Biology subjects

Stervander, M.

Publications and source records attributed to Stervander, M..

5 recordsLinked to original sources

bioRxiv2022

First genetic data for the Critically Endangered Cuban endemic Zapata Rail Cyanolimnas cerverai, and the taxonomic implications

The taxonomic affinity of the near-flightless Zapata Rail Cyanolimnas cerverai, a Critically Endangered and highly localized species endemic to Cuba, has long been debated. Morphological analyses have suggested that this species, which constitutes a monotypic genus, could be related either to the extinct Tahitian Cave Rails (Nesotrochis sp.) or to the South American rail tribe Pardirallini, i.e., the genera Neocrex, Mustelirallus, and Pardirallus. Whilst pronounced phenotypic convergence-and divergence-among rails have repeatedly proven morphology-based phylogenies unreliable, thus far no attempt to sequence DNA from the enigmatic Cyanolimnas has succeeded. In this study, we extracted historic DNA from a museum specimen collected in 1927 and sequenced multiple short fragments that allowed us to assemble a partial sequence of the mitochondrial cytochrome oxidase I gene. Phylogenetic analyses confirm that Cyanolimnas belongs in tribe Pardirallini as sister to genus Neocrex, from which it diverged about six million years ago. Their divergence from Mustelirallus was estimated at about eight million years ago. Based on morphology and our mitochondrial phylogeny, we conclude that it is unjustified to retain the monotypic genus Cyanolimnas and tentatively recommend that C. cerverai and the two Neocrex species are ascribed to genus Mustelirallus. O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

zoology↗

bioRxiv2022

Genomic signatures of isolation, hybridization, and selection during speciation of island finches

Sister species occurring sympatrically on islands are rare and offer unique opportunities to understand how speciation can proceed in the face of gene flow. The Sao Tome grosbeak is a massive-billed, giant finch endemic to the island of Sao Tome in the Gulf of Guinea, where it has diverged from its co-occurring sister species the Principe seedeater, an average-sized finch that also inhabits two neighbouring islands. Here, we show that the grosbeak carries a large number of unique alleles different from all three Principe seedeater populations, but also shares many alleles with the sympatric Sao Tome population of the seedeater, a genomic signature signifying divergence in isolation as well as subsequent introgressive hybridization. Furthermore, genomic segments that remain unique to the grosbeak are situated close to genes, including genes that determine bill morphology, suggesting the preservation of adaptive variation through natural selection during divergence with gene flow. This study reveals a complex speciation process whereby genetic drift, introgression, and selection during periods of isolation and secondary contact all have shaped the diverging genomes of these sympatric island endemic finches. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=60 SRC="FIGDIR/small/474904v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@5b18a5org.highwire.dtl.DTLVardef@af0c4forg.highwire.dtl.DTLVardef@512a60org.highwire.dtl.DTLVardef@b51c61_HPS_FORMAT_FIGEXP M_FIG C_FIG

evolutionary biology↗

bioRxiv2020

Evolutionary history of the Galapagos Rail revealed by ancient mitogenomes and modern samples

The biotas of the Galapagos Islands are probably one of the best studied island systems and have provided a broad model of insular species origins and evolution. Nevertheless, some Galapagos species remain poorly characterized, such as the Galapagos Rail Laterallus spilonota. This bird species is one of the less explored groups of endemic vertebrates on these islands, due to its elusive behavior, cryptic plumage and restricted distribution. To date there is no genetic assessment of its origins and sister relationships to other taxa, and importantly, there is no data on its current genetic diversity. This lack of information is critical given the adverse fate of island rail species around the world in the recent past. Here we examine the genetics of Galapagos Rails using a combination of mitogenome de novo assembly with multi-locus sequencing (mtDNA+nuDNA) from both modern and historical samples. We show that the Galapagos Rail is part of the American black rail clade, sister to Black Rail L. jamaicensis, with a colonization of Galapagos dated to 1.2 Mya. The separate analysis of cytb, ND2, and RAG-1 markers demonstrates shallow population structure across sampled islands, possibly due to elevated island connectivity. Additionally, birds sampled from Pinta possessed the lowest levels of genetic diversity, most likely reflecting the impact of past bottlenecks due to habitat loss caused by invasive goats grazing on sensitive habitat. The data presented here highlights the low genetic diversity in this endemic rail species and suggests the use of genetic data (both modern and historical) to guide conservation efforts.

evolutionary biology↗

bioRxiv2020

Non-random association of MHC-I alleles in favor of high diversity haplotypes in wild songbirds revealed by computer-assisted MHC haplotype inference using the R package MHCtools

Major histocompatibility complex (MHC) genes play a central role for pathogen recognition by the adaptive immune system. The MHC genes are often duplicated and tightly linked within a small genomic region. This structural organization suggests that natural selection acts on the combined property of multiple MHC gene copies in segregating haplotypes, rather than on single MHC genes. This may have important implications for analyses of patterns of selection on MHC genes. Here, we present a computer-assisted protocol to infer segregating MHC haplotypes from family data, based on functions in the R package MHCtools. We employed this method to identify 107 unique MHC class I (MHC-I) haplotypes in 116 families of wild great reed warblers (Acrocephalus arundinaceus). In our data, the MHC-I genes were tightly linked in haplotypes and inherited as single units, with only two observed recombination events among 334 offspring. We found substantial variation in the number of different MHC-I alleles per haplotype, and the divergence between alleles in MHC-I haplotypes was significantly higher than between randomly assigned alleles in simulated haplotypes. This suggests that selection has favored non-random associations of divergent MHC-I alleles in haplotypes to increase the range of pathogens that can be recognized by the adaptive immune system. Further studies of selection on MHC haplotypes in natural populations is an interesting avenue for future research. Moreover, inference and analysis of MHC haplotypes offers important insights into the structural organization of MHC genes, and may improve the accuracy of the MHC region in de novo genome assemblies.

evolutionary biology↗

bioRxiv2020

High MHC gene copy number maintains diversity despite homozygosity in a Critically Endangered single-island endemic bird, but no evidence of MHC-based mate choice

AO_SCPLOWBSTRACTC_SCPLOWSmall population sizes can, over time, put species at risk due to the loss of genetic variation and the deleterious effects of inbreeding. Losing diversity in the major histocompatibility complex (MHC) could be particularly harmful, given its key role in the immune system. Here, we assess MHC class I (MHC-I) diversity and its effects on mate choice and survival in the Critically Endangered Raso lark Alauda razae, a species restricted to the 7 km2 islet of Raso (Cape Verde) since ~1460, whose population size has dropped as low as 20 pairs. Exhaustively genotyping 122 individuals, we find no effect of MHC-I genotype/diversity on mate choice or survival. However, we demonstrate that MHC-I diversity has been maintained through extreme bottlenecks by retention of a high number of gene copies (at least 14), aided by co-segregation of multiple haplotypes comprising 2-8 linked MHC-I loci. Within-locus homozygosity is high, contributing to comparably low population-wide diversity. Conversely, each individual had comparably many alleles, 6-16 (average 11), and the large and divergent haplotypes occur at high frequency in the population, resulting in high within-individual MHC-I diversity. This functional immune gene diversity will be of critical importance for this highly threatened species adaptive potential.

evolutionary biology↗