Barbara A. Stewart

Phylogenetic relationships of the southern African freshwater crab fauna (Decapoda: Potamonautidae: Potamonautes) derived from multiple data sets reveal biogeographic patterning.

The phylogenetic relationships among the southern African freshwater crab species were examined using partial sequence data from three mitochondrial genes (12S rRNA, 16S rRNA, and mtDNA COI) 26 morphological characters and 14 allozyme loci. The aims of the present study were firstly to determine whether freshwater crab species that live in the same geographic region share a close phylogenetic relationship. Secondly, to investigate whether hybridizing species are genetically closely related and thirdly, to test for the validity of subgenera based on the genetic data sets. Phylogenetic analysis based on sequence data revealed largely congruent tree topologies and some associations had consistently high bootstrap support, and these data did not support Botts subgeneric divisions. The morphological data were less informative for phylogenetic reconstruction while the allozyme data generally supported patterns recovered by the sequence data. A combined analysis of all the data recovered two monophyletic clades, one comprised of small-bodied mountain stream species and the other clade consisting of large-bodied riverine species. The combined analyses reflected clear biogeographic patterning for these river crabs. In addition, there was a clear correlation between genetic distance values and the ability of sympatric species to hybridize.

Geographic patterns of genetic and morphological divergence amongst populations of a river crab (Decapoda, Potamonautidae) with the description of a new species from mountain streams in the Western Cape, South Africa

Recent systematic research has revealed that Potamonautes brincki comprises two genetically and morphologically distinct population groups. The systematic affinities between these population groups have remained uncertain. In the present study, the relationship between the population groups was examined. Eleven populations were collected from high mountain streams in the Western Cape, South Africa and used in the genetic and morphological analyses. Allozyme electrophoresis of 13 protein coding loci separated two main population groups: group A (Cape Peninsular groups) and group B (Hottentot’s Holland) at I = 0.73. Two additional genetic groups were evident, with group B being conspecific to group A, and group D being conspecific to group C. Morphological examination of pleopod 1 and the terminal segment of the mandibular palp showed considerable differences between the two main population groups, with groups A and B being similar and groups C and D being similar. The morphometric data for the four main groups were examined using discriminant functions analysis and the two main groups were compared using analyses of covariance. Discriminant functions analysis showed a moderate degree of overlap between the groups. Additional morphometric data showed a clear discrimination between the two main population groups. The genetic and morphometric data sets exhibited congruent patterns of variation and the data showed the presence of a species boundary. A new freshwater crab species, P. parvicorpus sp. n., is described. The results of the present study are discussed in the light of historical and contemporary factors that are likely to have contributed to speciation.

COMPARATIVE POPULATION GENETIC STRUCTURES AND LOCAL ADAPTATION OF TWO MUTUALISTS

Abstract Similar patterns of dispersal and gene flow between closely associated organisms may promote local adaptation and coevolutionary processes. We compare the genetic structures of the two species of a plant genus (Roridula gorgonias and R. dentata) and their respective obligately associated hemipteran mutualists (Pameridea roridulae and P. marlothi) using allozymes. In addition, we determine whether genetic structure is related to differences in host choice by Pameridea. Allozyme variation was found to be very structured among plant populations but less so among hemipteran populations. Strong genetic structuring among hemipteran populations was only evident when large distances isolated the plant populations on which they live. Although genetic distances among plant populations were correlated with genetic distances among hemipteran populations, genetic distances of both plants and hemipterans were better correlated with geographic distance. Because Roridula and Pameridea have different scales of gene flow, adaptation at the local population level is unlikely. However, the restricted gene flow of both plants and hemipterans could enable adaptation to occur at a regional level. In choice experiments, the hemipteran (Pameridea) has a strong preference for its carnivorous host plant (Roridula) above unrelated host plants. Pameridea also prefers its host species to its closely related sister species. Specialization at the specific level is likely to reinforce cospeciation processes in this mutualism. However, Pameridea does not exhibit intraspecific preferences toward plants from their natal populations above plants from isolated, non-natal populations.

Upper thermal tolerances of key taxonomic groups of stream invertebrates

Southwestern Australia has already undergone significant climatic warming and drying and water temperatures are increasing particularly in small streams where riparian vegetation has been cleared. The ability to predict how freshwater fauna may respond to these changes requires understanding of their thermal tolerances. A review of relevant literature and laboratory testing of four aquatic species from southwestern Australia were used to compare upper thermal tolerance (UTT) among key taxonomic groups. UTT for selected species determined by LT50 tests were similar to that of species tested elsewhere. Mean UTT, based on relevant literature and LT50 experiments, ranged from 22.3°C for Ephemeroptera to 43.4°C for Coleoptera. Mean UTT for both Coleoptera and Odonata (41.9°C) were significantly higher than those for all the other groups (22.3–31.5°C) with the exception of Planaria. The mean UTT value of 22.3°C for Ephemeroptera was significantly lower than for Decapoda (29.6°C), Trichoptera (30.1°C) and Mollusca (31.5°C). For three insect orders tested, eurytherms had significantly higher UTT values than stenotherms. The variation in UTT among taxa suggests that additional thermal shifts, caused by riparian disturbance and/or climate change, are likely to create novel assemblages due to the replacement of temperature-sensitive taxa by more tolerant taxa. This has implications for the sustainability of regionally important endemic cool water species.

Extreme levels of intra-specific divergence among Cape Peninsula populations of the Cape Galaxias, Galaxias zebratus Castelnau 1861, reveals a possible species complex

The Cape galaxias, Galaxias zebratus, is part of the paleao-endemic fauna characteristic of the south-western Cape, South Africa, and is the only galaxiid found in continental Africa. A 284-bp fragment of the cytochrome b region of the mtDNA was sequenced from 48 individual galaxiids, representing 10 populations from the Cape Peninsula. Five sequences, for four additional populations sampled at the extremes of the species range, were obtained from the literature. Analysis of cyt b mtDNA from these 14 populations of G. zebratus revealed five distinct and highly divergent lineages with low levels of intra-population mtDNA haplotype diversity. A new and distinct genetic lineage is described from the southern part of the Cape Peninsula. Estimates of genetic divergence between populations ranged from <1% to >17%. The observed level of sequence divergence represents the largest yet reported for any single fish species. The distribution of these lineages and their degree of sequence divergence refutes a model of isolation by distance. Results suggest that periods of low sea level may have been important in creating opportunities and alternative routes for dispersal and migration for Cape Peninsula populations.

Congruent patterns of genetic variation in a burrowing freshwater crab revealed by allozymes and mt DNA sequence analysis

Five populations of the burrowing freshwater crab, Potamonautes calcaratus representing a total of 100 specimens, were collected from the Kruger National Park, South Africa. The population genetic structure of this species was investigated using both nuclear genetic markers (allozymes), and direct sequencing of a 610 base pair fragment the cytochrome oxidase 1(CO 1) subunit of the mitochondrial DNA. Electrophoresis of 21 allozyme loci revealed that moderate levels of genetic differentiation (F(ST) = 0.12) was present among populations. Sequence data for 20 individuals revealed the presence of ten haplotypes, the distribution of which showed no geographic structuring. The ΦCT of 0.43 corroborates a moderate degree of genetic structuring. The nucleotide diversity (π) was low and ranged from 0.00 to 0.007. Sequence divergence amongst populations ranged from 0.49% to 1.47%. Both genetic markers revealed moderate population structuring, supporting the conclusion that populations share a common recent ancestry, with moderate levels of recent gene flow. These results provide evidence that allozyme and sequencing data may be congruent and that these independent markers can detect similar patterns of genetic differentiation. Results are discussed in light of contemporary factors that have been likely in sculpting the genetic structure.

Facilitated Selfing Offers Reproductive Assurance: A Mutualism Between A Hemipteran And Carnivorous Plant

Reproductive assurance is frequently used to explain the evolution of selfing but has become controversial from lack of evidence. We studied the pollination system of the near carnivorous plant genus Roridula and showed that reproductive assurance is important in this system. Hemipterans have a digestive mutualism with Roridula and have been implicated in pollination but flowers show adaptations to hymenopteran pollination. We deduce that hemipterans are the primary pollinators of Roridula because seed set is significantly reduced when hemipterans are excluded from the flowers. Using allozyme electrophoresis, we show that hemipterans are responsible for mostly selfed progeny. Although bees still pollinate Roridula on very rare occasions, their exclusion does not affect seed set. The complicated floral structures that occur in Roridula most likely evolved as adaptations for bee pollination. Resident hemipterans facilitate selfing by Roridula, and this acts as a reproductive assurance mechanism because it increases seed production and ensures that plants still reproduce in the absence of more motile, outcrossing pollinators.

Potamonautes Granularis Sp. Nov. (Brachyura, Potamonautidae), a New Cryptic Species of River Crab From the Olifants River System, South Africa

A new species of river crab, Potamonautes granularis sp. nov., from the lower reaches of the Olifants River, South Africa is described and illustrated. The orange tips of the chelipeds and the granulation of the postfrontal crest can distinguish this species from other freshwater crabs in the area. The morphological differences between P. granularis sp. nov., P. perlatus, and P. sidneyi are investigated and quantified and the new species is compared with other freshwater crabs from the region.

A new species of freshwater crab (Decapoda, Potamonautidae) from the swamp forests of KwaZulu-Natal, South Africa: Biochemical and Morphological evidence.

Potamonautid river crabs were collected from e ve localities in northeastern KwaZulu-Natal to determine biochemical and morphological differentiation among these populations. Two distinct forms were included in these collections. One of the forms could be identie ed as Potamonautes sidneyi, whereas the other was previously unknown. Biochemical analysis of 21 presumptive allozyme loci showed the two forms to be distinct, separating at a genetic identity value of 0.829. A e xed allele difference at the HEX locus in the sympatric populations of the two forms indicated that they were reproductively isolated. Morphometric analysis of seven carapace variables, by means of a discriminant function analysis, showed the two forms to be distinct. The unidentie ed form, which appears to be cone ned to patches of swamp forest in northeastern KwaZulu-Natal, is described in this paper as Potamonautes lividus sp. nov.

From genetic structure to wetland conservation: a freshwater isopod Paramphisopus palustris (Phreatoicidea: Amphisopidae) from the Swan Coastal Plain, Western Australia

The freshwater isopod Paramphisopus palustris is ubiquitous and abundant in the groundwater-fed wetlands of the Swan Coastal Plain around Perth, Western Australia. Taxonomically, an additional variety (P. palustris fairbridgei) and species (P. montanus) are recognized from geographically outlying localities. Here a 486 bp fragment of cytochrome c oxidase subunit I (COI) mtDNA was sequenced in 68 individuals from 23 localities in order to evaluate the accepted taxonomy, to examine the evolutionary history of the species, and to identify lineages to prioritize conservation of wetlands already substantially modified. MtDNA showed individual populations to be largely distinct and differentiated. The 41 unique haplotypes formed seven independent, geographically defined networks. Phylogenetic analysis retrieved corresponding subclades, with three well-supported larger clades occurring (1) north of the Swan River, (2) south of the Swan River, and (3) in an area further south. A clear pattern of isolation by distance was detected suggesting an ancient serial founder event, with the pattern possibly persisting in the face of limited gene flow through priority effects. The possibility of incipient speciation, the monophyly of the recognized subspecies and the paraphyly of P. palustris with respect to P. montanus, suggest that the current taxonomy is invalid and requires re-examination. Divergences suggest a mid- to early Pliocene divergence of the major clades, with early Pliocene divergences among subclades probably driven by documented intense arid periods. Lineages are present in wetlands in geologically younger environments suggesting in situ survival and persistence. Seven Evolutionarily Significant Units were identified for the conservation of Paramphisopus, two of which are not currently represented in conservation reserves. With increased water demand and the negative impact of surrounding land-use, the current study provides a first phylogeographic assessment of conservation priorities for wetlands of the Swan Coastal Plain.