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Premise of research. Narrow hybrid zones are maintained by the counteracting forces of selection and gene flow. Understanding the mechanisms of formation and maintenance of narrow hybrid zones helps elucidate the evolutionary forces shaping reproductive biology, distribution, and diversification. We studied the ecology of the hybrid zone of two Impatiens species, Impatiens rosea and Impatiens balsamina , and the causes of the hybrid zone's restriction in space. Methodology. We characterized floral morphometry for the identification of hybrids and parents. To understand the selection on floral traits, we modeled and compared geographic clines of floral traits. We assessed the effect of environmental niche, local adaptation, reproductive niche, and hybrid fitness on maintaining the structure of the hybrid zone. We studied two hybridization sites, one with an altitudinal gradient (Mulshi) and one without (Dapoli), to test the importance of environmental gradients. Pivotal results. We found that pollination-related floral traits, the length of the nectar spur and the size and shape of the wing petal, differ strongly between the parental populations; that these traits are intermediate in hybrids; and that they form the steepest coincident clines across the hybrid zone. Abiotic environmental niche and hybrid fitness do not regulate the hybrid zone structure. Parental species and hybrids show overlapping pollinators but differ in visitation frequencies. Local adaptation for reproductive success influences hybridization only in the site with an altitudinal gradient. Conclusions. The hybrid zone structure and its influencing factors differ across hybridization sites with and without altitudinal gradient. Neither the tension zone model nor the environment-dependent selection model completely explain this hybrid zone. Pollinator-mediated selection on floral traits is important in maintaining the narrow hybrid zone structure. Ecological factors primarily responsible for lineage divergence are also most likely to govern the dynamics of hybridization of the lineages. [ABSTRACT FROM AUTHOR]

Overwintering monarch (Danaus plexippus) populations have declined since the 1990s. In response, restoration of milkweeds, including Asclepias syriaca (common milkweed), an important host plant in their breeding grounds, has become increasingly common. However, latitudinal variation in milkweed populations suggests the possibility of regional adaptation and the potential for seed provenance to affect restoration success. Using seeds from 20 populations throughout the range of A. syriaca, we tested whether seed mass, germination success, and germination time in the greenhouse demonstrate geographic clines consistent with available evidence for this species from other studies. In addition, we tested for patterns in germination traits consistent with adaptation to spring thermal conditions by planting seeds from 10 populations in growth chambers simulating Minnesota and Kentucky spring temperatures. Even after accounting for seed mass, seeds from higher latitudes germinated faster on average under all conditions. Elevated temperatures accelerated germination time and leaf development time; however, we did not detect geographic patterns in leaf development time, indicating that the processes underlying the latitudinal cline in germination time may be unique to the germination stage. In the thermal adaptation study, high‐latitude populations produced larger seeds and seeds that germinated at a higher rate; however, neither latitudinal trend was observed in the geographic clines study, even though individual seed mass predicted germination success. High‐latitude populations express more favorable germination traits in every setting measured, perhaps due to reduced dormancy. Consequently, we conclude that latitudinal clines are more consistent with adaptation to growing season length than to spring temperatures. [ABSTRACT FROM AUTHOR]

Despite the presence of several cross-variety studies on spoken varieties of regional Italian, research on the intonational transition across geographically close varieties is still scarce. This article tackles this issue by providing a first cross-variety comparison of question intonation in three neighboring varieties of Italian spoken in Campania, namely Neapolitan, Salerno and Cilento Italian. The three varieties are chosen based on their position with respect to the isoglosses identifying the Eboli-Lucera line. Such comparison is made possible using the methodological protocol outlined by Gili Fivela et al. (2015) and specifically concerns yes-no, wh- and disjunctive questions. This explorative study aims at identifying intonational features differenced by frequency of occurrence across space, thereby providing a basis for further quantitative studies on spatial distribution. Based on a corpus elicited with a combination of Discourse Completion Task and reading task, we analyze the phonological features of question tunes in Cilento Italian, while also comparing them to their counterparts in Neapolitan and Salerno Italian. Results show that the three varieties present systemic, realizational and phonotactic differences as well as differences in the frequency of occurrence of tonal events. The intraregional variation across Campania Italian varieties hints at an intonational transition featuring a smooth geographic cline. [ABSTRACT FROM AUTHOR]

Studies of natural hybrid zones can provide documentation of range shifts in response to climate change and identify loci important to reproductive isolation. Using a temporal (36–38 years) comparison of the black‐capped (Poecile atricapillus) and Carolina (P. carolinensis) chickadee hybrid zone, we investigated movement of the western portion of the zone (western Missouri) and assessed whether loci and pathways underpinning reproductive isolation were similar to those in the eastern portion of the hybrid zone. Using 92 birds sampled along the hybrid zone transect in 2016 and 68 birds sampled between 1978 and 1980, we generated 11,669 SNPs via ddRADseq. These SNPs were used to assess movement of the hybrid zone through time and to evaluate variation in introgression among loci. We demonstrate that the interface has moved ~5 km to the northwest over the last 36–38 years, that is, at only one‐fifth the rate at which the eastern portion (e.g., Pennsylvania, Ohio) of the hybrid zone has moved. Temperature trends over the last 38 years reveal that eastern areas have warmed 50% more than western areas in terms of annual mean temperature, possibly providing an explanation for the slower movement of the hybrid zone in Missouri. Our results suggest hybrid zone movement in broadly distributed species, such as chickadees, will vary between areas in response to local differences in the impacts of climate change. [ABSTRACT FROM AUTHOR]

Climate warming is predicted to shift species’ ranges as previously uninhabitable environments just beyond the leading range edges become suitable habitat and trailing range edges become increasingly unsuitable. Understanding which aspects of the environment and species traits mediate these range shifts is critical for understanding species’ possible redistributions under global change, yet we have a limited understanding of the ecological and evolutionary responses underlying population spread or extinction at species’ range edges. Within plant populations, shifts in flowering phenology have been one of the strongest and most consistent responses to climate change, and are likely to play an important role in mediating population dynamics within and beyond species’ ranges. However, the role of phenological shifts, and particularly phenological plasticity, in species’ range shifts remains relatively unstudied. Here, we synthesize literature on phenology, plasticity, and adaptation to suggest ways in which phenological responses to climate may vary across species’ ranges and review the empirical evidence for and against these hypotheses. We then outline how phenological plasticity could facilitate or hinder persistence and potential consequences of phenological plasticity in range expansions, including phenological cues, shifts in correlated traits, altered species interactions, and effects on gene flow. Finally, we suggest future avenues for research, such as characterizing reaction norms for phenology across a species’ range and in beyond-the-range transplant experiments. Given the prevalence and magnitude of phenological shifts, future work should carefully dissect its costs and benefits for population persistence, and incorporate phenological plasticity into models predicting species’ persistence and geographic range shifts under climate change.

Most species and therefore most hybrid zones have historically been defined using phenotypic characters. However, both speciation and hybridization can occur with negligible morphological differentiation. Recently developed genomic tools provide the means to better understand cryptic speciation and hybridization. The Northwestern Crow (Corvus caurinus) and American Crow (Corvus brachyrhynchos) are continuously distributed sister taxa that lack reliable traditional characters for identification. In this first population genomic study of Northwestern and American crows, we use genomic SNPs (nuDNA) and mtDNA to investigate the degree of genetic differentiation between these crows and the extent to which they may hybridize. Our results indicate that American and Northwestern crows have distinct evolutionary histories, supported by two nuDNA ancestry clusters and two 1.1%‐divergent mtDNA clades dating to the late Pleistocene, when glacial advances may have isolated crow populations in separate refugia. We document extensive hybridization, with geographic overlap of mtDNA clades and admixture of nuDNA across >900 km of western Washington and western British Columbia. This broad hybrid zone consists of late‐generation hybrids and backcrosses, but not recent (e.g., F1) hybrids. Nuclear DNA and mtDNA clines had concordant widths and were both centred in southwestern British Columbia, farther north than previously postulated. Overall, our results suggest a history of reticulate evolution in American and Northwestern crows, perhaps due to recurring neutral expansion(s) from Pleistocene glacial refugia followed by lineage fusion(s). However, we do not rule out a contributing role for more recent potential drivers of hybridization, such as expansion into human‐modified habitats. [ABSTRACT FROM AUTHOR]

The article discusses the role of pollinator-mediated selection in the maintenance of pollen color variation. Topics discussed include site-specific pollen color preference in pollen color polymorphism in Erythonium americanum showed by bee pollinators, prevalence of light-colored pollen in Campanula americana; and determination of pollen color by flavonoid and carotenoid compounds that accumulate in the pollen grains.

The genic species concept implies that while most of the genome can be exchanged somewhat freely between species through introgression, some genomic regions remain impermeable to interspecific gene flow. Hence, interspecific differences can be maintained despite ongoing gene exchange within contact zones. This study assessed the heterogeneous patterns of introgression at gene loci across the hybrid zone of an incipient progenitor-derivative species pair, Picea mariana (black spruce) and Picea rubens (red spruce). The spruce taxa likely diverged in geographic isolation during the Pleistocene and came into secondary contact during late Holocene. A total of 300 SNPs distributed across the 12 linkage groups (LG) of black spruce were genotyped for 385 individual trees from 33 populations distributed across the allopatric zone of each species and within the zone of sympatry. An integrative framework combining three population genomic approaches was used to scan the genomes, revealing heterogeneous patterns of introgression. A total of 23 SNPs scattered over 10 LG were considered impermeable to introgression and putatively under diverging selection. These loci revealed the existence of impermeable genomic regions forming the species boundary and are thus indicative of ongoing speciation between these two genetic lineages. Another 238 SNPs reflected selectively neutral diffusion across the porous species barrier. Finally, 39 highly permeable SNPs suggested ancestral polymorphism along with balancing selection. The heterogeneous patterns of introgression across the genome indicated that the speciation process between black spruce and red spruce is young and incomplete, albeit some interspecific differences are maintained, allowing ongoing species divergence even in sympatry. The approach developed in this study can be used to track the progression of ongoing speciation processes. [ABSTRACT FROM AUTHOR]

Clonal plants produce semi-autonomous modules (ramets). The spatial distribution of ramets affects lifetime reproductive success via self-pollination, kin competition and competition among genotypes over space and nutrients. These, in turn, influence the evolution of the timing of flowering in monocarps (flowering is fatal), such as bamboos., The vegetative growth period (flowering interval) in bamboos shows a geographic cline from tropical (short-interval) to temperate (long-interval) regions. However, the mechanisms underlying the emergence of this geographic trend in flowering interval remain elusive., We hypothesized that differences in flowering interval are determined by ecological features that affect the spatial arrangement of ramets and the degree of kin competition. Using a spatially explicit mathematical model, we examined the effects of rhizome elongation, seed and pollen dispersal ranges and inbreeding depression on the evolution of flowering interval., Flowering interval became longer as rhizome length increased but was shorter as seed dispersal range increased. However, flowering interval was less affected when these ranges were extremely large. These results could be caused by intragenet competition due to the spatial structure of genets. If the rhizome is short, each genet forms a clumping structure by vegetative growth and is subject to high intragenet competition. Early flowering may reduce this competition. When seed dispersal range is shorter, kin competition among seeds becomes greater and delayed flowering is a better strategy. When these parameters are extremely large, the effects of this type of competition are reduced, and flowering interval does not change., The effect of inbreeding depression depends on the spatial distribution of ramets formed by vegetative growth. Inbreeding depression reduces reproductive success, and hence, delayed flowering is selected for when both rhizome length and pollen dispersal range are short, and inbreeding with neighbouring siblings is unavoidable., Synthesis. The evolutionary consequences of flowering interval in clonal plants are affected by the spatial distribution of genets. Geographic patterns in flowering interval of bamboos can be explained by differences in rhizome length. Interspecific comparisons among species with different rhizome lengths should be examined by collecting long-term demographic data on the spatial arrangement of ramets. [ABSTRACT FROM AUTHOR]

Abstract: In the last two decades a considerable number of studies have described geographic variation in morphometric, physiological and behavioral traits of over a dozen species of wild south-Asian drosophild fruit flies. Due to strong latitudinal and altitudinal gradients this region is highly diverse with respect to climatic conditions, making it important for studies in evolutionary ecology. In this review, we examine spatial heterogeneity across the Indian subcontinent in almost all of the traits previously investigated (body weight, desiccation tolerance, pigmentation, copulation duration, fecundity, ovariole number, wing length, alcohol dehydrogenase fast allele frequency, rate of water loss and starvation resistance). We find a linear correlation between trait variation and latitude. Our data suggest that a single climatic component, the coefficient of variance of monthly temperature averages, which is strongly correlated with latitude, explains a large proportion of variation in the traits investigated. [Copyright &y& Elsevier]

Differential patterns of introgression between species across ecological gradients provide a fine-scale depiction of extrinsic and intrinsic factors that contribute to the maintenance of species barriers and adaptation across heterogeneous environments., Introgression was examined for 721 individuals collected from the ecological transition zone spanning maritime to continental climates within the Picea sitchensis- Picea glauca contact zone using a panel of 268 candidate gene single nucleotide polymorphisms., Geographic clines showed a strong spatial relationship between allele frequencies and both distance from the ocean along major rivers and mean annual precipitation, indicating a strong role for environmental selection. Interspecific patterns of differentiation using outlier tests revealed three candidate genes that may be targets of long-term divergent selection between the parental species, although contemporary genomic clines within the hybrid zone suggested neutral patterns of introgression for these genes., This study provides a fine-scale analysis of locus-specific introgression, identifying a suite of candidate loci that may be targets of extrinsic or intrinsic selection, with broad application in understanding local adaptation to climate. [ABSTRACT FROM AUTHOR]

Cyphomyrus discorhynchus occurs in the Zambezi River and in the linked systems of the Kwando and the Okavango. We collected specimens from both above and below the Victoria Falls and recorded Electric Organ Discharges. We found a marked degree of anatomical differentiation among the specimens from the Zambezi delta to the Victoria Falls that represents a subspecific, geographical cline, reflecting the great length (1400 km) and high ecological diversity of that river section (Lower and Middle Zambezi). We confirm that the populations above the Falls (i.e. Upper Zambezi, Kwando and Okavango) are differentiated from those below, possessing fewer dorsal fin rays (a median of 30–31 rather than 33–34). The waveforms of the electric organ discharge pulses have four phases and show geographic variation but were briefer for specimens from below the Falls. We resurrect Cyphomyrus cubangoensis (Pellegrin, 1936) for the Upper Zambezi/Kwando/Okavango system. [ABSTRACT FROM AUTHOR]

We tested the applicability of Allen's rule in 47 species and 32 unnamed forms (populations that are probably good species or undefined taxa within a superspecies or species group) of the South American subterranean Hystricomorph rodents of the genus Ctenomys (tuco-tucos) (Rodentia: Ctenomyidae) by analyzing tail length in relation with head and body length, and body mass. Tail length allometry was analyzed by Reduced Major Axis regression while the possible correlation of relative tail length with temperature, precipitation and evapotranspiration variables was explored through Simultaneous Autoregression to account for spatial autocorrelations. Our results indicate that tuco-tucos do not follow Allen's rule but its converse, tail proportion relative to body mass increasing with latitude while body size decreases in the same direction (the trend is similar for tail length relative to head and body length but not statistically significant). Regarding climatic variables, the main predictors of relative tail length were temperature and evapotranspiration variables with trends confirming the positive (non-Allenian) correlation of relative tail length with latitude. We conclude that tuco-tucos, being almost fully subterranean, thermoregulate behaviorally by maintaining constant temperatures within their burrows independent of geographic location. The former confirms previous results that indicated that Ctenomys follows the converse to Bergmann's rule. Relative tail length variation would be a result of simple allometric growth. [ABSTRACT FROM AUTHOR]

Abstract: DNA sequence data often appear to contradict low-level avian taxonomy, which is usually based on patterns of external phenotypic similarity. We examined such an apparent contradiction in the Nearctic rosy-finches. On the basis of several phenotypic characters the finches were divided into three species congeneric with three Asian species. When Nearctic taxa were analyzed in a principal components analysis, 66.9% of phenotypic variation was explained by differences between the Bering Sea and continental populations, sexual dimorphism and a latitudinal cline. Our phylogenetic analysis of mitochondrial ND2 sequences revealed four clades among six species of rosy-finches. Three clades corresponded to three Asian species. The fourth clade included all three Nearctic species. Their haplotypes were not reciprocally monophyletic and the combined genetic variability of all Nearctic taxa was lower than in two of their Asian congeners. A Z-specific intron (ACO1I9) and an autosomal coding locus (MC1R) provided little additional phylogenetic information, most likely because of the longer coalescence times relative to ND2. Phylogeographic analyses of ND2 data revealed significant gene flow among neighboring localities regardless of their taxonomic assignment. Our analyses showed that DNA and phenotypic data are not in conflict, but rather complement each other, and together help clarify species limits. Our data are consistent with a single species in North America, not three. [Copyright &y& Elsevier]

We investigated geographic color variation of the beetle Phelotrupes auratus in the Kinki region of central Japan using a spectrophotometer. The reflectance spectrum of the dorsal surface of the elytron was measured for beetles collected from 23 sites. We focused on λmax(α), the wavelength at the peak (α peak) between 400 and 700 nm (human visual sensitivity range), for analyses of color variation. In populations distributed on the Kii Peninsula, in the southern part of the Kinki region, average λmax(α) values were lower (480–497 nm) than in populations distributed in the area west of Lake Biwa, the western part of the Kinki region (618–633 nm). For populations distributed in the areas south and southeast of Lake Biwa, a geographic cline of λmax(α) was observed approximately along an east–west transect, with average λmax values varying continuously from 624 to 557 nm. The easternmost populations along this cline had almost the same λmax(α) values as the populations distributed west of Lake Biwa. The coefficient of variation for λmax(α) tended to be larger in populations with intermediate averages than those with lower or higher average values. [ABSTRACT FROM AUTHOR]

Individuals of the following Asian populations were surveyed for the presence of a 9-base-pair deletion of mitochondrial DNA (mtDNA): Ainu, Japanese, Korean, Negrito, and Vedda. Although the variation was detected in every population except the Vedda, the frequencies of the variation differed widely among the populations, suggesting a geographic dine. [ABSTRACT FROM AUTHOR]

Background and Aims: Pollinators often drive the evolution of floral traits, but their capacity to influence the evolution of pollen colour remains unclear. Pollen colour in Campanula americana is variable and displays a longitudinal cline from prevalence of deep purple in western populations to white and light-purple pollen in eastern populations. While selection for thermal tolerance probably underlies darker pollen in the west, factors contributing to the predominance of light pollen in eastern populations and the maintenance of colour variation within populations throughout the range are unknown. Here we examine whether pollinators contribute to the maintenance of pollen colour variation in C. americana., Methods: In a flight cage experiment, we assessed whether Bombus impatiens foragers can use pollen colour as a reward cue. We then established floral arrays that varied in the frequency of white- and purple-pollen plants in two naturally occurring eastern populations. We observed foraging patterns of wild bees, totalling >1100 individual visits., Key Results: We successfully trained B. impatiens to prefer one pollen colour morph. In natural populations, the specialist pollinator, Megachile campanulae, displayed a strong and consistent preference for purple-pollen plants regardless of morph frequency. Megachile also exhibited a bias toward pollen-bearing male-phase flowers, and this bias was more pronounced for purple pollen. The other main pollinators, Bombus spp. and small bees, did not display pollen colour preference., Conclusions: Previous research found that Megachile removes twice as much pollen per visit as other bees and can deplete pollen from natural populations. Taken together, these results suggest that Megachile could reduce the reproductive success of plants with purple pollen, resulting in the prevalence of light-coloured pollen in eastern populations of C. americana. Our research demonstrates that pollinator preferences may play a role in the maintenance of pollen colour variation in natural populations., (© The Author(s) 2018. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The genic species concept implies that while most of the genome can be exchanged somewhat freely between species through introgression, some genomic regions remain impermeable to interspecific gene flow. Hence, interspecific differences can be maintained despite ongoing gene exchange within contact zones. This study assessed the heterogeneous patterns of introgression at gene loci across the hybrid zone of an incipient progenitor-derivative species pair, Picea mariana (black spruce) and Picea rubens (red spruce). The spruce taxa likely diverged in geographic isolation during the Pleistocene and came into secondary contact during late Holocene. A total of 300 SNPs distributed across the 12 linkage groups (LG) of black spruce were genotyped for 385 individual trees from 33 populations distributed across the allopatric zone of each species and within the zone of sympatry. An integrative framework combining three population genomic approaches was used to scan the genomes, revealing heterogeneous patterns of introgression. A total of 23 SNPs scattered over 10 LG were considered impermeable to introgression and putatively under diverging selection. These loci revealed the existence of impermeable genomic regions forming the species boundary and are thus indicative of ongoing speciation between these two genetic lineages. Another 238 SNPs reflected selectively neutral diffusion across the porous species barrier. Finally, 39 highly permeable SNPs suggested ancestral polymorphism along with balancing selection. The heterogeneous patterns of introgression across the genome indicated that the speciation process between black spruce and red spruce is young and incomplete, albeit some interspecific differences are maintained, allowing ongoing species divergence even in sympatry. The approach developed in this study can be used to track the progression of ongoing speciation processes., (© 2015 John Wiley & Sons Ltd.)