Goldberg Grant for Dr Joanna Malukiewicz: The Speciation Continuum 30006585

Project: Research project

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Goldberg Grant for Dr Joanna Malukiewicz: The Speciation Continuum 30006585 The Speciation Continuum of the Callithrix Genus: Understanding Genomic Speciation in Primates The Speciation Continuum of the Callithrix Genus: Understanding Genomic Speciation in Primates The origin of species is a major primatological focus, and a central task of speciation genetics is to reconstruct the sequence of genetic factors that lead to the cessation of gene flow (i.e., reproductive isolation) between lineages. Reconstruction of the sequence of genetic barriers to gene flow ideally involves an unbiased view of the entire genome along the speciation process (Seehausen et al, 2104), for the ultimate goal of addressing the major and pertinent questions of speciation genetics. These questions include: (1) How localized is divergence across the genome at different stages of speciation? (2) What is the role of different types of selection and drift during speciation? (3) How are these factors influenced by geographic isolation? However, this task remains a tall order for long-lived, sexually reproducing organisms such as primates, and established methodologies favor either model organisms or those with available genomes. Indeed, the current genetic understanding of primate speciation is based on many crucial (and often laborious) studies of single genes/gene families or reduced representations of the genome. However, with the availability of cost-effective whole genome sequencing and the recently proposed continuum approach to speciation research (Seehausen et al., 2014), a broader understanding of speciation is finally tenable at both genetic and genomic scales in primatological research. The continuum approach integrates studies of closely related species belonging to the same lineage that vary in their level of divergence to infer the chronology and importance of various genetic factors involved in speciation. In fact, using species at various stages of divergence makes the continuum approach especially attractive for differentiating between the causes and consequences of speciation. Here, I propose to use the Callithrix marmoset genus, to address the above speciation questions within the continuum framework. Several features of this Brazilian genus make it a wellsuited model for the study of primate speciation genetics. Much speciation work stresses the importance of studying divergence as close to the onset of reproductive isolation as possible. This step is taken to not cofound genetic differences important to speciation with those difference that arose after speciation, as might be the case with older species. The youngest Callithrix species, C. jacchus and C. penicillata diverged about 1 million years ago (Perelman et al., 2011), and still may be undergoing the speciation process as they show relatively low levels of reproductive isolation. For example, hybrid swarming has been documents in these two species in the absence of a strong physical barrier to gene flow (Malukiewicz et al., 2014; Malukiewicz et al., in review). Also, the two species show weaker signs developmental incompatibilities with experimental crosses with each other than in crosses with other marmoset species (Coimbra-Filho et al., 1993), which suggests variable divergence between Callithrix species. Ecological processes may be important in driving divergence between species, and marmoset species are found across three different major biomes (Rylands et al., 2009). More specifically, C. jacchus and C. penicillata subpopulations occur (allopatrically) within the semi-arid, shrubby Caatinga, the savannah-like Cerrado, and Atlantic Forest. Callithrix penicillata has the widest distribution of any Callithrix species, and is the only species to share species distribution borders with all of its congeners. Reports exist of hybridization between C. penicillata and other marmoset species at contact zones between species geographic distributions. These factors will allow for the investigation of role of ecological selection, introgression, and geography isolation marmoset speciation. Finally, the availability of a published C. jacchus genome (The Marmoset Genome Sequencing and Analysis Consortium, 2014) will allow for the identification of candidate genes important to speciation within the Callithrix genus. Marmoset DNA will be obtained from each Callithrix species across their respective geographical ranges. For C. jacchus and C. penicillata, samples will be collected across subpopulations that occur across three different biomes. DNA will also be obtained from natural marmoset hybrids that occur at contact points between C. penicillata and other marmoset species. Marmosets exhibit high levels of chimerism (Ross et al., 2007) due to sharing of stem cells by twins in utero through blood that passes via fused placentas (Benirshke et al., 1962). As a result, highly chimeric tissues may show 1-4 alleles at autosomal loci, a state which may confound later genotyping of sampled individuals. Thus, this study will prioritize the collection of low chimerism epithelial tissue such as skin and cheeks swabs. Marmoset DNA will be collected in collaboration and with logistical support from Drs. Vanner Boere, Ita de Oliveira e Silva, Sergio Mendes, and Luiz Pereira. Marmoset DNA will be extracted from biological tissue in the laboratory of Dr. Jorge
StatusFinished
Effective start/end date9/1/158/31/18

Funding

  • Nacey Maggioncalda Foundation: $12,018.00

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