Summer Rainfall Areas Research Articles

Monitoring eucalypt bud temperature using mobile temperature loggers

Winter chilling is a key environmental trigger of floral induction in temperate Eucalyptus. Over the past two decades, considerable site × eucalypt flowering interaction research has been undertaken over a range of high elevation (>1 100 m asl) forestry sites in the South African summer rainfall area. A practical method of accurately monitoring eucalypt bud temperature at remote sites in these areas was needed for this research. Utilisation of traditional methods of air and bud temperature measurement were not viable, due to significant risks of data and meteorological equipment loss posed by severe weather, vandalism and theft. Between 1996 and 2004, a robust structure for housing the miniature Hobo® temperature logger (hereafter termed ‘Hobo pole’) was designed and utilised for in-field monitoring of air temperature in the research trials. During 2009 and 2010, an experiment was conducted to investigate the relationship between E. nitens bud temperature (BudT), Hobo pole air temperature (HoboAT) and radiation screen air temperature (ScrnAT), and develop appropriate calibration models. Attempts to develop a single model for predicting hourly BudT from hourly HoboAT over the entire annual period yielded unsatisfactory results (maximum R 2 value 0.49). Separate winter and summer regression models were subsequently developed for predicting BudT from HoboAT, ScrnAT from HoboAT, and BudT from ScrnAT. In these regressions, R 2 values were generally slightly higher, and SE values lower, for mid-winter data than for mid-summer data. In mid-winter, BudT on HoboAT gave the highest R 2 value (0.99) and lowest SE value (0.49 °C) of all regressions. The Hobo logger/Hobo pole combination, together with developed regression models (presented in this paper), offers one practical, cost-effective solution for accurately monitoring eucalypt bud temperature at remote, high-elevation forestry sites in South Africa.

Identifying high-yielding dryland wheat cultivars for the summer rainfall area of South Africa

Drought is a major challenge to dryland wheat (Triticum aestivum L.) production in the summer rainfall area (SRA) of South Africa. Dryland wheat farming in the SRA is unique in that the crop is dry-planted on high-water-table soils in winter, relying on stored moisture for germination and vegetative growth. Drought risk is high as only 260–300 mm rainfall is received during the growth period of the wheat from May to December. A number of new, improved dryland wheat cultivars released for the SRA during the recent period from 2003 to 2012 were evaluated for yield over several seasons under the National Wheat Cultivar Evaluation Program. As preliminary work for improving drought tolerance of wheat in the SRA, yield data of this genetic pool was re-analysed to identify the best-adapted cultivars based on means and coefficients of variation across years and geographic regions. Cultivars SST 347, PAN 3120, SST 356, PAN 3377, Matlabas, PAN 3161, PAN 3368, PAN 3379, PAN 3144, PAN 3355 and PAN 3118 had above-average yield and stability. These are recommended for adoption by farmers, as well as possible utilisation by researchers in improving drought tolerance of wheat.

Effects of Conservation Agriculture and Fertilization on Soil Microbial Diversity and Activity

Soil microbial communities perform critical functions in ecosystem processes. These functions can be used to assess the impact of agricultural practices on sustainable crop production. In this five-year study, the effect of various agricultural practices on soil microbial diversity and activity was investigated in a summer rainfall area under South African dryland conditions. Microbial diversity and activity were measured in the 0–15 cm layer of a field trial consisting of two fertilizer levels, three cropping systems, and two tillage systems. Using the Shannon–Weaver and Evenness diversity indices, soil microbial species richness and abundance were measured. Microbial enzymatic activities: β-glucosidase, phosphatase and urease, were used to evaluate ecosystem functioning. Cluster analysis revealed a shift in soil microbial community diversity and activity over time. Microbial diversity and activity were higher under no-till than conventional tillage. Fertilizer levels seemed to play a minor role in determining microbial diversity and activity, whereas the cropping systems played a more important role in determining the activity of soil microbial communities. Conservation agriculture yielded the highest soil microbial diversity and activity in diversified cropping systems under no-till.

A molecular physiological review of vegetative desiccation tolerance in the resurrection plant Xerophyta viscosa (Baker).

Main conclusionProvides a first comprehensive review of integrated physiological and molecular aspects of desiccation toleranceXerophyta viscosa. A synopsis of biotechnological studies being undertaken to improve drought tolerance in maize is given.Xerophyta viscosa (Baker) is a monocotyledonous resurrection plant from the family Vellociacea that occurs in summer-rainfall areas of South Africa, Lesotho and Swaziland. It inhabits rocky terrain in exposed grasslands and frequently experiences periods of water deficit. Being a resurrection plant it tolerates the loss of 95 % of total cellular water, regaining full metabolic competency within 3 days of rehydration. In this paper, we review some of the molecular and physiological adaptations that occur during various stages of dehydration of X. viscosa, these being functionally grouped into early and late responses, which might be relevant to the attainment of desiccation tolerance. During early drying (to 55 % RWC) photosynthesis is shut down, there is increased presence and activity of housekeeping antioxidants and a redirection of metabolism to the increased formation of sucrose and raffinose family oligosaccharides. Other metabolic shifts suggest water replacement in vacuoles proposed to facilitate mechanical stabilization. Some regulatory processes observed include increased presence of a linker histone H1 variant, a Type 2C protein phosphatase, a calmodulin- and an ERD15-like protein. During the late stages of drying (to 10 % RWC) there was increased expression of several proteins involved in signal transduction, and retroelements speculated to be instrumental in gene silencing. There was induction of antioxidants not typically found in desiccation-sensitive systems, classical stress-associated proteins (HSP and LEAs), proteins involved in structural stabilization and those associated with changes in various metabolite pools during drying. Metabolites accumulated in this stage are proposed, inter alia, to facilitate subcellular stabilization by vitrification process which can include glass- and ionic liquid formation.

A 1000-Year Carbon Isotope Rainfall Proxy Record from South African Baobab Trees (Adansonia digitata L.).

A proxy rainfall record for northeastern South Africa based on carbon isotope analysis of four baobab (Adansonia digitata L.) trees shows centennial and decadal scale variability over the last 1,000 years. The record is in good agreement with a 200-year tree ring record from Zimbabwe, and it indicates the existence of a rainfall dipole between the summer and winter rainfall areas of South Africa. The wettest period was c. AD 1075 in the Medieval Warm Period, and the driest periods were c. AD 1635, c. AD 1695 and c. AD1805 during the Little Ice Age. Decadal-scale variability suggests that the rainfall forcing mechanisms are a complex interaction between proximal and distal factors. Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean. The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static. Wetter conditions are associated with predominantly El Niño conditions over most of the record, but since about AD 1970 this relationship inverted and wet conditions are currently associated with la Nina conditions. The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone.

Lachenalia arenicola (Asparagaceae: Scilloideae), a new species from western South Africa

Lachenalia Jacquin in Murray (1784: 314) is a deciduous, geophytic genus endemic to western, southern, southeastern and central South Africa and to western and southern Namibia (Duncan et al. 2005). All South African members produce leaves in the winter, including those from essentially summer-rainfall areas, and L. pearsonii (Glover 1915: 105) Barker (1969: 321) from southern Namibia is the only summer-growing species (Duncan & Condy 2013). Flower and seed characters are most important for identification of Lachenalia, especially perianth shape including the perianth tube shape and length, relative position of outer and inner tepals, stamen orientation, seed shape and strophiole length. A recent monograph of Lachenalia provided a new classification for the genus based on a phylogenetic study of morphological characters and recognized 133 species (Duncan 2012). Living material of a new species from the Namaqualand coastal plain became available for study in 2013, although pressed specimens were first gathered in 2006. The total number of species for the genus now stands at 134.

Probabilistic assessment of the rainwater harvesting potential of schools in South Africa

Abstract. In comparison to other sources of water supply, rainwater harvesting (RWH) has the typical advantages of being cheaper and easier to operate and maintain. This study aimed at assessing the hydrologic rainwater harvesting potential of rural schools in South Africa by obtaining RWH storage capacity (level of supply) reliability relationships of representative schools. Thirty-two schools located in three rural areas that have varied rainfall characteristics were selected for the analysis. For each school, a daily time-step behaviour analysis of the rainwater harvesting system with a specified storage was carried out for a period of 101 years (over which rainfall data was available) and the number of days that the school’s daily water demand was met in each year obtained. Using the Weibull plotting position formula, the expected number of days that the demand can be met per year was then obtained for 85, 90 and 95 % reliability. For the two summer rainfall regions where a large proportion of rain falls during school holidays, the expected number of days of supply per year improved up to a storage capacity of 25 m3. For the winter rainfall region where the rainfall periods and school learning times have more co-incidence, a tank volume of 5 m3 obtained similar supply levels as larger capacities. At 90 % reliability, the supply levels for different schools in the summer rainfall area with a mean annual precipitation (MAP) of 800–1000 mm/year ranged from 60 to 120 days per year, while the summer rainfall region with a lower MAP (500–600 mm) gave supply levels ranging from 40 to 70 days per year. The winter rainfall area had a MAP of 500–600 mm and obtained supply levels ranging from 60 to 80 days at 90 % reliability.

Impact of precession on the climate, vegetation and fire activity in southern Africa during MIS4

Abstract. The relationships between climate, vegetation and fires are a major subject of investigation in the context of climate change. In southern Africa, fire is known to play a crucial role in the existence of grasslands and Mediterranean-type biomes. Microcharcoal-based reconstructions of past fire activity in that region have shown a tight correlation between grass-fueled fires and the precessional cycle, with maximum fire activity during maxima of the climatic precession index. These changes have been interpreted as the result of changes in fuel load in response to precipitation changes in eastern southern Africa. Here we use the general circulation model IPSL_CM5A (Institut Pierre Simon Laplace Climate Model version 5A) and the dynamic vegetation model LPJ-LMfire to investigate the response of climate, vegetation and fire activity to precession changes in southern Africa during marine isotopic stage 4 (74–59 kyr BP). We perform two climatic simulations, for a maximum and minimum of the precession index, and use a statistical downscaling method to increase the spatial resolution of the IPSL_CM5A outputs over southern Africa and perform high-resolution simulations of the vegetation and fire activity. Our results show an anticorrelation between the northern and southern African monsoons in response to precession changes. A decrease of the precession climatic index leads to a precipitation decrease in the summer rainfall area of southern Africa. The drying of climate leads to a decrease of vegetation cover and fire activity. Our results are in qualitative agreement with data and confirm that fire activity in southern Africa during MIS4 is mainly driven by vegetation cover.

Forecasting cyclic coastal erosion on a multi-annual to multi-decadal scale: Southeast African coast

Coastal erosion on the southeast African coastline shows an apparent 18 year cycle which last peaked in 2006. It is in phase with the longshore sediment transport cycle. Both these cycles appear to be in phase with the Lunar Nodal Cycle (LNC). However, the dominant tidal erosion driver on this coast appears to be the 4.4 year Lunar Perigean Subharmonic (LPS). We suggest that the apparent 18 year coastal erosion and longshore sediment budget cycle is a response to the 18 year Mean Annual Precipitation Cycle. This cycle is 180° out of phase with the apparent coastal erosion- and longshore sediment transport- cycles.The summer rainfall areas, of southeastern Africa show an 18 year MAP cyclicity, which drives river runoff and hence controls sediment input to the coast and nearshore environment. The MAP cycle dominates the coastal sediment budget during the LNC trough and suppresses the LPS coastal erosion cycle during this time. This explains why LPS coastal erosion occurs close to the LNC peak. Thus although the LPS cycle dominates the coastline, it is masked during the wet portion of the 18 year MAP cycle. It seems very likely that the LNC drives the MAP cycle in some way but this process is not known. Nevertheless, these relationships can be used to predict, in a general way, both cyclic coastal erosion and the longshore sediment volume fluctuation. This can be translated into a vital coastal planning tool which has the potential to forecast cyclic coastal erosion and hence significantly reduce the sea-defense expenditure bill. Based on this, severe cyclic coastal erosion is anticipated in 2023 and 2024.

Unexpected occurrence of Haemonchus placei in cattle in southern Western Australia

Haemonchus placei is an abomasal parasite of cattle, primarily in tropical and subtropical areas of the world. In Australia, this nematode can be extremely pathogenic in summer rainfall areas, particularly in the hot, sub-tropical Kimberley region, in the far north of the state of Western Australia (WA). Although cattle are occasionally transferred to southern parts of WA, it was believed that H. placei did not occur in southern regions of WA, as it is less cold-adapted than Haemonchus contortus, and the free-living stages would not develop during the cold winter and dry summer periods. Here, we show that, although H. contortus is found in cattle in the temperate southern region of WA, it appears that H. placei also occurs in southern WA. While investigating the prevalence of anthelmintic resistance in nematodes of cattle in WA, the existence of H. placei was suspected on a range of participating farms, following the morphological examination of third-stage larvae cultured from faeces, and of adult worms recovered from sheep experimentally infected with these larvae. Genomic DNAs from individual worms as well as eggs from pooled faecal samples from seven farms in southern WA were subjected to PCR-based mutation scanning and sequence analyses of the second internal transcribed spacer (ITS-2) of nuclear ribosomal DNA. The results showed that both H. contortus and H. placei were harboured by cattle. This first record of H. placei in cattle in southern WA raises questions as to the prevalence and distribution of this parasite in other temperate and cool climatic regions of Australia. Although clinical disease due to H. placei has not yet been seen in southern WA, global, climatic trends might suggest an increased importance of this parasite in the longer term.

Genetic characterisation of a Eucalyptus nitens base breeding population in South Africa

The measurement and statistical analysis of data from eight Eucalyptus nitens trials, established in the summer rainfall forestry region of South Africa during the 1980s and 1990s, have enabled the characterisation of the Institute for Commercial Forestry Research's breeding population. Provenance testing showed that the more northerly New South Wales (Australia) Eucalyptus nitens provenances of Barren Mountain and Barrington Tops are distinctly better suited to the summer rainfall areas of South Africa than the southern New South Wales provenances and the Victorian provenance, Penny Saddle. Generally, the species was not badly affected by Coniothyrium canker. High type B genetic correlations for all site pairs, except one comparison, ranged from 0.75 to 0.99 for diameter at breast height (dbh), indicating very little or no genotype × environment interaction for dbh for the genotypes tested in this study. Narrow-sense heritability coefficients ranged from 0.01 to 0.34, indicating that the species generally exhibited sufficient breeding opportunity for improvement of diameter growth. High genetic correlations of greater than 0.90 between diameter measurements at 52 to 62 months after establishment and diameter measurements at 94 or 113 months were found, indicating that selections can be reliably made at five or six years. Predicted genetic gains were highest in the trials at Goedehoop and Arthur's Seat, with increases in dbh of 3.07 cm (17.1%) and 3.17 cm (20.7%), respectively, at full rotation.

Characterisation of power system events on South African transmission power lines

Records of faults occurring on the South African power transmission system over a 16-year period have been collected. Over 12,000 faults were analysed to find statistical relationships between local climate, key design parameters of the overhead lines, and the main causes of power system faults identified as bird streamers, lightning, fire and pollution. The results characterise the performance of the South African transmission system on a probabilistic basis and illustrate differences in fault cause statistics for the summer and winter rainfall areas of South Africa and for different times of the year and day. The analysis illustrates the effectiveness of bird guards on towers.

Consequences of warming up a hotspot: species range shifts within a centre of bee diversity

AbstractAim Bees are the most important pollinators of flowering plants and essential ecological keystone species contributing to the integrity of most terrestrial ecosystems. Here, we examine the potential impact of climate change on bees’ geographic range in a global biodiversity hotspot.Location South Africa with a focus on the Cape Floristic Region (CFR) diversity hotspot.Methods Geographic ranges of 12 South African bee species representing dominant distribution types were studied, and the climate change impacts upon bees were examined with A2 and B2 climate scenarios of HadCM3 model, using MaxEnt for species distribution modelling.Results The predicted levels of climate change‐induced impacts on species ranges varied from little shifts and range expansion of 5–50% for two species to substantial range contractions between 32% and 99% in another six species. Four species show considerable range shifts. Bees of the winter rainfall area in the west of South Africa generally have smaller range sizes than in the summer rainfall area and generally show eastward range contractions toward the dry interior. Bee species prevalent in summer rainfall regions show a tendency for a south‐easterly shift in geographic range.Main conclusions The bee fauna of the CFR is identified as the most vulnerable to climate change due to the high level of endemism, the small range sizes and the island‐like isolation of the Mediterranean‐type climate region at the SW tip of Africa. For monitoring climate change impact on bees, we suggest to establish observatories in the coastal plains of the west coast that are predicted to be worst affected and areas where persistence of populations is most likely. Likely impacts of climate change on life history traits of bees (phenology, sociality, bee‐host plant synchronization) are discussed but require further investigation.

Genetic variation in growth and stem straightness in Eucalyptus saligna trials in Fujian

Summary Trials of two groups of Eucalyptus saligna families, with 84 open-pollinated families representing nine natural stand provenances from Australia, were established at three sites in central and northern Fujian province in 2002. At age 3.5 y (about half the average rotation length for eucalypt plantations in south-eastern China) these were assessed for tree growth, stem straightness, branching habit and self-pruning ability, whilst cold tolerance was assessed at the coolest site at about age 3 y. Significant differences were observed in some of the trials variously between provenances and families-within-provenances for growth (average tree volume), stem and branch form traits and cold tolerance. Average individual-tree volume was sensitively dependent on both genetics and environment—tree volume among trial sites varied up to six-fold, but within any one trial, average tree volume of the best provenance was only about 30% above that of the poorest provenance. The magnitude of variation between families-within-provenances was generally greater and more often significant than the variation between provenances—especially for average tree volume. The magnitude of variations observed for stem and branch form traits were generally minor. At the coldest site, some significant provenance differences were also found for cold tolerance. Estimates of within-provenance individual-tree heritability for individual-tree volume ranged from 0.00 to 0.21 ± 0.12 and those for stem straightness, branching habit and self-pruning ability ranged from 0.00 to 0.10±0.09. A number of provenances tested ranked highly for average tree volume at one or more sites but performance across sites was generally not consistent and significant site x provenance interactions were found for both volume and stem straightness. For volume the site x family-within-provenance interaction was also significant. Consequently, definitive conclusions regarding provenance potential could not made, though a provenance from Blackdown Tableland in Queensland was notable for combining good growth and cold tolerance. It was concluded that the best path for genetic improvement of E. saligna in such environments would involve vegetative clonal propagation of the best individual trees, regardless of provenance or family, for commercial plantation deployment; acquiring a wider sample of provenances and families of this species from higher-elevation, summer-rainfall areas (e.g. tablelands of northern NSW and Queensland) to expand the breeding population; and initiating sublines within the breeding population for markedly different target environments.

Discriminating the early stages of Sirex noctilio infestation using classification tree ensembles and shortwave infrared bands

The woodwasp Sirex noctilio is causing extensive damage to Pinus patula trees in the summer rainfall areas of South Africa. The ability to remotely detect S. noctilio infestation remains crucial for monitoring purposes and for the effective deployment of suppression activities. In this study, we evaluated whether random forest and boosting trees can accurately discriminate between healthy trees and the early stages of S. noctilio infestation using reflectance measurements in the shortwave infrared (SWIR). Three variable selection methods, namely, a filter, the random forest out-of-bag samples and a wrapper algorithm, were used to select the smallest subset of SWIR bands. The results show that random forest produces better classification results than the competing boosting trees for all three variable selection methods, even when noise is introduced into the SWIR bands and class labels. The ability of the bands centred at 1990, 2009, 2028, 2047 and 2065 nm to discriminate between healthy trees and the early stages of infestation could be explained due to the rapid physiological changes that occur as a result of the toxic mucus and a fungus that S. noctilio injects into the tree. Overall, the results are encouraging and show that there is a link between the selected SWIR bands and existing physiological knowledge, thereby improving the chances of detecting the early stages of S. noctilio infestation at a canopy or landscape level.

Discriminating the early stages of Sirex noctilio infestation using classification tree ensembles and shortwave infrared bands

The woodwasp Sirex noctilio is causing extensive damage to Pinus patula trees in the summer rainfall areas of South Africa. The ability to remotely detect S. noctilio infestation remains crucial fo...

Aspalathus abbottii (Fabaceae: Crotalarieae), a new species from KwaZulu-Natal, South Africa

A new species Aspalathus abbottii C.H. Stirt. & Muasya, is described. The species is known only from Oribi Flats, KwaZulu-Natal, where it grows in grassland vegetation. The new species is characterised by its rigid spreading habit, densely and shortly villous branches, glabrous bracts and bracteoles, and 1(2) bright yellow flowers borne on short lateral shoots. It is most similar to other grassland species, A. frankenioides DC. and A. gerrardii H. Bol., all from the summer rainfall area of South Africa but differs in its rigid spreading habit, few bright yellow flowers per flowering branchlet, glabrous bracts and bracteoles, villous yellowish-green seasonal shoots, and its pale brown to tan over-seasonal branches with a blackish lattice of peeled bark.

A Survey of the Arthropod Pests and Plant Parasitic Nematodes Associated with Commercial Figs,Ficus carica(Moraceae), in South Africa

Edible figs originate from Arabia Felix, present-day Yemen (Eisen 1901) and have been cultivated in the Lower Jordan valley since 11 400-11 200 B.C. (Kislev et al. 2006). Genetic distinction of fig cultivars in Italian isles and natural populations occurring in the Mediterranean basin (Khadari et al. 2005), indicate introduction from the east Arabian Peninsula (Kislev et al. 2006). Eisen (1901) suggested that this introduction to Europe occurred around 800 B.C. by the Phoenicians and Greeks. Under Roman rule they spread to the rest of Europe, but only slowly towards the east, with the first documented edible figs appearing in China by A.D. 1550. At first the fig was considered a luxury for the rich, but it soon became a traded commodity, forming an integral part of the human diet. The ideal climate of Portugal for fig production secured the development of a superior industry there. With the explorations of the Spanish and Portuguese, figs were subsequently established in almost all countries they visited. Today figs are grown all over the world, but they especially favour a warm-temperate Mediterranean-type climate. Figs require sufficient moisture during the active growth period, but a warm dry climate when fruit are ripening (P. Botma, pers. comm.). The winter rainfall areas of South Africa, such as the Swartland and Klein Karoo in the Western Cape are therefore ideal for fig cultivation whereas fruit quality is negatively affected by higher fungal contamination in summer rainfall areas (M. Wohlfarter, pers. obs.).

Biological Control of Dense-Thorned Bitter Apple,Solanum sisymbriifoliumLam. (Solanaceae), in South Africa

Solanum sisymbriifolium Lam. is a weed of disturbed areas in South Africa, particularly in the high-elevation summer rainfall areas of the country. Despite the introduction of the South American leaf-feeding tortoise beetle, Gratiana spadicea (Klug) (Coleoptera: Chrysomelidae: Cassidinae) in 1994, the weed has continued to spread. Although established in a number of regions, beetle populations appear to persist in relatively low numbers, inflicting minimal damage to the weed. Consequently, a number of variables have been investigated in order to explain this lack of efficacy, and in some cases, failure to establish. Gratiana spadicea populations in South Africa are under considerable stress both from abiotic and biotic sources. Population-limiting factors such as disturbance of overwintering sites, climatic incompatibility, and high rates of pupal parasitism translate into low numbers of the agent at the start of each growing season. Small early-season populations which are slow to build-up, coupled with asynchronous development of S. sisymbriifolium, limit the beetles' effectiveness and pre-empt any impact on the weeds' reproductive output. Consequently, G. spadicea alone is unlikely to control S. sisymbriifolium infestations in South Africa. The flower-feeding weevil Anthonomus sisymbrii Hustache (Coleoptera: Curculionidae: Anthonominae), may therefore warrant study as it could have the potential, if released, to curtail fruit production and further spread of S. sisymbriifolium.

Phylogeography of the Clicking Stream Frog Strongylopus grayii (Anura, Pyxicephalidae) reveals cryptic divergence across climatic zones in an abundant and widespread taxon

The Clicking Stream Frog (Strongylopus grayii) occurs throughout southern and eastern South Africa across summer, aseasonal and winter rainfall areas. Because of its contiguous distribution and extended breeding season this species might be expected to show a phylogeographic pattern of isolation by distance rather than divergent geographical lineages. To investigate population structure and make inferences about physical processes that have influenced gene flow in this species, two mitochondrial genes (ND2 and 16S) were sequenced for 64 frogs from across the distribution of the species. Phylogenetic analyses (parsimony and Bayesian) revealed two well-supported clades partitioning the range of this taxon, with one clade restricted to the northeast (summer rainfall) and the other restricted to the south (winter and aseasonal rainfall). The magnitude of sequence divergence between these clades is higher than expected, and is typical of levels of sequence divergence found among closely related species of pyxicephalid frogs. Phylogeographic analyses of sequence networks and spatial analysis of molecular variance (SAMOVA) revealed additional geographical structure within each of these lineages. This study demonstrates the effectiveness of climatic transitions as barriers to gene flow and as potential agents for vicariant speciation.