Aim Amphibians are a model group for studies of the biogeographical origins of salt-intolerant taxa on oceanic islands. We used the Gulf of Guinea islands to explore the biogeographical origins of island endemism of one species of frog, and used this to gain insights into potential colonization mechanisms.



Location  Sao Tome and Principe, two of the four major islands in the Gulf of Guinea, West Africa, are truly oceanic and have an exceptionally high biodiversity.



Methods  Mitochondrial DNA is used to test the endemic status of a frog from Sao Tome and compare it with congeneric taxa from tropical Africa. Existing data on surface currents, surface salinity, atmospheric circulation and bird migration in the Gulf of Guinea are summarized to address hypotheses concerning colonization mechanisms.



Results  The endemic status of Ptychadena newtoni (Bocage) is supported here by mitochondrial DNA sequences, and analysis of this and other molecular data indicates that an East African species close to Ptychadena mascareniensis (Dumeril and Bibron) is its nearest relative. We refute the possibility that this population was anthropogenically introduced, in favour of a natural dispersal mechanism.



Main conclusions  With six endemic frogs and one caecilian, the Gulf of Guinea islands harbour a diverse amphibian fauna. Five of these species appear to have their closest relatives in East Africa. Insufficient evidence exists for transportation by storms, birds or rafts alone. However, we propose a synergy of rafting, favourable surface currents and a reduction in salinity of surface waters. Catastrophic events, or wet periods in climatic history, could allow freshwater paths to open far enough to enable continental flora and fauna to reach these and other isolated oceanic islands.

Freshwater paths across the ocean : molecular phylogeny of the frog Ptychadena newtoni gives insights into amphibian colonization of oceanic islands

Amphibians in general are considered poor dispersers and thus their dispersal curve should be dominated by short movements. Additionally, as male toads do not compete for females and sexual selection is by female choice, dispersal should be male-biased. Furthermore, since adults are site-loyal and polygynous, juveniles should move farther and faster than adults. We tested the hypotheses that dispersal would be limited and both sex- and age-biased in a population of Fowler's toads Bufo fowleri at Lake Erie, Ontario, Canada. Based on a mark-recapture study of 2816 toads, 1326 recaptured at least once, we found that although the toads did show high site fidelity, the dispersal curve was highly skewed with a significant "tail" where the maximum distance moved by an adult was 34 km. Dispersal was neither sex-biased nor age-biased despite clear theoretical predictions that dispersal should be biased towards males and juveniles. We conclude that the resource competition hypothesis of sex-biased dispersal does not predict dispersal tendencies as readily for amphibians as for mammals and birds. Toad dispersal only appears to be juvenile-biased because the juveniles are more abundant than the adults, not because they are the more active dispersers.

https://www.jstor.org/stable/pdfplus/30243156.pdf

Sex, isolation and fidelity: unbiased long-distance dispersal in a terrestrial amphibian

Special issue: Comparative biogeography of Neotropical primates.

Primates were surveyed at two sites in the Xingu-Tocantins interfluvium, in eastern Amazonia, where at least eight platyrrhines are known to occur, including the endemic Chiropotes satanas utahicki, vulnerable to extinction. Only three other forms; Alouatta belzebul belzebul, Cebus apella apella, and Saguinus midas niger; were recorded at both sites. Data on habitat use (forest type and strata) were collected in standard line transect surveys and analyzed with relation to the availability of forest types, as well as between sites and species. The smallest- (S. midas) and largest-bodied (A. belzebul) species were relatively common at the continuous forest site, where they exhibited a significant preference for primary terra firme forest. At this site, Cebus demonstrated a significant preference for liana and flooded forest in contrast with primary or secondary terra firme forests. The medium-sized Cebus and Chiropotes were more common in the isolated forest fragment (where they were also observed together frequently), but no clear habitat preferences were found at this site for any species. A. belzebul occupied significantly higher forest strata than other species, which all used relatively similar levels. C.s. utahicki was active in much lower forest strata than other bearded sakis, whereas S. midas was observed at much higher levels than at other sites in eastern Amazonia. It remains unclear whether and to what extent observed patterns are determined by differences between taxa, populations, or ecosystems, but the data indicate that C.s. utahicki is relatively tolerant of habitat disturbance.

Habitat use by Chiropotes satanas utahicki and syntopic platyrrhines in eastern Amazonia

Aim
Our aim was to investigate how the distance to water (flooding gradients) and riverine barriers (Tapajos and Jamanxim rivers) influence the distributional patterns of amphibian and squamate assemblages in the middle Tapajos River region, south-eastern Amazonia. We also considered the planned hydroelectric dams on both rivers in reviewing the possible impacts of these factors on the amphibian and squamate assemblages.

Location
Middle Tapajos River system, south-eastern Amazonia.

Methods
We conducted diurnal and nocturnal surveys combining pitfall traps and active searches along both banks of the Tapajos and Jamanxim rivers. We identified specimens using an integrative morphological, acoustic, ecological and molecular approach and evaluated the influence of riverine barriers and distance to water using uni- and multivariate ordinations, regressions and ANOVA.

Results
We found changes in species composition for both groups along the flooding gradient and differential riverine barrier effects. The rivers restricted the distribution of 33% of the amphibian species and 8% of the squamates. For amphibians, the main distributional barrier was the Tapajos River, while for squamates both rivers were of similar importance. The assemblages most affected by riverine barriers were non-riparian amphibians and squamates, as well as riparian amphibians associated with small streams. The functional groups most affected were small, diurnal terrestrial amphibians and small–medium, diurnal partly tree-dwelling squamates.

Main conclusions
The Tapajos River is a distributional boundary for lineages centred in western and eastern Amazonia. The fact that many taxa occur on both banks suggests that the Tapajos is a recent or semi-permeable barrier, while the Jamanxim is an even more recent or weaker barrier. Anthropogenic activities that affect water level, flooding cycles and river flow may influence these natural patterns and cause changes to the equilibrium of the riverine barrier effect. Studies seeking to identify these influences should focus on the most affected functional groups.

The combined influence of riverine barriers and flooding gradients on biogeographical patterns for amphibians and squamates in south‐eastern Amazonia

Large rivers have played a prominent role in biogeographic theory for their potential to act as barriers for the dispersal of terrestrial organisms,and therefore be involved in the generation of species diversity (Brown & Lomolino 1998). In this paper, we document the potential role of macrophyte rafts as a mechanism by which Amazonian rivers could act as dispersal agents rather than barriers, transferring organisms across banks and possibly across very large distances. These vectors could therefore act against speciation and towards homogenization of the local biota.

/pdf/macrophyte-rafts-as-dispersal-vectors-for-fishes-and-hv41g8rgoe.pdf

Macrophyte rafts as dispersal vectors for fishes and amphibians in the Lower Solimoes River, Central Amazon

Five species of titi monkey (Callicebus brunneus, Callicebus caligatus Callicebus cinerascens, Callicebus donacophilus, andCallicebus moloch) were recorded in surveys of primate populations at 26 sites throughout the Brazilian state of Rondonia. The distribution of the two species,C. cinerascens andC. donacophilus (recorded in the state for the first time), appeared to be related to that of non-forest ecosystems, the former in thecerrado woodlands, and the latter in gallery forests of the Guapore grasslands. The results of the surveys also indicate thatC. brunneus has a more restricted distribution in southern Rondonia than was previously thought, whereasC. moloch is more widespread. However, the ecological factors that determine species distribution in the south of the state remain unclear on the basis of the available data. All species were observed in small social groups of no more than five individuals, which are typical of the genus, generally in the middle and lower forest strate.

Titi monkeys (Callicebus spp., Atelidae : Platyrrhini) in the Brazilian state of Rondonia

White-nosed bearded sakis (Chiropotes albinasus) are endemic to the Madeira–Xingu interfluvium in southern Amazonia, though recent fieldwork has produced conflicting data on the southwestern limits of the species's geographic range. We reevaluated the distribution of bearded sakis on the basis of surveys from 34 sites throughout the Brazilian state of Rondonia. Chiropotes albinasus occurred at seven sites in the eastern part of the state, including two west of the Jiparana–Pimenta Bueno river system in the extreme south, but there is no record of their presence further north and west in the Jiparana–Guapore interfluvium and they were absent from the Jiparana–Mamore interfluvium. The data suggest that ecological, rather than geographic barriers restrict the distribution of Chiropotes albinasus in southern Rondonia, but are contradictory with regard to the possible determining factors. Chiropotes albinasus appears able to thrive in transitional, savanna-like ecosystems in southern Rondonia, but is unexpectedly absent from adjacent areas of terra firme forest. Syntopy with the only other pitheciine found in the state (Pithecia irrorata) appears to have a negative effect on the abundance of Chiropotes albinasus which implies that interspecific competition may reinforce a complex of limiting factors, such as the availability of key plant species. Despite showing that Chiropotes albinasus is widespread in southern Rondonia, we also confirm its absence from the western two thirds of the state, a significant reduction in the known range of the species.

Mariluce R. Messias

Papers

Macrophyte rafts as dispersal vectors for fishes and amphibians in the Lower Solimoes River, Central Amazon

Titi monkeys (Callicebus spp., Atelidae : Platyrrhini) in the Brazilian state of Rondonia

Zoogeography of Chiropotes albinasus (Platyrrhini, Atelidae) in Southwestern Amazonia