Around or across the Carpathians: colonization model of the Danube basin inferred from genetic diversification of stone loach (Barbatula barbatula) populations

Despite increasing information about postglacial recolonization of European freshwater systems, very little is known about pre-Pleistocene history. We used data on the recent distribution and phylogenetic relationships of stone loach mitochondrial lineages to reconstruct the initial colonization pattern of the Danube river system, one of the most important refuges for European freshwater ichthyofauna. Fine-scale phylogeography of the Danubian populations revealed five highly divergent lineages of pre-Pleistocene age and suggested the multiple origin of the Danubian stone loach. The mean sequence divergence among lineages extended from 7.0% to 13.4%, which is the highest intraspecific divergence observed so far within this river system. Based on the phylogeographical patterns, we propose the following hypothesis to relate the evolution and dispersal of the studied species with the evolution of the Danube river system and the Carpathian Mountains: (i) during the warmer period in the Miocene, the areas surrounding the uplifting Alps and Carpathians served as mountainous refuges for cold-water adapted fish and promoted the diversification of its populations, and (ii) from these refuges, colonization of the emerging Danube river system may have taken place following the retreat of the Central Paratethys. Co-existence of highly divergent mtDNA lineages in a single river system shows that range shifts in response to climatic changes during the Quaternary did not cause extensive genetic homogenization in the stone loach populations. However, the wide distribution of some mtDNA lineages indicates that the Pleistocene glaciations promoted the dispersal and mixing of populations through the lowlands.     

Genetic diversity of North American populations of Cristatella mucedo, inferred from microsatellite and mitochondrial DNA

Research over the past 20 years has shown, with the help of molecular markers, that the population genetics and distribution patterns of freshwater invertebrates in North America are often more complex than was previously believed. Here we extend this research to an, as yet, unstudied but widespread and common group, the freshwater bryozoans. Colonies of the bryozoan Cristatella mucedo were collected from a number of lakes across central North America, and were characterized genetically by analysis of microsatellite loci and mitochondrial DNA (mtDNA) cytochrome b sequences. The microsatellites illustrate a pattern of generally diverse and highly differentiated populations that contain little evidence of recent gene flow. The mtDNA sequences yielded highly variable levels of divergence, ranging from 0.0 to 8.8% within populations, and 0.0 to 9.8% among populations. The multiple divergent mtDNA lineages within populations provide evidence for repeated colonization events. The lack of clustering of haplotypes by site suggests that there has been widespread dispersal of multiple genetic lineages since the last ice age. While some of the haplotype lineages may have evolved in disjunct glacial refugia, the maximum levels of divergence predate the time since the last glacial-interglacial cycles. It is likely that multiple factors including vicariance events, patterns of dispersal, localized extinction, and an unusual life history, explain the unique phylogeographic patterns evident today in populations of C. mucedo.     

Low interbasin connectivity in a facultatively diadromous fish: evidence from genetics and otolith chemistry

Southern smelts (Retropinna spp.) in coastal rivers of Australia are facultatively diadromous, with populations potentially containing individuals with diadromous or wholly freshwater life histories. The presence of diadromous individuals is expected to reduce genetic structuring between river basins due to larval dispersal via the sea. We use otolith chemistry to distinguish between diadromous and nondiadromous life histories and population genetics to examine interbasin connectivity resulting from diadromy. Otolith strontium isotope (⁸⁷Sr:⁸⁶Sr) transects identified three main life history patterns: amphidromy, freshwater residency and estuarine/marine residency. Despite the potential for interbasin connectivity via larval mixing in the marine environment, we found unprecedented levels of genetic structure for an amphidromous species. Strong hierarchical structure along putative taxonomic boundaries was detected, along with highly structured populations within groups using microsatellites (F_ST = 0.046–0.181), and mtDNA (Φ_ST = 0.498–0.816). The presence of strong genetic subdivision, despite the fact that many individuals reside in saline water during their early life history, appears incongruous. However, analysis of multielemental signatures in the otolith cores of diadromous fish revealed strong discrimination between river basins, suggesting that diadromous fish spend their early lives within chemically distinct estuaries rather than the more homogenous marine environment, thus avoiding dispersal and maintaining genetic structure.     

Dispersal history of a spider (Stegodyphus lineatus) across contiguous deserts: vicariance and range expansion

Israel marks a crossroads between three continents encompassing several phytogeographical and zoogeographical zones. In this complex area, the flow of species from different biogeographical regions creates opportunities to study how geographical division and colonization routes affect current distribution and structure of resident populations of organisms associated with desert and arid environments, habitats that may have persisted throughout Pleistocene glacial periods. The present paper analyses the population history of the spider Stegodyphus lineatus in the contiguous Negev and Judean deserts in Israel using allozyme and mtDNA variation. The distinct patterns of variation indicate that Judean and Negev populations are vicariant lineages. The residence time was longer in Judea, where populations were more polymorphic for mtDNA, showed isolation by distance and were less structured than in the Negev. The Negev population, possibly linked to other Mediterranean populations of S. lineatus , consisted of two subdivisions derived from a recent eastward expansion across the central Negev watershed. Despite differences in age and level of structure, all lineages show similar dispersal processes dominated by restricted gene flow. The distribution patterns of allozyme and mtDNA markers are unrelated to geographical patterns of precipitation and vegetation. Rather, they follow large-scale topographic features, namely the water divide between Mediterranean and Afro-Syrian rift drainages and between eastern and western Negev drainages.   © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 739–754.     

Biogeography of ‘Cyprinella lutrensis’: intensive genetic sampling from the Pecos River ‘melting pot’ reveals a dynamic history and phylogenetic complexity

Thorough sampling is necessary to delineate lineage diversity for polytypic ‘species’ such as Cyprinella lutrensis. We conducted extensive mtDNA sampling (cytochrome b and ND4) from the Pecos River, Rio Grande, and South Canadian River, New Mexico. Our study focussed on the Pecos River due to its complex geological history and potential to harbour multiple lineages. We used geometric–morphometric, morphometric, and meristic analyses to test for phenotypic divergence and combined nucDNA with mtDNA to test for cytonuclear disequilibrium and combined our sequences with published data to conduct a phylogenetic re‐assessment of the entire C. lutrensis clade. We detected five co‐occurring mtDNA lineages in the Pecos River, but no evidence for cytonuclear disequilibrium or phenotypic divergence. Recognized species were interspersed amongst divergent lineages of ‘C. lutrensis’. Allopatric divergence among drainages isolated in the Late Miocene and Pliocene apparently produced several recognized species and major divisions within ‘C. lutrensis’. Pleistocene re‐expansion and subsequent re‐fragmentation of a centralized lineage founded younger, divergent lineages throughout the Rio Grande basin and Edwards Plateau. There is also evidence of recent introductions to the Rio Grande, Pecos and South Canadian Rivers. Nonetheless, deeply divergent lineages have coexisted since the Pleistocene.     

Genetic surfing,not allopatric divergence,explains spatial sorting of mitochondrial haplotypes in venomous coralsnakes

Strong spatial sorting of genetic variation in contiguous populations is often explained by local adaptation or secondary contact following allopatric divergence. A third explanation, spatial sorting by stochastic effects of range expansion, has been considered less often though theoretical models suggest it should be widespread, if ephemeral. In a study designed to delimit species within a clade of venomous coralsnakes, we identified an unusual pattern within the Texas coral snake (Micrurus tener): strong spatial sorting of divergent mitochondrial (mtDNA) lineages over a portion of its range, but weak sorting of these lineages elsewhere. We tested three alternative hypotheses to explain this pattern—local adaptation, secondary contact following allopatric divergence, and range expansion. Collectively, near panmixia of nuclear DNA, the signal of range expansion associated sampling drift, expansion origins in the Gulf Coast of Mexico, and species distribution modeling suggest that the spatial sorting of divergent mtDNA lineages within M. tener has resulted from genetic surfing of standing mtDNA variation—not local adaptation or allopatric divergence. Our findings highlight the potential for the stochastic effects of recent range expansion to mislead estimations of population divergence made from mtDNA, which may be exacerbated in systems with low vagility, ancestral mtDNA polymorphism, and male‐biased dispersal.     

Age, phylogeography and population structure of the microendemic banded spring snail, Mexipyrgus churinceanus

Recent theoretical and empirical studies of phylogeography and population structure indicate that many processes influence intraspecific evolutionary history. The present study represents the first examination of various forces influencing the spatial and temporal patterns of sequence variation in the freshwater Mexican banded spring snail, Mexipyrgus churinceanus. This snail occurs in one of the most critically endangered centres of freshwater endemism, the desert ecosystem of Cuatro Ciénegas. From cytochrome b mtDNA sequence variation, there is strong evidence of long-term isolation of three regions, suggesting that these regions represent evolutionarily distinct lineages. Molecular clock estimates of clade age indicate a time to most recent common ancestor of approximately 2.5 million years ago (Ma). The three regions differ considerably in the historical and demographic forces affecting population structure. The western populations have extremely low mtDNA diversity consistent with a severe bottleneck dating to 50,000 years before present (bp). The nearby Rio Mesquites drainage is characterized by fragmentation events, restricted gene flow with isolation by distance, and higher levels of mtDNA polymorphism. These patterns are consistent with the long-term stability of this drainage along with habitat heterogeneity and brooding contributing to population isolation and restricted gene flow. Southeastern populations show evidence of range expansion and a strong influence of genetic drift. Migration rates between drainages indicate very little gene flow between drainages except for asymmetric migration from the Rio Mesquites into both western and southeastern drainages.     

Reconciling patterns of genetic variation with stream structure, earth history and biology in the Australian freshwater fish Craterocephalus stercusmuscarum (Atherinidae)

We examined the consequences of barriers, stream architecture and putative dispersal capability on levels of genetic differentiation among populations of the freshwater fish Craterocephalus stercusmuscarum. Seven polymorphic allozyme loci and sequences of a 498-bp fragment of the ATPase 6 mitochondrial DNA (mtDNA) gene were used to assess patterns of genetic variation among 16 populations from upland and lowland streams of five drainages in northern Queensland, Australia. Concordant patterns at both genetic markers revealed that there were significant levels of genetic subdivision among all populations, while an analysis of molecular variation showed that the distribution of genetic diversity was not consistent with contemporary drainage structure. There were reciprocally monophyletic mtDNA clades and fixed or large frequency differences at allozyme loci either side of instream barriers such as waterfalls. This implied barriers were effective in restricting gene flow between upland and lowland populations separated by waterfalls. However, there were two genetically distinct groups in upland areas, even within the same subcatchment, as well as high levels of genetic subdivision among lowland populations, suggesting barriers alone do not explain the patterns of genetic diversity. The data revealed a complex phylogeographic pattern, which we interpreted to be the result of one or more invasion events of independent lineages to different sections of each drainage, possibly mediated by well documented geomorphological changes. Our results highlight the importance of earth structure and history in shaping population genetic structure in stream organisms where dispersal capability may be limited, and reveal that the contemporary structure of drainages is not necessarily a good indicator of genetic relationships among populations.     

Late glacial history of the cold-adapted freshwater fish Cottus gobio,revealed by microsatellites

The distribution of genetic diversity at 10 highly polymorphic microsatellite loci within the European freshwater fish, Cottus gobio, L. was examined. The sampling range comprised a large geographical scale including lineages known to be highly divergent at both mitochondrial DNA (mtDNA) and allozymes. An analysis of genetic variability within populations showed that expected heterozygosity and allelic richness could be explained largely by current effective population sizes. Evidence was found, however, that historical processes predating the last major glaciation affected allelic richness. In addition to confirming the large-scale patterns from earlier studies, the microsatellite data revealed new insights into recent processes by analysing genetic structure within ancient lineages defined by mtDNA data. Stepwise mutation model (SMM) and nonSMM-based methods demonstrated a clear genetic structuring within the Northwestern European lineage comprising populations from Britain and Belgium, and within the Central European lineage populations from the rivers Danube, Elbe and Main. Supported by an analysis of genetic variability within populations these results showed that the bullhead populations most probably persisted throughout the last major glaciation within the British Isles and within the drainages of the rivers Elbe and Main. Such observations provide the first genetic evidence for a glacial refugium in such close proximity to the European glacial margins.     

Tropical and temperate freshwater amphidromy: a comparison between life history characteristics of Sicydiinae,ayu, sculpins and galaxiids

Amphidromy is a distinctive form of diadromy, but differences in the life histories of tropical and temperate amphidromous fishes suggest that there are two types of freshwater amphidromy. The life histories of Sicydiinae gobies, ayu (Plecoglossus altivelis), Japanese sculpins (Cottus) and galaxiids (Galaxiidae), suggest that the Sicydiinae are representatives of tropical freshwater amphidromy, whereas ayu, sculpins and galaxiids are representatives of temperate freshwater amphidromy. The Sicydiine larval stage may be required to occur in the ocean for all species, but ayu, sculpins and galaxiids have landlocked or fluvial forms with larvae that do not need to enter the ocean for larval feeding and growth. This suggests that Sicydiine larvae have a high oceanic dependency whereas ayu, sculpins and galaxiid larvae have a low oceanic dependency. Freshwater amphidromous fish in tropical and temperate zones appear to have developed two different strategies in the evolution of their life histories. It is likely that the evolutionary direction of the larval stage of tropical amphidromy is to remain in the sea and that of temperate amphidromy is towards having the ability to remain in freshwater if needed. Tropical and temperate amphidromy appear to be biologically informative categories and evaluations of this hypothesis will facilitate better understanding of the various forms of amphidromy in the future.     

Population genetics of the endangered South American freshwater turtle, Podocnemis unifilis, inferred from microsatellite DNA data

We studied the population genetics of Podocnemis unifilis turtles within and among basins in the Orinoco and Amazon drainages using microsatellites. We detected high levels of genetic diversity in all sampled localities. However, ‘M-ratio’ tests revealed a substantial recent population decline in ten localities, in accord with current widespread exploitation. Our results reveal a consistent pattern across multiple analyses, showing a clear subdivision between the populations inhabiting the Amazon and Orinoco drainages despite a direct connection via the Casiquiare corridor, and suggesting the existence of two biogeographically independent and widely divergent lineages. Genetic differentiation followed an isolation-by-distance model concordant with hypotheses about migration. It appears that migration occurs via the flooded forest in some drainages, and via river channels in those where geographic barriers preclude dispersal between basins or even among nearby tributaries of the same basin. These observations caution against making generalizations based on geographically restricted data, and indicate that geographically proximate populations may be demographically separate units requiring independent management.     

Phylogeography of an Island endemic, the Puerto Rican Freshwater Crab (Epilobocera sinuatifrons)

The endemic Puerto Rican crab, Epilobocera sinuatifrons (Pseudothelphusidae), has a freshwater-dependant life-history strategy, although the species has some capabilities for terrestrial movement as adults. In contrast to all other freshwater decapods on the island (e.g., caridean shrimp), E. sinuatifrons does not undertake amphidromous migration, and is restricted to purely freshwater habitats and adjacent riparian zones. As Puerto Rico has a dynamic geologic history, we predicted that both the life history of E. sinuatifrons and the geological history of the island would be important determinants of phylogeographic structuring in the species. Using a fragment of the cytochrome c oxidase subunit 1 mtDNA (mitochondrial DNA) gene, we tested for deviations from panmixia among and within rivers draining Puerto Rico and used statistical phylogeography to explore processes that may explain extant patterns of genetic variation in the species. While populations of E. sinuatifrons were significantly differentiated among rivers, they were likely to be recently derived because nested clade analysis (NCA) indicated evolutionarily recent restricted gene flow with isolation by distance (IBD) and contiguous range expansion at various spatial scales. Ongoing drainage rearrangements associated with faulting and land slippage were invoked as processes involved in sporadic gene flow among rivers throughout the Pleistocene. Patterns of genetic differentiation conformed to IBD and population demographic statistics were nonsignificant, indicating that although recently derived, populations from different rivers were in drift-mutation equilibrium. A shallow (0.6 million years ago), paraphyletic split was observed in the haplotype network, which NCA indicated arose via allopatric fragmentation. This split coincides with an area of high relief in central Puerto Rico that may have experienced relatively little drainage rearrangements. Shallow but significant genetic isolation of populations of E. sinuatifrons among Puerto Rican rivers suggests phylogeographic patterns that are intermediate to terrestrial habitat specialists (highly divergent populations) and other freshwater biota, such as amphidromous species and insects with aerial adult dispersal (highly connected populations).     

Population structure in the freshwater shrimp (Paratya australiensis) inferred from allozymes and mitochondrial DNA

In 1995, an allozyme study was conducted on the genetic structure of a population of the common atyid shrimp, Paratya australiensis, in the Conondale Range, south-eastern Queensland with two subcatchments each within two river drainages sampled. The allozyme study revealed a high degree of population structure, with the data interpreted as reflecting a pattern of restricted contemporary gene flow, primarily between streams within subcatchments. High levels of differentiation occurred between all subcatchments. In this study, we analysed a partial fragment of the mitochondrial COI gene in order to further test and verify these results. The mtDNA data largely conflicted with the hypothesis of restricted gene flow indicating that contemporary dispersal was highly unlikely, even between streams within subcatchments, with many sites fixed for unique mtDNA haplotypes. Additionally, the level of divergence between the Stony Creek subcatchment and all other sampling sites indicated that it had been isolated for approximately 2-3 million years, while low levels of divergence were detected across the Conondale Range between the Kilcoy and Booloumba Creek subcatchments. The sharing of alleles at certain allozyme loci between all subcatchments is, therefore, likely to be the result of ancestral retention and possibly because of the effects of balancing selection.     

Genetic divergence and phylogeographic relationships among european perch (Perca fluviatilis) populations reflect glacial refugia and postglacial colonization

We used the widely distributed freshwater fish, perch (Perca fluviatilis), to investigate the postglacial colonization routes of freshwater fishes in Europe. Genetic variability within and among drainages was assessed using mitochondrial DNA (mtDNA) D-loop sequencing and RAPD markers from 55 populations all over Europe as well as one Siberian population. High level of structuring for both markers was observed among drainages and regions, while little differentiation was seen within drainages and regions. Phylogeographic relationships among European perch were determined from the distribution of 35 mtDNA haplotypes detected in the samples. In addition to a distinct southern European group, which includes a Greek and a southern Danubian population, three major groups of perch are observed: the western European drainages, the eastern European drainages including the Siberian population, and Norwegian populations from northern Norway, and western side of Oslofjord. Our data suggest that present perch populations in western and northern Europe were colonized from three main refugia, located in southeastern, northeastern and western Europe. In support of this, nested cladistic analysis of mtDNA clade and nested clade distances suggested historical range expansion as the main factor determining geographical distribution of haplotypes. The Baltic Sea has been colonized from all three refugia, and northeastern Europe harbours descendants from both eastern European refugia. In the upper part of the Danube lineages from the western European and the southern European refugia meet. The southern European refugium probably did not contribute to the recolonization of other western and northern European drainages after the last glaciation. However, phylogenetic analyses suggest that the southern European mtDNA lineage is the most ancient, and therefore likely to be the founder of all present perch lineages. The colonization routes used by perch probably also apply to other freshwater species with similar distribution patterns.     

Mitochondrial DNA phylogeography of the three-spined stickleback (Gasterosteus aculeatus) in Europe-evidence for multiple glacial refugia

An analysis of mitochondrial DNA sequence variation in 172 three-spined sticklebacks (Gasterosteus aculeatus) sampled across the European distribution range revealed three major evolutionary lineages occupying relatively large and separate geographic areas. The trans-Atlantic lineage comprised of populations spanning from the East Coast of USA to the continental Europe and was basal group to the other European lineages in the phylogeny. The European lineage included populations located in the Western and Eastern Europe, British Isles, Scandinavia as well as some parts of the Mediterranean region. The third lineage was specific to the Black Sea drainages. The within lineage structure was characterized by significant excess of low frequency haplotypes and star-like mtDNA genealogies, which suggest a recent population expansions to the formerly glaciated marine and freshwater environments. A coalescent-based method dated the splits between the major lineages to have occurred during the Saalian and Weichselian glaciations in the late Pleistocene, depending on the molecular clock calibration. The coalescent simulations further indicate high degree of genetic diversity within the lineages and a substantial increase in the genetic diversity in the European lineage relative to the ancestral level. In addition to the three major lineages, the freshwater populations in R. Neretva and L. Skadar in the Adriatic Sea coast region harboured unique and highly divergent haplotypes suggesting long independent histories of these populations. Evidence from mtDNA analyses suggests that these populations deserve a status of an evolutionary significant unit.     

Mitochondrial DNA signatures of restricted gene flow within divergent lineages of an atyid shrimp (Paratya australiensis)

We measured spatial genetic structure within three previously described mitochondrial lineages of the atyid shrimp, Paratya australiensis, occurring in upland streams of two major catchments within the Sydney Water Supply Catchment, New South Wales, Australia. In all three lineages, there was significant spatial structuring of genetic variation between catchments. In two lineages, recurrent but restricted maternal gene flow has apparently predominated in shaping within-catchment genetic structure, although this framework may be overlaid with episodic contiguous/long-distance expansion events. In the third lineage, there was no evidence of spatial genetic structuring within one of the catchments, because one haplotype was both common and widespread throughout the sampled area. High-frequency haplotypes were also shared among subcatchments in the other two lineages, and we discuss both historical and contemporary processes that may have left these genetic signatures. Our results are generally concordant with previous reports of significant population structuring in P. australiensis, occurring in upland river reaches elsewhere in eastern Australia. We propose that restricted dispersal and gene flow among upland populations of P. australiensis is linked to dramatic architectural structuring within and among mountain streams.     

Fine-scale spatial partitioning of genetic variation and evolutionary contestability in the invasive estuarine mussel Xenostrobus securis

Initial studies of Australian populations of the widely invasive mussel Xenostrobus securis raised the possibility of non-random spatial partitioning within estuaries of mitochondrial DNA (mtDNA) clades that have dispersed intercontinentally and those that have not. A fine-scale phylogeographic investigation was made to examine this possibility using cytochrome c oxidase DNA sequences and data from five microsatellite loci developed here. X. securis in the study region was found to comprise multiple robustly supported mtDNA clades, many of which were genetically very distinct. Frequently, the clades comprised numerous haplotypes that have narrow ranges and may have evolved in situ within drainages or nearby. Microsatellite data reveal significant intra- and inter-drainage differentiation but at lower levels than mtDNA. Variation in mtDNA appears to reflect not only recolonization after infrequent local extinction within drainages but also the low probability of migratory haplotypes successfully establishing during evolutionary contests, with resident haplotypes having selective or demographic advantages derived from local occupation. The patterns of mtDNA haplotype distribution suggest that central New South Wales is the source of the internationally invasive lineages of X. securis.     

Allopatric origins of sympatric brook charr populations: colonization history and admixture

Natural selection is presumed to be the driving force behind the occurrence of phenotypically and genetically divergent populations in sympatry within many north temperate freshwater fishes. If, however, these populations have different ancestral origins, history could also contribute to their divergence. We previously found evidence for the role of selection in the evolution of divergent outflow and inflow breeding populations of migratory brook charr (Salvelinus fontinalis) inhabiting postglacial Mistassini Lake (Quebec, Canada). Here, we show that these populations do not have a common origin, through the use of admixture and spatial analyses with seven microsatellite loci. Divergent populations clustered into two different population groups when compared to samples from surrounding drainages, although inflow populations appeared to be more admixed between the two population groups than the outflow population. These results are noteworthy since outflow and inflow populations were monomorphic at mitochondrial DNA (338-bp sequence of the control region) and are only moderately differentiated (mean F(ST) = 0.10). Colonization by two ancestral populations was also consistent with known outflow direction changes throughout lake formation. In addition to providing insight into how phenotypic divergence in sympatry may have been affected by the nature (i.e. timing and direction) of colonization of ancestral populations, our results also suggest that ancestral populations may have differed in their ability to colonize certain lake habitats.     

A Passerine Bird's evolution corroborates the geologic history of the island of New Guinea

New Guinea is a biologically diverse island, with a unique geologic history and topography that has likely played a role in the evolution of species. Few island-wide studies, however, have examined the phylogeographic history of lowland species. The objective of this study was to examine patterns of phylogeographic variation of a common and widespread New Guinean bird species (Colluricincla megarhyncha). Specifically, we test the mechanisms hypothesized to cause geographic and genetic variation (e.g., vicariance, isolation by distance and founder-effect with dispersal). To accomplish this, we surveyed three regions of the mitochondrial genome and a nuclear intron and assessed differences among 23 of the 30 described subspecies from throughout their range. We found support for eight highly divergent lineages within C. megarhyncha. Genetic lineages were found within continuous lowland habitat or on smaller islands, but all individuals within clades were not necessarily structured by predicted biogeographic barriers. There was some evidence of isolation by distance and potential founder-effects. Mitochondrial DNA sequence divergence among lineages was at a level often observed among different species or even genera of birds (5-11%), suggesting lineages within regions have been isolated for long periods of time. When topographical barriers were associated with divergence patterns, the estimated divergence date for the clade coincided with the estimated time of barrier formation. We also found that dispersal distance and range size are positively correlated across lineages. Evidence from this research suggests that different phylogeographic mechanisms concurrently structure lineages of C. megarhyncha and are not mutually exclusive. These lineages are a result of evolutionary forces acting at different temporal and spatial scales concordant with New Guinea's geological history.     

A comparative analysis of population structuring and genetic diversity in sympatric lineages of freshwater shrimp (Atyidae: Paratya): concerted or independent responses to hydrographic factors?

1. We determined whether two sympatric mitochondrial DNA (mtDNA) lineages of freshwater shrimp (Decapoda: Atyidae: Paratya australiensis) represent biological species and if they had concerted or independent population responses to hydrographic factors in small streams (the Granite Creeks) in southeastern Australia. 2. Allozyme data indicated the presence of two gene pools at sites where the P. australiensis lineages were co‐occurring and the gene pools were statistically assigned with high probability to each respective lineage. This indicated that these mtDNA lineages in P. australiensis were reproductively isolated and thus biological species. 3. Populations of both lineages were genetically homogeneous among lowland sites within streams, but were isolated by steep stream gradients among upland sites and for lowland–upland site comparisons. However, the magnitude of differentiation was markedly different between the two lineages. Allozyme diversity also differed between the two lineages, suggesting that they have different effective population sizes. Thus, differences in the magnitude of genetic divergence among populations were probably because of different life‐history characteristics, including dispersal ability and population size. 4. Genetic population structure was mostly temporally stable, despite the extreme effects of drought during the first year and substantial stream‐flow during the second. However, stable isotope analyses revealed greater local movement in both lineages during the second year, as greater hydrological connectivity provided more opportunities for dispersal. Thus, although lowland populations within streams were genetically homogeneous, stable isotope data indicated that connections may be sporadic and result from accumulated small‐scale movements among refugial pools. 5. Both lineages were therefore found to have similar small‐scale population responses to the unstable habitats of the Granite Creeks. Results highlight the importance of refugia for the capacity of biota to recover from drought and the need for multiple restored patches to reinstate natural population processes (e.g. resilience, recolonization) in degraded systems.