Neotropical seasonally dry forests and Quaternary vegetation changes

Seasonally dry tropical forests have been largely ignored in discussions of vegetation changes during the Quaternary. We distinguish dry forests, which are essentially tree‐dominated ecosystems, from open savannas that have a xeromorphic fire‐tolerant, grass layer and grow on dystrophic, acid soils. Seasonally dry tropical forests grow on fertile soils, usually have a closed canopy, have woody floras dominated by the Leguminosae and Bignoniaceae and a sparse ground flora with few grasses. They occur in disjunct areas throughout the Neotropics. The Chaco forests of central South America experience regular annual frosts, and are considered a subtropical extension of temperate vegetation formations. At least 104 plant species from a wide range of families are each found in two or more of the isolated areas of seasonally dry tropical forest scattered across the Neotropics, and these repeated patterns of distribution suggest a more widespread expanse of this vegetation, presumably in drier and cooler periods of the Pleistocene. We propose a new vegetation model for some areas of the Ice‐Age Amazon: a type of seasonally dry tropical forest, with rain forest and montane taxa largely confined to gallery forest. This model is consistent with the distributions of contemporary seasonally dry tropical forest species in Amazonia and existing palynological data. The hypothesis of vicariance of a wider historical area of seasonally dry tropical forests could be tested using a cladistic biogeographic approach focusing on plant genera that have species showing high levels of endemicity in the different areas of these forests.     

Evolutionary and biogeographic relationships of related Ranunculus taxa: dispersal,vicariance and pseudovicariance as mechanisms of change

Background: The disjunct distribution patterns of a taxon may arise when previously continuous distribution ranges are fragmented. The phenomena of vicariance and dispersal, together with hybridisation as an important source of genetic variation in natural populations, can play an important role for structuring the distribution of taxa.

Aims: We investigated the biogeographical relationships of the Iberian endemic plant Ranunculus angustifolius s.l. by reconstructing ancestral geographical distributions, using a combination of phylogenetic and distributional information.

Methods: Phylogenetic and network analyses of nuclear internal transcribed spacers and plastid sequence data (rpl32-trnL, rps16-trnQ, trnK-matK and ycf6-psbM) were used to infer vicariance and dispersal events.

Results: Phylogenetic and biogeographical analyses suggested that both dispersal and vicariance were important in creating the current disjunct distribution pattern. Some other factors, such as hybridisation, introgression and vicariance (or pseudovicariance), were important in the evolutionary history of the taxa R. angustifolius s.l.

Conclusions: Our results demonstrate the importance for analysing biogeographical patterns with the use of both nuclear and chloroplast DNA to infer the evolutionary history of plant species with a disjunct distribution. Our results show that phenomena such as dispersal, vicariance and pseudovicariance are not mutually exclusive.     

Biogeography of Nicotiana section Suaveolentes (Solanaceae) reveals geographical tracks in arid Australia

Aim Nicotiana section Suaveolentes is largely endemic to Australia but includes one species endemic to Africa, one to New Caledonia and Tongatupa, and one to the Marquesas Islands in the Pacific. Other sections of Nicotiana are found in the New World. In Australia, Suaveolentes is widespread across the continent, with many taxa adapted to the Eremean zone. We aim to analyse the biogeography of the Australian clade, both to shed light on the evolution of the group and to determine general area relationships that provide insight into the history of the arid‐zone biota. Location Mesic and arid regions of continental Australia, the Central–South Pacific and Namibia, Africa. Methods A phylogeny of Suaveolentes, based on morphology and molecular data, was used to analyse the relationships of areas in which the taxa occur. The section is monophyletic, and all but three taxa were included (25). The method of paralogy‐free subtree analysis was employed, with the basal taxon Nicotiana africana used as the outgroup. Results Paralogy‐free subtree analysis found five area subtrees that, when combined, resulted in a minimal area cladogram with six resolved nodes. Pacific and mesic eastern Australia (including Lord Howe Island) are at the base of the area cladogram, followed by the differentiation of North West Australia and later South East Australia. Arid regions of Australia are related, revealing three biogeographical tracks: a northern track including the Great Sandy Desert and Tanami, which are related to the Pilbara; a central track relating the Western Desert, Central Ranges, Eastern Desert and North East Interzone; and a southern track relating the South West Interzone, Nullarbor, Adelaide/Eyre and the South East Interzone. Plesiomorphic taxa with chromosome number n = 24–23 occur on the periphery of the continent, and derived taxa with n = 21, 20, 18, 16–15 identify the tracks across arid Australia. Main conclusions The patterns of distribution and differentiation of Suaveolentes in Australia show that the age of the clade is at least Early Miocene, dating to before the onset of aridification in Australia about 15 Ma. The patterns are also interpreted as evidence that it was vicariance that largely shaped speciation in the Eremean zone, with range expansion of some widespread taxa probably occurring in the most recent cycles of severe drying and mobilization of desert dune sands.     

Marine dispersal as a pre‐requisite for Gondwanan vicariance among elements of the galaxiid fish fauna

Aim The aim of this study was to determine the contributions of Gondwanan vicariance and marine dispersal to the contemporary distribution of galaxiid fishes. This group has been central in arguments concerning the roles of dispersal and vicariance in the Southern Hemisphere, as some taxa have marine life history stages through which transoceanic dispersal may have been facilitated, yet other galaxiids are entirely restricted to freshwaters. Location Southern Hemisphere land masses of Gondwanan derivation. Methods Biogeographic hypotheses of Gondwanan vicariance and marine dispersal were tested using four lines of evidence: (1) concordance of species–area phylogenetic relationships, (2) molecular estimates of lineage divergence times with a priori expectations based on plate tectonics, (3) reconstructions of ancestral dispersal capabilities, and (4) reconstructions of distribution inheritance scenarios (using the dispersal–extinction–cladogenesis model to infer historical ranges and dispersal and extinction events). Results Phylogenetic relationships were reconstructed from 4531 mitochondrial and nuclear nucleotide characters, and 181 morphological characters, across 53 of the 56 presently recognized species. Phylogenetic relationships were generally well resolved and supported among galaxiids using the combined dataset, and conflicting relationships between molecular and morphological datasets typically received low topological support from either or both datasets. Transoceanic disjunctions were exhibited at 16 nodes, but only three pre‐dated relevant continental fragmentation events; furthermore, ancestral distribution inheritance scenarios for two of these nodes reflected cladogenesis within, rather than between, Gondwanan land masses, and ancestral marine dispersal capability could not be rejected for all three. Instead, the four lines of evidence surveyed suggest that Gondwanan vicariance occurred twice, but in both instances was preceded by marine dispersal between land masses, and in at least one instance was initiated by the cessation of marine dispersal subsequent to continental fragmentation. Main conclusions Gondwanan vicariance appears to have been preceded by marine dispersal in the few instances where it may explain contemporary galaxiid distribution, such that these biogeographic mechanisms may sometimes have a synergistic relationship.     

Bayesian transmogrification of clade divergence dates: a critique

The crucial step in Bayesian dating of phylogenies is the selection of prior probability curves for clade ages. In studies on regions derived from Gondwana, many authors have used steep priors, stipulating that clades can only be a little older than their oldest known fossil. These studies have ruled out vicariance associated with Gondwana breakup, but only because of the particular priors that were adopted. The use of non‐flat priors for fossil‐based ages is not justified and is unnecessary. Tectonic calibrations can be integrated with fossil calibrations that are used to give minimum clade ages only.     

The historical ecology of yellow perch (Perca flavescens[Mitchill]) and their parasites

Aim To determine the origins of the host–parasite association between among yellow perch (Perca flavescens[Mitchill]) and the parasites Crepidostomum cooperi Hopkins, Proteocephalus pearsei La Rue and Urocleidus adspectus Beverly Burton. Of secondary interest are the parasites Bunodera luciopercae (Muller) and Proteocephalus percae (Muller) predictably associated with the Eurasian perch. Location The areas considered are the Holarctic, since the upper‐Cretaceous, and contemporary North America. Methods Published and new information from host and parasite phylogenies, palaeontology, palaeogeography and plate tectonics and host biology is incorporated to assess the origins of yellow perch and several of its parasites. This information is used to determine the origins for these host–parasite associations. Results Cladistic analysis suggests a Laurasian origin for Percidae and Perca, and that Perca is sister to the other genera in the family. Parasite phylogenies support a North American origin for the three species associated with yellow perch and a Laurasian origin for B. luciopercae. Proteocephalus pearsei and P. percae are not sister taxa. The fossil record for Perca dates to the Miocene in Europe and the Pleistocene in North America. North America and Europe were connected across the North Atlantic since at least the upper Cretaceous with separation complete by the Miocene. Europe was separated from Asia by the Obik Sea from the late Cretaceous until the Oligocene. Western cordillera orogeny and its accompanying high rates of water flow and Pleistocene glaciation represent barriers to Perca dispersal. Main conclusions The origin of Perca in North America dates at least to the late Oligocene when North America and Europe were connected across the North Atlantic and Europe and Asia were separate landmasses, and does not result from Pleistocene dispersal across Beringia from Asia. The present disjunction of Perca species in North America and Europe is due to the vicariant separation of North America and Europe. Based on the available information, yellow perch and its parasites have a North America origin. The association between yellow perch and the parasites in all cases is a consequence of host switching from other sympatric host species in North America and is not explained by co‐speciation. Even the association between the host‐specific Urocleidus adspectus and yellow perch originated with a host switch and is not due to co‐speciation. The basis for this host switching is geographical and ecological sympatry, especially shared feeding habits, with other North American fish hosts.