The utility of reptile blood transcriptomes in molecular ecology

Reptiles and other non-mammalian vertebrates have transcriptionally active nucleated red blood cells. If blood transcriptomes can provide quantitative data to address questions relevant to molecular ecology, this could circumvent the need to euthanize animals to assay tissues. This would allow longitudinal sampling of animals' responses to treatments, as well as sampling of protected taxa. We developed and annotated blood transcriptomes from six reptile species. We found on average 25,000 proteins are being transcribed in the blood, and there is a CORE group of 9,282 orthogroups that are found in at least four of six species. In comparison to liver transcriptomes from the same taxa, approximately two-thirds of the orthogroups were found in both blood and liver; and a similar percentage of ecologically relevant gene groups (insulin and insulin-like signaling, electron transport chain, oxidative stress, glucocorticoid receptors) were found transcribed in both blood and liver. As a resource, we provide a user-friendly database of gene ids identified in each blood transcriptome. Although, on average 37% of reads mapped to hemoglobin, importantly, the majority of non-hemoglobin transcripts had sufficient depth (e.g., 97% at >10 reads) to be included in differential gene expression analysis. Thus, we demonstrate that RNAseq blood transcriptomes from a very small blood sample (<10 ul) is a minimally invasive option in non-mammalian vertebrates for quantifying expression of a large number of ecologically relevant genes longitudinally and in protected populations.