Temporal stability and directional change in a color cline of a marine snail from NW Spain.

The evolution and maintenance of color clines is a classic topic of research in evolutionary ecology. However, studies analyzing the temporal dynamics of such clines are much less frequent, due to the difficulty of obtaining reliable data about past color distributions along environmental gradients. In this article, we describe a case of decades-long temporal stability and directional change in a color cline of the marine snail Littorina saxatilis along the coastal inlet of the Ría de Vigo (NW Spain). L. saxatilis from this area shows a clear color cline with 3 distinct areas from the innermost to the more wave-exposed localities of the Ría: the inner, protected localities show an abundance of fawn-like individuals; the intermediate localities show a high diversity of colors; and the outer, wave-exposed localities show populations with a high frequency of a black and lineated morph. We compare data from the 1970s and 2022 in the same localities, showing that the cline has kept relatively stable for at least over half a century, except for some directional change and local variability in the frequency of certain morphs. Multiple regression analyses and biodiversity measures are presented to provide clues into the selective pressures that might be involved in the maintenance of this color cline. Future research avenues to properly test the explanatory power of these selective agents as well as the possible origins of the cline are discussed.

Identification of Sympetrum depressiusculum Sélys, 1841 in South Korea (Odonata: Libellulidae) According to Morphology and Genetic Markers.

In South Korea, both Sympetrum depressiusculum Sélys, 1841 (Odonata: Libellulidae), which is distributed throughout Europe and from Russia to the Korean Peninsula, and Sympetrum frequens Sélys, 1883, which is endemic to Japan, are recorded. However, the identity of South Korean populations and the validity of listing the two species have not yet been settled. In this study, we collected seventy-four individuals of Sympetrum species from South Korea (five localities), Russia, The Netherlands, and Japan. These samples were examined for morphology and sequenced for partial COI, 16S rRNA, and a nuclear internal spacer (ITS) region, after which these molecular data were combined with available public data from Russia, Japan, and The Netherlands. Major morphological characters that have been used to distinguish the two species and phylogenetic, network, and structure analyses all consistently suggest that South Korean populations form a single species. Consequently, it could be valid to treat South Korean populations as one species, S. depressiusculum, by applying the senior name. Nevertheless, the validity of maintaining each as an independent species in other countries may need additional study considering that our samples were focused more on South Korea and limited for Europe, Russia, and Japan.

Clinal variation in the temperature and photoperiodic control of reproductive diapause in Drosophila montana females.

Insect adaptation to climatic conditions at different latitudes has required changes in life-history traits linked with survival and reproduction. Several species, including Drosophila montana, show robust latitudinal variation in the critical day length (CDL), below which more than half of the emerging females enter reproductive diapause at a given temperature. Here we used a novel approach to find out whether D. montana also shows latitudinal variation in the critical temperature (CTemp), above which the photoperiodic regulation of diapause is disturbed so that the females develop ovaries in daylengths that are far below their CDL. We estimated CTemp for 53 strains from different latitudes on 3 continents after measuring their diapause proportions at a range of temperatures in 12 h daylength (for 29 of the strains also in continuous darkness). In 12 h daylength, CTemp increased towards high latitudes alongside an increase in CDL, and in 3 high-latitude strains diapause proportion exceeded 50% in all temperatures. In continuous darkness, the diapause proportion was above 50% in the lowest temperature(s) in only 9 strains, all of which came from high latitudes. In the second part of the study, we measured changes in CTemp and CDL in a selection experiment favouring reproduction in short daylength (photoperiodic selection) and by exercising selection for females that reproduce in LD12:12 at low temperature (photoperiodic and temperature selection). In both experiments selection induced parallel changes in CDL and CTemp, confirming correlations seen between these traits along latitudinal clines. Overall, our findings suggest that selection towards strong photoperiodic diapause and long CDL at high latitudes has decreased the dependency of D. montana diapause on environmental temperature. Accordingly, the prevalence and timing of the diapause of D. montana is likely to be less vulnerable to climate warming in high- than low-latitude populations.

Post-introduction evolution of a rapid life-history strategy in a newly invasive plant.

A central question in invasion biology is whether adaptive trait evolution following species introduction promotes invasiveness. A growing number of common-garden experiments document phenotypic differences between native- and introduced-range plants, suggesting that adaptive evolution in the new range may indeed contribute to the success of invasive plants. However, these studies are often subject to methodological pitfalls, resulting in weak evidence for post-introduction adaptive trait evolution and leaving its role in the invasion process uncertain. In a common-garden glasshouse study, we compared the growth, life-history, and reproductive traits of 35 native- and introduced-range Polygonum cespitosum populations. We used complementary approaches including climate-matching, standardizing parental conditions, selection analysis, and testing for trait-environment relationships to determine whether traits that increase invasiveness adaptively evolved in the species' new range. We found that the majority of introduced-range populations exhibited a novel trait syndrome consisting of a fast-paced life history and concomitant sparse, reduced growth form. Selection analysis confirmed that this trait syndrome led to markedly higher fitness (propagule production) over a limited growing season that was characteristic of regions within the introduced range. Additionally, several growth and reproductive traits showed temperature-based clines consistent with adaptive evolution in the new range. Combined, these results indicate that, subsequent to its introduction to North America over 100 generations ago, P. cespitosum has evolved key traits that maximize propagule production. These changes may in part explain the species' recent transition to invasiveness, illustrating how post-introduction evolution may contribute to the invasion process.

Stomatal density in Pinus sylvestris as an indicator of temperature rather than CO2 : Evidence from a pan-European transect.

The commonly observed negative relationship between stomatal density (SD) and atmospheric CO2 has led to SD being proposed as an indicator of atmospheric CO2 concentration. The use of SD as a proxy for CO2 , however, has been hampered by an insufficient understanding of the intraspecific variation of this trait. We hypothesized that SD in Pinus sylvestris, a widely distributed conifer, varies geographically and that this variation is determined by major climatic variables. By sampling needles from naturally growing trees along a latitudinal range of 32.25°, equivalent to 13.7°C gradient of mean annual temperature (MAT) across Europe, we found that SD decreased from the warmest southern sites to the coldest sites in the north at a rate of 4 stomata per mm2 for each 1°C, with MAT explaining 44% of the variation. Additionally, samples from a provenance trial exhibited a positive relationship between SD and the MAT of the original localities, suggesting that high SD is an adaptation to warm temperature. Our study revealed one of the strongest intraspecific relationships between SD and climate in any woody species, supporting the utility of SD as a temperature, rather than direct CO2 , proxy. In addition, our results predict the response of SD to climate warming.

Genotypic variation in C and N isotope discrimination suggests local adaptation of heart-leaved willow.

Plants acquire multiple resources from the environment and may need to adjust and/or balance their respective resource-use efficiencies to maximize grow and survival, in a locally adaptive manner. In this study, tissue and whole-plant carbon (C) isotopic composition (δ13C) and carbon/nitrogen (C/N) ratios provided long-term measures of use efficiencies for water (WUE) and nitrogen (NUE), and a nitrogen (N) isotopic composition (δ15N)-based mass balance model was used to estimate traits related to N uptake and assimilation in heart-leaved willow (Salix eriocephala Michx.). In an initial common garden experiment consisting of 34 populations, we found population-level variation in δ13C, C/N ratio and δ15N, indicating different patterns in WUE, NUE and N uptake and assimilation. Although there was no relationship between foliar δ13C and C/N ratios among populations, there was a significant negative correlation between these measures across all individuals, implying a genetic and/or plastic trade-off between WUE and NUE not associated with local adaptation. To eliminate any environmental effect, we grew a subset of 21 genotypes hydroponically with nitrate as the sole N source and detected significant variation in δ13C, δ15N and C/N ratios. Variation in δ15N was mainly due to genotypic differences in the nitrate efflux/influx ratio (E/I) at the root. Both experiments suggested clinal variation in δ15N (and thus N uptake efficiency) with latitude of origin, which may relate to water availability and could contribute to global patterns in ecosystem δ15N. There was a tendency for genotypes with higher WUE to come from more water-replete sites with shorter and cooler growing seasons. We found that δ13C, C/N ratio and E/I were not inter-correlated, suggesting that the selection of growth, WUE, NUE and N uptake efficiency can occur without trade-off.

Variation in seasonal timing traits and life history along a latitudinal transect in Mimulus ringens.

Seasonal timing traits are commonly under recurrent, spatially variable selection, and are therefore predicted to exhibit clinal variation. Temperate perennial plants often require vernalization to prompt growth and reproduction; however, little is known about whether vernalization requirements change across the range of a broadly distributed species. We performed a critical vernalization duration study in Mimulus ringens, coupled with population genomic analysis. Plants from eight populations spanning the latitudinal range were exposed to varying durations of 4°C vernalization between 0 and 56 days, and flowering response was assessed. RADSeq was also performed to generate 1179 polymorphic SNPs, which were used to examine population structure. We found unexpected life history variation, with some populations lacking vernalization requirement. Population genomic analyses show that these life history variants are highly divergent from perennials, potentially revealing a cryptic species. For perennial populations, minimum vernalization time was surprisingly consistent. However, once vernalized, northern populations flowered almost 3 weeks faster than southern. Furthermore, southern populations exhibited sensitivity to vernalization times beyond flowering competency, suggesting an ability to respond adaptively to different lengths of winter. Mimulus ringens, therefore, reveals evidence of clinal variation, and provides opportunities for future studies addressing mechanistic and ecological hypotheses both within and between incipient species.

Clinal and seasonal changes are correlated in Drosophila melanogaster natural populations.

Spatial and seasonal variations in the environment are ubiquitous. Environmental heterogeneity can affect natural populations and lead to covariation between environment and allele frequencies. Drosophila melanogaster is known to harbor polymorphisms that change both with latitude and seasons. Identifying the role of selection in driving these changes is not trivial, because nonadaptive processes can cause similar patterns. Given the environment changes in similar ways across seasons and along the latitudinal gradient, one promising approach may be to look for parallelism between clinal and seasonal changes. Here, we test whether there is a genome-wide correlation between clinal and seasonal changes, and whether the pattern is consistent with selection. Allele frequency estimates were obtained from pooled samples from seven different locations along the east coast of the United States, and across seasons within Pennsylvania. We show that there is a genome-wide correlation between clinal and seasonal variations, which cannot be explained by linked selection alone. This pattern is stronger in genomic regions with higher functional content, consistent with natural selection. We derive a way to biologically interpret these correlations and show that around 3.7% of the common, autosomal variants could be under parallel seasonal and spatial selection. Our results highlight the contribution of natural selection in driving fluctuations in allele frequencies in natural fly populations and point to a shared genomic basis to climate adaptation that happens over space and time in D. melanogaster.

Local adaptation to precipitation in the perennial grass Elymus elymoides: Trade-offs between growth and drought resistance traits.

Understanding local adaptation to climate is critical for managing ecosystems in the face of climate change. While there have been many provenance studies in trees, less is known about local adaptation in herbaceous species, including the perennial grasses that dominate arid and semiarid rangeland ecosystems. We used a common garden study to quantify variation in growth and drought resistance traits in 99 populations of Elymus elymoides from a broad geographic and climatic range in the western United States. Ecotypes from drier sites produced less biomass and smaller seeds, and had traits associated with greater drought resistance: small leaves with low osmotic potential and high integrated water use efficiency (δ13C). Seasonality also influenced plant traits. Plants from regions with relatively warm, wet summers had large seeds, large leaves, and low δ13C. Irrespective of climate, we also observed trade-offs between biomass production and drought resistance traits. Together, these results suggest that much of the phenotypic variation among E. elymoides ecotypes represents local adaptation to differences in the amount and timing of water availability. In addition, ecotypes that grow rapidly may be less able to persist under dry conditions. Land managers may be able to use this variation to improve restoration success by seeding ecotypes with multiple drought resistance traits in areas with lower precipitation. The future success of this common rangeland species will likely depend on the use of tools such as seed transfer zones to match local variation in growth and drought resistance to predicted climatic conditions.

Pervasive Genomic Signatures of Local Adaptation to Altitude Across Highland Specialist Andean Hummingbird Populations.

Populations along steep environmental gradients are subject to differentiating selection that can result in local adaptation, despite countervailing gene flow, and genetic drift. In montane systems, where species are often restricted to narrow ranges of elevation, it is unclear whether the selection is strong enough to influence functional differentiation of subpopulations differing by a few hundred meters in elevation. We used targeted capture of 12 501 exons from across the genome, including 271 genes previously implicated in altitude adaptation, to test for adaptation to local elevations for 2 highland hummingbird species, Coeligena violifer (n = 62) and Colibri coruscans (n = 101). For each species, we described population genetic structure across the complex geography of the Peruvian Andes and, while accounting for this structure, we tested whether elevational allele frequency clines in single nucleotide polymorphisms (SNPs) showed evidence for local adaptation to elevation. Although the 2 species exhibited contrasting population genetic structures, we found signatures of clinal genetic variation with shifts in elevation in both. The genes with SNP-elevation associations included candidate genes previously discovered for high-elevation adaptation as well as others not previously identified, with cellular functions related to hypoxia response, energy metabolism, and immune function, among others. Despite the homogenizing effects of gene flow and genetic drift, natural selection on parts of the genome evidently optimizes elevation-specific cellular function even within elevation range-restricted montane populations. Consequently, our results suggest local adaptation occurring in narrow elevation bands in tropical mountains, such as the Andes, may effectively make them "taller" biogeographic barriers.

Divergent patterns between phenotypic and genetic variation in Scots pine.

In boreal forests, autumn frost tolerance in seedlings is a critical fitness component because it determines survival rates during regeneration. To understand the forces that drive local adaptation in this trait, we conducted freezing tests in a common garden setting for 54 Pinus sylvestris (Scots pine) populations (>5000 seedlings) collected across Scandinavia into western Russia, and genotyped 24 of these populations (>900 seedlings) at >10 000 SNPs. Variation in cold hardiness among populations, as measured by QST , was above 80% and followed a distinct cline along latitude and longitude, demonstrating significant adaptation to climate at origin. In contrast, the genetic differentiation was very weak (mean FST 0.37%). Despite even allele frequency distribution in the vast majority of SNPs among all populations, a few rare alleles appeared at very high or at fixation in marginal populations restricted to northwestern Fennoscandia. Genotype-environment associations showed that climate variables explained 2.9% of the genetic differentiation, while genotype-phenotype associations revealed a high marker-estimated heritability of frost hardiness of 0.56, but identified no major loci. Very extensive gene flow, strong local adaptation, and signals of complex demographic history across markers are interesting topics of forthcoming studies on this species to better clarify signatures of selection and demography.

Taxonomic review of the pipefish genus Pseudophallus Herald, with the description of a new species (Syngnathiformes: Syngnathidae).

We present a taxonomic review of the genus Pseudophallus, based on morphological characters, originally described to include two freshwater pipefish species from the Pacific coastal drainages of the neotropics: P. starksii and P. elcapitanensis, with the later addition of P. mindii, described from Atlantic coastal drainages. Pseudophallus mindii was formerly recognized as a single species ranging from the Brazilian state of São Paulo to Belize in Central America. Five species are recognized in the present study: P. elcapitanensis and P. starksii from the Pacific drainages; P. mindii and P. brasiliensis, the latter so far considered a junior synonym of P. mindii, and a new species. Pseudophallus mindii is redefined to include specimens with higher meristic values and narrow range of variation compared to P. brasiliensis and is restricted to the northern coastal drainages from Venezuela to Central America including the Caribbean region. Pseudophallus brasiliensis is revalidated and occurs from the drainages east of the mouth of the Orinoco to southern Brazil. The new species, Pseudophallus galadrielae sp. nov. is endemic to Lago Izabal in Guatemala. An updated identification key to the currently recognized species is provided.

Genetic data reveals a complex history of multiple admixture events in presently allopatric wild gingers (Asarum spp.) showing intertaxonomic clinal variation in calyx lobe length.

Clinal variation is a major pattern of observed phenotypic diversity and identifying underlying demographic processes is a necessary step to understand the establishment of clinal variation. The wild ginger series Sakawanum (genus Asarum) comprises four taxa, which exhibit intertaxonomic clinal variation in calyx lobe length across two continental islands isolated by a sea strait. To test alternative hypotheses of the evolutionary history and to determine the implications for the formation of clinal variation, we conducted approximate Bayesian computation (ABC) analysis and ecological niche modeling (ENM). ABC analysis indicated that the scenario assuming multiple admixture events was strongly supported. This scenario assumed two admixture events occurred between morphologically distinct taxa, likely leading to the generation of intermediate taxa. One of the admixture events was estimated to have occurred during the last glacial maximum (LGM), during which the taxa were estimated to have formed a common refugia in southern areas by ENM analysis. Although four taxa are currently distributed allopatrically on different islands and trans-oceanic dispersal appears unlikely, the formation of a land bridge and the geographic range shift to refugia would have allowed secondary contact between previously isolated taxa. This study suggests that clinal variation can be shaped by demographic history including multiple admixtures due to climatic oscillations.

Life-history variation along environmental and harvest clines of a northern freshwater fish: Plasticity and adaptation.

Plasticity, local adaptation and evolutionary trade-offs drive clinal variation in traits associated with lifetime growth. Disentangling the processes and determinants that cause these traits to vary helps to understand species' responses to changing environments. This is particularly urgent for exploited populations, where size-selective harvest can induce life-history evolution. Lake trout (Salvelinus namaycush) are an exploited fish with a life history adapted to low-productivity freshwaters of northern North America, which makes them highly vulnerable to ecosystem changes and overfishing. We characterized life-history variation across a broad and diverse landscape for this iconic northern freshwater fish and evaluated whether clinal variation was consistent with hypotheses for local adaptation or growth plasticity. We estimated growth-associated traits for 90 populations exposed to a diversity of environments using a Bayesian multivariate hierarchical model. We tested for clinal variation in their somatic growth, size at maturity and reproductive allocation along environmental gradients of lake productivity, climate, prey and exploitation clines under competing hypotheses of plasticity and local adaptation. Clinal life-history variation was consistent with growth plasticity and local adaptations but not harvest-induced evolution. Variation in somatic growth was explained by exploitation, climate and prey fish occurrence. Increased exploitation, from pristine to fully exploited conditions, led to increased somatic growth (from 32 to 45 mm/year) and adult life spans, and reduced age at maturity (from 11 to 8 years). Variation in size at maturity was explained by climate and, less certainly, prey fish occurrence, while reproductive allocation was explained by evolutionary trade-offs with mortality and other traits, but not environment. Lake trout life-history variation within this range was as wide as that observed across dozens of other freshwater species. Lake trout life histories resulted from evolutionary trade-offs, growth plasticity and local adaptations along several environmental clines. Presuming a plastic response, we documented ~1.4-fold growth compensation to exploitation-lower growth compensation than observed in many freshwater fishes. These results suggest that harvested species exposed to spatially structured and diverse environments may have substantial clinal variation on different traits, but due to different processes, and this has implications for their resilience and successful management.

Standing geographic variation in eclosion time and the genomics of host race formation in Rhagoletis pomonella fruit flies.

Taxa harboring high levels of standing variation may be more likely to adapt to rapid environmental shifts and experience ecological speciation. Here, we characterize geographic and host-related differentiation for 10,241 single nucleotide polymorphisms in Rhagoletis pomonella fruit flies to infer whether standing genetic variation in adult eclosion time in the ancestral hawthorn (Crataegus spp.)-infesting host race, as opposed to new mutations, contributed substantially to its recent shift to earlier fruiting apple (Malus domestica). Allele frequency differences associated with early vs. late eclosion time within each host race were significantly related to geographic genetic variation and host race differentiation across four sites, arrayed from north to south along a 430-km transect, where the host races co-occur in sympatry in the Midwest United States. Host fruiting phenology is clinal, with both apple and hawthorn trees fruiting earlier in the North and later in the South. Thus, we expected alleles associated with earlier eclosion to be at higher frequencies in northern populations. This pattern was observed in the hawthorn race across all four populations; however, allele frequency patterns in the apple race were more complex. Despite the generally earlier eclosion timing of apple flies and corresponding apple fruiting phenology, alleles on chromosomes 2 and 3 associated with earlier emergence were paradoxically at lower frequency in the apple than hawthorn host race across all four sympatric sites. However, loci on chromosome 1 did show higher frequencies of early eclosion-associated alleles in the apple than hawthorn host race at the two southern sites, potentially accounting for their earlier eclosion phenotype. Thus, although extensive clinal genetic variation in the ancestral hawthorn race exists and contributed to the host shift to apple, further study is needed to resolve details of how this standing variation was selected to generate earlier eclosing apple fly populations in the North.

Delineating species along shifting shorelines: Tropheus (Teleostei, Cichlidae) from the southern subbasin of Lake Tanganyika.

BACKGROUND: Species delineation is particularly challenging in taxa with substantial intra-specific variation. In systematic studies of fishes, meristics and linear measurements that describe shape are often used to delineate species. Yet, little is known about the taxonomic value of these two types of morphological characteristics. Here, we used Tropheus (Teleostei, Cichlidae) from the southern subbasin of Lake Tanganyika to test which of these types of characters best matched genetic lineages that could represent species in this group of stenotypic rock-dwelling cichlids. We further investigated intra-population variation in morphology. By linking this to a proxy of a population's age, we could assess the evolutionary stability of different kinds of morphological markers. RESULTS: Morphological data was collected from 570 specimens originating from 86 localities. An AFLP approach revealed the presence of five lineages in the southern subbasin: T. moorii, T. brichardi, T. sp. 'maculatus', T. sp. 'Mpimbwe' and T. sp. 'red', which we consider to represent distinct species. Although both types of morphological data supported this classification, a comparison of PST-values that describe inter-population morphological differentiation, revealed a better correspondence between the taxon delineation based on AFLP data and the patterns revealed by an analysis of meristics than between the AFLP-based taxon delineation and the patterns revealed by an analysis of shape. However, classifying southern populations of Tropheus was inherently difficult as they contained a large amount of clinal variation, both in genetic and in morphological data, and both within and among species. A scenario is put forward to explain the current-day distribution of the species and colour varieties and the observed clinal variation across the subbasin's shoreline. Additionally, we observed that variation in shape was larger in populations from shallow shores whereas populations from steep shores were more variable in meristics. This difference is explained in terms of the different timescales at which small and large scale lake level fluctuations affected populations of littoral cichlids at steep and shallow shores. CONCLUSIONS: Our results showed meristics to be more evolutionary stable, and of higher taxonomic value for species delimitation in Tropheus, than linear measurements that describe shape. These results should be taken into account when interpreting morphological differences between populations of highly stenotypic species, such as littoral cichlids from the Great East African Lakes.

Climate-based seed transfer of a widespread shrub: population shifts, restoration strategies, and the trailing edge.

Genetic resources have to be managed appropriately to mitigate the impact of climate change. For many wildland plants, conservation will require knowledge of the climatic factors affecting intraspecific genetic variation to minimize maladaptation. Knowledge of the interaction between traits and climate can focus management resources on vulnerable populations, provide guidance for seed transfer, and enhance fitness and resilience under changing climates. In this study, traits of big sagebrush (Artemisia tridentata) were examined among common gardens located in different climates. We focus on two subspecies, wyomingensis and tridentata, that occupy the most imperiled warm-dry spectrum of the sagebrush biome. Populations collected across the sagebrush biome were recorded for flower phenology and survival. Mixed-effects models examined each trait to evaluate genetic variation, environmental effects, and adaptive breadth of populations. Climate variables derived from population-source locations were significantly associated with these traits (P < 0.0001), explaining 31% and 11% of the flower phenology and survival variation, respectively. To illustrate our model and assess variability in prediction, we examine fixed and focal point seed transfer approaches to map contemporary and climate model ensemble projections in two different regions of the sagebrush biome. A comparison of seed transfer areas predicts that populations from warmer climates become more prevalent, replacing colder-adapted populations by mid-century. However, these warm-adapted populations are often located along the trailing edge, margins of the species range predicted to be lost due to a contraction of the climatic niche. Management efforts should focus on the collection and conservation of vulnerable populations and prudent seed transfer to colder regions where these populations are projected to occur by mid-century. Our models provide the foundation to develop an empirical, climate-based seed transfer system for current and future restoration of big sagebrush.

From transects to transcripts: Teasing apart the architecture of reproductive isolation.

Understanding the processes underlying speciation has long been a challenge to evolutionary biologists. This spurs from difficulties teasing apart the various mechanisms that contribute to the evolution of barriers to reproduction. The study by Rafati et al. () in this issue of Molecular Ecology combines spatially explicit whole-genome resequencing with evaluation of differential gene expression across individuals with mixed ancestry to associate the genomic architecture of reproductive barriers with expression of reproductive incompatibilities. In a natural hybrid zone between rabbit subspecies, Oryctolagus cuniculus cuniculus and O. c. algirus (Figure ), Rafati et al. () use landscape-level patterns of allele frequency variation to identify potential candidate regions of the genome associated with reproductive isolation. These candidate regions are used to test predictions associated with the genomic architecture of reproductive barriers, including the role of structural rearrangements, enrichment of functional categories associated with incompatibilities, and the contribution of protein-coding versus regulatory changes. A lack of structural rearrangements and limited protein-coding changes in candidate regions point towards the importance of regulatory variation as major contributors to genetic incompatibilities, while functional enrichments indicate overrepresentation of genes associated with male infertility. To quantify phenotypic expression of proposed incompatibilities, the authors assess gene expression of experimental crosses. Extensive misregulation of gene expression within the testes of backcross hybrids relative to F1 and parental individuals provides an important link between genotype and phenotype, validating hypotheses developed from assessment of genomic architectures. Together, this work shows how pairing natural hybrid zones with experimental crosses can be used to link observations in nature to mechanistic underpinnings that may be tested experimentally.

Review and clinal variation of New Zealand Anabaxis Raffray (Coleoptera: Staphylinidae: Pselaphinae: Goniaceritae).

The New Zealand members of the genus Anabaxis Raffray are revised to accommodate three species, including one new species: Anabaxis chathamensis sp. nov. A key and an illustrated catalogue to the described species from New Zealand and Australia are included. Lectotypes are designated for A. brevis Oke, A. electrica King, A. foveolata Broun, A. inusitata Blackburn, A. lunatica King, A. quinquefoveolata Raffray, and A. vagus Oke. The widespread New Zealand species A. foveolata exhibits an unusual form of clinal variation in sex-linked characters of the male legs. The length of the tibial spine increased with increasing latitude and the length of the mesotrochanteral spine decreased with increasing latitude.

Patterns of geographic variation of thermal adapted candidate genes in Drosophila subobscura sex chromosome arrangements.

BACKGROUND: The role of chromosomal arrangements in adaptation is supported by the repeatable clinal variation in inversion frequencies across continents in colonizing species such as Drosophila subobscura. However, there is a lack of knowledge on the genetic variation in genes within inversions, possibly targets of climatic selection, across a geographic latitudinal gradient. In the present study we analysed four candidate loci for thermal adaptation, located close to the breakpoints, in two chromosomal arrangements of the sex (A) chromosome of Drosophila subobscura with different thermal preferences. Individual chromosomes with A2 (the inverted arrangement considered warm adapted) or AST (the standard ancestral arrangement considered cold adapted) were sequenced across four European localities at varying latitudes, up to ~ 2500 Kms apart. RESULTS: Importantly, we found very low differentiation for each specific arrangement across populations as well as no clinal patterns of genomic variation. This suggests wide gene exchange along the cline. Differentiation between the sex chromosome arrangements was significant in the two more proximal regions relative to the AST orientation but not in the distal ones, independently of their location inside or outside the inversion. This can be possibly due to variation in the levels of gene flux and/or selection acting in these regions. CONCLUSIONS: Gene flow appears to have homogenized the genetic content within-arrangement at a wide geographical scale, despite the expected diverse selective pressures in the specific natural environments of the different populations sampled. It is thus likely that the inversion frequency clines in this species are being maintained by local adaptation in face of gene flow. The differences between arrangements at non-coding regions might be associated with the previously observed differential gene expression in different thermal regimes. Higher resolution genomic scans for individual chromosomal arrangements performed over a large environmental gradient are needed to find the targets of selection and further elucidate the adaptive mechanisms maintaining chromosomal inversion polymorphisms.