Does Sex Speed Up Evolutionary Rate and Increase Biodiversity?

Most empirical and theoretical studies have shown that sex increases the rate of evolution, although evidence of sex constraining genomic and epigenetic variation and slowing down evolution also exists. Faster rates with sex have been attributed to new gene combinations, removal of deleterious mutations, and adaptation to heterogeneous environments. Slower rates with sex have been attributed to removal of major genetic rearrangements, the cost of finding a mate, vulnerability to predation, and exposure to sexually transmitted diseases. Whether sex speeds or slows evolution, the connection between reproductive mode, the evolutionary rate, and species diversity remains largely unexplored. Here we present a spatially explicit model of ecological and evolutionary dynamics based on DNA sequence change to study the connection between mutation, speciation, and the resulting biodiversity in sexual and asexual populations. We show that faster speciation can decrease the abundance of newly formed species and thus decrease long-term biodiversity. In this way, sex can reduce diversity relative to asexual populations, because it leads to a higher rate of production of new species, but with lower abundances. Our results show that reproductive mode and the mechanisms underlying it can alter the link between mutation, evolutionary rate, speciation and biodiversity and we suggest that a high rate of evolution may not be required to yield high biodiversity

Variability of the bushcricket Ephippiger ephippiger: RAPDs and song races

The tettigoniid bushcricket, Ephippiger, shows extensive variability in morphology and behaviour in Western Europe. Several species and subspecies have been described, but many may only represent local forms of uncertain origin. Within Ephippiger ephippiger, patterns of variation differ between morphology (upon which most taxonomic forms are defined) and behaviour. There is sufficient variation in a sexual signal (calling song) within the species that 'song races' have been described, which show strong premating isolation from each other. Here RAPD markers (138 fragments from 10 primers) have been used to examine the extent and pattern of genetic differentiation within the species and between two congeneric species. Ephippiger ephippiger is clearly distinguished from its relatives. High genetic similarity has been found within E. ephippiger, Nei and Li's S averaging 0.67. Using both distance and parsimony methods resolves the relationships of the song races and morphological forms of E. ephippiger with the exception of one population. The song races represent the deepest division within the species, but the lack of concordance in different traits suggests that a complex pattern of subspecific variation is found within this species.</p

Population structure in two sympatric species of the Lake Tanganyika cichlid tribe Eretmodini: evidence for introgression

Patterns of genetic differentiation were analysed and compared in two sympatric species of the endemic Lake Tanganyika cichlid tribe Eretmodini by means of mitochondrial DNA (mtDNA) sequences of the control region and six microsatellite DNA loci. The sample area covers a total of 138 km of mostly uninterrupted rocky shoreline in the Democratic Republic of Congo and includes the entire distribution range of Tanganicodus cf. irsacae that stretches over a distance of 35 km. Both markers detected significant genetic differentiation within and between the two species. T. cf. irsacae contained lower overall genetic variation than Eretmodus cyanostictus, possibly due to its more restricted range of distribution and its smaller effective population sizes. Complete fixation of Tanganicodus mtDNA haplotypes was observed in Eretmodus at two localities, while at two other localities some Tanganicodus individuals possessed Eretmodus mtDNA haplotypes. Taking into account the relatively large average sequence divergence of 6.2% between the two species, as well as the geographical distribution of mtDNA haplotypes in the lake, the observed pattern is more likely to be a consequence of asymmetric introgression than of shared ancestral polymorphism. As there is significant population differentiation between sympatric Tanganicodus and Eretmodus populations, the events of introgressions may have happened after secondary contact, but our data provide no evidence for ongoing gene flow and suggest that both species are reproductively isolated at present time