability, and this pattern was in accordance with the common genetic origin of their founders. To conclude, more than 14 generations later, genetic signatures of first introduction are not only still detectable among females, but they also represent the main factor shaping their present‐time genetic structure.     

Suburban sprawl: environmental features affect colony social and spatial structure in the black carpenter ant,Camponotus pennsylvanicus

1. In social insects, the number of nests that a colony inhabits may have important consequences for colony genetic structure, the number of queens, sex allocation, foraging efficiency, and nestmate recognition. Within the ants, colonies may either occupy a single nest (monodomy) or may be organised into a complex network of nests and trails, a condition known as polydomy. 2. The current study is a large‐scale, long‐term, comprehensive field examination of various features of colony social and spatial structure in the facultatively polydomous black carpenter ant, Camponotus pennsylvanicus (DeGeer). The study examined the density, persistence, and the spatiotemporal distribution of colonies across a gradient of land disturbance associated with urban development. The temporal and spatial pattern of nest use was compared between fragmented landscapes where nesting sites were interspersed among human‐built structures (urban plots) and less disturbed landscapes with higher tree density (suburban plots). In addition, nesting site fidelity and changes in colony spatial structure were monitored over 7 years. 3. Long‐term monitoring and extensive sampling over a large spatial area allowed the first comprehensive insight into the spatiotemporal dynamics of colony and population structure in C. pennsylvanicus. A total of 1113 trees were inspected over 233 ha. Camponotus pennsylvanicus were active on 348 of the 1113 trees (31%) and these represented 182 distinct colonies. The colonisation rate remained relatively stable over 7 years suggesting that an equilibrium point had been reached. Relative to the suburban plots, tree density was 65% lower in the urban plots. The proportion of trees colonised by C. pennsylvanicus was significantly higher in the urban plots suggesting that intraspecific competition for nesting sites may be especially high in areas with lower tree density. Colony spatial structure also differed significantly between habitats and a higher incidence of monodomy was observed in the urban environment. The average number of trees per colony across all subplots was 1.95 (range 1–4) indicating that C. pennsylvanicus are weakly polydomous. 4. The composite picture that emerges for C. pennsylvanicus colonies in the urban habitat is a chain reaction of events: (i) the urban habitat has a lower tree density, (ii) lower tree density results in higher tree colonisation rate, (iii) higher tree colonisation rate results in simpler colony spatial structure (i.e. higher incidence of monodomy), and (iv) simpler colony spatial structure results in numerically smaller colonies. Long‐term monitoring of the spatiotemporal pattern of nest site use in selected colonies revealed a unique trend. While worker counts in selected colonies remained relatively stable throughout the course of the study, colony spatial structure changed considerably with 28% of colonies experiencing a change. Furthermore, the likelihood of detecting a change in colony spatial structure increased with the amount of time passing from the initial inspection. 5. In conclusion, tree density has a significant effect on a number of important colony features in C. pennsylvanicus. Besides tree density, other environmental features such as human‐built structures cause habitat fragmentation and may act as natural barriers to worker dispersal and/or foraging. Such barriers may ultimately affect the social and/or spatial structure at both the colony and the population level.     

Diversity among peripheral populations: genetic and evolutionary differentiation of Salamandra atra at the southern edge of the Alps

Separate populations at the edge of a species range are receiving great attention and have been shown to be often different from populations in the core area. However, it has rarely been tested whether neighboring peripheral populations are genetically and evolutionarily similar to each other, as expected for their geographical proximity and similar ecological conditions, or differ due to historical contingency. We investigated isolation and differentiation, within‐population genetic diversity and evolutionary relationships among multiple peripheral populations of a cold‐adapted terrestrial salamander, Salamandra atra, at the southern edge of the species core range. We carried out population genetic, phylogeographic, and phylogenetic analyses on various molecular markers (10 autosomal microsatellite loci, three mitochondrial loci with total length >2,100 bp, two protein‐coding nuclear genes) sampled from more than 100 individuals from 13 sites along the southern Prealps. We found at least seven isolated peripheral populations, all highly differentiated from the remaining populations and differentiated from each other at various levels. The within‐population genetic diversity was variable in the peripheral populations, but consistently lower than in the remaining populations. All peripheral populations along the southern Prealps belong to an ancient lineage that is also found in the Dinarides but did not contribute to the postglacial recolonization of the inner and northern Alps. All fully melanistic populations from the Orobian mountains to the southern Dinarides represent a single clade, to the exclusion of the two yellow‐patched populations inhabiting the Pasubio massif and the Sette Comuni plateau, which are distinguished as S. atra pasubiensis and S. atra aurorae, respectively. In conclusion, multiple populations of S. atra at the southern edge of the species core area have different levels of differentiation, different amount of within‐population genetic diversity, and different evolutionary origin. Therefore, they should be regarded as complementary conservation targets to preserve the overall genetic and evolutionary diversity of the species.     

Egg‐size plasticity in Apis mellifera: Honey bee queens alter egg size in response to both genetic and environmental factors

Social evolution has led to distinct life‐history patterns in social insects, but many colony‐level and individual traits, such as egg size, are not sufficiently understood. Thus, a series of experiments was performed to study the effects of genotypes, colony size and colony nutrition on variation in egg size produced by honey bee (Apis mellifera) queens. Queens from different genetic stocks produced significantly different egg sizes under similar environmental conditions, indicating standing genetic variation for egg size that allows for adaptive evolutionary change. Further investigations revealed that eggs produced by queens in large colonies were consistently smaller than eggs produced in small colonies, and queens dynamically adjusted egg size in relation to colony size. Similarly, queens increased egg size in response to food deprivation. These results could not be solely explained by different numbers of eggs produced in the different circumstances but instead seem to reflect an active adjustment of resource allocation by the queen in response to colony conditions. As a result, larger eggs experienced higher subsequent survival than smaller eggs, suggesting that honey bee queens might increase egg size under unfavourable conditions to enhance brood survival and to minimize costly brood care of eggs that fail to successfully develop, and thus conserve energy at the colony level. The extensive plasticity and genetic variation of egg size in honey bees has important implications for understanding life‐history evolution in a social context and implies this neglected life‐history stage in honey bees may have trans‐generational effects.     

Evidence of stable genetic structure across a remote island archipelago through self‐recruitment in a widely dispersed coral reef fish

We used microsatellite markers to assess the population genetic structure of the scribbled rabbitfish Siganus spinus in the western Pacific. This species is a culturally important food fish in the Mariana Archipelago and subject to high fishing pressure. Our primary hypothesis was to test whether the individuals resident in the southern Mariana Island chain were genetically distinct and hence should be managed as discrete stocks. In addition to spatial sampling of adults, newly‐settled individuals were sampled on Guam over four recruitment events to assess the temporal stability of the observed spatial patterns, and evidence of self‐recruitment. We found significant genetic structure in S. spinus across the western Pacific, with Bayesian analyses revealing three genetically distinct clusters: the southern Mariana Islands, east Micronesia, and the west Pacific; with the southern Mariana Islands being more strongly differentiated from the rest of the region. Analyses of temporal samples from Guam indicated the southern Mariana cluster was stable over time, with no genetic differentiation between adults versus recruits, or between samples collected across four separate recruitment events spanning 11 months. Subsequent assignment tests indicated seven recruits had self‐recruited from within the Southern Mariana Islands population. Our results confirm the relative isolation of the southern Mariana Islands population and highlight how local processes can act to isolate populations that, by virtue of their broad‐scale distribution, have been subject to traditionally high gene flows. Our results add to a growing consensus that self‐recruitment is a highly significant influence on the population dynamics of tropical reef fish.     

Colony social organization and population genetic structure of an introduced population of formosan subterranean termite from New Orleans, Louisiana

The Formosan subterranean termite, Coptotermes formosanus Shiraki, is an invasive species in many parts of the world, including the U.S. mainland. The reasons for its invasive success may have to do with the flexible social and spatial organization of colonies. We investigated the population and breeding structure of 14 C. formosanus colonies in Louis Armstrong Park, New Orleans, LA. This population has been the focus of extensive study for many years, providing the opportunity to relate aspects of colony breeding structure to previous findings on colony characteristics such as body weight and number of workers, wood consumption, and intercolony aggression. Eight colonies were headed by a single pair of outbred reproductives (simple families), whereas six colonies were headed by low numbers of multiple kings and/or queens that were likely the neotenic descendants of the original colony (extended families). Within the foraging area of one large extended family colony, we found genetic differentiation among different collection sites, suggesting the presence of separate reproductive centers. No significant difference between simple family colonies and extended family colonies was found in worker body weight, soldier body weight, foraging area, population size, or wood consumption. However, level of inbreeding within colonies was negatively correlated with worker body weight and positively correlated with wood consumption. Also, genetic distance between colonies was positively correlated with aggression levels, suggesting a genetic basis to nestmate discrimination cues in this termite population. No obvious trait associated with colony reproductive structure was found that could account for the invasion success of this species.     

Metapopulation dynamics and foraging plasticity in a highly vagile seabird,the southern rockhopper penguin

Population connectivity is driven by individual dispersal potential and modulated by natal philopatry. In seabirds, high vagility facilitates dispersal yet philopatry is also common, with foraging area overlap often correlated with population connectivity. We assess the interplay between these processes by studying past and current connectivity and foraging niche overlap among southern rockhopper penguin colonies of the coast of southern South America using genomic and stable isotope analyses. We found two distinct genetic clusters and detected low admixture between northern and southern colonies. Stable isotope analysis indicated niche variability between colonies, with Malvinas/Falklands colonies encompassing the species entire isotopic foraging niche, while the remaining colonies had smaller, nonoverlapping niches. A recently founded colony in continental Patagonia differed in isotopic niche width and position with Malvinas/Falklands colonies, its genetically identified founder population, suggesting the exploitation of novel foraging areas and/or prey items. Additionally, dispersing individuals found dead across the Patagonian shore in an unusual mortality event were also assigned to the northern cluster, suggesting northern individuals reach southern localities, but do not breed in these colonies. Facilitated by variability in foraging strategies, and especially during unfavorable conditions, the number of dispersing individuals may increase and enhance the probability of founding new colonies. Metapopulation demographic dynamics in seabirds should account for interannual variability in dispersal behavior and pay special attention to extreme climatic events, classically related to negative effects on population trends.     

Small‐scale spatial variation in evolvability for life‐history traits in the storm petrel

The evolutionary potential in the timing of recruitment and reproduction may be crucial for the ability of populations to buffer against environmental changes, allowing them to avoid unfavourable breeding conditions. The evolution of a trait in a local population is determined by its heritability and selection. In the present study, we performed pedigree‐based quantitative genetic analyses for two life‐history traits (recruiting age and laying date) using population data of the storm petrel over an 18‐year period in two adjacent breeding colonies (only 150 m apart) that share the same environmental conditions. In both traits, natal colony effect was the main source of the phenotypic variation among individuals, and cohort variance for recruitment age and additive genetic variance for laying date were natal colony‐specific. We found significant heritability only in laying date and, more specifically, only in birds born in one of the colonies. The difference in genetic variance between the colonies was statistically significant. Interestingly, selection on earlier breeding birds was detected only in the colony in which heritable variation in laying date was found. Therefore, local evolvability for a life‐history trait may vary within a unexpectedly small spatial scale, through the diversifying natural selection and insulating gene flow. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 439–446.     

Outlier analyses to test for local adaptation to breeding grounds in a migratory arctic seabird

Investigating the extent (or the existence) of local adaptation is crucial to understanding how populations adapt. When experiments or fitness measurements are difficult or impossible to perform in natural populations, genomic techniques allow us to investigate local adaptation through the comparison of allele frequencies and outlier loci along environmental clines. The thick‐billed murre (Uria lomvia) is a highly philopatric colonial arctic seabird that occupies a significant environmental gradient, shows marked phenotypic differences among colonies, and has large effective population sizes. To test whether thick‐billed murres from five colonies along the eastern Canadian Arctic coast show genomic signatures of local adaptation to their breeding grounds, we analyzed geographic variation in genome‐wide markers mapped to a newly assembled thick‐billed murre reference genome. We used outlier analyses to detect loci putatively under selection, and clustering analyses to investigate patterns of differentiation based on 2220 genomewide single nucleotide polymorphisms (SNPs) and 137 outlier SNPs. We found no evidence of population structure among colonies using all loci but found population structure based on outliers only, where birds from the two northernmost colonies (Minarets and Prince Leopold) grouped with birds from the southernmost colony (Gannet), and birds from Coats and Akpatok were distinct from all other colonies. Although results from our analyses did not support local adaptation along the latitudinal cline of breeding colonies, outlier loci grouped birds from different colonies according to their non‐breeding distributions, suggesting that outliers may be informative about adaptation and/or demographic connectivity associated with their migration patterns or nonbreeding grounds.     

BIDIRECTIONAL SHIFTS IN COLONY QUEEN NUMBER IN A SOCIALLY POLYMORPHIC ANT POPULATION

The breeding system of social organisms affects many important aspects of social life. Some species vary greatly in the number of breeders per group, but the mechanisms and selective pressures contributing to the maintenance of this polymorphism in social structure remain poorly understood. Here, we take advantage of a genetic dataset that spans 15 years to investigate the dynamics of colony queen number within a socially polymorphic ant species. Our study population of Formica selysi has single‐ and multiple‐queen colonies. We found that the social structure of this species is somewhat flexible: on average, each year 3.2% of the single‐queen colonies became polygynous, and conversely 1.4% of the multiple‐queen colonies became monogynous. The annualized queen replacement rates were 10.3% and 11.9% for single‐ and multiple‐queen colonies, respectively. New queens were often but not always related to previous colony members. At the population level, the social polymorphism appeared stable. There was no genetic differentiation between single‐ and multiple‐queen colonies at eight microsatellite loci, suggesting ongoing gene flow between social forms. Overall, the regular and bidirectional changes in queen number indicate that social structure is a labile trait in F. selysi, with neither form being favored within a time‐frame of 15 years.     

Social constraint and an absence of sex‐biased dispersal drive fine‐scale genetic structure in white‐winged choughs

This study used eight polymorphic microsatellite loci to examine the relative effects of social organization and dispersal on fine‐scale genetic structure in an obligately cooperative breeding bird, the white‐winged chough (Corcorax melanorhamphos). Using both individual‐level and population‐level analyses, it was found that the majority of chough groups consisted of close relatives and there was significant differentiation among groups (F_ST = 0.124). However, spatial autocorrelation analysis revealed strong spatial genetic structure among groups up to 2 km apart, indicating above average relatedness among neighbours. Multiple analyses showed a unique lack of sex‐biased dispersal. As such, choughs may offer a model species for the study of the evolution of sex‐biased dispersal in cooperatively breeding birds. These findings suggest that genetic structure in white‐winged choughs reflects the interplay between social barriers to dispersal resulting in large family groups that can remain stable over long periods of times, and short dispersal distances which lead to above average relatedness among neighbouring groups.     

Colony‐level behavioural variation correlates with differences in expression of the foraging gene in red imported fire ants

Among social insects, colony‐level variation is likely to be widespread and has significant ecological consequences. Very few studies, however, have documented how genetic factors relate to behaviour at the colony level. Differences in expression of the foraging gene have been associated with differences in foraging and activity of a wide variety of organisms. We quantified expression of the red imported fire ant foraging gene (sifor) in workers from 21 colonies collected across the natural range of Texas fire ant populations, but maintained under standardized, environmentally controlled conditions. Colonies varied significantly in their behaviour. The most active colonies had up to 10 times more active foragers than the least active colony and more than 16 times as many workers outside the nest. Expression differences among colonies correlated with this colony‐level behavioural variation. Colonies with higher sifor expression in foragers had, on average, significantly higher foraging activity, exploratory activity and recruitment to nectar than colonies with lower expression. Expression of sifor was also strongly correlated with worker task (foraging vs. working in the interior of the nest). These results provide insight into the genetic and physiological processes underlying collective differences in social behaviour. Quantifying variation in expression of the foraging gene may provide an important tool for understanding and predicting the ecological consequences of colony‐level behavioural variation.     

Population genetic evidence for sex‐specific dispersal in an inbred social spider

Dispersal in most group‐living species ensures gene flow among groups, but in cooperative social spiders, juvenile dispersal is suppressed and colonies are highly inbred. It has been suggested that such inbred sociality is advantageous in the short term, but likely to lead to extinction or reduced speciation rates in the long run. In this situation, very low levels of dispersal and gene flow among colonies may have unusually important impacts on fitness and persistence of social spiders. We investigated sex‐specific differences in dispersal and gene flow among colonies, as reflected in the genetic structure within colonies and populations of the African social spider Stegodyphus dumicola Pocock, 1898 (Eresidae). We used DNA fingerprinting and mtDNA sequence data along with spatial mapping of colonies to compare male and female patterns of relatedness within and among colonies at three study sites. Samples were collected during and shortly after the mating season to detect sex‐specific dispersal. Distribution of mtDNA haplotypes was consistent with proliferation of social nests by budding and medium‐ to long‐distance dispersal by ballooning females. Analysis of molecular variance and spatial autocorrelation analyses of AFLPs showed high levels of genetic similarity within colonies, and STRUCTURE analyses revealed that the number of source populations contributing to colonies ranged from one to three. We also showed significant evidence of male dispersal among colonies at one site. These results support the hypothesis that in social spiders, genetic cohesion among populations is maintained by long‐distance dispersal of female colony founders. Genetic diversity within colonies is maintained by colony initiation by multiple dispersing females, and adult male dispersal over short distances. Male dispersal may be particularly important in maintaining gene flow among colonies in local populations.     

Central–periphery gradient of individual quality within a colony of Black‐headed Gulls

Central nesting sites within avian colonies are often more profitable in terms of fitness, as they can offer better protection against predators compared with colony edges. Thus, central sites are expected to attract high‐quality individuals, which should produce a clear central–periphery gradient in the phenotypic quality of nesting individuals and reproductive output within colonies. The aim of this study was to assess spatial patterns of individual quality within a colony of a common larid, the Black‐headed Gull Chroicocephalus ridibundus. We found that laying was advanced in the central zone of the colony when compared with the periphery, and central pairs tended to lay larger eggs and had higher hatching success than peripheral pairs. Centrally nesting individuals had higher blood haemoglobin concentrations, size‐corrected body mass and heterozygosity (males only), indicating their better condition and higher genetic quality. In contrast, central females had lower plasma albumin concentration, which could possibly be attributed to their greater investment in egg production. Finally, pairs breeding in the central zone of the colony had an elevated heterophil/lymphocyte ratio, suggesting that social stress can be recognized as an important cost of nesting in dense aggregations. The results provide empirical support for central–periphery gradients in the individual quality of colonially nesting Black‐headed Gulls, indicating that spatial gradients in pair quality should be carefully taken into account when conducting research on colonial birds.     

Genetic diversity and colony structure of Tapinoma melanocephalum on the islands and mainland of South China

Aim

Tapinoma melanocephalum is listed as one of the most important invasive pest species in China. Information regarding the patterns of invasion and effects of geographic isolation on the population genetics of this species is largely lacking.

Location

South China.

Methods

To address this problem, we genotyped 39 colonies (two colonies were collapsed due to genetic similarity) using microsatellite markers and mitochondrial DNA sequencing to compare colony genetic structure of T. melanocephalum on the mainland and islands of South China.

Results

An analysis of the colony genotypes showed that the genetic diversity of the mainland population was slightly higher than that of the island populations but not significantly so. However, the observed heterozygosity on Shangchuan Island (SCD) was significantly lower than that of the other colonies. We also found six haplotypes in 111 mitochondrial DNA COI sequences. The relatedness (r) value between colonies of SCD was 0.410, higher than that of the other populations. The genetic clusters among colonies were not related to geographic locations and exhibited admixture likely due to frequent human‐mediated dispersal associated with trade between the mainland population and the islands. Pairwise F_STs between populations showed differentiation among mainland populations, while SCD displayed high levels of divergence (F_ST > 0.15) from most mainland populations. There was no significant isolation by distance among colonies. Most populations showed signs of a bottleneck effect.

Main conclusions

Our study suggests that there was no significant difference in the genetic diversity among the islands and the mainland; however, the lower genetic diversity, the higher degree of genetic divergence from other colonies, and the higher relatedness among nestmates made the SCD population stand out from all the others.     

Population genetics of the socially polymorphic ant <Emphasis Type="Italic">Formica podzolica</Emphasis>

Summary. We used microsatellite markers to analyze the hierarchical genetic structure of the North American mound building ant, Formica podzolica. About one-third of all colonies were headed by a single queen (monogynous) whose effective mating frequency was close to one (nestmate worker relatedness r = 0.70), while the remaining colonies were polygynous, with low average nestmate relatedness (r = 0.16). The low worker relatedness found in most polygynous colonies furthermore suggested that the numbers of queens in polygynous colonies of this ant are usually high. Contrary to what has been described from other ants with a queen number dichotomy, we did not find an effect of social form variation on the partitioning of genetic variation above the level of the colony. We found no significant differentiation between the sympatric social forms of F. podzolica, nor did differentiation among populations appear to be affected by colony social organization. These unexpected patterns of genetic structure may have resulted from differences either in the spatial distribution of the social forms or in their social flexibility.Received 12 January 2004; revised 23 February 2004; accepted 10 March 2004.     

Genetic evidence for landscape effects on dispersal in the army ant Eciton burchellii

Inhibited dispersal, leading to reduced gene flow, threatens populations with inbreeding depression and local extinction. Fragmentation may be especially detrimental to social insects because inhibited gene flow has important consequences for cooperation and competition within and among colonies. Army ants have winged males and permanently wingless queens; these traits imply male‐biased dispersal. However, army ant colonies are obligately nomadic and have the potential to traverse landscapes. Eciton burchellii, the most regularly nomadic army ant, is a forest interior species: colony raiding activities are limited in the absence of forest cover. To examine whether nomadism and landscape (forest clearing and elevation) affect population genetic structure in a montane E. burchellii population, we reconstructed queen and male genotypes from 25 colonies at seven polymorphic microsatellite loci. Pairwise genetic distances among individuals were compared to pairwise geographical and resistance distances using regressions with permutations, partial Mantel tests and random forests analyses. Although there was no significant spatial genetic structure in queens or males in montane forest, dispersal may be male‐biased. We found significant isolation by landscape resistance for queens based on land cover (forest clearing), but not on elevation. Summed colony emigrations over the lifetime of the queen may contribute to gene flow in this species and forest clearing impedes these movements and subsequent gene dispersal. Further forest cover removal may increasingly inhibit Eciton burchellii colony dispersal. We recommend maintaining habitat connectivity in tropical forests to promote population persistence for this keystone species.     

Fine scale genetic structure in the wild ancestor of maize (Zea mays ssp. parviglumis)

Analysis of fine scale genetic structure in continuous populations of outcrossing plant species has traditionally been limited by the availability of sufficient markers. We used a set of 468 SNPs to characterize fine‐scale genetic structure within and between two dense stands of the wild ancestor of maize, teosinte (Zea mays ssp. parviglumis). Our analyses confirmed that teosinte is highly outcrossing and showed little population structure over short distances. We found that the two populations were clearly genetically differentiated, although the actual level of differentiation was low. Spatial autocorrelation of relatedness was observed within both sites but was somewhat stronger in one of the populations. Using principal component analysis, we found evidence for significant local differentiation in the population with stronger spatial autocorrelation. This differentiation was associated with pronounced shifts in the first two principal components along the field. These shifts corresponded to changes in allele frequencies, potentially due to local topographical features. There was little evidence for selection at individual loci as a contributing factor to differentiation. Our results demonstrate that significant local differentiation may, but need not, co‐occur with spatial autocorrelation of relatedness. The present study represents one of the most detailed analyses of local genetic structure to date and provides a benchmark for future studies dealing with fine scale patterns of genetic diversity in natural plant populations.     

Host plant associations and geography interact to shape diversification in a specialist insect herbivore

Disentangling the processes underlying geographic and environmental patterns of biodiversity challenges biologists as such patterns emerge from eco‐evolutionary processes confounded by spatial autocorrelation among sample units. The herbivorous insect, Belonocnema treatae (Hymenoptera: Cynipidae), exhibits regional specialization on three plant species whose geographic distributions range from sympatry through allopatry across the southern United States. Using range‐wide sampling spanning the geographic ranges of the three host plants and genotyping‐by‐sequencing of 1,217 individuals, we tested whether this insect herbivore exhibited host plant‐associated genomic differentiation while controlling for spatial autocorrelation among the 58 sample sites. Population genomic structure based on 40,699 SNPs was evaluated using the hierarchical Bayesian model entropy to assign individuals to genetic clusters and estimate admixture proportions. To control for spatial autocorrelation, distance‐based Moran's eigenvector mapping was used to construct regression variables summarizing spatial structure inherent among sample sites. Distance‐based redundancy analysis (dbRDA) incorporating the spatial variables was then applied to partition host plant‐associated differentiation (HAD) from spatial autocorrelation. By combining entropy and dbRDA to analyse SNP data, we unveiled a complex mosaic of highly structured differentiation within and among gall‐former populations finding evidence that geography, HAD and spatial autocorrelation all play significant roles in explaining patterns of genomic differentiation in B. treatae. While dbRDA confirmed host association as a significant predictor of patterns of genomic variation, spatial autocorrelation among sites explained the largest proportion of variation. Our results demonstrate the value of combining dbRDA with hierarchical structural analyses to partition spatial/environmental patterns of genomic variation.     

Genetic structure of the Canarian palm tree (Phoenix canariensis) at the island scale: does the ‘island within islands’ concept apply to species with high colonisation ability?

• Oceanic islands are dynamic settings that often promote within‐island patterns of strong population differentiation. Species with high colonisation abilities, however, are less likely to be affected by genetic barriers, but island size may impact on species genetic structure regardless of dispersal ability.
• The aim of the present study was to identify the patterns and factors responsible for the structure of genetic diversity at the island scale in Phoenix canariensis, a palm species with high dispersal potential. To this end, we conducted extensive population sampling on the three Canary Islands where the species is more abundant and assessed patterns of genetic variation at eight microsatellite loci, considering different within‐island scales.
• Our analyses revealed significant genetic structure on each of the three islands analysed, but the patterns and level of structure differed greatly among islands. Thus, genetic differentiation fitted an isolation‐by‐distance pattern on islands with high population densities (La Gomera and Gran Canaria), but such a pattern was not found on Tenerife due to strong isolation between colonised areas. In addition, we found a positive correlation between population geographic isolation and fine‐scale genetic structure.
• This study highlights that island size is not necessarily a factor causing strong population differentiation on large islands, whereas high colonisation ability does not always promote genetic connectivity among neighbouring populations. The spatial distribution of populations (i.e. landscape occupancy) can thus be a more important driver of plant genetic structure than other island, or species′ life‐history attributes.