Mitochondrial DNA Phylogeny of the Family Cichlidae: Monophyly and Fast Molecular Evolution of the Neotropical Assemblage

A mitochondrial DNA (mtDNA) phylogeny of cichlid fish is presented for the most taxonomically inclusive data set compiled to date (64 taxa). 16S rDNA data establish with confidence relationships among major lineages of cichlids, with a general pattern congruent with previous morphological studies and less inclusive molecular phylogenies based on nuclear genes. Cichlids from Madagascar and India are the most basal groups of the family Cichlidae and sister to African–Neotropical cichlids. The cichlid phylogeny suggests drift-vicariance events, consistent with the fragmentation of Gondwana, to explain current biogeographic distributions. Important phylogenetic findings include the placement of the controversial genus Heterochromis basal among African cichlids, the South American genus Retroculus as the most basal taxon of the Neotropical cichlid assemblage, and the close relationship of the Neotropical genera Cichla with Astronotus rather than with the crenicichlines. Based on a large number of South American genera, the Neotropical cichlids are defined as a monophyletic assemblage and shown to harbor significantly higher levels of genetic variation than their African counterparts. Relative rate tests suggest that Neotropical cichlids have experienced accelerated rates of molecular evolution. But these high evolutionary rates were significantly higher among geophagine cichlids. Received: 18 September 1998 / Accepted: 16 December 1998     

Identifying biases at different spatial and temporal scales of diversification: a case study in the Neotropical parrotlet genus Forpus

The temporal origins of the extraordinary biodiversity of the Neotropical region are highly debated. Recent empirical work has found support for alternative models on the tempo of speciation in Neotropical species further fuelling the debate. However, relationships within many Neotropical lineages are poorly understood, and it is unclear how this uncertainty impacts inferences on the evolution of taxa in the region. We examined the robustness of diversification patterns in the avian genus Forpus by testing whether the use of different units of biodiversity (i.e. biological species and statistically inferred species) impacted diversification rates and inferences regarding important biogeographic breaks in the genus. We found that the best‐fit model of diversification for the biological species data set was a declining rate of diversification; whereas a model of constant diversification was the best‐fit model for statistically inferred species or subspecies. Moreover, the relative importance of different landscape features in delimiting genetic structure across the landscape varied across data sets with differing units of biodiversity. Patterns based on divergence times among biological species indicated old speciation events across major geographic and river barriers. In contrast, data sets more inclusive of the diversity in Forpus illustrate the role of both old divergence across major landscape features and more recent divergences that are possibly attributed to Pleistocene climatic changes. Overall, these results indicate that conflicting models on the temporal origins of Neotropical birds may be attributable to sampling biases.     

Titi monkey biogeography: Parallel Pleistocene spread by Plecturocebus and Cheracebus into a post‐Pebas Western Amazon

Titi monkeys, subfamily Callicebinae, are a diverse, species‐rich group of Neotropical primates with an extensive range across South America. Their distribution in space and time makes them an interesting primate model for addressing questions of Neotropical historical biogeography. Our aim was to reconstruct the biogeographic history of Callicebinae to better understand their diversification patterns and the history of their colonisation of South America since the late Miocene. We reconstructed a time‐calibrated phylogeny of 19 titi species under Bayesian inference using two mitochondrial and 11 nuclear loci. Species were assigned across eight Neotropical areas of endemism, and statistical biogeographic methods implemented in BioGeoBEARS were employed to estimate ancestral areas using 12 biogeographic models. Our results indicate that the most recent common ancestor to extant titi monkeys was widespread from the present‐day Andean foothills in the Colombian Amazon, through the wet and dry savannas of Bolivia and Brazil, to the southern Atlantic forest of eastern Brazil. Genus‐level divergences were characterised by vicariance of ancestral range in the late Miocene. Species‐level diversification in Cheracebus and the Plecturocebus moloch group occurred as they spread across the Amazon in the Pleistocene and were largely characterised by a sequential, long‐distance “island‐hopping” dispersal model of speciation from a narrow area of origin through jump dispersal across rivers. This study comprises the first large‐scale investigation of the evolutionary history of titi monkeys in the context of Amazonian and South American historical biogeography and sheds light on the processes that generated the great diversity found among Callicebinae.     

Areas of endemism and distribution patterns for Neotropical Piper species (Piperaceae)

Aim The study aimed to establish areas of endemism and distribution patterns for Neotropical species of the genus Piper in the Neotropical and Andean regions by means of parsimony analysis of endemicity (PAE) and track‐compatibility analysis. Location The study area includes the Neotropical region and the Northern Andean region (Páramo‐Punan subregion). Methods We used distribution information from herbarium specimens and recent monographic revisions for 1152 species of Piper from the Neotropics. First, a PAE was attempted in order to delimit the areas of endemism. Second, we performed a track‐compatibility analysis to establish distribution patterns for Neotropical species of Piper. Terminology for grouping Piper is based on recent phylogenetic analyses. Results The PAE yielded 104 small endemic areas for the genus Piper, 80 of which are in the Caribbean, Amazonian and Paranensis subregions of the Neotropical region, and 24 in the Páramo‐Punan subregion of the Andean region. Track‐compatibility analysis revealed 26 generalized tracks, one in the Páramo‐Punan subregion (Andean region), 19 in the Neotropical region, and six connecting the Andean and Neotropical regions. Both the generalized tracks and endemic areas indicate that distribution of Piper species is restricted to forest areas in the Andes, Amazonia, Chocó, Central America, the Guayana Shield and the Brazilian Atlantic coast. Main conclusions Piper should not be considered an Andean‐centred group as it represents two large species components with distributions centred in the Amazonian and Andean regions. Furthermore, areas of greater species richness and/or endemism are restricted to lowland habitats belonging to the Neotropical region. The distribution patterns of Neotropical species of Piper could be explained by recent events in the Neotropical region, as is the case for the track connecting Chocó and Central America, where most of the species rich groups of the genus are found. Two kinds of event could explain the biogeography of a large part of the Piper taxa with Andean–Amazonian distribution: pre‐Andean and post‐Andean events.     

Molecular systematics and historical biogeography of tree boas (Corallus spp.)

Inferring the evolutionary and biogeographic history of taxa occurring in a particular region is one way to determine the processes by which the biodiversity of that region originated. Tree boas of the genus Corallus are an ancient clade and occur throughout Central and South America and the Lesser Antilles, making it an excellent group for investigating Neotropical biogeography. Using sequenced portions of two mitochondrial and three nuclear loci for individuals of all recognized species of Corallus, we infer phylogenetic relationships, present the first molecular analysis of the phylogenetic placement of the enigmatic C. cropanii, develop a time-calibrated phylogeny, and explore the biogeographic history of the genus. We found that Corallus diversified within mainland South America, via over-water dispersals to the Lesser Antilles and Central America, and via the traditionally recognized Panamanian land bridge. Divergence time estimates reject the South American Caribbean-Track as a general biogeographic model for Corallus and implicate a role for events during the Oligocene and Miocene in diversification such as marine incursions and the uplift of the Andes. Our findings also suggest that recognition of the island endemic species, C. grenadensis and C. cookii, is questionable as they are nested within the widely distributed species, C. hortulanus. Our results highlight the importance of using widespread taxa when forming and testing biogeographic hypotheses in complex regions and further illustrate the difficulty of forming broadly applicable hypotheses regarding patterns of diversification in the Neotropical region.     

PATTERNS AND PROCESSES OF DIVERSIFICATION: SPECIATION AND HISTORICAL CONGRUENCE IN SOME NEOTROPICAL BIRDS

This paper documents congruence in geographical patterns of speciation for four clades of birds having taxa endemic to the same areas within the Neotropics. Two genera, Pionopsitta parrots and Selenidera toucans, corroborate a well known biogeographic disjunction in which taxa endemic to southern Central America and the Chocó region of northwestern South America are the sister-group to a radiation within the Amazon basin. These two genera, along with two lineages within the toucan genus Pteroglossus, also document a pattern of historical interrelationships for four well known areas of endemism within Amazonia: Guyanan + (Belém-Pará + (Inambari + Napo)). These generalized historical patterns are interpreted to have arisen via fragmentation (vicariance) of a widespread ancestral biota. A review of the paleogeographic evidence suggests that these vicariance events could have originated as a result of several different mechanisms operating at various times during the Cenozoic. The inference that diversification of the Neotropical biota is primarily the result of the most recent of these possible vicariance events, namely isolation within Quaternary forest refugia, is unwarranted, given present data. These patterns of historical congruence are also interpreted as direct evidence against the hypothesis that diversification of the forest biota was a consequence of parapatric differentiation along recently established ecological gradients.     

The combined role of dispersal and niche evolution in the diversification of Neotropical lizards

Ecological requirements and environmental conditions can influence diversification across temporal and spatial scales. Understanding the role of ecological niche evolution under phylogenetic contexts provides insights on speciation mechanisms and possible responses to future climatic change. Large‐scale phyloclimatic studies on the megadiverse Neotropics, where biomes with contrasting vegetation types occur in narrow contact, are rare. We integrate ecological and biogeographic data with phylogenetic comparative methods, to investigate the relative roles of biogeographic events and niche divergence and conservatism on the diversification of the lizard genus Kentropyx Spix, 1825 (Squamata: Teiidae), distributed in South American rainforests and savannas. Using five molecular markers, we estimated a dated species tree, which recovered three clades coincident with previously proposed species groups diverging during the mid‐Miocene. Biogeography reconstruction indicates a role of successive dispersal events from an ancestral range in the Brazilian Shield and western Amazonia. Ancestral reconstruction of climatic tolerances and niche overlap metrics indicates a trend of conservatism during the diversification of groups from the Amazon Basin and Guiana Shield, and a strong signal of niche divergence in the Brazilian Shield savannas. Our results suggest that climatic‐driven divergence at dynamic forest‐savanna borders might have resulted in adaptation to new environmental niches, promoting habitat shifts and shaping speciation patterns of Neotropical lizards. Dispersal and ecological divergence could have a more important role in Neotropical diversification than previously thought.     

Fundamental biogeographic patterns across the Mexican Transition Zone: an evolutionary approach

Transition zones, located at the boundaries between biogeographic regions, represent events of biotic hybridization, promoted by historical and ecological changes. They deserve special attention, because they represent areas of intense biotic interaction. In its more general sense, the Mexican Transition Zone is a complex and varied area where Neotropical and Nearctic biotas overlap, from southwestern USA to Mexico and part of Central America, extending south to the Nicaraguan lowlands. In recent years, panbiogeographic analyses have led to restriction of the Mexican Transition Zone to the montane areas of Mexico and to recognize five smaller biotic components within it. A cladistic biogeographic analysis challenged the hypothesis that this transition zone is biogeographically divided along a north‐south axis at the Transmexican Volcanic Belt, as the two major clades found divided Mexico in an east‐west axis. This implies that early Tertiary geological events leading to the convergence of Neotropical and Nearctic elements may be younger (Miocene) than those that led to the east‐west pattern (Paleocene). The Mexican Transition Zone consists of five biogeographic provinces: Sierra Madre Occidental, Sierra Madre Oriental, Transmexican Volcanic Belt, Sierra Madre del Sur, and Chiapas. Within this transition zone, at least four cenocrons have been identified: Paleoamerican, Nearctic, Montane Mesoamerican, and Tropical Mesoamerican. Future studies should continue refining the identification of cenocrons and the reconstruction of a geobiotic scenario, as well as integrating ecological biogeographic studies, to allow a more complete understanding of the patterns and processes that have caused the biotic complexity of this transition zone.     

Reconstructing biogeographic temporal events in the evolution of the livebearer fish genus Jenynsia based on total evidence analysis (Cyprinodontiformes: Anablepidae)

The current distribution of the Neotropical ichthyofauna has been widely affected by the main geological events that occurred in South and Central America. However, robust biogeographic information is still scarce or absent for most fish families. The biogeographic relationships of the most diverse anablepid genus, Jenynsia, are herein analysed, using temporal and spatial approaches based on a total evidence dataset, including 167 morphological characters and seven nuclear genes, totalling 6075?bp. A time calibrated analysis recovered the origin of Jenynsia at the Miocene and the diversification of its two subgenera between the Late Miocene and Early Pliocene. This result combined with the analysis of reconstruction of ancestral states indicates that the ancestor of Jenynsia colonized the Paranean Sea, and the current distribution of the species of the genus is probably a result of geological events, including: (1) ancient connections between Iguaçu and upper Uruguay River basins; (2) sea level variation along the Pliocene in the South American Atlantic coast; and (3) the decrease of the Paranean Sea along the Pliocene and Pleistocene.     

Prey resources are equally important as climatic conditions for predicting the distribution of a broad-ranged apex predator

Aim

A current biogeographic paradigm states that climate regulates species distributions at continental scales and that biotic interactions are undetectable at coarse-grain extents. However, advances in spatial modelling show that incorporating food resource distributions are important for improving model predictions at large distribution scales. This is particularly relevant to understand the factors limiting the distribution of widespread apex predators whose diets are likely to vary across their range.

Location

Neotropical Central and South America.

Methods

The harpy eagle (Harpia harpyja) is a large raptor, whose diet is largely comprised of arboreal mammals, all with broad distributions across Neotropical lowland forest. Here, we used a hierarchical modelling approach to determine the relative importance of abiotic factors and prey resource distribution on harpy eagle range limits. Our hierarchical approach consisted of the following modelling sequence of explanatory variables: (a) abiotic covariates, (b) prey resource distributions predicted by an equivalent modelling for each prey, (c) the combination of (a) and (b), and (d) as in (c) but with prey resources considered as a single prediction equivalent to prey species richness.

Results

Incorporating prey distributions improved model predictions but using solely biotic covariates still resulted in a high-performing model. In the Abiotic model, Climatic Moisture Index (CMI) was the most important predictor, contributing 76% to model prediction. Three-toed sloth (Bradypus spp.) was the most important prey resource, contributing 64% in a combined Abiotic-Biotic model, followed by CMI contributing 30%. Harpy eagle distribution had high environmental overlap across all individual prey distributions, with highest coincidence through Central America, eastern Colombia, and across the Guiana Shield into northern Amazonia.

Main Conclusions

With strong reliance on prey distributions across its range, harpy eagle conservation programmes must therefore consider its most important food resources as a key element in the protection of this threatened raptor.     

Early and dynamic colonization of Central America drives speciation in Neotropical army ants

The emergence of the Isthmus of Panama is one of the most important events in recent geological history, yet its timing and role in fundamental evolutionary processes remain controversial. While the formation of the isthmus was complete around 3 million years ago (Ma), recent studies have suggested prior intercontinental biotic exchange. In particular, the possibility of early intermittent land bridges facilitating colonization constitutes a potential mechanism for speciation and colonization before full closure of the isthmus. To test this hypothesis, we employed genomic methods to study the biogeography of the army ant genus Eciton, a group of keystone arthropod predators in Neotropical rainforests. Army ant colonies are unable to disperse across water and are therefore ideally suited to study the biogeographic impact of land bridge formation. Using a reduced representation genome sequencing approach, we show that all strictly Central American lineages of Eciton diverged from their respective South American sister lineage between 4 and 7 Ma, significantly prior to the complete closure of the isthmus. Furthermore, three of the lineage pairs form extensive and coincident secondary contact zones in Costa Rica and Nicaragua, with no evidence of gene flow. Such a discrete and repeated biogeographic pattern indicates at least two waves of army ant dispersal into Central America that were separated by significant genetic divergence times. Thus, by integrating phylogenomic, population genomic and geographic evidence, we show that early colonization of Central America across the emerging Isthmus of Panamá drove parallel speciation in Eciton army ants.     

The Casiquiare river acts as a corridor between the Amazonas and Orinoco river basins: biogeographic analysis of the genus Cichla

The Casiquiare River is a unique biogeographic corridor between the Orinoco and Amazonas basins. We investigated the importance of this connection for Neotropical fishes using peacock cichlids (Cichla spp.) as a model system. We tested whether the Casiquiare provides a conduit for gene flow between contemporary populations, and investigated the origin of biogeographic distributions that span the Casiquiare. Using sequences from the mitochondrial control region of three focal species (C. temensis, C. monoculus, and C. orinocensis) whose distributions include the Amazonas, Orinoco, and Casiquiare, we constructed maximum likelihood phylograms of haplotypes and analyzed the populations under an isolation‐with‐migration coalescent model. Our analyses suggest that populations of all three species have experienced some degree of gene flow via the Casiquiare. We also generated a mitochondrial genealogy of all Cichla species using >2000 bp and performed a dispersal‐vicariance analysis (DIVA) to reconstruct the historical biogeography of the genus. This analysis, when combined with the intraspecific results, supports two instances of dispersal from the Amazonas to the Orinoco. Thus, our results support the idea that the Casiquiare connection is important across temporal scales, facilitating both gene flow and the dispersal and range expansion of species.     

The dispersal between Amazonia and Atlantic Forest during the Early Neogene revealed by the biogeography of the treefrog tribe Sphaenorhynchini (Anura,Hylidae)

The Amazonia and the Atlantic Forest, separated by the diagonal of open formations, are two ecoregions that comprise the most diverse tropical forests in the world. The Sphaenorhynchini tribe is among the few tribes of anurans that occur in both rainforests, and their historical biogeographic have never been proposed. In this study, we infer a dated phylogeny for the species of the Sphaenorhynchini and we reconstructed the biogeographic history describing the diversification chronology, and possible patterns of dispersion and vicariance, providing information about how orogeny, forest dynamics and allopatric speciation affected their evolution in South America. We provided a dated phylogeny and biogeography study for the Sphaenorhynchini tribe using mitochondrial and nuclear genes. We analyzed 41 samples to estimate the ancestral areas using biogeographical analysis based on the estimated divergence times and the current geographical ranges of the species of Sphaenorhynchini. We recovered three characteristic clades that we recognize as groups of species (S. lacteus, S. planicola, and S. platycephalus groups), with S. carneus and G. pauloalvini being the sister taxa of all other species from the tribe. We found that the diversification of the tribe lineages coincided with the main climatic and geological factors that shaped the Neotropical landscape during the Cenozoic. The most recent common ancestor of the Sphaenorhynchini species emerged in the North of the Atlantic Forest and migrated to the Amazonia in different dispersion events that occurred during the connections between these ecoregions. This is the first large‐scale study to include an almost complete calibrated phylogeny of Sphaenorhynchini, presenting important information about the evolution and diversification of the tribe. Overall, we suggest that biogeographic historical of Sphaenorhynchini have resulted from a combination of repeated range expansion and contraction cycles concurrent with climate fluctuations and dispersal events between the Atlantic Forest and Amazonia.     

Two centuries of spatial and temporal dynamics of freshwater fish introductions

Aim

Investigating major freshwater fish flows (translocations) between biogeographic regions and their temporal dynamics and also quantifying spatial patterns and temporal changes in the array of introduced species, and the emergence and distance between major donor and recipient regions.

Location

Global.

Time Period

1800–2020.

Major Taxa Studied

Freshwater fishes.

Methods

We analysed a global dataset on freshwater fish introductions (4241 events of 688 species). Freshwater fish flows were investigated with flow diagrams and χ² tests, while PERMANOVA (permutational multivariate analysis of variance) was used to test the association between species and regions and temporal shifts. Cluster analysis revealed major recipient areas and composition of the introduced species. Finally, changes in distances between donor and recipient sites were tested with PERMANOVA.

Results

The number of introductions between biogeographic regions mirrored the European and North American dominance before World War II (WWII) and the trends in recreational fishing, biocontrol programmes and food production, especially in the Sino-Oriental region, which has a long tradition of aquaculture and fishkeeping. Over the years, the origins and composition of introduced species changed uniquely in each biogeographic region, although the most introduced species are common to every region. Salmonids and other cold-water species were frequently introduced before the 1950s, whereas tropical ornamental and aquaculture species currently prevail. Distances between donor and recipient sites did not vary over the time. After WWII, the Sino-Oriental region consolidated its dominance and the Ethiopian and Neotropical regions emerged as new global donor and recipient regions.

Main Conclusions

Global policy should focus on tropical ornamental and aquaculture species, which could benefit from global warming, especially in the Sino-Oriental region, because it currently dominates freshwater fish species flows, and the Ethiopian and Neotropical regions, because they recently emerged as important global donor and recipient regions of freshwater fish introductions.     

Biodiversity, molecular ecology and phylogeography of marine sponges: patterns, implications and outlooks

Marine sponges are an ecologically important and highly diversecomponent of marine benthic communities, found in all the world'soceans, at all depths. Although their commercial potential andevolutionary importance is increasingly recognized, many pivotalaspects of their basic biology remain enigmatic. Knowledge ofhistorical biogeographic affinities and biodiversity patternsis rudimentary, and there are still few data about genetic variationamong sponge populations and spatial patterns of this variation.Biodiversity analyses of tropical Australasian sponges revealedspatial trends not universally reflected in the distributionsof other marine phyla within the Indo-West Pacific region. Atsmaller spatial scales sponges frequently form heterogeneous,spatially patchy assemblages, with some empirical evidence suggestingthat environmental variables such as light and/or turbiditystrongly contribute to local distributions. There are no apparentlatitudinal diversity gradients at larger spatial scales butstochastic processes, such as changing current patterns, thepresence or absence of major carbonate platforms and historicalbiogeography, may determine modern day distributions. Studieson Caribbean oceanic reefs have revealed similar patterns, onlyweakly correlated with environmental factors. However, severalquestions remain where molecular approaches promise great potential,e.g., concerning connectivity and biogeographic relationships.Studies to date have helped to reveal that sponge populationsare genetically highly structured and that historical processesmight play an important role in determining such structure.Increasingly sophisticated molecular tools are now being applied,with results contributing significantly to a better understandingof poriferan microevolutionary processes and molecular ecology.     

Estimation and interpretation of egg provisioning in marine invertebrates

Per-offspring maternal investment is an integral part of life-historytheory. To understand the evolution of per-offspring maternalinvestment in marine invertebrates, a number of mathematicalmodels have been developed. These models examine how selectionaffects the proportion of maternally derived egg energy usedto produce a newly metamorphosed juvenile (s) and make predictionsabout the distribution of s in nature. However, there are veryfew published values of s and therefore it is difficult to evaluatehow well these models match nature. We present several equationsto empirically estimate values of s for any group of marineinvertebrate, and use data from echinoderms to compare the differentequations. The calculations that directly estimate s requireinformation on the amount of egg energy, juvenile energy, andenergy metabolized during development. Currently, there arefew data available for directly estimating s, and thus generatingdistributions of s derived from direct estimates is not possible.Furthermore, the direct estimations of s are informative forplanktotrophy but not for lecithotrophy. We have developed anequation that can be used to directly estimate s for lecithotrophs.The calculations to indirectly estimate s only require egg energyor egg size for the species in question and the value of s andegg energy or size for a reference species. This reference speciesreplaces the need to measure juvenile energy and energy metabolizedduring larval development. Because egg energy or size is currentlyavailable for many species, the indirect estimates will be usefulfor generating distributions of s, and will allow comparisonswith models. Although these indirect methods are good for generatingdistributions of s, they do not provide reliable estimates ofs for any particular species. Estimating values of s to comparemodels is a critical gap in our current evaluations of marineinvertebrate life-history models.     

Relaxed Molecular Clock Provides Evidence for Long-Distance Dispersal of Nothofagus (Southern Beech)

Nothofagus (southern beech), with an 80-million-year-old fossil record, has become iconic as a plant genus whose ancient Gondwanan relationships reach back into the Cretaceous era. Closely associated with Wegener's theory of “Kontinentaldrift”, Nothofagus has been regarded as the “key genus in plant biogeography”. This paradigm has the New Zealand species as passengers on a Moa's Ark that rafted away from other landmasses following the breakup of Gondwana. An alternative explanation for the current transoceanic distribution of species seems almost inconceivable given that Nothofagus seeds are generally thought to be poorly suited for dispersal across large distances or oceans. Here we test the Moa's Ark hypothesis using relaxed molecular clock methods in the analysis of a 7.2-kb fragment of the chloroplast genome. Our analyses provide the first unequivocal molecular clock evidence that, whilst some Nothofagus transoceanic distributions are consistent with vicariance, trans-Tasman Sea distributions can only be explained by long-distance dispersal. Thus, our analyses support the interpretation of an absence of Lophozonia and Fuscospora pollen types in the New Zealand Cretaceous fossil record as evidence for Tertiary dispersals of Nothofagus to New Zealand. Our findings contradict those from recent cladistic analyses of biogeographic data that have concluded transoceanic Nothofagus distributions can only be explained by vicariance events and subsequent extinction. They indicate that the biogeographic history of Nothofagus is more complex than envisaged under opposing polarised views expressed in the ongoing controversy over the relevance of dispersal and vicariance for explaining plant biodiversity. They provide motivation and justification for developing more complex hypotheses that seek to explain the origins of Southern Hemisphere biota.     

Origin and diversification of the soldier meadow springsnails (Hydrobiidae: Pyrgulopsis), a species flock in the northwestern Great Basin, United States

The large, western North American hydrobiid gastropod genusPyrgulopsis (commonly known as springsnails) includes a seriesof locally endemic faunas that are thought to be species flocks.Although these assemblages are of interest from the evolutionary,biogeographic and conservation perspectives, their monophylyand phylogenetic relationships have yet to be rigorously evaluated.Here we present a molecular phylogeny (based on mitochondrialsequence data) of a putative flock of four thermal spring-dwellingspringsnails that is distributed in many sites in Soldier Meadowand a single locality in Bog Hot Valley (northwestern Nevada).Our analyses support monophyly of this assemblage (‘SoldierMeadow clade’) and a close relationship with other regionalspecies and suggest that the invasion of thermal habitats bythese springsnails occurred independently of other such radiationswithin the genus. The divergence of the Soldier Meadow claderelative to its sister group is substantial (6.79–10.36%for COI, 10.35–15.88% for NDI), suggesting a split inthe early Pliocene, based on the application of a COI clockfor Pyrgulopsis. The splits within the Soldier Meadow cladeinto three main subunits also appear to be old events, basedon their 5.78–8.54% COI divergence relative to each other.These findings are consistent with a long history of springsnailevolution in Soldier Meadow, which is intriguing given thatthis basin was flooded by Lake Lahontan during periods of theearly and middle Pleistocene. We suggest that progenitors ofthe contemporary fauna survived in high elevation springs thatmay have been present in the basin during these pluvial periodsand subsequently colonized contemporary habitats following thetermination of the extreme Lake Lahontan highstands. We speculatethat the broadly disjunct population (of P. militaris) in BogHot Valley, which is consistently nested within the SoldierMeadow clade in our phylogenetic analyses, is either a vicariantrelict of a spring zone that may have once extended betweenthese two areas; or was founded by a past ‘jump’dispersal event from Soldier Meadow. Phylogeographic structureof springsnail populations in Soldier Meadow bears the strongstamp of geologically recent, allopatric diversification, perhapsreflecting the short time that basin floor habitats have beenoccupied. We describe a new species (P. varneri) for a seriesof recently discovered populations that are monophyletic, substantiallydivergent and morphologically distinctive. Additional studieswill be necessary to confidently assess the taxonomic statusof morphologically distinctive P. limaria and P. umbilicata,which are shown herein to be little divergent genetically; anda recently discovered minute springsnail that is morphologicallydivergent yet closely similar genetically to P. notidicola. (Received 20 December 2006; accepted 22 February 2007)     

Relaxed molecular clock provides evidence for long-distance dispersal of Nothofagus (southern beech)

Nothofagus (southern beech), with an 80-million-year-old fossil record, has become iconic as a plant genus whose ancient Gondwanan relationships reach back into the Cretaceous era. Closely associated with Wegener's theory of “Kontinentaldrift”, Nothofagus has been regarded as the “key genus in plant biogeography”. This paradigm has the New Zealand species as passengers on a Moa's Ark that rafted away from other landmasses following the breakup of Gondwana. An alternative explanation for the current transoceanic distribution of species seems almost inconceivable given that Nothofagus seeds are generally thought to be poorly suited for dispersal across large distances or oceans. Here we test the Moa's Ark hypothesis using relaxed molecular clock methods in the analysis of a 7.2-kb fragment of the chloroplast genome. Our analyses provide the first unequivocal molecular clock evidence that, whilst some Nothofagus transoceanic distributions are consistent with vicariance, trans-Tasman Sea distributions can only be explained by long-distance dispersal. Thus, our analyses support the interpretation of an absence of Lophozonia and Fuscospora pollen types in the New Zealand Cretaceous fossil record as evidence for Tertiary dispersals of Nothofagus to New Zealand. Our findings contradict those from recent cladistic analyses of biogeographic data that have concluded transoceanic Nothofagus distributions can only be explained by vicariance events and subsequent extinction. They indicate that the biogeographic history of Nothofagus is more complex than envisaged under opposing polarised views expressed in the ongoing controversy over the relevance of dispersal and vicariance for explaining plant biodiversity. They provide motivation and justification for developing more complex hypotheses that seek to explain the origins of Southern Hemisphere biota.     

Climate,physiological tolerance and sex‐biased dispersal shape genetic structure of Neotropical orchid bees

Understanding the impact of past climatic events on the demographic history of extant species is critical for predicting species' responses to future climate change. Palaeoclimatic instability is a major mechanism of lineage diversification in taxa with low dispersal and small geographical ranges in tropical ecosystems. However, the impact of these climatic events remains questionable for the diversification of species with high levels of gene flow and large geographical distributions. In this study, we investigate the impact of Pleistocene climate change on three Neotropical orchid bee species (Eulaema bombiformis, E. meriana and E. cingulata) with transcontinental distributions and different physiological tolerances. We first generated ecological niche models to identify species‐specific climatically stable areas during Pleistocene climatic oscillations. Using a combination of mitochondrial and nuclear markers, we inferred calibrated phylogenies and estimated historical demographic parameters to reconstruct the phylogeographical history of each species. Our results indicate species with narrower physiological tolerance experienced less suitable habitat during glaciations and currently exhibit strong population structure in the mitochondrial genome. However, nuclear markers with low and high mutation rates show lack of association with geography. These results combined with lower migration rate estimates from the mitochondrial than the nuclear genome suggest male‐biased dispersal. We conclude that despite large effective population sizes and capacity for long‐distance dispersal, climatic instability is an important mechanism of maternal lineage diversification in orchid bees. Thus, these Neotropical pollinators are susceptible to disruption of genetic connectivity in the event of large‐scale climatic changes.