Barlow's Lark: a new species in the Karoo Lark Certhilauda albescens complex of southwest Africa

The Karoo Lark Certhilauda albescens complex, endemic to southwest Africa, is characterized by regional phenotypic variation. Recent consensus has been to recognize two species, Dune Lark Certhilauda erythrochlamys and Karoo Lark Certhilauda albescens, but intermediate forms around the mouth of the Orange River have resulted in some authors treating it as a single polytypic species complex. We reexamined the status of taxa in this group by sequencing a segment of the mitochondrial DNA cytochrome b gene. Most samples were from the area around the mouth of the Orange River, where there is considerable local phenotypic variation. Our results indicate that the complex comprises three species, Karoo Lark, Dune Lark and Barlow's Lark Certhilauda barlowi, separated by 1.9-5.5% sequence divergence. There were no sequence differences among described subspecies, but there was limited variation among Dune Lark individuals (sequence divergence values 0.2-0.4%). The Red Lark Certhilauda burra is closely related to the Karoo Lark complex; indeed, it may be that Karoo Lark is the ancestral form. There was morphological (biometrics and plumage) and behavioural (male display song structure) support for the recognition of Barlow's Lark as a separate species. Species ranges within the complex are allopatric or narrowly parapatric, and they occur in different habitats and climatic conditions. Discriminant function analysis correctly identified 99% of skins assigned to taxa based on range, but a few individuals collected in the contact zone between Karoo and Barlow's Larks exhibited intermediate phenotypes, and further investigations are warranted to search for evidence of hybridization. The newly recognized Barlow's Lark has a maximum range of 18,000 km². It appears to have disappeared from heavily grazed farms around Aus, southern Namibia, and occurs almost exclusively in diamond mining areas, where domestic livestock are excluded. Changes to land use practices which reduce vegetation cover could seriously impact this species.     

Hybrid sterility and inviability in the parasitic fungal species complex Microbotryum

Microbotryum violaceum, the anther‐smut fungus, forms a complex of sibling species which specialize on different plants. Previous studies have shown the presence of partial ecological isolation and F1 inviability, but did not detect assortative mating apart from a high selfing rate. We investigated other post‐mating barriers and show that F1 hybrid sterility, the inability of gametes to mate, increased gradually with the increasing genetic distance between the parents. F2 hybrids showed a reduced ability to infect the plants that was also correlated with the genetic distance. The host on which the F2 hybrids were passaged caused a selection for alleles derived from the pathogen species originally isolated from that host, but this effect was not detectable for the most closely related species. The post‐mating barriers thus remain weak among the closest species pairs, suggesting that premating barriers are sufficient to initiate divergence in this system.