Genetic divergence and the frequency of hybridization are central for defining species delimitations, especially among cryptic species where morphological differences are merely absent. Rotifers are known for their high cryptic diversity and therefore are ideal model organisms to investigate such patterns. Here, we used the recently resolved Brachionus calyciflorus species complex to investigate whether previously observed between species differences in thermotolerance and gene expression are also reflected in their genomic footprint. We identified a Heat Shock Protein gene (HSP 40 kDa) which exhibits cross species pronounced sequence variation. This gene exhibits species-specific fixed sites, alleles, and sites putatively under positive selection. These sites are located in protein binding regions involved in chaperoning and may therefore reflect adaptive diversification. By comparing three genetic markers (ITS, COI, HSP 40 kDa), we revealed hybridization events between the cryptic species. The low frequency of introgressive haplotypes/alleles suggest a tight, but not fully impermeable boundary between the cryptic species.

Domestic cattle were brought to Spain by early settlers and agricultural societies. Due to missing Neolithic sites in the Spanish region of Galicia, very little is known about this process in this region. We sampled 18 cattle subfossils from different ages and different mountain caves in Galicia, of which 11 were subject to sequencing of the mitochondrial genome and phylogenetic analysis, to provide insight into the introduction of cattle to this region. We detected high similarity between samples from different time periods and were able to compare the time frame of the first domesticated cattle in Galicia to data from the connecting region of Cantabria to show a plausible connection between the Neolithization of these two regions. Our data shows a close relationship of the early domesticated cattle of Galicia and modern cow breeds and gives a general insight into cattle phylogeny. We conclude that settlers migrated to this region of Spain from Europe and introduced common European breeds to Galicia.

In mammals, the number of vertebrae and the somites they derive from is highly limited. Nevertheless, there are some lineages that have an increased number of presacral vertebrae and thus an elongated trunk. This suggests that somitogenesis, the process of somite formation in early development, is altered in these lineages. According the ‘clock and wavefront’ model of somitogenesis, temporal information of somite boundary formation is generated by a traveling wave of cyclic expression of oscillator genes. Hes7 has been suggested to be a key oscillator gene of this molecular segmentation clock. A previous study showed that reducing the number of introns within the Hes7 gene results in a more rapid tempo of Hes7 oscillation and an increased number of presacral vertebrae. Variation in Hes7 intron number could therefore be a potential evolutionary mechanism for varying vertebral number across mammals. In order to test this hypothesis, Hes7 intron number is here compared to presacral vertebral number across a variety of mammals.No significant relationship between both metrics could be detected as their variation across the mammalian phylogeny is fundamentally different. Integrating our data in the previously published mathematical model of Hes7 oscillation confirms the finding that variation in intron number does not predict variation in presacral vertebrae, rendering a direct causal relationship unlikely. However, our data support the previous suggestion that at least two introns are required for Hes7 pace making function of the segmentation clock.

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