Genetic Discontinuity Research Articles

Translocation and Aquaculture Impact on Genetic Diversity and Composition of Wild Self-Sustainable Ostrea edulis Populations in the Adriatic Sea

The European flat oyster, Ostrea edulis, is a keystone species suffering major population declines due to overfishing, habitat loss and parasite diseases. Knowledge of its fine-scale population genetic structure and connectivity, needed for effective conservation, restoration and management, is largely lacking. Along the eastern Adriatic Sea, genotyping of 1178 O. edulis individuals at 12 microsatellite loci was conducted, grouping the sampled populations by geographical origin (North, Middle, South Adriatic), shell-farm association (farmed, farm-impacted, wild oysters) and sampling year (2017, 2018), in order to explore spatio-temporal genetic variation and potential footprint of known human-mediated spat translocation events for aquaculture purpose. Short-term temporal genetic structuring of O. edulis populations was less pronounced compared to their spatial variability, which showed genetic discontinuity between O. edulis populations from different geographical regions, with the main boundary separating the North from the Middle and South Adriatic, and the weaker one limiting the flow between the Middle and South Adriatic. While the present culture practise and ongoing spat translocation promotes genetic heterogeneity in the investigated farms, reduced genetic diversity and smallest effective populations size of impacted, i.e. farm-associated O. edulis was consistently recorded in all geographical regions. Taken together, the results reflect regional oceanographic features, ongoing spat translocation and intensive harvesting, which might have reduced the wild O. edulis densities below the critical threshold for reproductive success, compromising settlement and favoring unidirectional gene-flow towards higher density farmed O. edulis. Genetic structure of Adriatic O. edulis populations revealed some concerning demographic changes and farm-wild oyster interactions and hence further investigation and management recommendations are given.

Navigating the Ship of Theseus from typology to cartography

Taxonomy is the business of describing and naming organismal diversity. What that means exactly must shift as our conceptual framework shifts (as it did during the time of Darwin) and as what we are able to see shifts as a result of technological assists. We are at a moment of profound conceptual and technological change. Here I give some personal thoughts on three top questions in taxonomy. Are traditional naming conventions compatible with massive cryptic genetic discontinuity? Can we agree on what we are delimiting and naming? Can we excite public interest without typology?

Revisiting the North-South genetic discontinuity in Central African tree populations: the case of the low-density tree species Baillonella toxisperma

How the Central African rain forests have been affected by climatic fluctuations of the Quaternary remains debated. Phylogeographical studies have shown that tree species from western Central Africa often display spatially congruent genetic discontinuities, supporting the hypothesis that the forest was previously fragmented. Extensive seed dispersal is expected to accelerate the admixture between gene pools but most of the species studied so far have presumably limited seed dispersal abilities. Here, we genotyped 15 nuclear and three plastid microsatellite markers in a low-density Central African tree species with long-distance seed dispersal: Baillonella toxisperma (Sapotaceae). While plastid markers revealed a weak structure in Cameroon, nuclear markers highlighted three genetic clusters: two distributed in Cameroon and separating Atlantic coastal forests from the inland forests, and one cluster occurring in Gabon. Substantial genetic differentiation with a phylogeographical signal was detected only between Cameroonian and Gabonese populations, suggesting two major genetic clusters located approximately North and South of the equatorial climatic hinge. Genetic differentiation was very low between the clusters within Cameroon. This pattern could be partially explained by the climate niche distribution modelling applied on the Last Glacial Maximum (LGM) which predicts a unique remnant population per country. The deep North-South differentiation in a species with long-distance seed dispersal supports the hypothesis that Central African rain forests have been fragmented at the height of the equator during a substantial part of the Quaternary.

Karyological and molecular analysis of Leucanthemum (Compositae, Anthemideae) in Corsica

Karyological, flow-cytometric and molecular analyses indicate that the genus Leucanthemum Mill. (Compositae, Anthemideae) is represented in Corsica (Corse) by two species: the tetraploid L. ircutianum DC. and the hexaploid L. corsicum (Less.) DC. The indication of the occurrence of the diploid L. vulgare Lam. on the island and of a tetraploid chromosome number for L. corsicum, given in former treatments of the genus for Corsica, could not be corroborated. AFLP fingerprinting further suggests that the infraspecific taxonomy of L. corsicum with two subspecies (L. corsicum subsp. corsicum and subsp. fenzlii) and three forms (L. corsicum f. corsicum, f. pinnatifidum and f. eschenlohrianum), which is mainly based on differences in the degree of leaf dissection, is not backed by genetic discontinuities. Owing to the observed little variation in leaf dissection within populations in the wild and the constancy of these features under cultivation, we propose the rank of varieties to taxonomically acknowledge these different stages in the broad spectrum of leaf-dissection grades exhibited by L. corsicum. As a consequence, the two new combinations L. corsicum var. eschenlohrianum (Gamisans) Vogt, Hugot & Oberpr. and L. corsicum var. fenzlii (Gamisans) Vogt, Hugot & Oberpr. are proposed.

Inferring potential barriers to gene flow in tropical populations of Avicennia germinans

Genetic variation within- and divergence among-populations is essential for conservation and management efforts. In plants that are dispersed mainly by ocean currents, physical features of the landscape may influence rates of gene flow among populations by preventing or facilitating dispersal of buoyant propagules. The complex landscape and the pattern of superficial currents acting along the wide latitudinal range of the coasts of Mexico offer an ideal opportunity to evaluate the relevance of oceanographic factors to the genetic diversity of a mangrove species. Here, we infer the role of some oceanic features as potential barriers to gene flow among populations of Avicennia germinans. We used eight nuclear microsatellite markers to estimate recent migration rates and geographic barriers among populations of A. germinans along Mexico’s Atlantic and Pacific coasts. Along the Pacific, we identified potential barriers to gene flow related to the circulation pattern at the mouth of the Gulf of California and Gulf of Tehuantepec in the Pacific. On the Atlantic, population genetic variation coincides with the trends of major ocean currents around the Yucatan Peninsula. Our results suggest that ocean currents and a physical barrier (Baja California Peninsula) have maintained and generated genetic discontinuities along the coasts of Mexico. We find compelling evidence that suggests that northern and southern populations evolve as independent units. Genetic drift has had an important role in determining distribution of genetic diversity in local populations of A. germinans. We strongly recommend the conservation of northern and southern mangrove communities of Mexico; we also suggest use individuals from adjacent populations as genetic source for restoration programs.

Consequences of marine barriers for genetic diversity of the coral-specialist yellowbar angelfish from the Northwestern Indian Ocean.

Ocean circulation, geological history, geographic distance, and seascape heterogeneity play an important role in phylogeography of coral‐dependent fishes. Here, we investigate potential genetic population structure within the yellowbar angelfish (Pomacanthus maculosus) across the Northwestern Indian Ocean (NIO). We then discuss our results with respect to the above abiotic features in order to understand the contemporary distribution of genetic diversity of the species. To do so, restriction site‐associated DNA sequencing (RAD‐seq) was utilized to carry out population genetic analyses on P. maculosus sampled throughout the species’ distributional range. First, genetic data were correlated to geographic and environmental distances, and tested for isolation‐by‐distance and isolation‐by‐environment, respectively, by applying the Mantel test. Secondly, we used distance‐based and model‐based methods for clustering genetic data. Our results suggest the presence of two putative barriers to dispersal; one off the southern coast of the Arabian Peninsula and the other off northern Somalia, which together create three genetic subdivisions of P. maculosus within the NIO. Around the Arabian Peninsula, one genetic cluster was associated with the Red Sea and the adjacent Gulf of Aden in the west, and another cluster was associated with the Arabian Gulf and the Sea of Oman in the east. Individuals sampled in Kenya represented a third genetic cluster. The geographic locations of genetic discontinuities observed between genetic subdivisions coincide with the presence of substantial upwelling systems, as well as habitat discontinuity. Our findings shed light on the origin and maintenance of genetic patterns in a common coral reef fish inhabiting the NIO, and reinforce the hypothesis that the evolution of marine fish species in this region has likely been shaped by multiple vicariance events.

Genetic discontinuities and abundant historical gene flow in wild lotus Nelumbo nucifera populations from the Yangtze River

Wild populations of Nelumbo nucifera are valuable genetic resources and provide significant ecological functions for aquatic ecosystems. However, they have suffered from habitat fragmentation and degradation. Here, the genetic connectivity and variation of N. nucifera wild populations were analysed based on 22 microsatellite markers and 10 populations along the Yangtze River. Abundant historical gene flows were found among populations (Nm: 1.806–3.735). In contrast, low levels of recent migration rates were revealed and only two migrants were detected in the first generation among populations. The results indicated that habitat deteriorations have resulted in dramatically reduced gene flow, and the seasonal floods failed to act as a valid path for migration. The bidirectional gene flows, combined with the lack of accumulation effects in downstream populations, suggested that both river flow and zoochory (or human activity) contributed to gene exchange. High levels of genetic differentiation were found in all pairs of populations (FST: 0.208 - 0.666; G”ST: 0.306 - 0.866) and in the global estimate across all populations (FST = 0.403, G”ST = 0.593), indicating genetic discontinuities among populations. The genetic depauperation (HE = 0.273) and obvious genetic structure in N. nucifera populations were explained by reduced gene flow and accentuated genetic drift, combined with the inbreeding and repeated genetic bottlenecks. Based on these results, a conservation strategy for protecting all isolated populations to maintain genetic diversity of wild lotus is proposed, and hydrological connectivity should be facilitated across the aquatic system.

Genetic variation, demographic history and phylogeography of tire track eel, Mastacembelus favus (Synbranchiformes: Mastacembelidae) in Southeast Asia

The complex climatic and geological history of Southeast Asia has been hypothesised to determine the most important aspects of the current phylogeographical structure and distribution of living organisms throughout the region. To test existing hypotheses, the genetic structure of the tire track eel, Mastacembelus favus, was investigated using 823 bp of mitochondrial DNA cytochrome b from 469 individuals from 51 localities encompassing its native range. The results classified all haplotypes into two major lineages, Lineage 1, which was further divided into Lineages 1a (lower Mekong, eastern Gulf of Thailand and Malay—Thai Peninsula), 1b (Banpakong River), 1c (Chao Phraya, Gulf of Thailand and Malay—Thai Peninsula) and 1d (Khlang Yai River), and Lineage 2, the upper reaches of the lower Mekong and the middle Mekong. Strong genetic discontinuities dated approximately 5 MYA were discovered in the Mekong with limited geographical overlap, suggesting a historically dissected drainage between two sections and species colonisation via different routes. The widespread Lineage 1 showed a strong signature of population expansion during the Pleistocene climate oscillation. Haplotype characteristics in the Malay—Thai Peninsula are hypothesised to result from postglacial dispersal from the Mekong and Chao Phraya through an extended Pleistocene drainage network.

Does the widely distributed rodent Calomys tener (Cricetidae: Sigmodontinae) constitute a single evolutionary unit?

The nominal species Calomystener (Winge, 1887) ranges broadly in open lands of the Caatinga, Cerrado, Pantanal and Mata Atlântica of Brazil, and was recently reported from the Pampas of southern Brazil, and in the Selva Paranaense of eastern Paraguay and northeastern Argentina. This rodent can be infected with the pathogenic Araraquara hantavirus in Brazil. Given that most epidemiological studies have not taken into account updated taxonomic findings of their rodent hosts, in this study, we obtained sequence data of the Cyt-b and COI genes of specimens of C.tener from 22 different geographical localities from throughout the currently known distribution of the species (including individuals from Argentina, Paraguay, Bolivia, and Brazil) to test if it constitutes a single genetic unit or if it presents genetic discontinuities that may represent different evolutionary lineages. Phylogenetic analyses including several species of Calomys recovered several clades with strong support. Regarding C.tener, it is recovered as sister to the node that cluster C.laucha (Fischer, 1814) sensu lato, C.expulsus (Lund, 1841) and species in the C.callosus (Rengger, 1830) species complex. At the intraspecific level there are no genetic gaps among haplotypes of C.tener that could suggest more than one species. The recent captures in the Pampas of southern Brazil and in the Selva Paranaense suggest that the species may be colonizing new geographic areas.

Global phylogeography of toxic cyanobacteria Moorea producens reveals distinct genetic partitioning influenced by Proterozoic glacial cycles

Lyngbya majuscula is a marine filamentous cyanobacteria belonging to the family Oscillatoriaceae. Recent phylogenetic analyses of L. majuscula have reclassified a subset of this species into various genera such as Moorea, Okeania and Dapis. From the genus Moorea, Moorea producens is a toxic invasive cyanobacterium that produces bioactive secondary metabolites that can cause severe inflammation and blistering. Despite the global distribution of M. producens, little information is available on their origin, patterns of dispersal and population structure. In this study, the spatial population structure of M. producens was investigated using near-complete 16S rRNA sequences. Analysis of the global population of M. producens by Isolation by Distance and STRUCTURE revealed two significantly distinct cosmopolitan populations that were separated by a genetic break. Lineage-specific divergence estimates of 147 cyanobacterial taxa, based on a relaxed molecular clock indicated the first global emergence of M. producens during the Mesoarchean and a subsequent global recolonization during the Mesoproterozoic period. We conclude that the genetic discontinuity between both cosmopolitan populations is attributed to refugia associated with Proterozoic glacial cycles.

Phylogeography of the Neotropical epiphytic orchid, Brassavola nodosa: evidence for a secondary contact zone in northwestern Costa Rica.

Spatial patterns of genetic variation can reveal otherwise cryptic evolutionary and landscape processes. In northwestern Costa Rica, an approximately concordant genetic discontinuity occurs among populations of several plant species. We conducted phylogeographic analyses of an epiphytic orchid, Brassavola nodosa, to test for genetic discontinuity and to explore its underlying causes. We genotyped 18 populations with 19 nuclear loci and two non-coding chloroplast sequence regions. We estimated genetic diversity and structure, relative importance of pollen and seed dispersal, and divergence time to understand how genetic diversity was spatially partitioned. Nuclear genetic diversity was high with little differentiation among populations (GSTn = 0.065). In contrast, chloroplast haplotypes were highly structured (GSTc = 0.570) and reveal a discontinuity between northwestern and southeastern populations within Costa Rica. Haplotype differences suggest two formerly isolated lineages that diverged ~10,000-100,000 YBP. Haplotype mixing and greater genetic diversity occur in an intermediate transition zone. Patterns of nuclear and chloroplast data were consistent. Different levels of genetic differentiation for the two genomes reflect the relative effectiveness of biotic versus abiotic dispersers of pollen and seeds, respectively. Isolation of the two lineages likely resulted from the complex environmental and geophysical history of the region. Our results suggest a recent cryptic seed dispersal barrier and/or zone of secondary contact. We hypothesize that powerful northeasterly trade winds hinder movement of wind-borne seeds between the two regions, while the multi-directional dispersal of pollen by strong-flying sphinx moths resulted in lower differentiation of nuclear loci.

Hitchhiking the high seas: Global genomics of rafting crabs.

Population differentiation and diversification depend in large part on the ability and propensity of organisms to successfully disperse. However, our understanding of these processes in organisms with high dispersal ability is biased by the limited genetic resolution offered by traditional genotypic markers. Many neustonic animals disperse not only as pelagic larvae, but also as juveniles and adults while drifting or rafting at the surface of the open ocean. In theory, the heightened dispersal ability of these animals should limit opportunities for species diversification and population differentiation. To test these predictions, we used next‐generation sequencing of genomewide restriction‐site‐associated DNA tags (RADseq) and traditional mitochondrial DNA sequencing, to investigate the species‐level relationships and global population structure of Planes crabs collected from oceanic flotsam and sea turtles. Our results indicate that species diversity in this clade is low—likely three closely related species—with no evidence of cryptic or undescribed species. Moreover, our results indicate weak population differentiation among widely separated aggregations with genetic indices showing only subtle genetic discontinuities across all oceans of the world (RADseq F ST = 0.08–0.16). The results of this study provide unprecedented resolution of the systematics and global biogeography of this group and contribute valuable information to our understanding of how theoretical dispersal potential relates to actual population differentiation and diversification among marine organisms. Moreover, these results demonstrate the limitations of single gene analyses and the value of genomic‐level resolution for estimating contemporary population structure in organisms with large, highly connected populations.

The hidden side of a major marine biogeographic boundary: a wide mosaic hybrid zone at the Atlantic-Mediterranean divide reveals the complex interaction between natural and genetic barriers in mussels.

The Almeria-Oran Front (AOF) is a recognised hotspot of genetic differentiation in the sea, with genetic discontinuities reported in more than 50 species. The AOF is a barrier to dispersal and an ecological boundary; both can determine the position of these genetic breaks. However, the maintenance of genetic differentiation is likely reinforced by genetic barriers. A general drawback of previous studies is an insufficient density of sampling sites at the transition zone, with a conspicuous lack of samples from the southern coastline. We analysed the fine-scale genetic structure in the mussel Mytilus galloprovincialis using a few ancestry-informative loci previously identified from genome scans. We discovered a 600-km-wide mosaic hybrid zone eastward of the AOF along the Algerian coasts. This mosaic zone provides a new twist to our understanding of the Atlantic-Mediterranean transition because it demonstrates that the two lineages can live in sympatry with ample opportunities to interbreed in a large area, but they hardly do so. This implies that some form of reproductive isolation must exist to maintain the two genetic backgrounds locally cohesive. The mosaic zone ends with an abrupt genetic shift at a barrier to dispersal in the Gulf of Bejaia, Eastern Algeria. Simulations of endogenous or exogenous selection in models that account for the geography and hydrodynamic features of the region support the hypothesis that sister hybrid zones could have been differentially trapped at two alternative barriers to dispersal and/or environmental boundaries, at Almeria in the north and Bejaia in the south. A preponderantly unidirectional north-south gene flow next to the AOF can also maintain a patch of intrinsically maintained genetic background in the south and the mosaic structure, even in the absence of local adaptation. Our results concur with the coupling hypothesis that suggests that natural barriers can explain the position of genetic breaks, while their maintenance depends on genetic barriers.

Phylogeographic structuring of the amphidromous shrimp Atya scabra (Crustacea, Decapoda, Atyidae) unveiled by range-wide mitochondrial DNA sampling

Species with biological traits favourable to long-distance marine larval dispersal might show a phylogeographic structuring over broad regions, even when they are genetically connected within smaller scales. Here, we evaluated this hypothesis by using the widespread amphidromous shrimp Atya scabra, predicting a genetic discontinuity across biogeographical barriers throughout the Western Gulf of Mexico (WGM), Caribbean Sea (CS), south-western Atlantic (SWA) and eastern Atlantic (EA). Using cytochrome oxidase subunit 1 (COI) and 16S ribosomal unit (16S) gene fragments, we did a phylogeographic assessment and genetic characterisation with Bayesian clustering, AMOVA, haplotype networks and demographic analyses. As predicted, three discrete genetic groups, corresponding to the regions WGM, CS and EA, were uncovered by COI, as well an unpredicted SWA+CS group. The 16S fragment detected a low genetic variation, probably owing to a recent lineage differentiation, which was estimated by the COI molecular clock. We evaluated the role of the biological traits of A. scabra, as well as the consequences of Panama Isthmus closure and Pleistocene glaciation cycles in the lineage isolation of WGM and EA, as well as the genetic connectivity shown within regions and between CS and SWA. Our results highlighted that amphidromous species genetically connected over large scales should be genetically characterised in their wide distribution to provide more comprehensive systematics and to assist decision-making in biological conservation.

Genetic diversity and structure of natural Juglans regia L. populations in the southern Kyrgyz Republic revealed by nuclear SSR and EST-SSR markers

Persian walnut (Juglans regia L.), also known as common walnut, is an economically and ecologically important species in the Kyrgyz Republic. Natural forests of J. regia, walnut forests, grow between western and southwestern slopes of the Fergana and Chatkal mountain ridges in the southern Kyrgyz Republic. We investigated 11 natural populations of J. regia across its geographic range in the Kyrgyz Republic using eight nuclear microsatellite (nSSR) and eight expressed sequence tag (EST)-derived SSR (EST-SSR) markers. The SSR markers revealed comparatively high levels of genetic diversity (HO = 0.538, HE = 0.524). The overall genetic differentiation among populations was low, but statistically significant (FST = 0.068). Significant correlation between genetic and geographic distances was observed, indicating an isolation-by-distance (IBD) model for J. regia. Spatial analysis of molecular variance (SAMOVA) and Bayesian analysis assigned individuals to two main genetic groups separating central region walnut populations (Jalal-Abad province) and southeastern region walnut populations (Osh province). Genetic diversity parameters such as gene diversity and allelic richness were significantly lower in the Osh province than in the Jalal-Abad province. Detection of significant genetic discontinuities suggested the existence of physical barriers to migration and gene flow among regions. We suggest that the Osh province and Jalal-Abad province populations should be considered as two evolutionary significant units (ESUs) for conservation efforts.

Ancient DNA of Phoenician remains indicates discontinuity in the settlement history of Ibiza

Ibiza was permanently settled around the 7th century BCE by founders arriving from west Phoenicia. The founding population grew significantly and reached its height during the 4th century BCE. We obtained nine complete mitochondrial genomes from skeletal remains from two Punic necropoli in Ibiza and a Bronze Age site from Formentara. We also obtained low coverage (0.47X average depth) of the genome of one individual, directly dated to 361–178 cal BCE, from the Cas Molí site on Ibiza. We analysed and compared ancient DNA results with 18 new mitochondrial genomes from modern Ibizans to determine the ancestry of the founders of Ibiza. The mitochondrial results indicate a predominantly recent European maternal ancestry for the current Ibizan population while the whole genome data suggest a significant Eastern Mediterranean component. Our mitochondrial results suggest a genetic discontinuity between the early Phoenician settlers and the island’s modern inhabitants. Our data, while limited, suggest that the Eastern or North African influence in the Punic population of Ibiza was primarily male dominated.

Porous barriers? Assessment of gene flow within and among sympatric long-eared bat species.

Species are the basic units for measuring biodiversity and for comprehending biological interactions. Yet, their delineation is often contentious, especially in groups that are both diverse and phenotypically conservative. Three cryptic species of long‐eared bats, Plecotus auritus, P. austriacus, and P. macrobullaris, co‐occur over extensive areas of Western Europe. The latter is a fairly recent discovery, questioning the overall diversity of the entire Plecotus complex. Yet, high morphological and acoustic similarities compromise the reliable identification of long‐eared bats in the field. We postulate that such extensive phenotypic overlap, along with the recurrent observation of morphologically intermediate individuals, may hide rampant interspecific hybridization. Based on a geographic sampling centered on areas of sympatry in the Alps and Corsica, we assessed the level of reproductive isolation of these three Plecotus species with mitochondrial and nuclear markers, looking at both inter‐ and intraspecific genetic population structuring. No sign of hybridization was detected between these three species that appear well separated biologically. Genetic structuring of populations, however, reflected different species‐specific responses to environmental connectivity, that is, to the presence of orographic or sea barriers. While the Alpine range and the Ligurian Sea coincided with sharp genetic discontinuities in P. macrobullaris and P. austriacus, the more ubiquitous P. auritus showed no significant population structuration. There were clear phylogeographic discrepancies between microsatellite and mitochondrial markers at the intraspecific level, however, which challenges the reliance on simple barcoding approaches for the delineation of sound conservation units.

High throughput ANI analysis of 90K prokaryotic genomes reveals clear species boundaries

A fundamental question in microbiology is whether there is continuum of genetic diversity among genomes, or clear species boundaries prevail instead. Whole-genome similarity metrics such as Average Nucleotide Identity (ANI) help address this question by facilitating high resolution taxonomic analysis of thousands of genomes from diverse phylogenetic lineages. To scale to available genomes and beyond, we present FastANI, a new method to estimate ANI using alignment-free approximate sequence mapping. FastANI is accurate for both finished and draft genomes, and is up to three orders of magnitude faster compared to alignment-based approaches. We leverage FastANI to compute pairwise ANI values among all prokaryotic genomes available in the NCBI database. Our results reveal clear genetic discontinuity, with 99.8% of the total 8 billion genome pairs analyzed conforming to >95% intra-species and <83% inter-species ANI values. This discontinuity is manifested with or without the most frequently sequenced species, and is robust to historic additions in the genome databases.

Habitat discontinuities form strong barriers to gene flow among mangrove populations, despite the capacity for long‐distance dispersal

AbstractAimMangrove forests are among the world's most important ecosystems but are declining rapidly worldwide. Effective conservation management requires a better understanding of the patterns and drivers of gene flow across a range of spatial scales. Despite the capacity for long‐distance propagule dispersal, field studies suggest that mangrove propagules tend not to disperse far from the release point, which has important implications for the impact of habitat discontinuities on gene flow. We use a comprehensive seascape genomics approach to investigate this concept in the world's most widely distributed mangrove species, Avicennia marina.LocationTwenty‐one sites along 2,400 km of Western Australian coastline.MethodsWe used 6,162 neutral SNP loci and a hierarchical sampling design to investigate patterns of gene flow and structuring among 21 populations of A. marina. We combined these data with GIS spatial analyses in a regression model to test the relative influence of habitat continuity and geographic distance on patterns of genetic differentiation.ResultsWe found a complex pattern of gene flow; broadscale isolation‐by‐distance, disrupted by strong genetic discontinuities that coincided with gaps in mangrove distribution. These genetic discontinuities formed seven discrete subpopulations with negligible evidence for recent migration among them. The regression model combining marine geographic distance and habitat continuity as explanatory variables best fit the data, explaining 86% of the total genetic variation.Main ConclusionsOur results validate previous assertions that propagule dispersal in A. marina is spatially limited and demonstrate that significant gaps in mangrove distribution present strong barriers to stepping‐stone gene flow in this species. This reiterates that dispersive life history features cannot be assumed to lead to widespread connectivity and demonstrates that effective management of these important ecosystem builders should prioritize restoring habitat continuity and minimizing further fragmentation.

Genetic discontinuity of Digenea (Rhodomelaceae, Rhodophyta) from Mexico supports recognition of two new species, D. mexicana and D. rafaelii

Genetic discontinuity of Digenea (Rhodomelaceae, Rhodophyta) from Mexico supports recognition of two new species, D. mexicana and D. rafaelii