Homeobox DNA polymorphisms (RFLPs) in subterranean mammals of theSpalax ehrenbergi superspecies in Israel: Patterns, correlates, and evolutionary significance

Spatial genetic diversity in the Cape mole-rat, Georychus capensis: Extreme isolation of populations in a subterranean environment

The subterranean niche harbours animals with extreme adaptations. These adaptations decrease the vagility of taxa and, along with other behavioural adaptations, often result in isolated populations characterized by small effective population sizes, high inbreeding, population bottlenecks, genetic drift and consequently, high spatial genetic structure. Although information is available for some species, estimates of genetic diversity and whether this variation is spatially structured, is lacking for the Cape mole-rat (Georychus capensis). By adopting a range-wide sampling regime and employing two variable mitochondrial markers (cytochrome b and control region), we report on the effects that life-history, population demography and geographic barriers had in shaping genetic variation and population genetic patterns in G. capensis. We also compare our results to information available for the sister taxon of the study species, Bathyergus suillus. Our results show that Georychus capensis exhibits low genetic diversity relative to the concomitantly distributed B. suillus, most likely due to differences in habitat specificity, habitat fragmentation and historical population declines. In addition, the isolated nature of G. capensis populations and low levels of population connectivity has led to small effective population sizes and genetic differentiation, possibly aided by genetic drift. Not surprisingly therefore, G. capensis exhibits pronounced spatial structure across its range in South Africa. Along with geographic distance and demography, other factors shaping the genetic structure of G. capensis include the historical and contemporary impacts of mountains, rivers, sea-level fluctuations and elevation. Given the isolation and differentiation among G. capensis populations, the monotypic genus Georychus may represent a species complex.

Local and regional scale genetic variation in the Cape dune mole-rat, Bathyergus suillus

The distribution of genetic variation is determined through the interaction of life history, morphology and habitat specificity of a species in conjunction with landscape structure. While numerous studies have investigated this interplay of factors in species inhabiting aquatic, riverine, terrestrial, arboreal and saxicolous systems, the fossorial system has remained largely unexplored. In this study we attempt to elucidate the impacts of a subterranean lifestyle coupled with a heterogeneous landscape on genetic partitioning by using a subterranean mammal species, the Cape dune mole-rat (Bathyergus suillus), as our model. Bathyergus suillus is one of a few mammal species endemic to the Cape Floristic Region (CFR) of the Western Cape of South Africa. Its distribution is fragmented by rivers and mountains; both geographic phenomena that may act as geographical barriers to gene-flow. Using two mitochondrial fragments (cytochrome b and control region) as well as nine microsatellite loci, we determined the phylogeographic structure and gene-flow patterns at two different spatial scales (local and regional). Furthermore, we investigated genetic differentiation between populations and applied Bayesian clustering and assignment approaches to our data. Nearly every population formed a genetically unique entity with significant genetic structure evident across geographic barriers such as rivers (Berg, Verlorenvlei, Breede and Gourits Rivers), mountains (Piketberg and Hottentots Holland Mountains) and with geographic distance at both spatial scales. Surprisingly, B. suillus was found to be paraphyletic with respect to its sister species, B. janetta-a result largely overlooked by previous studies on these taxa. A systematic revision of the genus Bathyergus is therefore necessary. This study provides a valuable insight into how the biology, life-history and habitat specificity of animals inhabiting a fossorial system may act in concert with the structure of the surrounding landscape to influence genetic distinctiveness and ultimately speciation.

Genetic microstructure in two Spanish cat populations. I: genic diversity, gene flow and selection

The genetic microstructure of two Spanish cat populations (in Barcelona and Alicante) was studied. These populations were in Hardy-Weinberg equilibrium at the locus O . There was significant genetic heterogeneity for most of the loci studied at the colony level, especially, and the subpopulation level in Barcelona, and at the subpopulation level in Alicante, although the amount of heterogeneity was relatively small compared with that found in other mammal species. Therefore, the major part of the gene diversity found was at the level of the small population structure (colonies). This agrees quite well with high theoretical gene flow estimates. The Lewontin-Krakauer test showed, in some cases, significant F tests, which appears to indicate the presence of several selective events on some of the loci studied (diversifying and/or unifying), although some other causes, such as differential gene flow, some different historical and demographic parameters at the time of the introduction of the different alleles within the cities studied, as well as different mutation rates of the loci analyzed, could produce significant Lewontin-Krakauer test values, as well.

Genetic polymorphisms in subterranean mammals (Spalax ehrenbergi superspecies) in the near east revisited: patterns and theory

Allozyme diversity in the superspecies Spalax ehrenbergi has been revisited by studying 36 gene loci in 241 subterranean mole rats from 22 populations and nine chromosomal species, four from Turkey (2n = 52E (east), 52W (west), 56 and 58), four from Israel (2n = 52, 54, 58 and 60), and one from Egypt (2n = 60). The following results were indicated. (1) Genetic patterns: 11 of the 36 loci analysed (30.5 per cent) were monomorphic across the range, fifteen (41.7 per cent) were weakly polymorphic and the remaining 10 loci (27.8 per cent) were strongly polymorphic. (2) Heterozygosity: the average H was 0.051, range 0.00-0.098. In Israel, H increased with aridity and climatic unpredictability towards the northern Negev Desert, and was remarkably high in small steppic semi-isolates and desert isolates. (3) Species discrimination: some of the S. ehrenbergi species can be discriminated qualitatively. (4) Genetic distances (D): between species these values averaged 0.077, range 0.001-0.269, with the highest D between the ancestor Turkish and descendant Israeli and Egyptian species. The phylogenetic tree supports the Turkish origin of the Israeli Spalax ehrenbergi species, and the recent speciation of the Egyptian Spalax. (5) Genetic diversity is mostly (58 per cent) within populations. (6) Allozyme correlates: allozyme diversity was significantly correlated with the external physical (both climatic and edaphic) and biotic (parasite infection and plant cover) environment. (7) Spatial autocorrelation of allozyme frequencies suggests that migration is not influential. (8) Gametic phase disequilibria were significant in four out of five species tested, and were associated with climatic and edaphic factors. These results support the environmental selection hypothesis of genetic diversity including the niche-width variation hypothesis in space and time. Natural selection appears to play a major role in genetic differentiation of proteins in adaptive radiation and speciation.