Image: College of Veterinary Medicine & Biomedical Sciences
Research scientists at Texas A&M University and Faculdade de Biociências in Brazil have moved a step closer to understanding the rich evolutionary history of the cat family. In a paper, featured on the cover of Genome Research, the researchers constructed extensive family trees of the 38 cat species, which illustrated maternal, paternal, and biparental lineages within the cat family. However, they found that lineages are not completely linear. Instead, the study revealed that feline ancestry has been shaped throughout its evolutionary history by hybridization.
Researchers used genome-wide Single Nucleotide Polymorphism (SNP) data—which identifies differences in individual base pairs—with genes from both the X and Y chromosomes and autosomal, or non-sex chromosomes, in addition to sequencing complete mitochondrial genomes, which indicate maternal lineage. This data was complemented by new whole genome sequencing data from the closest species to the domestic cat, as well analysis of the tiger, snow leopard, and lion genomes.
“Our results finally resolve much of the discrepancies in the literature over the past two decades as to how cats are related and the cause for many of the conflicts between different scientific publications, ” said one of the study’s authors, William Murphy, a professor in the Department of Veterinary Integrative Biosciences at the Texas A&M College of Veterinary Medicine & Biomedical Sciences.
“The results also highlight an emerging trend in the literature that hybridization between different species is common and may actually be adaptive,” Murphy said. “One novelty of our study is the illustration as to how common this process is across a broader phylogenetic scale—within an entire family of mammals—than previously has been shown in isolated pairs of species.”
The researchers found that there were nine differences between the maternal and biparental trees. For example, the maternal tree indicated that the puma lineage was more closely related to the lynx/bay cat group, whereas the biparental tree showed the puma lineage as more closely related to the Asian leopard cat/domestic cat group.
Researchers concluded that the most likely cause of this, and other discrepancies between family trees based on different modes of inheritance, is due to ancient hybridizations. Hybrids may have then mated with non-hybrids, introducing variations back into the species.
Additional factors influencing feline evolution include the fact than male hybrids are more often sterile than female hybrids and the males are often more geographically dispersed than females.
“We identified traces of hybridization within the genomes of more than half of the eight cat lineages, where stretches of DNA sequences are far more closely related between pairs of non-sister species than would be expected by random processes,” Murphy said. “In several of these cases, the evidence for hybridization in the nuclear genome, which is inherited from both parents, is matched by similar patterns in the mitochondrial DNA, which is only inherited from the mother.”